Ch 13: The Peripheral Nervous System and Reflex Activity

Most central nervous system axons are able to regenerate following injury.

False Unlike axons of peripheral nerves, axons of CNS (brain and spinal cord) neurons do not regenerate following injury. Thus, damage to the brain or spinal cord is typically considered irreversible.

Which of the following is FALSE regarding the sciatic nerve?

The sciatic nerve is a single nerve.

All spinal nerves are mixed nerves.

True

Most nerves are able to transmit impulses both to and from the central nervous system.

True

Proprioceptors advise the brain of __________.

body movements Proprioceptors advise the brain of our body movements by monitoring how much the organs containing these receptors (skeletal muscles, tendons, joints, and ligaments and in connective tissue coverings of bones and muscles) are stretched.

Which of the following structures is NOT a part of the peripheral nervous system (PNS)?

brain The PNS includes all neural structures outside of the brain and spinal cord—that is, the sensory receptors, peripheral nerves and their associated ganglia, and efferent motor endings.

Match the following sensory receptors to the stimuli they detect.

1) Mechanoreceptors - C) stretch 2) Thermoreceptors - A) temperature 3) Photoreceptors - D) light energy 4) Chemoreceptors - B) chemicals in solution 5) Nociceptors - E) pain

If the phrenic nerve were severed, what would be the most immediate effect?

Breathing would stop. The phrenic nerve serves the diaphragm. If this nerve is irritated, then hiccups result. If this nerve is crushed or damaged, the diaphragm becomes paralyzed and independent breathing ceases.

Which of the following statements about cranial nerves is FALSE?

The cranial nerves are limited to the head and neck region. The vagus nerves (X) innervate structures in the thorax and abdomen.

Choose the true statement.

The flexor reflex is initiated by painful stimuli. The knee jerk reflex is an example of a stretch reflex. Stretch reflexes are important for maintaining muscle tone and adjusting it reflexively. The flexor (or withdrawal) reflex is initiated by a painful stimulus. Muscles and tendons are protected from tearing in response to potentially damaging stretch forces by the tendon reflex. Tendon reflexes also help to ensure smooth onset and termination of muscle contractions. Superficial reflexes are elicited by gentle cutaneous stimulation. The plantar and abdominal reflexes are examples of superficial reflexes.

The first two pairs of cranial nerves attach to the __________.

forebrain The first two pairs of cranial nerves attach to the forebrain. The other 10 pairs of cranial nerves are associated with the brain stem.

Which of the following have nonencapsulated (free) nerve endings?

hair follicle receptors Hair follicle receptors, free nerve endings of sensory neurons, and tactile (Merkel) discs have nonencapsulated (free) nerve endings. All of the other receptors listed have encapsulated nerve endings.

Simple receptors that are particularly abundant in epithelia and connective tissue tend to __________.

have nonencapsulated (free) nerve endings Based on overall receptor structure, there are simple and complex receptors. The complex receptors are sense organs. The simple receptors are more abundant, and can have encapsulated or nonencapsulated (free) nerve endings. Those with nonencapsulated (free) nerve endings are especially prevalent in epithelia and connective tissue.

The pinching motion (with opposed thumb and forefinger) is highly dependent upon impulses transmitted by the __________.

median nerve The pinching motion that is important for picking up small objects is highly dependent upon the median nerve. The median nerve descends through the arm to the anterior forearm. It then branches off to innervate the skin and flexor muscles of this region. On reaching the hand, the median nerve innervates five intrinsic muscles of the lateral palm. In carpal tunnel syndrome, the median nerve is compressed, making it painful and difficult to make a pinching motion.

The final level of neural integration in the somatosensory system is the __________ level.

perceptual

Fast-adapting receptors are called __________.

phasic receptors Many sensory receptors exhibit adaptation. Adaptation is a change in sensitivity (and nerve impulse generation) in response to a constant stimulus. Phasic receptors are fast-adapting receptors. Tonic receptors provide a sustained response with little or no adaptation. Nociceptors and most proprioceptors are tonic receptors because of the protective nature of the information they convey.

Which of the following structures is involved in the projection level of motor control?

primary motor cortex

The lowest level of motor control is the __________.

segmental level The hierarchy of motor control from lowest to highest level of control is: segmental level, projection level, and precommand level.

In a reflex arc, the __________ transmits afferent impulses to the central nervous system.

sensory neuron

A nerve that carries autonomic signals away from the central nervous system is classified as a __________.

visceral efferent Visceral refers to autonomic nervous system fibers. Afferent (sensory) means toward the CNS, while efferent (motor) means away from the CNS. Thus, a nerve that carries autonomic signals away from the CNS is classified as a visceral efferent nerve.