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motor nervous system : Stretch reflex
- 1. Dr: Dina Merzeban DeptofPhysiology Motor nervous system Stretch reflex
- 2. What is areflex? • Response to a stimulus • Stimulus Response Task: Write down 3 reflexes .
- 3. What is areflex? Afferent nerve Central connections Efferent nerve Receptor Stimulus Response Effector organ
- 4. 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 .
- 6. skeletal muscle • twotypes of muscle fibres – extrafusal • normally contracting fibres – intrafusal • non contractile fibres present inside the muscle spindle • lie parallel to extrafusal fibres • contains stretch receptors .
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- 9. Nerve supply Sensory tointrafusal fibre: Ia afferent II afferent Motor: to extrafusal fibre motor neuron to intrafusal fibre motor neuron .
- 10. Ia afferent nerve motorneuron one synapse muscle stretchmuscle contraction Stretch reflex
- 11. • 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 isstimulated • muscle is contracted • Monosynaptic • Neurotransmitter is glutamate
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- 13. Stretch Reflex -Knee Jerk
- 14. – nuclear bagfibre • primary (Ia) afferent – supplies annulospiral ending in the centre – nuclear chain fibre • primary (Ia) and secondary (II) afferent – supplies flower spray ending . two types of intrafusal fibres
- 15. Ia afferent fibre IIafferent fibre nuclear bag fibre motor neuron nuclear chain fibre motor neuron
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- 17. Importance of stretchreflex • detects muscle length and changes in muscle length .
- 18. motorneuron • cellbody is located in the anterior horn • motor neuron travels through the motor nerve • supplies the intrafusal fibres (contractile elements at either end) .
- 19. motor neuron motorneuron motor neuron
- 20. • When motor neuron isactive – 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 .
- 21. at rest muscle stretched active motor neuron Ia Ia Ia afferents are stimulated stretch reflex is initiated .
- 22. 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 .
- 24. 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 • Prevent unloading
- 29. Stretch reflex 2types -Response that is transmitted: Dynemic: -when there is change in the length of the spindle receptor (stretching of the sensory receptor area of the muscle spindle by stretching of the muscle spindle or the whole muscle). Detect Change in length. -transmitted by the primary fiber Aα type Static continuous information about the length of the muscle (not the change in length). transmitted by both the primary Aα and secondary (Aβ and Aγ)
- 30. STATIC AND DYNAMICRESPONSE OF MUSCLE SPINDLE AFFRENTS Static response is the discharge at any constant length of the muscle. The greater the muscle length greater is the stretch in the spindle and the higher is the static response of the spindle affrents. Both the primary (Iα) and secondary II spindle affrents gives static or length sensitive responses. The dynamic response of a spindle affrents refer to the discharge during stretch of the muscle. If the spindle affrents gives greater response during a fast stretch than it dose during a slow stretch (velocity different but distance of stretch same) it is said to poses a dynamic response component. Only the primary spindle affrents gives a dynamic or velocity sensitive response.
- 31. STATIC AND DYNAMICFUSIMOTOR NEURONS Dynamic fusimotor fiber increase the dynamic response of the primary spindle affrents (Iα) and have little or no effect on secondary. Static fusimotor fibers increases the static response of both the primary and secondary spindle affrents. However the effect of static fusimotor fiber on primary spindle affrents is less marked than their effect on the secondary. Static fusimotor fiber terminate as trail endings (mostly present in nuclear chain fibers). Experiment using depletion of muscle glycogen as an index of muscle fiber activity have shown that repetitive stimulation of the static fusimotor fiber result primarily in chain fiber glycogen depletion. Dynamic fusimotor stimulation produces mostly bag fiber glycogen depletion.
- 32. Significance of stretch reflex Maintain muscle length Control of voluntary movement Muscle tone
- 33. Servoassistant function: alphaand gamma motor neurons are coactivated during voluntary movements Damping function Role of stretch reflex in the control of voluntary movement
- 34. Muscle tone Def.:continuous alternatingreflex subtetanic contraction of muscle fibers Cause :continuous stretch of muscle spindle (rest) Short dist. Between origin and insertion Gravity Gamma efferent discharge No fatigue!
- 35. Function: Posture againstgravity Background for voluntary movement Regulation of body temp. Venous and lymph return
- 36. Inverse stretch reflex •When the muscle is strongly stretched • 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 .
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- 39. motorneuron Undue stretch Golgitendon organ muscle relaxation Ib afferent nerve inhibitory interneuron Inverse stretch reflex
- 40. Importance of inverse stretchreflex • detects muscle tension .
- 41. Supraspinal regulation Facilitatory areas Facilitatory reticular formation(pons) Area 4 Neocerebellum Vestibular nuclei Inhibitory areas Inhibitory reticular formation (medulla) Area4s Paleocerebellum Basal ganglia Red nucleus
- 43. Disorders of muscle tone •Abnormalities of the tone : Hypertonia – Pyramidal hypertonia (Spasticity) Extrapyramidal hypertonia (Rigidity) Hypotonia
- 44. Pyramidal hypertonia (Spasticity) •Spasticity – a motor disorder characterized by velocity- dependent increase in muscle tone with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex. • Pyramidal hypertonia is most pronounced in the muscle groups most used in voluntary movements.
- 45. CLASP KNIFE REFLEX Seen in decerebrate rigidity On stretching the muscle beyond a point causes Ib affrent inhibitory discharge from GTO which reflexly inhibits homonymous stretched muscle
- 46. Spasticity • Physiologic evidencesuggests that interruption of reticulospinal projections is important in the genesis of spasticity. • In spinal cord lesions, bilateral damage to the pyramidal and reticulospinal pathways can produce severe spasticity and flexor spasms, reflecting increased tone in flexor muscle groups and weakness of extensor muscles.
- 47. Clonus • Clonus isthe phenomenon of involuntary rhythmic contractions in response to sudden sustained stretch. • A sudden stretch activates muscle spindles, resulting inthe stretch reflex. • Tension produced by the muscle contraction activates the Golgi tendon organs, which in turn activate an „inverse stretch reflex‟, relaxing the muscle. • If the stretch is sustained, the muscle spindles are again activated, causing a cycle of alternating contractions and relaxations.
- 48. Cerebellum and muscle tone •The cerebellum does not seem to have a direct effect on muscle tone determining spinal reflex pathways as there is no direct descending cerebellospinal tract. • The cerebellum mainly influences muscle tone through its connections with the vestibular and brain stem reticular nuclei. • Pure cerebellar lesions classically produce hypotonia.
- 49. Extrapyramidal hypertonia (Rigidity) • Rigidityis characterized by an increase in muscle tone causing resistance to externally imposed joint movements. • It does not depend on imposed speed and can be elicited at very low speeds of passive movement. • It is felt in both agonist and antagonist muscles and in movements in both directions.
- 50. Extrapyramidal hypertonia (Rigidity) • 'Cogwheel'rigidity and 'leadpipe' rigidity are two types. • 'Leadpipe' rigidity results when an increase in muscle tone causes a sustained resistance to passive movement throughout the whole range of motion, with no fluctuations. • 'Cogwheel' rigidity occus in association with tremor which presents as a jerky resistance to passive movement as muscles tense and relax. • Basal ganglia structures are clearly implicated in pathophysiology of rigidity.
- 51. Hypotonia • Hypotonia mayaffect muscleresistance to passive movement and/or its extensibility. • Aetiological types of hypotonia : 1. Nerve trunk and root lesion 2. A lesion of anterior horn 3. Cerebellar lesions 4. Cerebral lesions
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- 53. Clinical Examination Tone isdifficult to assess. The determination of tone is subjective and prone to interexaminer variability. The most important part of the examination of tone is determination of the resistance of relaxed muscles to passive manipulation as well as the extensibility, flexibility, and range of motion. The examination of tone needs a relaxed & cooperative patient
- 54. Methods • Inspection :Attitude of the limb atrest. • Palpation : Feel of the muscle – normal, firm orflabby. • Range of movement at the joints. • Passive movement - first slowly and through complete range ofmotion and then at varying speeds. • Shake the distal part of the limb. • Brace a limb and suddenly remove support. • Bilateral examination of homologous parts helps comparefor differences in tone on the two sides of the body.