Chapter 4

The Nervous System

Key Concepts

• autonomic nervous system

• axon• central nervous

system• crossed extensor

reflex• dendrites• endolymph

• extrafusal muscle fibers (EF)

• extrapyramidal system

• flexion reflex• golgi tendon

organs• internuncial

neuron• intrafusal muscle

fibers (IF)

• kinesthesis• motor cortex• myotatic reflex• neuron• parasympathetic

branch• peripheral nervous

system• premotor cortex• proprioception

• pyramidal system• reciprocal inhibition• righting reflex• somatic nervous

system• spinal reflex• sympathetic branch• vestibular receptors

Review Questions

What part of the nervous system controls the heart, smooth muscle, and glands?

The autonomic nervous system

What part of the nervous system controls muscular activity under voluntary control?

The somatic nervous system

In the following diagram of a neuron, what are A, B, and C?

A.B.C.

DendritesCell BodyAxon

A

B

C

What type of neurons conduct impulses from the periphery to the CNS?

Efferent (sensory) neurons

What type of neurons conduct impulses from the CNS to the muscles?

Afferent (motor) neurons

Describe the spinal reflex.

• Involves a minimum of two neurons

Describe the path of the reflex.• The afferent neuron receives a stimulus

and carries an impulse to the spinal cord where the impulse is transmitted across a synapse to an efferent neuron, which carries the impulse to a muscle or gland.

Describe the myotatic reflex.

• A simple, two-neuron reflex

Give an example.• An example is the knee jerk response.

Describe the path of the reflex.• Stretch of a muscle or its tendon

initiates an impulse that travels in an afferent neuron to the muscle that was originally stretched. The result is the contraction of the muscle.

Describe the flexion reflex.

• A simple reflex involving an internuncial neuron

Give an example.• Moving your hand away from a hot surface is an

example

Describe the path of the reflex.• Sensory nerve endings in hand detect heat and

generate an impulse that travels along the sensory neuron to the spinal cord.

• There it synapses with an internuncial neuron, which acts as an intermediary between the sensory neuron and the motor neuron to the forearm flexor muscle.

• When the impulse arrives at the forearm flexor, your forearm flexes and pulls your hand away.

Reflexes are developed before birth. True or False?

False. Most reflexes are learned responses

that involve higher brain centers.

Describe the two types of receptors involved in proprioception and their function.

• Vestibular receptors in the semicircular canals of the inner ear– Contain crista, which are sensitive to the

movement of endolymph and provide information about rotational deceleration or deceleration of movement

• Vestibular receptors in the utricle– Provide information regarding linear

acceleration and tilting, which helps spatial orientation

Which reflex originates in the muscle spindles?

The stretch (myotatic) reflex

What are two functions of the Golgi tendon organs?

• To prevent damage to a muscle or joint caused by excessive contraction of a muscle

• To respond to muscle contraction by inhibiting further contraction and stimulating the muscle’s antagonist.

Why is it important to avoid bouncing or jerking movements in stretching?

• Such movements cause many spindles to discharge at the same time, initiating the myotatic reflex and causing the muscle to contract.

For the coach or physical educator, what are two important differences between the pyramidal and extrapyramidal systems?

• Electrical stimulation of the pyramidal system (area 4, or motor cortex) produces specific movements, so it is thought that learning a new skill involves this area.

• Stimulation of the extrapyramidal system (area 6, or premotor cortex) produces large, general movement patterns. As skill increases, it is thought that the origin of the movement shifts to this area.

What two roles does the cerebellum play in the proprioceptive-cerebellar system?

• Receives sensory information regarding position, balance, and movement from receptors in muscles, joints, tendons, and skin as well as from visual, auditory, and vestibular organs.

• Modifies muscular activity during movement.

Exercise should be avoided by people with chronic neurological disorders. True or False?

False. Evidence suggests that resistance training may improve strength and

musclefunction in victims of strokes, partial

paralysis,and polio.

Useful Websites

The Autonomic Nervous Systemwww.ndrf.org/ans.htm

Neuronswww.ultranet.com/~jkimball/BiologyPages/N/

Neurons.html

North American Congress on Biomechanics

http://asb-biomech.org/archives/conference98.html

Selected Images

Figure 4.3 The neuron and its components.

Figure 4.4 Diagram of a two-neuron reflex, from a spindle in a muscle back to the muscle fibers of the same muscle.

Figure 4.5 Diagram illustrating how impulses from a cutaneous receptor reach an effector (skeletal muscle) by a three-neuron arc at the level of entrance.

Figure 4.6 Structural relations of innervation of the human labyrinth.

Anterior semicircular canal

Posterior semicircular canal

Lateral semicircular canal

Utricle (otoliths are within the utricle)

Saccule

Cochlea

Auditory nerve

Vestibular nerve

Figure 4.7 Muscle spindle.

Figure 4.8 Golgi tendon organ.

Figure 4.9 The areas of the human cerebral cortex involved in the extrapyramidal system. In the frontal lobe are areas 4, 6, and 8. In the post central region are areas 1, 2, 3, and 5. Down in the temporal lobe, area 22 is concerned in the extrapyramidal pathways.