reflex- para md2(2)

8/8/2019 Reflex- Para Md2(2)

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1. ..

LabLAB

2. PRETEST LabLAB

3. BRIFT LAB ..

Lab


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Reflex:An automatic response to a stimulus

- same type of response (stereotypedresponse)

- subconscious

- conscious

Function of reflexes

- protection

- homeostasis: regulation of HR, BP, RR, GI

motility and secretion,.


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Reflex arc 1. receptors 2. afferent fiber

3. integrating center: CNS(brain and spinal cord),often receives signals (informations) from manyreceptors. The output from the center is the neteffect of the total afferent in puts.

4. efferent fiber 5. effectors: muscle, glands


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Properties of reflex

1. Adequate stimulus rods cones :light taste buds:taste

2. Reflex timebeginning of stimulation to thebeginning of response

3. Fatique of reflex: synapse


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Classification of reflexes1. Amount of synapse in the CNS

- monosynaptic reflex- disynaptic reflex- polysynaptic reflex

2. Kind of nerve fiber- somatic reflex- autonomic reflex

3. Origin of nerve fiber- cranial reflex

- spinal reflex


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4. Based on timing- inborn reflex

- acquired reflex (Pavlov reflex ,conditioned reflex)

5. Location of receptors- superficial reflex:corneal reflex, abdominal

reflex- deep reflex :patellar, ankle- visceral reflexes

6. Pathological reflex: Babinski sign


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Anterior motor neuron: each segment of thecord are located several thousand neurons;

MN, MN motor neuron (final common pathway) :to extrafusal muscle fibers.

A motor unit : an motor neuron, itsmotor axon, and all the skeletal musclefibers that its supplies, a few to several

hundred skeletal muscle fibers

motor neurons : to intrafusal muscle

fibers


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Musclesensory receptors1. Musclespindles : distributed throughout the

musclemuscle length, rate of change of its lengthstretch reflexesfine movements

2. Golgi tendon organs : muscle tendonstendon tension, rate of change of tension clasp knife reflex

Both receptors send signals to spinal cord,cerebellum, and cerebral cortex to control musclecontraction

subconscious level


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Musclespindles 3-10 mm long, 3-12intrafusal muscle fibers,

small skeletal muscle fibers central region: no or few actin myosin

filaments the end portions are supplied by MN

nuclear bag fiber, nuclear chain fiber Ia afferent fiber: primary ending (annulospiral

ending) on nuclear bag and nuclear chain fibers IIbafferent fiber : secondary ending, mostly

on nuclear chain fiberMuscle spindle can beexcited by

1. lengthening the whole muscle2. contraction of the end portions of the

intrafusal muscle fiber.


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Under normal conditions

motor neuron activity: action potentials

from muscle spindles


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Cerebellum, basal ganglia , cerebralcortex, bulboreticular area

+ -

MN


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Clinical application of thestretchreflex

1.To examine the intactness of thereflex arc.

2.To assess the degree offacilitation (excitation) or inhibition tospinal cord centers, i.e.,knee jerk reflex,ankle jerk reflex

facilitatory impulses hyperreflexia

facilitatory impulses hyporeflexia


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Reflex testing is a standard,

useful procedure in search ofneurological pathology. However,interpretation of reflexresponses is often subjective andrequires considerable experience

on the part of diagnosis


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The clinical significance of

deviations in the activity of muscle-stretch reflexes from normal willdepend on comparison on the

opposite side. And also otherneurological examination, i.e., motorpower, sensation, consciousness,are are used to make diagnosis.Moreover x-ray and MRI are very

helpfull.


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Grading of reflexes

Grade

0.Areflexia

.No response,any

lesion that interrupts the reflex arc.

Grade1. Hyporeflexia. A reflex may be

depressed by any lesion that interrupts the reflexarc.

Grade

2.Normal response

.

Grade3. Hyperreflexia with no pathology.

Grade4. Hyperreflexia with pathology.


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Clonus

Rhythmic contraction of muscles

Increased facilitatory impulses of

the brain to spinal cord centers


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Golgi tendon reflex

Golgi tendon organ(GTO), a sensory

receptor connected in series withmuscle fibers (GTO:muscle fiber= 1:10-15)

detect muscle tension (not muscle length

or rate of change of muscle length)

has both dynamic & static responses

type Ib nerve fibers connects toinhibitory interneuron,cerebellum,cerebral cortex


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Muscle tension + GTO + inhibitory

interneuron

muscle tension motor neuronactivity

Golgi tendon reflex- To prevent tearing of muscle , tendon

- To equalize the contractile force of

muscle fibers


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Flexor Reflex (Withdrawal reflex)

Stimulation of any cutaneous sensoryreceptor on a limb, i.e., touchreceptor,painreceptor(nociceptive receptor)


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Abnormal reflexesAbnormal reflexes

11. Babinski sign : UMN lesions. Babinski sign : UMN lesions

2. Clonus : excitatory impulses to spinal

cord centers, motor neuron activity,

hyperreflexia3. Hyperreflexia : motor neuron activity,

receptor sensitivity

4. Hyporeflexia : motor neuron activity,receptor sensitivity, LMN lesion,

abnormality of NMJ, muscle


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UMNlesions

weakn

ess,para

lysis

spasticity

tendon reflexes

+ Babinski sign

little,if any,muscle

atrophy

no fasiculation

LMNlesions

weakness, paralysis

flaccidity, hypotonia

Hypo- /no tendon

reflex

- Babinski sign

muscle atrophy

fasiculationof

involved muscle


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Light reflex (pupillary light reflex )

Accommodation reflex


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References1. Guyton AC, Hall JE. Textbook of medical physiology, 11 th

ed. Philadelphia: Elsevier Saunders, 2006: Chap 54.2. Ganong WF. Review of medical physiology, 22nd ed. Boston :

McGraw Hill, 2005: Chap 6.3. Rhoades R, Tanner. Medical physiology, 2 nd ed. New

York: Lippincot Williams & Wilkins, 2003: Chap 9.4. Aminoff MJ, Greenberg DA, Simson RP. Clinical neurology,

6 th ed. New York: Lange Medical Books/ McGraw Hill,2005: Chap 5.

reflex- para md2(2)

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