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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.
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• 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
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• 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
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• Contraction is over with in fraction of second • As soon the muscle contracts stimulation is lost & discharge decreases • Eg. Various jerks
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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
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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
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• 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
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• 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)
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• 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
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• 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 Tectospinal tract
www.examrace.com54 Functions subserved at spinal level
Neuronal circuits in spinal cord can cause (Spinal Animal) • Withdrawal reflex—to take part of body away from the damaging object • +ve supporting reaction to support the body against gravity • Stepping and Walking movements Mark Time Reflex
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• Galloping Reflex • Reflexes that control local blood vessels • Micturition Reflex
www.examrace.com56 www.examrace.com57 Somato sensory system
Includes • Receptors • Pathway (tracts): A bundle of nerve fibers in spinal cord or brain that makes an Anatomical & Functional unit • Role of thalamus • Role of cerebral cortex
www.examrace.com58 Tracts in the spinal cord
Two types • Ascending Tracts • Descending tracts Ascending tracts / Sensory Tract • Tracts of post. or dorsal column • Fasciculus Gracilis • Fasciculus Cuneatus
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• In Lateral Column • Lateral Spinothalamic Tract • Dorsal (posterior) Spinocerebellar Tract • Ventral (Anterior) Spinocerebellar Tract • In Ventral (ant.) column • Anterior (ventral) spinothalamic Tract
www.examrace.com60 Sensation carried by various Tracts
Fasciculus gracilis & F. Cuneatus Fine touch, Tactile Localization & 2 point discrimination Pressure Vibration, stereognosis Sense of position & sense of movement • Ant. Spinothalamic Tract: Tactile sensation & Crude touch • Lateral SpinothalamicTract : Pain Temperature
www.examrace.com61 • All Sensory….. fibers enter through Dorsal Nerve Root Dorsal root divides into two parts • Medial part contains • Proprioceptive fibers from muscles • Sensory fib. conveying touch, pressure & vibration sense • Lateral part • Slow Pain & Fast Pain • Temperature • Visceral Pain
www.examrace.com62 www.examrace.com63 Post. Column Tracts: tracts of Gall & Burdach/ Medial lemniscal pathway
• I order neurons: are axons of post. Root ganglia they enter in dorsal column. Here they have definite arrangement of fib. • Fasciculus Gracilis-- is located medially and fib. are from sacral & lumbar region arranged from medial to lateral side • Fasciculus cuneatus—is lateral & fibers are from thoracic and cervical region • Fib. ascend up to medulla
www.examrace.com64 ,____ Fasciculus gracillis
,__ Fasciculus cuneatu
www.examrace.com65 II order neuron
• I order neurons end in Nucleus Gracilis & Cuneatus • II order neurons begin from here • They cross to opposite side (sensory decussation) • Ascend up through medulla, pons & mid brain as medial lemniscal fibers • Terminate in Ventro Post. Lateral nucleus of thalamus
www.examrace.com66 III order neuron
• Begins from VPL of thalamus • Fibers pass through Internal capsule & Corona radiata • End in Somato Sensory area of cerebral cortex Sensory tracts have total three neurons
www.examrace.com67 ICEREBRUM I
I MID BRAIN I
Nucleus gracilis
Nucleus cuneatus MEDULLA
ｫＧＭｶｯＢＢＢＡ｡ＮｾＮＺＭＭ Ｍ ＭＭＭ Fasciculus gracilis ...... !,idii!Jii;pqf ｟ＬＮﾥＭ ｾＭＫＭＴＭＭＭＭ Fasciculus cuneatus
Discriminative touch, proprioceptive, pressure SPINAL CORD www.examrace.com68 or vibration receptors I I Ant./ Ventral Spinothalamic Tract
• I order neurons are central processes of dorsal root ganglia • Fibers end on the cells situated in the medial part of dorsal horn (I relay station) from here II order neurons arise
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• II order neurons cross in ant. white commissure to opposite side of same segment • Few fibers are uncrossed • Fibers ascend up to end in VPL nucleus of thalamus • III order neurons end in somato sensory area
www.examrace.com70 ----Internal capsule------
ｾＭＭＭ Third-order neuron ----
Ventroposterior nucleus of thalamu_s____ _
I CEREBRUM I
MID BRAIN
MEDULLA
Anterior Anterior white column mic tract spinothalamic tract www.examrace.com71 Lateral Spinothalamic Tract
• I Order neurons: begin from axons of post. Root ganglia the fibers ascend or descend for one or two segments in Tract of Lissauer. • A fibers terminate mainly on neurons in lamina I of spinal cord • Type C fibers on neurons in lamina II & III
www.examrace.com72 LT
-
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• II Order neurons– some neurons before crossing run up & down for few seg. • Majority of neurons cross in white commisure, obliquely to opposite side • They ascend in Lateral Spinothalamic Tr • Fibers end in the Thalamus (Ventro posterior lateral Nucleus)
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.. Lateral spinothalamic tract --- (convey pain and temperature) www.examrace.com76 ….
• III Order Neurons: Starts from Thalamus • Fibers pass from Post. Limb of Internal Capsule • End in Sensory Cortex (postcentral gyrus)
www.examrace.com77 VVI I U..l"V--• •--•, --• ._,, (postcentral gyrus) ......
,---- - Internal capsule-
'----Third-order neuron -
Ventroposterior nucleus of thalamus
ICEREBRUM I
I MID BRAIN I
Second-order neuron ------
MEDULLA
First-or< neuron
www.examrace.com78 Neospinothalamic Tract
• Fibers are type A , Fast Pain • In Brain Stem--- • Most fibers to Thalamus • Few terminate in Reticular formation • thalamus—Fibers end in ventro postero lateral nucleus • Cerebral cortex-somatosensory area
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• Functions: fast pain appears within 0.1 ms. after the application of stimulus • Well localized (simultaneous stimulation of touch receptors help) • Meaningful interpretation • Elicits withdrawal Reflex • Produces Symp. Response like ↑BP, tachycardia etc.
www.examrace.com80 Paleospinothalamic tract
• Fibers are type C • Brain stem • Mainly in Reticular Formation • Tectal area • Periaqueductal Grey • Thalamus • Intralaminar Nuclei
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• Cerebral Cortex– All parts of brain • Some fibers go to Hypothalamus also Functions: • Slow pain begins a second or more after the application of stimulus but it increases slowly and lasts for a longer time
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• Difficulty in sleeping • Activating or alerting response • Emotional disturbances make pain unbearable , intense unpleasantness • Associated with nausea, vomiting, lowering of BP.
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