Download preganglionic neuron postganglionic neuron nicotinic receptors

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
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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
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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
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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