Chapter 13 Integrative Physiology I Control of Body

Chapter 13 Integrative Physiology I: Control of Body Movement

About this Chapter • • • Neural reflexes Autonomic reflexes Skeletal muscle reflexes The integrated control of body movement Control of movement in visceral muscles

Neural Reflexes Table 13 -1

Somatic Motor Reflexes • Monosynaptic and polysynaptic somatic motor reflexes (a) A monosynaptic reflex has a single synapse between the afferent and efferent neurons. Stimulus Sensory neuron Receptor Spinal cord Integrating center Skeletal muscle Somatic motor neuron Response Target cell effector Efferent neuron One synapse Figure 13 -1 a

Somatic Motor Reflexes (b) Polysynaptic reflexes have two or more synapses. Synapse 1 Stimulus Receptor Spinal cord Integrating center Sensory neuron Interneuron Response Target cell effector Efferent neuron Synapse 2 Figure 13 -1 b

Autonomic Reflexes Some visceral reflexes are spinal reflexes no brain involvement, or brain modulated “bashful bladder” / toilet training / goose pimples Stimulus Receptor Sensory neuron CNS integrating center Preganglionic autonomic neuron Response Postganglionic autonomic neuron Target cell Autonomic ganglion Figure 13 -2

Skeletal Muscle Reflexes • Proprioceptors are located in skeletal muscle, joint capsules, and ligaments • Proprioceptors carry input sensory neurons to CNS • CNS integrates input signal • Somatic motor neurons carry output signal • Alpha motor neurons α • Effectors are contractile skeletal muscle fibers extrafusal muscle fibers

Proprioceptors • Muscle spindle • Response to stretch • Within muscle fibers as intrafusal fibrer • Automonic with gamma motor neurons • Golgi tendon organ • Muscle tension especially during isometric • Relaxation reflex - protective • Joint receptors • Are found in capsules and ligaments around joints

Proprioceptors • Muscle spindles and Golgi tendon organs are sensory receptors in muscle Extrafusal muscle fibers Alpha motor neuron Golgi tendon organ (a) Muscle spindle Tendon Figure 13 -3 a

Proprioceptors Spindle fibers: Sense stretch Gamma motor neurons To CNS Tonically active sensory neurons Central region lacks myofibrils. Gamma motor neurons from CNS Muscle spindle Intrafusal fibers Extrafusal fiber (b) Muscle spindle Figure 13 -3 b

Proprioceptors Extrafusal muscle fibers Afferent neuron Capsule Sensory neuron Collagen fiber Tendon (c) Golgi tendon organ Figure 13 -3 c

Muscle Spindles • Muscle spindles monitor muscle length and prevent overstretching 1 Sensory neuron endings Intrafusal fibers of muscle spindle 3 2 1 Extrafusal muscle fibers at resting length 2 Sensory neuron is tonically active. Sensory neuron 3 Spinal cord integrates function. Alpha motor neuron Spinal cord 4 4 Alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles. 5 (a) Spindles are firing even when muscle is relaxed. 5 Extrafusal fibers maintain a certain level of tension even at rest. Figure 13 -4 a

Muscle Spindles Figure 13 -4 b

Alpha-Gamma Coactivation (a) Alpha-gamma coactivation 1 1 2 1 1 Alpha motor neuron fires and gamma motor neuron fires. 2 3 Muscle shortens Muscle length 2 Muscle contracts. 3 Stretch on centers of intrafusal fibers unchanged. Firing rate of afferent neuron remains constant. Intrafusal fibers do not slacken so firing rate remains constant. Action potentials of spindle sensory neuron Muscle shortens Time Figure 13 -5 a

Without Gamma Motor Neurons (b) 1 1 Alpha motor neuron fires. 3 2 2 Muscle contracts. 4 3 Less stretch on center of intrafusal fibers 4 Firing rate of spindle sensory neuron decreases. Muscle shortens Muscle length Less stretch on Action potential intrafusal fibers Action potentials of spindle sensory neuron Muscle shortens Time Figure 13 -5 b

Muscle Reflexes Help Prevent Damage Muscle spindle reflex Sensory neuron Spindle Spinal cord Add load Motor neuron Muscle (a) Load added to muscle. Figure 13 -6 a

Muscle Reflexes Help Prevent Damage Figure 13 -6 b

GTO’s Figure 13 -7

Movement • • Types of movement Reflex Voluntary Rhythmic

CNS Integrates Movement • Spinal cord integrates spinal reflexes and contains central pattern generators • Brain stem and cerebellum control postural reflexes and hand eye movements • Cerebral cortex and basal ganglia • Voluntary movement

CNS Integrates Movement Table 13 -3

CNS Control of Voluntary Movement Figure 13 -10

CNS Control of Voluntary Movement • Feedforward reflexes and feedback of information during movement Figure 13 -13

Parkinson’s Disease • Progressive neural disorder • Characterized by abnormal movements, speech difficulties, and cognitive changes • Loss of basal ganglia that release dopamine

Visceral Movement • Moves products in hollow organs • Controlled by ANS • Some create own action potentials

Summary • Neural reflexes • Somatic reflexes, autonomic reflexes, spinal reflexes, cranial reflexes, monosynaptic reflex, and polysynaptic reflex • Autonomic reflexes • Skeletal muscle reflexes • Extrafusal muscle fibers, alpha motor neurons, muscle spindles, intrafusal fibers, gamma motor neurons, muscle tone, and stretch reflex

Summary • Skeletal muscle reflexes (continued) • Alpha-gamma coactivation, golgi tendon organs, myotatic unit, reciprocal inhibitions, flexion reflexes, crossed extensor reflex, and central pattern generator • Integrated control • Reflex movement, postural reflexes, voluntary movement, rhythmic movements, corticospinal tract, basal ganglia, and feedforward reflexes • Control of movement in visceral muscles