Autonomic Nervous System by Dr. Haitham Sewilam

Nervous System Overview

• Divided into Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• CNS consists of the brain and spinal cord.
• PNS includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.

PNS Functional Divisions

• Afferent (sensory) nerve fibers carry impulses from receptors to CNS.
• Efferent (motor) nerve fibers transmit impulses from CNS to effectors.

Autonomic Nervous System (ANS)

• Regulates involuntary actions.
• Divided into Sympathetic Nervous System and Parasympathetic Nervous System.

Sympathetic Nervous System

• Prepares the body for vigorous activities (fight or flight).
• Originates from thoracic and upper lumbar segments (thoraco-lumbar).

Functions of the Sympathetic Nervous System

• Gastrointestinal Tract: Walls relax; sphincters contract.
• Liver: Stimulates glycogenolysis.
• Spleen: Contraction of smooth muscle; increases blood circulation.
• Adrenal Medulla: Secretes adrenaline (80%) and noradrenaline (20%).
• Kidneys: Increases renin secretion; decreases urine output.
• Bladder: Wall relaxation; internal urethral sphincter contraction for urine retention.
• Rectum: Wall relaxation; internal anal sphincter contraction for fecal retention.
• Skeletal Muscle: Vasodilation enhances blood flow.

Parasympathetic Nervous System

• Controls viscera activity during rest and digestion.
• Originates from cranial (nerves III, VII, IX, X) and sacral (nerves S2, S3, S4) regions (cranio-sacral outflow).

Functions of the Parasympathetic Nervous System

• Oculomotor Nerve (III): Causes pupil constriction (miosis), facilitates near vision.
• Facial Nerve (VII): Stimulates salivary glands for watery saliva secretion.
• Glossopharyngeal Nerve (IX): Stimulates parotid gland for salivary secretion.

Neurotransmitters

• Acetylcholine (ACh) released from all preganglionic fibers and postganglionic parasympathetic fibers.
• Noradrenaline released from sympathetic postganglionic fibers and adrenal medulla.

Receptors

• Parasympathetic Receptors:
  • Cholinergic: Muscarinic (at most organs), Nicotinic (at adrenal gland, ganglia).
• Sympathetic Receptors:
  • Adrenergic: Alpha (α) receptors (stimulatory) and Beta (β) receptors (inhibitory).

Autonomic Ganglia

• Lateral: Sympathetic relay beside the spinal cord.
• Collateral: Sympathetic relay midway between the spinal cord and organs.
• Terminal: Parasympathetic relay at organ walls.

Fibers Length Comparison

• Sympathetic preganglionic fibers are shorter than postganglionic fibers.
• Parasympathetic preganglionic fibers are longer than postganglionic fibers.

Cardiac and Respiratory Functions

• Sympathetic Stimulation of Heart: Increases heart rate, contraction, conduction velocity, excitability.
• Parasympathetic (Vagus Nerve): Decreases heart rate, force of contraction, and excitability; causes bronchoconstriction and mucus secretion.

Gastrointestinal Functions

• Sympathetic: Inhibits gastrointestinal motility.
• Parasympathetic: Stimulates motility, gastrointestinal secretions, and gall bladder contractions.

Urinary and Defecation Functions

• Parasympathetic Outflow: Stimulates bladder contraction and defecation while inhibiting sphincters.

This concise structure captures the essential knowledge about the autonomic nervous system and its functions, aiding in effective revision and understanding.

Learn about the autonomic nervous system, its divisions, and functions. This quiz covers the central and peripheral nervous systems, including cranial and spinal nerves, and afferent and efferent nerve fibers.