Chapter 13 Integrative Physiology I Control of Body Movement 2013 Pearson Education Inc About This Chapter Neural reflexes Autonomic reflexes Skeletal muscle reflexes The integrated control of body movement Control of movement in visceral muscles 2013 Pearson Education Inc Table 13 1 Classification of Neural Reflexes Figure 13 1a ESSENTIALS Neural Reflexes A monosynaptic reflex has a single synapse between the afferent and efferent neurons Stimulus Receptor Sensory neuron Skeletal muscle Somatic motor neuron Response Target cell Efferent neuron Spinal cord integrating center One synapse Figure 13 1b ESSENTIALS Neural Reflexes Polysynaptic reflexes have two or more synapses This somatic motor reflex has both synapses in the CNS Stimulus Receptor Sensory neuron Synapse 1 Spinal cord center integrating Interneuron Response Target cell Efferent neuron Synapse 2 Figure 13 1c ESSENTIALS Neural Reflexes AUTONOMIC REFLEXES All autonomic reflexes are polysynaptic with at least one synapse in the CNS and another in the autonomic ganglion Stimulus Receptor Sensory neuron CNS integrating center Preganglionic autonomic neuron Response Postganglionic autonomic neuron Target cell Autonomic ganglion Skeletal Muscle Reflexes Proprioceptors are located in skeletal muscle joint capsules and ligaments Input signals from proprioceptors go to the CNS through sensory neurons CNS integrates input signal Somatic motor neurons carry output signal Alpha motor neurons Effectors are contractile skeletal muscle fibers or extrafusal muscle fibers 2013 Pearson Education Inc Proprioceptors Muscle spindle In skeletal muscles Golgi tendon organ In skeletal muscles Joint receptors In capsules and ligaments around joints 2013 Pearson Education Inc Figure 13 2a 2013 Pearson Education Inc Figure 13 2a 2013 Pearson Education Inc Figure 13 3a 1 of 2 Spindles are tonically active and firing even when muscle is relaxed Sensory neuron endings Intrafusal fibers of muscle spindle Sensory neuron Alpha motor neuron Spinal cord Extrafusal muscle fibers at resting length Sensory neuron is tonically active Spinal cord integrates function Alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles Extrafusal fibers maintain a certain level of tension even at rest Figure 13 3a 1 of 2 Slide 1 Extrafusal muscle fibers at resting length Spinal cord Sensory neuron endings Intrafusal fibers of muscle spindle 2013 Pearson Education Inc Figure 13 3a 1 of 2 Slide 2 Sensory neuron endings Intrafusal fibers of muscle spindle Sensory neuron Spinal cord Extrafusal muscle fibers at resting length Sensory neuron is tonically active 2013 Pearson Education Inc Figure 13 3a 1 of 2 Slide 3 Sensory neuron endings Intrafusal fibers of muscle spindle Sensory neuron Spinal cord Extrafusal muscle fibers at resting length Sensory neuron is tonically active Spinal cord integrates function 2013 Pearson Education Inc Figure 13 3a 1 of 2 Slide 4 Sensory neuron endings Intrafusal fibers of muscle spindle Sensory neuron Alpha motor neuron Spinal cord Extrafusal muscle fibers at resting length Sensory neuron is tonically active Spinal cord integrates function Alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles 2013 Pearson Education Inc Figure 13 3a 1 of 2 Slide 5 Sensory neuron endings Intrafusal fibers of muscle spindle Sensory neuron Alpha motor neuron Spinal cord Extrafusal muscle fibers at resting length Sensory neuron is tonically active Spinal cord integrates function Alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles Extrafusal fibers maintain a certain level of tension even at rest 2013 Pearson Education Inc Figure 13 3b 2 of 2 Muscle stretch can trigger a stretch reflex When muscles stretch and lengthen muscle spindle sensory afferent neurons fire more The reflex response is muscle contraction to prevent damage from over stretching 1 Muscle stretch afferent signals Increased to spinal cord Spinal cord efferent output alpha motor Increased through neurons Muscle contracts Time Muscle length Action potentials in spindle sensory neuron Muscle is stretched 2 Firing rate of afferent sensory neuron decreases Negative feedback Muscle returns to initial length Figure 13 4b 2 of 2 Without gamma motor neurons muscle contraction causes the spindle firing rate to decrease Alpha motor neuron fires Muscle contracts Less stretch on center of intrafusal fibers Firing rate of spindle sensory neuron decreases Muscle shortens Muscle length Less stretch on intrafusal fibers Action potential Action potentials of spindle sensory neuron Muscle shortens Time Figure 13 4a 1 of 2 Alpha gamma coactivation maintains spindle function when muscle contracts Alpha motor neuron fires and gamma motor neuron fires Muscle and intrafusal fibers both contract Stretch on centers of intrafusal fibers unchanged Firing rate of afferent neuron remains constant Muscle shortens Muscle length Intrafusal fibers do not slacken so firing rate remains constant Action potentials of spindle sensory neuron Muscle shortens Time Figure 13 5a 2 of 7 Sensory neuron Spindle Motor neuron Muscle Spinal cord Add load Load added to muscle Figure 13 5b 3 of 7 Muscle and muscle spindle stretch as arm extends Figure 13 5c 4 of 7 Reflex contraction initiated by muscle spindle restores arm position Figure 13 2b 2 of 2 Figure 13 5d 6 of 7 Inhibiting interneuron Muscle contracts Motor neuron Golgi tendon organ Muscle contraction stretches Golgi tendon organ Figure 13 5e 7 of 7 If excessive load is placed on muscle Golgi tendon reflex causes relaxation thus protecting muscle Neuron from Golgi tendon organ fires Motor neuron is inhibited Muscle relaxes Load is dropped Figure 13 6 THE PATELLAR TENDON KNEE JERK REFLEX The patellar tendon knee jerk reflex illustrates a monosynaptic stretch reflex and reciprocal inhibition of the antagonistic muscle Afferent path Action potential travels through sensory neuron Receptor Muscle spindle stretches and fires Integrating center Sensory neuron synapses in spinal cord Stimulus Tap to tendon stretches muscle Response Quadriceps contracts swinging lower leg forward Efferent path 1 Somatic motor neuron onto Effector 1 Quadriceps muscle Efferent path 2 Interneuron inhibiting somatic motor neuron Effector 2 Hamstring muscle Response Hamstring stays relaxed allowing extension of leg reciprocal inhibition Figure 13 7 THE CROSSED EXTENSOR REFLEX A flexion reflex in one limb causes extension in the opposite