Chapter 11 learning objectives

LO 11.1.1 - Describe the physiological role of the autonomic division and its branches

The autonomic division maintains physiological homeostasis by regulating involuntary functions of smooth muscle, cardiac muscle, and glands through its sympathetic and parasympathetic branches.

The autonomic nervous system (ANS) works automatically without conscious control. It keeps essential body processes stable, such as heart rate, blood pressure, digestion, breathing, and temperature.

• The sympathetic branch prepares the body for stress, danger, or exercise (fight-or-flight).

• The parasympathetic branch conserves energy and supports rest, recovery, and digestion (rest-and-digest).
  These two branches often work in opposite ways to balance each other and maintain homeostasis.

LO 11.1.2 - Compare and contrast the anatomy and chemical communication of the sympathetic and parasympathetic
branches

Anatomy differences

• Sympathetic:

  • Originates in the thoracic and lumbar spinal cord.

  • Preganglionic neurons are short.

  • Postganglionic neurons are long.

  • Ganglia sit close to the spinal cord

• Parasympathetic:

  • Originates in the brainstem and sacral spinal cord.

  • Preganglionic neurons are long.

  • Postganglionic neurons are short.

  • Ganglia are located near or on the target organ.

Chemical differences

• Both branches Preganglionic neurons use ACh on nicotinic receptors in the ganglia.

• Sympathetic postganglionic neurons release norepinephrine onto adrenergic receptors.

• Parasympathetic postganglionic neurons release ACh onto muscarinic receptors.

LO 11.1.3 - Describe the synthesis and breakdown of autonomic neurotransmitters

1. NE synthesized in axon varicosities.

2. Action potential → depolarization of varicosite

3. Ca2+ channel opens

4. Vesicles release NE

5. NE binds adrenergic receptors (triggers response)

6. NE removed synapse via:

• Reuptake into neuron (main)

• Diffusion away

• Enzymatic breakdown (MAO)

7. ACh breakdown at NMJ by AChE

LO 11.1.4 - Describe the structure and secretions of the adrenal medulla

• Inner part of adrenal gland.

• Modified sympathetic ganglion.

• Chromaffin cells act as postganglionic neurons.

• Releases epinephrine (and some NE) into bloodstream.

• Produces widespread, long-lasting sympathetic effects

LO 11.2.2 - Compare the anatomy, neurotransmitters and receptors of the somatic motor, sympathetic, and parasympathetic divisions

Somatic Motor

• One neuron.

• ACh → nicotinic receptor.

• Always excitatory.

• Target: skeletal muscle.

Sympathetic

• Two neurons.

• ACh (nicotinic) → NE (adrenergic).

• Targets smooth muscle, heart, glands.

Parasympathetic

• Two neurons.

• ACh (nicotinic) → ACh (muscarinic).

Targets smooth muscle, heart, glands.