This document discusses the physiology of reflexes. It defines a reflex as a coordinated involuntary motor response initiated by a stimulus to peripheral receptors. Reflexes are then classified in several ways, including by clinical presentation (superficial, deep, visceral), anatomic components (segmental, intersegmental, suprasegmental), and number of synapses involved (asynaptic, monosynaptic, polysynaptic).
Monosynaptic reflexes are described in more detail. The stretch reflex involves muscle spindles in skeletal muscle sensing stretch and initiating contraction via a single synapse. Other monosynaptic reflexes include the inverse stretch reflex, reciprocal innervation, and clonus. The role of muscle spindles and gamma
12. Others
• Unconditioned reflexes – inborn or inherent
reflexes .
• Conditioned reflexes – acquired reflexes.
Secretion of saliva when food is kept in mouth is
unconditioned reflex and,
secretion even with thought is ‘conditioned’.
15. Stretch reflex
• When a skeletal muscle with intact nerve
supply is stretched, it contracts – stretch reflex.
• Stimulus – stretch
• Response – contraction
• Sense organ – muscle spindle
16.
17. Muscle spindle
• Proprioceptor present in skeletal muscle.
• 6-14 muscle fibers - Intrafusal fibers (IFF) - in a
spindle shaped fibrous sheath.
NBF - nuclear bag fibers
NCF – nuclear chain fibers
18.
19. • Afferents : I a and II fibers
I a - from central part of all fibers (annulospiral ends)
II – only from NCF ( flower spray ends )
• Efferent :
gamma fibers to both NBF and NCF.
alpha motor neurons supply extrafusal fibers
I a and gamma 1 – dynamic response
II and gamma 2 – static response
20.
21. Functions of muscle spindle :
• Maintains length of muscle fibers (EFF) at rest
or activity – gives feed back to higher centers
for comparing with intended movement.
• Monitor velocity of muscle contraction.
22. Gamma efferent discharge
• IFF are not strong enough or not plentiful enough
to cause shortening of muscle.
• It causes shortening thru reflex arc (indirectly) –
shortening of IFF – stretch of NBF and 1a aff -
reflex muscle contraction through alpha fibers .
• If muscle is stretched during the gamma
stimulation, additional AP s are stimulated and
rate of discharge of 1a afferents increases .
23. (gamma motor neurons increases sensitivity of
muscle spindle to stretch)
Normally there is increased gamma discharge in
parallel to alpha. Due to this alpha-gamma
linkage, spindle also shortens along with muscle.
Due to this continues response of spindle
through out muscle contraction , the physiologic
oscillation is reduced and muscle contraction is
smoothened.
24. • Factors influencing gamma discharge –
noxious stimulus of skin
anxiety
Jendrassik’s maneuver : strong simultaneous
motor act causes increased gamma discharges and
thru irradiation influences other levels.
when voluntary act precedes by 0.5 sec, jerk
is inhibited (negative reinforcement)
25. Higher centers also influence muscle tone
through influencing gamma efferents – brain
stem nuclei, cerebellum and motor cortex.
Cortex inhibits gamma neurons and
cerebellum facilitates them.
26.
27. Importance of stretch reflex
• Production of muscle tone – “partially contracted
state of muscle”.
• Maintenance of posture – in erect posture gravity
tends to flex hip/knee - this slight initial flexion
stretches the extensor , causing its contraction
reflexly.
due to this man remains standing.
Mainly in anti-gravity muscles
Non fatigueble
Simple reflex arc (short latency)
28.
29. • DTR are monosynaptic reflexes.
• Electrical analogue for DTR is the HOFFMAN’s
reflex or H – reflex,