The Stretch Reflex o Exciting a muscle spindle (A)Muscle spindle occurs in two ways a Motor neuron Applying a force that Extrafusal lengthens the entire Y Motor muscle neuron Activating the y motor afferent neurons that stimulate afferent) the distal ends of the intrafusal fibers to Intrafusal contact fibers thus stretching the mid portion of the spindle (internal stretch)
The Stretch Reflex ⚫ Exciting a muscle spindle occurs in two ways – Applying a force that lengthens the entire muscle – Activating the motor neurons that stimulate the distal ends of the intrafusal fibers to contact, ⚫ thus stretching the midportion of the spindle (internal stretch)
The stretch Reflex ● Whatever the Muscle Muscle during stretch during contraction stimulus. when the Muscle spindles are spl Intrafusal activated muscle fiber ● their associated Primary ry (la) sensory neurons nerve fiber transmit impulses Extrafusal at a higher muscle fiber frequency to the Time d (a)Action potential frequency (b)Action potential frequency pinal cord increases during stretch declines during contraction BENJAMIN/CUMMINGS
The Stretch Reflex ⚫ Whatever the stimulus, when the spindles are activated ⚫ their associated sensory neurons transmit impulses at a higher frequency to the spinal cord
(a)A monosynaptic reflex has a single synapse between the afferent and efferent neurons Stimulus Receptor Sensory neuron Spinal cord Integrating Skeletal muscle center Somatic motor neuron arget cell Efferent ne Response effector neuron synapse (b) Polysynaptic reflexes have two or more synapses 补s Spin Stimulus Receptor Sensory cord neuron Integrating center Interneuron Synapse 2 Efferent Response Target cell effector neuron
① Afferent pulses sensory neuron from stretch receptor to Molor neuron serving quadriceps ② Efferent Motor neuron cause muscle group contraction (hamstrings) of the stretched Spinal cord muscle that resistsreverses e stretch Muscle Patella Quadriceps Muscle Patellar inhibit exors) contraction of antagon Excitatory synapse hibition) (a) o The reflexive muscle contraction resists further stretching of the muscle
The Stretch Reflex ⚫ The reflexive muscle contraction resists further stretching of the muscle
Receptor: Muscle travels through sensory neuron spindle stretches and fires center Stimulus; ensor neuron Tap to tendon synapses in stretches muscle spinal cord Efferent path 1: onto Somatic motor neuron Effector 1: Quadriceps Efferent path 2: Interneuron inhibiting somatic motor neuron contracts, swinging lower ea forward Effector 2: Hamstring The patellar tendon(knee jerk) reflex illustrates a monosynaptic stretch reflex and reciprocal inhibition of the antagonistic muscle o Branches of the afferent fibers also synapse with inter neurons that inhibit motor neurons controlling the antagonistic muscles
The Stretch Reflex ⚫ Branches of the afferent fibers also synapse with interneurons that inhibit motor neurons controlling the antagonistic muscles