Cranial nerves - function Flashcards
More detail on functions of cranial nerves
Cranial Nerves involved in Speech and Swallowing
Trigeminal (V), Facial (VII), Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), Hypoglossal (XII)
Cranial Nerves involved in Respiration
Spinal Accessory (XI)
Cranial Nerves involved in Reading
Optic (II), Occulomotor (III), Trochlear (IV), Abducens (VI)
Optic Nerve (CN II) Functions
- Carries neural signals from the retina to the brain
- The medial (nasal) half of the retina receives information from the lateral half of the visual field
Symptoms of Optic Nerve (CNII) Dysfunction
Common - Reduced visual acuity = blurred vision - Visual field defects = reduced or absent vision in part of visual field in one or both eyes Less common - Desaturated colour vision
Occulomotor Nerve (CN III) Function
- Innervates most of the extraocular muscles (muscles
that move the eyeball) - Innervates the muscle that lifts the upper eyelid
(levator palpebrae superioris) to keep the eye open - Innervates some of the muscles that control pupil size
and lens shape in the eye
Symptoms of Occulomotor Nerve (CN III) dysfunction
- Double vision (diplopia, Gr. di- ‘two’ + ops ‘eye’)
- Drooping upper eyelid (ptosis = Gr. ‘to fall’)
Trochlear (CN IV) and Abducens (CN VI) Nerve Function
- CN IV supplies the superior oblique muscle, which turns the eye downwards and inwards
- CN VI supplies the lateral rectus muscle, which pulls the eye sideways away from the nose (laterally)
Symptoms of Trochlear (CN IV) and Abducens (CN VI) dysfunction
Diplopia (double vision)
Trigeminal (CN V) Nerve Function (sensory and motor)
CN V sensory functions:
- Facial proprioception (feeling the position of facial muscles and jaw)
- Touch, pain and temperature sensation on face
CN V motor functions:
- Innervates the muscles of mastication
Symptoms of Trigeminal (CN V) Nerve dysfunction
Sensory symptoms – altered or reduced sensation on the face and inside the mouth = paraesthesia (para ‘irregular’ + Gr. aesthesis ‘sensation’)
Sensory symptoms on same side as cranial nerve lesion (ipsilateral)
Motor – difficulty chewing, jaw deviates towards side of lesion when opening mouth (due to unopposed action of muscles on intact side)
Facial Nerve (CN VII) Function - summary
Motor
- Muscles of facial expression
- Stapedius (middle ear)
Sensory
-Cutaneous (skin) sensation to external auditory meatus
Special sensory
-Taste to anterior 2/3 of tongue
Autonomic
-Lacrimal & salivary glands
Symptoms of Facial Nerve (CN VII) dysfunction
Motor
-Ipsilateral weakness of muscles of facial expression
Sensory
-Altered cutaneous sensation around ipsilateral external auditory meatus
Special sensory
- Altered taste on ipsilateral anterior 2/3 of tongue
- Sounds are loud in ipsilateral ear (if nerve to stapedius affected)
Autonomic
-Dry mouth and eyes, due to reduced parasympathetic supply to lacrimal & salivary glands
Function of Vestibulocochlear/Acoustic Nerve (CN VIII) and symptoms of dysfunction
Function
-Sensory nerve from the cochlear to the brainstem
Dysfunction
- Hearing loss
- Tinnitus (continuous ringing noise)
- Altered balance
Glossopharyngeal Nerve (CN IX) function
Sensory
- Pharynx, posterior 1/3 of tongue
- Cutaneous sensation external ear
- Gag reflex - afferent = CN IX (+ CN X); efferent = CN X
Motor
-Stylopharyngeus – elevates larynx and
pharynx, dilates pharynx during swallowing
Special sensory
-Taste to posterior 1/3 tongue
Autonomic
-Parotid salivary gland
Symptoms of Glossopharyngeal Nerve (CN IX) dysfunction
- Symptoms may be subtle or absent
- Altered bitter/sour taste
- Reduced pharyngeal sensation
- Mild dysphagia
Symptoms of Vagus Nerve (CN X) dysfunction
Altered voice
- Vocal fold paralysis due to recurrent laryngeal nerve or vagus nerve lesions
- Unilateral lesions - hoarse, weak or breathy voice, vocal fatigue
- Bilateral complete lesions – aphonia
- Superior laryngeal nerve lesion – vocal folds can still adduct for phonation, but cricothyroid muscle weakness causes loss of pitch control, especially in upper pitch range
Noisy breathing (stridor), ineffective cough, shortness of breath
Dysphagia, aspiration, choking or coughing when swallowing
(Other symptoms relating to autonomic functions of CN X, e.g. gastroparesis – reduced contraction of intestinal muscles leading to nausea or stomach pain)
Vagus Nerve (CN X) Function
The pharyngeal branch of the vagus nerve innervates the muscles of the soft palate and the pharynx (except Stylopharyngeus), and intrinsic muscles of the larynx
Spinal Accessory Nerve (CN XI) Function and symptoms of dysfunction
Functions
- Spinal accessory nerve supplies motor innervation to:
- Trapezius muscle - elevates shoulder (e.g. shrug)
- Sternocleidomastoid muscle – turns head to contralateral side
Symptoms of dysfunction
- Shoulder weakness, head tilt
- Breathless on exertion (weakness of accessory muscles of respiration)
Hypoglossal Nerve (CN XII) Function
Functions
- Hypoglossal nerve provides motor innervation for:
- All extrinsic tongue muscles except palatoglossus (CN X)
- All intrinsic tongue muscles
Symptoms of dysfunction
- Tongue weakness
- Dysarthria
- Difficulty moving food around mouth when chewing
