final revision autonomic, physiology of nerve and muscle 2022 (1).pdf

the nervous system Central nervous system Peripheral nervous system Brain spinal cord Sensory division (afferent) Motor division (efferent...

the nervous system Central nervous system Peripheral nervous system Brain spinal cord Sensory division (afferent) Motor division (efferent Autonomic Nervous system Somatic Two efferent neuron system in which the impulses Nervous system are carried from the central nervous system to the - One efferent neuron system in which effector organ by two neurons. the impulses are carried from the C.N.S The first neuron is called preganglionic and the second is called postganglionic and the area of to the target organ by only one neuron meeting is called autonomic ganglion. - The target organ is skeletal Muscle The target organs are 1. Cardiac muscle (heart) 2. Smooth muscles in the wall of viscera and blood vessels 3. Glands as salivary and sweat glands Autonomic Nervous System Preganglionic neurons originate from the CNS and relay at autonomic ganglia outside CNS. From autonomic ganglia originate postganglionic neurons to the target organs Preganglionic neurons originate from Sympathetic Nervous System Parasympathetic Nervous System 12 thoracic and upper 2 lumber segments brain with 3rd, 7th, 9th and 10th cranial nerves & From 2nd, 3rd and 4th sacral segments 1  A ganglion is defined as collection of bodies of neurons outside the CNS Autonomic Ganglia (site of relay between pre and post -ganglionic neurons) Sympathetic Parasympathetic Paravertebral ganglia: Terminal ganglia On both sides of the vertebral near to or above the target organ Column as a pair of ganglia for each spinal segment 1- Celiac 1- Ciliary except for the 8 cervical 2- superior mesenteric 2-submandibular segment only 3 pairs of ganglia 3- inferior mesenteric 3- sphinopalatine superior cervical, 4- Otic middle cervical inferior cervical. Collateral Ganglia Mid way between CNS and target organ 2 Effects of stimulation of Sympathetic nervous system: Region Effects skin: 1. Stimulation of sweat glands (secretion of sweat) 2. Contraction of erector pili muscle leading to erection of hair 3. Vasoconstriction of cutaneous blood vessels (pale and cold skin). Eyes Head and 1. Contraction of the dilator papillae muscle leading to dilatation of pupil (mydriasis). Neck 2. Relaxation of ciliary muscles of eyes leading to decrease power of lens for far vision. 3. Contraction of smooth muscles of upper eyelids leading to widening of palpebral fissure (increase field of vision) salivary Stimulates salivary glands (especially submandibular) to secret viscid secretion (small in volume glands: and rich in mucous). Heart Thoracic 1. Increases heart rate and force of contraction of ventricles. i.e. increases cardiac output viscera 2. Vasodilatation of coronary blood vessels Lungs 1. Relaxation of bronchial muscles leading to dilatation of bronchioles. 2. Vasoconstriction of pulmonary vessels. 3 Abdominal GIT 1. Inhibition (relaxation) of plain muscles in the wall of stomach, small intestine and proximal Viscera part of large intestine and contraction of sphincters leading to delay evacuation of food from stomach and intestine. Preganglionic neurons pass 2. Decrease in secretion of GIT glands. with greater 3. Vasoconstriction of most of the abdominal blood vessels. splanchnic nerve and relay Stimulation of glycogenolysis (break down of glycogen to glucose) and increase in blood glucose celiac and Liver level. superior mesenteric Contraction of splenic capsule and evacuation of stored blood into circulation. ganglia. Spleen Secretion of epinephrine (adrenalin) and norepinephrine (noradrenaline). These two hormones have Adrenal the same effects of sympathetic stimulation on different organs. (suprarenal) (considered as a modified collateral sympathetic ganglion) Medulla On Pelvic Large Inhibition of the muscles in the wall of the distal part of large intestine and rectum and contraction Viscera intestine of the internal anal sphincter leading to retention of feces and inhibition of defecation. Preganglionic neurons pass Urinary within the bladder Inhibition of the muscles in the wall of the bladder and contraction of internal urethral sphincter lesser leading to retention of urine and inhibits micturition. splanchnic Male genital 1. Vasoconstriction of blood vessels of external genital male organs and other pelvic viscera. nerve and relay organ 2. During ejaculation, it stimulates contraction of vas deferens, seminal vesicles and prostate at the inferior gland mesenteric ganglion 4 Effects of parasympathetic stimulation Region Effects Cranial Eyes Preganglionic neurons pass with oculomotor a. Contraction of constrictor papillae muscle leading to outflow nerve and relay at ciliary ganglion narrowing of the pupil (miosis). b. Contraction of the ciliary muscle preparing the eye lens for near vision. lacrimal and nasal glands Stimulates increase in secretions preganglionic neurons pass with facial nerve and relay at sphenopalatine ganglion. Subligual and submandibular salivary Stimulate salivary secretion large in volume and rich in water glands and enzymes preganglionic neurons pass with facial nerve and relay at submandibular ganglion. Parotid salivary gland Preganglionic neurons pass with glossopharyngeal nerve and relay at otic ganglion thoracic and abdominal viscera Heart 1. Inhibition of atrial cardiac muscle leading to Preganglionic neurons pass with decrease in heart rate and force of vagus nerve and relay contraction of atria at terminal ganglia 2. Decrease in coronary blood flow. (The vagus nerve does not innervate the ventricles) Lungs 1. Constriction of bronchioles. 2. Stimulation of bronchial glands secretion 5  GIT 1. Contraction of the plain muscles in the wall of esophagus, stomach, small intestine and proximal part of large intestine and relaxation of all sphincters. It helps evacuation of food. 2. Stimulates secretion of GIT glands, liver pancreas Gall Contraction of the wall and relaxation of the bladder sphincter of Oddi leading to evacuation of bile into the duodenum. Sacral Preganglionic fibers arise from the second, third Rectum Defecation due to contraction of the wall of the and fourth sacral segments and relay in terminal rectum and relaxation of the internal anal sphincter outflow ganglia Urinary Micturition due to contraction of wall of urinary bladder bladder and relaxation of internal urethral sphincter genital 1. Erection due to vasodilatation of blood organs vessels of penis in male 2. Vasodilatation of blood vessels o female genital organs 6 7  Chemical Transmitters in the Autonomic Nervous System acetylcholine Noradrenaline (norepinephrine) Fibers that release acetylcholine Fibers that release noradrenaline are called adrenergic fibers and are called cholinergic fibers the receptors upon which it acts are adrenergic receptors. the receptors upon which it act are cholinergic receptors Sites of release: Sites of release: 1. All preganglionic fibers sympathetic and parasympathetic From most postganglionic sympathetic fibers at organs (except at sweat glands and blood vessels of skeletal 2. Preganglionic sympathetic fibers at adrenal medulla. muscles). 3. All postganglionic parasympathetic fibers. 4. Few postganglionic sympathetic fibers as secretory fibers to sweat glands and vasodilator fibers to blood vessels of skeletal muscles Removal of Acetylcholine Removal of Norepinephrine: acetylcholine is removed and its action is terminated by an 1- Active re- uptake by the adrenergic nerve fiber itself enzyme called acetylcholine esterase 2- Destruction by enzymes as a. M.A.O. (monoamine oxidase) b. C.O.M.T (catych0l-O- methyl- transferase). Cholinergic Receptors: Adrenergic Receptors: Activated by acetylcholine. Two types: Activated by norepinephrine and epinephrine (catecholamines) 1- Nicotinic receptors are found on all postganglionic and found on target organs innervated by sympathetic adrenergic neurons (at all autonomic ganglia) postganglionic fibers and some other sites (as adipose cells). 1- Alpha receptors (α1 &α2 ) 2- Muscarinic receptors are found on: When stimulated leads to: a- Effectors (target organs) innervated by cholinergic a. Vasoconstriction 8 parasympathetic postganglionic fibers. b. Contraction of : b- The effectors innervated by cholinergic sympathetic i. Dilator papillae muscle postganglionic fibers (at sweat glands and blood vessels of skeletal muscles). ii. GIT sphincters iii. Internal urethral sphincter iv. Spleen v. Seminal vesicles and vas deferens 2- Beta receptors ( β1, β2 & β3 ): Stimulation of β2 leads to; Relaxation of plain muscles of: i. Bronchioles ii. Urinary bladder iii. GIT Stimulation of β1 leads to: i. Increase in heart rate ii. Increase in force of contraction of the heart Stimulation of β3 on adipose tissues leading to lipolysis. 9 10  Excitability is the ability of the nerve cells to respond to a stimulus. The response of the neuron is in the form of production of an action Each neuron consists of three main parts: potential. (1) The soma “body”: containing the nucleus. Resting Membrane Potential (2) Cytoplasmic processes (extensions): - It is the difference in electric potential (voltage) between the inside and the (a) The dendrite: receive signals “impulses” from other neurons. Physiology of Nerve outside of the membrane under resting condition. The potential difference is – 70 mV which means that outside is more positive and inside is more negative. (b) The axon: through which the impulses leave the cell. In other wards there is accumulation of more positive change outside the membrane. At resting state, the membrane is said to be polarized Types of neurons according to number of processes: 1) Multipolar: with many dendrites and single axon Causes of Resting Membrane Potential 2) Bipolar: with one dendrite and one axon at the two opposite poles of the (1) Selective permeability of the cell membrane. cell - At rest, the permeability of the membrane to K+ is more 100 time than for 3) Unipolar: with single process divided into two branches, one acts as sodium. Therefore. the outflow of K+ is more than the inflow of Na+. This dendrite and the other as axon leads to accumulation of more positive charges outside. - At the same time, the negative protein ions cannot diffuse to outside Types of nerve fibers: following K+ and accumulate on the inner surface of the membrane. (a) Myelinated Nerve fiber. surrounded by a myelin sheath, (2) Sodium – Potassium pump: interrupted at point called Nodes of Ranvier. (b) Unmyelinated nerve - There is a carrier protein in the membrane. This carrier can transport 3 Na+ fibers without myelin sheath. from inside to outside in exchange with 2 K+ from outside to inside. - The process is an active transport and needs energy from ATP. 11 Action Potential Excitatory changes During Action potential: It is the rapid change in membrane potential following stimulation of the nerve by a 1- Absolute refractory period: suitable “threshold” stimulus.The action potential consists of the following phases: It is the period during which the neuron cannot be stimulated by any stimulus whatever its strength. During this period, the excitability is zero. This period (1) Slow depolarization: Due to opening of small number of gated channel for sodium and corresponds to the time between the firing level till the early one third of slow inflow of Na+ till reaching a membrane potential –55 mV. This is called the firing repolarization (rapid depolarization and reverse of polarity and beginning of level. repolarization). (2) Rapid depolarization and Reverse of polarity: 2- Relative refractory period: Due to opening of all gated channels for Na+ and rapid inflow of Na+. Now, the It is the period during which the neuron can be excited (stimulated) by a stimulus membrane charge is reversed and inside is positive and outside is negative. stronger than normal giving another action potential. This period corresponds to the (3) Repolarization: remaining of repolarization. When the membrane potential is +35 mV, the Na+ gated channel close and K+ gated Factors Affecting Excitability: channels open leading to outflow of K+ returning to the resting potential. 1- Factors that increase excitability: (4) Hyperpolarization: Any factor that increases permeability of membrane to Na+ or helps to decreases It is due to outflow of excess K+ to outside as some K gates are still open. positive charges outside. (5) Then all K gates are closed, and the membrane returns to resting polarizing state. 2- Factors that decrease Excitability: Any factor that decreases permeability of membrane to Na+ or helps to increase Threshold stimulus is the minimal stimulus which succeed to open enough number of positive charges outside and the membrane becomes hyperpolarized. Example is local sodium gated channels to reach the firing level. Subthreshold stimulus causes a state of anesthesia. depolarization without reaching the firing level. Therefore, it causes a local response (local excitatory state) instead of propagating action potential. Repeated local responses due to repeated stimulation with subthreshold stimuli may be summated and reach the firing level and propagated action potential is generated. 12 - The skeletal muscle is formed of many muscle fibers (cells). Neuromuscular junction - Each group (bundle) of muscle fibers / are connected to and separated from each other by a fibrous connective tissue called endomysium. - Each bundle is Structure surrounded by another C.T. called perimysium. - All bundles are covered by Neuromuscular junction is the site of meeting between the end of the C.T. called epimysium. - All these connective tissues are continuous at the two axon of a somatic motor neuron “fiber” and the surface of the muscle ends of the muscle with tendons. fiber. It is also called motor and plate. The end of the axon is swollen in Structure of the muscle fiber: the form of a sole. It contains many vesicles filled with a substance - Each muscle fiber is elongated and cylindrical surrounded by a Sarcolemma. - called acetyl choline. The surface of the muscle fiber is folded and The cytoplasm contains many parallel myofibrils showing alternating dark contains receptors “binding sites” for acetyl choline. There is no (A) and light (I) bands. - At the middle of each I-band there is a dark Z-disk, cytoplasmic continuity or connection between the axon and the and in the middle of each A-band there is light H-zone. The distance between Physiology of Muscles muscle fiber but there is a narrow gap called synaptic cleft. two successive Z-disks is called Sarcomere which represents the functional unit of the muscle. Mechanism of transmission: Inside each sarcomere two types of protein filaments are present 1- Arrival of nerve impulse “action potential” along the motor neuron. (1) Thick filaments: formed of units of protein called myosin and present in the 2- Inflow of calcium ions from outside to inside the sole of the axon. A-band. Each molecule of myosin consists, of a tail, cross bridge, and head. 3- Release of acetyl choline from the axon. (2) Thin filaments: Attached to Z-disks and extend through I-band and A- band till the limits of H-zone. 4- Acetyl choline crosses the gap and binds to the receptors on the Each thin filament consists of 3 types of proteins: (a) Actin —→ containing membrane of muscle fiber. binding sites for the heads of myosin. (b) Tropomyosin —→ covering the binding sites during relaxation. (c) Troponin —→ connected to tropomyosin. 5- Binding of acetyl choline to the receptors stimulate the production of an action potential on the membrane of the muscle fiber. - In the middle of the A band and H zone there is the M- line which represents the protein to which myosin thick filaments are attached 6- Cholinesterase enzyme destroys acetyl choline and removes it from There are two other giant proteins in each sarcomere: the receptors. a- Titin: A huge elastic protein extends from the Z disk to the M line passing through the thick filament. It stabilizes the contractile filaments and elastic enough to return the muscle to its origin after contraction. b- Nebulin: An inelastic giant protein inside the thin filament and attached to the Z- disk and help to align the actin filaments. Sarcoplasmic reticulum (S.R.) is present under the cell membrane at intervals. S.R. is the site of storage of calcium ions Ca+. From the membrane, invaginations called transverse tubules (T-tubules) are formed at intervals and pass beside the S.R. This system of T-tubules conducts the action potential from the membrane to S.R. 13  Motor Unit Mechanism of muscle contraction: Each motor neuron innervates a group of muscle fibers in a skeletal muscle. 1- The action potential is propagated along the membrane of muscle fiber and then The motor neuron, its axon and the number of muscle fibers it innervates are called together to the T-tubules. motor unit. 2- T tubules conduct action potential to membrane of sarcoplasmic reticulum The stimulation of the motor unit by a single action potential from the brain leads to a very leading to opening of gates and release of calcium ions short rapid contraction is called muscle twitch. When the motor unit is stimulated by many rapid successive action potentials, the muscle 3- Calcium ions combine with troponin leading to removal of tropomyosin from fibers become in a continuous sustained contraction called Tetanus (don't mistake it with a its position bacterial disease has the same name) 4- Removal of tropomyosin leads to exposure of the binding sites on the actin of Muscle tension is the mechanical force exerted by a muscle. The more motor units the thin filaments. stimulated, the greater the muscle tension. Any force opposing muscle tension is called load, 5- The heads of the cross bridges of myosin combine with the binding sites and in like the weight of an object... presence of energy coming from ATP, sliding of thin filaments takes place Isotonic contraction is the contraction of a muscle with shortening in length when between the thick filaments. the muscle tension exceeds the load and succeeds to lift it. 6- The thin filaments pull the 2 Z-disks leading to shortening of sarcomere Isometric contraction is the contraction of a muscle without shortening when the (contraction). During contraction sarcomeres become dark. load exceeds the muscle tension. 7- Relaxation takes place by active reuptake of calcium ions by the sarcoplasmic then troponin and tropomyosin return to their position and cover again the binding sites preventing cross bridges from binding again leading to relaxation. 14 15