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Neurology Chapter 15

Cranial Nerves

TermDefinition
Classification for the 31 Spinal Nerves General- Efferent or Afferent neurons that serve general motor and sensory functions (movement of fingers, sensation of temp or touch)
Cranial nerve Classification 3 ways to classify: 1. Afferent/Efferent 2. General/Special 3. Somatic/Visceral
General CN Classification Efferent and/or Afferent (just like spinal nerves)
Special CN Classification -Efferent and/or Afferent. -Use special receptors and neurons to serve additional specialized functions (i.e. vision, smell, taste)
Somatic CN Classification -Efferent and/or Afferent. -Innervate somatic muscles (muscles that arise from the soma in the embryological stage) –Usually related to voluntary muscle control
Visceral CN Classification -Afferent and/or Efferent. -Innervate visceral structures.
3 comparrisions of Cranial nerves to Spinal nerves 1. More specialized function than spinal nerves. 2. Cortical area responsible for cranial nerves larger than area responsible for spinal nerves. 3. Special receptors for things like taste and smell only found in the cranial nerves.
Only classification combination for CN that does NOT exist Special, somatic, efferent.
General Somatic Efferent CN Nerves -Involved in Activating Muscles from Somites -Skeletal, Extraocular (outside of the eye), Glossal (mussels of of the tongue)
General Visceral Efferent Activates Visceral Organs
Special Visceral Efferent -Activates Muscles of face, palate, mouth, pharynx and larynx -Excludes eye and tongue muscles -Some originate from the branchial arches
Special Visceral Afferent -Mediates visceral sensation of taste from tongue -Olfaction from Nose
General Visceral Afferent -Mediates sensory innervation from visceral organs
General Somatic Afferent -Mediates information from muscles, skin, ligament and joints
Special Somatic Afferent -Mediates special sensations of vision from retina and audition and equilibrium from inner ear
Why are speech related muscles considered visceral? -during Embryo develop some speech related muscles develop from branchial arches and are under voluntary control
Branchial arches in the embryo -Six branchial arches present in embryo -One disappears during development -Some cranial nerves originate from 5 brachial arches and are special visceral efferent nerves
CN's that originate from the Brachial Arches 1. Trigeminal (V) 2. Facial (VII) 3. Glossopharyngeal (IX) 4. Superior laryngeal and recurrent laryngeal branches of Vagus (X)
3 Midbrain Nuclei -Two Motor N. of Oculomotor: Control Eye Muscles -One Motor N. of Trochlear: Controls Eye Muscles
6 Pons Nuclei -3 Sensory N. of Trigeminal: Mesencephalic N, Primary Sensory N, Spinal Trigeminal N. -1 Motor N. of Trigeminal N. -1 Abducens N. -1 Facial Motor N.
9 Medulla Nuclei 1Cochlear N-Hearing 2Vestibular N-Equilibrium 3Salivary N-Secretions 4Dorsal Motor N-Visceral Motor 5Hypoglossal N-Tongue 6N Solitarius-Visceral Sensory 7Spinal Trigeminal N-Sensory 8N Ambiguus-Laryngeal/pharyn Motor 9Inferior Olivary N-cerebellum
Nucleus Solitarius & Nucleus Ambiguus -Nucleus Solitarius takes in info that triggers the swallowing reflex. -The loop goes through to the Nucleus Ambiguus which puts out the motor response to swallow. -Lesion in these areas will cause an absent of the swallowing reflex.
Pathway of Upper Motor Corticobulbar Neurons Motor neurons that come from cortex down to brainstem -crosses midline at different levels of the brainstem
Pathway of Lower Motor Corticobulbar Neurons -Starts at nuclei and carries info away from brainstem
Clinical signs of Upper Motor Neuron Lesion in Corticobulbar Tract -Spasticity -Increased Tendon Reflexes -Contralateral Paresis(weakness of voluntary movement)
Clinical signs of Lower Motor Neuron Lesion in Corticobulbar Tract -Paralysis -Absent Reflexes -Flaccid Muscle Tone -Fibrillation (twitching of muscles) -Fasciculations (small tremors in the tongue) -Atrophy (waiting away of muscles)
Pathway Sensory Neurons -1st Order: Enters the brainstem -2nd order: Cell bodies in gray matter of brainstem (Goes from brainstem up to thalamus) -3rd order:Cell bodies in ventral posterior medial N. of Thalamus project to sensory cortex in parietal lobe
Exception to 3rd order in Sensory Neurons Smell, hearing and vision are exceptions b/c they go through different nuclei in the thalamus
Olfactory Nerve (I) -Special, visceral, afferent -Function: Smell -Parts:Olfactory Bulb, Olfactory Tract, Extends into the Temporal Cortex
Clinical signs for lesion of Olfactory Nerve -Olfactory ability decreases with age -Tested by asking patient to identify odors
Anosmia -impaired sense of smell
Optic Nerve (II) -Special, somatic, afferent -Carries info from the Retina to Optic Nerve to Optic Chiasm -Info Relayed To Lateral Geniculate Body of the thalamus -To Optic Radiations -To Visual Cortex in Occipital Lobe
Injury of Optic Nerve - Results in common visual field losses -Testing: Patient closes one eye and fixes gaze straight ahead. Determine when patient can see objects in parts of visual field
Visual field neglect -In attention to one side of the visual field. Usually due to a stroke in right parietal lobe. Will ignore everything on left side.
General somatic efferent path of the Oculomotor Nerve (III) -Innervate extrinsic muscles of eye -Controls all eye muscles except for lateral rectus -Regulates eye lid elevation
General visceral efferent path of the Oculomotor Nerve (III) -Provides motor innervation for iris/pupil and ciliary muscles to adjust to light and lens to focus for near vision -Starts in the Edinger-Westphal Nucleus
What does Left Oculomotor Nerve Paralysis result in? -left eye will deviate laterally causing diplopia. Eased when good eye moves to left. Diplopia results in lazy eye & info in 1 eye becomes ignored. -Ptosis (eyelid droop) -Ophthalmoplegia:problems in adjusting to light and deviation of eye movements
Trochlear IV -General, somatic, efferent -Only CN to exit brainstem dorsally -Anterior oblique muscle for eye movement is only function -One of the 2 nerves that only innervate one muscle in each eye
Injury of Trochlear IV results in? Problems with this nerve will cause Difficulty looking downward and outward when paralyzed
General, somatic, afferent Trigeminal (V) -Principal sensory nerve for head, face, orbit and oral cavity -Mediate sensations of pain, temperature, proprioception and fine discriminative touch -Sensations from anterior 2/3 of tongue. Very important for swallowing
Special visceral efferent Trigeminal (V) Motor for mastication muscles for chewing and speaking -Internal and external pterygoid -Temporalis -Masseter -Mylohyoid -Anterior belly of digastric -Tensor veli palatini -Tensor tympani
Three sensory branches of the Trigeminal (V) 1. Ophthalmic 2. Maxillary 3. Mandibular
Test for Trigeminal V issue -Reflex test for jaw jerk reflex (mandibular)
Pimary function of the Trigeminal V nerve -To innervate muscles for chewing -Has more sensory than motor fibers.
Tic of douloureux (trigeminal neuralgia) -Disorder of the sensory portion of the Trigeminal V nerve. -Causes excruciating pain in mandibular part of face
Signs of Sensory Trigeminal V issue -Test for touch discrimination in different facial zones (sensory) -Check for sneeze and corneal reflexes (sensory) -Tic of douloureux (trigeminal neuralgia)
Signs of Motor Trigeminal V issue -paralysis or paresis of ipsilateral muscles of mastication -absent or exaggerated jaw reflex -deviation of jaw toward side of injury --------Unilateral lesion has mild effect on bite strength while bilateral has severe effect on bite strength
Abducens (VI) -General, somatic, efferent -Innervates lateral rectus muscle which moves eye laterally -Only innervates one muscle in each eye
Lesions in Abducens (VI) -Susceptible to disruption due to lesion in brainstem -Check for medial strabismus: Eye Turns in medially and patient has Double vision
Facial Nerve (VII)General visceral efferent -Parasympathetic innervation of lacrimal gland which secretes palatal saliva -Innervation of mucous membrane secretions in mouth and pharynx
Facial Nerve (VII)Special visceral afferent Gustatory sensations from anterior 2/3 of tongue( taste of 2/3 of tongue)
Facial Nerve (VII)Special visceral efferent -Primary motor nerve for movement of facial muscles. Innervates: -Extrinsic Muscles of ear -Stapedius Muscle of the middle ear -Stylohyoid Muscle -Posterior Belly of Digastric Muscle
Upper Motor Neuron Disease of Facial Nerve (VII) -Unilateral paresis of muscles of lower half of face -Top facial Muscles bilaterally innervated -lower muscles unilaterally innervated -Bilateral lesion can cause paralysis of upper and lower muscles bilaterally -lesion located contralaterally
Lower Motor Neuron Disease of Facial Nerve (VII) -Can be caused by injury near pons -Unilateral Paralysis of all facial muscles, stapedial muscle and taste in 2/3 of tongue -entire side of face droops -ipsilateral leasion location
Bell’s Palsy -LMN syndrome with sudden onset of paralysis of ipsilateral facial muscles -Inflammatory injury, infection or degenerative disease that effects the facial nerve usually unilaterally (most cases it’s an unknown origin)
Vestibulo-acoustic Nerve (VIII) -Special somatic afferent nerves -Relays info from Cochlea & semi circular canals of the vestibular system -Vestibular Nerve:Gives feedback about position of head & balance -Acoustic Nerve:Carries info for hearing from organ of corti to brainstem
Signs of damage in Vestibulo-acoustic Nerve (VIII) -Lack of equilibrium, vertigo or dizziness, nystagmus system (due to lack of coordination of info from vestibular system and coordination of the eyes) and and hearing loss
Glosso- pharyngeal Nerve (IX) -Important for initiating the swallowing reflex along with the Vagus nerve b/c it relays touch and taste from the mouth witch helps trigger the swallow reflex.
Glosso- pharyngeal Nerve (IX)General, visceral, afferent -Mediates general visceral sensation from soft palate, palatal arch, posterior 1/3 of tongue and carotid sinus -touch
Glosso- pharyngeal Nerve (IX)General visceral efferent -Secretion from parotid gland (salivary gland)
Glosso- pharyngeal Nerve (IX)Special visceral afferent -Taste sensation form posterior 1/3 of tongue
Glosso- pharyngeal Nerve (IX)Special visceral efferent -Contributes to swallowing through stylopharyngeus and upper pharyngeal constrictor fibers
Signs of damage to the Glosso- pharyngeal Nerve (IX) -May be evident in dysphagia or loss of taste to posterior 1/3 of tongue -Loss of gag reflex -Excessive oral secretions -Dry mouth -Need bilateral damage of nerve to have strong clinical signs due to bilateral innervation
Vagus Nerve (X)General visceral afferent -Takes care of Sensation from pharynx, larynx, thorax, abdomen -Regulates nausea, oxygen intake, lung inflation
Vagus Nerve (X) General visceral efferent -Innervates glands, cardiac muscles, trachea, bronchi, esophagus, stomach and intestine
Vagus Nerve (X)Special visceral afferent -Mediates taste sensation from posterior pharynx and epiglottis
Vagus Nerve (X)Special visceral efferent -Controls muscles of larynx, pharynx, soft palate for phonation, swallowing and resonance
Signs of damage to the Vagus Nerve (X) -Bilateral lesion can be fatal due to respiratory involvement -Unilateral lesion can result in ipsilateral paresis or paralysis of soft palate, pharynx and larynx -Autonomic reflexes reduced -Anesthesia of pharynx and larynx and loss of taste
Branches of the Vagus Nerve (X) -Pharyngeal Branch -Recurrent Laryngeal Branch -Superior Laryngeal Branch
Lesion in Pharyngeal Branch of the Vagus Nerve (X) -Pharynx and soft palate involvement -Uvula pulled to unaffected side, bilateral soft palate droops
Lesion in Recurrent Laryngeal Branch of the Vagus Nerve (X) -Unilateral: Paralysis of a single vocal fold (person will still have a voice) -Bilateral: Causes Inspiratory stridor and aphonia (person will not have a voice in bilateral leagion)
Lesion in Superior Laryngeal Branch of the Vagus Nerve (X) Loss of ability to change pitch
Spinal Accessory Nerve (XI) -General visceral efferent -Purely a motor nerve -Controls head and shoulders by innervating the trapezius and sternocleidomastoid muscles
Lesion in the Spinal Accessory Nerve (XI) -Affects ability to control head movements -Ask patient to rotate head and raise shoulders to note control
Hypoglossal Nerve (XII) -General somatic efferent -Controls tongue movement -Controls extrinsic and intrinsic muscles of tongue except palatoglossal (X) -Eating, sucking and chewing reflexes
Lesion in the Hypoglossal Nerve (XII) -LMN unilateral lesion can cause wrinkling and flaccidity of tone with atrophy over time resulting in Dysarthria and Dysphagia -Unilateral UMN lesions do not have much affect as tongue is bilaterally innervated To test- Ask to complete tongue movements
Nerves for Eyes muscle control Oculomotor III, trochlear IV, Abducens VI
Nerve Sensory supply to tongue -Anterior 2/3 special and general sensation: Facial and Trigeminal, -Posterior 1/3 special and general sensation: Glossopharyngeal
Motor Nerves that Supply to Soft Palate and Pharynx Vagus, Trigeminal and Glossopharyngeal
Sensory Nerves that Supply to Soft Palate and Pharynx Glossopharyngeal, Vagus and Trigeminal
Created by: aramos139