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I Order Neurons: Are Axons of Post www.examrace.com1 Re www.examrace.com2 rcaiEI'Iｾﾷ＠ ｾｴ＠ www.examrace.com3 Reflex Action • Definition : It is an involuntary response to a peripheral stimulation • Sensory impulse is automatically converted into a motor effect • It forms the functional unit of nervous system • It depends on integrity of reflex arc www.examrace.com4 Reflex Arc Following components • An Afferent from a receptor • Synapse, may be one or many • An Efferent to effector organ www.examrace.com5 Receptors skin -Afferent neuron Efferent neuron Effector (muscle) www.examrace.com6 Classification: A: Clinical classification • Superficial • Deep or Tendon reflexes • Visceral: at least one part of reflex arc is formed by autonomic nerve eg. Pupillary reflex, carotid sinus reflex • Pathological eg. Babinski’s sign www.examrace.com7 B: Anatomical cl. • Segmental Reflexes: end of afferent & beginning of efferent neuron are in the same seg. of spinal cord • Intersegmental Reflex : here the end & beginning are in different seg. • Suprasegmental Reflex: centre for such reflex lies above the spinal cord www.examrace.com8 C: Inborn or Acquired • Conditioned or Acquired: are acquired after learning or training eg. Reflex salivation • Unconditioned or Inborn: present since birth eg. Salivation when an object is placed in mouth. www.examrace.com9 D: depending upon no. of Synapses • Monosynaptic • Bisynaptic • Polysynaptic E : physiological classification • Flexor reflex • Extensor re. www.examrace.com10 Monosynaptic Reflex Stretch Reflex or Myotatic Reflex Reflex Arc • Stimulus—Stretch to muscle • Receptor– Muscle spindle (gpIa & II fib) • Central conn.—On alpha motor neuron • Response—Contraction of same muscle • Central delay— 0.5 ms. ( one synapse) www.examrace.com11 Afferent Muscle nerve ceptor Motor neuron www.examrace.com12 Structure of receptor • Muscles have two types of fibers • Extrafusal fib.----contractile fib. • Intrafusal fib.----form muscle spindle Muscle spindles: Receptors • Intrafusal fib. are more embryonal • Muscle Spindles are parallel to extrafusal fib. www.examrace.com13 …. • Only ends of the intrafusal fibers are contractile • 2 to 12 intrafusal fib. are enclosed in a connective tissue capsule www.examrace.com14 m.tflbtra a www.examrace.com15 Efferent Fib. Afferent Nerve . Primary Aff Gp. I a Secondary Aff. Gp. II Plate E. www.examrace.com16 Axon of Axonsof a motor Extrafusal r motor Group I and TI neuron muscle fibers afferent axons Intrafusal Nuclear Subcapsular Nuclear Capsule musde fibers chain fiber space bag fiber surrounding spindle www.examrace.com17 Characteristic features • Do not under go rapid adaptation • Do not spread to other muscles • Examples: biceps, triceps, knee jerk • Best developed in antigravity muscles • Chief mechanism for the production of muscle tone & Posture regulation • Neurotramsmitter----Glutamate www.examrace.com18 M.S.-- Have two types of fib. • Nuclear bag fib. • Nuclear chain fib. www.examrace.com19 Innervation Sensory / Afferent • Group Ia fibers form Annulospiral or primary sensory endings • Carry sensation from nuclear bag & nuclear chain fib. • Diameter about 17 microns • Conduction Velocity 70 to 120 m/sec www.examrace.com20 … • Gr.II fib. Also called flower spray or sec. endings • Carry sensation mainly from nuclear chain fib. • Diameter about 8 microns • Conduction velocity app. 30 to 70 m/sec www.examrace.com21 Motor supply • Gamma –D (dynamic) • Supply striated poles of nuclear bag fib. • Control the dynamic response • Gamma –S (static) • Supply the striated poles of nuclear chain fib. • Control the static response www.examrace.com22 Mech. of stimulation M. spindle can be stimulated by • Stretching the entire muscle • Stimulating the Gamma motor neuron www.examrace.com23 Dynamic versus static reflex Dynamic reflex • The primary nerve endings supplying the nuclear bag fibers discharge most rapidly while the muscle is being stretched • It causes instantaneous strong contraction of the same muscle www.examrace.com24 ….. • Contraction is over with in fraction of second • As soon the muscle contracts stimulation is lost & discharge decreases • Eg. Various jerks www.examrace.com25 ….. Static Response: • If the muscle is stretched slowly & kept stretched, signals are sent continuously through primary & secondary nerve endings supplying the nuclear chain fibers • Muscle contracts, as long it is stretched • Important in Antigravity muscles. www.examrace.com26 α-γ Co-activations • During voluntary muscle contraction there is increased discharge along with the increased α discharge and movement goes on smoothly & continuously • It is also called Follow up Servo Mechanism www.examrace.com27 Functions: • Maintenance of tone • Regulation of posture • Control of voluntary mov. www.examrace.com28 Muscle Tone • Definition: is tension present in resting muscles due to low frequency & asynchronous discharge of Gamma M.N. • It is a state of partial tetanus or partial muscle contraction • Hypotonia : tone is less, muscle becomes flaccid • Hypertonia : an increase in tone www.examrace.com29 Hypotonia : Causes • Destruction of reflex arc • Damage to efferent fib. Eg. Injury or polio. • Destruction of dorsal column eg.Tabes dorsalis • Stimulation of inhibitory area • Destruction of facilitatory area • Drugs. Barbiturates, tranquilizers • Sleep www.examrace.com30 Hypertonia : Causes • Stimulation of facilitatory areas • Destruction of inhibitory area Whenever Gamma M.N. discharge is more tone increases • UMN lesions produce Spasticity • Pathology of Basal Ganglia produces Rigidity www.examrace.com31 Imp. terms • Spasticity: hypertonia is confined to one group of muscle, either agonist or antagonist eg. Upper Motor Neuron Lesion (UMNL) • Spastic mus. show • Clasp – knife type of hypertonia • Lengthening reaction present eg. Clonus www.examrace.com32 Lengthening Reaction • Seen when tone is high • Also called clasp knife effect (because it resembles closing of pocket knife) and the muscle is spastic muscle • Is due to operation of stretch reflex and inverse stretch reflex. www.examrace.com33 www.examrace.com34 Clonus • Is characterized by repetitive muscular contractions produced if foot is dorsiflexed suddenly & pressure is maintained to keep the foot dorsiflexed • It is also due to operation of stretch reflex & inverse stretch reflex eg. Ankle clonus www.examrace.com35 Rigidity • Tone increases in both groups of muscles i.e. agonist & antagonist • Lesions of basal Basal Ganglia leads to it. • Hypertonia is described as • Lead-pipe Rigidity • Cog-Wheel Rigidity www.examrace.com36 Bi synaptic Reflex Two examples • Reciprocal Innervation: when agonist muscles contract & antagonist muscles are relaxed • Inverse Stretch Reflex: mediated by Golgi Tendon Organ www.examrace.com37 Reciprocal Innervation www.examrace.com38 Inverse Stretch Reflex /Golgi Tendon Reflex Operates as follows: • Stimulus—hard stretching of muscle beyond certain point • Receptor—Golgi Tendon Organ • Central connection--- in spinal cord on inhibitory interneuron which terminates on the concerned motor neuron • Response—relaxation of muscle www.examrace.com39 Structure of GTO or Neurotendinous organ • Present at musculotendon junction • They are in series with the muscles • There are 3 to 25 muscle fibers per tendon organ www.examrace.com40 …. Functions : • Regulates tension during normal muscle activity • Results in autogenic inhibition • Protective Reflex: Prevents tearing of muscles. A very strong contraction can be damaging www.examrace.com41 www.examrace.com42 Group Ib fibers Tendon Muscle www.examrace.com43 ---Bone ｾｾＭＭ Golgi tendon organ lb afferent Inhibitory interneuron Alpha motor neuron www.examrace.com44 Poly synaptic Reflex / Flexor Reflex Withdrawal Reflex or Crossed Extensor Reflex Definition: Is a protective reflex.It is prepotent & immediate attention is paid blocking all other activities • Stimulus—Nociceptive (pain) • Receptors—Free nerve endings www.examrace.com45 ….. • Central Pathway:In spinal cord fibers synapse on many interneurons • Convey information to CNS • Form several reflex pathways • Irradiation of the stimulus up and down if stimulus is strong • Form reverberating circuits responsible for after discharge • Effector organ —skeletal muscles www.examrace.com46 neuron www.examrace.com47 … • Response—Various types (depends on strength of stimulus) • 1. Local sign (one limb response) • The stimulated limb is withdrawn • 2. Crossed Extensor Response (two limb response) • Ipsilateral limb—flexion & withdrawal • Opposite limb—extension www.examrace.com48 Stimulus • • t ••••••• ...... Skin \ I ｜ｾ＠ Extensor (+) Flexor Inhibitory (+) interneurons Flexor Extensor (-) (-) (A) Ipsilateral limb (B) Contralateral limb (Flexor reflex) · (Extensor reflex) www.examrace.com49 ……. • 3. Shifting Reaction— 4 limb response (seen in spinal animal only) • Ipsilateral hind limb-----Flexion • Contralateral hind limb—Extension • Ipsilateral fore limb-------Extension • Contralateral fore limb---Flexion • 4. Widespread Withdrawal– If stimulus is very strong whole body moves away. www.examrace.com50 Properties of Reflex Action • Adequate stimulus • Delay • Summation: spatial & temporal • Occlusion • Subliminal fringe • Irradiation • Final common pathway • Facilitation www.examrace.com51 …. • Inhibition • After discharge • Fatigue • Fractionation • Habituation & sensitization www.examrace.com52 b=3 a=3 a+b- 12 (B) : Subliminal fringe www.examrace.com53 Lateral corticospinal tract Rubrospinal tract Muscle Anterior corticospinal tract Reticulospinal tract
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