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