Neuroscience Chapter 14: Cranial Nerves

Severe pain that does not involve sensory loss and occurs in the distribution of one or more branches of the trigeminal nerve is known as ___________________.

ANS: Trigeminal neuralgia

5. Which cranial nerve provides control of the muscles of facial expression?

The facial nerve provides control of the muscles of facial expression

Which cranial nerve provides afferents for the gag reflex?

The glossopharyngeal nerve provides afferents for the gag reflex.

Which cranial nerve provides efferents for the pupillary reflex?

The oculomotor nerve provides the efferents for the pupillary reflex.

What is the function of the organ of Corti?

The organ of Corti converts mechanical displacement information into neural signals for the perception of sounds.

Which cranial nerve provides somatosensation from the face?

The trigeminal nerve provides somatosensation from the face.

Trigeminal neuralgia

Trigeminal nerve dysfunction that produces severe, sharp, stabbing pain in the distribution of one or more branches of the trigeminal nerve. Pain is triggered by normally innocuous noxious, including eating, talking, or touching the face. The pain begins and ends abruptly, lasts less than 2 minutes, and is not associated with sensory loss.

Match each structure with its function. Glossopharyngeal nerve

Triggers the swallowing reflex.

Match each condition with its definition. Sensorineural deafness

Hearing loss as a result of damage of the receptor cells or the cochlear nerve

Match each condition with its definition. Conductive deafness

Hearing loss as a result of obstruction of the transmission of vibrations in the outer or middle ear

Match each structure with its function. Medial geniculate body

Sensory relay station to the primary auditory cortex

Main sensory nucleus of the trigeminal nerve

Site of synapse between first- and second-order discriminative touch neurons in the trigeminothalamic pathway.

Spinal trigeminal nucleus

Site of synapse between first- and second-order neurons conveying nociceptive information from the face; it located in the lower pons and medulla.

What is the difference between the pupillary and consensual reflexes?

ANS: Both the pupillary and consensual reflexes are elicited by shining a bright light into one eye. The pupillary reflex is constriction of the pupil in the eye stimulated by the light, and the consensual reflex is constriction of the pupil of the other eye. These reflexes are useful for evaluating brainstem function.

Match each structure with its function. Inferior colliculus

Detection of the location of sounds

Why is there a difference between an authentic smile and a false smile?

Different brain areas produce authentic and inauthentic smiles. The limbic system is the source of authentic smiles, and voluntary signals from the cerebral cortex produce inauthentic smiles.

Lesions of what structures could cause double vision?

Double vision can result from lesions of cranial nerves III, IV, or VI or their nuclei, or from lesions of the medial longitudinal fasciculus.

Labyrinth

Inner ear that consists of the cochlea and vestibular apparatus.

Match each structure with its function. Reticular formation

Modulation of central nervous system excitability

Organ of Corti

Organ of hearing; is located within the cochlea.

Medial geniculate body

Thalamic relay station for auditory information to the primary auditory cortex.

The temporalis, medial and lateral pterygoid, and masseter muscles are innervated by which of the following? A. Trigeminal nerve B. Glossopharyngeal nerve C. Accessory nerve D. Facial nerve E. Hypoglossal nerve

ANS: A Rationale: The muscles of mastication (temporalis, medial and lateral pterygoid, and masseter muscles) are innervated by the trigeminal nerve.

First-order neurons conveying discriminative touch information from the face synapse in which of the following? A. Ciliary ganglion B. Trigeminal ganglion C. Main sensory nucleus of the trigeminal nerve D. Ventral posteromedial nucleus of the thalamus E. Mesencephalic nucleus

ANS: C Rationale: The main sensory nucleus of the trigeminal nerve is the site of synapse for first-order neurons conveying discriminative touch information from the face. The ciliary ganglion is the site of synapse for parasympathetic neurons innervating the ciliary muscle that increases the curvature of the lens in the eye. The trigeminal ganglion contains cell bodies of first-order neurons conveying somatosensory information from the face. The ventral posteromedial nucleus of the thalamus is the site of synapse between second and third-order neurons conveying somatosensory information from the face to the cerebral cortex. The mesencephalic nucleus receives proprioceptive information from the muscles of mastication.

What is the autonomic function of CN III?

ANS: CN III (Oculomotor) provides parasympathetic regulation of the pupillary sphincter and ciliary muscles for autonomic control of pupil constriction and lens curvature.

Why is the (spinal) accessory nerve considered a CN if the cell bodies are in the upper cervical spinal cord?

ANS: CN XI (accessory) is categorized as a CN because the axons ascend through the foramen magnum and then exit the skull via the jugular foramen.

Asymmetrical elevation of the palate and hoarseness indicate a complete lesion of which CN?

ANS: Complete lesion of the Vagus nerve causes asymmetrical elevation of the palate and hoarseness.

List the locations of lesions that may cause diplopia.

ANS: Lesions of the oculomotor, trochlear, or abducens nerves or of the medial longitudinal fasciculus may cause diplopia (double vision).

Which CNs are involved in the gag reflex?

ANS: The glossopharyngeal is the afferent and vagus nerve is the efferent innervation in the gag reflex.

Mesencephalic nucleus

Collection of cell bodies that process proprioceptive information from the face.

Sensorineural deafness

Hearing defect as a result of damage to the receptor cells or the cochlear nerve.

Case 2 A.K., a 46-year-old engineer, is complaining of double vision. She cannot read or drive unless she closes one eye. Results of the cranial nerve examination: •Olfaction, vision, facial sensation, control of the muscles of facial expression, mastication, hearing, equilibrium, gag and swallowing reflexes, and contraction of the sternocleidomastoid, trapezius, and tongue muscles are normal. Pupillary responses and movements of the left eye are normal. •When A.K. is instructed to look straight ahead, her right eye looks outward and down. •A.K. cannot look in, down, or up with her right eye. •A.K. can open the right eyelid only halfway. •No pupillary reflex or consensual response occurs when a flashlight is shined into her right eye, nor does the pupil constrict when she focuses on an object 6 inches from her right eye. Questions 1. Is this an upper motor neuron lesion? Why or why not? 2. Where is the lesion?

1. This is not an upper motor neuron lesion, because an upper motor neuron lesion would spare the pupillary reflexes. In an upper motor neuron lesion, the afferent limb by the optic nerve would be intact, the connections in the brainstem would be intact, and the efferent limb via the oculomotor nerve would be intact. 2. The absence of any cognitive or consciousness disorders and the absence of vertical tract signs, such as paresis elsewhere in the body and/or a loss of sensation, indicate that the lesion is probably in the peripheral nervous system. The oculomotor nerve supplies the extraocular muscles that move the pupil up, down, in, and up and in, as well as the pupillary reflexes. The two muscles innervated by the trochlear and abducens nerves are intact. Therefore the lesion involves the oculomotor nerve.

The facial nerve innervates which of the following? A. Muscles that close the eyes, move the lips, and produce facial expressions B. Sternocleidomastoid and trapezius muscles C. Masseter, pterygoids, and temporalis D. Both A and B E. A, B, and C

ANS: A Rationale: The facial nerve innervates the muscles that close the eyes, move the lips, and produce facial expressions. The accessory nerve innervates the sternocleidomastoid and trapezius muscles. The trigeminal nerve innervates the masseter, pterygoids, and temporalis muscles.

What is Bell's palsy? A. Loss of the consensual reflex B. Increased sweating and vasodilation on one side of the face C. Contralateral paralysis of the muscles innervated by CN VII D. Ipsilateral paralysis of the muscles innervated by CN VII E. Severe pain in the facial region near the jaw

ANS: D Rationale: Bell's palsy is ipsilateral paralysis of the muscles of facial expression caused by a lesion affecting axons of the facial nerve, CN VII.

First-order neurons that transmit fast sensory information perceived as pain from the face synapse in which of the following? A. Mesencephalic nucleus B. Trigeminal ganglion C. Reticular formation D. Main sensory nucleus E. Spinal trigeminal nucleus

ANS: E Rationale: Central axons of Aδ neurons enter the pons, then descend as the spinal tract of the trigeminal nerve into the cervical spinal cord. These neurons synapse with second-order neurons in the spinal trigeminal nucleus. Axons of second-order neurons transmitting fast pain information cross the midline and ascend in the trigeminal lemniscus to the ventral posteromedial nucleus of the thalamus. Third-order neurons arise in the ventral posteromedial nucleus and project to the somatosensory cortex

Which of the following are controlled by the oculomotor nerve? A. Superior rectus muscle that moves the eye B. Constriction of the pupil of the eye C. Adjusting the shape of the lens of the eye D. Both A and B E. A, B, and C

ANS: E Rationale: The oculomotor nerve controls the superior, medial, and inferior rectus and inferior oblique muscles that move the eye. The oculomotor nerve also includes parasympathetic neurons that provide the efferent signals for constricting the pupil and increasing the curvature of lens of eye.

Lower motor neuron involvement of which CNs may cause dysarthria?

ANS: Lower motor neuron involvement of CN V, VII, X, or XII can cause dysarthria. Upper motor neuron lesions affecting the signals to the CN nuclei of these CNs can also cause dysarthria.

Axons of the optic nerve synapse in which region of thalamus?

ANS: Optic nerve axons synapse in the lateral geniculate of thalamus and the pretectal nucleus in the midbrain (for the pupillary and consensual reflexes).

A client's right eye moves normally. The left eye cannot be voluntarily adducted but cannot simultaneously look downward and toward midline. Where is the lesion?

ANS: The lesion is to the left trochlear nerve.

Accommodation

Adjustments of the eyes to view a near object: the pupils constrict, the eyes converge (adduct), and the lens becomes more convex. The optic nerve is the afferent (sensory) limb of the reflex, and the oculomotor nerve provides the efferent (motor) limb.

Optic tract

Axons conveying visual information from the optic chiasm to the lateral geniculate body of the thalamus.

Match each structure with its function. Secondary auditory cortex

Comparison of sounds with memories and categorization of sounds

Match each structure with its function. Wernicke's area

Comprehension of spoken language

Consensual reflex

Constriction of the pupil in the opposite eye when a bright light is shined into one eye. The optic nerve is the afferent (sensory) limb of the reflex, and the oculomotor nerve provides the efferent (motor) limb.

Conductive deafness

Hearing defect as a result of the inability to transmit vibrations in the outer or middle ear.

Match each cranial nerved with it's function CN VII: Facial

Motor innervation of facial muscles; innervates lacrimal and salivary glands

Match each cranial nerved with it's function CN III: Oculomotor

Motor innervation of some ocular muscles; innervates intrinsic, smooth muscles of the eye

Match each cranial nerved with it's function CN IV: Trochlear

Motor innervation of the superior oblique

Match each cranial nerved with it's function CN XII: Hypoglossal

Motor innervation of the tongue

Bell's palsy

Paralysis or paresis of the muscles of facial expression on one side of the face; is caused by a lesion of the facial nerve.

Match each condition with its definition. Tinnitus

Perception of auditory buzzing, hissing, or ringing sounds in the absence of corresponding external stimuli

Pupillary reflex

Pupil constriction in the eye directly stimulated by a bright light. The optic nerve is the afferent (sensory) limb of the reflex, and the oculomotor nerve provides the efferent (motor) limb.

Match each structure with its function. Descending limbic pathways

Regulates the production of facial expressions associated with real emotions.

Diagram the accommodation reflex.

See Figure 13-7 for an illustration of the accommodation reflex.

Match each cranial nerved with it's function CN V: Trigeminal

Sensory innervation of face and temporomandibular joint (TMJ); motor innervation to muscles for chewing

Match each cranial nerved with it's function CN IX: Glossopharyngeal

Sensory innervation of the pharynx, soft palate and posterior tongue

Optic chiasm

Site where the optic nerve fibers from the nasal half of the retina cross the midline.

Cochlea

Snail shell-shaped organ, formed by a spiraling, fluid-filled tube. The cochlea contains a mechanism, the organ of Corti, which converts mechanical vibrations into the neural impulses that produce hearing.

Dysarthria

Speech disorder resulting from paralysis, incoordination, or spasticity of muscles used for speaking; due to upper or lower motor neuron lesions or muscle dysfunction. Comprehension of spoken language, writing, and reading are not affected by dysarthria. Three types of dysarthria may be distinguished: (1) spastic, as a result of damage to the upper motor neurons; and (2) flaccid, as a result of damage to the lower motor neurons; and (3) ataxic, as a result of cerebellar damage.

Match each structure with its function. Vagus nerve

Supplies both afferent and efferent innervation to the larynx, trachea, lungs, heart, gastrointestinal tract (except the lower large intestine), pancreas, gallbladder, and liver.

Movements and pupillary responses of a client's left eye are normal. The right eye looks downward and outward. The pupil is dilated and unresponsive to light, and the eyelid droops. Where is the lesion?

ANS: The lesion is to the right oculomotor nerve.

A client's right eye moves normally. The left eye cannot adduct on voluntary gaze, yet adducts during convergence eye movements. What is the name of this condition, and where is the lesion?

ANS: This condition is known as internuclear ophthalmoplegia. The lesion is in the medial longitudinal fasciculus between the abducens and oculomotor nuclei.

Match each cranial nerved with it's function CN II: Optic

Conducts sensory signal from receptors of the eye

Match each structure with its function. Primary auditory cortex

Conscious awareness of sound intensity

How are the eyes voluntarily moved to follow an examiner's finger to the right and then look up? Include both muscle and cranial nerve activity in the answer.

Contraction of the lateral rectus muscle, innervated by the abducens nerve, moves the right eye toward the right. Next, contraction of the superior rectus muscle, innervated by the oculomotor nerve, moves the right eye upward. Contraction of the medial rectus muscle, innervated by the oculomotor nerve, moves the left eye toward the right. Contraction of the inferior oblique muscle, innervated by the oculomotor nerve, moves the left eye upward.

Match each structure with its function. Organ of Corti

Converts mechanical energy into neural signals conveyed by the cochlear nerve.

Which cranial nerves are required for swallowing?

Cranial nerves V, VII, IX, X, and XII are all involved in swallowing.

Case 4 P.F., a 52-year-old accountant, was referred to physical therapy for Bell's palsy. She had right facial paralysis, pain on the right side of the face, and increased loudness of sound in the right ear. The onset of paralysis was gradual, progressively worsening for 3 weeks. The pain began after the paralysis. At the time of referral, she was 5 months post onset. The neurologic examination was normal, except for the following: •Inability to feel touch or pinprick in the mandibular division of the right CN V (chin and lower mandible region) •No contraction of the right masseter and temporalis muscles when asked to clench teeth •Complete paralysis of muscles of facial expression on the right; inability to close the right eye Question What is the most likely location of the lesion?

The gradual onset and lack of any improvement in the paralysis, as well as the pain, loss of somatosensation, and paralysis of muscles of mastication, are inconsistent with Bell's palsy. The onset of Bell's palsy is acute or subacute, and Bell's palsy paralysis typically improves. The somatosensory loss and paralysis of muscles of mastication are signs and symptoms of CN V, not CN VII, involvement. The patient was referred to a head and neck specialist. The MD diagnosed a tumor of the parotid gland that was treated surgically.

Which cranial nerve provides efferents to the tongue muscles?

The hypoglossal nerve provides efferents to the tongue muscles

Case 1 R.F. is a 62-year-old man who was involved in a car accident 5 days ago. He sustained fractures of the skull, both femurs, and the right tibia. He complains of double vision. •Consciousness, cognition, language, memory, and somatosensation are normal. •All autonomic functions, including pupillary and accommodation reflexes, are normal. •Motor function is normal except for an inability to look downward and inward with the right eye. All other eye movements, including the ability to look medially and laterally with the right eye, are normal. When asked, he says he has been having trouble reading since the accident. Question What is the most likely location of the lesion?

The most likely location of the lesion is the trochlear nerve, damaged or severed by the skull fracture, because the trochlear nerve innervates the superior oblique muscle that moves the eye to look down and in. The intact pupillary and accommodation reflexes and the normal movements of the eyes up, down, in, and up and in indicate that the oculomotor nerve is undamaged. The ability to look laterally indicates that the abducens nerve is also intact.

Case 3 M.R., a 56-year-old electrician, awoke with an inability to move the left side of his face. His neurologic examination was normal, including facial sensation and control of the muscles of mastication and the tongue, except for the following: •Drooping of the left side of the face •Complete lack of movement of the muscles of facial expression on the left. Examples include M.R.'s inability to voluntarily smile, pucker his lips, or raise his eyebrow on the left side. Emotional facial expressions were also absent; when he smiled with the right side of his lips, the left half of his lips did not move. •Inability to close his left eye Question What is the most likely location of the lesion?

There are no signs of vertical tract involvement, because the absence of signs below the face indicates that the connections between the brain and the spinal cord are normal. The lesion spares facial sensation, the muscles of mastication, and the tongue, so the trigeminal nerve and hypoglossal nerves are intact. The facial nerve controls the muscles of facial expression, including the orbicularis oculi, so the lesion involves the facial nerve. The disorder affects either.