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Lecture - 2 Dr. Zahoor Ali Shaikh. SPINAL CORD REFLEXES. Spinal Reflex. What is Reflex? -- It is a response that occurs automatically without conscious effort. . Reflex . Components of reflex arc are Five: 1- Sensory Receptor 2- Afferent pathway 3- Center 4- Efferent pathway
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Lecture - 2 Dr. Zahoor Ali Shaikh SPINAL CORD REFLEXES
Spinal Reflex • What is Reflex? -- It is a response that occurs automatically without conscious effort.
Reflex Components of reflex arc are Five: 1- Sensory Receptor 2- Afferent pathway 3- Center 4- Efferent pathway 5- Effector organ
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
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)
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
Stretch Reflex [monosynaptic] • Sudden stretch to a muscle leads to contraction of that muscle is known as stretch reflex.
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)
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
Types of motor neuron • α – motor neuron (supply Extrafusal fibers ) • γ - motor neuron (supply Intrafusal fibers)
Patellar Tendon Reflex KNEE JERK – MONOSYNAPTIC REFLEX
Polysynaptic Reflex • In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway • We will study withdrawal reflex
POLYSYNAPTIC REFLEXES Withdrawal 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).
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.
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
DIFFERENT REFLEXES SHOWN JendressikPhenomenon (Reinforcement)
Jendressik Phenomenon (Reinforcement) Superficial Reflexes
Dermatomes of Spinal roots and divisions of trigeminal nerve (V1 ,V2, V3)
Cranial Nerve Spinal Cord Reflexes
Other Reflexes • 1- Golgi tendon Reflex • 2- Crossed Extensor Reflex We will discuss first Golgi endon Reflex
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
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.
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.