Characteristics of the Peripheral Nervous System

somatic nervous system

• Skeletal muscles

• Neurons involved:

  • One extends from brain to another neuron in the spinal cord

    • Only thing in the periphery is the axons

• Cell bodies of somatic motor neurons located in CNS

• Neuron cell bodies located in motor nuclei of cranial nerves

  • Also ventral horn of spinal cord

• Axons are myelinated

• Voluntary movements

• Effect of somatic motor neurons on skeletal muscles → excitatory

• Only ACh used

• Receptor molecules for ACh = nicotinic

autonomic nervous system

• involuntary control

• Neurons extends from the brain to another neuron that is completely in the periphery

  • Cell body of first neuron remains in CNS

• Two synapses occur: 

  • In autonomic ganglia

  • Then in target tissue

• Preganglionic neurons have myelinated axons

  • Cell bodies in autonomic nuclei of cranial nerves

    • In lateral horn too

• Postganglionic neurons have unmyelinated axons

  • Cell bodies in autonomic ganglia

• Can have an excitatory or inhibitory effect

• ACh, epinephrine, and norepinephrine used

sympathetic division

• readies body for physical activity → fight-or-flight

• lowers digestion → uses energy instead to face a threat

• increases heart rate, BP, excretion

• location of ganglia: near spinal cord

  • preganglionic: in CNS

    • uses ACh

  • postganglionic: located far away from target organ

    • uses norepinephrine

  • longer postganglionic axon than parasympathetic NS

  • shorter preganglionic axon

  • each preganglionic synapses with many postganglionic

parasympathetic division

• regulates resting functions → rest and digest division

• for homeostasis

• location of ganglia: near target

  • preganglionic: in the CNS

    • uses ACh

  • postganglionic: really close to target organ

    • uses ACh

  • longer preganglionic axon than sympathetic NS

  • shorter postganglionic

  • one preganglionic synapses with only TWO post ganglionic