AP 2 2.3: Cranial Nerves

Question 1

peripheral nervous system

Answer 1

As a review, the peripheral nervous system lies outside the central nervous system. The peripheral nervous system is made up of nerves, which are part of either the somatic system or autonomic system.

Question 2

somatic nervous system

peripheral nervous system

Answer 2

The somatic nervous system contains nerves that control skeletal muscles, skin, and joints. The somatic nervous system includes all nerves that serve the musculoskeletal system and exterior sense organs, including the skin. Exterior sense organs, including sense organs embedded in the skin, are receptors

Question 3

Receptors

peripheral nervous system

Answer 3

Receptors receive environmental stimuli, and then initiate nerve impulses towards the central nervous system

Question 4

effectors

peripheral nervous system

Answer 4

Muscle fibers and glands are effectors, which bring about a reaction to the stimulus in the peripheral nervous system.

Question 5

autonomic system contains

peripheral nervous system

Answer 5

The autonomic system contains nerves that control the smooth muscles of the internal organs and glands.

Question 6

visceral motor

peripheral nervous system

Answer 6

The nerves in the autonomic system are called visceral motor when they control smooth muscles or involuntary functions.

Question 7

Cranial Nerves

Answer 7

Humans have twelve pairs of cranial nerves attached to the brain (Figure 2.22). Cranial nerves are either sensory nerves (having long dendrites of sensory neurons only), motor nerves (having long axons of motor neurons only), or mixed nerves (having both long dendrites and long axons). Cranial nerves are abbreviated with the prefix CN, followed by a number.

Question 8

sensory nerves

Cranial Nerves

Answer 8

Cranial nerves are either sensory nerves (having long dendrites of sensory neurons only),

Question 9

motor nerves

Cranial Nerves

Answer 9

Cranial nerves are either, motor nerves (having long axons of motor neurons only)

Question 10

mixed nerves

Cranial Nerves

Answer 10

mixed nerves (having both long dendrites and long axons)

Question 11

Cranial nerves are abbreviated

Cranial Nerves

Answer 11

Cranial nerves are abbreviated with the prefix CN, followed by a number. The number corresponds to their location in relation to their position on brainstem. Except for the vagus nerve, all cranial nerves control the head, neck, and face. The vagus nerve controls the internal organs. Cranial nerves can also be categorized based on the type of sensory information they are carrying.

Question 12

Special sensory

Answer 12

Special sensory nerves carry information responsible for sight, smell, hearing, or balance.

Question 13

optic (CN II)

Answer 13

The second cranial nerve is the optic (CN II). See Figure 2.24 to see the nerve inside the brain. It is a special sensory nerve responsible for the sense of sight. The optic nerve originates in the retinas of each eye and cross at the optic chiasm and synapse in the thalamus. The neurons then connect to send information to the visual cortex of the occipital lobe.

Question 14

olfactory (CN I)

Answer 14

The first cranial nerve is the olfactory (CN I). See Figure 2.23 to see the nerve inside the brain. It is a special sensory nerve responsible for the sense of smell. The nerve originates in olfactory epithelium and terminates in the olfactory bulbs. The olfactory nerves are the only cranial nerves that are attached to the cerebrum, not the brainstem.

Question 15

oculomotor (CN III)

Answer 15

The third cranial nerve is the oculomotor (CN III). See Figure 2.25 to see the nerve inside the brain. It is a motor nerve responsible for eye movement in both somatic motor and visceral motor systems. Somatic motor movement controls the superior, inferior, and medial rectus (the inferior oblique muscles for movement of the eye). The visceral motor division controls the dilation of the pupil. Dilation (opening) or contraction (closing) of the pupil changes the amount of light that is let into the eye.

Question 16

trochlear (CN IV)

Answer 16

The fourth cranial nerve is the trochlear (CN IV). See Figure 2.26 to see the nerve inside the brain. It is a somatic motor nerve also responsible for eye movement. The trochlear nerve innervates the superior oblique muscle.

Question 17

trigeminal (CN V)

Answer 17

The fifth cranial nerve is the trigeminal (CN V). See Figure 2.27 to see the nerve inside the brain. It is a mixed motor and sensory nerve. It is responsible for chewing (or mastication) and sensation of the face, nose, and mouth.
There are three branches:

1) The ophthalmic branch is entirely sensory. It receives sensory information from skin around the forehead to the eyebrows and the upper part of the nose.

2) The maxillary branch is sensory only. It receives information from the lower eyelids, upper lip, upper gums, and even part of the pharynx.

3) The mandibular branch is mixed, receiving sensations from the lower gums, teeth, and lips. It receives sensory information from the tongue for sensation of heat, cold, and pressure, not taste. The motor portion of the mandibular branch controls the muscles of mastication.

Question 18

abducens (CN VI)

Answer 18

The sixth cranial nerve is the abducens (CN VI). See Figure 2.28 to see the nerve inside the brain. It is a motor nerve responsible for eye movement innervating the lateral rectus muscles. Contracting the lateral rectus muscles makes the eye move outward (abduction of the eye).

Question 19

facial (CN VII)

Answer 19

he seventh nerve is the facial (CN VII). See Figure 2.29 to see the nerve inside the brain. It is a mixed motor and sensory nerve. It is responsible for facial expressions. It is also responsible for sensation of the tongue and taste on the anterior portion of the tongue. There are also visceral motor functions of the facial nerve controlling tear glands (lacrimal) and nasal mucous glands.

Question 20

vestibulocochlear (CN VIII)

Answer 20

The eighth cranial nerve is the vestibulocochlear (CN VIII). See Figure 2.30 to see the nerve inside the brain. It is a special sensory nerve responsible for hearing and balance. CN VIII travels through a hole in the temporal bone called the internal acoustic meatus. The vestibular branch is responsible for balance and equilibrium. The cochlear branch is responsible for the sense of hearing.

Question 21

glossopharyngeal (CN IX)

Answer 21

The ninth cranial nerve is the glossopharyngeal (CN IX). See Figure 2.31 to see the nerve inside the brain. It is a mixed motor and sensory nerve. The motor portion is responsible for the swallowing muscles. The sensory portion is responsible for taste on the posterior portion of the tongue. CN IX also contains visceral motor neurons that control the parotid salivary glands.

Question 21

vagus (CN X)

Answer 21

The tenth cranial nerve is the vagus (CN X). See Figure 2.32 to see the nerve inside the brain. It is a mixed motor and sensory nerve, which spreads out widely in the abdomen. It is responsible for digestion, regulation of heart rate, and sensation of the digestive tract.

Question 22

accessory (CN XI)

Answer 22

The eleventh nerve is the accessory (CN XI), also called spinal accessory. See Figure 2.33 to see the nerve inside the brain. It is a motor nerve, and it is responsible for the control of muscles involved in rotation of the head and movement of the upper shoulders.

Question 22

hypoglossal (CN XII)

Answer 22

The twelfth cranial nerve is the hypoglossal (CN XII). See Figure 2.34 to see the nerve inside the brain. It is a motor nerve responsible for voluntary tongue movements.