Nervous System
Chapter 7
Three Basic Functions:

Sensory Input


Integration


Uses 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
Processes and interprets the sensory input and
makes decisions about what should be done at
each moment…a process called integration
Motor Output

Effects a response by activating muscles or
glandes (effectors) through motor output
Organization of
Nervous System:
 Structural

Structures
 Functional

Activities
Structural Organization:
 Includes
all nervous
system organs
 2 subdivisions:


Central Nervous System
(CNS)
Peripheral Nervous System
(PNS)
Central Nervous System (CNS):
 Consists
of the brain and spinal cord
Peripheral Nervous System (PNS):




Consists mainly of nerves that
extend from the brain and spinal
cord
Spinal nerves: carry impulses to
and from the spinal cord (31
pairs)
Cranial nerves: carry impulses to
and from the brain (12 pairs)
These are the communication
lines…linking all parts of the
body by carrying impulses from
sensory receptors to the CNS
and from the CNS to
appropriate glands/muscles
Cranial Nerves:




Listed on pages 250-251 and picture on page
252
12 pairs
Serve the head and neck
Most are mixed nerves (send impulses both
ways…to and from CNS)

Only 1 pair-the vagus nerve-extends to the
thoracic and abdominal cavities

Giraffe Vagus Nerve Dissection
Spinal Nerves:







Listed on page 255
31 pairs of human spinal nerves are formed by the
combination of the ventral and dorsal roots of the spinal
cord
Each spinal nerve is only about ½ inch long and almost
immediately after being formed divides into dorsal and
ventral “rami”
The rami contain both motor and sensory fibers…thus
damage to a spinal nerve or its “rami” results in loss of
sensation and paralysis of area of body served
Smaller dorsal rami serve the skin and muscles of the posterior
body trunk
Ventral rami of spinal nerves T1-T12 supply the muscles
between the ribs and skin and muscles of the anterior and
lateral trunk
The ventral rami of all other spinal nerves form the complex
networks or nerves called plexuses, which serves the motor
and sensory needs of the limbs.
Functional Classification:
 Concerns
only PNS structures
 Divides them into 2 principal subdivisions


Sensory (or afferent) division
Motor (or efferent) division
Functional Subdivisions:
Sensory (Afferent):
 Consists
of nerve
fibers that convey
impulses to the
CNS from sensory
receptors
Motor (Efferent):



Carry impulses from
the CNS to effector
organs, muscles, and
glands
These impulses
activate muscles
and glands…they
“effect” a motor
response
Has 2 subdivisions…
2 subdivisions of Motor division:
 Somatic


Nervous System
Allows us to consciously,
or voluntarily, control our
skeletal muscles
Often referred to as
“voluntary nervous
system”

Autonomic Nervous
System



Regulates events that
are automatic or
involuntary such as the
activity of smooth and
cardiac muscles and
glands
Referred to as
“involuntary nervous
system”
Has 2 parts:

Sympathetic &
Parasympathetic:

Bring about opposite
effects…one stimulates
while one inhibits
Nervous Tissue:
Structure & Function
 Nervous
tissue is made up of just 2 types of
cells…supporting cells and neurons
 You should remember neurons from the
tissue chapter….probably easiest slide to
ID!
“Neuroglia” (supporting cells)
 Neuroglia
literally
means “nerve glue”
 6 types:
1.
2.
3.
4.
5.
6.
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Schwann cells
Satellite cells
Neurons (nerve cells)


Highly specialized to
transmit messages
(nerve impulses) from
one part of the body to
another
Neurons can differ
structurally, but have
many common features
like the cell body (that
includes the nucleus
and is metabolic center
of cell)and one or more
processes (or fibers)…
Processes:




Vary in length from microscopic to
3 or 4 feet…longest ones in humans
reach from lumbar region of the
spine to the great toe!
Processes that convey incoming
messages toward the cell body are
dendrites (dendr=tree)
Processes that generate nerve
impulses and conduct them away
from the cell body are axons (a&a)
Neurons may have hundreds of the
branching dendrites, depending of
the neuron types, but each neuron
has only one axon…all axons
branch profusely at their terminal
end…forming hundreds to
thousands of axon terminals!
Axons continued….




Axon terminals contain hundreds of tiny vesicles, or
membranous sacs that contain chemicals called
neurotransmitters
As said earlier, axons transmit nerve impulses away
from the cell body…when these impulses reach
the axon terminals, they stimulate the release of
neurotransmitters into extracellular space
Each axon terminal is separated from the next
neuron y a tiny gap called the synapse
Although they are close, neurons never actually
touch other neurons!
More Neuron Anatomy:

Myelin:



Schwann cells:



Whitish, fatty material that covers long nerve fibers
Protects and insulates the fibers and increases the
transmission rate of nerve impulses
Specialized 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 sheath, encloses
the axon
Nodes of Ranvier:

Since the myelin sheath is formed by many
individual Schwann cells, it has gaps or
indentations, called nodes of Ranvier at regular
internals
Nerve Impulses:

2 major functions:

1. irritability


The ability to respond to a stimulus and convert it into
a nerve impulse
2. conductivity

The ability to transmit the impulse to other neurons,
muscles or glands.




*Figure 7.9, pg.232 describes how nerve impulses work in a
step by step manner. Here are some videos:
Nerve Impulse Animation
Animation: Transmission Across a Synapse
Nerve impulse Animation - YouTube
Reflexes
 Rapid,
predictable, and involuntary
responses to stimuli
 Like one way streets-once it begins,
always goes in the same direction
 Occur over neural pathways called reflex
arcs
 Involve both CNS and PNS
Types of Reflexes:
Somatic


All reflexes that stimulate skeletal system
Ex: When you pull your hand away from hot
object
Autonomic



Regulate activity of smooth muscles, heart, and
glands
Regulate digestion, elimination, blood pressure,
and sweating
Ex: Changes in size of pupil
Reflex Arcs 5 Elements:
1.
2.
3.
4.
5.
Receptor
Effector organ
Sensory neuron
Integration center
Motor neuron
Brain Anatomy:
4
1.
2.
3.
4.
major regions:
Cerebral hemispheres
Diencephalon
Brain stem
Cerebellum
Cerebral Hemispheres
“cerebrum”
 Most
superior part of
brain and together
are larger than the
other 3 brain regions
combined!
 Controls sensory and
motor functions and
higher mental function
like memory and
reasoning and higher
mental function (like
memory and
reasoning).
Diencephalon (interbrain):
 Sits
atop the brain
stem and is
enclosed by the
cerebral
hemispheres
 Includes:

Thalamus,
hypothalamus,
and epithalamus
Brain Stem:
 About
the size of a thumb
in diameter and about 3
inches long
 Includes:
1.
2.
3.
Midbrain: reflex centers
involved with vision and
hearing
Pons: nuclei involved in
the control of breathing
Medulla oblongata:
contains centers that
control heart rate, blood
pressure, breathing,
swallowing, vomiting,
and others.
Cerebellum:
 Large,
cauliflower-like
structure that projects
dorsally
 Has 2 hemispheres (like
cerebrum)
 Provides the precise
timing for skeletal muscle
activity and controls our
balance and
equilibrium…Because of
its activity, body
movements are smooth
and coordinated
Meninges (Protection of CNS)
3
connective tissue membranes that
cover and protect the CNS

Dura mater
 Outermost

Arachnoid mater
 “spider”

layer “tough or hard mother”
some think it looks like web
Pia mater
 Innermost
layer “gentle mother”-clings tightly
to surface of brain and spinal chord
Spinal Cord:







About 17in, glistening white
continuation of brain stem
Provides a 2-way conduction
pathway to and from the brain
Major reflex center
Is enclosed within the vertebral
column
Extends from the foramen
magnum of the skull to the first or
second lumbar vertebra, where it
ends just below the ribs
Also protected by meninges
In humans, 31 pairs of spinal
nerves arise from the cord and
exit from the vertebral column to
serve the body area close by!