Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Importance of somatosensory feedback to the motor cortex • Nerve signals from motor cortex – Muscle contraction – Generation of somatosensory signals – Somatosensory signals return to the motor cortex • Source of signals – Muscle spindle – Tendon organs – Tactile receptors on the skin overlaying the muscle • Somatosensory signals – Positive feedback – Further increase in muscle contraction • Autocorrection of muscle fiber length (muscle spindle) • Adjustment of grips (pressure against skin) – Precise muscle contraction Stimulation of spinal motor neurons • Organization of nerve fibers within the spinal cord – Multiple sensorimotor and motor neurons entering the cord – Anterior motor neurons in the anterior horn gray matter Stimulation of spinal motor neurons • Organization of nerve fibers within the spinal cord – Large number of rubrospinal and reticulospinal fibers terminate on the anterior motor neurons • Control of hands and fingers • Direct route for brain to control hands and fingers Damage to motor cortex • Removal/damage of primary motor cortex – Removal of Benz cells • Paralysis • Loss of voluntary control and fine control of muscle contraction • Removal/damage of areas adjacent to the motor cortex – Muscle spasm on the muscles controlled by particular region • Opposite side Role of brain stem • Brain stem – Medulla, pons, and mesencephalon – Extension of spinal cord • Performs motor and sensory function for head and face – Controls • • • • • • Respiration Cardiovascular system GI tract Stereotyped movement Equilibrium Eye movement – Relay the signals from higher brain • Important anatomical structure – Reticular nuclei – Vestibular nuclei • Antagonistic function of reticular nuclei – Pointe reticular nuclei • Excitation of atigravity muscles via pointe reticulospinal tract – Excitation of anterior motor neurons and muscles (spinal column and extensor muscles) • Antagonistic function of reticular nuclei – Medullary reticular nuclei • Relaxation of antigravity muscles – Inhibitory signals via medullary reticulospinal tract (signals from corticospinal, rubrospinal, and other motor neuron pathways) • Counterbalabce pointe reticular system – Proper tension of muscle • Function can be overridden by the higher brain – Standing • Vestibular nuclei – Function in association with pointe reticular nuclei • Excitatory signals via lateral and medial vetivulospinal tract – Critical for excitation of axial antigravity muscles – Selective control of excitatory signals to different antigravity muscles • Maintenance of equilibrium Vestibular apparatus • Sensory organ – Sensation of equilibrium – Encased in bony tubes and chambers • Located in bony labyrinth of temporal bone • Membranous labyrinth (functional unit) • Membranous labyrinth – – – – Cochlea (hearing) Semicircular canals (3) Utricle Saccule • Maculae – Sensory area – Lies in the inside of uticle and saccle • Detection of orientation of head • Horizontal plane (uticle)head in upright position • Vertical plane (saccle)head when lying down – Coated with gelatinous layer • Small calcium bicarbonate crystals (staoconia) • Hair cells – Synapse with nerve endings of the vestibular nerve – Directional sensitivity • Uniformed bending of stereocilia and kinocellium • Generation of membrane potential – Degree of bending • Amount of membrane potential generated • Orientation of head in space • Hair cells – Degree of bending • Amount of membrane potential generated • Orientation of head in space – Different orientation within the maculla • Different pattern of excitation based on orientation of head Semicircular ducts • Three in each vestibular apparatus – Anterior, posterior, and lateral – Arranged in the right angle to one another • Represents all three planes in space – Ampulla • Enlargement filled with endolymph – Excitation of sensory organ • Excitation – Crista ampullaris • Small crest within the ampulla • Contains cupula (gelatinous tissue mass) – Bending of cupula by flow of fluid • In response to turning of head • Bending of kinocilia by cupula – Sending of appropriate signals to vestibular nerve • CNS regarding changes in rotation and rate of change in three planes Maintenance of equilibrium • Pattern of stimulation of different hair cells – Transmission of signal to the brain regarding the position of head in regards to gravity pull – Stimulation of appropriate vestibular, reticular, and cerebellar motor nerve system • Excitation of appropriate muscles to maintain equilibrium • Utricle and saccule – Highly efficient (detect half-degree dysequilibrium) • Detection of Linear acceleration – Statoconia falls backward during forward acceleration • Feeling of falling backward • Lean forward to correct dysequilibrium – Moving statoconia to original state – Cannot detect linear velocity • Detection of acceleration • Lean forward during running – Minimize air resistance • Detection of angular acceleration/head rotation – Flow of fluid within the semicircular ducts • Opposite direction to the rotation • Bending of hair cells – Excess discharge during initial rotation – Return to tonic level within the few seconds • Adaptation – Rotation of endolymph • Back resistance to the flow of fluid in the semicircular duct and past bent ccupula • When the rotation suddenly stops – Endolymph continues to rotate while semicircular duct stops • Opposite bending of cupula (termination of discharge) • Returns to normal when endolymph stop rotating (tonic discharge) Predictive function of semicircular duct system • Anticipatory correction of equilibrium – Prediction of dysequilibrium – Anticipatory adjustment of equilibrium by the equilibrium center in cerebellum • Other factors involved in maintenance of equilibrium – Joint receptors in neck (rotation of head in relation to the rest of body) – Visual sensory information (detection of shift in images) Autonomic nervous system General organization • Visceral organ function – Arterial pressure – GI motility – GI secretion – Emptying the urinary bladder – Sweating/body temperature regulation • Components – Spinal cord, brain stem, and hypothalamus • Visceral reflexes – Subconscious signals from visceral organs • Autonomic ganglia • Brain stem • Hypothalamus • Subconscious reflex responses – Subconscious signals to visceral organs – Transmitted via sympathetic or parasympathetic nervous system Sympathetic nervous system • Components – Paravertebral sympathetic chain of ganglia – Prevertebral ganglia (2) • Celiac ganglia • Hypogastric ganglia – Nerve endings • Ganglia to the organs Pre-and post-ganglionic sympathetic neurons • Motor neurons to the skeletal muscle – One neuron • Sympathetic pathway – Two neurons (pre-ganglionic and postganglionic neurons) • Pre-ganglionic neurons – Lies in the intermediolateral horn of the spinal cord • Pass through a white ramus into one of the ganglia of the sympathetic chain – Synapses with post-ganglionic neurons in the ganglion – Pass upward/downward in the chain and synapses with one of other ganglia of the chain – Synapses in a peripheral sympathetic ganglion • Post-ganglionic sympathetic neuron – Origin • Sympathetic chain ganglia • Peripheral sympathetic ganglia – Travel to various organs Parasympathetic nervous system • Origin – Cranial nerves III, VII, IX, and XI – Lowermost part of spinal cord • Second and third sacral nerves • 75 % vagus nerves – Entire thoracic and abdominal cavity • Pre- and post-ganglionic neurons – Pre-ganglionic nerouns • Uninterrupted all the way to the organ – Post-ganglionic neurons • Located on the surface of the organ • Very short Characteristics of sympathetic and parasympathetic function • Neurotransmitters – Preganglionic neurons • Cholinergic (secretes acetylcholine) • Identical between sympathetic and parasympathetic – Postganglionic neurons • Cholinergic in parasympathetic system • Adrenergic in sympathetic system – Secretes norepinephrine – Some cholinergic neurons in sympathetic system • Terminal nerve endings – Cholinergic in parasympathetic – Adrenergic in sympathetic • Some cholinergic • Acetylcholine (choline plus acetyl-CoA) – Parasympathetic neurotransmitter • Norepinephrine (tyrosine metabolite) – Sympathetic neurotransmitter Receptors of the Autonomic Nervous System adrenergic receptors sympathetic preganglionic neuron postganglionic neuron parasympathetic nicotinic receptors muscarinic receptors Neurotransmitter receptors • Mediation of neurotransmitter action – Membrane permeability to ions • Na • Ca – Activation/inactivation of intracellular signaling system • Production of cAMP by adenyl cyclase Acetylcholine receptors • Two types – Muscarinic receptors • Found in cell surface of all organs stimulated by cholinergic system (sympathetic and parasympathetic) – Nicotinic receptors • Found in autonomic ganglia between pre- and post-synaptic neurons (parasympathetic and sympathetic) • Activated by nicotine Adrenergic receptors • Two receptors – Alpha receptors (alpha1 and alpha2) • Main receptor for norepinephrine – Binds to epinephrine – Beta receptors (beta1 and beta2) • Bind both norepinephrine and epinephrine – Weak signaling by norepinephrine • Distribution of these receptors – Differences in response of organs to particular neurotransmitter • Alpha receptors – – – – Vasoconstriction Iris dilation Intestinal relaxation Intestinal sphincter constriction – Pilomotor contraction – Bladder sphincter contraction • Beta receptors – Vasodilation (2) – Cardioacceleration (1) – Increased myocardial strength (1) – Intestinal relaxation (2) – Uterine relaxation (2) – Broncodilation (2) – Calorigenesis (2) – Glycogenesis (2) – Lipilysis (1) – Bladder wall relaxation (2) Excitation and inhibition • Sympathetic and parasympathetic stimulation – Excitatory effects on some organs – Inhibitory effects on other organs – One can act as a regulator of the other • Eyes (pupillary opening and focus of the lens) – Sympathetic • Contraction of meridional fiber of the iris (dilation of pupil) – Parasympathetic • Contraction of circular muscle (constriction of pupil) • Contraction of ciliary muscle (thickening of lens to focus on the object near at hand) • Glands of body – Parasympathetic • Secretion by mouth and stomach – Diluted substances – Sympathetic • Concentration of substances – Concentrated secretion • Secretion by sweat and apocrine glands • GI tract – Parasympathetic • Increases overall activity by promoting peristalsis and relaxing sphincter – Sympathetic • Inhibits peristalsis if storng enough • Heart – Sympathetic • Increased activity – Parasympathetic • Decreased activity • Blood vessels – Sympathetic • Constriction • Acutely increases arterial pressure (increased heart activity and vessel constriction) – Depends on kidney function – Parasympathetic • Dilation of some blood vessels • Very little effects on arterial pressure – Could stop heart when vagus nerves are strongly stimulated Role of adrenal medulla • Release of epinephrine and norepinephrine when stimulated by sympathetic nerves – Mainly epinephrine (80% of total adrenalines in the blood) – Prolonged stimulation of adrenergic neurons – Activation of organs that are not innervated by sympathetic neurons Sympathetic and parasympathetic tone • Both systems are continually active – Basal rate of activity • Function – Increase and decrease the activity of a stimulated organ by a single nervous system • Constriction and dilation – Background parasympathetic tone in intestine • Critical for health of the organ Exposure to stress • Mass discharge by the sympathetic system – Fear/pain perceived by the hypothalamus – Several physiological changes to anticipate and deal with threatening situation • Metabolic rates to adapt for vigorous physical activity – Fight/flight response Pharmacology • Sympathomimeric drugs – Acts on adrenergic effector organs – Induce identical/similar response to endogenous epinephrine or norepinephrine • Phenylephrine (binds to alpha receptors) • Isoproterenol (binds to beta receptors) • Albuterol (binds to beta 2 receptor only) – Indirect sympathomimeric durgs • Cause release of epinephrine/norepinephrine • Ephedrine, tyramine, and amphetamine • Drugs that block adrenergic activity – Inhibition of synthesis and storage (reserpine) – Inhibition of release (guanethidine) – Alpha receptor blockers (phenoxybenzamine and phentalamine) – Beta receptor blockers (propranolnol, metoprolol) – Inhibition of nerve impulse (hexamethonium) • Parasympathomimeric drugs (cholinergic) – Acts like acetylcholine • Pilocarpine and methacholine – Inhibits cholineesterase activity • Potentiating effects – Neostigmine, pyridostigmine, ambenonium • Antimuscarinic drugs (inhibits cholinergic activity at effector organs) – Atropin and scoplamine