Physiology 2025 Lec 3 PDF

Lec 3  Physiology physiology of the nervous system Peripheral nervous system Somatic motor system Autonomic nervous system Skeletal muscles. Cardiac muscle, s...

Lec 3  Physiology physiology of the nervous system Peripheral nervous system Somatic motor system Autonomic nervous system Skeletal muscles. Cardiac muscle, smooth muscle, Effectors glands. Control voluntary functions Regulates many non-voluntary Function functions. ▪ Heavily myelinated axons of the ▪ Axons area two-neuron chain somatic motor neurons extend from ▪ The preganglionic (first) neuron the CNS to skeletal muscle. has a lightly myelinated axon Efferent ▪ Axons conduct impulses rapidly ▪ The ganglionic (second) neuron pathway ▪ no ganglia extends to an effector organ ▪ Conduction is slower due to thinly or unmyelinated axons All somatic motor neurons release ▪ Preganglionic fibers release ACh Target Acetylcholine (ACh), which has an ▪ Postganglionic fibers release. organ excitatory effect. Norepinephrine or Ach and the responses effect is either stimulatory or inhibitory. Divisions of the Autonomic Nervous System Sympathetic and parasympathetic divisions Innervate mostly the same structures Cause opposite effect DOC Q Page | 1  Physiology physiology of the nervous system Sympathetic – “fight, or flight” Parasympathetic – “rest and digest” Activated during exercise, excitement, and Concerned with conserving energy. emergencies. Anatomical Differences in Sympathetic and Parasympathetic Divisions Issue from different regions of the CNS Parasympathetic Sympathetic also called the craniosacral division also called the thoracolumbar division Differences between Sympathetic & Parasympathetic Divisions Sympathetic Parasympathetic Origin Thoracolumbar outflow Craniosacral outflow Preganglionic Short “sympathetic ganglia are Long “parasympathetic ganglia near fibers bilateral to spinal cord” effector organs” Postganglionic Long Short fibers Branching of highly branched few branched axons Neurotransmitter released by Acetylcholine Acetylcholine preganglionic axons Neurotransmitter released by Norepinephrine Acetylcholine postganglionic (Except sweat glands). axons DOC Q Page | 2 Physiology physiology of the nervous system Neurotransmitters ✓ Chemical substances that transmit impulses across junctions (synapses): Definition ✓ neuron-neuron synapse= ganglion. ✓ neuron- effector synapse = synaptic cleft. Communication between nerve cells and between nerve cells and effector organs. Neurotransmitters are too hydrophilic to penetrate Role the membranes. Their signal is mediated by binding to specific receptors on the cell surface. 1. Synthesis 2. Storage 3. Release Steps 4. Receptor binding 5. Effects 6. Termination of action Adrenergic neurotransmitter: NEP. Types of Cholinergic neurotransmitter: ACh. autonomic Non-Adrenergic Non-Cholinergic transmitters (NANC): ATP, neurotransmitters adenosine, GABA, 5-HT, VIP, etc. DOC Q Page | 3 Physiology physiology of the nervous system Parasympathetic neurotransmission Cranial Outflow Sacral Outflow Preganglionic fibers run via: Emerges from S2-S4.  Oculomotor nerve (III)  Eye Innervates organs of the pelvis and  Facial nerve (VII)  Salivary, nasal, lower abdomen lacrimal glands. Form splanchnic nerves  Glossopharyngeal nerve (IX)   Large intestine, urinary bladder, ureters, Parotid salivary glands reproductive organs.  Vagus nerve (X)  Heart, lung, liver, small intestine. Acetylcholine Synthesis Hemicholinum inhibits ACh synthesis (by preventing choline uptake into nerve terminal). Substances Vesamicol inhibits ACh storage. affect Excess Magnesium or lack of Calcium or botulinum toxin inhibit ACh its synthesis release. Presynaptic M2 agonists (autoreceptors) →  ACh release Termination of Action of ACh is hydrolyzed by cholinesterase enzymes. How? action acetic acid ‫ و‬choline ‫عن طريق انه بيكسره و بيحوله ل‬ 1. All autonomic ganglia 3. Post-ganglionic sympathetic to 2. Parasympathetic thermoregulatory sweat gland. 1ry transmitter postganglionic neurons 4. Neuro-muscular junction in (Skeletal muscles) 5. Suprarenal gland. ❑The two types of receptors that bind ACh are nicotinic and muscarinic ❑These are named after drugs that bind to them and mimic ACh effects Cholinergic  Muscarinic receptors: Receptors M1, M2, M3, M4, M5  Nicotinic receptors: Nn & Nm DOC Q Page | 4 Physiology physiology of the nervous system  Nicotinic receptors are found on:  Motor end plates (skeletal muscles)…NM Nicotinic  All preganglionic neurons of both sympathetic and parasympathetic Receptors divisions….NN (cholinergic)  The hormone-producing cells of the adrenal medulla ….NN  The effect of ACh binding to nicotinic receptors is always stimulatory Receptor Location Action(s) Mechanism Nicotinic -Autonomic 1-Stimulate all Opening of Na+/K+ (N1or NN) ganglia autonomic ganglia& channels depolarization---- -Adrenal medulla Depolarization & firing -----???? 2-Secretion of NE and Nicotinic EP from suprarenal gland Nicotinic -Neuromuscular Skeletal muscle As N1 (N2or NM) junctions contraction Muscarinic -Autonomic 1. Autonomic ganglia: Act on Gs stimulates (M1) ganglia facilitate transmission. phospholipase C increase -Parietal cells of 2. In CNS: Cognitive inositol triphosphate (IP3) stomach function. Basal ganglia: and Diacylglycerol (DAG) -GIT smooth balance between ACh& increase intracellular muscles dopamine. calcium. 3. increase HCl Cholinergic secretion from stomach 4. Saliva: salivary secretions. Muscarinic Heart 1. Decrease heart rate, Act on Gi inhibit adynylyl (M2) Presynaptic heart conductivity and cyclase ----- Decrease cholinergic atrial contraction cAMP and activates K+ DOC Q Page | 5 Physiology physiology of the nervous system 2. Presynaptic feed- channels → inhibitory back regulation response (decrease ACh release). Muscarinic -Secretory 1-Contraction of As M1 M3 receptors of (M3) glands smooth muscles excitatory function in -smooth muscles (miosis, glandular and smooth (GIT, UB, bronchoconstriction, muscles activity but of Bronchial and contraction of urinary inhibitory function in BV. eye) bladder and GIT) -Blood vessels 2-Relaxation of ureter and sphincters of GIT and UT 3-Increase secretion of glands (salivation, sweat, …) 4-Vasodilation due to release of nitric oxide (NO) DOC Q Page | 6 Physiology physiology of the nervous system Sympathetic Neurotransmission Fight or flight response results in: 1. Increased BP 2. Increased blood flow to brain, heart and skeletal muscles 3. Increased muscle glycogen for energy 4. Increased rate of coagulation 5. Pupil dilation  Issues from T1-L2 (all thoracic + lumbers1-2)  They have short preganglionic fibers, and it relays in sympathetic chain The Sympathetic ganglia& release ACh in ganglia. Division  They have long postganglionic fibers that innervate their body organs & release Norepinephrine. ✓ Major organ of the sympathetic nervous system Adrenal medulla ✓ Secretes great quantities epinephrine (a little norepinephrine) ✓ Stimulated to secrete by preganglionic sympathetic fibers  Synthesis of NE  Metabolism (COMT 20% + MAO Neurotransmission  Storage of DA and NE in vesicles 80%) at adrenergic Release of NE  Binding to receptors neurons  Uptake mechanism Biosynthesis of Nor-epinephrine After secretion of NE by the terminal nerve endings, it is removed from the secretory site in different ways: 1. Re-uptake “into the adrenergic nerve endings themselves by an active transport process” Major pathway  Neuronal uptake (uptake 1): For NEP & metabolized by MAO enzyme.  Vesicular uptake: For NEP that escapes MAO degradation. Termination of  Extra-neuronal uptake (uptake 2): Non-selective, Diffusion away from NE action the nerve endings into the surrounding body fluids and then into the blood and finally metabolized by COMT in the Liver. 2. Enzymatic degradation “Destruction by enzymes” Minor pathway  80% by monoamine oxidase (MAO) in presynaptic nerve terminals after reuptake” Neuronal NE”.  15% by catechol-O-methyl transferase (COMT) in postsynaptic membrane, liver. “Circulating catecholamines” DOC Q Page | 7 Physiology physiology of the nervous system Adrenoreceptors DOC Q Page | 8 Physiology physiology of the nervous system α-receptors α1 α2 DOC Q Page | 9 Physiology physiology of the nervous system β-receptors β1 β2 β3 Excitatory Inhibitory Excitatory Less clinically relevant. DOC Q Page | 10