The nervous system is composed of two main divisions: the central nervous system (CNS) containing the brain and spinal cord, and the peripheral nervous system (PNS) containing nerves. Sensory neurons carry messages from receptors to the CNS, where they are integrated and motor commands are sent via motor neurons to elicit responses. Motor actions are either somatic, occurring in skeletal muscle voluntarily, or autonomic, occurring involuntarily in smooth and cardiac muscle. The cells of the nervous system are neurons, which transmit nerve impulses, and neuroglial cells which support neurons. Neuroglia include astrocytes, microglia, ependymal cells, and oligodendrocytes in the CNS or Schwann
2. Composition of Nervous System
Two main divisions
1) Central Nervous
system (CNS) brain
and spinal chord
2)Peripheral Nervous
System (PNS) nerves
3. Remember from Homeostasis
Message is received from
sensory receptor along
sensory neuron (afferent
pathway)
Messages reaches brain
and is integrated (control
center)
Reaction command sent
down efferent pathway
along motor neuron
(motor output)
4. Types of Motor Actions
Somatic
Happens in skeletal
muscle
voluntary
Autonomic
Happens in smooth
and cardiac muscle
Involuntary
2 parts
Sympathetic and
parasympathetic
5. Cells of the Nervous System
Broken down into two
groups
1) supporting cells
2) neurons
6. Examples of Neuroglia (supporting
cells)
1) astrocytes –
anchor neurons to
capillaries
2) microglia –
phagocytes (digest
debris and dead cells)
3) Ependymal cells-
ciliated; always on
surface near spinal
fluid; circulates fluid
7. One more Neuroglial cell (in CNS)
4)Oligodendrocytes –
fatty; insulated nerve
fibers
Produce myelin
sheath which
surround and insulate
the nerve fiber
8. In PNS
Instead of
oligodendrocytes,
they have Schwann
cells, which insulate
the nerve fiber
Satellite cells – form
protective layer
around nerve cell
body
10. Parts of a Neuron
1)Cell Body- contains
nucleus
2) fiber (process)-
carries message to
next neuron
Toward cell body =
dendrites
Away from cell body =
axon
11. Axonal Terminal
As an axon ends, it
branches into
hundreds of
synapses.
Releases
neurotransmitters to
next neuron or
muscle
12. Myelination of Neurons
In CNS, the fatty
covering is
oligodendrocyte
In PNS, fatty myelin
forms Schwann cells,
which increase
transmission rate.
Gaps between
Schwann cells= Nodes
of Ranvier