Autonomic Nervous System Quiz

Course Information

• Academic Year: 2024-2025
• Year: 1
• Semester: 1
• Module: Human Body Function (HBF) 102

Sympathetic Nervous System III & Parasympathetic Nervous System I

• Topic: Sympathetic Nervous System and Parasympathetic Nervous System.
• Focus: Functions of the Sympathetic and Parasympathetic nervous systems, both in normal and emergency conditions.

Objectives

• Students should be able to describe the function of the sympathetic system on limbs (skin and skeletal muscles).
• Students should be able to describe general functions of the sympathetic system during rest (sympathetic tone) and emergency conditions (alarm response).
• Students should be able to define the origin of the parasympathetic nervous system (craniosacral outflow).
• Students should be able to list which parts of the body are supplied by the parasympathetic system.
• Students should be able to describe the functions of the parasympathetic cranial nerves (oculomotor nerve III).

Introduction

• The Autonomic Nervous System (ANS) is responsible for homeostasis.
• The ANS is composed of:
  • Sympathetic nervous system
  • Parasympathetic nervous system

Sympathetic Nervous System

• The sympathetic nervous system is catabolic and energy consuming.
• Its function is associated with stress, fight, fear, and flight.

Sympathetic Nervous System - Somatic Division

• This division of the sympathetic nervous system accompanies the somatic nerves.
• The somatic nerves arise from the anterior horn cells.
• This division supplies skin and skeletal muscle blood vessels.

Sympathetic Nervous system - Somatic Origin

• Sympathetic nerves supplying upper limbs originate in the thoracic segments (4th to 8th).
• They travel to the upper limbs vía the brachial plexuses.
• Sympathetic nerves supplying lower limbs originate in the thoracic segments (10th to 12th).
• They travel to the lower limbs via the lumbosacral plexuses.

Sympathetic Nervous System - Detailed Functions

• Dilates pupils (increases light into eyes)
• Inhibits salivation
• Relaxes bronchi (widens airway)
• Accelerates heartbeat (increase rate)
• Inhibits peristalsis and secretion (slowing digestion)
• Stimulates glucose production and release
• Secretion of adrenaline and noradrenaline (hormones related to the fight or flight)
• Inhibits bladder contraction
• Stimulates orgasm.

Sympathetic Nervous System - Somatic Division - Relay

• The relay is via lateral ganglia.

Sympathetic Nervous System - Somatic Division - Effects (Skin)

• Sweat secretion
• Hair erection
• Constriction of dermal blood vessels

Sympathetic Nervous System - Somatic Division - Effects (Skeletal Muscle Blood Vessels)

• Skeletal muscles receive both noradrenergic and cholinergic sympathetic nerve fibers.
• Noradrenergic fibers cause vasoconstriction (VC).
• Cholinergic fibers cause vasodilation (VD).
• Sympathetic stimulation may cause either VC or VD depending on condition.

Sympathetic Nervous System - Somatic Division - Effects (Skeletal Muscle Blood Vessels) - Case Study

• During hemorrhage, vasoconstriction occurs to elevate arterial blood pressure.
• During muscular exercise, vasodilation occurs to increase blood supply to active muscles.

Sympathetic Nervous System - Somatic Division - Effects (General Sympathetic Actions)

• Continuous sympathetic impulses occur even during rest.
• This causes continuous partial constriction in many blood vessels (vasomotor tone).
• The sympathetic nervous system helps to maintain blood pressure and blood glucose levels.

Alarm (Stress) Response of Sympathetic Nervous System - Trigger

• The sympathetic nervous system discharges as one unit during emergencies.
• It prepares the individual for reaction to cope with danger.

Alarm (Stress) Response of Sympathetic Nervous System - Effects

• Dilates pupils.
• Accelerates the heart.
• Raises blood pressure.
• Better blood perfusion to organs & muscles.
• Constricts skin blood vessels.
• Lowers bleeding risk.
• Reinforces the alert and the aroused state.
• Stimulates the release of glucose and free fatty acids (energy providing).

Alarm (Stress) Response of Sympathetic Nervous System - Summary

• The sympathetic system is catabolic (energy consuming)
• The parasympathetic system is anabolic (energy preserving).

Parasympathetic Nervous System - I. Cranial Outflow

• The cranial outflow consists of:
  • Oculomotor nerve (III)
  • Facial nerve (VII)
  • Glossopharyngeal nerve (IX)
  • Vagus nerve (X).

Parasympathetic Nervous System - I. Cranial Outflow (Detailed Functions)

• The cranial nerves supply visceral structures in the head and neck.
• The vagus nerve (X) supplies thoracic and abdominal viscera.

Parasympathetic Nervous System - II. Sacral Outflow

• The sacral outflow supplies pelvic viscera via pelvic nerve branches and the sacral spinal nerves.

Parasympathetic Nervous System - Notes on Structure

• Preganglionic parasympathetic fibers end on short postganglionic neurons located near visceral structures (terminal autonomic ganglia).

Parasympathetic Nervous System - Detailed Functions

• Constrict pupils (miosis).
• Stimulates salivary gland secretion.
• Slows heart rate.
• Constrict bronchi.
• Stimulates peristalsis and secretion.
• Stimulates bile release.
• Contracts bladder.

Sympathetic and Parasympathetic Supply

• Most visceral organs are innervated by both sympathetic and parasympathetic fibers.
• This dual innervation is called dual innervation.

Organs Without Dual Innervation

• Adrenal medulla

• Erector pili muscles

• Sweat glands,

• Most blood vessels

• Regulation is achieved by increases or decreases in the tone (firing rate) of sympathetic fibers.

• Sympathetic fiber tone on blood vessels keeps them in partial constriction (vasomotor tone).

Functions of Parasympathetic Nervous System

• The parasympathetic system is anabolic (energy preserving).
• Functions associated with rest, digest, and reading.
• Inhibits cardiac properties.
• Increases GIT activity.

The Oculomotor Nerve (Cranial Nerve III) - Function

a) Contraction of the constrictor pupillae muscle leading to pupil constriction (miosis). b) Contraction of the ciliary muscle increasing the power of the lens, preparing the eye for near vision.

Question

• Adrenal medulla:
  • Receives preganglionic parasympathetic fibers. (Incorrect)
  • Secretes adrenaline and noradrenaline in response to sympathetic stimulation. (Correct)
  • Secretes 80% noradrenaline. (Incorrect)
  • Secretes 20% adrenaline. (Incorrect)
  • Has short postganglionic fibres. (Incorrect)

Summary

• The sympathetic system is catabolic (energy consuming)
• The parasympathetic system is anabolic (energy preserving), favoring digestion and absorption of food.
• Sympathetic tone maintains blood pressure and blood glucose.