Divisions of the Motor/Efferent Division of the Peripheral Nervous System

Overview

• Focus on the motor division of the peripheral nervous system.
• Contrast between somatic and autonomic nervous systems.
• Deep dive into the autonomic nervous system's two subdivisions: sympathetic and parasympathetic.

Somatic Nervous System

• Located in the peripheral nervous system's motor division.
• Somatic Motor Neuron:
  • Myelinated, single neuron pathway.
  • Target: Skeletal muscle.
  • Exits spinal cord at ventral root (motor division, efferent).
• Damage to somatic motor neuron leads to muscle paralysis.

Autonomic Nervous System (ANS)

• Autonomic Pathway:
  • Two neuron chain: pre-ganglionic and postganglionic.
  • Pre-ganglionic neuron in CNS, postganglionic neuron in a ganglion.
  • Pre-ganglionic neuron is myelinated, multi-polar.
  • Postganglionic neuron is unmyelinated, targets smooth muscle or glands.
• Damage to ANS allows effectors to still function as it regulates rather than instigates.

Differences from Somatic System:

• Complexity: Two neurons (pre-ganglionic and postganglionic) allow for more control and communication.
• Neuronal convergence and divergence.
• Fast response affecting multiple effectors simultaneously.

Sympathetic vs Parasympathetic Nervous System

Sympathetic Nervous System (Fight or Flight)

• Prepares body for activity:
  • Preganglionic Neuron: Short, myelinated, terminates at autonomic ganglion near vertebral column.
  • Postganglionic Neuron: Long, unmyelinated, uses norepinephrine.
• Highly branched, influences multiple effectors at once.
• Effects: Accelerates heart rate, widens bronchial passages, decreases digestive motility, dilates pupils, increases blood pressure.
• Thoracolumbar Division: Nerves emerge from thoracic and lumbar spinal regions.
  • Paravertebral ganglion chain next to spinal column.
  • Three branching paths: synapse in ganglion, collateral ganglion, or directly to adrenal medulla.

Parasympathetic Nervous System (Rest and Digest)

• Conserves energy, regulates resting functions:
  • Preganglionic Neuron: Long, myelinated, originates in brain stem or sacral spinal cord.
  • Postganglionic Neuron: Short, unmyelinated, uses acetylcholine.
• Little branching, point-to-point control.
• Craniosacral Division: Nerves emerge from brain stem and sacral region.
• Strong association with vagus nerve (Cranial Nerve X), controls multiple organs including the heart.
• Effects: Slows heart rate, increases gland activity, relaxes gastrointestinal tract sphincters.

Summary

• Sympathetic and parasympathetic systems have distinct structures and functions.
• Sympathetic: quick, widespread response to stress.
• Parasympathetic: localized, rest-focused regulation.

Use these notes to understand the basic structure and function of the motor division of the peripheral nervous system, especially the differences and roles of the somatic and autonomic nervous systems and their divisions.