Transcript PNS and Transmission

PNS and Transmission
February 09, 2010
PNS
• Composed of neurons and ganglia.
Ganglia are swellings associated with
nerves that contain collections of cell
bodies.
• Somatic division: serves the skin,
skeleton, and tendons.
• Autonomic division: regulates the activity
of cardiac and smooth muscles and
glands.
Types of PNS Nerves
• Cranial: 12 pairs; many belong to the
somatic division; includes the vagus nerve
which has branches to most of the internal
organs.
• Spinal: 31 pairs; associated with the 3
regions of the vertebral column;
Somatic Division
• Most actions are voluntary which means
they originate in the cerebral cortex.
• Others are reflexes: cranial (blinking) and
spinal reflexes (hand on stove).
Autonomic Division
• Sympathetic: most arise from the lower thoracic
or lumbar region. Highly involved in the fight or
flight reflex.
• Parasympathetic: Craniosacral; promotes all the
internal responses we associated with a relaxed
state.
• Commonalities: 1) they function automatically
and usually involuntary, 2) they innervate all
internal organs, and 3) they utilize 2 motor
neurons and 1 ganglion for each impulse.
Nerve Impulses
• Resting Potential: membrane is polarized (outside +
inside -). The sodium potassium pumps are responsible
for setting this up.
• Action Potential: 1) depolarization (inside +); 2)
repolarization (inside -).
• If an axon is myelinated, the action potentials are
stimulated between the nodes of Ranvier (faster potential)
in non-myelinated it stimulates another part of the
axomembrane.
• All or None event. One way from cell body to axion
terminal.
Transmission
• Every axon terminates in an axon terminal.
All of these lie close to a dendrite or the
cell body of another neuron.
• Pre-synaptic and Postsynaptic region.
Between them is the Synaptic cleft.
Transmission
• Transmission is carried out by molecules called
neurotransmitters. These are stored in vesicles
in the axon terminals.
• Impulse reaches terminal  opens calcium
channels  Calcium enters the terminal 
vesicles move toward membrane for exocytosis
neurotransmitters are released and diffuse
through synaptic cleft neurotransmitters bind
with receptors on postsynaptic membrane.
• Depending on the neurotransmitter and
receptor the response will be excitation or
inhibition.
Integration
• Neurons can have many dendrites and can
synapse with many other neurons.
• An excitatory NT produces a potential change
called a signal. The signal drives the polarity of
a neuron closer to an action potential. An
inhibitory NT does the opposite.
• Integration is the summing up of all of the
excitatory and inhibitory signals. Which ever
side wins determines if an Action Potential will
be transmitted.