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Refex Physiology

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• Refexes are automatic, unconscious tochanges, either inside or outside the body.

a.Refexes maintain homeotasis (autonomicrefexes) – heart rate, breathing rate, bp,digestion.

b.Refexes also carry out the automatic actionso swallowing, sneezing, coughing, omiting.

c.Refexes maintain balance and posture! e.g .,spinal refexes control trun" and limb muscles.

d.#rain refexes in ol e refex center inbrainstem! e.g ., refexes or eye mo ement.

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Refex $rc• %he refex arc go erns the operation o refexes.

&er e impulses ollow ner e pathways as theytra el through the ner ous system. %he simplest othese pathways, which include only a ew neurons,is called the refex arc . Refexes whose arc passesthrough the spinal cord are called spinal refexes.

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Parts o the Refex $rc

'. Receptor – detects the stimulus. a)escription the receptor end o a

particular dendrite or a specialized

receptor cell in a sensory organ. b)*unction sensiti e to a speci+c type ointernal or external change.

. -ensory neuron – con eys the sensoryin o. to brain or spinal cord. a.

escription endrite, cell body, and axono a sensory neuron. b. *unction transmitner e impulses rom the receptor into thebrain or spinal cord.

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Parts o the Refex $rc

. /nterneuron relay neurons. a. escriptiondendrite, cell body, and axon o a neuronwithin the brain or spinal cord. b. *unction

ser es as processing center, conductsner e impulses rom the sensory neuron toa motor neuron.

0. 1otor neuron conduct motor output to

the periphery. a. escription endrite, cellbody, and axon o a motor neuron. b.*unction transmits ner e impulse rom thebrain or spinal cord out to an e2ecter.

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Parts o the Refex $rc

3. 42ector a. escription a muscle or gland. b.*unction Response to stimulation by the motorneuron and produces the refex or beha ioralaction.

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-pinal Refexes

-ensory eedbac" rom muscle

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-tretch and eep %endonRefexes

*or s"eletal muscles to per ormnormally

%he 5olgi tendon organs(proprioceptors) must constantlyin orm the brain as to the state o othe muscle.

-tretch refexes initiated by musclespindles must maintain healthy muscletone.

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1uscle -pindles• $re composed o a ew intra usal muscle +bers

that lac" actin and myosin in their central regions,are noncontractile, and ser e as recepti esur aces.

• 1uscle spindles are wrapped with two types oa2erent endings primary sensory endings o type/a +bers and secondary sensory endings o type //+bers.

• %hese regions are inner ated by gamma ( )e2erent +bers.

• &ote contractile muscle +bers are extra usal +bersand are inner ated by alpha ( ) e erent ibers.

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6peration o the 1uscle-pindles

• -tretching the muscles acti ates themuscle spindle.

%here is an increased rate oaction potential in /a +bers.

• 7ontracting the muscle reducestension on the muscle spindle.

%here is a decreased rate o actionpotential on /a +bers

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Operation of theMuscle Spindles

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-tretch Refex• -tretching the muscle acti ates the muscle

spindle.• 4xcited motor neurons o the spindle cause the

stretched muscle to contract.• $2erent impulses rom the spindle result in

inhibition o the antagonist inhibition o theantagonist.

• 4xample patellar refex.

%apping the patellar tendon stretches the8uadriceps and starts the refex action. %he 8uadriceps contract and the antagonistichamstrings relax.

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-tretch Refex

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5olgi %endon Refex• %he opposite o the stretch refex.• 7ontracting the muscle acti ates the 5olgi

tendon organs.• $2erent 5olgi tendon neurons are

stimulated, neurons inhibit the contractingmuscle, and the antagonistic muscle isacti ated.

• $s a result, the contracting muscle relaxesand the antagonist muscle contracts.

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Golgi Tendon Re ex

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4 ents in the 1onosynaptic -tretchRefex 9 -ummary

• '. Passi e stretch o a muscle (produced by tappingits tendon) stretches the spindle (intra usal) +bers.

• . -tretching o a spindle distorts its central (chain)region, which stimulates dendritic endings osensory ner es.

• . $ction potentials are conducted by a2erent(sensory) +bers into the spinal cord on the dorsalroots o spinal ner es.

• 0. $xons o sensory neurons synapse with dendritesand cell bodies o somatic motor neurons located inthe entral horn gray matter o the spinal cord.

• 3. 42erent impulses in the axons o somatic motorneurons (which orm the entral roots o the spinalner es) are conducted to the ordinary (extra usal)muscle +bers. %hese neurons are (alpha) motor

neurons.

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%he =ithdrawal Refex (*lexorRefex)

• %he automatic withdrawal o anextremity rom a pain ul stimulus.

• $ polysynaptic refex.• -ensory pain signals excite motor

neurons to the fexor muscles, elicitingfexion and withdrawal o the leg.

• 1otor neurons to the extensor musclesare inhibited ia inhibitory interneurons.

• %his would relax the extensors o thesame leg.

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%he =ithdrawal Refex

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%he 7rossed 4xtensor Refex• $ polysynaptic refex.• E.g., Pain ul stimulation o one oot

causes fexion (withdrawal) o theipsilateral leg as well as the extensiono the contralateral leg, to stabilizethe posture! thus the ipsilateral legfexors are acti ated and theextensors are inhibited and vice versain the contralateral leg.

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-uper+cial Refexes• #iceps >er" refex the examiner places +nger

on the inside o the extended elbow o er thetendon o the biceps muscle and the +nger istapped. %he biceps contracts in response, andthe orearm fexes at the elbow.

• %riceps >er" refex tapping the short tendon othe triceps muscle close to its insertion nearthe tip o the elbow elicit this refex. %hemuscle contracts in response, and the orearm

extends, slightly.• $bdominal refex the examiner stro"es thes"in o the abdomen with a dull pin rom theside o abdomen upward towards the midlineand abo e the umbilicus. %he umbilicus mo estowards the stimulated region.

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-uper+cial Refexes• $n"le – >er" refex (plantar refex)

tapping the $chilles tendon >ust abo e itsinsertion on the 7alcaneous elicits this

refex. %he response is plantar fexion,produced by contraction o thegastrocnemius and the solues muscles.

• 7remastric refex this refex is elicited in

males by stro"ing the upper inside o thethigh. /n response, the testis on the sameside is ele ated by contracting muscles.

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7linical %erms•

$nalgesia loss or reduction in the ability to sensepain, without loss o consciousness.• $nalgesic pain – relie ing drug.• $nesthesia loss o eeling.• $taxia partial or complete inability to coordinate

oluntary mo ements.• 4pilepsy isorders o the 7&- that is

characterized by temporary disturbances innormal brain impulses! it may be accompaniedby con ulsi e seizures and loss o consciousness.

•

?untington disease ?ereditary disorders o thebrain producing progressi ely worsening,uncontrollable dance9li"e mo ements andpersonality changes.

• &euralgia sharp, recurring pain associated with a

ner e usually caused by infammation or in>ury