Central Nervous System PDF

Diagram of CNS Anatomy Cerebral hemispheres Brain Cerebral cortex Sensory area Motor area Medulla oblongata Cerebellum CTZ Spinal cord Thalamus...

Diagram of CNS Anatomy Cerebral hemispheres Brain Cerebral cortex Sensory area Motor area Medulla oblongata Cerebellum CTZ Spinal cord Thalamus Hypothalamus  Anatomy of CNS CNS mainly consists of I-Brain II-Medulla oblongata III-Spinal cord extend 1-Cerebrum Vagal Center in vertebral ( Motor area, Vasomotor Center column Sensory area) Vomiting Center Sex Center 2-Cerebellum Respiratory Center Sweat Cen. 3-Thalamus Cough Center Micturation 4-Hypo- center thalamus  Transmission in CNS Presynaptic Inhibitory fiber Glycine & GABA released from Glycine R R R Postsynaptic Presynaptic inhibition inhibition R Aspartate and Presynaptic Glutamate excitatory fiber  Amino Acids and Neurotransmitters in CNS Type Transmitter Action 1-Excitatory Glutamate and Stimulation due to depolarization Aspartate by acting on glutamate and amino acids aspartate receptors. 2-Inhibitory Glycine and Inhibition due to hyperpolarization produced by GABA amino acids increase chloride conductance. 3- Choline Acetylcholine Stimulation and inhibition on esters (Ach) central nicotinic receptors Stimulation of peripheral muscarinic receptors 4-Adrenergic Adrenaline Stimulation on  and  drugs Noradrenaline receptors. Dopamine act on Dopamine dopamine receptors 5- HT (Central and peripheral)  Classification of CNS Drugs I- CNS stimulants II- CNS depressants 1- Cerebral stimulants 1- Nerve sedatives 2- Medullary stimulants 2- Anticonvulsants 3- Spinal cord stimulants 3- Tranquilizers 4- Hypnotics 5- Anaesthetics 6- Analgesics  1- Cerebral Stimulants Definition : Are drugs which increase the functional activity of neurons in the cerebral cortex and stimulate motor and sensory areas so cause wakefulness and refreshment in man. They are used in case of mental and muscular fatigue. In Vet. Med., they are used to awake animals from anaesthesia. Classification : Xanthine derivatives Amphetamine Retalin ----------------------------------------------------------------------------------------------------------------------------- Xanthine derivatives: Ex.: Caffeine Theophylline Theobromine  1- Xanthine Derivatives They include: Caffeine Theophylline Theobromine All are alkaloids from All have the same actions and mechanism of action, but they differ in their potency and therapeutic uses. Actions of caffeine: 1- Cerebral stimulant 2- Smooth muscle relaxant 3- Cardiac stimulant 4- Secondary diuretic 5- On GIT : Caffeine increases gastric secretions so it is contraindicated in patients with gastric ulcer. 1- Mode of action of caffeine as cerebral stimulant: It inhibits phosphodiesterase enzyme in neurons of the cerebral cortex increases the amount of cyclic Adenosine monophosphate (c-AMP) increases mental and muscular activity and reduces feeling by fatigue. It reduces the pain of headache as it causes vasoconstriction of cerebral blood vessels.So it is used with aspirin for headache, muscular fatigue, pain and fever in man. 2- As smooth muscle relaxant: Caffeine inhibits directly the smooth muscle of the bronchi (spasmolytic effect), but aminophylline (a derivative of theophylline) is more powerful bronchial dilator and used for treatment of bronchial asthma. 3- As cardiac stimulant: In small doses, caffeine stimulates the cardiac muscle directly by increasing Ca++ ions influx to the myocardium and increase force of contractility. Moreover, it causes coronary vasodilatation. Both effects produce a slight rise in blood pressure, so caffeine is contraindicated in hypertensive patients. 4- As secondary diuretic Caffeine: Increases renal blood flow due to its cardiac stimulant effect. Causes renal vasodilatation so increase the GFR. Increases the number of active functioning glomeruli so increase the amount of GFR. Inhibits the release of ADH, so decreases water reabsorption from the renal tubules to the blood.  Therapeutic uses of caffeine: 1- For respiratory depression and to awake animals from anesthesia. 2- For headache and fever given with aspirin. 3- For edema due to congestive heart failure (CHF). Differences Caffeine Theophylline Theobromine Plant origin Coffee seeds Tea leaves Coca seeds Chemistry 1,3,5 Trimethyl 3,5 Dimethyl 1,3 Dimethyl Xanthine Xanthine Xanthine Effects: Cerebral Stim. +++ + + + Cardiac Stim. + + ++ ++ 2nd Diuretic + + ++ ++ Sm. M. relax. + + ++ ++ 2- Amphetamine (Benzidrine): It has a  Stimulant effect on both CNS & sympathetic nerves.  It increases mental and muscular activity, so used in barbiturate and narcotic poisoning.  It is illegally used as an activator for race horses (doping).  It causes rise in BP due to stimulation of sympathetic nerves. 3- Retalin:  It is a synthetic chemical comp.  Act as a cerebral stimulant like caffeine.  It has no effect on blood pressure.  It is used in case of narcotic poisoning.  2-Medullary Stimulants (Analeptics) Definition: Are drugs which stimulate the vital centers in M.O. especially the depressed respiratory center. classification Direct Reflex Picrotoxin Camphor (s/c) Coramine Ammonia sol.( Inhalation) Cardiazol Bemegride Doxapram 1-Picrotoxine: IV, IM Powerful respiratory stimulant by: 1- Inhibiting the inhibitory GABA transmitter at presynaptic nerve endings. 2- Stimulating the chemoreceptors at the aortic sinus in the heart so stimulate the heart and circulation. Used in barbiturate poisoning. 2- Coramine: similar to picrotoxine but it is: a- Less effective b- Less toxic c- Has no effect on the heart d- Given orally 3- Cardiazol : Stimulate respiratory and vasomotor centers. It is used in deep anaesthesia or narcotic poisoning. Its large doses cause muscular convulsions. 4- Bemegride: powerful respiratory stimulant in barbiturate poisoning. Its large doses cause muscular convulsions. 5- Doxapram: The most powerful analeptic with a wide safety margin. It acts both centrally by direct stimulation of respiratory center and peripherally by stimulation of CRs in the aortic and carotid body in the heart. 6- Camphor: It is a reflex analeptic when injected S/C cause irritation of the cutaneous sensory nerves so it reflexly stimulate medullary centers. It is used in coma or respiratory depression. Externally, it used as a counter irritant for rheumatic pain. 7- Ammonia solution: It is a reflex analeptic after inhalation it causes irritation of the sensory nerve endings of the nose and reflexly stimulates the medullary center.  3- Spinal Cord Stimulants Definition: Are drugs which stimulate spinal cord and centers in it so increase the muscular activity Examples: Strychnine Strychnine Origin: Alkaloid from Strychnus nux vomica seeds. Actions: 1- Spinal cord stimulant: by inhibition of the inhibitory transmitter glycine at post-synaptic nerve endings, so increase the reflex excitability to external stimuli. Its large doses cause convulsion of skeletal muscles and diaphragm. 2- Aphrodisiac: by stimulating sex centers in the spinal cord. 3- General tonic and stomachic: Orally it stimulates taste buds of the tongue so improve appetite.  3- Spinal Cord Stimulants Strychnine 4- Neuromuscular purgative: by stimulation of Aurbach’s plexus of the intestinal mucosa, so increase the intestinal motility. 5- Ruminal tonic: by increasing the ruminal motility.  Therapeutic uses of strychnine: 1- For weak and debilitating animals as a general tonic 2- For ruminal atony as a ruminal tonic 3- For sexual impotency in males as aphrodisiac 4- It is illegally used as a motor activator for race horses to increase their physical activity for running (doping) 5- It is used as a poison for stray dogs. ---------------------------------------------------------------------------------------------------------- Toxic symptoms of strychnine in dogs: 1- Convulsions in all skeletal muscles and diaphragm. 2- Characteristic posture (Opisistonous position) of the animal. 3- Tonic convulsions i.e. interrupted by periods of rest. 4- The period of convulsion increased by increasing the dose. 5- Death occurs due to asphyxia by contraction of diaphragm M.  Treatment of strychnine poisoning: 1- Keep the animal in a dark place. 2- Artificial respiration. 3- Inhalation of volatile anesthetic as chloroform. 4- Administration of antidotes: in dogs give barbiturates or bromides, in horses give chloral hydrate and in man give mephenesin (Sk. M. Relaxant).