Also see IVMS-Neurotransmitters

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Part of IVMS Autonomics - Neurobiology and the 4 P's Series
(For USMLE Step 1 Preparation)

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Neurobiology Review| Overview Notes
The Biology of Behavior
1. The Nervous System - comprised of the following subsystems which control all
activity in our body.
1. Central Nervous System
1. Brain
2. Spinal Cord
2. Peripheral Nervous System - connections to muscles and organs of the
body.
1. Somatic or Skeletal - controls our voluntary muscles.
2. Autonomic - Controls autonomic functions that we have no
voluntary control over such as breathing, heart rate etc.
1. Sympathetic - Responds to stress or demands put upon the
body.
2. Parasympathetic - Work in opposition to the sympathetic NS
to return body to homeostasis.
2. How the System works and interacts
1. Neurons - Over 200 billion in our body.
1. Sensory, Motor and Interneurons
2. Historical Notes
1. Glavani: 1700's first demonstrated neural conductivity with
use of frog legs, first concept of electrical conduction
2. Volta: Explained process as electrical conductance
3. Golgi: Developed a staining method that allowed entire
neurons to viewed and studied
3. No two neurons are the same, over 200 billion cells in brain
4. Main components of the neuron
1. Cell body or Soma (Greek word for body)
1. Spherical or pyramidal in shape, contains the nucleus
2. Synthesizes enzymes for cell function,
neurotransmitters and other nutrients
2. Dendrites
1. Branch from cell body, receive signals only, transfer
them to the cell body
2. Receive this signal from other neurons or the
environment
3. Axon
1. Extends from the cell body to other neurons in the
brain
2. Longer and thinner than dendrites
3. Covered with Myelin Sheath

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4. Glial Cells used for support
5. Neurilemma is the covering of axons which are
outside the brain and spinal cord
6. Every mm or so is interrupted by a Node of Ranvier.
These server to insulate and speed conductance
Impulses pass from neuron to neuron but the cells
never touch
4. Synapse
1. Site where information is passed from one neuron to
another
2. The enlargement at the end of the axon is called the
Terminal Button and extends into the synaptic cleft of
the next dendrite
3. The button contains synaptic vesicles which contain
the neurotransmitters that are eventually released to
continue conductance of the impulse across the
synaptic cleft
4. The release of the neurotransmitters that find and lock
into a specific binding site on the dendrite of the
neighboring neruon. This elicits an action potential in
the dendrite and the process continues on from cell to
cell
5. Neurotransmitters tend to be either excitatory or
inhibitory in nature

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5. Neurotransmitters
1. Over 50 identified, may recognize some such as
acetylcholine, epinephrine, dopamine and serotonin
2. Transmitter secretion or re-uptake may be affected by drugs
or environmental chemicals
3. Other chemicals act to mimic (agonistic) or block
(antagonistic) the effect of neurotransmitters.
4. The chemical may affect concentration of the
neurotransmitter by increasing secretion or reducing normal
reuptake
5. Neuropeptides affect the actions of the neurons themselves,
for example in the case of enkephalin, the natural painkillers
produced in the brain, mimics the effect of opiates or pain
medications. Most commonly known as an endorphins.
2. The Nerve Impulse or Action Potential
1. Neuron is in a resting state with negative charge on the outside.
1. K+
and Cl-
ions on the inside
2. Na+
on the outside

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3. This gives the outside a more negative charge than the
positive inside
4. Result is a polarized condition. The resting state is called
polarization
2. The cell membrane is semipermeable
3. In the presence of a stimulus that reaches the neuron's threshold
the membrane opens and additional Na+ ions enter, depolarizing
the cell
4. This change in charge results in a neural impulse called the Action
Potential
5. As the process continues additional gates open to allow more +
ions to enter along the cell and subsequent depolarization results in
the impulse moving down along the cell, like a wave. This energy
can be measured as electrical energy
6. This change in charge is what stimulates the ion gates to open and
close along the cell allow ions to move
7. The action is "all or none," the impulse itself remains constant
8. After the action potential a small refractory period exists as the ion
pumps work to restore the cell to its original polarized state. No
firing can take place until this process is complete (Relative
Refractory Period)
9. The whole process may be repeated again upon a stimulus of
sufficient threshold

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3. Divisions of the Nervous System
1. Central Nervous System
1. Brain - Hindbrain, Midbrain, and Forebrain
1. Hindbrain
1. Controls autonomic functions of the body
2. Medulla ("Marrow or Core") - controls breathing, heart
rate, blood pressure and reflex actions
3. Pons ("bridge") - Some control over hearing, sleeping
and waking functions
4. Cerebellum ("little brain") - coordinates voluntary
movement and balance
2. Midbrain
1. Reticular Formation ("Net Like") - control over
alertness and sleepiness
2. Affects reflexes associated with the senses
3. Forebrain
1. Complex network of neurons covered by the cerebral
cortex ("rind or shell")
2. White Matter - mass of neuron axons which are
covered with myelin and appears a white color
3. Grey Matter - The cortex area that appears grey in
color
4. Cerebral Cortex - 2 lobes or hemispheres separated
by the longitudinal fissure and connected by the
Corpus Callosum. The center of brain functions. The

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ridges and valleys you see increase the surface area
of the brain
5. Hypothalamus - Controls body temperature, hunger
functions, thirst, sex drive, motivations and emotions.
6. Thalamus - Relays sensory input (except smell) to the
cortex
7. Limbic System ("Border or Edge") - many areas
forming a ring around the lower forebrain, connecting
the hypothalamus and cortex
1. Hippocampus
2. Amygdala
3. Hypothalamus
4. Septal Area
5. Fornix
6. Cingulate Gyrus
7. Thalamus
4. Cerebral Cortex in more detail
1. Frontal Lobe
1. Control personality, social control, attention and planning.
Remember the accident of Phineas Gage
2. Olfactory information present
3. Motor cortex
2. Parietal Lobe
1. Anterior part is concerned with somatosensory (body senses)
function
2. Posterior controls motor function
3. Occipital Lobe

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1. Processes visual information
4. Temporal Lobe
1. Mostly concerned with speech and hearing
2. Left side most often site of speech. Aphasia results for stroke or
trauma to area
3. Right side trauma results in Amusia
4. Wernicke's area - changes sounds into recognizable words, allows
association of meaning
5. Boca's Area - Involved in the process of articulating speech
6. Most of the cortex is known for being area of association.
5. Peripheral Nervous System
1. Somatic or Skeletal
2. All nerves are both afferent or sensory, efferent or motor, in function
1. Messages only can travel in one direction across a synapse
2. The Reflex Arc is a part of this system
1. Impulse from afferent neurons are processed first in the
vertebrae and sent out to efferent neurons to produce a

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response. By responding this way without involving the brain
immediately responses are much faster
3. Autonomic Nervous System
1. The stress response
2. Carry messages to and from glands and visceral organs.
3. Affect messages to skeletal muscles during stress
1. Sympathetic Nervous System
1. The Stress Response or GAS
2. Prepares body to respond to stressor
2. Parasympathetic Nervous System
1. Reverses effect of sympathetic system
2. Maintains Homeostasis
3. Only the sexual response is invoked by both systems
6. Endocrine Glands ("to secrete within")
1. An additional system for sending chemical messages throughout the body.
1. The chemical messengers are called hormones
2. Pituitary - The Master Gland
1. Primarily for the growth hormone
2. Also involved in continued growth and in the menstrual cycle
3. Thyroid
1. Produces thyroxin for control of metabolism
2. Over or under secretion may result in emotional and physical
symptoms
4. Parathyroid Gland
1. Secrete parathormone that affects excitability of the nervous
system by regulating ion levels in the neuron

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5. Adrenal Glands
1. Produces adrenaline and noradrenaline from cortex of Adrenal
Gland on top of the kidneys
2. Adrenaline is a strong stimulant that is used to stimulate the heart
in heart attacks and to reduce inflammations from acute
anaphylactic shock. The chemical found in sting kits carried by
those allergic to stings
6. Islets of Langerhans
1. Secretes Glucagon that causes liver to convert stored sugar or
starch into blood sugar
2. Secretes insulin that helps cells effectively utilize blood sugar for
energy
7. Gonads
1. Male and Female sex organs that secrete estrogen and
testosterone
8. Pineal Gland
1. Effects activity levels over the course of a day. Secrets melatonin,
the chemical touted as a health supplement to help induce sleep
7. Right/Left Brain Research
1. Fechner originally reasoned we have 2 brains since we have 2
hemispheres. Tried to prove with surgery to sever the 1/4 inch band of 200
million nerve fibers called the Corpus Callosum. Technology in the 1800's
could note complete such procedures
2. Others like McDougal reasoned that it appeared we had 2 brains we only
have one mind. Didn't believe there would be any effect to severing the
Corpus Callosum
3. Later research suggested localization of function
1. 1836 - Dax found that Aphasic patients suffered damage on left
side of brain
2. 1861 - Boca coined the term Aphasia to indicate patients who could
not articulate ideas. Also found damage to left side of brain
3. 1952 - Sperry and Meyers discovered that when the Corpus
Callosum was severed that the hemispheres acted independently
4. Early experiments used cats to test effects. Found learning with
only one uncovered eye resulted in learning in only one
hemisphere. Even so the cat still acted like a cat with no other
deficits observed
5. In the 1950's the procedure called a commissurotomy was used to
treat epileptic seizures.
1. It worked without loss of mental facilities or change in
personality or IQ
2. Found with testing that learning when patient focuses on
center of split screen with images flashed to sides that

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learning took place in the hemisphere where the image was
flashed. Each hemisphere was better at specific function.
3. Language seemed centered in left hemisphere and
kinesthetic senses in the right. When object was seen in the
right hemisphere the patient could not identify by label but
could identify it by touch
4. Hemispheric Function
1. Language for most people is in the left hemisphere
2. Left hemisphere is better at language, reading, math, writing,
spelling and math tasks
3. Right is better for spatial, symbolic, and creative ideas
Key Terms
Neuron The neuron, or nerve cell, is the basic building block of the nervous system.
Dendrites The dendrites of a neuron are the bushy, branching extensions that receive
messages from other nerve cells and conduct impulses toward the cell
body.
Axon The axon of a neuron is the extension that transmits messages to other
nerve cells, muscles or glands.
Myelin Sheath The myelin sheath is a layer of fatty cells that covers many axons and
helps speed neural impulses.
Action Potential An action potential, or neural impulse, is a brief electrical charge that travels
down an axon similar to the motion of a wave. It is generated when a
stimulus to a nerve cell reaches the cells threshold causing the axon to
depolarize as the Na+ ions enter the axon. This depolarization causes the
electrical charge. It is an all or none response.
Threshold A neuron's threshold is the level of stimulation that must be exceeded in
order for the neuron to fire or generate an electrical impulse.
Synapse A synapse is the junction between the axon tip of the sending neuron and
the dendrite or cell body of the receiving neuron. The tiny gap at this
junction is called the synaptic gap or cleft.
Neurotransmitters Neurotransmitters are chemicals that, when released into synaptic gaps,
transmit neural messages from neuron to neuron.
Endorphins Endorphins are natural, opiate like neurotransmitters linked to pain control
and to pleasure.
Nervous System The nervous system is the body's electrochemical communication system,
consisting of all the nerve cells of the peripheral and central nervous
systems.

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Central Nervous
System
The central nervous system consists of the brain and spinal cord; it is
located at the center, or internal core, of the body.
Peripheral Nervous
System
The peripheral nervous system connects the central nervous system to the
rest of the body; it is at the periphery of the body relative to the brain and
spinal cord.
Nerves Nerves are bundles of neural axons that connect the central nervous
system with muscles, glands, and sense organs.
Sensory Neurons Sensory neurons carry incoming information from the sense organs to the
central nervous system.
Interneurons Interneurons are the neurons of the central nervous system that link the
sensory and motor neurons in the transmission of sensory input and motor
output.
Motor Neurons Motor neurons carry information and instructions for action from the central
nervous system to muscles and glands.
Skeletal Nervous
System
The skeletal nervous system is the division of the peripheral nervous
system that controls the body's skeletal muscles.
Autonomic Nervous
System
The autonomic nervous system is the division of the peripheral nervous
system that controls the glands and the muscles of internal organs and
thereby controls internal functioning; it regulates the automatic behaviors
necessary for survival.
Sympathetic Nervous
System
The sympathetic nervous system is the division of the autonomic nervous
system that arouses the body to react to demands put upon it.
Parasympathetic
Nervous System
The parasympathetic nervous system is the division of the autonomic
nervous system that calms the body, conserving its energy and restores
homeostasis.
Reflex A reflex is a simple, automatic, inborn response to a sensory stimulus; it is
governed by a very simple neural pathway that does not involve the brain.
Endocrine System The endocrine system, the body's "slower" chemical communication
system, consists of glands that secrete hormones into the bloodstream.
Hormones Hormones are the chemical messengers of the endocrine system; they are
secreted by endocrine glands and circulate through the bloodstream to their
target tissues, on which they have specific effects.
Brainstem The brainstem, the oldest part of the brain, is an extension of the spinal
cord and is the central core of the brain; its structures direct automatic
survival functions.
Medulla Located in the brainstem, the medulla is involved in the regulation of
breathing and heartbeat.
Electroencephalogram
(EEG)
An electroencephalogram (EEG) is an amplified recording of the waves of
electrical activity of the brain. Encephalo comes from a Greek word
meaning "related to the brain."
CAT (Computerized The CAT (computerized axial tomograph) scan is a series of x-ray

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Axial Tomograph) Scan photographs of the brain taken from different positions and analyzed by
computer, creating an image that represents a slice through the brain.
PET (Positron
Emission Tomograph)
Scan
The PET (positron emission tomograph) scan measures the levels of
activity of different areas of the brain by tracing their consumption of
glucose.
MRI (Magnetic
Resonance Imaging)
MRI (magnetic resonance imaging) uses magnetic fields and radio waves to
produce computer-generated images that show brain structures more
clearly.
Reticular Formation Also part of the brainstem, the reticular formation is a nerve network that
plays an important role in controlling arousal.
Thalamus Located atop the brainstem, the thalamus routes incoming messages to the
appropriate cortical centers and transmits replies to the medulla and
cerebellum. The Grand Central Station of the Brain.
Cerebellum The cerebellum assists in the coordination of voluntary movement and
balance.
Limbic System A doughnut-shaped neural system, the limbic system plays an important
role in the regulation of emotions and drives such as those for food and sex.
(From the Latin word limbus, meaning "border"); the limbic system is at the
border of the brainstem and cerebral hemispheres.
Amygdala Part of the limbic system, the amygdala is linked to the emotions of
aggression and fear.
Hypothalamus Also part of the limbic system, the hypothalamus regulates hunger, thirst,
and body temperature and contains the so-called pleasure centers of the
brain. It also helps govern the endocrine system through the pituitary gland.
Cerebral Cortex The cerebral cortex is the outer covering of the cerebral hemispheres. The
seat of information processing, the cortex is responsible for those complex
functions that make us distinctively human. (Cortex in Latin means "bark."
As bark covers a tree, the cerebral cortex is the "bark of the brain.")
Frontal Lobes Located at the front of the brain, just behind the forehead, the frontal lobes
contain the motor cortex and are involved in making plans and judgments.
The accident of Phineas Gage helped psychologists understand the role of
the frontal lobes in personality.
Parietal Lobes Situated between the frontal and occipital lobes, the parietal lobes contain
the sensory cortex.
Occipital Lobes Located at the back and base of the brain, the occipital lobes contain the
visual cortex, which receives information from the eyes.
Temporal Lobes Located on the sides of the brain, the temporal lobes contain the auditory
areas, which receive information from the ears.
Motor Cortex Located at the back of the frontal lobes, the motor cortex controls voluntary
movements.
Sensory Cortex The sensory cortex is located at the front of the parietal lobes, just behind

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the motor cortex. It receives information from the skin and muscles.
Association Areas Located throughout the cortex, association areas of the brain are involved in
higher mental functions, such as learning, remembering, thinking, and
speaking. Most of the brain consists of association areas of the cortex that
are involved in integrating, or associating, information from different areas
of the brain.
Aphasia Aphasia is an impairment of language as a result of left-hemisphere
damage, either to Broca's area or to Wernicke's area .
Broca's Area Broca's area is located in the left frontal lobe and is involved in controlling
the motor ability to produce speech.
Wernicke's Area Wernicke's area is located in the left temporal lobe and is involved in
language comprehension.
Plasticity Plasticity refers to the ability of the brain to reorganize itself in order to
compensate for the destruction of brain tissue. The plasticity of the brain
diminishes with age.
Corpus Callosum The corpus callosum is a wide band of axon fibers that links the right and
left cerebral hemispheres. Without this band of nerve fibers, the two
hemispheres could not interact.
Split Brain Split brain is a condition in which the major connections between the two
cerebral hemispheres (the corpus callosum) are severed, literally resulting
in a split brain. Early experimenters believed this surgery would eliminate
the seizures of epilepsy.