Human Physiology for Medical Students: Autonomic Nervous System & Nerve and Muscle

HUMAN PHYSIOLOGY FOR MEDICAL STUDENTS

AUTONOMIC NERVOUS SYSTEM & NERVE AND MUSCLE

Magdi Sabry M.D.

CONTENTS

  • SECTION I : AUTONOMIC NERVOUS SYSTEM
        - Chapter 1 : General features of the autonomicN.S ……….. 1
        - Chapter 2 : The sympathetic nervous system ………………… 8
        - Chapter 3 : The parasympathetic nervous system . .. . . . . . . 19
  • SECTION II : NERVE AND MUSCLE
        - Chapter 1 : The nerve ……………………………………… 30
        - Chapter 2 : Neuromuscular transmission ……………….. 48
        - Chapter 3 : The skeletal muscle …………………….. 50
        - Chapter 4 : The smooth (plain) muscle …………….. 77
        - Chapter 5 : Transport of substances through cell membranes …………………………………… 82

SECTION I

AUTONOMIC NERVOUS SYSTEM

CHAPTER I : GENERAL FEATURES OF THE AUTONOMIC N.S.

  • Definition of the autonomic nervous system (A.N.S.)
        The A.N.S. is a part of the nervous system that controls the involuntary functions in the body, i.e., functions of the viscera, glands, heart, and blood vessels. It is also called the visceral or involuntary nervous system, in contrast to the voluntary functions controlled by the larger part of the nervous system known as the somatic nervous system (S.N.S.) or central nervous system (C.N.S.).

  • Functional Anatomy of the Nervous System
        Anatomically, the nervous system is divided into two parts:
        - (A) Central Nervous System (C.N.S.)
            - Brain
                - Composed of the cerebral cortex formed of two cerebral hemispheres, with several important nuclei below, including the thalamus, hypothalamus, and basal ganglia.
                - Brain Stem: Consists of
                    - Midbrain
                    - Pons
                    - Medulla oblongata
                - Cerebellum
            - Spinal Cord: Formed of 31 segments:
                - 8 Cervical segments
                - 12 Thoracic segments
                - 5 Lumbar segments
                - 5 Sacral segments
                - 1 Coccygeal segment

    - (B) Peripheral Nervous System
        - Consists of peripheral nerves:
            - Cranial Nerves: 12 pairs arising mostly from the brain stem.
            - Spinal Nerves: 31 pairs arising from the spinal cord, each supplying various structures in the body.
            - Autonomic Nerves: Includes both sympathetic and parasympathetic nerve fibers, controlling involuntary functions all over the body.

Divisions of the A.N.S.
  1. Sympathetic Nervous System
        - Arises from the lateral horn cells of the thoracic and upper lumbar spinal cord, also known as the thoracolumbar outflow.
  2. Parasympathetic Nervous System
        - Arises from the sacral segments and specific cranial nerve nuclei (3rd, 7th, 9th, and 10th cranial nerves), forming the craniosacral outflow.
General Arrangement of the A.N.S.
  • Autonomic Reflex Arc (Illustration 4)
        - Afferent autonomic neurons relay impulses to various levels that control these involuntary functions. The efferent autonomic nerve fibers arise from the lateral horn cells and some cranial nerve nuclei, proceeding to the autonomic ganglia where they synapse with other neurons.
        - Preganglionic Neurons: Type B myelinated fibers.
        - Postganglionic Neurons: Type C unmyelinated fibers.
Autonomic Ganglia
  • Autonomic ganglia are characterized by being situated away from effector organs, allowing marked divergence of sympathetic impulses leading to generalized sympathetic functions. In contrast, parasympathetic fibers relay close to effector organs, limiting divergence of signals for localized control.

Types of Autonomic Ganglia

  1. Lateral Ganglia: Situated alongside the vertebral column, containing about 23 ganglia (sympathetic chains).
  2. Collateral Ganglia: Found mainly in the abdomen close to the aorta, known as prevertebral ganglia (e.g., celiac ganglion).
  3. Terminal Ganglia: Near or in the walls of effector organs (e.g., intramural ganglia).
Functions of the Autonomic Ganglia

  - Sympathetic preganglionic fibers can relay at lateral or collateral ganglia, facilitating generalized responses for functions like the fight-or-flight response.
  - Parasympathetic fibers, however, control more localized responses.

Determination of Relay Sites in Autonomic Ganglia
  1. Langley's Nicotine Test: Helps determine if a preganglionic fiber has relayed in the ganglion by observing response to nicotine.
  2. Histological Method: Involves cutting the preganglionic fiber and observing the degeneration pattern to identify relay sites.
Section Summary
  • The A.N.S. involves a complex network governing involuntary body functions through sympathetic (thoracolumbar) and parasympathetic (craniosacral) pathways. Its influence is integrated through ganglia which guide responses from various areas of the body, facilitating proper functioning in states of rest and stress.

CHAPTER II : THE SYMPATHETIC NERVOUS SYSTEM

General Overview
  • The sympathetic nervous system can be dissected into multiple divisions, including the cervical, cardio-pulmonary, splanchnic, and somatic divisions.
The Cervical Sympathetic Division
  • Supplies structures in head and neck and integrates various physiological responses modifying ocular activity, metabolic rates, and glandular secretions. Effects include:
        - Mydriasis (pupil dilation), increased heart rate, and vasoconstriction in specific regions.
The Cardio-Pulmonary Sympathetic Division
  • Supplies the heart and lungs, influencing cardiovascular dynamics through increased cardiac output and bronchodilation under stress.
The Splanchnic Nervous Division
  • Regulates vital organ activity in the abdomen by providing innervation that affects digestive efficiency and visceral blood flow distribution based on rapid shifts in bodily demands under stress.