Nervous System
(Chapter 12)
Functions of the Nervous System
1. Coordination
•
of all body systems: sensory input, integration,
motor output.
2. Orientation
•
awareness of body position
3. Perception
•
of changes that occur in the immediate environment
4. Conceptual thought
•
capacities to record, store, and relate information
received and use it at a later date.
Anatomical Classification of the N.S.
Nervous System
Central Nervous System
1. Brain
2. Spinal Cord
Peripheral Nervous System
1. Nerves
2. Ganglia
3. Sensory Receptors
Functional Classification of the NS
Nervous System
Afferent Division
(sensory division)
Efferent Division
(motor division)
Involuntary or Voluntary Control
Autonomic
Sympathetic
“Stress”
Afferent: → brain
Efferent: brain →
Somatic
Parasympathetic
“Calm”
Cells of the NS
• Nerve Cells (Neurons)
• Carry electrical impulses and are electrically
excitable.
• Many types of nerve cells are found in the body.
• Longest cell in the body.
DRAW
Generalized Nerve Cell (Neuron) Component
Parts and Function
•
Dendrites
–
–
–
–
conduct information toward the nerve cell body
typically multiple and highly branched
generally shorter than axon
irregular in size (diameter)
•
Cell body - contains the nucleus of the cell
•
Axon
–
–
–
–
•
conducts the impulse away from the nerve cell body
generally single but may have many branches to axon terminals
longer, may be 3 feet (1 meter) in length
uniform diameter within a nerve cell
Axon terminal (terminal bouton) - neuron ending
– Contains synaptic vesicles that contain neurotransmitter (chemical
messenger)
– Carries the nervous system message from one neuron to the next
across a gap between the neurons known as a synapse
Myelin - is a segmented sheath (white matter) that serves to increase the speed
of the nerve impulse. Non-myelinated is known as gray matter.
Saltatory Conduction - impulse “jumps” from one node of Ranvier to the next, so
impulse is regenerated only at the nodes.
Cells of the NS
• Supporting Cells
– Glial cells (neuroglia), (50:1, CNS)
Phagocytes
Nutrient
providers
Myelin sheaths
– Glial cells of PNS
• Satellite cells – surround cell bodies, “nerve glue”
• Schwann cells (neurolemocytes) - produce myelin
around axons in PNS
Major Components of the PNS
• Nerves - a bundle of neurons or
nerve cells.
• Two important categories of PNS
nerves are:
– Cranial nerves (12 pr.) that
branch to and from the brain
– Spinal nerves (31 pr.) that exit
the spinal cord from between
each vertebrae.
Major Components of the PNS
• Ganglia - Ganglia are aggregations of nerve cell
bodies.
• Sensory receptors (sense organs)
– Provides the body with information about the immediate
environment, both internal and external.
• e.g. sense organs for taste, touch, sight, hearing, or
smell.
Structure of
Peripheral Nerves
•
The nerve consists of bundles of
nerve fibers (axons) surrounded by
connective tissue, which is
vascularized to nourish neurons and
Schwann cells.
•
Epineurium
– Outer sheath of dense,
collagenous C.T.
Perineurium
– Each bundle of nerve fibers
(fascicle) is enclosed by sleeve of
less dense C.T.
Endoneurium
– Individual fibers are surrounded
by loose C.T.
•
•
3 Types of Neurons
•
•
•
Afferent (sensory)
Efferent (motor)
Interneurons (“linker”)