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Motor system reflexes for students
This document discusses motor reflexes and their components. It begins by defining reflexes as involuntary responses to stimuli that do not involve significant brain involvement. It then discusses the stretch reflex in detail, including the roles of muscle spindles, Ia afferent fibers, and alpha and gamma motor neurons. Additional reflexes discussed include withdrawal reflexes, reciprocal innervation, and primitive reflexes seen in infants. The clinical importance of assessing reflexes to localize lesions in the motor system is also mentioned.
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Motor system reflexes for students
- 1. Motor system Reflexes Prof. VajiraWeerasinghe Professor of Physiology Faculty of Medicine
- 2. Motor Functions • 1.Voluntary Functions – Voluntary movement • 2. Involuntary Functions – Reflexes
- 3. What is areflex? • Response to a stimulus • Involuntary, without significant involvement of the brain • Stimulus Response Task: Write down 3 reflexes
- 4. What is areflex? Stimulus Effector organ Response Central connections Efferent nerve Afferent nerveReceptor Higher centre control
- 5. Stretch reflex • Thisis a basic reflex present in the spinal cord • Stimulus: muscle stretch • Response: contraction of the muscle • Receptors: stretch receptors located in the muscle spindle
- 7. skeletal muscle • twotypes of muscle fibres – extrafusal • normally contracting fibres – Intrafusal • fibres present inside the muscle spindle • lie parallel to extrafusal fibres • either end of the fibre contractile • central part contains stretch receptors
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- 10. Nerve supply Sensory tointrafusal fibre: Ia afferent II afferent Motor: to extrafusal fibre A motor neuron to intrafusal fibre A motor neuron
- 11. Ia afferent nerve motor neuron one synapse muscle stretchmuscle contraction Stretch reflex
- 12. • When amuscle is stretched • stretch receptors in the intrafusal fibres are stimulated • via type Ia afferent impulse is transmitted to the spinal cord • motor neuron is stimulated • muscle is contracted • Monosynaptic • Neurotransmitter is glutamate
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- 14. Stretch Reflex -Knee Jerk
- 15. – nuclear bagfibre • primary (Ia) afferent – supplies annulospiral ending in the centre – provide information on muscle length and velocity (phasic response) fast stretch reflex – nuclear chain fibre • primary (Ia) and secondary (II) afferent – supplies flower spray ending – monitor the length of the muscle (tonic response) – slow stretch reflex Two types of intrafusal fibres
- 16. Ia afferent fibre IIafferent fibre nuclear bag fibre nuclear chain fibre motor neuron motor neuron
- 17. Importance of stretchreflex • detects muscle length and changes in muscle length
- 18. • Phasic stretchreflex – Stretching the quadriceps muscle quickly (e.g. by tapping the patellar tendon) evokes a discharge in the primary afferent (Ia) fibres – These form monosynaptic excitatory connections with motor neurons supplying physiological extensors of the knee, which contract briefly • Tonic stretch reflex – Passive bending of the joint elicits a discharge from the group II afferents that increases the tone of physiological extensor (antigravity) muscles – Tonic stretch reflex is important for maintaining erect body posture
- 19. motor neuron •cell body is located in the anterior horn • motor neuron travels through the motor nerve • supplies the intrafusal fibres (contractile elements at either end)
- 20. motor neuron motor neuron motor neuron
- 21. • When motor neuron is active – extrafusal fibres are contracted – muscle contracts • when motor neuron is active – intrafusal fibres are contracted – stretch receptors are stimulated – stretch reflex is activated – impulses will travel through Ia afferents – alpha motor neuron is activated – muscle contracts
- 22. at rest muscle stretched active motor neuron Ia Ia Ia afferents are stimulated stretch reflex is initiated
- 28. motor neuronactivity • active all the time - mild contraction • Maintain the sensitivity of the muscle spindle to stretch • modified by the descending pathways • descending excitatory and inhibitory influences • sum effect is generally inhibitory in nature
- 29. Alpha gamma co-activation •gamma motoneurons are activated in parallel with alpha motoneurons to maintain the firing of spindle afferents when the extrafusal muscles shorten • Activity from brain centres often causes simultaneous contraction of both extra- and intrafusal fibres, thereby ensuring that the spindle is sensitive to stretch at all muscle lengths
- 31. Inverse stretch reflex •When the muscle is strongly stretched -> muscle is relaxed • Golgi tendon organs are stimulated • Via type Ib afferents impulse is transmitted to the spinal cord • inhibitory interneuron is stimulated • motor neuron is inhibited • muscle is relaxed
- 32. motor neuron Unduestretch Golgi tendon organ muscle relaxation Ib afferent nerve inhibitory interneuron
- 33. motor neuron Unduestretch Golgi tendon organ muscle relaxation Ib afferent nerve inhibitory interneuron
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- 35. Importance of inverse stretchreflex • detects muscle tension
- 36. Deep tendon reflexes(DTR) • Biceps jerk • Triceps jerk • Supinator jerk • Knee jerk • Ankle jerk • Jaw jerk
- 37. • reflex level •biceps jerk C56 • supinator jerk C56 • triceps jerk C78 • knee jerk L34 • ankle jerk S12 Spinal cord level of stretch reflexes (tendon jerks)
- 38. Superficial reflexes • Withdrawalreflex • Superficial abdominal reflex • Flexor plantar reflex
- 39. Withdrawal Reflex • Stimulus: –cutaneous stimulation (usually noxious) • Response: – withdrawal of the hand • Polysynaptic reflex
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- 44. • Elbow flexion,extension • Wrist flexion, extension • Forearm supination, pronation • Shoulder adduction, abduction • Hip flexion, extension • Thigh adduction, abduction • Knee flexion, extension • Ankle dorsiflexion, plantar flexion
- 45. Reciprocal innervation • insidethe spinal cord – Agonist and antagonistic muscles are reciprocally innervated – stimulation of flexor muscles – inhibition of extensor muscles – excitatory neurotransmitter is glutamate – inhibitory neurotransmitter is glycine flexor extensor +++ ----
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- 47. Withdrawal Reflex Flexor &Crossed extensor reflex
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- 49. Superficial abdominal reflexes • lightscratch of the abdominal skin • brisk unilateral contraction of the abdominal wall
- 50. Flexor plantar reflex •Scratching the sole of foot • Plantar flexion • Normal response
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- 52. Primitive reflexes • Theseare reflexes present in newborn babies but disappear as the child develops • They were evolutionarily primitive in origin • In adults these reflexes are inhibited by the higher centres
- 53. Other primitive reflexes •Moro reflex: startle reaction • Walking/stepping reflex • Sucking reflex • Tonic neck reflex • Palmar grasp reflex
- 54. Babinski sign • whenouter border of the sole of the foot is scratched • upward movement of big toe (dorsiflexion) • fanning out of other toes • also called extensor plantar reflex • feature of • upper motor neuron lesion • seen in infants during 1st year of life (because of immature corticospinal tract)
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- 56. Clinical Importance ofreflexes (tendon jerks) • Locate a lesion in the motor system • To differentiate upper motor neuron lesion from a lower motor neuron lesion