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NERVOUS SYSTEM

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Benjamin Ponsoy Jr.

on 14 August 2014

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Transcript of NERVOUS SYSTEM

N
E
R
V
O
U
S
Y
S
T
E
M
S
NERVOUS SYSTEM
introduction
functions
divisions
BY: JEMIMA ANGELIKA LASTIMOSA
CELLS OF THE NERVOUS SYSTEM
neurons
types of neurons
neuroglia
BY: MARK FONTAMILLAS
myelin sheats
organization of nervous tissue
BY: ANNE MAGDALEINE RAMIREZ
functions of the nervous system
divisions of the nervous system
cells of the nervous system
electric signal and neural pathways
central and peripheral nervous system
spinal cord
spinal nerves
brain

sensory functions
motor dunctions
other brain functions
meninges and cerebrospinal fluid
cranial nerves
autonomic nervous system
effecets of aging on the nervous system

NERVOUS SYSTEM
brain
ganglia
spinal cord
nerves
FUNCTIONS OF THE NERVOUS SYSTEM
NERVOUS SYSTEM
sensory input
integration
homeostasis
mental activity
control of musles and glands
Sensory Input
sensory receptors monitor numerous external and internal stimuli that may be interpreted as touch, temperature, taste, smell, sound, blood pressure, and body position. Action potentials from the sensory receptors travel along nerves to the spinal cord and brain, where they are interpreted.
Integration
the brain and spinal cord are the major organs for processing sensory input and initiating responses. The input may produce an immediate response, may be stored as memory, or may be ignored.
Homeostasis
the nervous system plays an important role in the maintenance of homeostasis. This function depends on the ability of the nervous system to detect, interpret, and respond to changes in internal external conditions.
Mental Activity
the brain is the center of mental activity, including consciousness, memory, and thinking.
Control of Muscles and Glands
skeletal muscles normally contract only when stimulated by the nervous system.
through the control of skeletal muscle, the nervous system controls the major movements of the body.
the nervous system also participates in controlling cardiac muscle, smooth muscle, and many glands.

DIVISIONS OF THE NERVOUS SYSTEM
central nervous system (CNS)
peripheral nervous system (PNS)
CENTRAL NERVOUS SYSTEM (CNS)
consists of the brain and spinal cord
PERIPHERAL NERVOUS SYSTEM (PNS)
lies outside the CNS (Central Nervous System)
consists of nerves and ganglia
PERIPHERAL NERVOUS SYSTEM SUBDIVISIONS
sensory division
motor division
somatic motor nervous system
autonomic nervous system
Sensory Division
conducts action potentials from sensory receptors to the CNS
neurons that transmit action potentials from the periphery to the CNS
sensory neurons
Motor Division
Somatic Motor Nervous System
Autonomic Nervous System
neurons that transmit action potentials from the periphery to the CNS
neurons that transmit action potentials from the periphery to the CNS
sympathetic
parasympathetic
enteric portions
CELLS of the nervous system
cell body
axon
myelin sheaths
NEURON AND NEUROGLIA
Neurons or Nerve Cells
receive stimuli and transmit action potentials to other neurons or to effector organs.
each neuron consists of a cell body and two types of processes: dendrites and axons.
NEURON
Dendrites
are short, often highly branching cytoplasmic extensions that are tapered from their bases at the neuron cell body to their tips.
dendrites function is to receive information from other neurons or sensory receptors and transmit the information toward the neuron cell body
is a long cell process extending from the neuron cell body.
Axon
*
axon hillock
- an area where the axon leaves the neuron cell body
axons of motor neurons
- conduct action potentials
away
from the CNS
axons of sensory neurons
- conduct action potentials
toward
the CNS
axons also conduct action potentials from one part of the brain or spinal cord to another part.

axons are surrounded by neuroglia called
Schwann cells
,
which form a highly specialized insulating layer of cells called
myelin sheath
.
axon hillock
schwann cell
TYPES OF NEURON
Multipolar Neuron
have many dendrites and a single axons.
most of the neurons within the CNS, including nearly all motor neurons, are multipolar.
cell body
dendrite
axon
Bipolar Neuron
have two processes: one dendrite and one axon.
located in some sensory organ like retina of the eye and in the nasal cavity.
dendrite
cell body
axon
Unipolar Neuron
a neuron whose cell body emits a single axonal process resulting from the fusion of two polar processes during development, one branch of the process serving as a sensory nerve fiber and a second branch entering into synaptic contact with neurons in the spinal cord or brainstem.
has an axon and no dendrites

cell body
axon
sensory receptors
Neuroglia or Glial Cells
are the nonneuronal cells of the CNS and PNS
are far more numerous than neurons
most neuroglia retain the ability to divide, whereas most neurons do not
TYPES OF NEUROGLIA
astrocyte
microglial cell
ependymal cells
oligodendocyte
Schwann cells
Astrocyte
provide structural support
Microglial Cell
protects CNS from infection
Ependymal Cells
circulates cerebrospinal fluid
Sensory neuron with Schwann Cells and Satellite Cells
form myelin sheaths around the axon
Oligodendrocyte
cell processes form myelin sheaths around axons
dendrites
axon terminal
cells of the nervous system
Myelin Sheaths
is a protective covering that surrounds fibres called axons
serves as an electrical insulator that speeds nerve impulses to muscles and other effectots

Unmyelinated Axons
Myelinated Axons
rest in identations of the oligondendrocytes in the CNS and the Schwann cells in the PNS.
have specialized sheaths, called myelin sheaths wrapped around them.
Axons are surrounded by the cell processes of oligodendrocytes in the CNS and Schwan cells in the PNS
Each oligodendrocyte process or Schwann cell repeatedly wraps around a segment of an axon to form a series of tightly wrapped cell membranes.
A typical small nerve usually contains more unmyelinated than myelinated axons
Myelin
- is an excellent insulator, which prevents almost all electrical current flow througn the cell membrane.
Nodes of Ranvier
- gaps in the myelin sheath
- can be seen about every millimeter between the oligodendrocyte segments or between individual Schwann cells.
- current flows easily between the extracellular fluid and the axon, and action potentials can develop at the nodes of ranvier.
Organization of Nervous Tissue
groups of neuron cell bodies and their dendrites, where there is very little myelin, form gray matter
cortex
- gray matter on the surface of the brain
nuclei
- clusters of gray matter located deeper within the brain
ganglion
- a cluster of neuron cell bodies in the PNS
white matter

- is the bundles of parallel whitish color axons with their myelin sheath
- forms conduction pathways or nerve tracts, which propagate action potentials from one area in the CNS to another
nerves
- bundles of axons and their connective tissue sheaths in the PNS

ELECTRIC SIGNALS AND NEURAL PATHWAYS
the resting membrane potential
action potentials
the synapse
BY: JESSA GARAIS
ELectric signals and neural pathways
The Resting Membrane Potential
All cells exhibit electrical properties.
The outside of most cell membranes is positively charged compared with the inside of the cell membrane, which is negatively charged.
This charge difference across the membrane of an unstimulated cell is called the
resting membrane potential
.
The cell is said to be
polarized
.
The outside of the cell membrane can be thought of as the positive pole of a battery, and the inside as the negative pole.
The resting membrane potential results from differences in the concentration of ions across the cell membrane and the permeability characteristics of the cell membrane.
Comparison of Myelinated and Unmyelinated Axons
myelinated axons
unmyelinated axons
Myelinated axons
- with two Schwann cells forming the myelin sheaths around a single axon. Each Schwann cell surrounds part of one axon.
Unmyelinated axons
- with two Schwann cells surrounding several axons in parallel formation. Each Schwann cell surrounds part of several axons.
Major Ion Concentration Differences Across a Cell Membrane
Na+ concentrated outside the cell membrane
K+ concentrated inside the cell membrane
There is a higher concentration of K+ inside the cell and a higher concentration of Na+ outside the cell.
Na+ are pumped out of the cell
K+ are pumped into the cell
sodium-potassium exchange pump
The sodium-potassium exchange pump moves Na+ out of the cell in exchange for K+ that move into the cell.
Cell Membrane
is a biological membrane that separates the interior of all cells from the outside environment.
is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells.

Ion Channels and Ion Concentrations Across a Cell Membrane
Concentrations of Na+, K+, Cl-, and negatively charged proteins across the cell membrane are represented.
Some K+ channels are open but Na+ channels are not.
As a result, K+ diffuse out of the cell down their concentration gradient.
The membrane is not permeable to the negatively charged proteins inside the cell.
The tendency for the K+ to diffuse to the outside of the cell down their concentration gradient is opposed by the tendency for the positively charged K+ to be attracted back into the cell by the negatively charged proteins inside the cell.
Ion Channels and the Action Potential
Resting Membrane Potential
Na+ channels and most, but not all K+ channels are closed.
The outside of the plasma membrane is positively charged compared to the inside.
Depolarization
Na+ channels open
Depolarization results because the inward movementof Na+ makes the inside of the membrane move positive.
Repolarization
Na+ channels close and additional K+ channels are open.
Na+ movement into thecell stops and K+ move out the cell, causing repolarization.
Depolarization and repolarization constitute an action potential.
The elevated permeability to K+ last only a very short time.
Action potentials occur in an all-or-none fashion, that is, if threshold is reached, the charge reversal is complete; if the threshold is not reached, no action potential occurs.
Action potentials in a given cell type are all of the same magnitude, that is, the amount of charge reversal is always the same.
Stronger stimuli produce a greater frequency of action potentials but do not increase the size of each action potential.
ACTION POTENTIALS are conducted slowly in UNMYELINATED AXONS and more rapidly in MYELINATED AXONS
Action Potential Conduction in an Unmyelinated Axon
- an action potential generates local currents that tend to depolarize the membrane immediately adjacent to the action potential.
- when depolarization caused by the local currents reaches threshold, a new action potential is produced adjacent to where the original action potential occurred.
- the action potential is conducted along the axon cell membrane.
Saltatory Conduction: Action Potential Conduction in a Myelinated Axon
SALTATORY CONDUCTION
- greatly increases the conduction of velocity because the nodes of Ranvier make it unnecessary for the action potentials to travel along the entire cell membrane.
- an action potential at a node of Ranvier generates local currents.
- the local currents flow to the next node of Ranvier because the myelin sheath of the Schwann cell insulates the axon between nodes.
- when the depolarization caused by the local currents reaches threshold at the next node of Ranvier, a new action potential is produced.
- action potential conduction is rapid in myelinated axons because the action potentials are produced at successive nodes of Ranvier (1-5) instead of at every part of the membrane along the axon.
The Synapse
Action Potential
Synapse
- is a junction where the axon of one neuron interacts with another neuron or an effector organ such as a muscle or gland.
Presynaptic terminal
- end of the axon
Postsynaptic membrane
- membrane of the dendrite or effector cell
Synaptic cleft
- space separating the presynaptic terminal and postsynaptic membrane.
Neurotransmitter
- chemical substances

The Synapse
- consists of the end of a neuron (presynaptic terminal), a small space (synaptic cleft), and the postsynaptic membrane of another neuron or an effector cell such as a muscle or gland cell.
- action potentials arriving at the presynaptic terminal cause synaptic vesicles to release neurotransmitter molecules, such as
acetylcholine.
- neurotransmitter molecules diffuse from the presynaptic terminal across the synaptic cleft.
- neurotransmitter molecules combine with their receptors and cause Na+ channels to open. Na+ diffuse into the cell and cause depolarization. If depolarization reaches threshold, an action potential is produced in the postsynaptic cell.
Neurotransmitters
Neurotransmitters
The neurotransmitters are released by exocytosis from the presynaptic terminal in response to each action potential.
The neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules on the postsynaptic membrane.
The binding of neurotransmitters to these membrane receptors causes channels for Na+, K+, or Cl- to open or close in the postsynaptic membrane, depending on the type of neurotransmitter in the presynaptic terminal and the type of receptors on the postsynaptic membrane.
The response may be either stimulation or an inhibition of an action potential in the postsynaptic cell.
For example:
if Na+ channels open, the postsynaptic cell becomes depolarized, and an action potential will result if threshold is reached.
If K+ or Cl- channels open, the inside of the postsynaptic cell tends to become more negative, or
hyperpolarized
, and an action potential is inhibited from occurring.
Neurotransmitters
reflexes
neuronal pathways
CENTRAL AND PERIPHERAL NERVOUS SYSTEM
BY: MATTHEW VARGAS
Reflexes
is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS.
allow a person to react to stimuli more quickly than is possible if conscious thought is involved.
most reflexes occur in the spinal cord or brainstem and not the higher brain centers
Reflex Arc
is the neuronal pathway by which a reflex occurs
is the basic functional unit of the nervous system because it is the smallest, simplest pathway capable of receiving a stimulus and yielding a response.
REFLEX ARC BASIC COMPONENTS
sensory receptor
sensory neuron
interneurons
motor neuron
effector organ
Sensory Receptor
- is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism
Sensory Neuron
- are nerve cells responsible for converting external stimuli from the organism's environment into internal electrical impulses
Interneuron
- serve as the connection point between sensory neurons and motor neurons
Motor Neuron
- responsible for stimulating a muscular or glandular response
Effector Organ
- any muscle or gland that mediates overt behavior, that is, movement or secretion

the result of a
reflex
can be seen when a
person's finger touches a hot stove
Pain receptors in the skin are stimulated by the hot stove, and action potentials are produced.
Sensory neurons
conduct the action potentials to the spinal cord, where they synapse with
interneurons
.
The
interneurons
, in turn, synapse with
motor neurons
in the spinal cord that conduct action potentials along their axons to flexor muscles in the upper limb
These muscles contract and pull the finger away from the stove.
No conscious thought is required for this reflex, and withdrawal of the finger from the stimulus begins before the person is consciously aware of any pain.
Neuronal Pathways
Neurons
are organized within the CNS to form pathways ranging from relatively simple to extremely complex.
The two simplest pathways are
converging
and
diverging pathways.
Converging Pathways
- have two or more neurons that synapse with the same neuron
Diverging Pathways
- the axon from one neuron divides and synapses with more than one other neuron.
- allows information transmitted in one neuronal pathway to diverge into two or more pathways
Central Nervous System CNS
CENTRAL AND PERIPHERAL NERVOUS SYSTEM
- consists of the brain and spinal cord.
- the
brain
is that part of the CNS housed within the braincase.
- the
spinal cord
is in the vertebral column.
Peripheral Nervous System (PNS)
- consists of all the nerves and ganglia located outside the brain and spinal cord.
- the PNS collects information from numerous sources both inside and on the surface of the body and relays it by way of sensory fibers to the CNS, where the information is ignored, triggers a reflex, or is evaluated more extensively.
- motor fibers in the PNS relay information from the CNS to muscles and glands in various parts of the body, regulating activity in those structures.
- nerves of the PNS can be divided into two groups: 12 pairs of cranial nerves and 31 pairs of spinal nerves.
SPINAL CORD
spinal cord reflexes
BY: ALLYSA AYLA MANLANGIT
Spinal cord
level of foramen magnum
rootlets of spinal nerves
spinal nerves
level of the second lumbar vertebra
cauda equina
coccygeal nerve
Spinal Cord
- extends from the foramen magnum at the base of the skull to the second lumbar vertebra
Cross section of the Spinal Cord
A cross section of the spinal cord reveals that the cord consist of a peripheral white matter portion and a central gray matter portion
The white matter consists of myelinated axons, and the gray matter is mainly a collection of neuron cell bodies.
White matter columns
dorsal (posterior)
ventral (anterior)
lateral columns
Each column of the spinal cord contains
nerve tracts
.
Nerve Tracts
Ascending Tracts
Descending Tracts
- consists of axons that conduct action potentials toward the brain
- consists of axons that conduct action potentials away from the brain
The gray matter of the spinal cord is shaped like the letter
H
, with posterior and anterior horns.
Small lateral horns exist in levels of the cord associated with the autonomic nervous system.
The
central canal
is a fluid-filled space in the center of the cord.
Spinal nerves
arise from numerous rootlets along the dorsal and ventral surfaces of the spinal cord.
The
ventral rootlets
combine to form a ventral root on the ventral (anterior) side of the spinal cord.
The
dorsal rootlets
combine to form a dorsal root on the dorsal (posterior) side of the cord at each segment.
The
ventral and dorsal roots
unite just lateral to the spinal cord to form a spinal nerve.
The
dorsal root
contains a ganglion, called the
dorsal root ganglion
.
The cell bodies of unipolar sensory neurons are in the dorsal root ganglia .
The axons of these neurons originate in the periphery of the body.
They pass through spinal nerves and the dorsal roots to the posterior horn of the spinal cord gray matter.
In the posterior horn, the axons either synapse with interneurons or pass into the white matter and ascend or descend in the spinal cord.
The cell bodies of motor neurons, which supply muscles and glands, are located in the anterior and lateral horns of the spinal cord gray matter.
Somatic motor neurons are in the anterior horn.
Autonomic neurons are in the lateral horns.
Axons from the motor neurons from the ventral roots and pass into the spinal nerves.
The dorsal root contains sensory axons, the ventral root motor axons, and the spinal nerve has both sensory and motor axons
Spinal Cord Reflexes
Knee-Jerk Reflex
Withdrawal Reflex
Knee-Jerk Reflex
The simplest reflex is the stretch reflex, a reflex in which muscles contract in response to a stretching force applied to them.
The knee-jerk reflex, or patellar reflex is a classic example of the stretch reflex.
When the patellar ligament is tapped, the quadriceps femoris muscle tendon and the muscles themselves are stretched.
Activity is important in maintaining posture and coordinating muscular activity.
The knee-jerk reflex is used by clinicians to determine if the higher CNS centers that normally influence this reflex are functional.
All spinal reflexes are lost below the level of injury for a few weeks after a severe spinal cord injury.
By about 2 weeks after injury the knee-jerk reflex returns, but it is often exaggerated.
When the stretch reflex is absent or greatly exaggerated, it indicated that the neurons within the brain or spinal cord that modify this reflex have been damaged.
Knee-Jerk Reflex
Sensory receptors in the muscle detect stretch of the muscle.
Sensory neurons conduct action potentials to the spinal cord.
Sensory neurons synapse with motor neurons. Descending neurons within the spinal cord also synapse with the neurons of the stretch reflex and modulate their activity.
Stimulation of the motor neurons causes the muscle to contract and resist being stretched.
Withdrawal Reflex
The function of the
withdrawal or flexor reflex
is to remove a limb or other body part from painful stimulus.
The sensory receptors are
pain receptors
.
Action potentials resulting from painful stimuli are conducted by sensory neurons.
These neurons stimulate muscles, usually flexor muscles that remove the limb from the source of the painful stimulus.
Withdrawal Reflex
Pain receptors detect a painful stimulus
Sensory neurons conduct actio potentials to the spinal cord.
Sensory neurons synapse with interneurons that synapse with motor neurons.
Excitation on the motor neurons result in contraction of the flexor muscles and withdrawal of the limb from the painful stimulus.
to the brain:
example of diverging circuit in the spinal cord. A sensory neuron from the periphery diverges and sends information to a motor neuron by way of an interneuron and sends information to the brain
from the brain:
example of converging circuit in the spinal cord. A sensory neuron from the periphery and a descending neuron from the brain converge on a single motor neuron.
Spinal Cord Converging and Diverging Pathways
SPINAL NERVE
- communicate between the spinal and the body
CAUDA EQUINA
- inferior end of the spinal cord and the spinal nerves exiting there resemble a horse's tail.
BRAIN
regions of the brain
BY: BENJAMIN PONSOY JR.
Regions of the
BRAIN
brainstem
diencephalon
cerebrum
cerebellum
Regions of the BRAIN
corpus callosum
cerebellum
epithalamus
thalamus
hypothalamus
midbrain
pons
medulla oblongata
diencephalon
brainstem
BRAINSTEM
connects the spinal cord to the remainder of the brain
consists of the:
medulla oblongata
pons
midbrain
contains several nuclei involved in vital body functions such as:
control of heart rate
blood pressure
breathing
CEREBELLUM
means little brain

is attached to the brainstem by several large connections called
cerebellar penduncles

these connections provide routes of communication between the cerebellum and other parts of the CNS.
Diencephalon
two prominent enlargements called pyramids
extend the length of the medulla oblongata
consists of descending nerve tracts which transmit action potentials from the brain to motor neurons of the spinal cord and are involved in the conscious control of skeletal muscles.
Pyramid
Brainstem
Pons
immediately superior to the medulla oblongata
it contains ascending and descending nerve tracts, as well as several nuclei
some of the nuclei in the pons relay information between cerebrum and the cerebellum
the term pons means bridge and it describes both the structure and function of the pons
pons is a functional bridge between cerebrum and cerebellum
PONS
is also resembles as an arched footbridge
several nuclei of the medulla oblongata, extends into the lower part of the pons
pons control fuctions:
breathing
swallowing
balance
chewing
salivation
is the smallest region of the brainstem
contains nuclei involved in the coordination of eye movements and in the control of pupil diameter and lens shape.
it also contains a black nuclear mass called
substantia nigra
- is a part of the basal nuclei
- is involved in the regulation of general body movements
the rest of the midbrain consists largely of ascending tracts from the spinal cord to the cerebrum and descending tracts from the cerebrum to the spinal cord or cerebellum
the dorsal part of the midbrain consists of four mounds called the
colliculi
- the
two inferior colliculi
are major relay centers for the auditory nerve pathways in the CNS
- the
two superior colliculi
are involved in visual reflexes
is a group of nuclei collectively scattered throughout the brainstem
it plays important regulatory functions in the brain
it is particularly involved in regulating cyclical motor functions such as respiration, walking and chewing
is a major component of the reticular activating system - which plays an important role in arousing and maintaining consciousness and in regulating the sleep -- wake cycle
Reticular Formation
is the part of the brain between the brainstem and the cerebrum.

its main components are:
thalamus
epithalamus
hypothalamus
Thalamus
is by far the largest part of the diencephalon.

it consists of a
cluster of nuclei
and is shaped somewhat like a yo-yo, with two large, lateral parts connected in the center by a small
interthalamic adhesion
Epithalamus
is a small area superior and posterior to the thalamus
it consist of a few small nuclei that are involved in the emotional and visceral response to odors, and the pineal body.
the pineal body is an endocrine gland that may influence the onset of puberty.
it also may play a role in controlling some long-term cycles that are influenced by the light-dark cycle.
Hypothalamus
is the most inferior part of the diencephalon and contains several small nuclei, which are very important in maintaining homeostasis.

plays a central role in the control of body temperature, hunger and thirst

sensation such as sexual pleasure, feeling relaxed and "good" after a meal, rage and fear are related to hypothalamus functions.
CEREBRUM
is the largest part of the brain
it is divided into left and right hemispheres by a longitudinal fissure.

the most conspicuous features on the surface of each hemisphere are numerous folds called gyri, which greatly increase the surface area of the cortex, and intervening grooves called sulci.
Midbrain
just superior to the pons
Medulla Oblongata
is the most inferior portion of the brinstem and is continous with the spinal cord

it extends from the level of the foramen magnum to the pons

it contains discrete nuclei with specific functions such as:
regulation of heart rate
blood vessel diameter
breathing
swallowing
vomiting
coughing
sneezing
balance
coordination
receives sensory input from the spinal cord as well as from its own nerves

perception and processing of sensory stimuli

execution of voluntary motor responses

regulation of homeostatic mechanism
BRAIN
cerebrum
Brainstem
connects the spinal cord to the remainder of the brain
consists of the:
medulla oblongata
pons
midbrain
contains several nuclei involved in vital body functions such as:
control of heart rate
blood pressure
breathing
Did you know?
Damage to small areas of the brain stem can
cause death
Damage to relatively large areas of the cerebrum or cerebellum often
do not cause death
Nuclei for the first two cranial nerves are also located in the brainstem
BRAINSTEM
DIENCEPHALON
Medulla Oblongata
is the most inferior portion of the brinstem and is continous with the spinal cord

it extends from the level of the foramen magnum to the pons

it contains discrete nuclei with specific functions such as:
regulation of heart rate
blood vessel diameter
breathing
swallowing
vomiting
coughing
sneezing
balance
coordination
MEDULLA OBLONGATA
medulla
oblongata
PONS
pons
Pons
immediately superior to the medulla oblongata

it contains ascending and descending nerve tracts, as well as several nuclei

is a functional bridge between cerebrum and cerebellum

some of the
nuclei in the pons relay information
between cerebrum and the cerebellum
the term
pons
means
bridge
and it describes both the structure and function of the pons
PONS
is also resembles as an arched footbridge

several nuclei of the medulla oblongata, extends into the lower part of the pons

pons control functions:
breathing
swallowing
balance
chewing
salivation
MIDBRAIN
midbrain
Midbrain
just superior to the pons

is the smallest region of the brainstem

contains nuclei involved in the coordination of eye movements and in the control of pupil diameter and lens shape.

it also contains a black nuclear mass called
substantia nigra
- is a part of the basal nuclei
- is involved in the regulation of general body movements
the rest of the midbrain consists largely of ascending tracts from the spinal cord to the cerebrum and descending tracts from the cerebrum to the spinal cord or cerebellum

the dorsal part of the midbrain consists of four mounds called the
colliculi

- the
two inferior colliculi
are major relay centers for the auditory nerve pathways in the CNS
- the
two superior colliculi
are involved in visual reflexes
Reticular Formation
is a group of nuclei collectively scattered throughout the brainstem
it plays important regulatory functions in the brain
it is particularly involved in regulating cyclical motor functions such as respiration, walking and chewing
is a major component of the reticular activating system - which plays an important role in arousing and maintaining consciousness and in regulating the sleep -- wake cycle
Did you know?
Stimuli such as an alarm clock ringing, sudden bright lights, smelling salts, or cold water being splashed
Removal of visual or auditory stimuli may lead to drowsiness or sleep
Damage to cells of the reticular formation can result in coma
THALAMUS
EPITHALAMUS
HYPOTHALAMUS
thalamus
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