nervous system Ⅳ wei yuanyuan. control of motor function spinal cord brain stem cerebellum ...
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Nervous system Ⅳ
Wei yuanyuan
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Control of motor function
Spinal cord Brain stem Cerebellum Cerebral cortex
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Somatic movement
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Motor function of spinal cord Anterior of motor neuron
Anterior horn of spinal cord gray matter
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Types of motor neuron α motor neuron
A α motor nerve fiber (branch many times)→ large skeletal muscle fiber
Innervate 3--hundreds skeletal muscle fibers Final common path of cord reflex
γ motor neuron A γ motor neuron fiber → intrafusal fiber
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Motor unit
A single α nerve fiber + skeletal muscle fiber
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α motor neuron
Final common path
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Overview - organization of motor systemsMotor CortexMotor Cortex
Brain StemBrain Stem
Spinal CordSpinal Cord
Skeletal muscle
-motor neuron
Final common path
P711
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The spinal cord reflex
Stretch reflex Crossed extensor reflex Flexor reflex
Flexor reflex
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stretch reflex
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Muscle stretch reflex
Definition : when a skeletal muscle with an intact nerve supply is stretched, it contracts.
Types : Tendon reflex :Monosynaptic reflex Muscle tonus :Polysynaptic reflex
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Reflex arc of stretch reflex
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Tendon reflex Tendon reflex (dynamic stretch reflex)
Rapid : within a fraction of a second tendon is suddenly knocked → instant, very strong reflex con
traction. e.g. knee jerk Monosynaptic reflex
Contraction opposes the stretch (opposes sudden change in length)
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Tendon reflex
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Muscle tonus• Muscle tonus (static stretch reflex )• is the continuous and passive partial contraction of the
muscles, or the muscle’s resistance to passive stretch during resting state• Process: slow stretch →weaker continuous contraction
of muscle. • Significance: maintenance of posture.• Polysynaptic reflex
Ⅰa fiber, Ⅱ fiberE.g. gravity
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Reflex arc of stretch reflex
Muscle spindle: Stimulation : muscle length or the changing rate of its length Afferent fiber : Ⅰa fiber, Ⅱ fiber
Receptor
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Intrafusal muscle fiber
Ⅰa fiber: Nuclear bag fibers :annulospiral
ending Ⅰa fiber Ⅱ fiber: Nuclear chain fibers,
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a motor neuron → extrafusal muscle fibers
γ motor neuron → intrafusal muscle fibers
Efferent fiber
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intrafusal muscle relaxExtralfusal muscle contration
Muscle spindle (+)
stretch
Α motor neuron (+)
γ Ⅰa fiber Ⅱ fiber运动 N元
Mechanism of muscle tonus
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Finally, the skeletal muscle slightly contract continuously maintenance of posture
Mechanism of muscle tonus
γmotor neuron (+)
intrafusal muscle contranction
Muscle spindle (+)
αmotor neuron (+)
Extralfusal muscle contration continuously
γ运动 N元
γ circuit
Impulse from higher center
γ Ⅰa fiber Ⅱ fiber运动 N元
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muscle tonus
Higher center neuron discharge
↑
γmotor neuron
αmotor neuron
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Reflex arc of stretch reflex
Receptor Golgi tendon
Stimulation : tendon tension Significance : providing a negative feedback Afferent fiber : Ⅰb fiber
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Ⅰb fiber
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Reflex arc of stretch reflex
(+) Golgi tendon→(-) stretch reflex →prevent too much tension develop on the muscle then damage the muscle
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Afferent nerve : Muscle spindle: Ⅰa fiber, Ⅱ fiber Golgi tendon :Ⅰb fiber
Summary of stretch reflex
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Neural Center Anterior motor neuron
Efferent nerve Large α motor nerve fiber Small γ motor nerve fiber
Effector α motor nerve fiber → extrafusal muscle fibers γ motor nerve fiber → intrafusal muscle fibers
Summary of stretch reflex
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When stretch reflex fire, α fiber excite and muscle contract When the Golgi tendon organ fires , α fiber inhibit (by an inhibitory in
terneuron) and muscle relax
Summary of stretch reflex
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Flexor reflex Nociceptive reflex or pain reflex Withdrawal reflex
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Crossed extensor reflex
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Flexor reflex : protective reflexCrossed extensor reflex : postural reflex
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Spinal shock
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Spinal shock
Definition spinal cord transected, all cord f
unctions( e.g. the cord reflexes) disappear temporarily
Below 5th cervical segment Spinal animal Mechanism
Loss of higher center’s control
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Spinal shock
Symptom: At onset of spinal shock:
muscle tonus↓ vascular resistance↓---Bp↓; sweating reflexes disappear; urine and feces retention
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Spinal shock
Symptom:
After some time : reflexes gradually recover The better the species evolved , the more difficult to recover The more complex the reflex, the more difficult to recover
flexor reflex , tendon reflex recover first. The more complex reflex, cross extensor reflex
Physical sensations and involuntary movement ability of the body below transection area never recover
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Brain stem control of motor function
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Decerebrate rigidity
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Brain stem control of motor function
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Brain stem control of motor function
Roles of the Pontine Reticular nuclei and Vestibular nuclei Excite the antigravity muscles Pontine reticular nuclei receive the e
xcitatory signals from the deep nuclei of the cerebellum
Roles of Medullary Reticular nuclei Inhibit the antigravity muscles
•Support of the Body Against Gravity
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Cause of decerebrate rigidity
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αrigidity : enhance activity of α motor neuron directly by higher level.
γrigidity : γ motor neuron
Decerebrate rigidity
afferent signal
α motor neuron
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γrigidity ? or αrigidity ?
Decerebrate rigidity
cut afferent fiber , if rigidity disappear--γ rigidity
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Cerebellum control of motor function
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Cerebellum and its motor function
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Anatomical function areas of cerebellum
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Motor function of cerebellum
The most primitive
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Clinical abnormality of the cerebellum
positional nystagmus
occurs or is exacerbated as a result of changing one's gaze toward or away from a particular side which has an affected vestibular apparatus
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Motor function of cerebellum
especially hand and fingers
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Clinical abnormality of the cerebellum
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Motor function of cerebellum
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Basal ganglia and their motor function
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Basal ganglia and their motor function
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Motor function of basal ganglia
Responsible for smooth and proper implementation of voluntary movement
Inhibiting muscle tone throughout the body.
Helping monitor and coordinate slow,sustained contraction.
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Circuit in basal ganglia
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DA
ACh
GABA
(-)
cortex
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Parkinson’s Disease Parkinson’s Disease
Disease of meso-striatal dopaminergic system
Muhammad Ali in Atlanta Olympic Game, 1996
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Parkinson’s Disease
The mechanism: Deficiency of dopamine Destruction substantia nigra, that
sends dopamine -secreting nerve fibers
treatment: L-DOPA; ACh-R antagonist
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Damage to basal ganglia
Parkinson’s disease The characteristics:
Increased muscle tone,or rigidity;
involuntary, continuous static tremor (at a fixed rate 3-6 cyc/s).
Slowness in initiating and carrying out different motor behaviors.
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Substantia Nigra,
DOPAminergic Neuron
Slowness of Movement- Difficulty in Initiation and Cessation of Movement
Clinical Feature (1)
Parkinson’s Disease
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Clinical Feature (2)Clinical Feature (2)
Resting TremorResting TremorRigidityRigidity
Parkinson’s Disease Parkinson’s Disease
Paralysis AgitansParalysis Agitans
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Huntington’s disease: Huntington’s disease: a degenerative heredity dis
order that usually begins to cause symptoms at age 30 to 40 years. The characteristics:
Severe dementia,cognitive impairment : loss of ACh-secreting neurons, especially in the thinking areas of the cerebral cortex.
involuntary movements, : individual joints Distortional movement : the entire body
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Huntington’s disease
The reason: Malfunction in caudate nucleu
s and putamen : GABA-secreting neurons ACh –secreting neurons
ACh release lessen DOPAminergic Neuron overaci
tivity Treatment
Decrease the DA level
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Huntington’s disease The reason:
Malfunction in caudate nucleus and putamen : GABA-secreting neurons ACh –secreting neurons
ACh release lessen DOPAminergic Neuron overacitivity
Treatment Decrease the DA level
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Motor function of cerebral cortex
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Motor function of cerebral cortex
Primary Motor Cortex(4)
Premotor Areas(6)
Supplementary motor area
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Primary Motor Cortex
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Primary Motor Cortex (PMC)
Characteristics of the PMC: Cross innervations:
influence the opposite side of the body (except some portions of the face)
It is organized in a homunculus pattern with inversed order (face is exception)
The finer the motor, the larger the PMC area (Face and fingers have large representative area)
Stimulation of a certain part of PMC can cause very specific muscle contractions but not coordinate movement
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Transmission of signal from the motor cortex to the muscle
Interneurons →αneuron: the common pathway
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Regulation of cerebral cortex on somatic movement
Flaccid paralysis (poliomyelitis): lower motor neuron spastic paralysis: babinski sign upper motor neuron
Loss of descending inhibition from the brain to the spinal cord
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Summary Final common path Spinal reflex Spinal shock Decebrate rigidity Clinical abnormality of the cerebellum The treatment and mechanism of Parkinson’
s Disease and Huntington’s disease: The characteristics of PMC