The Nervous System
Chapter 9
General Functions of Nervous
System
Maintain HOMEOSTASIS by:
 Receiving, interpreting and integrating sensory information
from the environment
 Sending signals to muscles and glands so they can respond
Divisions of Nervous System
 Central Nervous System
(CNS)
 Brain
 Spinal cord
 Controls all conscious and
unconscious activity
 Peripheral Nervous
System (PNS)
 Cranial nerves
 Spinal nerves
 Connects CNS to the rest of
the body
Cranial Nerves
Spinal Nerves
Divisions of PNS
 Somatic NS
 Autonomic NS
 Nerves that connect to
skeletal muscles and skin
 Nerves that connect to
viscera, heart, smooth
muscle, glands
 Controls
voluntary/conscious
responses
 Controls
involuntary/subconscious
responses
Divisions of Autonomic NS
 Sympathetic NS
 Parasympathetic NS
 Regulates body’s
responses to stress, anger,
fear, anxiety…
 Restores homeostatic
conditions after stress,
anger, fear…
 Controls “fight or flight”
mechanisms
 Controls “rest and digest”
mechanisms
Nervous System
Structures
Functions
Central
Brain
Spinal cord
Receives/processes
sensory info; sends
responses to muscles and
glands via motor nerves
Peripheral
Cranial nerves
Spinal nerves
Connects CNS to entire
body
Somatic
Nerve fibers that connect Controls skeletal muscle;
CNS to skin and skeletal Oversees conscious
muscles
activity
Autonomic
Nerve fibers that connect Controls smooth and
cardiac muscle and glands,
CNS to viscera, smooth
Oversees involuntary
muscle and glands
activities; responds to stress
Parasympathetic
Nerve fibers from spinal
cord to heart, stomach,
glands…
Restores body after
stress; “rest and digest”
Sympathetic
Nerve fibers from spinal
cord to heart, stomach,
glands…
Preps body for energy
expending, stress,
emergency, “fight or
flight”
Cells of the Nervous System
 Neurons
-found in CNS and PNS
-have unique cells and structure
-transmit signals to other neurons
 Neuroglial Cells
-neuron “helper” cells; not neurons themselves
-Found only in CNS
Neurons
 Include
 Dendrites, cell body, and axon
 Dendrites receive impulses and send them to cell body
 Axons transmit impulses away from cell body
Neurons in PNS
 axons are surrounded by SCHWANN CELLS
 Schwann cell membranes have MYELIN in them
 NEURILEMMA- extra protection around axon
 NODES OF RANVIER: narrow gaps in the myelin sheath
between Schwann cells
Neurons in CNS
 Some axons have myelin (MYLELINATED) others don’t
(UNMYELINATED)
 Myelin in CNS comes from Oligodendrocytes
 Myelinated axons appear as white matter
 Unmyelinated axons are gray matter
Can we fix it?
 Peripheral neurons are able to regenerate if damaged
 Myelin sheath is surrounded by a tube of neurilemma
 CNS neurons are not able to regenerate if damaged
 Not surrounded by neurilemma
More on Neurons
 Neurons can be classified based on structure
 Multipolar-brain and SC
 Bipolar-eyes, nose, ears
 Unipolar-ganglia outside CNS
More on Neurons
 Neurons can be classified based on function:
 Sensory Neurons- (afferent) carry impulses from body parts to
brain or spinal cord (unipolar, some bipolar)
 Interneurons- lie entirely within the brain or spinal cord (CNS);
transmit impulses from one part of the brain or spinal cord to
another. (Multipolar)
 Motor Neurons- (efferent) carry impulses out of the brain or spinal
cord to effectors (multipolar)
Neuroglial Cells
 Fill spaces, support neurons, provide structural frameworks,
produce myelin, and carry on phagocytosis.
 Types: microglial, oligodendrocytes, astrocytes, ependymal
cells, schwann cells