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