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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.

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PNS and Transmission

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  1. PNS and Transmission February 09, 2010

  2. 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.

  3. 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;

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

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