Transcript Nerve activates contraction - Silver Falls School District

Chapter 7
The Nervous System
Functions of the Nervous System
1. Sensory input – gathering
information
 monitor changes inside and
outside the body
 Changes = stimuli
2. Integration
 process and interpret input
and decide on action
3. Motor output
 response to stimuli
 activates muscles or glands
Structural Classification
1. Central nervous
system (CNS)
 Brain
 Spinal cord
2. Peripheral nervous
system (PNS)
 Nerves outside the
brain & spinal cord
2 Divisions of the PNS
Sensory (afferent) division
 Nerve fibers that carry
information to the
central nervous
system
Motor (efferent) division
 Nerve fibers that carry
impulses away from
the central nervous
system
2 Parts of Motor Division
1. Somatic = voluntary
2. Autonomic = involuntary
Which side is fight or flight response?
Neuroglia : Support Cells
1. Astrocytes
 Abundant, star-shaped
cells
 Brace neurons
 Form barrier
between capillaries
and neurons
 Control chemical
environment of brain
2. Microglia
 Spider-like phagocytes
 Dispose of debris
3. Ependymal cells
 Line cavities of
brain and spinal cord
 Circulate
cerebrospinal
fluid
4. Oligodendrocytes
 Produce myelin sheath around
nerve fibers in CNS
5. Satellite cells
 Protect neuron cell bodies
6. Schwann cells
 Form myelin sheath in the peripheral nervous system
Neurons = nerve cells
1. specialized to transmit
messages
2. Major regions
 Cell body – nucleus and
metabolic center of the
cell
 Processes – fibers that
extend from the cell
body
Neuron Anatomy
 Cell body
a. Nissl substance –
specialized rough
endoplasmic reticulum
b. Neurofibrils –
intermediate
cytoskeleton that
maintains cell shape
c. Nucleus
d. Large nucleolus
 Processes Extensions outside the
cell body
a. Dendrites –
conduct impulses
toward the cell body
b. Axons – conduct
impulses away from
the cell body
Axons and Nerve Impulses
 Axons end in
axonal terminals
 terminals contain
vesicles with
neurotransmitters
 Synaptic cleft –
gap between
adjacent neurons
Nerve Fiber Coverings
 Schwann cells –
produce myelin
sheaths in jelly-roll like
fashion
 Nodes of Ranvier –
gaps in myelin sheath
along the axon
Figure 7.5
Neuron Cell Body Location
 In CNS (Most)
1. Gray matter – cell bodies
and unmylenated fibers
2. Nuclei – clusters of cell
bodies within the white
matter of the central
nervous system
 Outside CNS
1. Ganglia – collections of
cell bodies
Functional Classification of Neurons
1. Sensory (afferent) neurons
 Carry impulses from sensory receptors to CNS
a. Cutaneous sense organs
b. Proprioceptors – detect stretch or tension
2. Motor (efferent) neurons
 Carry impulses from CNS
3. Interneurons (association neurons)
 Found in neural pathways in CNS
 Connect sensory and motor neurons
Structural Classification of Neurons
1. Multipolar neurons – many extensions from cell body
2. Bipolar neurons – one axon and one dendrite
3. Unipolar neurons –short single process leaving cell body
Properties of Neurons
1. Irritability –respond to stimuli
2. Conductivity –transmit impulses
 plasma membrane at rest is polarized
 Fewer + ions inside than outside the cell
Starting a Nerve Impulse
 Depolarization – a
stimulus depolarizes the
neuron’s membrane
 allows Na+ to flow
inside membrane
 exchange of ions
initiates an action
potential in neuron
The Action Potential
 If action potential (nerve
impulse) starts, it is propagated
over the entire axon
 K+ rush out after Na+ rush in,
which repolarizes the membrane
 Sodium-potassium pump
restores the original
configuration - requires ATP
 Impulse moves toward the cell
body
 Impulses travel faster when
fibers have a myelin sheath
Continuation between Neurons
Impulses are able to
cross the synapses
 Neurotransmitter
released from
nerve’s axon
terminal
 Dendrite of the next
neuron has
receptors that are
stimulated by
neurotransmitter
 Action potential is
started in the
dendrite