all about the nervous system

1. The Nervous System
Anabel S. Ledesma
Angelita M. Ibona
Merlyn Albaño

2. 3 overlapping functions of the
nervous system
1. Much like a sentry, it uses its millions of sensory
receptors to monitor changes occurring both inside and
outside the body. These changes are called stimuli and
the gathered information is called sensory input.
2. It processes and interprets the sensory input and makes
decisions about what should be done at each moment- a
process called integration.
3. It then effects a response by activating muscles or
glands; the response called motor output.

3. Functions of the nervous system
• maintain body homeostasis with electric
signals
• provide for sensation, higher mental
functioning, and emotional response
• Activate muscles and glands

4. NERVOUS SYSTEM
• master controlling and communicating
system of the body
• every thought, action and emotion reflects its
activity
• Electrical impulses
 signaling device or means of communicating
with body cells
 rapid, specific and cause almost immediate
responses

5. ORGANIZATION OF THE NERVOUS SYSTEM
Central
Nervous System
Central
Nervous System
Peripheral Nervous System
(Cranial and Spinal Nerves)
Sensory (afferent)
Sense Organs
Somatic
(voluntary)
Sympathetic Parasympathetic
Autonomic
(involuntary)
Motor (efferent)

6. STRUCTURAL CLASSIFICATION
CENTRAL NERVOUS SYSTEM
CONSISTS OF THE BRAIN AND
SPINAL CORD, WHICH OCCUPY
THE DORSAL CAVITY AND ACT
AS INTEGRATING AND
COMMAND CENTERS OF THE
NERVOUS SYSTEM
THEY INTERPRET INCOMING
SENSORY INFORMATION AND
ISSUE INTRUCTIONS BASED ON
PAST EXPERIENCE AND
CURRENT CONDITIONS
PERIPHERAL NERVOUS SYSTEM
CONSISTS MAINLY OF THE NERVES
THAT EXTEND FROM THE BRAIN AND
SPINAL CORD
Spinal Nerves carry impulses to and
from the spinal cord;
Cranial nerves carry impulses to and
from the brain. These nerves serve as
communication lines. They link all parts
of the body by carrying impulses from the
sensory receptors to the CNS and from
the CNS to the appropriate glands or
muscles.

7. FUNCTIONAL CLASSIFICATION
-concerned only with PNS structure
2 PRINCIPAL DIVISIONS
A.) SENSORY OR AFFERENT: consists of nerve fibers that convey impulses
to the central nervous system from sensory receptors located on various parts of the
body. Sensory fibers delivering impulses from the skin, skeletal muscles and joints are
called somatic sensory fibers, whereas those transmitting impulses from the visceral
organs are called visceral sensory fibers or visceral afferents. The sensory division
keeps the CNS constantly informed of events going on both inside and outside the
body.
B.) MOTOR OR EFFERENT: carries impulses from the CNS to effector organs,
the muscles and glands. These impulses activate muscles and glands, that is, they
effect (bring about) a motor response.

8. 2 SUBDIVISIONS OF THE MOTOR DIVISION
b.1 SOMATIC NERVOUS SYSTEM
-allows us to consciously, or voluntarily, control our skeletal muscles.
Hence, this subdivision is often referred to a the voluntary nervous system.
b.2 AUTONOMIC NERVOUS SYSTEM
-regulates events that are autonomic or involuntary, such as the activity of
smooth and cardiac muscles and glands. This subdivision is commonly
called the involuntary nervous system, itself has two parts, the sympathetic
and parasympathetic.
Remember that the nervous system acts as a coordinated unit,
both structurally and functionally.

9. NERVOUS TISSUE: STRUCTURE AND
FUNCTION
TWO PRINCIPAL TYPES OF CELLS- NEUROGLIA AND NEURONS
1. Neuroglia - include many types of cells that generally support, insulate
and protect the delicate neurons in the CNS. Each of the different types
of neuroglia, also simply called glial, or supporting cells has special
functions.
The star-shaped astrocytes are particularly abundant and account for nearly half of the neural tissue.
They form a living barrier between capillaries and neurons and may have a role in making
exchanges between the two. In this way, they help protect the neurons from harmful substances that
might be in the blood.
The spiderlike microglia are phagocytes that dispose of debris-dead brain cells, bacteria and the
like.
Ependymal cells line the cavities of the brain and spinal cord.
The oligodendrocytes wrap their flat extensions tightly around the nerve fibers, producing fatty
insulating coverings called myelin sheaths.
Most brain tumors are gliomas, or tumors formed by glial cells (neuroglia).

11. NERVOUS TISSUE: STRUCTURE AND
FUNCTION
2. Neurons (nerve cells), are highly specialized to transmit messages
(nerve impulses) from one part of the body to another.
All have a cell body, which contains the nucleus and is the metabolic center of the cell, and one or
more slender processes, or fibers, extending from the cell body.
Neuron processes that typically conduct impulses toward the cell body are dendrites, whereas those
that generally conduct impulses away from the cell body are axons. Neurons may have hundreds of
the branching dendrites, depending on the neuron type, but each neuron has only one axon.
An occasional axon gives off a collateral branch along its length, but all axons branch profusely at
their terminal end, forming hundreds to thousands of axonal terminals. When these impulses reach the
axonal terminals, they stimulate the release of chemicals called neurotransmitters into the extracellular
space.

12. Nucleus- cell bodies found in the CNS in collections. This well-protected location within the bony skull
or vertebral column is essential to the well-being of the nervous system.
Ganglia-small collections of cell bodies, found in a few sites outside the CNS.
Tracts-bundles of nerve fibers (neuron processes) running through the CNS. It is called nerves in PNS.
White matter -consist of dense collections of myelinated fibers.
Gray matter – contains mostly unmyelinated fibers and cell bodies.

13. An enlarged view of an axional terminal shows that it is separated from the next neuron by a tiny gap,
the synaptic cleft; this functional junction called a synapse. Although they are close, neurons never
actually touch other neurons.
Most long nerve fibers are covered with a whitish, fatty material, called myelin, that has a waxy
appearance. Myelin protects and insulates the fibers and increases the transmission rate of nerve
impulses.
Axons outside the CNS are myelinated by Schwann cells, special supporting cells that wrap
themselves tightly around the axon jelly-roll fashion. When the wrapping process is done, a tight coil of
wrapped membranes, the myelin sheat, encloses the axon.
This part of the Schwann cell, external to the myelin sheath, is called the neurilemma. Since the
myelin sheath is formed by many indivdual Schwann cells, it has gaps or indentations, called nodes of
Ranvier. Myelinated fibers are also found in the central nervous system.

14. MYELINATION OF NEURON PROCESSES BY INDIVIDUAL
SCHWANN CELLS.
(a) A Schwann cell becomes opposed to an axon and envelops
it in a trough. It then begins to rotate around the axon,
wrapping it loosely in successful layers of its plasma
membrane. Eventually, the Schwann cell cytoplasm is forced
from between the membranes and comes to lie peripherally
just beneath the exposed portion of the Schwann cell
membrane. The tight membrane wrappings surrounding the
axon form the myelin sheath. The area of Schwann cell
cytoplasm and its exposed membrane are referred to as the
neurilemma, or sheath of Schwann. (b) Longitudinal view of
myelinated axon showing portions of adjacent Schwann cells
and the node of Ranvier between them (c) Electron micrograph
of cross-section through a myelinated axon.

16. MOTOR NEURONS
known as efferent neurons meaning 'moving away from a central organ or point', that is they move
impulses away from the CNS. This type of neuron takes information or responses from the brain to
muscles or organs, which are referred to as effectors. The information enters a motor neuron through
the dendrites, which then passes it into the cell body. From here it is sent down through the axon until it
reaches the end of the neuron (axon terminals). If a motor neuron connects with a muscle, the axon
terminals are called motor end plates. In a motor neuron, the dendrites are usually short and the
axons are typically long. Information about a response required has been formulated in the brain and
sent through motor neurons in the form of a series of electrical impulses, similar to the impulses sent
along sensory fibres.
1) Sensory
2) Motor
3) Association
FUNCTIONAL CLASSIFICATION OF
NEURONS

17. FUNCTIONAL CLASSIFICATION OF
NEURONS
1) Sensory
2) Motor
3) Association
SENSORY NEURONS
- also known as afferent neurons, meaning moving towards a central organ or point, that is
they move impulses towards the CNS . This type of neuron receives information or stimuli
from sensory receptors found in various locations in the body, for example the eyes, ears,
tongue, skin. This information enters sensory neurons through the dendron and passes it to
the cell body – the control centre of the cell. From here it is sent through the axon, until it
reaches the end of the neuron (axon terminals). Electrical impulses flow in one direction
only through a neuron. So just like a series of electrical power lines that pass electricity
through the suburbs of a city, so too do electrical impulses flow through the body along
thousands of tiny neurons.
In sensory neurons, the cell body and dendrons are located outside the spinal cord in the
torso, arms and legs. The dendrites (dendrons) are usually long and the axons short.

18. ASSOCIATION NEURONS
-also called interneurons. They connect the motor and sensory neurons in neutral
pathways. Like the motor neurons, their cell bodies are always located in the CNS.
FUNCTIONAL CLASSIFICATION OF
NEURONS
1) Sensory
2) Motor
3) Association

19. PHYSIOLOGY
NERVE IMPULSES
A nerve impulse is an electrical signal that travels along an axon. There is an electrical difference between the
inside of the axon and its surroundings, like a tiny battery. When the nerve is activated, there is a sudden change
in the voltage across the wall of the axon, caused by the movement of ions in and out of the neuron. This triggers
a wave of electrical activity that passes from the cell body along the length of the axon to the synapse.
1)IRRITABILITY-the ability to respond to a stimulus and convert it to a
nerve impulse.
2) CONDUCTIVITY-the ability to transmit the impulse to other neurons,
muscles or glands.

20. REFLEX ARC
Reflexes- rapid, predictable and involuntary responses to stimuli.
- occur over neural pathways called reflex arcs.
Types of reflexes
1)Autonomic- regulate the activity of smooth muscles, the heart, and glands. It regulate body
functions such as digestion, elimination, blood pressure and sweating. Examples: Production
of saliva(salivary reflex) and changes in the size of the eye pupils (pupillary reflex)
2)Somatic – include all reflexes that stimulate skeletal muscles.
Ex. When you quickly pull your hand away from a hot object.
Elements of reflex arc
1)Sensory receptor (which reacts to a stimulus)
2) an effector organ (the muscle or gland eventually stimulated)
3 and 4) efferent and afferent neurons to connect the two.

21. CENTRAL NERVOUS SYSTEM

22. The adult brain is about two good fistfuls of pinkish gray
tissue, wrinkled like a walnut, and about the texture of
cold oatmeal.
It weighs a little over three pounds.

23. 1. CEREBRUM
• Cerebral hemispheres - the most superior part of the brain.
• enclose and obscure most of the brain stem so that many brain stem structures cannot normally be seen unless a
sagittal section is made
• its entire surface exhibits elevated ridges of tissue called gyiri separated by grooves called fissures
• separated by a single deep fissure, the longitudinal fissure.
• Other fissures divide each cerebral hemisphere into a number of lobes, named for the cranial bones that may lie over
them.
• Somatic sensory area is located posterior to the central fissure in the parietal lobe.
 Impulses traveling from the body’s sensory receptors (except for the special senses) are localized and interpreted
in this area of the brain.
 allows you to recognize pain, coldness or a light touch
 Body regions with the most sensory receptors-the lips and fingertips-send impulses to neurons that make up a
large part of the sensory part of the sensory cortex.
 The sensory pathways are crossed pathways-meaning that the left side of the sensory cortex receives impulses
from the right side of the body and vice versa.
 impulses from the special sense organs are interpreted in other cortical areas.
• Primary motor area - allows us to consciously move our skeletal muscles
 anterior to the central fissure in the frontal lobe. The axons of these motor neurons form the major voluntary
motor tract-the pyramidal, or corticospinal tract, which descends to the cord.
 Most of the neurons in this primary motor area control body areas having the finest motor control; that is the face,
mouth, and hands.

24. 1. CEREBRUM

25. • visual area is located in the posterior part of the occipital lobe
• auditory area is in the temporal lobe bordering the lateral fissure
• olfactory area is found deep inside the temporal lobe.
• speech area is located at the junction of the temporal, parietal, and occipital lobe
 Allows one to understand words, and to make connections between them, whether they are spoken or read.
• Broca’s area - a specialized area that is very involved in our ability to speak
 damage to this area causes inability to say words properly
• Areas involved in higher intellectual reasoning are believed to be in the anterior part of the frontal lobes;
complex memories appear to stored in the temporal and frontal lobes.
• Cell bodies of neurons involved in the cerebral hemisphere functions are found only in the outermost gray
matter of the cerebrum, the cerebral cortex
• Most of the remaining cerebral hemisphere tissue-deeper cerebral white matter is composed of fiber tracts
(bundles of nerve fibers) carrying impulses to or from the cortex
• Corpus callosum - large fiber tract that connects the cerebral hemispheres ; arches above the structures of
the brain and allows the cerebral hemispheres to communicate with one another.
• Basal nuclei – several islands of gray matter, buried deep within the white matter of the cerebral
hemispheres
• Help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor
cortex
Basal nuclei problem : unable to walk normally or carry out other voluntary movements in a normal way
1) HUNTINGTON’S CHOREA – a genetic disease in which the individual is unable to control muscles and exhibits abrupt, jerky and most
continuous movements.
2) PARKINSON’S DISEASE - people who have this disease have trouble initiating movement or getting their muscle going. They also have
a persistent hand tremor in which their thumb and index finger make continuous circles with one another in what is called the “pill-rolling”
movement. It is due to a deficit of the neurotransmitter dopamine, and drugs that help to replace it benefit some
1. CEREBRUM

26. 1. CEREBRUM

27. 2. DIENCEPHALON
Also called interbrain, sits atop the brain
stem and is enclosed by the cerebral
hemispheres
MAJOR STRUCURES:
1)THALAMUS – encloses the shallow third
ventricle of the brain; a relay station for sensory
impulses passing upward to the sensory cortex
2)HYPHOTHALAMUS - make up the floor of the
diencephalon; an important autonomic nervous
system center because it plays a role in the
regulation of body temperature, water balance
and metabolism; center for many drives and
emotions; important part of the so-called limbic
system or “emotional-visceral brain”
3) EPITHALAMUS – forms the roof of the third
ventricle
Important parts:
1) Pineal body
2) Chloroid plexus

28. 3. BRAIN STEM
-about the size of a thumb in diameter and approximately 3 inch long
-provides a pathway for ascending and descending tracts
-has many small gray matter areas. These nuclei form the cranial nerves and control vital activities such as
breathing and blood pressure. Extending the entire length of the brain stem is a diffuse mass of gray matter,
the reticular formation-involved in consciousness and the awake/sleep cycles ; damage to this area can
result to permanent unconsciousness (COMA)
1)MIDBRAIN – relatively small part of the brain stem ; extends from the mammillary bodies to the pons
inferiorly
Cerebral aqueduct – tiny canal that travels through the midbrain and connects the third ventricle of the
diecephalon to the fourth ventricle below
Cerebral peduncles – two bulging fiber tracts which convey ascending and descending impulses; these are
reflex centers involved with vision and hearing
1)PONS- means “bridge” is rounded structure that protrudes just below the midbrain; this area is mostly
fiber tracts; have important nuclei involved in the control of breathing
2)MEDULLA OBLONGATA – most inferior part of the brain stem; merges into the spinal cord below without
any obvious change in structure; contains many nuclei that regulate vital visceral activities; contains centers
that control heart rate, blood pressure, breathing, swallowing and vomitting; the fourth ventricle lies posterior
to the pons and medulla and anterior to the cerebellum.

29. - large, cauliflowerlike which projects dorsally from under the occipital lobe of the cerebrum
- Has two hemispheres and a convoluted surface
- Has an outer cortex made up of gray matter and an inner region of white matter
- Provides the precise timing for skeletal muscle activity and controls our balance and
equilibrium
- If damaged, movements become clumsy and disorganized.
4. CEREBELLUM

30. PROTECTION OF THE CENTRAL
NERVOUS SYSTEM
Nerve tissue is very soft and delicate, and the irreplaceable neurons are injured
even the slightest pressure.
1)MENINGES – three connective tissues membranes covering and protecting the CNS.
 Dura mater –outermost layer which is a double-layered membrane where it surrounds the brain
 Meningeal layer – forms the outermost covering of the brain and continues as the dura mater of
the spinal cord
 Arachnoid-a weblike middle meningeal layer; its threadlike extensions span the subarachnoid
space to attach it to the innermost membrane, the pia mater – clings tightly to the surface of the
brain and spinal cord following every fold.
 The subarachnoid space is filled with cerebrospinal fluid-absorbed into the venous blood in the
dural sinuses through the arachnoid villi
 Arachnoid villi- specialized projections of the arachnoid membrane
Meningitis- inflammation of the meninges, a serious threat to the brain because bacterial or
viral meningitis may spread into the nervous tissue of the CNS. This condition of brain
inflammation is called encephalitis.
- usually diagnosed by taking a sample of cerebrospinal fluid from the subarachnoid space

31. PROTECTION OF THE CENTRAL
NERVOUS SYSTEM
MENINGES

32. 2) CEREBROSPINAL FLUID (CSF)- similar to
plasma, is continually formed from blood by the
choroid plexuses, which are clusters of capillaries
hanging from the roof in each of the brain’s
ventricles.
•Inside the brain the CSF is continually moving
•Forms and drains at a constant rate so that its normal
pressure and volume (100-160 ml –about half a cup) is
maintained.
•Major absolutes in CSF are glucose, proteins and sodium
chloride
•CSF sample for testing is obtained by a spinal (lumbar)
trap
•If something obstructs its drainage(ex. Tumor) CSF begins
to accumulate and exert pressure on the brain
•Hydrocephalus- “water on the brain” ;
• HYDROCEPHALUS in a newborn baby causes
the head to enlarge as the brain increases size.
PROTECTION OF THE CENTRAL
NERVOUS SYSTEM

33. 3) BLOOD-BRAIN BARRIER
-if the brain were exposed to such chemical changes, uncontrolled
neutral activity might result
-neurons are kept separated from blood-borne substances by a so-
called blood-brain barrier
-composed of the least permeable capillaries in the whole body
-only water, glucose, some amino acids and respiratory gases pass
easily through the walls of these capillaries
-the bulbous “feet” of the astrocytes that cling to the capillaries may
contribute to the barrier, the relative impermeability of the brain
capillaries probably is the most responsible for providing this
protection
PROTECTION OF THE CENTRAL
NERVOUS SYSTEM

34. 1. TRAUMATIC BRAIN INJURIES
•Brain damage is caused not only by injury at the site of the blow, but also by the effect of the ricocheting brain
hitting the opposite end of the skull.
•Concussion occurs when brain injury is slight. The victim may be dizzy or lose consciously briefly, but no
permanent brain damage occurs
•Brain contusion –result of marked tissue destruction. If the vortex is injured, the individual may remain
conscious but severe stem contusions always result in coma ranging from hours to a lifetime because of injury
to reticular activating system
2. DEGENERATIVE BRAIN DISEASES
1. CEREBROVASCULAR ACCIDENTS-occur when blood circulation to a brain area is
blocked, as by a blood clot or rapture of a blood vessel, and vital brain tissue dies.
 aphasias – common result of damage to the left cerebral hemisphere, where the language
areas are located
 Motor aphasia- damage to Broca’s area and a loss of ability to speak
 Sensory aphasia-person loses ability to understand written or spoken language
1. ALZHEIMER’S DISEASE-progressive degenerative disease of the brain that ultimately
results in dementia (mental deterioration)
 Obvious structural changes occur in the brain, particularly in areas concerned with
cognitive functions and memory
 Abnormal protein deposits and twisted fibers appear with neurons and there is localized
brain atrophy
BRAIN DYSFUNCTIONS

35. SPINAL CORD
-continuation of the brain stem; approximately 17
inches (42m long)
-provides a two-way conduction pathway to and from
the brain
-major reflex center
-enclosed within the vertebral column, it extends from
the foramen magnum of the skull to the first or second
lumbar vertebra, where it ends just below the ribs
-cushioned and protected by meninges
-in humans, 31 pairs of spinal nerves arises from the
cord and exit from the vertebral column to serve the
body area close by
-about the size of a thumb for most of its length but
enlarged in the cervical and lumbar regions where the
nerves serving the upper and lower limbs leave the
cord
Cauda equina -collection of spinal nerves at the
inferior end of the vertebral canal

36. GRAY MATTER OF THE SPINAL CORD AND
SPINAL ROOTS
-the gray matter of the cord looks like a butterfly or the
letter H
-two posterior projections: dorsal or posterior, horns;
-two anterior projections: ventrial or anterior, horns
-central canal - contains the cerebrospinal fluid
-The cell bodies of the sensory neurons whose
fibers enter the cord by the dorsal root, are found
in an enlarged are called the dorsal root
ganglion. If the dorsal root or its ganglion is
damaged, sensation from the body area served will
be lost.
-The ventral horns of the gray matter contain cell
bodies of motor neurons of the somatic (voluntary)
nervous system, which sends their axons out the
ventral root of the cord.
-Damage to the ventral root results in flaccid
paralysis of the muscles served.
-In flaccid paralysis, nerve impulses do not reach
the muscles affected, no voluntary movement of
those muscles is possible. The muscles begin to
atrophy because they are no longer stimulated.

37. -White matter of the spinal cord is composed of myelinated fiber tracts-some running
to higher centers, some traveling from the brain to the cord, and some conducting
impulses from one side of the spinal cord to the other.
-The white matter on each side of the cord is divided into three regions
1.)Posterior 2.) Lateral 3.) Anterior columns
-If the spinal cord is transected or crushed, spastic paralysis results. The affected
muscles stay healthy because they are still stimulated by spinal reflex arcs and
movement of those muscles does occur.
-Movements are involuntary and not controllable; this can be as much of a problem
as complete lack of mobility
WHITE MATTER OF THE SPINAL CORD

38. PERIPHERAL NERVOUS
SYSTEM

39. The peripheral nervous system (PNS) consist of nerves and scattered
groups of neural cell bodies called ganglia found outside the CNS, one is
considered the dorsal root ganglion of the spinal cord.
Structure of a Nerve
A nerve is a bundle of neuron fibers found outside the CNS. Each fiber
surrounded by a delicate connective tissue sheath, an endoneurium.
Groups of fibers are bound by a coarser connective tissue wrapping, the
perineum to form fiber bundles or fascicles. It is bound together by a
tough fibrous sheath, the epineurium to form the cordlike nerve.
Nerves carrying both sensory and motor fibers are called mixed nerves,
nerves that carry impulses towards the CNS are called afferent or
sensory nerves, whereas those that carry motor fibers are efferent or
motor nerves.

40. CRANIAL NERVES
The 12 pairs of cranial nerves primarily serve the head and neck. The vagus nerves extends to the
thoracic and abdominal cavities.
Most cranial nerves are mixed nerves; however, three pairs are purely sensory in function 1. Optic
nerves 2. Olfactory nerves 3. Vestibulocochlear nerves
Olfactory Purely sensory; carries impulses for the sense of smell
Optic Purely sensory; carries impulses for vision
Oculomotor Supplies motor fibers to four of the six muscles that direct the eyelid
And to the internal eye muscles controlling lens shape and pupil size.
Trochlear Supplies motor to the external eye muscle (superior oblique)
Trigeminal Conducts sensory impulses from the skin of the face and mucosa of the nose and mouth; contains motor fibers that
activate the chewing muscles.
Abducens Supplies motor fibers to the lateral rectus muscles, which rolls the eye laterally.
Facial Activate the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste
buds of anterior tongue
Vestibulocochlear Purely sensory; vestibular branch transmits impulses for the sense of balance and cochlear branch transmits impulses
for the sense of hearing
Glossopharyngeal Supplies motor fibers to the pharynx (throat) that promote swallowing and saliva production; carries sensory impulses
from taste buds of the posterior tongue and from pressure receptors of the carotid artery
Vagus Fibers carry sensory impulses from and motor impulses to the pharynx, larynx and the abdominal and thoracic viscera.
Most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity
Accessory Mostly motor fiber that activate the sternocleidomastoid and trapezius muscles
Hypoglossal Motor fibers control tongue movements; sensory fibers carry impulses from the tongue

42. SPINAL NERVES AND NERVE PLEXUSES
The 31 pairs of human spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord.
Each spinal nerve divides into dorsal and ventral rami, making each spinal nerve only about ½ inch long. The rami
contain both motor and sensory fibers.
Damage to a spinal nerve or either of its rami results in both loss of sensation and flaccid paralysis of the area of the
body served.
The ventral rami of all other spinal nerves form complex networks of nerves called plexuses, which serve the motor
and sensory needs of the limbs.
AUTONOMIC NERVOUS SYSTEM
-the motor subdivision of the PNS that controls body activities body activities automatically.
-composed of a special group of neurons that regulate cardiac muscle ( the heart), smooth muscles (found in the walls
of the visceral organs and blood vessels), and glands.
At every moment, signals flood from the visceral organs into the CNS and the autonomic nerves make adjustments as
necessary to best support body activities. The ANS is also called the involuntary nervous system
COMPARISON OF THE SOMATIC AND AUTONOMIC NERVOUS SYSTEM
In the somatic division, the cell bodies of the motor neurons are inside the CNS, and their axons (in spinal nerves)
extend all the way to the skeletal muscles they serve. On the other hand, the autonomic nervous system has a chain of
two motor neurons. The first motor neuron of each pair is in the brain or cord. Its axon, the preganglionic axon, leaves
the CNS to synapse with the second motor neuron in a ganglion outside the CNS. The axon of this neuron, the
postganglionic axon, then extends to the organ it serves.

43. 2 arms of autonomic nervous system
1. Sympathetic division- also called the thoracolumbar division because its first neurons are in the gray matter
of the spinal cord from T1 through L2
The preganglionic axons leave the cord in the ventral root, enter the spinal nerve and then pass through a
ramus communicans or small communicating branch, to enter a sympathetic chain ganglion.
The sympathetic chain or trunk lies alongside the vertebral column on each side.
After it reaches the ganglion, the axon may synapse with the second neuron in the sympathetic chain at the
same or a different level or the axon may pass through the ganglion without synapsing and form part of the
splanchnic nerves. The splanchnic nerves travel to the viscera to synapse with the second neuron, found in a
collateral ganglion anterior to the vertebral column.
The major collateral ganglia-the celiac and superior and inferior mesenteric ganglia – supply the abdominal and
pelvic organs. The postganglionic axon then leaves the collateral ganglion and travels to serve a nearby visceral
organ.
2. Parasympathetic division
The first neurons of the parasympathetic division are located in brain nuclei of several cranial nerves and in the
S2 through S4 level of the spinal cord. The neurons of the cranial region send their axons out in cranial nerves to
serve the head and neck organs. They synapse with the second motor neuron in a terminal ganglion. The
postganglionic axon extends a short distance to the organ it serves. In the sacral region, the preganglionic
axons leave the spinal cord and form the pelvic nerves, also called the pelvic splanchnic nerves which travel to
the pelvic cavity. In the pelvic cavity, the preganglionic axons synapse with the second motor neurons in
terminal ganglia on, or close to, the organs they serve.

45. AUTONOMIC FUNCTIONING
Body organs served by the autonomic nervous system receive fibers from both divisions.
When both divisions serve the same organ they cause antagonistic effects, mainly because
their postganglionic axons release different neurotransmitters. The parasympathetic fibers,
called cholinergic fibers, release acetylcholine; the sympathetic postganglionic fibers, called
adrenergic fibers, release norepinephrine. The preganglionic axons of both divisions release
acetylcholine.
The sympathetic division is often referred to as the “fight-or-flight” system.
A pounding heart; rapid, deep breathing; cold, sweaty skin; a prickly scalp; and dilated eye
pupils are sure signs of sympathetic nervous activity.
The sympathetic nervous system is working at full speed, not only when you are emotionally
upset, but also when you are physically stressed. It generates a head of steam that enables the
body to cope rapidly and vigorously with situations that threaten homeostasis. Its function is to
provide the best conditions for responding to some threat, whether the best response is to run,
to see more clearly, or to think more critically.
The parasympathetic division is most active when the body is at rest and not threatened in any
way. The division, sometimes called the “resting and digesting” system, is chiefly concerned
with promoting normal digestion and elimination, and with conserving body energy, particularly
by decreasing demands on the cardiovascular system.
We might also consider the parasympathetic division the “housekeeping” system of the body.

46. -END-
Thank you for listening!!!