motor system dr. zahoor ali shaikh. transvers section of spinal cord
TRANSCRIPT
MOTOR SYSTEM
Dr. Zahoor Ali Shaikh
TRANSVERS SECTION OF SPINAL CORD
MOTOR UNIT
Types of motor neuron
• α – motor neuron
• γ - motor neuron
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)
MUSCLE SPINDLE (INTRAFUSAL FIBERS)
MUSCLE EXTRAFUSAL FIBERS
MUSCLE INTRAFUSAL FIBERS
Muscle spindle
• Nuclear bag fiber
• Nuclear chain fiber
Sensory innervations of muscle spindle
• Ia – nuclear bag & nuclear chain fibers
• II – nuclear chain fibers
Motor supply – γ motor neuron
Dynamic & Static
Reflex
• Definition
• Components of reflex arcReceptorAfferent pathwayCenterEfferent pathwayEffector organ
Components of reflex arc
Classification of reflexes• Monosynaptic or stretch reflex or tendon jerk
eg. Bicep jerk tricep jerk, supinator jerk
knee jerk, ankle jerk• Polysynaptic reflex
eg. Withdrawal reflex
Abdominal reflex
Plantar reflex• Visceral reflex
eg. Micturation, defecation reflex
Jendressik Phenomenon
KNEE JERK – MONOSYNAPTIC REFLEX
POLYSYNAPTIC REFLEX
WITDRAWEL REFLEX - POLYSYNAPTIC REFLEX
DIFFERENT REFLEXES SHOWN
• Motor cortex
• corticospinal (pyramidal tract)
• Upper motor neuron (pyramidal & extrapyramidal tracts)
• Lower motor neuron
• Difference between upper & lower motor neuron lesion (UMNL & LMNL)
MOTOR TRACTSMOTOR TRACTS
DIFFERENCE BETWEEN UPPER & LOWER MOTOR NEURON LESION
UMN LESIONUMN LESION
• Paralysis affect movement rather than muscles
• Muscle wasting is only from disuse, therefore slight. Occasionally marked in chronic severe lesions.
• Spasticity of clasp-knife’ type. Muscles hypertonic.
LMN LESIONLMN LESION
• Individual muscle or group of muscles are affected.
• Wasting pronounced.
• Flaccidity. Muscles hypotonic.
• Tendon reflexes increased. Clonus often present.
• Superficial reflexes diminished or modified.
Abdominal reflex absent.
Babinski’s sign +ve, Increased jaw jerk.
• Tendon reflexes diminished or absent.
• Superficial reflexes often unaltered.