BELFAST, Northern Ireland and NEW JERSEY—September 20, 2022—Cumulus Neuroscience (Cumulus; the Company), a global digital health company developing multi-domain digital biomarkers for the brain, today appointed Aman Bhatti, MD, as Chief Executive Officer (CEO). Dr. Bhatti, a noted digital health executive with experience launching and scaling world-renowned consumer healthcare brands, joins Cumulus as the Company shifts toward healthcare and expands biopharma partnerships in its next growth phase. Dr. Bhatti’s appointment follows the recent award of a £1.5M UK National Institute for Health and Care Research (NIHR) grant to Cumulus and its academic research partners, using the Cumulus platform to improve early dementia diagnosis.

“Neurological disorders are a global health issue, and digital biomarkers – which require integrated, multi-domain assessment technologies – are key to supporting faster drug development, disease diagnosis, and therapeutic solutions,” said Ruth McKernan, PhD, co-founder & executive chair, Cumulus. “Dr. Bhatti’s proven track record of implementing strategies that achieve significant revenue growth in both the biopharma and healthcare industries, combined with his unique understanding of healthcare system priorities and patient, physician, biopharma and payer needs, makes him the ideal match to lead Cumulus in its next chapter. With Dr. Bhatti at the helm, Cumulus is poised to accelerate our BioPharma and Healthcare commercialization strategies – to help solve the biggest healthcare challenges in neurodegeneration and psychiatry.”

“My passion is finding the intersection of technological innovation, scientific understanding, and patient care, to make better health possible – and Cumulus technology is poised to do just that, by enabling better understanding and faster identification of neurodegenerative and neuropsychiatric diseases,” said Bhatti. “Our technology already plays a key role in helping biopharma partners accelerate drug development, and soon, the same technology will be deployed to physicians to lead to earlier diagnosis and treatment of Alzheimer’s and other CNS diseases. I look forward to expanding those opportunities for our biopharma partners and patients, and to building toward the launch of our Cumulus platform to clinicians in the US. I’m also particularly energized to continue leading the industry in its evolution from paper-based, single-timepoint and single-domain assessments to using repeatable, multi-domain, AI-based clinical insights that are changing the face of drug development and patient management,” he added.

Brian Murphy, PhD, co-founder and chief scientific officer, commented: “Current solutions to measuring brain function don’t satisfy patients, doctors or the scientists who are working to develop new life-changing therapies. Our machine-learning enabled platform directly measures how a disease affects thinking capability, sleep, mood, language and other aspects of a patient’s daily life. With Aman on-board, the team is excited to bring this easy-to-use solution to bear in global health-care systems.”

Before joining Cumulus, Dr. Bhatti was senior vice president of AliveCor BioPharma, where he led a team focused on establishing partnerships with CROs and biopharma companies, drawing upon more than 15 years of experience in prior executive roles at Sanofi, GSK, Novartis and Reckitt. A pioneer in forging technology-based alliances, he was part of efforts to launch and scale well known global consumer brands such as Mucinex, Theraflu, Flonase, Nicorette, and most recently, KardiaMobile.

Focused on transforming diagnosis and patient care for Alzheimer’s dementia and other central nervous system (CNS) disorders, Cumulus is backed by a strategic investment led by the Dementia Discovery Fund (DDF), a specialist venture capital fund which includes leading pharmaceutical companies Pfizer, Lilly, Biogen, J&J, GSK, and Takeda. Its science is validated by recent data demonstrating that an easy-to-use, task-driven electroencephalogram (EEG) can yield clinical-grade data in large-scale, real-world investigations in neuroscience with extremely high adherence rates (Front. Digit. Health, 29 July 2022) – providing drug development partners with advanced diagnostic tools that generate insights into neurological activity, and better serve patients.

To learn more, visit www.cumulusnero.com.

About Cumulus Neuroscience

With a mission to generate the data and insights required to accelerate diagnosis and management of central nervous system (CNS) disorders for millions of patients and caregivers around the world, Cumulus Neuroscience is advancing an AI-based, multi-domain digital biomarker platform to enable better, faster decision making in neurology and neuropsychiatry clinical trials and patient care, beginning with dementia and Alzheimer’s disease.

Designed to provide an industry-wide standard for real-world measurement of disease progression, Cumulus combines patented technology, in-house expertise and key industry partnerships to capture large amounts of real-world, clinical data repeated over time, across multiple behavioral and physiological domains in the patient’s home – all by a certified medical device package. Together with machine learning (ML) analytics and an extensive real-world database of annotated, longitudinal, matched data, Cumulus simplifies and improves the robustness of neuroscience clinical trials to provide the best and most cost-effective assessment of CNS treatment outcomes.

The Company is supported by highly experienced specialized investors, DDF/SV Health Investors, LifeArc and Future Fund, and a world-class Scientific and Technical Advisory Board.

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To varying degrees, everyone experiences stressors in life. Yet many people seem to be able to tolerate life’s stressors without showing symptoms of stress — symptoms like anxiety, depression, heightened emotions and/or chronic pain.

So, if you’re someone who seems to be highly sensitized to stress, you might get the impression that there’s something “wrong” with you. (Spoiler alert: there’s not.)

We live in a culture that pathologizes emotional sensitivity and normalizes emotional numbness.

But the truth is, numbness and heightened sensitivity are both symptoms of emotional repression. On the surface, they look different. But they’re two sides of the same coin.

Repressed emotions are compressed energy. And compressed energy can take on multiple forms:⁠

• Compressed energy can stay contained for a while, like a pot of boiling water with the lid jammed on.⁠ But eventually it explodes.
• In some people, the lid stays jammed on most of the time. You might not even be able to tell that there’s boiling water under the surface, and they appear to be “doing just fine,” meaning: they’re conforming to the standards of our societal norms.⁠
• In some people, the pot of water looks like it’s always on the verge of bursting … and from time to time it does.⁠
• In other people, the pot seems to be constantly bubbling over, with the lid nowhere to be found.⁠

All of these are symptoms of a culture that encourages us to reject our own emotions. “Under-expressed” emotions are simply more convenient to patriarchy than “over-expressed” emotions, so blunted sensitivity is considered normal while heightened sensitivity is pathologized.

All this to say, it may seem like others are “doing just fine” while you seem to be “overly sensitive” — physically and/or emotionally. And you may be asking yourself “why me?”

But the truth is that we are all impacted by living in a culture of emotional repression — even if that impact looks different from person to person. And we would all benefit from a shift in culture toward allowing, accepting and honoring emotions. (If you’re reading this, I have a feeling you’re already taking part in this collective culture shift.)

Instead of seeing your sensitivities as something “wrong,” what if you were to view them as your superpowers? Your finely attuned antennae letting you know that there’s actually a kinder, more wholesome, respectful and nurturing way of being that we could all be moving toward? What if your emotions are the guiding stars pointing us all in the direction of a healthier and more loving human culture?

What if you aren’t broken at all, just reacting to a world that’s aching for positive change?

With love and warmth,

💖 Anna

The post Being Sensitive Doesn’t Mean You’re Broken appeared first on Medika Life.

Today we learn how that substance — cerebrospinal fluid or CSF — washes in and out of our brain tissues in waves, helping to remove waste products. The cerebrospinal spinal fluid also bathes our brain with proteins or growth factors, facilitating normal development.

Decay theory of memory fading

When we learn something new, we create a neurochemical memory trace. The decay theory posits that our memory fades secondary to the passage of time, with information becoming less available for later retrieval as time goes by; the memory strength simply wears away.

Columbia University (USA) psychologist Edward Thorndike first coined the descriptor “decay theory” in The Psychology of Learning in 1914. Active rehearsal of the information can counteract the memory fading.

Memories fade like old photographs

Why do our memories, like old photographs, fade in quality over time? Not only do our recollections become less accurate over time, but we also experience decreases vibrancy and other visual qualities.

Are you like me? I sometimes have a memory that feels like I am reliving the moment. On other occasions, the details are remarkably fuzzy. An example of the former? After I had an emotionally significant event, getting engaged at New York’s Rainbow Room at Rockefeller Center, I have a good recall of the event, but everything has faded in my mind.

As events are forgotten or stored in memory, Boston College researchers wondered how their visual features evolve? Study participants reported changes in their memories akin to using a filter to edit a photograph on Instagram.

The researchers went a step further, inquiring if forgetting is similar to applying a filter to our experiences and whether the emotional significance of the event would change which filter we apply.

Here are the findings, as detailed by study author Rose Cooper:

“Memories seem to fade literally: people consistently remembered visual scenes as being less vibrant than originally experienced.” She continues, adding, “we had expected that memories would get less accurate after a delay, but we did not expect that there would be this qualitative shift in the way that they remembered them.”

Furthermore, negative emotions study participants experienced when viewing images raised the chances that they would accurately recall the images but did not influence memory fading.

In summary, the researchers discovered that the vibrancy of low-level details — colors and shapes, for example — fades in memory while we keep the general gist of the experience.

The fading appeared less for memories subjectively rated as more robust. Emotional memories did not influence the fading amount but did impact the likelihood with which the subjects remembered an exposure. My Rainbow is recalled, but not vividly.

What drives the memory fading? Do we forget over time, or is new material interfering with new information?

Cerebrospinal fluid basics

Researchers recently reversed memory loss in mice by injecting them with a brain fluid from younger peers. First, let’s take a quick look at that fluid, or cerebrospinal fluid (CSF).

The CSF is a body fluid surrounding the brain and cushion in the skull. Maiken Nedergaard and colleagues discovered that cerebrospinal fluid also acts as a lymph system in the brain.

Via a series of elegant experiments analyzing mice brains, the researchers visualized cerebrospinal fluid entering and flowing through the brain, ultimately draining into the same ducts used by the lymphatic system of the rest of the body.

The cerebrospinal fluid clears harmful amyloid-beta from the brain. The substance is associated with Alzheimer’s disease and other neurological conditions. While Nedergaard and co-investigators honed in on this protein, other leftover proteins are likely also removed.

In summary, cerebrospinal (spinal) fluid washes in and out of the crevices of our brains in waves. The process is central to waste removal.

Reversing memory loss in mice

Researchers reversed memory loss by injecting cerebrospinal fluid from younger mice peers.

Using a tiny tube and pump, the scientists infused cerebrospinal fluid from young adult mice into the brains of 18-month-old animals — the equivalent to about 60 years for humans — over seven days.

Imaging revealed higher levels of myelin, a fatty sheath that covers and protects nerve cells from damage. The injections led to practical changes, too: The elderly mice improved at a fear-conditioning task. The refreshed mice remembered a tone, and a flashing light meant a small electric shock was coming.

Growth factors and memory rejuvenation

Growth factors that can restore nerve cell function are the likely agents of memory improvement. Stimulated cells — oligodendrocytes — made more myelin, creating stronger connections between the nerve cells.

Genes normally expressed in oligodendrocytes appeared revved up or upregulated in the old mice who had received cerebrospinal fluid from young mice.

The researchers also found changes in gene expression in a structure important for memory, the hippocampus. The gene Fgf17 decreases activity with age; the CSF infusion restored function.

This research is stunning. With all of the troubles in the world, it is heartening to see brilliant scientists opening doors to a future where we may be able to improve memory. It is also disturbing. I hope we someday don’t go down this road; gene editing sounds much more appealing to me, especially for those with dementia.

Until we get a drug targeting memory in humans, I will continue to focus on a healthy diet, adequate sleep, regular physical activity, limiting alcohol consumption, and challenging my brain with activities such as my new Haydn Piano Sonatas.

The post Can We Reverse Memory Loss with Brain Liquid From Younger Folks? appeared first on Medika Life.

That’s the view of Dr. Denise Park, the Director of the Center for Vital Longevity at the University of Texas at Dallas (USA).

OUR HABITS CAN HAVE PROFOUND EFFECTS on our cognitive functions. There are many contributants to our brain health, but today I want to focus on a relatively simple way you can lower your chances of suffering from cognitive decline.

First, before we talk about too much sitting, let’s quickly list some brain hacks that may lower your risk of suffering from a cognitive decline.

1. Physical activity may provide some protection for many of us. Dr. Laura Baker, a neuropsychologist at the University of Washington (in my beloved Seattle), discovered that older adults with mild cognitive impairment demonstrated improvements on tests of executive function after six months of aerobic exercise (for four days weekly).
2. Stress is associated with an increase in beta-amyloid protein, a component thought by many (but not all) to be a causal agent for Alzheimer’s dementia, at least in mice brains.
3. Mental stimulation. A 2006 meta-analysis showed fewer years of education associated [emphasis added] with a greater risk of Alzheimer’s disease.
4. Short sleep is associated with brain dysfunction. I have written about the link here:

Short Sleep and DementiaSleep disturbance is associated with a higher risk of dementia.medium.comUse Sleep and Exercise to Drop Your Dementia RiskToo little (or too much) sleep may increase your dementia risk. Optimizing sleep and getting some exercise may reduce…drmichaelhunter.medium.com.

First, full disclosure: I am unaware of any high-level evidence pointing to a clear cause-and-effect relationship between lifestyle interventions and improvements in cognitive impairment risk.

The US National Institutes of Health agrees, with an expert panel concluding that there is not enough evidence to support any particular modifiable factor as reducing dementia risk.

Still, many habits are associated with poorer brain health, and today I want to look specifically at the effects of sitting too much.

Sitting and the brain

“Americans Sit More Than Anytime In History And It’s Killing Us.”

That’s the headline I recently stumbled across. Do you sit too much? In the United States, the average American adult sits more than at any other time in history.

As a radiation oncologist, I have a relatively sedentary job. Do you? According to the American Heart Association, these types of jobs have increased 83 percent since 1950.

We sit. A lot.

Did you know that physically active jobs comprise less than 20 percent of work in the USA? This low number is down from approximately half of jobs in 1960.

And, Johns Hopkins researchers contend that “physically active jobs now make up less than 20% of the U.S. workforce, down from roughly half of jobs in 1960.” The typical office worker sits a remarkable 15 hours daily. And then we sit on our commute home.

And there is this: Too much sitting can offset the health benefits of working out.

All of this sitting can do a job on our brains. A 2018 PLOS One study reports that sitting too much is associated with changes in a brain region central to memory.

University of California, Los Angeles (USA) researchers used magnetic resonance imaging (MRI) scans to peer into the brain’s medial temporal lobe (MTL), a zone that creates new memories. The research subjects ranged in age from 45 to 75 years.

They compared the scans with the average number of hours an individual sat each day. Those who sat for the most prolonged time had thinner MTL regions. Unfortunately, such brain changes can be precursors of cognitive decline and dementia.

Sitting and the brain — An action plan

I recommend moving after 30 minutes of sitting to all of my able patients. Many of us have reminders on our wrists: My FitBit device buzzes periodically to remind me to get up and move.

I recall a New York Times piece that suggested we exercise for three minutes every half hour to counter the harmful effects of sitting too long. Walk around the office or home. Climb stairs. Stretch. Just move. Even as few as 15 steps during mini-breaks can improve our blood sugar control.

The post One Simple Way to Protect Your Brain appeared first on Medika Life.

Researchers evaluated the National Institute on Aging’s Health and Retirement Study data. The 3,210 participants ranged in age from 65 to 89 years. The subjects reported how often they engaged in 33 activities, scoring the frequency as “never, at least once monthly, several times a month, and daily.”

Machine learning to predict dementia

The scientists built a machine learning model to analyze the effects of physical activity on memory. The model looked at a range of activities, including hobbies (cooking, for example), card playing, walking for 20 minutes, and socializing with friends or families (via letters, phone calls, email, or in-person visits).

You will not be surprised to learn that engaging in a combination of hobbies (for example, light exercise and connecting socially with others) can reduce memory decline in adults ages 65 to 89. Combining activities appears to drop this memory decline by more than any individual activity.

To punctuate these findings, the researchers report that the effects of engaging in a combination of activities increased with age. Activity appeared to have a more significant impact on memory retention than historical factors such as education level or baseline memory.

Social prescribing involves connecting older individuals to a wide range of community activities. Get out there and walk or garden. Take an art class or come to my hospital and volunteer. I know that I want to maintain healthy cognitive function as I age.

Thank you for joining me today.

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Researchers are increasingly reporting health benefits associated with the consumption of moderate amounts of black coffee. Do you drink three to five cups daily? Good for you — we have some evidence that you may be lowering your risk of Parkinson’s disease, type 2 diabetes, heart disease, and some forms of cancer.

Of course, it is best if you dodge milk, sugar, and fattening flavorings many of us tend to add.

Let’s look at some new research that highlights the importance of genetics in determining our preferences when adding cream and sugar to coffee and regarding chocolate types. By the end, you’ll understand why some call coffee a “cup of Joe.”

Coffee consumption is common.

More than 150 million Americans join me in my coffee drinking habit. The developed world accounts for nearly 72 percent of the world’s beverage consumption.

In the United States, the average adult’s consumption is roughly two cups daily. There is great variability in content by coffee type and retailer. Here’s a breakdown:

• Brewed coffee (8 ounces; 235 mL) — 133 mg (range 102–200)
• Instant coffee (8 ounces; 235 mL) — 93 mg (range 27–173)
• Coffee, decaffeinated (8 ounces; 235 mL) — 5 mg (range 3–12)
• Espresso (1 ounce; 30 mL) — 40 mg (range 30–90)
• Espresso, decaffeinated (1 ounce; 30 mL) — 4 mg

Males consume more coffee than females on average, at least in the USA. Consumption appears lower among African-Americans than among whites.

Tea consumption is on the rise

Tea to the English is really a picnic indoors. — Alice Walker

While tea is not the primary focus today, I wanted to share with you some interesting statistics.

More and more Americans are drinking tea. The Tea Association of the USA offers that 87 percent of consumption is black tea, 12.5 percent green tea, and the small remaining percentage oolong and herbal teas.

More than 80 percent of consumers in the United States drink tea, with millennials the most likely at more than 87 percent. On any given day, more than half of Americans drink tea. The highest consumption is in the Northeast and South regions, respectively.

Consumers prefer tea over coffee in Asia, Argentina, Chile, Paraguay, and Uruguay. Behind water, tea is the second most commonly consumed beverage globally. People take in three times as much tea as coffee.

Trivia question: Did you know that as much as 80 percent of tea consumed in the States is iced? I love that (without additives) it is nearly fat-free and has no sodium, carbonation, or sugar.

Tea contains flavonoids, natural substances that appear to have antioxidant properties. Tea flavonoids can help neutralize free radicals (which we believe can contribute to chronic disease).

Black coffee, dark chocolate, and genes

The greatest tragedies were written by the Greeks and Shakespeare … neither knew chocolate. — Sandra Boynton

Do you like your coffee black? If you answered yes, you probably also prefer dark and bitter chocolate. Recently writing in Nature Scientific Reports, Dr. Cornelis and colleagues analyzed types of coffee drinkers, separating black coffee lovers from those who prefer their coffee with cream and sugar (or more).

Let’s get right to the findings:

Coffee drinkers with a genetic variant reflecting a faster caffeine metabolism prefer bitter, black coffee. The same genetic variant is present in people who prefer plain rather than sweetened tea. We can find the gene change in those who prefer dark chocolate over milk chocolate.

Now it gets even more interesting: The researchers don’t think the coffee or tea preference is secondary to the taste of the drinks. Instead, they believe that people with this gene “prefer black coffee and tea because they associated bitter flavor with the improved mental alertness they crave from caffeine.”

In essence, we equate caffeine’s bitterness with a brain stimulation effect; this is a learned behavior and preference. The same holds for preferring dark chocolate over milk: Think caffeine, think bitter (and choose dark chocolate).

Dark chocolate has limited amounts of caffeine but also contains theobromine, a caffeine-related nervous system stimulant. High doses of theobromine may dampen your mood and increase your heart rate.

Researchers look forward to looking at genetic preferences for other bitter foods. Cornelis observes that bitter foods are “generally associated with more health benefits.”

Let’s hope that those genetically predisposed to prefer dark chocolate (or black coffee) are more likely to engage in other health-promoting behaviors.

Coffee shops

Do you have a favorite coffee shop? I searched for outstanding coffee and chocolate, cafes, and museums on my last visit to Barcelona. Here is a cafe that I highly recommend: Granja M. Viader.

This historical cafe dates back to 1870, and the owners do an excellent job placing memorabilia on the walls. Picasso enjoyed its chocolates, and I loved (repeat: loved) the fresh churros. If you miss your childhood, consider a Cacaolat, a vintage refreshment.

Now, a trivia question: What is coffee sometimes called “Joe?” The use of the term dates back to the early 1900s when Joseph Daniels served as Secretary of the US Navy. A new biography explains that Daniels attempted to “imbue the navy with a strict morality.”

The Secretary increased the number of chaplains, discouraged prostitution at naval bases, and banned alcohol consumption. Stewards purchased more coffee to substitute for the beverage, and Daniels’ name became associated with coffee. Less than pleased folks called it “a cup of Joeseph Daniels,” a label soon shortened to a “cup of Joe.”

Thank you for joining me. I hope you have a health- and joy-filled 2022.

The post Like Dark Chocolate or Black Coffee? Here’s Why appeared first on Medika Life.

The mastoid bone surrounds the middle ear. The external ear collects sound waves. The ear canal carries sound waves to the eardrum. The eardrum vibrates from sound waves, setting the middle ear bones in motion. The middle ear bones (ossicles) vibrate, transmitting sound waves to the inner ear. When the ear is healthy, air pressure remains balanced in the middle ear. The eustachian tube helps control air pressure in the middle ear. The semicircular canals help maintain balance. The vestibular nerve carries balance signals to the brain. The auditory nerve carries sound signals to the brain. The cochlea picks up sound waves and makes nerve signals. 

Structure

Parts of the External Ear

The external ear can be divided functionally and structurally into two parts; the auricle (or pinna), and the external acoustic meatus – which ends at the tympanic membrane.

Auricle

The auricle is a paired structure found on either side of the head. It functions to capture and direct sound waves towards the external acoustic meatus.

It is a mostly cartilaginous structure, with the lobule being the only part not supported by cartilage. The cartilaginous part of the auricle forms an outer curvature, known as the helix. A second innermost curvature runs in parallel with the helix – the antihelix. The antihelix divides into two cura; the inferoanterior crus, and the superoposterior crus.

In the middle of the auricle is a hollow depression, called the concha. It continues into the skull as the external acoustic meatus. The concha acts to direct sound into the external acoustic meatus. Immediately anterior to the beginning of the external acoustic meatus is an elevation of cartilaginous tissue – the tragus. Opposite the tragus is the antitragus.

External Acoustic Meatus

The external acoustic meatus is a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane. The walls of the external 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.

The external acoustic meatus does not have a straight path, and instead travels in an S-shaped curve as follows:

• Initially it travels in a superoanterior direction.
• In then turns slightly to move superoposteriorly.
• It ends by running in an inferoanterior direction.

Tympanic Membrane

The tympanic membrane lies at the distal end of the external acoustic meatus. It is a connective tissue structure, covered with skin on the outside and a mucous membrane on the inside. The membrane is connected to the surrounding temporal bone by a fibrocartilaginous ring.

The translucency of the tympanic membrane allows the structures within the middle ear to be observed during otoscopy. On the inner surface of the membrane, the handle of malleus attaches to the tympanic membrane, at a point called the umbo of tympanic membrane.

The handle of malleus continues superiorly, and at its highest point, a small projection called the lateral process of the malleus can be seen. The parts of the tympanic membrane moving away from the lateral process are called the anterior and posterior malleolar folds.

Vasculature

The external ear is supplied by branches of the external carotid artery:

• Posterior auricular artery
• Superficial temporal artery
• Occipital artery
• Maxillary artery (deep auricular branch) – supplies the deep aspect of the external acoustic meatus and tympanic membrane only.

Venous drainage is via veins following the arteries listed above.

Innervation

The sensory innervation to the skin of the auricle comes from numerous nerves:

• Greater auricular nerve (branch of the cervical plexus) – innervates the skin of the auricle
• Lesser occipital nerve (branch of the cervical plexus) – innervates the skin of the auricle
• Auriculotemporal nerve (branch of the mandibular nerve) – innervates the skin of the auricle and external auditory meatus.
• Branches of the facial and vagus nerves – innervates the deeper aspect of the auricle and external auditory meatus

Some individuals can complain of an involuntary cough when cleaning their ears – this is due to stimulation of the auricular branch of the vagus nerve (the vagus nerve is also responsible for the cough reflex).

Parts of the Middle Ear

The middle ear can be divided into two parts:

• Tympanic cavity – located medially to the tympanic membrane. It contains three small bones known as the auditory ossicles: the malleus, incus and stapes. They transmit sound vibrations through the middle ear.
• Epitympanic recess – a space superior to the tympanic cavity, which lies next to the mastoid air cells. The malleus and incus partially extend upwards into the epitympanic recess.

Borders

The middle ear can be visualised as a rectangular box, with a roof and floor, medial and lateral walls and anterior and posterior walls.

• Roof – formed by a thin bone from the petrous part of the temporal bone. It separates the middle ear from the middle cranial fossa.
• Floor – known as the jugular wall, it consists of a thin layer of bone, which separates the middle ear from the internal jugular vein
• Lateral wall – made up of the tympanic membrane and the lateral wall of the epitympanic recess.
• Medial wall – formed by the lateral wall of the internal ear. It contains a prominent bulge, produced by the facial nerve as it travels nearby.
• Anterior wall – a thin bony plate with two openings; for the auditory tube and the tensor tympani muscle. It separates the middle ear from the internal carotid artery.
• Posterior wall (mastoid wall) – it consists of a bony partition between the tympanic cavity and the mastoid air cells.
  • Superiorly, there is a hole in this partition, allowing the two areas to communicate. This hole is known as the aditus to the mastoid antrum.

Bones

The bones of the middle ear are the auditory ossicles – the malleus, incus and stapes. They are connected in a chain-like manner, linking the tympanic membrane to the oval window of the internal ear.

Sound vibrations cause a movement in the tympanic membrane which then creates movement, or oscillation, in the auditory ossicles. This movement helps to transmit the sound waves from the tympanic membrane of external ear to the oval window of the internal ear.

The malleus is the largest and most lateral of the ear bones, attaching to the tympanic membrane, via the handle of malleus. The head of the malleus lies in the epitympanic recess, where it articulates with the next auditory ossicle, the incus.

The next bone – the incus – consists of a body and two limbs. The body articulates with the malleus, the short limb attaches to the posterior wall of the middle, and the long limb joins the last of the ossicles; the stapes.

The stapes is the smallest bone in the human body. It joins the incus to the oval window of the inner ear. It is stirrup-shaped, with a head, two limbs, and a base. The head articulates with the incus, and the base joins the oval window.

Mastoid Air Cells

The mastoid air cells are located posterior to epitympanic recess. They are a collection of air-filled spaces in the mastoid process of the temporal bone. The air cells are contained within a cavity called the mastoid antrum. The mastoid antrum communicates with the middle ear via the aditus to mastoid antrum.

The mastoid air cells act as a ‘buffer system‘ of air –  releasing air into the tympanic cavity when the pressure is too low.

Muscles

There are two muscles which serve a protective function in the middle ear; the tensor tympani and stapedius. They contract in response to loud noise, inhibiting the vibrations of the malleus, incus and stapes, and reducing the transmission of sound to the inner ear. This action is known as the acoustic reflex.

The tensor tympani originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting. It is innervated by the tensor tympani nerve, a branch of the mandibular nerve. The stapedius muscle attaches to the stapes, and is innervated by the facial nerve.

Auditory Tube

The auditory tube (eustachian tube) is a cartilaginous and bony tube that connects the middle ear to the nasopharynx. It acts to equalise the pressure of the middle ear to that of the external auditory meatus.

It extends from the anterior wall of the middle ear, in an anterior, medioinferior direction, opening onto the lateral wall of the nasopharynx. In joining the two structures, it is a pathway by which an upper respiratory infection can spread into the middle ear.

The tube is shorter and straighter in children, therefore middle ear infections tend to be more common in children than adults.

Structure of the Inner Ear

The inner ear is located within the petrous part of the temporal bone. It lies between the middle ear and the internal acoustic meatus, which lie laterally and medially respectively. The inner ear has two main components – the bony labyrinth and membranous labyrinth.

• Bony labyrinth – consists of a series of bony cavities within the petrous part of the temporal bone. It is composed of the cochlea, vestibule and three semi-circular canals. All these structures are lined internally with periosteum and contain a fluid called perilymph.
• Membranous labyrinth – lies within the bony labyrinth. It consists of the cochlear duct, semi-circular ducts, utricle and the saccule. The membranous labyrinth is filled with fluid called endolymph.

The inner ear has two openings into the middle ear, both covered by membranes. The oval window lies between the middle ear and the vestibule, whilst the round window separates the middle ear from the scala tympani (part of the cochlear duct).

Bony Labyrinth

The bony labyrinth is a series of bony cavities within the petrous part of the temporal bone. It consists of three parts – the cochlea, vestibule and the three semi-circular canals.

Vestibule

The vestibule is the central part of the bony labyrinth. It is separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posterioly with the semi-circular canals. Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule.

Cochlea

The cochlea houses the cochlea duct of the membranous labyrinth – the auditory part of the inner ear. It twists upon itself around a central portion of bone called the modiolus, producing a cone shape which points in an anterolateral direction. Branches from the cochlear portion of the vestibulocochlear (VIII) nerve are found at the base of the modiolus.

Extending outwards from the modiolus is a ledge of bone known as spiral lamina, which attaches to the cochlear duct, holding it in position. The presence of the cochlear duct creates two perilymph-filled chambers above and below:

• Scala vestibuli: Located superiorly to the cochlear duct. As its name suggests, it is continuous with the vestibule.
• Scala tympani: Located inferiorly to the cochlear duct. It terminates at the round window.

Semi-circular Canals

There are three semi-circular canals; anterior, lateral and posterior. They contain the semi-circular ducts, which are responsible for balance (along with the utricle and saccule).

The canals are situated superoposterior to the vestibule, at right angles to each other. They have a swelling at one end, known as the ampulla.

Membranous Labyrinth

The membranous labyrinth is a continuous system of ducts filled with endolymph. It lies within the bony labyrinth, surrounded by perilymph. It is composed of the cochlear duct, three semi-circular ducts, saccule and the utricle.

The cochlear duct is situated within the cochlea and is the organ of hearing. The semi-circular ducts, saccule and utricle are the organs of balance (also known as the vestibular apparatus).

Cochlear Duct

The cochlear duct is located within the bony scaffolding of the cochlea. It is held in place by the spiral lamina. The presence of the duct creates two canals above and below it –  the scala vestibuli and scala tympani respectively. The cochlear duct can be described as having a triangular shape:

• Lateral wall – Formed by thickened periosteum, known as the spiral ligament.
• Roof – Formed by a membrane which separates the cochlear duct from the scala vestibuli, known as the Reissner’s membrane.
• Floor – Formed by a membrane which separates the cochlear duct from the scala tympani, known as the basilar membrane.

The basilar membrane houses the epithelial cells of hearing – the Organ of Corti. A more detailed description of the Organ of Corti is beyond the scope of this article.

Saccule and Utricle

The saccule and utricle are two membranous sacs located in the vestibule. They are organs of balance which detect movement or acceleration of the head in the vertical and horizontal planes, respectively.

The utricle is the larger of the two, receiving the three semi-circular ducts. The saccule is globular in shape and receives the cochlear duct.

Endolymph drains from the saccule and utricle into the endolymphatic duct. The duct travels through the vestibular aqueduct to the posterior aspect of the petrous part of the temporal bone. Here, the duct expands to a sac where endolymph can be secreted and absorbed.

Semi-circular Ducts

The semi-circular ducts are located within the semi-circular canals, and share their orientation. Upon movement of the head, the flow of endolymph within the ducts changes speed and/or direction. Sensory receptors in the ampullae of the semi-circular canals detect this change, and send signals to the brain, allowing for the processing of balance.

Vasculature

The bony labyrinth and membranous labyrinth have different arterial supplies. The bony labyrinth receives its blood supply from three arteries, which also supply the surrounding temporal bone:

• Anterior tympanic branch (from maxillary artery).
• Petrosal branch (from middle meningeal artery).
• Stylomastoid branch (from posterior auricular artery).

The membranous labyrinth is supplied by the labyrinthine artery, a branch of the inferior cerebellar artery (or, occasionally, the basilar artery). It divides into three branches:

• Cochlear branch – supplies the cochlear duct.
• Vestibular branches (x2) – supply the vestibular apparatus.

Venous drainage of the inner ear is through the labyrinthine vein, which empties into the sigmoid sinus or inferior petrosal sinus.

Innervation

The inner ear is innervated by the vestibulocochlear nerve (CN VIII). It enters the inner ear via the internal acoustic meatus, where it divides into the vestibular nerve (responsible for balance) and the cochlear nerve (responsible for hearing):

• Vestibular nerve – enlarges to form the vestibular ganglion, which then splits into superior and inferior parts to supply the utricle, saccule and three semi-circular ducts.
• Cochlear nerve – enters at the base of the modiolus and its branches pass through the lamina to supply the receptors of the Organ of Corti.

The facial nerve, CN VII, also passes through the inner ear, but does not innervate any of the structures present.

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The brain is arguably the most important organ in the human body. It controls and coordinates actions and reactions, allows us to think and feel, and enables us to have memories and feelings—all the things that make us human.

While the brain only weighs about three pounds, it is a highly complex organ made up of many parts. Years of scientific study have made it possible for scientists to identify the various areas of the brain and determine their specific functions. The following information provides a brief description of some of the major parts of the human brain.

The Cell Structure of the Brain

The brain is made up of two types of cells: neurons and glial cells, also known as neuroglia or glia. The neuron is responsible for sending and receiving nerve impulses or signals. Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin and facilitate signal transmission in the nervous system. In the human brain, glial cells outnumber neurons by about 50 to one. Glial cells are the most common cells found in primary brain tumors.

When a person is diagnosed with a brain tumor, a biopsy may be done, in which tissue is removed from the tumor for identification purposes by a pathologist. Pathologists identify the type of cells that are present in this brain tissue, and brain tumors are named based on this association. The type of brain tumor and cells involved impact patient prognosis and treatment.

The Meninges

The brain is housed inside the bony covering called the cranium. The cranium protects the brain from injury. Together, the cranium and bones that protect the face are called the skull. Between the skull and brain is the meninges, which consist of three layers of tissue that cover and protect the brain and spinal cord. From the outermost layer inward they are: the dura mater, arachnoid and pia mater.

Dura Mater: In the brain, the dura mater is made up of two layers of whitish, nonelastic film or membrane. The outer layer is called the periosteum. An inner layer, the dura, lines the inside of the entire skull and creates little folds or compartments in which parts of the brain are protected and secured. The two special folds of the dura in the brain are called the falx and the tentorium. The falx separates the right and left half of the brain and the tentorium separates the upper and lower parts of the brain.

Arachnoid: The second layer of the meninges is the arachnoid. This membrane is thin and delicate and covers the entire brain. There is a space between the dura and the arachnoid membranes that is called the subdural space. The arachnoid is made up of delicate, elastic tissue and blood vessels of varying sizes.

Pia Mater: The layer of meninges closest to the surface of the brain is called the pia mater. The pia mater has many blood vessels that reach deep into the surface of the brain. The pia, which covers the entire surface of the brain, follows the folds of the brain. The major arteries supplying the brain provide the pia with its blood vessels. The space that separates the arachnoid and the pia is called the subarachnoid space. It is within this area that cerebrospinal fluid flows.

Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is found within the brain and surrounds the brain and the spinal cord. It is a clear, watery substance that helps to cushion the brain and spinal cord from injury. This fluid circulates through channels around the spinal cord and brain, constantly being absorbed and replenished. It is within hollow channels in the brain, called ventricles, that the fluid is produced. A specialized structure within each ventricle, called the choroid plexus, is responsible for the majority of CSF production. The brain normally maintains a balance between the amount of CSF that is absorbed and the amount that is produced. However, disruptions in this system may occur.

The Ventricular System

The ventricular system is divided into four cavities called ventricles, which are connected by a series of holes, called foramen, and tubes.

Two ventricles enclosed in the cerebral hemispheres are called the lateral ventricles (first and second). They each communicate with the third ventricle through a separate opening called the Foramen of Munro. The third ventricle is in the center of the brain, and its walls are made up of the thalamus and hypothalamus.

The third ventricle connects with the fourth ventricle through a long tube called the Aqueduct of Sylvius.

CSF flowing through the fourth ventricle flows around the brain and spinal cord by passing through another series of openings.

Brain Components and Functions

Brainstem

The brainstem is the lower extension of the brain, located in front of the cerebellum and connected to the spinal cord. It consists of three structures: the midbrain, pons and medulla oblongata. It serves as a relay station, passing messages back and forth between various parts of the body and the cerebral cortex. Many simple or primitive functions that are essential for survival are located here.

The midbrain is an important center for ocular motion while the pons is involved with coordinating eye and facial movements, facial sensation, hearing and balance.

The medulla oblongata controls breathing, blood pressure, heart rhythms and swallowing. Messages from the cortex to the spinal cord and nerves that branch from the spinal cord are sent through the pons and the brainstem. Destruction of these regions of the brain will cause “brain death.” Without these key functions, humans cannot survive.

The reticular activating system is found in the midbrain, pons, medulla and part of the thalamus. It controls levels of wakefulness, enables people to pay attention to their environments and is involved in sleep patterns.

Originating in the brainstem are 10 of the 12 cranial nerves that control hearing, eye movement, facial sensations, taste, swallowing and movements of the face, neck, shoulder and tongue muscles. The cranial nerves for smell and vision originate in the cerebrum. Four pairs of cranial nerves originate from the pons: nerves five through eight.

Cerebellum

The cerebellum is located at the back of the brain beneath the occipital lobes. It is separated from the cerebrum by the tentorium (fold of dura). The cerebellum fine tunes motor activity or movement, e.g. the fine movements of fingers as they perform surgery or paint a picture. It helps one maintain posture, sense of balance or equilibrium, by controlling the tone of muscles and the position of limbs. The cerebellum is important in one’s ability to perform rapid and repetitive actions such as playing a video game. In the cerebellum, right-sided abnormalities produce symptoms on the same side of the body.

Cerebrum

The cerebrum, which forms the major portion of the brain, is divided into two major parts: the right and left cerebral hemispheres. The cerebrum is a term often used to describe the entire brain. A fissure or groove that separates the two hemispheres is called the great longitudinal fissure. The two sides of the brain are joined at the bottom by the corpus callosum. The corpus callosum connects the two halves of the brain and delivers messages from one half of the brain to the other. The surface of the cerebrum contains billions of neurons and glia that together form the cerebral cortex.

The cerebral cortex appears grayish brown in color and is called the “gray matter.” The surface of the brain appears wrinkled. The cerebral cortex has sulci (small grooves), fissures (larger grooves) and bulges between the grooves called gyri. Scientists have specific names for the bulges and grooves on the surface of the brain. Decades of scientific research have revealed the specific functions of the various regions of the brain. Beneath the cerebral cortex or surface of the brain, connecting fibers between neurons form a white-colored area called the “white matter.”

The cerebral hemispheres have several distinct fissures. By locating these landmarks on the surface of the brain, it can effectively be divided into pairs of “lobes.” Lobes are simply broad regions of the brain. The cerebrum or brain can be divided into pairs of frontal, temporal, parietal and occipital lobes. Each hemisphere has a frontal, temporal, parietal and occipital lobe. Each lobe may be divided, once again, into areas that serve very specific functions. The lobes of the brain do not function alone: they function through very complex relationships with one another.

Messages within the brain are delivered in many ways. The signals are transported along routes called pathways. Any destruction of brain tissue by a tumor can disrupt the communication between different parts of the brain. The result will be a loss of function such as speech, the ability to read or the ability to follow simple spoken commands. Messages can travel from one bulge on the brain to another (gyri to gyri), from one lobe to another, from one side of the brain to the other, from one lobe of the brain to structures that are found deep in the brain, e.g. thalamus, or from the deep structures of the brain to another region in the central nervous system.

Research has determined that touching one side of the brain sends electrical signals to the other side of the body. Touching the motor region on the right side of the brain would cause the opposite side or the left side of the body to move. Stimulating the left primary motor cortex would cause the right side of the body to move. The messages for movement and sensation cross to the other side of the brain and cause the opposite limb to move or feel a sensation. The right side of the brain controls the left side of the body and vice versa. So if a brain tumor occurs on the right side of the brain that controls the movement of the arm, the left arm may be weak or paralyzed.

Cranial Nerves

There are 12 pairs of nerves that originate from the brain itself. These nerves are responsible for very specific activities and are named and numbered as follows:

1. Olfactory: Smell
2. Optic: Visual fields and ability to see
3. Oculomotor: Eye movements; eyelid opening
4. Trochlear: Eye movements
5. Trigeminal: Facial sensation
6. Abducens: Eye movements
7. Facial: Eyelid closing; facial expression; taste sensation
8. Auditory/vestibular: Hearing; sense of balance
9. Glossopharyngeal: Taste sensation; swallowing
10. Vagus: Swallowing; taste sensation
11. Accessory: Control of neck and shoulder muscles
12. Hypoglossal: Tongue movement

Hypothalamus

The hypothalamus is a small structure that contains nerve connections that send messages to the pituitary gland. The hypothalamus handles information that comes from the autonomic nervous system. It plays a role in controlling functions such as eating, sexual behavior and sleeping; and regulates body temperature, emotions, secretion of hormones and movement. The pituitary gland develops from an extension of the hypothalamus downwards and from a second component extending upward from the roof of the mouth.

The Lobes

Frontal Lobes

The frontal lobes are the largest of the four lobes responsible for many different functions. These include motor skills such as voluntary movement, speech, intellectual and behavioral functions. The areas that produce movement in parts of the body are found in the primary motor cortex or precentral gyrus. The prefrontal cortex plays an important part in memory, intelligence, concentration, temper and personality.

The premotor cortex is a region found beside the primary motor cortex. It guides eye and head movements and a person’s sense of orientation. Broca’s area, important in language production, is found in the frontal lobe, usually on the left side.

Occipital Lobes

These lobes are located at the back of the brain and enable humans to receive and process visual information. They influence how humans process colors and shapes. The occipital lobe on the right interprets visual signals from the left visual space, while the left occipital lobe performs the same function for the right visual space.

Parietal Lobes

These lobes interpret simultaneously, signals received from other areas of the brain such as vision, hearing, motor, sensory and memory. A person’s memory, and the new sensory information received, give meaning to objects.

Temporal Lobes

These lobes are located on each side of the brain at about ear level, and can be divided into two parts. One part is on the bottom (ventral) of each hemisphere, and the other part is on the side (lateral) of each hemisphere. An area on the right side is involved in visual memory and helps humans recognize objects and peoples’ faces. An area on the left side is involved in verbal memory and helps humans remember and understand language. The rear of the temporal lobe enables humans to interpret other people’s emotions and reactions.

Limbic System

This system is involved in emotions. Included in this system are the hypothalamus, part of the thalamus, amygdala (active in producing aggressive behavior) and hippocampus (plays a role in the ability to remember new information).

Pineal Gland

This gland is an outgrowth from the posterior or back portion of the third ventricle. In some mammals, it controls the response to darkness and light. In humans, it has some role in sexual maturation, although the exact function of the pineal gland in humans is unclear.

Pituitary Gland

The pituitary is a small gland attached to the base of the brain (behind the nose) in an area called the pituitary fossa or sella turcica. The pituitary is often called the “master gland” because it controls the secretion of hormones. The pituitary is responsible for controlling and coordinating the following:

• Growth and development
• The function of various body organs (i.e. kidneys, breasts and uterus)
• The function of other glands (i.e. thyroid, gonads, and adrenal glands)

Posterior Fossa

This is a cavity in the back part of the skull which contains the cerebellum, brainstem and cranial nerves 5-12.

Thalamus

The thalamus serves as a relay station for almost all information that comes and goes to the cortex. It plays a role in pain sensation, attention and alertness. It consists of four parts: the hypothalamus, the epythalamus, the ventral thalamus and the dorsal thalamus. The basal ganglia are clusters of nerve cells surrounding the thalamus.

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In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and entering the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. The diameter of the spinal cord ranges from 13 mm (1⁄2 in) in the cervical and lumbar regions to 6.4 mm (1⁄4 in) in the thoracic area.

The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes.

It is also the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.

Anatomical Position and Structure

The spinal cord is a cylindrical structure, greyish-white in colour. It has a relatively simple anatomical course:

• The spinal cord arises cranially as a continuation of the medulla oblongata (part of the brainstem).
• It then travels inferiorly within the vertebral canal, surrounded by the spinal meninges containing cerebrospinal fluid.
• At the L2 vertebral level the spinal cord tapers off, forming the conus medullaris.

As a result of the termination of the spinal cord at L2, it occupies around two thirds of the vertebral canal. The spinal nerves that arise from the end of the spinal cord are bundled together, forming a structure known as the cauda equina.

During the course of the spinal cord, there are two points of enlargement. The cervical enlargement is located proximally, at the C4-T1 level. It represents the origin of the brachial plexus. Between T11 and L1 is the lumbar enlargement, representing the origin of the lumbar and sacral plexi.

The spinal cord is marked by two depressions on its surface. The anterior median fissure is a deep groove extending the length of the anterior surface of the spinal cord. On the posterior aspect there is a slightly shallower depression – the posterior median sulcus.

Spinal Meninges

The spinal meninges are three membranes that surround the spinal cord – the dura mater, arachnoid mater, and pia mater. They contain cerebrospinal fluid, acting to support and protect the spinal cord. They are analogous with the cranial meninges.

Distally, the meninges form a strand of fibrous tissue, the filum terminale, which attaches to the vertebral bodies of the coccyx. It acts as an anchor for the spinal cord and meninges.

Dura Mater

The spinal dura mater is the most external of the meninges. It extends from the foramen magnum to the filum terminale, separated from the walls of the vertebral canal by the epidural space. This space contains some loose connective tissue, and the internal vertebral venous plexus.

As the spinal nerves exit the vertebral canal, they pierce the dura mater, temporarily passing in the epidural space. In doing so, the dura mater surrounds the nerve root, and fuses with the outer connective tissue covering of the nerve, the epineurium.

The spinal arachnoid mater is a delicate membrane, located between the dura mater and the pia mater. It is separated from the latter by the subarachnoid space, which contains cerebrospinal fluid.

Distal to the conus medullaris, the subarachnoid space expands, forming the lumbar cistern. This space accessed during a lumbar puncture (to obtain CSF fluid) and spinal anaesthesia.

Pia Mater

The spinal pia mater is the innermost of the meninges. It is a thin membrane that covers the spinal cord, nerve roots and their blood vessels. Inferiorly, the spinal pia mater fuses with the filum terminale.

Between the nerve roots, the pia mater thickens to form the denticulate ligaments. These ligaments attach to the dura mater – suspending the spinal cord in the vertebral canal.

Formation of the Spinal Nerves

The spinal nerves are mixed nerves that originate from the spinal cord, forming the peripheral nervous system.

Each spinal nerve begins as an anterior (motor) and a posterior (sensory) nerve root. These roots arise from the spinal cord, and unite at the intervertebral foramina, forming a single spinal nerve.

The spinal nerve then leaves the vertebral canal via the intervertebral foramina, and then divides into two:

• Posterior rami – supplies nerve fibres to the synovial joints of the vertebral column, deep muscles of the back, and the overlying skin.
• Anterior rami – supplies nerve fibres to much of the remaining area of the body, both motor and sensory.

The nerve roots L2-S5 arise from the distal end of the spinal cord, forming a bundle of nerves known as the cauda equina.

Vasculature

The arterial supply to the spinal cord is via three longitudinal arteries – the anterior spinal artery and the paired posterior spinal arteries.

• Anterior spinal artery – formed from branches of the vertebral arteries. They travel in the anterior median fissure.
• Posterior spinal arteries – originate from the vertebral artery or the posteroinferior cerebellar artery. They anastamose with one another in the pia mater.

Additional arterial supply is via the anterior and posterior segmental medullary arteries – small vessels which enter via the nerve roots. The largest anterior segmental medullary artery is the artery of Adamkiewicz. It arises from the inferior intercostal or upper lumbar arteries, and supplies the inferior 2/3 of the spinal cord.

Venous drainage is via three anterior and three posterior spinal veins. These veins are valveless, and form an anastamosing network along the surface of the spinal cord. They also receive venous blood from the radicular veins. The spinal veins drain into the internal and external vertebral plexuses, which in turn empty into the systemic segmental veins. The internal vertebral plexus also empties into the dural venous sinuses superiorly.

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The peripheral nervous system refers to parts of the nervous system outside the brain and spinal cord. It includes the cranial nerves, spinal nerves and their roots and branches, peripheral nerves, and neuromuscular junctions.

Structure

Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.

Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.

Afferent, Efferent, and Mixed Nerves

Some of the nerves in the body are specialized for carrying information in only one direction, similar to a one-way street. Nerves that carry information from sensory receptors to the central nervous system only are called afferent nerves. Other neurons, known as efferent nerves, carry signals only from the central nervous system to effectors such as muscles and glands. Finally, some nerves are mixed nerves that contain both afferent and efferent axons. Mixed nerves function like 2-way streets where afferent axons act as lanes heading toward the central nervous system and efferent axons act as lanes heading away from the central nervous system.

Cranial Nerves

Extending from the inferior side of the brain are 12 pairs of cranial nerves. Each cranial nerve pair is identified by a Roman numeral 1 to 12 based upon its location along the anterior-posterior axis of the brain. Each nerve also has a descriptive name (e.g. olfactory, optic, etc.) that identifies its function or location. The cranial nerves provide a direct connection to the brain for the special sense organs, muscles of the head, neck, and shoulders, the heart, and the GI tract.

Spinal Nerves

Extending from the left and right sides of the spinal cord are 31 pairs of spinal nerves. The spinal nerves are mixed nerves that carry both sensory and motor signals between the spinal cord and specific regions of the body. The 31 spinal nerves are split into 5 groups named for the 5 regions of the vertebral column. Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. Each spinal nerve exits from the spinal cord through the intervertebral foramen between a pair of vertebrae or between the C1 vertebra and the occipital bone of the skull.

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