A&P 110 Chapter 9
The Nervous System:
The Spinal Cord and Spinal Nerves
•The Nervous System
•The STRUCTURE of the nervous system is
divided into two parts:
•The central nervous system (CNS), which
consists of the brain and spinal cord
•and
•The peripheral nervous system (PNS), which
consists of the nerves outside the brain and
spinal cord
•Peripheral Nervous System (PNS)
•The PNS connects the CNS to the limbs and
organs, serving as a relay between the brain
and spinal cord and the rest of the body
•SPINAL NERVES carry impulses to and from
the spinal cord, while CRANIAL NERVES carry
impulses to and from the brain
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Cohen: Memmler’s The Human Body in Health and Disease
Figure 9-1 Anatomic divisions
of the nervous system, posterior
view.
•PNS contd.
•The PNS has two parts:
•The Somatic Nervous System
and
•The Autonomic Nervous System
•The Somatic Nervous System
•The somatic nervous system controls
VOLUNTARY functions
•All the effectors of the somatic nervous
system are SKELETAL MUSCLES
•An EFFECTOR is any tissue or organ that
carries out a nervous system command
•The Autonomic Nervous System (ANS)
•The ANS controls INVOLUNTARY functions
•The effectors of the ANS are:
•SMOOTH MUSCLES
•CARDIAC MUSCLE
•GLANDS
•The Neuron or The Nerve Cell
•The NEURON is the functional cell of the
nervous system
•The CELL BODY contains the nucleus and other
organelles. Dendrites conduct impulses to the
cell body
•The AXON extends out from the cell body and
conducts impulses away from the cell body
•The Myelin Sheath
•Myelin is a whitish, fatty substance that covers
some axons
•Myelin insulates and protects the fiber
•In the PNS, myelin is actually entire cells called
SCHWANN CELLS
•Myelin Sheath contd.
•Schwann cells wrap many times around the
axon like a jelly roll
•The cell bodies and most of the cytoplasm get
squeezed into the outermost layer of the
Schwann cell wrapping, known as the
NEURILEMMA
•Myelin Sheath contd.
•When the sheath is complete, small spaces
remain between the individual Schwann cells
•These tiny gaps are called NODES, which
speed up nerve impulse conduction
•In the CNS, the myelin sheath is formed by
another type of cell, the OLIGODENDROCYTE
•Myelin Sheath contd.
•Schwann cells help injured neurons
regenerate
•Undamaged Schwann cells near the injury
