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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 post-
ganglionic 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
Systemsympathetic
parasympathetic
preganglionic neuron
postganglionic neuron
nicotinic receptors muscarinic receptors
adrenergic 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
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