SPINAL CORD REFLEXESLecture - 2Dr. Zahoor Ali Shaikh

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Spinal Reflex

What is Reflex?

-- It is a response that occurs automatically without conscious effort.

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Reflex

Components of reflex arc are Five:

1- Sensory Receptor2- Afferent pathway3- Center4- Efferent pathway5- Effector organ

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Components of reflex arc

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REFLEX

Receptor responds to the stimulus and produces action potential (AP)

AP is taken by afferent pathway to the integrating center (usually CNS)

Spinal cord and brain integrate basic (automatic) reflexes

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REFLEX

Integrating center processes all the information and makes the decision about the response

Instruction from integrated center are sent via efferent pathway to the Effector organ (muscle or gland)

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Classification of reflexes

Monosynaptic or stretch reflex or tendon jerkeg. Bicep jerk ,tricep jerk, supinator jerk

knee jerk, ankle jerk Polysynaptic reflexeg. Withdrawal reflex

Abdominal reflexPlantar reflex

Visceral reflexeg. Micturation, defecation reflex

Jendressik Phenomenon7

Stretch Reflex [monosynaptic] Sudden stretch to a muscle leads to

contraction of that muscle is known as stretch reflex.

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Stretch Reflex [monosynaptic] Stretch Reflex is basic (automatic)

spinal reflex. We will take example Knee jerk

There are 5 components of Stretch Reflex

1- Sensory receptor – muscle spindle in skeletal muscle

2- Afferent pathway – 1a fibers 3- Center – spinal cord 4- Efferent fibers – α motor neuron 5- Effector organ – skeletal muscle

contraction

Types of muscle fibers

Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron)

Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by

γ - motor neuron)

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11Fig 13.3 – Sensory receptors in muscle Silverthorn 2nd Ed

MUSCLE SPINDLE (INTRAFUSAL FIBERS)12

MUSCLE EXTRAFUSAL FIBERS

MUSCLE INTRAFUSAL FIBERS

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Muscle spindle

Nuclear bag fiber Nuclear chain fiberSensory innervations of muscle

spindle Ia – nuclear bag & nuclear chain

fibers II – nuclear chain fibersMotor supply – γ motor neuron Dynamic & Static

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Types of motor neuron

α – motor neuron (supply Extrafusal fibers )

γ - motor neuron (supply Intrafusal fibers)

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Patellar Tendon Reflex

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KNEE JERK – MONOSYNAPTIC REFLEX

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Polysynaptic Reflex

In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway

We will study withdrawal reflex

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POLYSYNAPTIC REFLEXESWithdrawal Reflex When a person touches a hot stove or pin

prick, a withdrawal reflex occurs from the painful stimulus

1. Receptor- pain and Temperature Receptors stimulated

2. Afferent impulse travels via Action potential

3. Center– Spinal cord.( Excitatory interneuron stimulated that stimulate efferent fibers).

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POLY SYNAPTIC REFLEX

4 .Efferent fibers to Biceps to cotract ( flextion of arm ) and inhibitory neuron stimulated to inhibit contraction of Triceps.

This type of connection causing stimulation of nerve supply to one muscle and simultaneous inhibition of the nerve to its Antagonistic muscle is known as RECIPROCAL INNERVATION. 20

Withdrawal reflex – Polysynaptic reflex21

Poly synaptic reflex

Important Afferent neuron stimulate also interneuron

that carry signals to the Brain ( Ascending tracts in the spinal cord )

Therefore Brain can modify the with drawl reflex. How?

By sending impulses via descending pathways to the efferent motor neuron supplying the involved muscles and prevent contracting of biceps inspite of painful stimulus e.g. pin prick

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DIFFERENT REFLEXES SHOWN

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Jendressik Phenomenon

(Reinforcement)

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Jendressik Phenomenon

(Reinforcement)

Superficial Reflexes

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Summary

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28TRANSVERS SECTION OF SPINAL CORD

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Dermatomes of Spinal roots and divisions of trigeminal nerve (V1 ,V2, V3)

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Spinal Cord Reflexes

Cranial Nerve

Other Reflexes

1- Golgi tendon Reflex 2- Crossed Extensor Reflex

We will discuss first Golgi endon Reflex

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Golgi Tendon Organs Composed of:

Nerve fiber endings that wind between collagen fibers inside connective tissue capsule

If muscle is stretched: Free nerve endings are pinched and they

fire Activation of Golgi tendon organs:

Inhibits alpha motor neurons and decreases muscle contraction

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The Golgi tendon reflex (inverse stretch reflex)

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Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed34

Crossed Extensor Reflex

Extension of opposite limb

Flexion & withdrawal of stimulated limb

Painful Stimuli

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POLYSYNAPTIC REFLEX37

Clinical Importance of reflexes To test the integrity of reflex arc. Localization of neurological lesion. Identifying the type of lesion. Monitoring the progress of

neurological deficit.

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Clinical Importance of reflexes Deep tendon reflexes are absent in

lower motor neuron lesion. The become exaggerated in upper

motor neuron lesions. Pendular jerks are observed in

cerebellar lesions.

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Thank you

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