Intro to ANS & SNS (3)

Overview of the Nervous System

• The nervous system oversees the functioning of organs and bodily responses during activities like playing volleyball or watching TV.

• Divisions:

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

  • Peripheral Nervous System (PNS): Consists of nerves outside the CNS, further divided into:

    • Somatic Nervous System

    • Autonomic Nervous System (ANS)

Somatic Nervous System (SNS)

• Functions:

  • Controls voluntary actions and conveys sensory information.

• Components:

  • Somatic Sensory Fibers:

    • Transmit sensory information like touch, pain, and temperature

    • E.g. signaling when a cup of coffee is too hot.

  • Somatic Motor Fibers:

    • Innervate skeletal muscles for voluntary movements, such as moving a hot cup away.

Autonomic Nervous System (ANS)

• Functions:

  • Controls involuntary activities within the body.

• Components:

  • Visceral Motor Fibers:

    • Carry motor signals to smooth and cardiac muscles, and glands.

  • Visceral Sensory Fibers:

    • Provide sensory information from internal organs (e.g., oxygen levels, blood pressure).

• Special Sensory Fibers:

  • Relay information related to senses (smell, sight, taste, hearing, balance) back to CNS.

Divisions of the Autonomic Nervous System

• Sympathetic Nervous System (SNS):

  • Activates the fight or flight response.

  • Effects:

    • Dilation of pupils, increased heart rate, redirected blood flow to essential organs (muscles and brain).

• Parasympathetic Nervous System (PSNS):

  • Responsible for rest and digest activities.

  • Effects:

    • Decreases heart rate, increases digestive activity, restores blood flow to non-essential organs (e.g., intestines).

Neural Pathways in ANS

• Basic Structure:

  • Uses a two-neuron system;

    • Preganglionic Neuron: Connects CNS to ganglia.

    • Postganglionic Neuron: Connects ganglia to organs.

• Sympathetic Pathways:

  • Pre-ganglionic neurons originate from thoracolumbar spinal cord (T1-L3).

  • Follow routes:

    • Synapse in paravertebral ganglia (same level).

    • Ascend or descend to different ganglia before synapsing.

    • Pass through ganglia to synapse at prevertebral ganglia.

• Parasympathetic Pathways:

  • Preganglionic neurons from cranial nerves and sacral spinal cord.

  • Synapse closer to or within target organs, resulting in long preganglionic, short postganglionic fibers.

Enteric Nervous System (ENS)

• Considered a third subdivision of the ANS.

• Components:

  • Contains two nerve plexuses within GI tract:

    • Submucosal (Meissner’s) Plexus: Regulates secretion and absorption.

    • Myenteric (Auerbach's) Plexus: Regulates gut wall tone and contraction intensity.

• Function:

  • Operates independently for local reflexes and functions but is modulated by the CNS (SNS and PSNS interactions).

Summary of Key Points

• Peripheral Nervous System Divisions:

  • Somatic Nervous System (voluntary movements)

  • Autonomic Nervous System (involuntary functions)

• Subdivisions of ANS:

  • SNS: Fight or flight (short preganglionic fibers, long postganglionic fibers).

  • PSNS: Rest and digest (long preganglionic fibers, short postganglionic fibers).

• Enteric Nervous System:

  • Independent control of GI function, influenced by CNS.