Nervous system Ⅳ
Wei yuanyuan
Control of motor function
Spinal cord Brain stem Cerebellum Cerebral cortex
Somatic movement
Motor function of spinal cord Anterior of motor neuron
Anterior horn of spinal cord gray matter
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
Motor unit
A single α nerve fiber + skeletal muscle fiber
α motor neuron
Final common path
Overview - organization of motor systemsMotor CortexMotor Cortex
Brain StemBrain Stem
Spinal CordSpinal Cord
Skeletal muscle
-motor neuron
Final common path
P711
The spinal cord reflex
Stretch reflex Crossed extensor reflex Flexor reflex
Flexor reflex
stretch reflex
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
Reflex arc of stretch reflex
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)
Tendon reflex
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
Reflex arc of stretch reflex
Muscle spindle: Stimulation : muscle length or the changing rate of its length Afferent fiber : Ⅰa fiber, Ⅱ fiber
Receptor
Intrafusal muscle fiber
Ⅰa fiber: Nuclear bag fibers :annulospiral
ending Ⅰa fiber Ⅱ fiber: Nuclear chain fibers,
a motor neuron → extrafusal muscle fibers
γ motor neuron → intrafusal muscle fibers
Efferent fiber
intrafusal muscle relaxExtralfusal muscle contration
Muscle spindle (+)
stretch
Α motor neuron (+)
γ Ⅰa fiber Ⅱ fiber运动 N元
Mechanism of muscle tonus
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
muscle tonus
Higher center neuron discharge
↑
γmotor neuron
αmotor neuron
Reflex arc of stretch reflex
Receptor Golgi tendon
Stimulation : tendon tension Significance : providing a negative feedback Afferent fiber : Ⅰb fiber
Ⅰb fiber
Reflex arc of stretch reflex
(+) Golgi tendon→(-) stretch reflex →prevent too much tension develop on the muscle then damage the muscle
Afferent nerve : Muscle spindle: Ⅰa fiber, Ⅱ fiber Golgi tendon :Ⅰb fiber
Summary of stretch reflex
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
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
Flexor reflex Nociceptive reflex or pain reflex Withdrawal reflex
Crossed extensor reflex
Flexor reflex : protective reflexCrossed extensor reflex : postural reflex
Spinal shock
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
Spinal shock
Symptom: At onset of spinal shock:
muscle tonus↓ vascular resistance↓---Bp↓; sweating reflexes disappear; urine and feces retention
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
Brain stem control of motor function
Decerebrate rigidity
Brain stem control of motor function
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
Cause of decerebrate rigidity
αrigidity : enhance activity of α motor neuron directly by higher level.
γrigidity : γ motor neuron
Decerebrate rigidity
afferent signal
α motor neuron
γrigidity ? or αrigidity ?
Decerebrate rigidity
cut afferent fiber , if rigidity disappear--γ rigidity
Cerebellum control of motor function
Cerebellum and its motor function
Anatomical function areas of cerebellum
Motor function of cerebellum
The most primitive
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
Motor function of cerebellum
especially hand and fingers
Clinical abnormality of the cerebellum
Motor function of cerebellum
Basal ganglia and their motor function
Basal ganglia and their motor function
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.
Circuit in basal ganglia
DA
ACh
GABA
(-)
cortex
Parkinson’s Disease Parkinson’s Disease
Disease of meso-striatal dopaminergic system
Muhammad Ali in Atlanta Olympic Game, 1996
Parkinson’s Disease
The mechanism: Deficiency of dopamine Destruction substantia nigra, that
sends dopamine -secreting nerve fibers
treatment: L-DOPA; ACh-R antagonist
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.
Substantia Nigra,
DOPAminergic Neuron
Slowness of Movement- Difficulty in Initiation and Cessation of Movement
Clinical Feature (1)
Parkinson’s Disease
Clinical Feature (2)Clinical Feature (2)
Resting TremorResting TremorRigidityRigidity
Parkinson’s Disease Parkinson’s Disease
Paralysis AgitansParalysis Agitans
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
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
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
Motor function of cerebral cortex
Motor function of cerebral cortex
Primary Motor Cortex(4)
Premotor Areas(6)
Supplementary motor area
Primary Motor Cortex
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
Transmission of signal from the motor cortex to the muscle
Interneurons →αneuron: the common pathway
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
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
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