Lab Activity 19 & 20 Cranial Nerves General Senses Portland Community College BI 232

2 Cranial Nerves Nerves that originate from the brain rather than the spinal cord Part of the peripheral nervous system (not the central nervous system) May contain one or more of the following: Sensory Somatic Motor (voluntary movement) Parasympathetic Motor (involuntary “rest and digest” part of the autonomic nervous system)

3 CN I: Olfactory Nerve Function: Sensory for smell Test: Have patient identify aromatic substances like vanilla or coffee (avoid irritating substances like smelling- salts, cloves, mint) Symptoms of nerve damage: Anosmia: diminished or absent sense of smell

4 CN II: Optic Nerve Function: Sensory for vision Tests: 1.Eye chart 2.Check peripheral vision 3.Funduscopic exam

5 CN II: Optic Nerve Optic chiasm: Fibers from the nasal half of each retina cross over to the opposite side of the brain. Symptoms of nerve damage: Loss of vision (peripheral or central) Abnormal funduscopic appearance

6 CN II: Optic Nerve Pathology Papilledema. Note swelling of the disc, hemorrhages, and exudates, with preservation of the physiologic cup. Proliferative Diabetic Retinopathy. Note the multiple hemorrhages throughout the retina.

7 Cranial Nerves III, IV & VI (Control Eye Movements)

8 CN III: Oculomotor nerve Function: Somatic Motor to extraocular muscles (voluntarily move the eye) Parasympathetic (motor) to iris and lens (pupillary constriction) Tests: 1.Check pupils for size, shape and equality 2.Shine light in each eye and check for pupil constriction 3.Have patient follow an object in all directions to check for symmetric eye movements Originates in the midbrain

9 CN III: Oculomotor Nerve Injury Symptoms of nerve damage: Double vision (diplopia): The affected eye turns outward when the unaffected eye looks straight ahead The affected eye can move only to the middle when looking inward and cannot look upward and downward. Ptosis: eyelid droop Pupil may be dilated and sometimes fixed

10 Oculomotor Nerve Injury Right Eye Normal side Injured side

11 Pupillary Reflex EfferentAfferent Consensual reflex: Both pupils should constrict at the same time

12 CN IV: Trochlear Nerve Function: Somatic motor to superior oblique muscle of the eye. Test: Check eye movements Symptoms of nerve damage: Outward rotation of the affected eye Vertical diplopia Injured sideNormal side Originates in the midbrain

13 CN VI: Abducens Nerve Function: Somatic Motor to lateral rectus muscle of the eye. Test: Check eye movements Symptoms of nerve damage: The affected eye will tend to be deviated inward because of the unopposed action of the medial rectus muscle. Cannot move eyeball laterally beyond the midpoint Injured side Normal side Originates in the pons

14 CN V: Trigeminal Nerve 3 Branches 1.Ophthalmic 2.Maxillary 3.Mandibular

15 CN V: Trigeminal Nerve Function: Somatic Motor (mandibular branch) to muscles of mastication (chewing) Sensory (all branches)to face and cornea. Originates in the pons

16 CN V: Trigeminal Nerve Test: Have patient bite down while you palpate the masseter muscle Test: Touch patient with an open paperclip and ask “sharp or dull” Test: Touch cornea with a wisp of cotton. Patient should blink

17 CN V: Trigeminal Nerve Symptoms of nerve damage: Inability to firmly bite down (mandibular branch only) Loss of sensation (each branch can be affected independently) Loss of corneal reflex (may indicate brain stem injury) Trigeminal Neuralgia (Tic Douloureux): debilitating intermittent pain on one side of the face

18 CN VII: Facial Nerve 5 Branches 1.Temporal 2.Zygomatic 3.Buccal 4.Mandibular 5.Cervical Function: Somatic Motor to muscles of facial expression Parasympathetic (motor) to lacrimal and salivary glands Sensory taste to anterior 2/3 tongue Originates in the pons

19 CN VII: Facial Nerve

20 CN VII: Facial Nerve Testing Tests: 1.Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter 2.Check symmetry of facial muscles: Close eyes, smile, whistle, puff out cheeks (make funny faces) 3.Check tearing with ammonia fumes

21 CN VII: Facial Nerve Symptoms of nerve damage: Mild weakness to total paralysis of facial muscles (may include twitching), Drooping eyelid Drooping corner of the mouth Drooling or dry mouth Impairment of taste Excessive tearing in the eye or dry eye

22 CN VII: Facial Nerve Injury (Bell’s Palsy) Paralyzed facial muscles Patients can still feel their face because sensory is supplied by the trigeminal nerve Injured side Normal side

23 CN VIII: Vestibulocochlear Function: Sensory Vestibular system for balance & equilibrium Cochlea for hearing Tests: Auditory component of the nerve: Hearing test Vestibular control of balance and movement: Romberg test (tests equilibrium) Originates in the medulla

24 CN VIII: Vestibulocochlear Tests Simple hearing test: Rub fingers together near the ear and ask “right or left” If there is lateralization (hearing louder on one side) there is a problem Other hearing tests: Performed by an audiologist with special equipment to determine tones, frequencies and degree of hearing loss

25 CN VIII: Vestibulocochlear Tests Romberg Test Have patient stand with arms at side and feet together Have patient stand with their eyes closed Stand close to prevent falls Normally, they should maintain position for 20 seconds with only minimal swaying If they loose their balance, they have failed the equilibrium test.

26 CN IX: Glossopharyngeal Function: Somatic Motor to muscles of pharynx Parasympathetic (motor) to salivary glands Sensory to pharynx and taste to posterior tongue

27 CN IX: Glossopharyngeal Tests: Gag reflex: Touch each side of the throat with the tongue depressor Evaluate swallowing movements Say AHH, and watch the palate and uvula elevate. Evaluate taste on posterior 1/3 of tongue Symptoms of nerve damage: Loss of gag reflex Difficulty swallowing Loss of taste Originates in the medulla

28 CN X: Vagus Nerve Function: Somatic Motor to muscles of pharynx and larynx Parasympathetic (motor) fibers of the heart and other viscera Sensory to pharynx and larynx Originates in the medulla

29 CN X: Vagus Nerve Test: Inspect palate Test gag reflex Symptoms of nerve damage: Loss of gag reflex Difficulty swallowing Hoarse voice

30 CN XI: Accessory Nerve Function: Somatic Motor to sternocleidomastoid and trapezius muscles Originates in the medulla

31 CN XI: Accessory Nerve Test: Shrug shoulders against resistance Turn head against resistance.

32 CN XI: Accessory Nerve Symptoms of nerve damage: Weakness Uneven shoulders Winged scapula

33 CN XII: Hypoglossal Nerve Function: Somatic Motor to tongue Originates in the medulla

34 Hypoglossal Nerve Injury Test: Ask patient to stick out tongue Symptoms of nerve damage: When paralyzed, the tongue will point to the damaged side Normal side Injured side

Lab Activity 20 General Senses

36 General Senses: Receptors Nociceptors: Pain receptors Thermoreceptors: Temperature receptors (free nerve endings) Chemoreceptors: Detect small changes in the concentration of specific chemicals or compounds Mechanoreceptors: Sensitive to stimuli that distort their cell membranes (contain mechanically gated ion channels) Tactile receptors Baroreceptors Proprioceptors

37 Classes of Mechanoreceptors Tactile receptors: sensations of touch, pressure and vibration Free nerve endings Root hair plexus Tactile discs (Merkel’s discs) Tactile corpuscles (Meissner’s corpuscles) Lamellated corpuscles (Pancinian corpuscles) Baroreceptors: Detect pressure changes in the walls of blood vessels and portions of the digestive, reproductive and urinary tracts Proprioceptors: Monitor the positions of joints and muscles.

38 Pancinian Corpuscle (aka: Lamellated Corpuscle) Lie deep in the dermis Respond only when deep pressure is first applied Monitor high frequency vibrations

39 Meissner’s Corpuscle (aka: Tactile Corpuscle) Lie in the dermal papillae of the skin Respond to light touch

40 The End