Foundation 1 Lecture 4 (Physiology) PDF

Lecture 4 Introduction to Autonomic nervous system (ANS) Dr. M. Abdelmohsen Assistant Professor of Physiology MBBCh, MSc, DMSc, DHPE Faculty of Med...

Lecture 4 Introduction to Autonomic nervous system (ANS) Dr. M. Abdelmohsen Assistant Professor of Physiology MBBCh, MSc, DMSc, DHPE Faculty of Medicine 2024-2025  Objectives ❖ At the end of this lecture, the first year student should be able to: Mention the components of an autonomic reflex. Compare the structural and functional differences between the somatic and autonomic nervous systems. Classify the autonomic N.S. Compare the structural differences between sympathetic and parasympathetic nervous system. ▪ Reference Text Book: Guyton & Hall physiology text book  Autonomic Nervous System “ANS” General functions of ANS: 1. Maintaining homeostasis. 2. Coordinating the body’s responses to exercise and stress. 3. Assisting the endocrine system to regulate reproduction. ANS is usually subdivided into three divisions: a) sympathetic b) parasympathetic and c) enteric. ❖ The enteric nervous system: ✓ regulates of gastrointestinal function. ✓ is a complex neuronal network within the GIT wall. ✓ this network involves sympathetic and parasympathetic fibers. ❖ Thoracolumbar division of the ANS "sympathetic division": ✓ T1- L2 spinal segments. Function: 1. It controls the involuntary functions of the body. 2. It has generalized functions (Fight & flight). ❖ Craniosacral division of the ANS (parasympathetic division): ✓ Brainstem and associated cranial nerves (III, VII, IX and X) ✓ S2 – S4 part of the spinal cord (Pelvic nerves) Function: 1. Controls the internal functions (GIT & Urinary). 2. It has specialized functions (Elimination of wastes) (at rest). ❑ Neurochemical classification of sympathetic and parasympathetic Nervous Systems: a) Sympathetic: called adrenergic. - The neurotransmitter released is noradrenaline. - It has adrenaline-like actions. b) Parasympathetic: called cholinergic - The neurotransmitter released is acetylcholine. - It has acetylcholine-like actions. ❑ Reciprocal fashion of innervation of sympathetic and parasympathetic nerves: ✓ The two divisions are activated in a reciprocal manner. ✓ An example: Controlling the heart rate: ↑ firing in sympathetic and simultaneous ↓ firing in parasympathetic result in ↑ heart rate. ✓ Exceptions: 1) Working synergistically: e.g., Secretion by exocrine glands of GIT: ✓ Parasympathetic ↑ volume and enzymes ✓ Sympathetic add mucus. 2) Only sympathetic: Some organs e.g., skin and blood vessels.  Autonomic Somatic Effector organ Glands, cardiac muscle & Skeletal muscle smooth muscle Response Stimulation or inhibition Contraction of effector organs Function Unconscious regulation of Conscious and effector organs but can be unconscious control of influenced by conscious skeletal muscle mental functions. movements. Number of neurons Two One between the center and effector organ Number of synapses Two One Location of neuron Preganglionic: autonomic Motor nuclei of cranial cell bodies nuclei of cranial nerves & nerves & ventral horn of lateral spinal cord spinal cord Postganglionic: autonomic ganglia Axons Preganglionic: myelinated Myelinated Postganglionic: unmyelinated Type of receptor a) For Acetylcholine: Nicotinic In ganglia: nicotinic In effector organs: Muscarinic b) For Norepinephrine: α or β adrenergic Neurotransmitter Preganglionic: Acetylcholine Acetylcholine Postganglionic: either Acetylcholine or Norepinephrine ❑Reflex Arc: It has 5 components: 1) Receptors: receive the stimulus and respond to it. 2) Afferent (sensory neuron). 3) Center (CNS): Present in hypothalamus, brain stem & spinal cord. 4) Efferent (motor neuron): From the CNS to the effector organs either: ✓ Somatic to skeletal muscles. ✓ Visceral (autonomic) to glands, cardiac & smooth muscles. 5) Effector organs. ❑ Efferent of ANS: ✓ 2 neurons: First one (preganglionic axon): ✓ The fibers from cell bodies of the autonomic motor neurons located in the spinal cord or specific brainstem nuclei. → ✓ An efferent preganglionic fiber emerges → ✓ synapses with neurons located in a peripheral ganglion. Second (postganglionic axon): ✓ Ganglionic fibers then projects as postganglionic fiber → ✓ To the autonomic effector cells.  Examplesof ❑Examples ofautonomic autonomicreflexes: reflexes: Cardiovascular Gastrointestinal Autonomic reflex Autonomic reflex Components Sympathetic & Parasympathetic parasympathetic Receptors Baroreceptors located at Smell & taste receptors aortic arch and carotid sinus Afferent Vagus (10th) nerve Facial (7th), glossopharyngeal (9th) & vagus (10th) nerves Center Cardiovascular centers in Facial, glossopharyngeal & brainstem. vagus nuclei in brainstem. Efferent Sympathetic fibers Parasympathetic fibers Effector organ Heart & arteries Secretory glands in the mouth & stomach Response Controls arterial blood Secretion of digestive juice pressure and gets it back to even before entrance of food normal after its elevation. to the mouth. (↓ sympathetic & ↑ parasympathetic)  Thank You Faculty of Medicine 2024-2025