Ch14ANS

Chapter 14: The Autonomic Nervous System

Overview of the ANS

• The Autonomic Nervous System (ANS) consists of motor neurons that innervate:

  • Smooth muscle

  • Cardiac muscle

  • Glands

• The ANS makes adjustments to ensure optimal support for body activities.

• Functions via subconscious control, also known as the involuntary nervous system or general visceral motor system.

Structural Organization

• Figure 14.1 illustrates the placement of the ANS in the structural organization of the nervous system:

  • Central nervous system (CNS)

  • Peripheral nervous system (PNS)

    • Sensory (afferent) division

    • Motor (efferent) division

      • Somatic nervous system

      • Autonomic nervous system (ANS)

        • Sympathetic division

        • Parasympathetic division

Somatic vs. Autonomic Nervous Systems

• Both systems have motor fibers but differ in:

  • Effectors (target organs):

    • Somatic: Skeletal muscles

    • Autonomic: Cardiac muscle, smooth muscle, and glands

  • Efferent pathways and ganglia

  • Target organ responses to neurotransmitters.

Effectors

• Somatic Nervous System:

  • Primary effectors are skeletal muscles.

• ANS:

  • Includes cardiac muscle, smooth muscle, and glands.

Efferent Pathways and Ganglia

• Somatic Nervous System:

  • Cell body in CNS;

  • Thick, myelinated, group A fiber extends to skeletal muscle.

• ANS Pathway:

  • Uses a two-neuron chain:

    • Preganglionic neuron: In CNS, has thin, lightly myelinated axon.

    • Postganglionic neuron: Located in autonomic ganglion outside CNS, with nonmyelinated axon extending to effector organ.

Neurotransmitter Effects

• Somatic Nervous System:

  • All motor neurons release acetylcholine (ACh); effects are always stimulatory.

• ANS:

  • Preganglionic fibers release ACh.

  • Postganglionic fibers release either norepinephrine (NE) or ACh; effects can be stimulatory or inhibitory based on receptor type.

Comparison of Motor Neurons

• In the Somatic Nervous System:

  • Single neuron from CNS to effector with heavily myelinated axon and ACh as neurotransmitter.

• In the ANS:

  • Two-neuron chain with lightly myelinated preganglionic axons and nonmyelinated postganglionic axons, releasing ACh or NE (depending on the division).

Dual Innervation and ANS Divisions

• ANS Divisions:

  • Sympathetic division:

    • Mobilizes the body during activity (