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Nervous system part 5
 

Nervous system part 5

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    Nervous system part 5 Nervous system part 5 Presentation Transcript

    • Cranial Nerves
    •  
    •  
    • Cranial Nerves
      • As many as 25
      • Named and numbered by Roman numerals from anterior to posterior
        • Why abandon numerical nomenclature?
        • Development/ origin/ evolution
        • Variation in function
          • Sensory
          • Motor
          • Mixed
        • Organization
        • Clinical application
      • Superficial origin vs. deep origin
    •  
      • Focus:
        • Origin/ location
        • Innervation
        • Type
        • Function
        • Notable location of cell bodies & nerve fibers
        • Clinical application
      • Derived from:
        • Neurectoderm
          • II, E
        • Neural crest
          • Ganglia of V, VII, IX, and X
        • Ectodermal placode
          • Ganglia of 0, I, VN, ALL and PLL
          • Taste bud components of VIII, VII, IX, and X
    • Sensory
      • 0
      • I (Olfactory)
      • VN (Vomeronasal)
      • II (Optic)
      • E (Epiphyseal Complex)
      • P (Profundus)
      • ALL & PLL (Lateral Line)
      • VIII (Vestibulocochlear)
    • O, Terminal
      • 13 th C.N. in humans
      • Last discovered C.N.
      • Gnathostome feature
      • Origin: ventral surface of forebrain
      • Innervation: nasal epithelium
      • Function: mediates responses to sex pheromones (pheromone receptor)
    • I, Olfactory
      • No ganglia
      • Location: olfactory bulb
      • Innervation: olfactory epithelium (cell bodies)
      • Function: smell
      • Fibers poorly developed in birds & platypus
      • Vestigial in marine mammals
      • Clinical application: anosmia, loss of smell, due to head injuries in which cribriform plate is injured
      • Olfactory pathway:
        • Olfactory mucosa > Cribriform plate > Olfactory bulb > Olfactory tract > Olfactory area of temporal lobe
    •  
    • VN, Vomeronasal
      • Innervation: vomeronasal organ (chemoreceptor)
    • II, Optic
      • No ganglia
      • Origin: optic chiasma
      • Innervation: retina (cell bodies)
      • Function: vision
      • Decussation – crossing over to the opposite
        • Non-mammalian
          • All decussate and enter opposite side of brain
        • Primates
          • Only axons from nasal side of retina decussate
          • Results in overlap of visual field (binocular vision)
          • Depth perception
      • Visual pathway
        • Optic nerve > Optic chiasm > Optic tract >
        • Lateral geniculate nucleus of thalamus >
        • Optic radiation > Primary visual area of cortex in occipital lobe
      • Optic nerve a misnomer because retina arises from paired optic vesicles from telencephalon
      • Lens derived from ectodermal placode
      • Clinical application: visual field defects, loss of visual acuity, anopia
    •  
    •  
    • E, Epiphyseal complex
      • Innervation: pineal and parapineal
      • Primitively fused with trigeminus as in sarcopterygians
      • Discrete in gnathostomes (derived)
      • Innervation: skin of snout
      P, Profundus
    • ALL and PLL, Lateral Line
      • Innervation: lateral line organs (mechanoreceptors) of aquatic anamniotes
      • Up to 6 (3 ALL and 3 PLL)
        • Hagfish only 2 ALL, unicellular vs. multicellular neuromast cells of lampreys and gnathostomes
    • VIII, Vestibulocochlear
      • Aka auditory nerve
      • Innervation: membranous labyrinth of inner ear
      • 2 branches:
        • Vestibular nerve
          • Saccule, utricle, ampulla of semicircular canal
          • Vestibular ganglion
        • Cochlear nerve
          • Cochlea, spiral organ (Organ of corti)
          • Cochlear or spiral ganglion
      • Function: conveys impulses related to hearing and equilibrium
      • Clinical application:
        • Injury to vestibular branch
          • Vertigo, feeling of rotation
          • Ataxia, muscular incoordination
          • Nystagmus, involuntary rapid eyeball movement
        • Injury to cochlear branch
          • Tinnitus, ringing in the ears
          • Deafness
    •  
    •  
    • Motor
      • III (Oculomotor)
      • IV (Trochlear)
      • VI (Abducens)
      • XI (Accessory)
      • XII (Hypoglossal)
    • III, Oculomotor
      • Origin: midbrain (mesencephalon)
      • Motor innervation
        • Levator palpebrae superioris
        • Superior, medial, inferior rectus
        • Inferior oblique
      • Sensory innervation
        • Proprioceptors in eyeball muscles
      • Autonomic innervation (parasympathetic)
        • Ciliary muscle for accomodation
        • Circular muscle of iris, pupil constriction
    • IV, Trochlear
      • Origin: midbrain
      • Motor innervation:
        • Superior oblique
      • Sensory innervation:
        • Proprioceptors
      • Few decussating fibers
      • Along with VI, smallest C.N.
      • No ganglion, cell bodies with nuclei in CNS
    • VI, Abducens
      • Origin: pons
      • Innervation
        • Lateral rectus
        • Proprioceptors
      • Along with IV, smallest C.N.
      • No ganglion, cell bodies with nucleus in CNS
      • Clinical application:
        • Strabismus, eyes do not fix on same object
        • Drooping upper eye lid
        • Movement of eyeball
        • Loss of accomodation
        • Diplopia, double vision
        • Fields of gaze
    •  
    • XI, Accessory
      • Origin: medulla
      • Innervation
        • Cranial root
          • Muscles of tongue, larynx, soft palate and pharynx (few)
          • Mediates swallowing movements
          • Internal ramus – joins X (vagus) to be distributed to autonomic ganglia in coelom (majority)
        • Spinal root
          • External ramus – innervates trapezii and sternocleidomastoid
          • Mediates movement of head and shoulders
      • Lack dorsal roots
      • Derived from posteriormost branchiomeric nerves of fishes and occipitospinal nerves
      • Clinical application: inability to raise shoulders, difficulty to turn head
    •  
    • XII, Hypoglossal
      • Spinal nerve that became locked up in braincase
      • Derivative of the occipitospinal series of fishes
      • Develops embryonic dorsal root and ganglion which regress
      • Origin: medulla
      • Innervation:
        • Motor
          • tongue muscles (hyoglossus, styloglossus, lingualis)
          • Movement of tongue during swallowing and speech
        • Sensory
          • Proprioceptors
      • Join spinal nerves that innervate hypobranchial muscles (geniohyoid, sternothyroid, sternohyoid, throhyoid)
    •  
    •  
    • Mixed
      • Carry both sensory and motor fibers
      • All carry somatic motor, sensory, and autonomic motor components except V (somatic and sensory)
      • Innervate pharyngeal arches (branchiomeric nerves)
      • V (Trigeminal)
      • VII (Facial)
      • IX (Glossopharyngeal)
      • X (Vagus)
    • V, Trigeminal
      • Lacks fibers for taste
      • Lacks autonomic (visceral) component
      • 3 branches all with sensory, only mandibular with motor
        • Opthalmic
          • Discrete profundus nerve
          • Seen in agnaths, sarcopterygians, actinopterygians, tetrapods
          • Innervates skin, upper eyelid, eyeball, lacrimal glands, nasal cavity, nose, forehead, anterior scalp
        • Maxillary
          • Infraorbital nerve of fishes
          • Innervates nasal mucosa, palate, pharynx, upper teeth, upper lip, lower eyelid
        • Mandibular
          • Sensory innervation
            • Anterior tongue (lateral lingual swellings), lower teeth, skin over mandible, cheek, side of head
            • Conveys impulses for touch, pain, temperature sensation
          • Motor innervation
            • Muscles of mastication (mandibular arch)
            • Functions in chewing
    •  
      • Clinical application:
        • Paralysis of chewing muscles
        • Loss of touch, pain, and temperature sensation in lower part of face
        • Dental anesthetic drugs
          • Maxillary nerve for upper teeth
          • Mandibular nerve for lower teeth
    •  
    • VII, Facial
      • Innervation
        • Sensory
          • Taste buds
            • Extend all the way to tail in fishes
            • Phrayngeal branch in fishes supply taste buds of pharygeal mucosa
            • Anterior tongue of tetrapods (glandular field)
          • Proprioceptors
          • Functions in taste and proprioception
          • Cell bodies located in facial or geniculate ganglion
        • Autonomic (Parasympathetic)
          • Innervate lacrimal, sublingual, submandibular, nasal, and palatine glands
          • Secretion of saliva and tears
        • Motor
          • Innervates facial, scalp, and neck muscles
          • Function in facial expression
      • Clinical application
        • Loss of taste
        • Decreased salivation
        • Loss of ability to close eyes
        • Bell’s palsy, paralysis of facial muscles
    •  
    •  
    • IX, Glossopharyngeal
      • Innervates two successive arches (shark)
      • Branches
        • Pretrematic
          • Monitors condition of gill filaments in anterior wall og a gill chamber
        • Posttrematic
          • Operate muscles of arch
          • Monitors condition of gill filaments in posterior wall
        • Pharyngeal
          • Extend as branch of pretrematic to palate
          • Monitors pharyngeal mucosa
    •  
      • Innervation
        • Sensory
          • Posterior taste buds (3 rd arch mesenchyme)
          • Proprioceptors
          • Functions in taste, touch, pain, and temperature sensation from posterior tongue
          • Functions in proprioception in swallowing muscles
        • Motor
          • Stylopharyngeus
          • Elevates larynx during swallowing
        • Autonomic (parasympathetic)
          • Parotid gland
          • Secretion of saliva
    •  
    •  
    • X, Vagus
      • Branchial trunks innervate 2 nd -5 th gill chamber as in IX
        • Pretrematic sensory to pretrematic demibranch
        • Posttrematic sensory and motor to posttrematic demibranch
        • Both sensory for general sensation and taste
      • Ramus visceralis (autonomic) to viscera
        • Major branch of vagus in tetrapods
        • Accompanied by visceral sensory fibers
      • Ramus lateralis (autonomic) to lateral-line canal
    •  
      • Innervation
        • Sensory
          • Taste buds in epiglottis and pharynx
          • Proprioceptors in neck and throat muscles
          • Visceral sensory receptors
          • Taste, touch, pain, and temperature sensation, proprioception
          • Sensation from viscera
        • Motor
          • Throat and neck muscles
          • Swallowing, coughing, voice production
        • Autonomic (parasympathetic)
          • Smooth muscle of GIT from esophagus to large intestine, gall bladder
          • Cardiac muscle
          • GIT glands
          • Contraction and relaxation of GIT muscles, slowing of heart rate, digestive fluid secretion
    •  
    •  
    •  
    • Tongue
      • Oral mucosa: V, VII, IX, and X from fish to humans
      • Tongue innervation of V, VII, IX because derived from I, II, III, pharyngeal arches
      • Tongue muscles (hypobranchial) myotomal receive XII
      • 4 C.N. innervate tongue but only 3 can be traced because VII unites with V