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- largest part of the human brain
- The cerebrum is divided
into two hemispheres — the right hemisphere and the
left hemisphere. Bridging the two hemispheres is a bundle
of fibers called the corpus callosum. The two hemispheres
communicate with one another across the corpus callosum.


cerebral cortex

Covering the outermost layer of the cerebrum is a
sheet of tissue called the cerebral cortex. Because of its gray
color, the cerebral cortex is often referred to as gray matter.
The wrinkled appearance of the human brain also can be
attributed to characteristics of the cerebral cortex. More than
two-thirds of this layer is folded into grooves. The grooves
increase the brain’s surface area, allowing for inclusion of
many more neurons.


basal ganglia

a key part of the forebrain; cerebral nuclei deep in the cerebral cortex. The basal ganglia are a cluster of interconnected areas
located beneath the cortex in the depths of the cerebral



consists of two pairs of small hills called
colliculi. These collections of neurons play a critical role
in visual and auditory reflexes and in relaying this type of
information to the thalamus. The midbrain also has clusters
of neurons that regulate activity in widespread parts of the
central nervous system and are thought to be important for
reward mechanisms and mood.



like the cerebrum, also has two hemispheres


spinal cord

the extension of the brain through the
vertebral column



formed by the forebrain, midbrain, hindbrain, and spinal cord. brain is protected by skull, spinal cord protected by vertebral column.



consists of nerves and small concentrations of gray matter called ganglia, a
term specifically used to describe structures in the PNS.


autonomic nervous system

made of neurons
connecting the CNS with internal organs. It is divided
into two parts: sympathetic and parasympathetic


cell body

contains the nucleus and cytoplasm



axon extends
from the cell body and often gives rise to many smaller
branches before ending at nerve terminals. Many axons are
covered with a layered myelin sheath, which accelerates the
transmission of electrical signals along the axon. This sheath
is made by specialized cells called glia.



from the neuron cell body and receive messages from other



are the contact points where one neuron
communicates with another. The dendrites are covered with
synapses formed by the ends of axons from other neurons


where is ACh present?

This chemical is released
by neurons connected to voluntary muscles,
causing them to contract, and by neurons that
control the heartbeat. ACh is also a transmitter
in many regions of the brain. ACh is synthesized in axon terminals.


where are amino acids present?

widely distributed
throughout the body and the brain


where are catecholamines present?

Dopamine and norepinephrine are widely present in the
brain and peripheral nervous system.


where is serotonin present?

This neurotransmitter is present in the
brain and other tissues, particularly blood platelets and the lining of the idgestive tract.


where are peptides present?

peptides are synthesized in the cell body and greatly
outnumber the classical transmitters discussed earlier (ACh, catecholamines, serotonin, AAs)


where are trophic factors present?

These small proteins are made in
brain cells, released locally in the brain, and bind to receptors
expressed by specific neurons.



Prostaglandins are a class of compounds made from lipids
by an enzyme called cyclooxygenase. They are very small. Type of lipid messenger.


amyloid plaques

in people who died from Alzheimer's, a small fibrillar peptide, termed beta amyloid, in the
spaces around synapses. These accumulations of tissue are
referred to as neuritic plaques.


tau tangles

in people who died from Alzheimer's. neurofibrillary tangles, have been identified
as a modified form of the protein tau, which is found in the
cell bodies of neurons. the protein tau is rod-shaped.


primary brain tumors

arise within the brain


metastatic / secondary brain tumors

spread from
other parts of the body through the bloodstream and enter
the brain


cerebral edema

swelling as a result of excess accumulation of
water in the brain



imaging can reveal lesions
produced by the initial injury. These lesions can consist of
bleeding on the surface or within the brain as well as the
formation of contusions, or bruises. Once blood leaks from
vessels and comes into direct contact with brain tissue, it
causes localized pressure, reducing cerebral blood flow. The
blood itself also can be toxic to brain cells.


neuropathic pain

comes from injury to the nervous


diabetic neuropathy

damage to nerves in the body resulting from high blood sugar



nerve pain or numbness, from viruses such
as shingles



the peripheral nerve
fiber that initially responds to the injury stimulus. The sensory fibers that respond to stimuli that damage
tissue and can cause pain


3 major cell types of the brain:

neurons; astrocytes, the cells
that nourish and protect neurons; and oligodendrocytes,
the cells that surround axons and allow them to conduct
their signals efficiently.


MRI image

Tissue that contains a lot of water and fat produces a
bright image; tissue that contains little or no water, such as
bone, appears black.



does about three-quarters of the focusing. vision begins with light passing thru the cornea.



- adjusts the focus. light passes thru the lens after it passes thru the cornea
- The shape
of the lens is altered by the muscles just behind the iris so that
near or far objects can be brought into focus on the retina.



a sheet of photoreceptors; part of CNS but located at the back of the eye. the cornea and lens combine to produce a clear image of the visual world on the retina. the image is reversed: objects to the right of the center project images to the left part of the retina



gather visual information by absorbing
light and sending electrical signals to other retinal neurons
for initial processing and integration. The signals are then
sent via the optic nerve to other parts of brain, which
ultimately processes the image and allows us to see.



The size of the pupil, which regulates how
much light enters the eye, is controlled by the iris.


lateral geniculate nucleus

an intermediate way station between the
retina and visual cortex


photoreceptor types

- rods: extremely sensitive to light and allow us to see in dim light,
but they do not convey color; 95 percent
- Most of our vision, however, comes
from cones that work under most light conditions and are
responsible for acute detail and color vision.


photoreceptor subtypes

The human eye contains three types of cones (red,
green and blue), each sensitive to a different range of colors.
Because their sensitivities overlap, cones work in combination
to convey information about all visible colors.


parts of the retina

- central part: FOVEA, where light is focused; only contains red and green cones
- around fovea: MACULA, critical for reading and driving


receptive field

region of visual space providing input to a
visual neuron is called its receptive field.


3 retina layers

The rod and cone photoreceptors in the first layer send signals
to the middle layer (interneurons), which then relays signals
to the third layer, consisting of multiple different types of
ganglion cells, specialized neurons near the inner surface of the
retina. Each neuron in the middle and third layer typically receives input from many cells in the previous layer.


optic nerve

The axons of the ganglion cells form the optic nerve.


primary visual cortex

a thin sheet of tissue (less
than one-tenth of an inch thick), a bit
larger than a half-dollar, which is located
in the occipital lobe in the back of the
brain. The primary visual cortex is densely packed with
cells in many layers, just as the retina is.


primary visual cortex layers

In its middle layer,
which receives messages from the lateral geniculate nucleus,
scientists have found responses similar to those seen in
the retina and in lateral geniculate cells. Cells above and
below this layer respond differently. They prefer stimuli in
the shape of bars or edges and those at a particular angle
(orientation). Further studies have shown that different
cells prefer edges at different angles or edges moving in a
particular direction.


oval window

stapes (stirrup) pushes on the oval window, separates the air-filled middle ear from the fluid-filled inner ear to produce pressure waves in the inner ear’s
snail-shaped cochlea.



snail shaped; The separation of frequencies occurs in the
cochlea, which is tuned along its length to different frequencies,
so that a high note causes one region of the cochlea’s basilar
membrane to vibrate, while a lower note has the same effect on
a different region of the basilar membrane.


hair cells

Riding on the vibrating basilar membrane are hair cells
topped with microscopic bundles of hairlike stereocilia, which
are deflected by the overlying tectorial membrane. Hair cells
convert the mechanical vibration to electrical signals, which in
turn excite the auditory nerve. Because each
hair cell rides on a different part of the basilar membrane, each
responds to a different frequency.


auditory nerve

30,000 fibers. The auditory
nerve then carries the signals (electrical, converted by hair cells) to the brainstem. each nerve fiber
carries information about a different frequency to the brain.


taste buds

special structures embedded within small protuberances on the
tongue called papillae. Other taste buds are found in the back of
the mouth and on the palate. Each taste bud consists of 50 to 100
specialized sensory cells, which are stimulated by tastants such
as sugars, salts, or acids.



Airborne odor molecules, called
odorants, are detected by specialized
sensory neurons located in a small patch
of mucus membrane lining the roof of the
nose. Odorants stimulate receptor proteins found on hairlike cilia at the tips of the sensory cells, a process that initiates a neural response.


odor pcoess

each odorant's pattern of activity is then
sent to the olfactory bulb, where other
neurons are activated to form a spatial map
of the odor. Neural activity created by this
stimulation passes to the primary olfactory
cortex at the back of the underside, or
orbital, part of the frontal lobe. Olfactory
information then passes to adjacent parts of the orbital cortex,
where the combination of odor and taste information helps
create the perception of flavor


skeletal muscles

Most muscles attach to points on the skeleton
and cross one or more joints. Each skeletal muscle is made up of thousands of
individual muscle fibers, and each muscle fiber is controlled
by one alpha motor neuron in either the brain or the
spinal cord.


motor unit

each single alpha motor neuron
controls many muscle fibers (ranging from a few to 100
or more); an alpha motor neuron and all the muscle
fibers it contains form a functional unit referred to as a
motor unit. Motor units are the critical link between the
brain and muscles.



Perhaps the simplest and most fundamental movements
are reflexes. These are relatively fixed, automatic muscle
responses to particular stimul.


inhibitory interneurons

same sensory stimulus that causes the stretch reflex causes inactivation, or inhibition,
of the motor neurons of the antagonist muscles through
connecting neurons, called inhibitory interneurons, within the spinal cord.


gamma motor neurons

the sensitivity
of the muscle spindle organs is monitored by the brain
through a separate set of gamma motor neurons that
control the specialized muscle fibers and allow the brain to
fine-tune the system for different movement tasks.


Golgi tendon organs

specialized sense organs in muscle tendons — the Golgi
tendon organs — detect the force applied by a contracting muscle, allowing the brain to sense and control the muscular
force exerted during movement.



source of potential injury


flexion withdrawal

that occurs when the bare foot encounters a sharp
object. The leg is immediately lifted from the source of
potential injury (flexion), but the opposite leg responds
with increased extension so that we can maintain our
balance. The latter event is called the crossed extension reflex.


motor cortex

One important brain area that is responsible for
voluntary movement is the motor cortex, which exerts
powerful control over the spinal cord, in part through
direct control of its alpha motor neurons. Some neurons
in the motor cortex appear to specify the coordinated
action of many muscles to produce the organized
movement of a limb to a particular point in space.
Others appear to control only two or three functionally
related muscles, such as those of the hand or arm, that
are important for finely tuned, skilled movement.


During the early stages of embryonic
development, three layers emerge

the endoderm, the
ectoderm, and the mesoderm. These layers undergo many
interactions to grow into organ, bone, muscle, skin, or
nerve tissue.


growth cone signaling molecules

These signaling
molecules include proteins with names such as netrin,
semaphorin, and ephrin. In most cases, these are families of
related molecules; for example, researchers have identified at
least fifteen semaphorins and at least nine ephrins.


cochlear implants

implants introduced in infancy are most effective in restoring
hearing to the congenitally deaf.