Download Anatomy Notes on the Brain

Anatomy Notes on the Brain
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 3 pounds, it is a highly complex organ made up of many
parts. Years of scientific study of the brain have made it possible for scientists to identify the
various areas of the brain and determine their specific functions. The following information
gives a brief description of some of the major parts of the human brain.
The cranium
The brain is protected by a bony covering called the cranium (which, along with the bones of
the face, make up the skull). Inside the cranium, the brain is surrounded by the meninges. The
meninges is made up of 3 layers of tissue:
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Pia mater – the layer closest to the surface of the brain
Arachnoid membrane – the middle layer of tissue
Dura mater – the outer-most layer
Note that the cerebral hemispheres of the brain are highly wrinkled. These structures are
named:
a. sulcus .(pIural: sulci) = "valley"
b. gyrus (pIural: gyn) = "hill"
The general pattern of sulci and gyri are similar among most individuals and these features are
all named, but there is a lot of individual variation.
The two major sulci:
a. Central sulcus: large deep groove or indentation running downward from the midpoint at the
top of the brain; it separates the parietal and frontal lobes (also called the Fissure of Rolando).
b. Lateral sulcus: large deep groove or indentation running horizontally from front of brain back
midway that separates forebrain from midbrain or that separates the parietal and temporal
lobes (also called the Fissure of Sylvius).
The cerebrum – the front of the brain
The largest part of the brain located in the front is called the cerebrum. The cerebrum is
responsible for:
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Movement
Body temperature
Touch
Vision
Hearing
Judgment
Reasoning
Problem solving
Emotions
Learning
The cerebrum has 2 parts: the right cerebral hemisphere and the left cerebral hemisphere. They
are connected at the bottom and have a deep groove running between them. In general, the
right cerebral hemisphere controls the left side of the body, and the left cerebral hemisphere
controls the right. The right side is involved with creativity and artistic abilities. The left side is
important for logic and rational thinking.
The hemispheres of the cerebrum are divided into lobes, or broad regions of the brain. Each
lobe is responsible for a variety of bodily functions:
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Frontal lobes are involved with personality, speech, and motor development
Temporal lobes are responsible for memory, language and speech functions
Parietal lobes are involved with sensation
Occipital lobes are the primary vision centers
The surface of the cerebrum appears wrinkled and is made up of deep grooves (called sulci) and
bumps or folds (called gyri). The outer part of the cerebrum is called gray matter and contains
nerve cells. The inner part is called white matter and contains connections of nerves via the
axons.
Higher Functions
Most of the cortex is concerned with functions that go beyond the primary perception of
sensation or primary control of motor movement.
1. Frontal lobe: cognition, behavior, emotion
2. Prefrontal association cortex: sides of frontal lobe
3. Parietal lobe
4. Temporal lobe: memory and emotions
Sensory and Motor Areas
5. Somatosensory cortex: perception of touch from surface of body
a. strip behind the central sulcus (post-central gyrus) in parietal lobe
b. The surface of the body can be mapped as a distorted representation (sensory homunculus)
• the lower limb is at the top, followed by trunk, shoulder, arm, hand, neck, face, lips, jaw and
tongue.
6. Primary motor cortex: final output from brain to spinal cord for voluntary control of
muscular movement
a. strip in front of central sulcus (pre-central gyrus) in frontal lobe
7. Premotor cortex: planning of movement
a. area in front of primary motor cortex in frontal lobe
Vision, Hearing, and Language
1. Primary visual cortex: perception of vision, first input from eyes
a. hindmost part of occipital lobe
b. surrounding areas of occipital lobe are concerned with analysis of vision. .
2. Primary auditory cortex: input from ears
a. upper surface of temporal lobe
b. both ears go to both sides of brain, organized by tone
3. Motor speech: Broca's area
a. lower region of frontal lobe on left side only
b. damage to this area results in the inability to produce meaningful language
4. Sensory speech: Wernicke's area
a. region of temporal and parietal lobe on left side only
b. damage to this area results in the inability to understand language
The cerebellum – the back of the brain
Behind the cerebrum at the back of the head is the cerebellum. In Latin, cerebellum means
“little brain.” However, the cerebellum contains more nerve cells than both hemispheres
combined. The cerebellum is primarily a movement control center, responsible for:
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Voluntary muscle movements
Fine motor skills
Maintaining balance, posture, and equilibrium
Unlike the cerebrum, the left cerebellum controls the left side of the body, and the right
cerebellum controls the right side of the body.
The cerebellum is involved in several functions of the body including:
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Fine Movement Coordination
Balance and Equilibrium
Muscle Tone
Location:
Directionally, the cerebellum is situated at the base of the skull, above the brainstem and
beneath the occipital lobes of the cerebral cortex.
Cerebellar injury results in movements that are slow and uncoordinated. Individuals with
cerebellar lesions tend to sway and stagger when walking.
Damage to the cerebellum can lead to:
1) loss of coordination of motor movement (asynergia)
2) the inability to judge distance and when to stop (dysmetria)
3) the inability to perform rapid alternating movements (adiadochokinesia)
4) movement tremors (intention tremor)
5) staggering, wide based walking (ataxic gait)
6) tendency toward falling
7) weak muscles (hypotonia)
8) slurred speech (ataxic dysarthria)
9) abnormal eye movements (nystagmus)
The brainstem – the middle of the brain
The brainstem is located in front of the cerebellum. The brainstem is like the hard-drive of a
computer. It is the main control panel for the body that passes messages back and forth
between the brain and other parts of the body. The cerebrum, the cerebellum, and the spinal
cord are all connected to the brainstem. The brainstem has three main parts, the midbrain, the
pons, and the medulla oblongata.
The brainstem controls vital functions of the body, including:
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Breathing
Consciousness
Cardiac function
Involuntary muscle movements
Swallowing
Movement of the eyes and mouth
Relaying sensory messages (pain, heat, noise, etc.)
Hunger
Other important parts of the brain
Ventricular system
The brain is not a solid organ. There are fluid-filled cavities within the brain called ventricles.
The ventricles are important in providing nourishment to the brain. The ventricular system
produces and processes cerebrospinal fluid – a clear, watery substance that flows around the
brain and helps cushion and protect it.
Cranial nerves
The brain also contains 12 pairs of cranial nerves each responsible for specific functions in the
body:
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Olfactory nerve – smell
Optic nerve – vision
Oculomotor – eye movements, eyelid opening
Trochlear – eye movements
Trigeminal – facial sensations, chewing
Abducens – eye movements
Facial – taste, facial expressions
Vestibulocochlear – hearing, balance
Glossopharyngeal – taste, swallowing
Vagus – swallowing, taste
Accessory – neck and shoulder muscles
Hypoglossal – tongue movement
Notes on Memory
Memory involves three main processes: encoding, storage and retrieval.
Encoding relates to perception of the information through senses or feelings.
Storage is the establishment of neural pathways through the establishment of synapse
networks.
Retrieval is the process of retracing the neural pathways to bring back the memory. Most
memories are retrieved through a pointer system where a connection is made using several
cues or pointers. Descriptors are accessed that are associated with the memory and that
pathway is retraced. The hippocampus coordinates the neural data.
There are three main subdivisions of memory depending on what part of the brain is processing
it.
Sensory memory is the shortest of all memories and is encoded through a short stimulation of
the senses.
Short term memory is storage of up to 7 items and lasts under a minute.
Working memory refers to memory processed in the prefrontal cortex. It coordinates long term
memories with sights, sounds and feelings
Long term memory is processed deep in the brain in an area called the hippocampus that
transfers newly gained memory into permanent memory
We forget memories because of three reasons;
1. Not encoded properly because of inattention or distraction ( cant do two things at once
and remember both of them for a long period of time)
2. No retention- neural pathway is never completed
3. Improper retrieval- pointers or cues are not retained or other pathways have been
associated with the memory
Aging can affect memory through any of the above reasons. The hippocampus shrinks up to
20% by the time a person reaches old age. The brain also shrinks in size as well.
Ways to improve memory include
1. Diet- proper nutrition provides nourishment to the brain. Omega 3 and antioxidants
assist in neural function
2. Using the brain helps control diminished memory as well as shrinkage of brain tissue.
Puzzles, word games, and learning all keep the brain functioning longer
3. Exercise sends more blood to the brain therefore more oxygen for cell usage
4. Mneumonic devices or method of loci help to organize and retrieve faster
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Chunking puts similar data together to be remembered and retrieved
Practice (studying) improves neural pathways
Reducing stress will improve memory by reducing distractions
Out of the ordinary visual reminders such as a string on the finger or an object placed in
an unusual or out of the ordinary place will help remember things.
Sleep
Why do we need to sleep?
During sleep the body:
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Repairs cells: Sleep slows metabolism, heartbeat and breathing rate, which helps the
body replenish after daily physical activity.
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Releases growth hormones in young adults: While you sleep, a hormone is released that
aids the growth of bones, tissues and new red blood cells.
Strengthens your immune and nervous systems.
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Kinds of sleep
There are two kinds of sleep: non-rapid eye movement eye movement (NREM) and rapid eye
movement (REM) sleep. These two states affect the body and mind in different ways.
NREM Sleep
If we are lucky, we fall asleep within 10 to 20 minutes of going to bed. Our bodies begin a cycle
of sleep. The first four stages are NREM. Stages one and two are light sleep where we can be
awakened easily and contractions of our muscles can be seen. In stages three and four our
brain waves slow and we enter into deep sleep -- it is very difficult to wake someone up in this
stage. There is no eye movement or muscle activity at this point. It is during this stage that
people can sleep walk or have night mares.
REM Sleep and Dreaming
The fifth stage of sleep occurs normally after about 90 minutes, and is characterized by
dreaming and rapid eye movement. No other muscles move during this time but the brain is
closest to being awake at this time.
We dream all night long. The cycles of NREM and REM sleep repeat throughout the night. The
first period of dreaming only lasts five minutes. REM periods are longer with each subsequent
cycle. We typically spend more than two hours each night dreaming. There is no time dilation
with REM. A 5 min dream takes 5 minutes of REM.
Studies have shown that animals can also dream.
How much sleep do I need?
Most teenagers need between nine and nine-and-a-half hours of sleep each night. Yet surveys
show that most teenagers get only six to seven hours. Twenty percent of high schoolers say
that they have fallen asleep in class.
If you don't get enough sleep, you may experience symptoms of sleep deprivation. These
include:
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Falling asleep in class.
Irritability.
Difficulty waking up in the morning.
Difficulty concentrating.
Depression after prolonged sleep deprivation
Sleep disorders
Some common sleep disorders include
Sleep deprivation- not getting enough sleep
Insomnia- the inability to get the amount of sleep you need to wake up feeling rested and
refreshed. Most common sleep disorder and could be a symptom of another disorder such as
depression or stress.
Restless leg syndrome- Restless legs syndrome (RLS) is a sleep disorder that causes an almost
irresistible urge to move your legs (or arms). The urge to move occurs when you’re resting or
lying down and is usually due to uncomfortable, tingly, aching, or creeping sensations.
Delayed sleep phase syndrome- teens suffer from this disorder. Their sleep patterns change to
staying up longer and wanting to sleep longer in the morning. Students end up sleep deprived
when they go to school.
Sleep apnea- temporary stoppage of breathing during sleep While most people with sleep
apnea don’t remember these awakenings, they feel the effects in other ways, such as
exhaustion during the day, irritability and depression, and decreased productivity..
Narcolepsy- Narcolepsy is a sleep disorder that involves excessive, uncontrollable daytime
sleepiness. It is caused by a dysfunction of the brain mechanism that controls sleeping and
waking. If you have narcolepsy, you may have “sleep attacks” while in the middle of talking,
working, or even driving.
Other temporary disordersJet lag is a temporary disruption in circadian rhythms that occurs when you travel across time zones. In
general, it usually takes one day per time zone crossed to adjust to the local time. So if you flew
from Los Angeles to New York, crossing three time zones, your jet lag should be gone within
three days.
Shift work sleep disorder occurs when your work schedule and your biological clock are out of
sync. In our 24-hour society, many workers have to work night shifts, early morning shifts, or
rotating shifts. These schedules force you to work when your body is telling you to go to sleep,
and sleep when your body is signaling you to wake.
Oversleeping The condition causes people to suffer from extreme sleepiness throughout the
day, which is not usually relieved by napping. It also causes them to sleep for unusually long
periods of time at night. Adults sleeping over 9-10 hours a day are more at risk of diabetes,
obesity and heart disease.
Improving your sleep
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Eliminate caffeine (or foods that have caffeine, such as chocolate).
Set a regular sleep schedule and stick with it, even on weekends.
Avoid exercise after dinner.
Wear comfortable clothes or pajamas to bed.
Make sure your room is not too hot or too cold.
Avoid stimulating TV, music or computer time before bed.
Use meditation or relaxation techniques.
Try the old standby: counting sheep -- in other words, activities that are repetitive and
lack stimulation.
What Are Dreams?
Dreams are a succession of images, emotions and sensations that involuntarily occur during
different stages of sleep. Dreams occur during REM sleep and can range from ordinary to
bizarre, last from a few seconds to 20 minutes. Most dreams are out of the control of the
dreamer except in the case of lucid dreaming where the dreamer is aware that he or she is
dreaming.
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Dreams through history have been used toForetell the future
Be a message from God
Contact with those who have passed away
Wish fulfillment (Freud)
Resolutions to problems or concerns (Jung)
New theories on dream activity
1. Activation synthesis theory is the cortex’s interpretation of the pons’ signals.
2. Continual activation theory- function of sleep is to encode and transfer data from short
term to long term memory and REM and dreams are a mechanism for processing this
information
3. Excitations of long term memory- long term memory is being established with our
dream state
4. Strengthening semantic memory- dreams help strengthen working memory or making
connections or understandings in general. It is not associated to a specific event but
helps make connections to things we learn.
Nightmares and Night Terrors
One out of two adults have nightmares
They occur during REM sleep and have many causes ; sleep deprivation or other sleep
disorders, medication, some disorders such as depression and PTSD even eating late at
night (metabolism increases to digest food and the brain becomes more active)
Night terrors occur during the first few hours of sleep and the person may seem awake but
is still sleeping. They can get up and run, scream. Children 2-6 tend to have the most night
terrors. Overtired is often a trigger in children.
Premonitions
Information believed to be from the future.
Psychology often explain the causes of premonitions to be
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Brain selecting to remember some events and forgetting others.
Coincidence
Unconscious recall
Self-fulfilling prophecies- bring into the present events that were thought about
Resonance theory-brain neurospatial comprehension proposes that we can recall events
in the future just like we recall events in the past. Timespace is one unit.
Déjà vu
Often felt as a sense of familiarity or vagueness. Often scientifically explained as an overlap
between short term and long term memory.
Jamais vu
Experiencing an event or memory that feels like the first time even though you know you
have experienced it before.
Presque vu
Difficulty recalling a word or phrase…..tip of the tongue