The Nervous System PDF

GALALA PT 2024
The Nervous System

Mod. By Prof. Dr. Magdi Ali El-Damarawi Professor of Medical Physiology Faculty of Medicine  Objectives (ILOs) By the end of this lecture, you should be able to: 1. List the different parts of the ne...

GALALA PT 2024
The Nervous System

Mod. By Prof. Dr. Magdi Ali El-Damarawi Professor of Medical Physiology Faculty of Medicine  Objectives (ILOs) By the end of this lecture, you should be able to: 1. List the different parts of the nervous system. 2. Define the autonomic nervous system. 3. Recognize the divisions of the autonomic nervous system. 4. Summarize the differences between somatic and autonomic reflex arcs. 5. Identify the types of autonomic ganglia. 6. Illustrate the functions of the sympathetic nervous system to different parts of the body. 1- Central Nervous System (CNS): A- Brain & Brain Stem. B- Spinal Cord. 2- Peripheral Nervous System (PNS): A- Cranial Nerves (12 pairs). B- Spinal Nerves (31 pairs). 1- Central Nervous System (CNS): A- The Brain & Brain Stem: - The brain: Two cerebral hemispheres & the cerebellum. - The brain stem: Mid brain, pons & medulla oblongata. B- THE SPINAL CORD (31 Segments): 1- Cervical: 8 segments. 2- Thoracic: 12 segments. 3- Lumbar: 5 segments. 4- Sacral: 5 segments. 5- Coccygeal: 1 segment. Brain & brain stem 2- Peripheral Nervous System: a- Cranial Nerves: I- Olfactory. II- Optic III- Oculomotor IV- Trochlear V- Trigeminal. VI- Abducent VII- Facial. VIII- Auditory IX- Glossopharyngeal. X- Vagus XI- Accessory. XII- Hypoglossal. b- Spinal Nerves: Each nerve have two roots: a- Dorsal roots: Sensory or afferent fibers. b- Ventral roots : motor or efferent.  Functionally , the nervous system is divided into: 1- Somatic nervous system: - depends on somatic fibers. - voluntary. - controls the movement of the skeletal muscles. 2- Autonomic nervous system : - depends on autonomic nerve fibers. - involuntary. - controls the movement of smooth & cardiac muscles and gland secretion.  Autonomic nervous system (ANS) 1. Sympathetic nervous system: (fight or flight) Works in stress conditions. Thoraco-lumbar outflow. Catabolic system. 2. Parasympathetic nervous system: (rest and digest) Acts at rest. Cranio-sacral outflow. Anabolic system. ANS  REFLEX ACTION It is the action that occurs through the reflex arc. The nervous system almost always acts through reflex arc. There are somatic reflex actions as flexor withdrawal reflex. There are autonomic reflex actions as micturition reflex.  The reflex arc components: a- Receptors. b- Afferent neuron. c- Center. d- Efferent neuron. e- Effector organ.  Activity 1 From the next slide, what are the differences between somatic and autonomic reflex arcs?  Autonomic Ganglia Definition : - It is a collection of nerve cells outside the central nervous system (CNS). - They are the sites of relay (synapse) of the preganglionic autonomic fibers with the postganglionic fibers. - The chemical transmitter in all the ganglia is” acetyl choline” (A.Ch.).  Types of autonomic ganglia 1- Lateral (para-vertebral) ganglia: - Purely sympathetic. - lie at both sides of the vertebral column (sympathetic chain). - There is one pair of ganglia for each spinal cord segment except for the cervical segments where the ganglia are collected into three pairs only (superior, middle, and inferior). - The postganglionic fibers are long. Autonomic ganglia  2- Collateral ganglia - lie between sympathetic chain & the viscera. - lie at the origin of big arteries from the abdominal aorta & and are named according to these vessels: Celiac, renal, superior & inferior mesenteric ganglia. - They are the site for the relay of both the sympathetic and parasympathetic preganglionic fibers (mainly sympathetic). Abdominal Aorta and Its Branches  3- Terminal ganglia -Lie near the organ of supply or inside its wall. -They are purely parasympathetic. -The post-ganglionic fibers are short.  Functions of the autonomic ganglia 1. Sites of relay of the preganglionic fibers to give postganglionic fibers. 2. Distributing centers: each preganglionic sympathetic fiber gives rise to 8-12 postganglionic fibers leading to widespread effects. 3. Sites of action of many drugs as ganglion blockers.  Sympathetic Nervous System (SNS) 1. Sympathetic To the Head & Neck: - Origin: from L.H.Cs of 1 & 2 thoracic segments. - Relay: preganglionic fibers relay in the superior cervical ganglia. - Chemical transmitters: The preganglionic fibers secretes acetyl choline while the postganglionic fibers secrete noradrenaline (norepinephrine). 
Functions:
1. To the eyes:  Dilatation of the eye pupil.  Elevation of the upper eye lid.  Forward protrusion of the eyeball.  Relaxation of ciliary muscles to help far accommodation. 2. To the salivary glands:  Acini: salivary secretion which is little in volume, viscid & rich in organic substances (trophic secretion).  Contraction of the myoepithelial cells leading to squeezing of the gland content outside.  Blood vessels: vasoconstriction (VC). 3. To the skin:  Sweat glands: sweat secretion.  Pilo-erector muscles: erection of hair.  Blood vessels: vasoconstriction (VC).  HORNER’S SYNDROME It is a group of signs which result from interruption of sympathetic supply to head & neck. They are present in the same side of the lesion. It is due to lesion in the 1st & 2nd thoracic segments or superior cervical ganglia. Its signs are: 1- Ptosis: dropping of the upper eye lid. 2- Miosis: constriction of the pupil due to paralysis of dilator pupillae muscle. 3- Enophthalmos: sinking of the eyeball slightly into the orbit due to paralysis of muller’s muscle. 4- Anhydrosis: dryness of the skin due to loss of sweat secretion. 5- Warm red skin: due to vasodilatation of the skin blood vessels.  2- Sympathetic to the Thorax Origin : from the L.H.Cs of the upper 4 thoracic segments. Relay : in the upper 4 thoracic ganglia & all cervical ganglia  To the heart: - Stimulation of all cardiac properties (contractility, conductivity, excitability & rhythmicity). - Dilatation of the coronary blood vessels.  To the lungs: - Widening of the bronchi & bronchioles due to relaxation of wall smooth muscles. - Decreased mucous secretion in the air passages. - Vasoconstriction of pulmonary blood vessels. 3- Sympathetic to the abdomen:
 Origin: - from L.H.Cs of 6 -12 thoracic segments (the fibers form the greater splanchnic nerve).  Relay: - in the collateral ganglia (celiac, renal & superior mesenteric). N.B.: The part of the ANS which supplies the GIT is called the enteric nervous system (ENS).  Assignment 1 - Write a summary about the enteric nervous system. 
To the G.I.T.

Relaxation of the smooth muscles of the wall of stomach, small intestine, proximal part of large intestine & Gall bladder.  Contraction of the sphincters. - Effect on the liver:  Stimulation of glycogenolysis.  In the spleen  Contraction of smooth muscles in splenic capsule. Blood vessels  Vasoconstriction of the blood vessels of stomach, intestine, liver, pancreas & kidney. Supra-renal medulla is a modified sympathetic ganglia (why?) - Stimulation of the SNS causes the secretion of two hormones from supra-renal medulla; Adrenaline 80% & noradrenaline 20%. They have almost the same effects as direct sympathetic stimulation except: 1. Their effects are more prolonged. 2. has widespread action (distributed by blood even to areas not supplied by sympathetic fibers). 4. Sympathetic to the pelvis (lesser splanchnic nerve): - Origin :
From the upper 2-3 lumbar segments. - Relay : inferior mesenteric ganglia - Functions:  Urinary bladder: Relaxation of the wall & contraction of internal urethral sphincter.  Rectum : Relaxation of smooth muscles of the wall & contraction of internal anal sphincter.  Sex organs: Shares in the execution of sexual act. 5- Sympathetic to Upper, Lower Limbs & Thoracic and Abdominal Walls  Origin: - Upper limbs: LHCs of 5-9 thoracic segments. - Lower limbs : LHCs of 10, 11 & 12 thoracic and 1& 2 lumbar segments. - Thoracic & abdominal walls: - from all thoracic & upper 2 lumbar segments.  Relay: In the sympathetic chain.  In the skin:

- Sweat secretion.
- Erection of hair.
- Vasoconstriction of blood vessels. In the skeletal muscle: - Vasodilatation (VD) of the skeletal muscle blood vessels.  Orbeli ‘s phenomenon - Sympathetic stimulation to the skeletal muscle causes: - better contraction, - delayed fatigue & - early recovery after fatigue. - It is due to : 1- increased blood flow due to vasodilatation (VD). 2- increase in the sensitivity of motor end plate (MEP) to the acetylcholine action.  Mass Discharge of SNS In many cases the sympathetic nervous system discharge almost as a complete unit (mass discharge). This occurs in emergency conditions e.g. sever muscular exercise, fear, fight, hemorrhage & exposure to cold. This result in widespread response throughout the body which prepare the person for fight or flight. Sympathetic supply to the body THANK YOU.