BMS 100 Clinical Physiology VI Fall 2022 PDF

Clinical Physiology VI Fundamental Physiologic Basis of the Neurologic Exam – part 2 BMS 100 Week 6 The Neurologic System Basic functional Anatomy of the Nervous System Cranial Nerves Types of information conveyed by cranial nerves Cranial nerve anatomy and function Major Somatic Sensory Pathways...

Clinical Physiology VI Fundamental Physiologic Basis of the Neurologic Exam – part 2 BMS 100 Week 6 The Neurologic System Basic functional Anatomy of the Nervous System Cranial Nerves Types of information conveyed by cranial nerves Cranial nerve anatomy and function Major Somatic Sensory Pathways Dorsal column-medial lemniscal system Spinothalamic tract Neurologic Physical Exam – Part II Cranial nerve exam Assessing dermatomes Cranial Nerves • Nerves that “emerge from the brain” and exit via skull foramina ▪ All other nerves exit the spinal cord and travel through the intervertebral foramina • Cranial nerves carry a wide variety of information: ▪ Special sensory information • Special senses – sight, sound, taste, smell, “balance” ▪ Somatic motor information • Somatic motor = skeletal muscles that we have voluntary control over ▪ Somatic sensory information • Somatic sensory = sensations that we can perceive OTHER THAN the special senses ▪ Motor and sensory information to/from structures that we cannot control or perceive • Mostly autonomic nervous system to glands/organs or from organs Cranial Nerves – general anatomy • The nuclei (cell bodies) in the brain that communicate to the cranial nerves are mostly found in the brainstem – some exceptions: ▪ Olfactory (CN I) – projects to the cortex (mostly ▪ Optic (CN II) – projects to the thalamus ▪ CN III and IV – nuclei are found in the midbrain ▪ CN V, VI, VII, VIII – nuclei are found in the pons ▪ CN IX, X, XI, XII – nuclei are (mostly) found in the medulla Inferior view – cranial nerves Cranial Nerve I • Function – sense of smell (special sense) ▪ From the superior part of the nasal cavity → olfactory bulb → many different locations in the temporal and frontal lobes ▪ Skull entry/exit point: Axons penetrate the skull via the tiny holes in the cribriform plate (ethmoid) • How do we test it? ▪ Ask the patient to identify a couple of distinctive smells (eyes closed if necessary) ▪ i.e. coffee, peppermint ▪ Loss of sense of smell = anosmia • Infections (COVID is famous for it), head injuries Cranial Nerve I Cranial Nerve II • Function – vision (special sense) ▪ From the retina (back of the eye) → thalamus → occipital lobe (cortex) • There are other connections between the optic nerve and the brain other than through the thalamus – mostly for mediating reflex eye and head movements ▪ Skull entry/exit point: optic foramen (canal) • How do we test it? ▪ The Snellen eye chart (central vision) ▪ Peripheral field tests (peripheral vision) ▪ Observation of the back of the eye (ophthalmoscope) • Assesses the retina (the “light sensor”) ▪ Others – pupillary movements, rapid involuntary eye movements Cranial Nerve II Cranial Nerve III, IV, VI • Main Function: Eye movements (somatic motor) ▪ CN III: from the midbrain → muscles around the eye • As well, CN III projects to your pupillary muscles (dilation, constriction) and your levator palpebrae superioris muscle (helps elevate your eyelid) ▪ CN IV: from midbrain → one of the muscles around your eye (superior oblique) ▪ CN VI: from the pons → one of the muscles around your eye (lateral rectus) ▪ Skull entry/exit point for all: superior orbital fissure • We’ll discuss the actions of all of these eye muscles in detail for later… but for now: ▪ CN III – most eye movements and control of pupils ▪ CN IV – directs your gaze down and outwards ▪ CN VI – directs gaze laterally (abducts eyeball) Cranial Nerves III, IV, VI Cranial Nerves III, IV, VI • How do we test them? ▪ You can see that these nerves innervate very small, quick, coordinated muscles that help us to control our eye movements ▪ Test them by: 1. Ask patient to “follow your finger with their eyes” 2. Move your finger so that you draw a big “H” in the air in front of them • Eyes should smoothly follow your finger 3. Shine a light into the patient’s eyes and hold an object close to patient’s eyes • Pupils should constrict in response Cranial Nerves III, IV, VI Cranial Nerve V • Two major functions: 1. Sensation over the face, scalp, nasal cavity and cornea (somatic sensation) ▪ Sensations include touch, pain, proprioception for facial muscles and tongue ▪ Cornea = clear, tough outer part of the eye that overlies the iris ▪ Exits from the pons, leaves skull through: • Superior orbital fissure: cornea, forehead, scalp, eyelids, nasal mucosa (upper face, scalp) • Foramen rotundum: face over the maxillary part of the face, including maxillary teeth (mid-face) • Foramen ovale: lower jaw, proprioception for tongue (lower face, mouth – but NOT taste) Cranial Nerve V • Two major functions: 2. Motor function (somatic motor) for the muscles of mastication (chewing) and some neck, middle ear muscles ▪ Main muscles – temporalis, masseters, pterygoids ▪ Exits through the foramen ovale • How do we test it? 1. Sensory – sharp, dull, and light touch over the face 2. Strength of jaw clenching and movements of the jaw Cranial Nerve V Sharp sensation → break the wooden “stick” of the cotton swab Cranial Nerve VII The trickiest nerve: • Functions: 1. Facial movements OTHER THAN the tongue, eye muscles, and muscles of mastication (somatic motor) ▪ Remember from anatomy? Eye opening? Pursed lips? Raised eyebrows? ▪ Controls many skeletal muscles in the head – actually controls more muscles than any other nerve in the body 2. Taste from the anterior 2/3 of the tongue (special sense → taste) 3. Autonomic motor input to glands (“autonomic” motor) ▪ Salivary and tears ▪ Nasal glands (nasal secretions) 4. Somatic sensation from the ear canal (somatic sensory) Cranial Nerve VII – keeping it simple • Simplified anatomy: ▪ Exits/enters the pons → passes through the internal acoustic meatus and facial canal, exits through the stylomastoid foramen ▪ Many branches – if you’re really curious, check out this excellent, free reference: https://www.ncbi.nlm.nih.gov/books/NBK526119/#!po=6. 25000 • How do we test it? ▪ Pretty simple – you ask the patient to use her facial muscles (make particular faces at you) Cranial Nerve VII Cranial Nerve VIII • Hearing apparatus: ▪ Sound waves enter the ear canal → vibration of the tympanic membrane ▪ Tympanic membrane vibrations → movements of tiny bones in the middle ear (malleus, incus, stapes) • all of these bones act as levers to increase the amplitude of sound vibrations ▪ Vibrations transmitted from the stapes into the cochlea (snail-looking thingy) within the inner ear ▪ Vibrations in cochlear fluid move hairs in the cochlea → ▪ Hairs transduce vibrations into electrical impulses → ▪ Electrical impulses are carried by CN VIII Cranial Nerve VIII • Function - Hearing and balance (special senses) ▪ From inner ear → internal acoustic meatus → pons • From pons it passes through the thalamus and synapses in the temporal lobe for the perception of sound • Hearing – how do we test it? ▪ Whisper to patient to test for auditory acuity ▪ Tuning forks – allow you to tell if there’s a problem with the nerve or with the ear canal → ear drum → cochlea pathway • Tuning forks can be “heard” by conduction of the tuning fork vibration through the bones of the skull • If you “hear” the tuning fork better when it’s sending vibrations through your skull (versus being held up to your ear) → ▪ have a problem with sound conduction through the ear canal, ear drum, or the tiny bones of your middle ear Cranial Nerve VIII Cranial Nerve VIII • Balance and equilibrium – how do we test it? ▪ We’ve already covered this a bit – the gravity- and motion-detecting apparatus of the ear feeds important information to the cerebellum • Vestibular apparatus ▪ If the vestibular apparatus or the vestibular component of CN VIII is compromised, balance is impaired • Can be observed when patient is standing with eyes closed (tends to fall over) or with abnormalities in gait (tends to veer to one side or the other) ▪ Many patients with impaired vestibular function are also very nauseous and have rapid, involuntary eye movements (nystagmus) Cranial Nerve IX • Function: 1. Swallowing – (somatic motor) 2. Sensation from the pharynx, part of the external ear (somatic sensory) and from chemoreceptors/baroreceptors in the carotid body (“autonomic sensory”) 3. Taste from posterior 1/3 of tongue (special sensory) 4. Innervation of a salivary gland – parotid (“autonomic motor”) ▪ Nerve enters/exits through the jugular foramen in the skull and projects to/leaves the medulla • How do we test it? ▪ Stimulate the posterior aspect of the pharynx (careful – this causes a gag reflex) ▪ The soft palate and tongue elevate (CN X) when stimulation is detected (CN IX) ▪ Not the most helpful test – many healthy people have a diminished gag reflex Cranial Nerve IX Cranial Nerve X • We’ll talk much more about CN X as we discuss the autonomic nervous system ▪ It projects to a wide variety of organs such as the lungs, heart, liver, and gastrointestinal tract (among others) ▪ Nerve is called the vagus nerve (“vagus” means “wanderer”) • Major functions: ▪ Pharyngeal muscles –swallowing - and laryngeal muscles vocal cords (somatic motor) ▪ Parasympathetic nervous system input to the visceral organs discussed above (“autonomic motor”) • “Rest and digest” aspect of the autonomic nervous system ▪ Sensation from the visceral organs it impacts (“autonomic sensory”) and some of the pharynx and external ear (“somatic sensory”) ▪ Sensory input from aortic baroreceptors and chemoreceptors (“autonomic sensory”) Cranial Nerve X • How do we test it? ▪ Usually by listening to the patient’s voice – if hoarse, then it may be due to damage of the vagus motor input to the vocal cords ▪ Ask the patient to say “ahhhh” → elevation of the palate is part of the somatic function of the vagus nerve ▪ We don’t usually test the function of parasympathetic nervous system at the vagus nerve level Cranial Nerve X Cranial Nerve XI • Function – innervation of the sternocleidomastoid and trapezius (somatic motor) ▪ CN XI isn’t really a true cranial nerve – the neuronal cell bodies are actually located in the cervical spinal cord • this nerve travels into the skull (foramen magnum)… • and then back out again (jugular foramen) • How do we test it? ▪ Turning the head against resistance ▪ Shrugging the shoulders Cranial Nerve XI Cranial Nerve XII • Function – innervation of the tongue (somatic motor) ▪ Key for speech and swallowing ▪ Exits the medulla and passes through the hypoglossal canal • How do we test it? ▪ Ask the patient to stick out her tongue, and move it side to side • If the tongue is deviated or the patient can’t follow these instructions, then damage could be at the level of the nerve, medulla, or motor cortex Cranial Nerve XII The foramina – from MSK anatomy The foramina – from MSK anatomy The major sensory pathways - review • The special senses are all carried via the cranial nerves – all will eventually project to the cortex ▪ Vision – occipital lobe ▪ Sound – temporal lobe ▪ Taste and smell – inferior-lateral frontal lobes • The other senses – pain, touch, vibration, proprioception, temperature – all project to the postcentral gyrus in the parietal lobe ▪ Touch, vibration, proprioception – dorsal column-medial lemniscal system ▪ Pain, temperature – spinothalamic tract ▪ These two pathways have somewhat different anatomy Major sensory pathways • Dorsal column-medial lemniscal system ▪ Neurons that receive sensory input (first order neurons) send their axons to the dorsal horn (gray matter of spinal cord) and then project into the dorsal columns (white matter of spinal cord) ▪ These axons stay on the same side until they enter the medulla • After entering the medulla, they synapse on another neuron → ▪ The next neuron (second-order neuron) crosses to the other side of the medulla, and then synapses with another neuron in the thalamus (third order neuron) → • The third order neuron projects to the post-central gyrus Dorsal Column System and Spinothalamic Tract Major sensory pathways • Spinothalamic Tract ▪ Neurons that receive sensory input (first order neurons) send their axons to the dorsal horn (gray matter of spinal cord) → • and then synapse with another cell in the dorsal horn (second-order neuron) ▪ The axon of the second order neuron crosses over in the gray matter, then sends its axon up to the brain in the lateral and anterior white matter of the spinal cord → ▪ The second-order neuron synapses with another neuron in the thalamus (third-order neuron) → • Third order neuron synapses with a neuron in the postcentral gyrus Dorsal Column System and Spinothalamic Tract Testing sensation • Each spinal nerve collects information from a part of the body and sends it to the thalamus and to the prefrontal gyrus ▪ Loss of sensation can be at the level of the spinal nerve, the spinal cord, the thalamus (rare) or at the level of the cortex ▪ We “map out” neurologic deficits in sensation by testing “dermatomes” • Specific dermatomes aren’t always the same among individuals ▪ some areas of the body will be supplied by one spinal nerve in one person and a totally different spinal nerve in someone else Classic Dermatomes • These dermatomal maps that correspond to the spinal nerves were drawn out many decades ago • Significant variation between individuals has been confirmed in numerous studies • Example of “old” and less accurate diagram → Dermatomes you can (sort of) bank on • The dermatomes illustrated here are a little more consistent across individuals ▪ In general, more peripheral regions (hands, feet) have a little more variability across individuals) ▪ i.e. thumb – literature suggests C6, C7 can variably contribute Testing dermatomes • Sharp – usually a “somewhat” sharp object ▪ A splintered wooden tongue depressor or cotton swab, for example ▪ Spinothalamic tract • Dull or soft – cotton swab ▪ Dorsal column-medial lemniscal • Vibration sense – tuning fork on bony prominence ▪ Dorsal column-medial lemniscal Sharp sensation → break the wooden “stick” of the cotton swab Reliable-ish dermatomes Level Area C2 Scalp C3 Front of Neck C4, C5 Shoulder C8, T1 Little finger T4 Nipple-level T10 Umbilicus L2 Thigh L4 malleoli, medial anterior lower leg L5 Malleoli, lateral anterior leg S1 Lateral posterior leg, lateral plantar foot S3, S4, S5 Perineal area