Chapter 9 Notes from Knowt

The autonomic nervous system (ANS) regulates involuntary bodily functions such as heart rate, blood circulation, smooth muscle activity, and endocrine gland responses. It consists of two primary divisions:

• Sympathetic Division: Triggers fight-or-flight responses, resulting in:

  • Increased heart rate

  • Narrowing of blood vessels

  • Decreased digestive activity

• Parasympathetic Division: Promotes rest-and-digest functions, characterized by:

  • Decreased heart rate

  • Widening of blood vessels

  • Enhanced digestive processes

1. Nervous System Structure

• Central Nervous System (CNS): Comprises the brain and spinal cord.

• Peripheral Nervous System (PNS): Contains spinal and cranial nerves, relaying sensory information to the CNS and motor commands to muscles and glands.

2. Autonomic Pathways

• Impulses are conveyed via a two-neuron pathway:

  1. Preganglionic Neuron: Cell body located in the CNS, synapses in an autonomic ganglion.

  2. Postganglionic Neuron: Extends from the ganglion to the target organ (e.g., smooth muscle, cardiac muscle, glands).

3. Autonomic Ganglia

• Preganglionic Neurons: Located within the CNS.

• Postganglionic Neurons: Found in autonomic ganglia outside the CNS, innervating target organs.

4. Activation Effects

• Sympathetic Activation: Norepinephrine release from postganglionic neurons leads to:

  • Increased heart rate

  • Enhanced energy mobilization in response to stress.

• Parasympathetic Activation: Acetylcholine from postganglionic fibers results in:

  • Decreased heart rate

  • Enhanced digestion by hyperpolarizing pacemaker cells.

5. Neurotransmitters

• Acetylcholine (ACh): Primary neurotransmitter for all preganglionic fibers and most parasympathetic postganglionic fibers.

• Norepinephrine (NE): Released by sympathetic postganglionic fibers, impacting adrenergic receptors, especially in cardiac tissues.