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

Figure 13-1a

StimulusSensoryneuron

Receptor

Efferentneuron

Target celleffectorResponse

(a) A monosynaptic reflex has a single synapse between the afferent and efferent neurons.

Spinalcord

Integrating center

Onesynapse

Somaticmotor neuron

Skeletal muscle

Somatic Motor Reflexes

Figure 13-1b

Response

StimulusSensoryneuron

Efferentneuron

Interneuron

(b) Polysynaptic reflexes have two or more synapses.

Target celleffector

Spinalcord

Integrating center

Receptor

Synapse 1

Synapse 2

Postganglionicautonomic

neuron

Preganglionicautonomic

neuron

CNSintegrating

center

SensoryneuronReceptorStimulus

Response

Targetcell

Autonomicganglion

Autonomic ReflexesSome visceral reflexes are spinal reflexes

no brain involvement, or brain modulated

“bashful bladder” / toilet training / goose pimples

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

Figure 13-3a

Musclespindle

Extrafusal muscle fibers

Tendon

Alpha motorneuron

Golgi tendon organ

(a)

Proprioceptors

Figure 13-3b

Musclespindle

Extrafusal fiber

Intrafusal fibers

Central regionlacks myofibrils.

Gamma motor neurons

Tonically active sensoryneurons

Gamma motor neuronsfrom CNS

(b) Muscle spindle

To CNSSpindle fibers: Sense stretch

Proprioceptors

Figure 13-3c

(c) Golgi tendon organ

Extrafusalmuscle fibers

Sensory neuron

Collagenfiber

Capsule

Tendon

Afferent neuron

Muscle Spindles

• Muscle spindles monitor muscle length and prevent overstretching

Figure 13-4a

Sensory neuronendings

Intrafusal fibersof muscle spindle

(a) Spindles are firing even when muscle is relaxed.

Spinal cord

Sensoryneuron

Alpha motorneuron

Extrafusal musclefibers at resting length

Sensory neuron is tonically active.

Spinal cord integrates function.

Alpha motor neurons toextrafusal fibers receive tonicinput from muscle spindles.

Extrafusal fibers maintain a certainlevel of tension even at rest.

1

2

3

4

5

1

2

3

4

5

Muscle Spindles

Figure 13-4b

Alpha-Gamma Coactivation

Figure 13-5a

1

1

1

2

2

3

(a) Alpha-gamma coactivation

Musclelength

Muscle shortens

Intrafusal fibers do not slacken sofiring rate remains constant.

Muscle shortens

Action potentialsof spindle

sensory neuron

Time

Alpha motor neuron firesand gamma motor neuronfires.

Muscle contracts.

Stretch on centers ofintrafusal fibers unchanged.Firing rate of afferentneuron remains constant.

1

2

3

Without Gamma Motor Neurons

Figure 13-5b

1

2

3

4

1

2

3

4

(b)

Muscle shortens

Action potential

Muscle shortens

Time

Alpha motor neuron fires.

Less stretch on centerof intrafusal fibers

Firing rate of spindlesensory neuron decreases.

Muscle contracts.

Less stretch onintrafusal fibers

Musclelength

Action potentialsof spindle

sensory neuron

Muscle Reflexes Help Prevent Damage

Figure 13-6a

Sensory neuron

Spindle Spinalcord

Motor neuron Add load

Muscle

(a) Load added to muscle.

Muscle spindle reflex

Muscle Reflexes Help Prevent Damage

Figure 13-6b

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 and 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