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Muscle tone roohi

Muscle tone roohi

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Muscle tone roohi

  1. 1. MUSCLE TONE By- Dr. Harshdeep Kaur Guide- Dr. Himanshu Dua
  2. 2. TONE- DEFINITION • Tone is defined as state of muscle contraction at rest. • It is functionally defined as resistance to passive movements. • Two types- phasic and postural
  3. 3. • Phasic tone is due to rapid stretching of muscle and muscle spindle. The response is rapid and short lived. • Postural tone is due to steady strained stretch on tendons and attached muscle with contraction of involved muscle.
  4. 4. TONE • The word TONUS was first used to designate the state of contraction of resting muscle by Muller in 1838. • Vulpian defined Tone as a state of permanent muscular tension. • Muscle tone is usually described as the resistance of a limb to passive movement (Foster 1892).
  5. 5. • Stretch reflex of Sherrington is the basic mechanism of tonic activity.
  6. 6. MUSCLE SPINDLE • Muscle spindle is a fusiform structure laying between and parallel to the muscle fibres and sharing their tendinous attachement.
  7. 7. MUSCLE SPINDLE • It consisting of about 4 to 12 intrafusal fibres, which have a smaller diameter than the extrafusal fibres. • Intrafusal fibres are of two types : Nuclear bag fibres and Nuclear chain fibres. • Serve to monitor both the length of the muscle and the velocity of its contraction
  8. 8. INTRAFUSAL FIBRES
  9. 9. MUSCLE SPINDLE
  10. 10. GOLGI TENDON ORGAN • These receptors are sensitive to the changes in tension generated by muscles as they contract. • Signals the tension and provides negative feedback control of muscle contraction and regulates muscle force rather than length
  11. 11. TONE PATHWAY Afferent pathway • Ia from muscle spindle passes via dorsal horn to synapse with α- motoneurons • II from muscle spindle synapse with interneurons • Ib from golgi tendon organ ends in nucleus dorsalis and synapse with interneurons.
  12. 12. TONE PATHWAY Efferent pathway • α-motoneurons runs from cell body in ant. horn to extrafusal muscle fibre. • γ- motoneurons runs from cell body in ant. horn to intrafusal muscle spindle.
  13. 13. TONE MECHANISM • γ- motoneurons activity causes the intrafusal fibre to contract this stretches the primary sensory ending, thus increasing afferent discharge causing depolarisation of α-motoneurons supplying the extrafusal muscle, thereby increasing muscle tone.
  14. 14. STRETCH REFLEX • The Myotatic (Stretch) Reflex When a muscle is stretched, the spindles in that muscle are also stretched. Stretch stimulates afferent fibers and send impulses into the cord. Some fibers synapse directly on alpha motor neurons supplying the same muscle which was initially stretched. This causes the muscle to contract and shorten, relieving the initial stretch. Such neurons are called homonymous alpha motor neurons. This "stretch-resulting-in-relieved- stretch" is known as the myotatic or stretch reflex.
  15. 15. STRETCH REFLEX • Stretch reflex is due to stimulation of muscle spindle. • it is a monosynaptic reflex involving one motor, one sensory neuron and one synapse in the pathway. • Reciprocal inhibition is also present
  16. 16. STRETCH REFLEX- MONOSYNAPTIC REFLEX.
  17. 17. TENDON REFLEX • Polysynaptic reflex • Operates as feedback mechanism to control muscle tension. • Receptor is golgi tendon organ. • Increase tension to muscle spindle- stimulation of tendon organ- nerve impulse transmitted by sensory neuron –synapse with inhibitory association neuron-inhibits motor neuron associated with muscle- relaxation of agonist muscle
  18. 18. • Motor neuron synapse with stimulatory association neuron-stimulate motor neuron of antagonist muscle-contraction of antagonist muscle.(reciprocal inhibition)
  19. 19. SUPRASPINAL CONTROL • The efferent fibres to the muscle spindle, γ- motoneurones, receive input form higher centres via : • Facilitatory fibres and • Inhibitory fibres
  20. 20. MOTOR(DESCENDING) PATHWAYS • The motor tracts can be functionally divided into two major groups: • Pyramidal tracts – These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. • Extrapyramidal tracts – These tracts originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
  21. 21. Pyramidal Tracts • Corticospinal tracts – supplies the musculature of the body. • Corticobulbar tracts – supplies the musculature of the head and neck.
  22. 22. Corticospinal tract Corticobulbar tract
  23. 23. EXTRAPYRAMIDAL TRACTS 1.Vestibulospinal Tracts- • There are two vestibulospinal pathways; medial and lateral. They arise from the vestibular nuclei. The tracts convey this balance information to the spinal cord, where it remains ipsilateral. • Fibres in this pathway control balance and posture by innervating the ‘anti-gravity’ muscles (flexors of the arm, and extensors of the leg), 2.Reticulospinal Tracts - • The two recticulospinal tracts have differing functions: • The medial reticulospinal tract arises from the pons. increases muscle tone. • The lateral reticulospinal tract arises from the medulla. reduces muscle tone
  24. 24. 3.Rubrospinal Tracts- • The rubrospinal tract originates from the red nucleus, a midbrain structure. As the fibres emerge, they decussate , and descend into the spinal cord. They have a contralateral innervation. • play a role in the fine control of hand movements 4.Tectospinal Tracts- • This pathway begins at the superior colliculus of the midbrain. The superior colliculus is a structure that receives input from the optic nerve. The neurones then quickly decussate, and enter the spinal cord. They terminate at the cervical levels of the spinal cord. • The tectospinal tract coordinates movements of the head in relation to vision stimuli
  25. 25. inhibitory excitatory
  26. 26. DECEREBRATION • Aka extensor posturing. • In decerebrate posturing, the head is arched back, the arms are extended by the sides, and the legs are extended. • A hallmark of decerebrate posturing is extended elbows. • The arms and legs are extended and rotated internally. • The patient is rigid, with the teeth clenched.
  27. 27. • A complete transection of the brain stem between the superior and inferior colliculi permits the brain stem pathways to function independent of their input from higher brain structures. This is called a midcollicular decerebration. The lesion is below the red nucleus.
  28. 28. • This lesion interrupts all input from the cortex (corticospinal and corticobulbar tracts) and red nucleus (rubrospinal tract), primarily to distal muscles of the extremities. • The excitatory and inhibitory reticulospinal pathways (primarily to postural extensor muscles) remain intact. • The excitatory reticulospinal pathway leads to hyperactivity in extensor muscles in all four extremities which is called decerebrate rigidity.
  29. 29. Decorticate Posture • Aka flexor posturing. Patients with decorticate posturing present with the arms flexed, or bent inward on the chest, the hands are clenched into fists, and the legs extended and feet turned inward. • There are two parts to decorticate posturing. .
  30. 30. • The rubrospinal tract facilitates motor neurons in the cervical spinal cord supplying the flexor muscles of the upper extremities. The rubrospinal tract and reticulospinal tract based flexion outweighs the vestibulospinal and pontine reticulospinal based extension in the upper extremities.
  31. 31. 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.
  32. 32. DISORDERS OF MUSCLE TONE • Abnormalities of the tone : Hypertonia – Pyramidal hypertonia (Spasticity) Extrapyramidal hypertonia (Rigidity) Hypotonia
  33. 33. METHOD TO ELICIT TONE  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 range of motion.
  34. 34. METHOD TO ELICIT TONE • Inspection : Attitude of the limb at rest. • Palpation : Feel of the muscle – normal, firm or flabby. -Range of movement at the joints. -Passive movement - first slowly and through complete range of motion 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 compare for differences in tone on the two sides of the body.
  35. 35. SPASTICITY-DEFINITION • Spasticity is a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (‘‘muscle tone‘‘) with exaggerated tendon jerks. • Involves mainly antigravity muscles-flexors in upper limb and extensors in lower limb
  36. 36. MECHANISMS OF SPASTICITY 1.Disynaptic reciprocal Ia inhibition- Reciprocal inhibition ensures that antagonist muscles remain relaxed when the agonist muscles are activated during voluntary movements . Reduced reciprocal inhibition may therefore contribute to the development of hyperreflexia and spasticity.
  37. 37. 2. . α- motoneuron excitability 3. γ- motoneuron excitability 4. Recurrent inhibition 5. Presynaptic inhibition
  38. 38. RIGIDITY • Rigidity is characterized by an increase in muscle tone causing resistance to external movements. • It is not velocity dependent and can be elicited at very low speeds of passive movement. • It is felt in both agonist and antagonist muscles.
  39. 39. • '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 occurs due to contraction of agonists and antagonists alternately so that increased tone is not felt throughout range of motion but intermittently. • Basal ganglia structures are clearly implicated in pathophysiology of rigidity.
  40. 40. CLONUS • Clonus is the phenomenon of involuntary rhythmic contractions in response to sudden sustained stretch. • A sudden stretch activates muscle spindles, resulting in the 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.
  41. 41. MYOTONIA • It is a state in which muscle contraction continues beyond a period of time. There is delay in relaxation. • Eg. Myotonic dystrophy and myotonia congenita.
  42. 42. HYPOTONIA CENTRAL PERIPHERAL WEAKNESS WEAKNESS<HYPOTONIA WEAKNESS>/=HYPOTONIA (PARALYTIC HYPOTONIA) COGNITION AFFECTED NOT AFFECTED DTR’s BRISK ABSENT DEVELOPMENT DELAY PRESENT NOT PRESENT PULL TO SIT HEAD LAG MARKED HEAD LAG ANTIGRAVITY MOVEMENTS IN PRONE AND SUPINE POSITION SOME ABSENT FACIAL DYSMORPHISM PRESENT ABSENT
  43. 43. • CENTRAL- -Cerebral palsy -HIE -Chromosomal disorders- down’s syndrome, Angelman syndromePrader willi syndrome -Metabolic –aminoacidurias, organic acidurias, Tay sach’s, Niemann pick’s, Zellweger syndrome,hypothyroidism • PERIPHERAL -anterior horn cells- poliomyelitis, SMA -peripheral nerve- neuropathies,GBS, HMSN, -neuromuscular junction- Botulism,myasthenia gravis -muscle-myopathies, myotonic dystrophies -skeletal and connective tissue disorders- marfan’s, ehler danlos,osteogenesis imperfecta.

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