Physiology_Lecture_Outline/md6

Module 6— Nerves & The Nervous System

Module Learning Outcomes

  1. Describe the physiological significance of the meninges, white matter, and grey matter.

  2. Explain the physiological significance of nerves, including action potentials.

  3. Compare the physiological roles of the sympathetic and parasympathetic nervous systems.

  4. Describe the physiological functions of the brain and brainstem.

  5. Describe the physiology of the olfactory and gustatory systems.

Section 1: Meninges, White Matter, and Grey Matter

  • Meninges: Three protective tissue layers covering the brain and spinal cord.

    • Dura Mater: Tough outer layer; provides a protective barrier, prevents brain displacement, forms dural venous sinuses for drainage of blood and cerebrospinal fluid (CSF).

      • Folds: Include the falx cerebri, separating the hemispheres.

    • Arachnoid Mater: Middle layer with a web-like structure; cushions the brain and spinal cord, circulates CSF in the subarachnoid space, facilitates CSF drainage via arachnoid granulations.

    • Pia Mater: Thin layer adhering to neural tissue; allows nutrient and oxygen exchange, contains small blood vessels supplying the CNS, involved in CSF production.

  • Subarachnoid Space: Area between the arachnoid and pia mater containing CSF for protection and nutrient supply.

  • Epidural Space: Between the dura mater and vertebral canal; contains fat and connective tissue, a site for epidural anesthesia.

Section 2: Nerves and Action Potentials

  • Nerves: Bundles of fibers carrying messages between the brain/spinal cord and the body; responsible for muscle movement and sensation.

  • Action Potentials: Electrical signals that travel along nerve fibers.

    • Triggered when a neuron gets excited (e.g., touching a hot surface).

    • Involves the movement of ions to create an electrical current.

Action Potential Phases

  1. Receptor Activation: Stimulus opens ligand-gated channels, allowing ions (e.g., Na⁺) to enter, leading to graded potential.

  • If sufficient, triggers action potential at axon hillock.

  1. Depolarization (Sodium Influx): Threshold reached; Na⁺ channels open, Na⁺ rushes into the neuron, causing rapid depolarization.

  2. Peak of Action Potential: At +30 mV; Na⁺ channels close, K⁺ channels open.

  3. Repolarization (Potassium Efflux): K⁺ flows out of the cell, returning membrane potential towards resting values.

  4. Hyperpolarization: K⁺ channels are slow to close; membrane potential becomes more negative than resting potential.

  5. Resting Membrane Potential: Maintains around -70 mV due to Na⁺ and K⁺ distribution.

    • Refractory Periods:

      • Absolute: No new action potential can be initiated.

      • Relative: A stronger stimulus is needed.

Section 3: Functions of the Sympathetic and Parasympathetic Nervous System

Sympathetic Nervous System

  • Activates