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Importance of somatosensory feedback to the motor cortex Nerve signals from motor cortex –Muscle contraction –Generation of somatosensory signals –Somatosensory.

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Presentation on theme: "Importance of somatosensory feedback to the motor cortex Nerve signals from motor cortex –Muscle contraction –Generation of somatosensory signals –Somatosensory."— Presentation transcript:

1 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

2 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

3 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

4 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

5 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

6 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

7 Important anatomical structure –Reticular nuclei –Vestibular nuclei

8 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)

9 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

10 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

11 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

12 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)

13 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

14 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

15 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

16 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

17 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)

18 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

19 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

20 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)

21 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)

22 Autonomic nervous system

23 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

24 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

25 Sympathetic nervous system Components –Paravertebral sympathetic chain of ganglia –Prevertebral ganglia (2) Celiac ganglia Hypogastric ganglia –Nerve endings Ganglia to the organs

26 Pre-and post-ganglionic sympathetic neurons Motor neurons to the skeletal muscle –One neuron Sympathetic pathway –Two neurons (pre-ganglionic and post- ganglionic neurons)

27 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

28 Post-ganglionic sympathetic neuron –Origin Sympathetic chain ganglia Peripheral sympathetic ganglia –Travel to various organs


30 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

31 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

32 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

33 Terminal nerve endings –Cholinergic in parasympathetic –Adrenergic in sympathetic Some cholinergic Acetylcholine (choline plus acetyl-CoA) –Parasympathetic neurotransmitter Norepinephrine (tyrosine metabolite) –Sympathetic neurotransmitter

34 Receptors of the Autonomic Nervous System sympathetic parasympathetic preganglionic neuron postganglionic neuron nicotinic receptors muscarinic receptors adrenergic receptors

35 Neurotransmitter receptors Mediation of neurotransmitter action –Membrane permeability to ions Na Ca –Activation/inactivation of intracellular signaling system Production of cAMP by adenyl cyclase

36 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

37 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

38 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)

39 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

40 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)

41 Glands of body –Parasympathetic Secretion by mouth and stomach –Diluted substances –Sympathetic Concentration of substances –Concentrated secretion Secretion by sweat and apocrine glands

42 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

43 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

44 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

45 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

46 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

47 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

48 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)

49 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

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