Structure, function and assessments of cranial nerves: Part 1 (CN 1-7) MSTN121 - Neurophysiology Session 12 Department of Myotherapy

Structure, function and assessments of cranial nerves: Part 1 (CN 1-7) MSTN121 - Neurophysiology Session 12 Department of Myotherapy

Session objectives List the four functions of the cranial nerves (CNs). Identify each CNs 1-7 by number, name, function(s), reflex activity (if any), and connection to the brain.

Cranial Nerves Exchange information between the peripheral nervous system (PNS) and the central nervous system (CNS). Serve sensory, motor, and autonomic functions. Differ from spinal nerves in specialization; some are only motor, others are only sensory, and some are both sensory and motor. (Lundy-Ekman, 2018, p. 386) Image: (Lundy-Ekman, 2018, p. 387)

Cranial Nerves Function Cranial Nerves (CNs) have four functions 1. Supply motor innervation to the muscles of the face, eyes, tongue, jaw, and two neck muscles 2. Transmit somatosensory information from the skin and muscles of the face and from the temporomandibular joint (TMJ) 3. Transmit special sensory information related to visual, auditory, vestibular, gustatory, olfactory, and visceral sensations 4. Provide parasympathetic regulation of pupil size, curvature of the lens of the eye, heart rate, blood pressure, breathing, and digestion (Lundy-Ekman, 2018, p. 386)

Cranial Nerves Image: (Lundy-Ekman, 2013, p. 388)

Cranial Nerve 1: Olfactory Olfactory nerve is sensory. Sense of smell is dependent on olfactory nerve function. Connection to the brain: inferior frontal lobe. Much of the information attributed to taste is olfactory in origin because the information from taste buds is limited to chemoreceptors for salty, sweet, sour, umami (i.e., savory ), and bitter. (Lundy-Ekman, 2018, p. 386) Image: (Lundy-Ekman, 2018, p. 389)

Cranial Nerve II: Optic Nerve Optic nerve is sensory. Connection to the brain: diencephalon Retina is the inner layer of the posterior eye; light striking the retina is converted into neural signals by the photosensitive cells. Visual signals sent to the midbrain are involved in reflexive responses of the pupil, awareness of light and dark, and orienting the head and eyes. (Lundy-Ekman, 2018, p. 389)

Cranial Nerves 3, 4, and 6: Oculomotor, Trochlear & Abducens Oculomotor, Trochlear, and Abducens nerves are primarily motor. A. Oculomotor: moves the eyes up, down, medially and raises the upper eyelid. Also constricts the pupil and adjusts the shape of the lens. B. Trochlear: moves eyes down, particularly when eye is adducted. C. Abducens: Abducts the eye Contain motor neuron axons innervating the six extraocular muscles that move the eye and control reflexive constriction of the pupil Connection to brain: Oculomotor: anterior midbrain Trochlear : posterior midbrain Abducens: between pons and medulla (Lundy-Ekman, 2018, p. 389 & 427) Image: (Lundy-Ekman, 2018, p. 434)

Cranial Nerve 5: Trigeminal Trigeminal nerve is a mixed nerve containing both sensory and motor fibers Sensory fibers transmit information from the face and TMJ. Trigeminal nerve named for its three branches Ophthalmic Maxillary Mandibular The motor axons are contained in the mandibular branch. Carry signal to muscles of mastication and tensor tympani. Sensory neurons transmit information from the face and the TMJ. All 3 branches convey somatosensory signals. Reflex: afferent limb corneal reflex Connection to the brain: pons (lateral) (Lundy-Ekman, 2018, p. 386)

Cranial Nerve 5: Trigeminal Image: (Lundy-Ekman, 2018, pp. 390-391)

Cranial Nerve 7: Facial Innervates muscles of facial expression and most glands in the head (tears, salivation etc.); also conveys sensory information from the posterior ear canal and taste from the anterior tongue Signals to and from CN VII are processed in the nuclei located in the pons, medulla, and upper spinal cord Reflex: Efferent limb corneal reflex. Connection to brain: between pons and medulla. (Lundy-Ekman, 2018, p. 392) Image: (Lundy-Ekman, 2018, p. 393)

Introduction to Cranial Nerve Examination MSTN121 - Neurophysiology Session 12 Department of Myotherapy

We do not routinely test cranial nerve I olfactory nerve. Routinely tested as a group Cranial Nerve Name Composition I Olfactory Sensory only II Optic Sensory only III Oculomotor Motor & sensory IV Trochlear Motor & sensory V Trigeminal Motor & sensory VI Abducens Motor & sensory VII Facial Motor & sensory VIII Vestibulocochlear Sensory only IX Glossopharyngeal Motor & sensory X Vagus Motor & sensory XI Spinal Accessory Motor & sensory XII Hypoglossal Motor & sensory Routinely tested as a group (Jarvis, 2016, pp. 644-647)

Cranial Nerve II Optic Nerve Test Visual Acuity This can be tested by asking the patient to read signs and describe pictures about 6 metres distance away. Test both eyes, asking her to cover one eye at a time. (Butler, 2000) Image: (Jarvis, 2016, p. 318)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Test Check Pupil Size This reflects the balance in tone between parasympathetic and sympathetic nervous system. Best examined in a dark room. Pupils should appear round, regular and equal in size. In adults the resting size is 3-5mm. Larger than normal pupil size suggests high sympathetic tone. If in both suggests systemic increase in tone, on one side suggests unilateral overactivity or under activity in the parasympathetic nervous system on the same side. Size variation from right to left must be noted may indicate lesion on either side. (Jarvis, 2016)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Test Pupillary Light Reflex In a dim room, shine the pen light into one of the clients eyes. Test both sides. Normal response: both pupils constricting at the same time and with equal velocity and size of constriction. Direct reflex is demonstrated when the light on one side = pupil constriction on same side Consensual reflex is demonstrated when the light on one side = pupil constriction on the opposite side. When a slow or absent response occurs it suggests a lesion of the pathway. (Jarvis, 2016)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Test Visual Fields Get the client to cover their left eye. Using the tip of a pen, move the pen from behind their ear (at a distance of 25cm from their head) into their vidual field. Get the client to say when they see the tip of the pen. Test the opposite side getting them to swap eyes covered. Normal response: demonstrated by the observation of the pen tip just after it passes the ear. If the client has lost vision on one side of their visual field it is called homonymous hemianopia normally due to visual pathway lesion. Left visual field loss suggests right side optic tract or occipital lobe lesion. (Jarvis, 2016)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Test Resting Eye Position Ask the client to look straight ahead, examine the height of the space between the upper and lower eyelids and the position of the eyelids relative to the iris and pupil. Then ask the client to look upwards without moving their head. Normal response: The position of the eyelids is symmetric with the upper eyelid covering the upper iris. The eyelid retracts with upwards gaze. Asymmetric space between the eyelids and iris the eyelid that is lower does not retract with upwards gaze. Suggest lesion of the oculomotor nerve. CNIII lesions normally will also include dilated pupil, lateral and downwards deviation of the eye when attempting to look forward and diplopia. (Jarvis, 2016)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Test Accommodation Reflex Get the client to look straight ahead at the tip of the pen, slowly move the pen towards the bridge of their nose and watch their eyes. Normal response: both eyes adduct equally and can maintain position. The client reports diplopia only when the pen is close to the nose. Pupils should constrict as eyes focus and as you take the pen away the eyes should dilate. One eye does not adduct as much as the opposite side and has early diplopia. Suggests an ipsilateral CNIII lesion. (Jarvis, 2016) Image: (Jarvis, 2016, p. 296)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Tests Visual Pursuits Get the client to follow the tip of a pen in each plane of eye motion side to side, up and down from corner to corner (oblique axis). Normal response: eyes move symmetrically and smoothly. Abnormal response: nystagmus/weakness in adduction, depression or elevation of the eye. May be due to single CNIII or VI lesion or an upper motor neuron lesion or medial longitudinal fasciculus lesion. Abducens nerve abnormal response: unable to move eyes laterally and may have nystagmus during the pursuit. (Jarvis, 2016) Image: (Lundy-Ekman, 2013, p. 434)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Image: (Lundy-Ekman, 2013, p. 437)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Tests Inferior Oblique Muscle Test The examiner gets the client to follow the tip of the pen to 50 degrees adduction and then lifts the pen up so the eye goes inwards and up. Normal response: eyes follows the pen tip. Eye is unable adduct and elevate. May be due to oculomotor nerve lesion or UMN/medial longitudinal fasciculus lesion. (Jarvis, 2016)

Cranial Nerve III, IV & VI Oculomotor, Trochlear & Abducens Nerves Tests Trochlear Nerve Test The examiner gets the client to follow the tip of the pen to 50 degrees adduction and then drops the pen so the eyes look down and inwards. Normal response: eyes follow the pen tip. Difficulty looking inferomedially and may present with diplopia, difficulty reading and/or difficulty descending stairs. May be due to trochlear nerve lesion or UMN lesion. (Jarvis, 2016)

Cranial Nerves V Trigeminal Nerve Test Trigeminal Nerve Motor Testing Active resisted testing of jaw opening and closing then palpating the masseters muscles on both sides while the client clenches their teeth, feeling for tone. Normal response: 5/5 in strength and normal resting tone compared with clenching. 4/5 or less in strength and high or low tone in masseter/temporalis. Low tone suggests a LMN lesion like trigeminal neuralgia, high tone suggests UMN lesion. (Jarvis, 2016) (Image: Jarvis, 2016, p. 645)

Cranial Nerves V Trigeminal Nerve Test Trigeminal Nerves Sensory Testing Pin prick, soft touch, vibration and cold testing for the face over the forehead, under the eyes, over the nose, over the cheeks, over the chin and lips. Ask the client to localise, describe and rate the stimulus from one side of the face compared to the other. Normal response: symmetry in sensation and localisation. Anesthesia over the face, hyperesthesia over the face, hyperalgesia in pin prick, allodynia in cold, vibration or soft touch. (Jarvis, 2016) (Image: Jarvis, 2016, p. 645)

Cranial Nerves V Trigeminal Nerve Test Corneal Reflex Using a wisp of cotton touch the outer cornea. Normal response: client blinks both eyes. (afferent = trigeminal, efferent = facial) Opposite side and/ or same side does not blink, suggesting a lesion in the CNV or CNVII (indicated if other tests are positive). Test Jaw Jerk Reflex Place your thumb on the clients jaw in a pistol grip fashion. Whilst your thumb is in this position tape on the clients chin with a reflex hammer. Normal response: masseter contraction and mandible elevation. Lost/ decreased reflex suggesting CNV lesion or if hypperreflexive suggesting UMN lesion. (Lundy-Ekman, 2013)

Cranial Nerves VII Facial Nerve Test Facial Expressions Get the client to lift their eye brows, close and open eyes, smile and puff up cheeks. Normal response: symmetry and able to do all movements. Asymmetry and paresis/paralysis. If upper and lower face affected this may suggest Bell s palsy. Corticobrainstem/UMN lesion results in paresis/paralysis of lower face. (Jarvis, 2016, p) (Image: Jarvis, 2016, p. 646)

Cranial Nerves VIII Vestibulocochlear Test Hearing Test Rub your fingers together near the client s ear, then slowly move away from their ears. Ask when they can no longer hear it. Compare both sides. Difference in acuity, may suggest reduce function of the same side cochlear nerve or UMN lesion. Normal response: Client hears both sides equally. (Butler, 2000)

Cranial Nerves VIII Vestibulocochlear Test Weber Test Using a tuning form, place it in the middle of the client s head. Ask the client if the sound is heard better in one ear or both (must be stated while the tuning fork is in the midline of their head). - With conductive hearing loss, the sound will localise towards the affected side. - With sensorineural hearing loss, the sound will localise towards the unaffected side. Normal response: sound is symmetrical with no lateralisation. (Butler, 2000)

Cranial Nerves IX Glossopharyngeal Test Gag Reflex Touch the soft palate with a cotton swab. Normal response: gagging and symmetrical elevation of the soft palate. Lack of gag reflex or asymmetrical elevation of soft palate suggesting either CNIX or CNX lesion. (afferent = CNIX, efferent = CNX). (Jarvis, 2016)

Cranial Nerves X Vagus Nerve Test - Uvula Elevation Depress the tongue and ask the client to say ah and observe the soft palate with your pen light. Normal response: Elevation of the soft palate symmetrically. Asymmetry of soft palate elevation and they may be present with voice hoarseness. Hoarse of brassy voice occurs with vocal cord dysfunction, nasal twang occur with weakness of soft palate. (Jarvis, 2016)

Cranial Nerves XI Spinal Accessory Nerve Test Muscle Strength Check equal strength of the SCM and trapezius muscles. Ask the client to resist cervical rotation, with resistance applied to the side of the chin (see Fig 23-13). Then ask the client to shrug against resistance (see Fig 23-14). Atrophy. Muscle weakness or paralysis occurs with a stroke or following injury to the peripheral nerves. Normal response: These movements should feel equally strong on both sides.5/5 strength. (Jarvis, 2016, pp. 644-647) (Image: Jarvis, 2016, p. 646)

Cranial Nerves XII Hypoglossal Nerve Test Tongue Deviation Ask the client to protrude their tongue out. Inspect the tongue but also it s positioning. No wasting or tremors should be present. Not the tongue is forward in the midline. Protruded tongue deviates to the side of the lesion. Ipsilateral tongue atrophy may also be observed. Normal response: tongue stays on the midline. (Jarvis, 2016)

Cranial Nerves XII Hypoglossal Nerve Test Tongue Strength Ask the client to push their tongue to the left and right side of the mouth/cheek. Whilst the client is doing so push their tongue inwards while asking them to resist. Tongue s force easily overcome, may suggest CNXII lesion. Normal response: tongue able to resist moderate force. (Butler, 2000)

Review Questions What do cranial nerves do? How do cranial nerves differ from spinal nerves? List the four functions of the cranial nerves. Identify each CN mentioned in this lecturer by number, name, function(s), reflex activity (if any), and connection to the brain.

Image References Jarvis, C. (2016). Physical Examination & Health Assessment (7 th ed.). Elsevier: Missouri. Lundy-Ekman, L.(2013). Neuroscience : Fundamentals for Rehabilitation (4 th ed.). Missouri: Elsevier.

References Butler, D.S. (2000). The Sensitive Nervous System. Noigroup Publications: Adelaide: City West. Jarvis, C. (2016). Physical Examination & Health Assessment (7 th ed.). Elsevier: Missouri. Lundy-Ekman, L.(2013). Neuroscience : Fundamentals for Rehabilitation (4 th ed.). Missouri: Elsevier.

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