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1. Chapter
(4)
Nervous system

2. Introduction
• As the primary control system of the body, the nervous system provides for
higher mental function and emotional expression, maintains homeostasis, and
regulates the activities of muscles and glands
• Communication by the nervous system involves a combination of electrical and
chemical signals.
• All body systems are under the control or regulation of the nervous system.
If the nervous systems stops functioning, the body can stay alive only with the
assistance of life-supporting machines.

3. • Every thought, action, and emotion reflects its activity. It
communicates with body cells using electrical impulses which are
rapid and specific and cause almost immediate responses
The nervous system does not work alone to regulate and maintain body
homeostasis; the endocrine system is a second important regulating
system.
Whereas the nervous system controls with rapid electrical nerve
impulses, the endocrine system produces hormones that are released
into the blood.

4. Structural Classification
1. The central nervous system (CNS):
consists of the brain and spinal cord, which occupy the dorsal body
cavity and act as the integrating and command centers of the nervous
system.
2. The peripheral nervous system (PNS): Includes all parts of the
nervous system outside the CNS.
It consists mainly of the nerves that extend from the spinal cord and
brain.
a. Spinal nerves carry impulses to and from the spinal cord.
b. Cranial nerves carry impulses to and from the brain.

5. The functional classification
1. The sensory division, or afferent (“to go toward”) division, consists
of nerves that convey impulses to the central nervous system
• from sensory receptors located in various parts of the body.
A)Sensory fibers delivering impulses from the skin, skeletal muscles,
and joints are called somatic sensory (afferent) fibers ( voluntary)
B) Sensory fibers delivering impulses from the visceral organs are
called visceral sensory (afferent) fibers.

6. The functional classification
2. The motor division, or efferent division, carries impulses from the
CNS to effector organs, the muscles and glands.
These impulses activate muscles and glands; that is, they effect (bring
about or cause) a motor response.
The motor division in turn has two subdivisions:
A) The somatic nervous system allows us to consciously, or voluntarily,
control our skeletal muscles.
B) The autonomic nervous system (ANS) regulates events that are
automatic, or involuntary, such as the activity of smooth muscle,
cardiac muscle, and glands

7. Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves
a.Sensory (afferent) sensory organs
b.motor( efferent) Somatic (voluntary) Skeletal muscles
Autonomic (involuntary) Cardiac and smooth muscle, glands
a. Parasympatheti
b. Sympathetic
which typically bring about opposite effects. What one stimulates,
the other inhibits. We will describe these later.

8. • It uses its millions of sensory receptors to monitor changes occurring both
inside and outside the body.
1. These changes are called stimuli, and the gathered information is called
sensory input.
(2) It processes and interprets the sensory input and decides what should be
done at each moment—a process called integration.
(3) It then causes a response, or effect, by activating muscles
• or glands (effectors) via motor output.

9. Nervous system function
•
sSe
Sensory
receptor
input
Effector
Motor
output

10. Neurons
• Neurons, also called nerve cells, are highly specialized to transmit
messages (nerve impulses) from one part of the body to another
a. Cell Body The cell body is the metabolic center of the neuron
b. Processes: (The armlike processes, or fibers) Neuron processes that
convey incoming messages (electrical signals) toward the cell body
are dendrites
c. Axons: generate nerve impulses and typically conduct them away
from the cell body

11. Neurons
d. Axon terminals: These terminals contain hundred of tiny vesicles, or
membranous sacs, tha contain chemicals called neurotransmitters
e. Myelin Sheaths Most long nerve fibers are covered with a whitish, fatty
material called myelin which has a waxy appearance.
Myelin protects and insulates the fibers and increases the transmission rate of
nerve impulses
e.