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 systems Motor Cortex Brain Stem Spinal 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 contraction. 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  Ⅰ a fiber, Ⅱ fiber E.g. gravity

Reflex arc of stretch reflex  Muscle spindle: Stimulation : muscle length or the changing rate of its length Afferent fiber : Ⅰ a fiber, Ⅱ fiber  Receptor

Intrafusal muscle fiber Ⅰ a fiber: Nuclear bag fibers :annulospiral ending Ⅰ a 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 Ⅰ a 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 Ⅰ a fiber Ⅱ fiber 运动 N 元

muscle tonus Higher center neuron discharge ↑ γmotor neuron α motor neuron

Reflex arc of stretch reflex  Receptor  Golgi tendon  Stimulation : tendon tension  Significance : providing a negative feedback  Afferent fiber : Ⅰ b fiber

Ⅰ b 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: Ⅰ a fiber, Ⅱ fiber  Golgi tendon : Ⅰ b 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 interneuron) and muscle relax Summary of stretch reflex

Flexor reflex  Nociceptive reflex or pain reflex  Withdrawal reflex

 Crossed extensor reflex

 Flexor reflex ： protective reflex  Crossed extensor reflex ： postural reflex

Spinal shock

 Definition  spinal cord transected, all cord functions( e.g. the cord reflexes) disappear temporarily  Below 5 th 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

 Roles of the Pontine Reticular nuclei and Vestibular nuclei  Excite the antigravity muscles  Pontine reticular nuclei receive the excitatory 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

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) Resting Tremor Rigidity Parkinson’s Disease Paralysis Agitans

Huntington’s disease:  Huntington’s disease: a degenerative heredity disorder 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 nucleus and putamen :  GABA-secreting neurons  ACh –secreting neurons  ACh release lessen  DOPAminergic Neuron overacitivity  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

 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