Cranial Nerves Notebook - Post-Midterm PDF

Notebook – Post-Midterm 2024-10-31 3:20 PM Cranial Nerves: 12 pairs of cranial nerves They originate in the brain and pass through various foramina in cranial bones Part of the PNS...

Notebook – Post-Midterm 2024-10-31 3:20 PM Cranial Nerves: 12 pairs of cranial nerves They originate in the brain and pass through various foramina in cranial bones Part of the PNS The number indicates the order (anterior to posterior) that nerves arise from the brain The name indicates the nerve's distribution or function Sensory nerves Most of their cell bodies are in ganglia outside the brain Motor nerves Their cell bodies are in nuclei within the brain Nerves: I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Accessory XII Hypoglossal Olfactory Nerve: I Olfactory Epithelium Shortest cranial nerve (in length) Olfactory Epithelium: Where is it? Superior part of nasal cavity Inferior surface of the cribriform plate (ethmoid) Along the superior nasal concha Consists of 3 types of cells: 1. Olfactory receptors 2. Supporting cells 3. Basal cells – stem cells, consistently divide to make more supporting cells and olfactory receptors Type: Sensory The Olfactory Pathway 1. Olfactory receptors 2. Axons of olfactory receptors form the olfactory nerve 3. Axons go through the olfactory foramina in cribriform plate 4. Olfactory bulbs 5. Olfactory tracts 6. Primary olfactory area (temporal lobe) + limbic system (emotions) + hypothalamus (satiety & ANS – salivation) 7. Frontal lobe (orbitofrontal area) ***Olfactory sensations are the only sensations that reach the cerebral cortex without first synapsing in the thalamus *** Definitions Hyperosmia Increased sense of smell Women often have a keener sense of smell than men do, especially during ovulation Anosmia Loss of sense of smell Cause: infections of nasal mucosa head injuries lesions along olfactory pathway Meningitis Smoking cocaine use Smoking seriously impairs smell in the short term and may cause long-term damage to olfactory receptors Sense of smell deteriorates with age Hyposmia Reduced ability to smell Affects half of those over 65 and 75% of those over 80 Can also be caused by neurological changes Optic Nerve: II 3 layers of retinal neurons: 1. Photoreceptors 2. Bipolar cell layer 3. Ganglion cell layer Type: Sensory 1. Photoreceptors Start the process of converting light rays to nerve impulses Cones Stimulated in bright light Colour vision High acuity – definition/clarity Concentrated in the center of retina Rods Allow us to see in dim light No colour – black/white/grey (they can't tell colour) Low acuity – definition/clarity Concentrated in the periphery Sensitive 2. Bipolar cell layer Also has horizontal + amacrine cells They form lateral connections involved in modifying signals 3. Ganglion cell layer Their axons extend posteriorly to optic disc and exit the eye as the optic nerve Light passes through the ganglion + bipolar cell layers before it reaches the photoreceptor layer Pathway 1. Rods + cones ( then to bipolar cells – then to ganglion cells ) 2. Optic nerve 3. Through the optic foramen 4. Optic chiasm ( where the optic nerves cross over – 50% ) 5. Optic tract -------------> superior colliculi (tectum – midbrain) 6. Lateral geniculate nucleus (thalamus) 7. Primary visual area (occipital lobe) Definitions Anopia Blindness due to a defect or loss of 1 or 2 eyes Cause: Fractures in orbit Brain lesions Damage along the pathway Disease of the nervous system Pituitary gland tumours – presses on the optic chiasm (b/w the hypothalamus & pituitary) Cerebral aneurysm Extrinsic Eye Muscles Extrinsic eye muscle extend from the bony orbit to the sclera Superior rectus – look upward Inferior rectus – look downward Lateral rectus – look laterally – abducens nerve Medial rectus – look medially Superior oblique – down and out (inferiorly and laterally) - trochlear nerve Inferior oblique – up and out (superiorly and laterally Oculomotor Nerve: III Types: 1. Motor Pathway 2. Autonomic Motor Pathway Motor Pathway Eye movement – superior, inferior, medial rectus & inferior oblique Open upper eyelid – levator palpebrae superioris Autonomic Motor Pathway Ciliary muscle – adjust the lens for near vision "accommodation" Circular mm of iris – pupil constriction Image Formation As light enters the eye, it is refracted at the cornea The lens further refracts the light rays so they come into exact focus on the retina Image formation: 1. Refraction or bending of light by the lens & cornea 2. Accommodation (the change in the shape of the lens) When an object is 20ft or more away, the light rays reflected from the object are nearly parallel to one another The lens must bend the rays just enough so that they fall on the central fovea Accommodation When the eye is focusing on a close object, the lens becomes more spherical, causing greater refraction of light rays Ciliary muscle Adjust the lens for near vision "accommodation" Circular mm of iris Pupil constriction Pupil Diameter Regulation How is pupil diameter regulated? Contraction of the circular muscles causes constriction of the pupil Contraction of the radial muscles cause dilation of the pupil Damage to Oculomotor Nerve 1. Strabismus A condition in which both eyes do not fix on the same object, since one or both eyes may turn inward or outward (lazy eye) 2. Ptosis Drooping of upper eyelid 3. Movement of eyeball downward + outward on damaged side 4. Loss of accommodation for near vision 5. Diplopia Double vision Trochlear Nerve: IV Smallest cranial nerve (in diameter) The only one that arises from the posterior brain stem Type: Motor Pathway 1. Trochlear nucleus in midbrain 2. Superior orbital fissure 3. Superior oblique mm of eyeball Damage to Trochlear Nerve 1. Strabismus A condition in which both eyes do not fix on the same object, since one or both eyes may turn inward or outward 2. Diplopia Double vision Abducens Nerve: VI Type: Motor Pathway 1. Abducens nucleus in pons 2. Superior orbital fissure 3. Lateral rectus mm of eyeball Damage to Abducens Nerve Affected eye can't move laterally beyond midpoint and eyeball is usually directed medially This leads to strabismus and diplopia Trigeminal Nerve: V Largest cranial nerve (in diameter) Types: 1. Sensory pathway 2. Motor pathway Sensory Pathway Ophthalmic branch: 1. Sensory from upper 1/3 of face (forehead ect.) 2. Superior orbital fissure 3. Ophthalmic branch 4. Trigeminal ganglion 5. Pons Maxillary branch: 1. Sensory from middle 1/3 of face (upper teeth ect.) 2. Foramen rotundum 3. Maxillary branch 4. Trigeminal ganglion 5. Pons Mandibular branch: 1. Sensory from lower 1/3 of face (jaw ect.) 2. Foramen ovale 3. Mandibular branch 4. Trigeminal ganglion 5. Pons Motor Pathway In mandibular branch Supply muscles of mastication These motor neurons mainly control chewing Tensor tempane (muscle in your ear) - don’t need to know Pathologies: Trigeminal Neuralgia Sharp cutting, intense pain that lasts for a few seconds to a minute Pain is within the nerve's distribution Cause By anything that presses on the trigeminal nerve or its branches Local compression Herpes zoster Vascular lesions Tumours Demyelinating conditions with subsequent scarring (MS) Idiopathic Symptoms Sudden painful attacks Pain is knife-like, "like a lightening bolt inside my head that lasts for seconds to minutes" Pain often occurs in clusters Unilateral Along one or more distributions of the nerve Usually CN V2 or CN V2 and CN V3 Usually more on the bottom half of the face (less on the top of the head or forehead) Any mechanical stimulation, chewing, smiling, a breeze felt on the cheek can trigger an attack Patients avoid stimulating the trigger zone Trigger zones Lips, face, tongue (touch, temp, facial movement) Facial Nerve: VII Types: 1. Sensory pathway 2. Motor pathway 3. Autonomic pathway Sensory Pathway 1. Taste buds of anterior 2/3 of tongue 2. Stylomastoid foramen 3. Geniculate ganglion 4. Pons 5. Thalamus 6. Gustatory area of cerebral cortex (the insula) Also sensory axons from skin in ear canal (touch, pain, temp) Motor Pathway 1. Nucleus in pons 2. Stylomastoid foramen 3. Facial expression muscles, stylohyoid mm, posterior digastric mm, stapedius mm smallest skeletal muscles = stapedius (clamp down so there are less vibrations) Autonomic Pathway Does a lot of stuff, innervates: Innervates tear glands Nasal glands (mucus) Palatine glands (mucus in mouth) Submandibular glands (salivary glands) Sublingual glands (salivary glands) Facial nerve goes underneath parotid gland - can cause problems Pathologies: Bell's Palsy Is a condition involving the facial nerve – facial nerve paralysis Results in paralysis of the muscles of facial expression on the same side as the lesion One of the most common neurological conditions It affects at least 25 out of 100,000 people each year Symptoms Unilateral weakness followed by flaccid paralysis of muscles of facial expression Onset of symptoms from weakness to flaccid paralysis is quite rapid If sensory + autonomic affected Can't control lacrimation Usually decrease in salivation Cant taste on anterior 2/3 of tongue Heightened sensitivity of hearing (hyperacusia) – stapedius Sagging of face and eyelid with possible pulling toward unaffected side Cause Nerve damage from Viral infection – shingles Bacterial infection – lyme's disease Compression from edema with Pregnancy Middle ear infection Diabetes Hypertension Hypothyroidism Leprosy Conditions involving the parotid gland – not innervated by the facial nerve but facial nerve runs under it Trauma Exposure to chill or draft Vaccines cause Bell's Palsy Prognosis If only segmental demyelination (as with compression) Recovery is usually in 2 – 8 weeks If Wallerian degeneration Poorer prognosis Treatment Treat the cause, if known Often no treatment because there is spontaneous recovery in 70% of cases Protect the eye with eye patch and antibiotic drops Stroke Differentiation People often fear paralysis of one side of face is from stroke (UMN) but stroke generally affects the lower muscles of face (not frontalis or muscles around eye) So during a stroke, patient can close eye and wrinkle forehead but can't smile Vestibulocochlear Nerve: VIII Type: Sensory Function Hearing and equilibrium 2 Branches 1. Vestibular branch (balance) 2. Cochlear branch (hearing) Injury to Vestibulocochlear Nerve Trauma Lesions Middle ear infection Vestibular Branch Carries impulses for equilibrium Pathway 1. Semicircular canals, the saccule + utricle of inner ear (balance portion of hear) 2. Vestibular ganglion 3. Vestibular nuclei in pons + medulla Injury to Vestibular Branch Vertigo A subjective feeling that one's own body or the environment is rotating Ataxia Muscular incoordination Nystagmus Involuntary rapid movement of the eyeball Cochlear Branch Carries impulses for hearing Pathway 1. Spiral organ (organ of corti) in cochlea of internal ear 2. Spiral ganglion 3. Internal acoustic meatus 4. Cochlear nuclei in medulla 5. Thalamus (medial geniculate) 6. Primary auditory area Injury to Cochlear Branch Tinnitus Ringing in ears More of a chronic problem – big question mark with this condition Deafness Glossopharyngeal Nerve: IX Types: 1. Sensory pathway 2. Motor pathway 3. Autonomic pathway Sensory pathway 1. Taste buds on posterior 1/3 of tongue 2. Proprioceptors from some swallowing muscles 3. Baroreceptors in carotid sinus that monitor BP 4. Chemoreceptors in carotid sinus 5. External ear to convey touch, pain, heat and cold | Superior and inferior ganglia (don’t worry about these) | Jugular foramen (2nd biggest foramen) | Medulla Only have baroreceptors in aorta and carotid The "junk drawer" Motor pathway 1. Nuclei in medulla 2. Jugular foramen 3. Stylopharyngeus muscle: helps elevate your pharynx when you swallow Autonomic pathway 1. Inferior salivary nucleus in medulla 2. Jugular foramen 3. Otic ganglion 4. Parotid gland Glossopharyngeal and facial nerve – innervate our salivary glands Injury to Glossopharyngeal Nerve Dysphagia – difficulty swallowing Aptyalia – lack of salivation Loss of sensation in throat – proprioception Ageusia – lack of taste Glossopharyngeal Neuralgia Recurrent attacks of severe pain in the CN IX nerve distribution Posterior pharynx, tonsils, back of tongue, middle ear Cause: Nerve compression Rare, more common in men – usually after 40 Get paroxysmal attacks of unilateral brief, excruciating pain Like in trigeminal neuralgia Occurs spontaneously or are precipitated by certain movements Chewing, swallowing, talking, sneezing Pain lasts seconds to a few minutes, usually begins in tonsil area or at base of tongue and may radiate to ipsilateral ear Distinguished from trigeminal neuralgia by: Location of pain In glossopharyngeal neuralgia, swallowing or touching the tonsils with an applicator triggers pain Vagus Nerve: X Types: 1. Sensory pathway 2. Motor pathway 3. Autonomic pathway "the wandering nerve" Longest of our cranial nerves (CNX) in length Sensory pathway 1. Skin of external ear for touch, pain, heat and cold 2. Taste buds in epiglottis and pharynx 3. Proprioceptors in mm of neck and throat 4. Baroreceptors in carotid sinus & chemoreceptors in carotid & aortic bodies 5. Most sensory axons come from visceral sensory receptors in most organs of thoracic & abdominal cavities that convey sensations (hunger, fullness, discomfort) | Superior and inferior ganglia (don’t worry about these) | Jugular foramen | Medulla Motor pathway 1. Medulla 2. Jugular foramen 3. Muscles of the pharynx, larynx & soft palate (swallowing, vocalization, coughing) Autonomic pathway 1. Medulla 2. Jugular foramen 3. Muscles Smooth muscle of lungs Cardiac mm Glands of GI tract Smooth mm of respiratory passageways Esophagus Stomach Gallbladder Small intestine Most of large intestine Injury to Vagus Nerve Vagal paralysis Interruptions of sensations from many organs in thoracic and abdominal cavities Vasovagal response (negative) Dysphagia - difficulty swallowing Tachycardia Accessory Nerve: XI Type: Motor Pathway 1. Motor axons from anterior grey horn of C1 – C5 2. Ascend through foramen magnum 3. Exit through jugular foramen 4. SCM & trapezius Its not really a cranial nerve – more like a spinal nerve cause it goes from C1 – C5 up to the head and then back down to the SCM & Trapezius Hypoglossal Nerve: XII Type: Motor Pathway 1. Hypoglossal nucleus in the medulla 2. Hypoglossal canal 3. Muscles of tongue (8 muscles in the tongue) Injury to Hypoglossal Nerve Difficulty chewing Dysarthia – difficulty speaking - happening at the end of the line (jaw/peripheral nerve problem) Dysphagia - difficulty swallowing Autonomic Nervous System: CNS: Central Nervous System Brain and spinal cord PNS: Peripheral Nervous System SNS Somatic nervous system Consciously controlled Voluntary Sensory receptors + motor neurons to skeletal muscles ANS Autonomic nervous system Involuntary Sensory from visceral organs Motor to smooth mm, cardiac mm & glands 2 subdivisions: sympathetic & parasympathetic Sympathetic "fight or flight" Increased alertness and metabolic activities in order to prepare the body for an emergency situation Parasympathetic "Rest and digest" Activities conserve and restore body energy Most output is to GI tract and respiratory tract ENS Enteric nervous system Involuntary Sensory from chemical changes in GI tract and stretching it Motor to GI smooth muscle Autonomic Tone: Most organs receive innervation from both divisions of the ANS, which typically work in opposition to one another Autonomic tone is the balance b/w sympathetic and parasympathetic activity What regulates the autonomic tone? Hypothalamus – king of the autonomic nervous system A few structures only receive sympathetic innervation: Sweat glands Arrector pili muscles Kidneys Spleen Most blood vessels Adrenal medullae Although they don’t have opposition from the parasympathetic nervous system, they still exhibit a range in responses: An increase in sympathetic tone has one effect A decrease in sympathetic tone has the opposite effect Sympathetic responses: During physical or emotional stress, the sympathetic division dominates the parasympathetic system High sympathetic tone favours body functions that can support vigorous physical activity and rapid production of ATP And reduces body function that favour storage of energy Emotions can stimulate sympathetic division (fear, embarrassment, rage) Fight or flight: Pupils dilate Heart rate, force of heart contraction and BP increases Airways dilate (faster movement of air into and out of lungs) BV to skeletal muscles dilate BV to cardiac muscles dilate BV to GI tract constrict BV to kidneys constrict BV to liver dilate – blood sugars BV to adipose tissue dilate – tryglycertides Parasympathetic responses: Rest and digest Parasympathetic responses support body functions that conserve and restore body energy during times of rest and recovery Rest and digest: Decreased heart rate Decreased diameter of airways Decreased diameter of pupils Increased salivation Increased lacrimation Increased urination Increased digestion Increased defecation Comparison: Somatic Nervous System Autonomic Nervous System Sensory Input From receptors for somatic senses (tactile, thermal, pain, From interoreceptors (sensory receptors located in BVs, proprioceptive sensations) visceral organs, mm and nn that monitor conditions in the internal environment) From receptors for special senses (sight, hearing, taste, smell, equilibrium) Not usually consciously percieved These are consciously percieved Control of motor output Primary motor area of cerebral cortex (frontal lobe) Involuntary control from hypothalamus Voluntary (with contributions from basal nuclei, cerebellum, brainstem and SC) Motor neuron pathway One neuron pathway Two neuron pathway Somatic motor neuron goes from CNS (anterior horn) to To chromaffin cells in adrenal medulla skeletal muscle Neurotransmitters Somatic motor neurons only release ACh Autonomic motor neurons release ACh or NE Hormones: NE (norepinephrine) & epinephrine Effectors Skeletal muscle Smooth muscle, cardiac muscle or glands Responses Contraction of skeletal muscle Contraction or relaxation of smooth muscle Increase or decreased rate & force of contraction of cardiac muscle Increased or decreased secretion of glands Anatomy of Autonomic Motor Pathways: The Main Parts: Preganglionic neuron Postganglionic neuron Autonomic ganglion Preganglionic Neuron: The first neuron in an autonomic motor pathway Cell body is in CNS Axon is a type B fiber Usually goes to an autonomic ganglion and synapses with a postganglionic neuron Sometimes goes to the adrenal medulla Two divisions: 1. Thoracolumbar division/sympathetic 2. Craniosacral division/parasympathetic 1. Thoracolumbar division/sympathetic In the sympathetic division preganglionic neurons have their cell bodies in the lateral horns of gray matter in T1 to L2 (sometimes L3) 2. Craniosacral division/parasympathetic In the parasympathetic division cell bodies of preganglionic neurons are in the nuclei of 4 cranial nerves (10, 9, 7, 3) and in the lateral gray matter of S2 to S4 Postganglionic neuron: The second neuron in an autonomic motor pathway In the PNS Cell body is in an autonomic ganglion Type C fiber Terminates in a visceral effector Autonomic Ganglia: Where the preganglionic and postganglionic neurons synapse Sympathetic division 1. Paravertebral ganglia (the sympathetic trunk ganglia) 2. Prevertebral ganglia Parasympathetic division 1. Terminal ganglia Sympathetic division 1. Paravertebral ganglia Aka. The Sympathetic Trunk Ganglia Aka vertebral chain ganglia Lie in a vertical row on either side of vertebral column The post ganglionic axons from here innervate organs above the diaphragm The ones in the neck have specific names: 1. Superior cervical ganglia 2. Middle cervical ganglia 3. Inferior cervical ganglia 2. Prevertebral ganglia Aka. collateral ganglia They lie anterior to the vertebral column Their post ganglionic axons innervate organs below the diaphragm 5 major ones: paired 1. Celiac ganglion 2. Superior mesenteric ganglion 3. Inferior mesenteric ganglion 4. Aorticorenal ganglion 5. Renal ganglion Parasympathetic division Terminal ganglia Most of these are located close to or within the wall of a visceral organ In the head they have specific names: 1. Ciliary ganglion (CN III) Ciliary muscles (oculomotor) Their post ganglionic neurons supply smooth muscle of the eye 2. Otic ganglion (CVIX) Parotid gland (glossopharyngeal) Supply parotid salivary glands 3. Pterygopalatine ganglion (CNVII) Facial nerve Their post ganglionic neurons supply nasal mucosa, palate, pharynx and lacrimal glands 4. Submandibular ganglion (CNVII) Salivation – Facial nerve Their postganglionic neurons supply submandibular and sublingual glands Connections: 4 ways sympathetic PREganglionic neurons connect with POSTganglionic neurons 1. In the first ganglion it reaches – This is always the first stop (paravertebral ganglion) 2. The axon may ascend or descend to a higher or lower ganglion and synapse there (goes to the next closest paravertebral ganglion) 3. The axon may go through the sympathetic trunk ganglion to synapse in a prevertebral ganglion (must pass through paravertebral first) - Splanchnic nerves (prevertebral) Greater splanchnic nerve Lesser splanchnic nerve Least (lowest) splanchnic nerve Lumbar splanchnic nerve 4. The axon may pass through the sympathetic trunk ganglion and prevertebral ganglion to synapse with chromaffin cells of the adrenal medulla (on top of the kidneys) Single sympathetic preganglionic fiber Has many axon collateral and may synapse with 20+ postganglionic neurons This is an example of divergence and helps to explain why many sympathetic responses affect almost the entire body simultaneously Parasympathetic preganglionic neurons Pass to terminal ganglia near or within a visceral effector They usually only synapse with 4 or 5 postsynaptic neurons, all of which supply a single effector Parasympathetic responses are localized to a single effect Autonomic Plexuses: Tangled network of axons of sympathetic and parasympathetic neurons In thorax, abdomen and plevis Also contain sympathetic ganglia and axons of autonomic sensory neurons Plexuses: Cardiac plexus In thorax – the heart Pulmonary plexus In throax - the lungs Celiac (solar) plexus Largest autonomic plexus Surrounds celiac trunk Contains 2 large celiac ganglia 2 aorticorenal ganglia Autonomic axons You can pass through the train station but you don’t have to get off at that stop Supplies stomach, spleen, pancreas, liver, gallbadder, kidneys, adrenal medullae, testes, ovaries Superior mesenteric plexus Supplies small + large intestines Inferior mesenteric plexus Supplies large intestines Hypogastric plexus Supplies pelvic viscera Renal plexus Supplies renal arteries and ureters Connections: 4 ways sympathetic POSTganglionic neurons connect with visceral effectors: 1. Spinal Nerves Postganglionic neurons enter a short pathway called the 'grey ramus' and then merge with the anterior ramus of the spinal nerve Grey rami communicantes contain sympathetic post ganglionic axons These axons provide sympathetic innervation to: visceral effectors in skin of neck, trunk, limbs (sweat glands, smooth mm in blood vessels and arrector pili muscles) 2. Cephalic periarterial nerves Axons coming off the superior cervical ganglion leave the trunk by forming cephalic periarterial nerves These are nerves that extend to the head by wrapping around and following the course of various arteries that pass from the neck to the head These neurons provide sympathetic innervation to: visceral effectors in the skin of the face (sweat glands, blood vessels, arrector pili muscles) visceral effectors of the head (smooth muscle of the eye, lacrimal glands, pineal gland, nasal mucosa and salivary glands 3. Sympathetic nerves Axons leave the sympathetic trunk by forming sympathetic nerves that extend to visceral effectors in the thoracic cavity Axons coming off the superior, middle, inferior ganglia and T1 – T4 ganglia form sympathetic nerves that enter the cardiac plexus to supply the heart Axons coming off T2 – T4 ganglia form sympathetic nerves that enter the pulmonary plexus to supply smooth muscle of the bronchi and bronchioles of the lungs To Adrenal Medulla: Preganglionic axons go to chromaffin cells in adrenal medullae of adrenal glands Adrenal medullae are modified sympathetic/autonomic ganglia (or modified postganglionic) Chromaffin cells release hormones into blood Epinephrine Norepinephrine Horners syndrome: Sympathetic innervation is lost when trauma or disease affect the sympathetic outflow through the superior cervical ganglion On the affected side: Ptosis – droopy eye Miosis – constricted pupils (lack of dilation) Anhydrosis – lack of sweat Enopthalmos – posterior displacement of eyeball Structure of the Parasympathetic Divison: Cranial Parasympathetic outflow: Cell bodies in nuclei in brain stem Preganglionic axons that extend from the brain stem along 4 cranial nerves *preganglionic axons that leave the brain as part of the vagus nerve carry about 80% of the total craniosacral outflow* 4 pairs of ganglia: 1. Ciliary ganglia (CN 3) Their post ganglionic neurons supply smooth muscle of the eye 2. Pterygopalatine ganglia (CN 7) Their post ganglionic neurons supply nasal mucosa, palate, pharynx and lacrimal glands