Chapter 14 - Brain & Cranial Nerves (Cranial Nerves) Flashcards
Cranial Nerves
- 12 pairs in total
- May be sensory, motor, or mixed
- Part of the PNS (Sensory neuron cell bodies reside in PNS ganglia & motor neurons extend into PNS
- Concerned w/ head, neck & facial regions except Cranial Nerve 10 (Vagus)
12 Cranial Nerves + Mnemonic
- Olfactory
- Optic
- Oculomotor
- Trochlear
- Trigeminal
- Abducens
- Facial
- Vestibulochochlear
- Glossopharyngeal
- Vagus
- (Spinal )Accessory
- Hypoglossal
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Olfactory Nerve (Cranial Nerve 1)
- Sensory nerve
- Transmits nerve impulses from olfactory epithelium to primary olfactory area
Olfactory Receptors
- Bipolar neurons w/ a single odor-sensitive dendrite & long unmyelinated axon
- They pass through olfactory foramina & form right & left olfactory nerves
- The nerves synapse w/ 2nd order relay neurons in olfactory bulbs, their axons form the olfactory tracts of the primary olfactory area
Optic Nerve (Cranial Nerve 2)
- Sensory nerve
- Photorceptors stimulate 1st order bipolar sensory neurons, whose axons synape w/ ganglion cells; ganglion cell axons extend to Optic Nerve
- Optic Nerve joins at Optic Chiasm, where axons from medial retina dscussate to contralateral side, but axons from lateral retina remain ipsilateral
Optic Nerve Pathway
Ganglion cell axons -> Optic tracts -> Lateral geniculate nucleus of thalamus (Synapse w/ 3rd order relay neurons) -> Primary visual area (Occipital Lobe)
*Some axons -> superior colliculi & brain stem motor nuclei (Synapse w/ motor fibers) -> Eye muscles
Oculomotor Nerve (Cranial Nerve 3)
- Motor nerve (since only motor fibers are present where cranial nerve 3 leaves brainstem)
- Controls extrinsic eye muscles as well as intrinsic eye muscles (motor portion)
- Confrol of proprioceptors of 4 extrinsic eye muscles (sensory portion)
4 Extrinsic Eye Muscles Controlled by Oculomotor
- Superior Rectus (Elevation)
- Medial Rectus (Adduction)
- Inferior Rectus (Depression)
- Inferior Oblique (Extorsion)
Mesencephalic Nucleus of Trigeminal
- A unique sensory ganglion embedded in the brain during embryonic development
- Sensory portions of Cranial Nerves 3, 4, 5, 6 & 7 have axons that carry proprioception info from their innervated muscles to the mesencephalic nucleus of the trigeminal (via the ophthalmic branch)
Trochlear Nerve (Cranial Nerve 4)
- Motor nerve
- Cranial nerve 4 fibers from trochlear nucleus decussate, projecting to superior oblique muscle muscle of contralateral eye
- Motor portion controls eyeball movement
Trigeminal Nerve (Cranial Nerve 5)
- Mixed nerve
- Has 3 Branches: ophthalmic, maxillary, and mandibular
Trigeminal Nerve (Motor Portion)
Motor neuron axons from trigeminal nucleus -> various effectors via cranial nerve 5
Trigeminal Nerve (Sensory Portion)
1st order unipolar sensory neurons’ cell bodies in trigeminal ganglion extend axons to trigeminal nucleus -> synapse w/ 2nd order relay neurons -> thalamus, synapse w/ 3rd order relay neurons that project to somatosensory cortex
*sensory axons carrying proprioception info -> mesencephalic nucleus of trigeminal
3 Functions of Trigeminal Motor Portion
- Innervate muscles of mastication (e.g., masseter, temporalis)
- Innervate muscles of roof & floor of oral cavity (e.g., tensor veli palatine)
- Innervate tensor tympani muscle (protection against eardrum damage during loud noises)
3 Functions of Trigeminal Sensory Portion
- In general, transmission of touch, pain, temperature &/ or muscle proprioception info
1. Ophthalmic Branch: From eyes, (outer) nose & forehead
2. Maxillary Branch: From (inner) nose, upper jaw & mouth
3. Mandibular Branch: From anterior tongue, lower teeth, skin of mandible, cheek & temple
Abducens Nerve (Cranial Nerve 6)
- Motor nerve
- Motor portion: motor neuron axons from abducens nucleus innervate lateral rectus muscle to produce eye abduction
Facial Nerve (Cranial Nerve 7)
- Mixed nerve
- Controls facial muscles & concerned w/ sense of taste
Facial Nerve (Motor Portion)
Axons from motor neurons from facial (motor) nucleus extend to PNS to:
- Supply facial muscles & anterior scalp
- Innervate stapedius muscle
- Innervate posterior belly of digastric & stylohyoid
* Also provides parasympathetic ANS innervation to submandibular & sublingual salivary glands & to lacrimal, nasal & palatine glands
Facial Nerve (Sensory Portion)
- From tastebuds of anterior 2/3 of tongue, 1st order unipolar sensory neuron cell bodies in geniculate ganglion -> solitary nucleus, synapsing there w/ 2nd order relay neurons -> thalamus, where synapsis occurs w/ 3rd order relay neurons -> primary gustatory area
- Touch, pain & temperature info from skin of ear canal -> somatosensory cortex (via a similar path to the one above)
Vestibulocochlear Nerve (Cranial Nerve 8)
- Sensory nerve
- Has 2 branches: vestibular and cochlear
Vestibular Branch (Sensory Portion)
- From mechanoreceptors for balance in semicircular canals, utricle & saccule, dendritic ends of bipolar 1st order sensory neurons -> vestibular ganglion, projecting axons -> vestibular nuclei & cerebellum
- In vestibular nuclei, 1st order sensory fibers synapse w/ 2nd order relay neurons, which extend axons from thalamus, where 3rd order relay neuron fibers -> vestibular area in parietal lobe
- Function: To transmit info on dynamic & static equilibrium
Vestibular Branch (Motor Portion)
From pons, motor fibers -> semicircular canals, utricla & saccule
-Function: To adjust mechanoreceptor sensitivity
Cochlear Branch (Sensory Portion)
- From mechanoreceptors of organ of Corti, dendritic ends of bipolar 1st order sensory neurons -> spiral gangion, projecting their axons -> cochlear nuclei
- In cochlear nuclei, 1st order sensory fibers synapse w/ 2nd order relay neurons, which extend axons to thalamus, from where 3rd order relay neuron fibers -> primary auditory of temporal lobes
- Function: To transmit info for hearing
Cochlear Branch (Motor Portion)
- From pons, motor fibers -> organ of Corti
- Function: Adjust mechanoreceptor sensitivity
Aminoglycoside Antibiotics
Cranial Nerve 8 neurotoxins (e.g., streptomycin)
Glossopharyngeal Nerve (Cranial Nerve 9)
- Mixed nerve
- Innervates stylopharyngeal muscle & parotid gland
- Also responsible for sensations from posterior 1/3 of tongue
Glossopharyngeal Nerve (Sensory Portion)
Dendritic ends of unipolar sensory neurons carrying:
1. Gustatory info from tastebuds of posterior 1/3 of tongue
2.Touch, temperature, pain info from posterior 1/3 of tongue & adjacent pharynx
3. Touch, temperature, pain info from external ear
4. Baroreceptor info from carotid sinus
5. Chemoreceptor info from carotid body
6. Proprioception info from swallowing muscles
Their cell bodies reside in inferior/superior ganglia of glossopharyngeal nerve, extending axons to solitary nucleus/ nucleus ambiguus
Glossopharyngeal Nerve (Motor Portion)
- Motor neurons in nucleus ambiguus extend axons to stylopharyngeal muscles
- Function: To raise pharynx & larynx
- For parasympathetic control of parotid salivary glands, preganglionic ANS neurons of inferior salivary nucleus project axons to otic ganglion to synapse w/ postganglionic neurons, which extend axons to parotid gland
Vagus Nerve (Cranial Nerve 10)
- Mixed nerve
- Controls cardiac & smooth muscle of viscera & receives sensations from viscera
Vagus Nerve (Motor Portion-Branchial Subdivision)
- Motor Neurons of nucleus ambiguus project axons to pharynx, soft palate & larynx skeletal muscles
- Function: Aids in swallowing, coughing & speaking
Vagus Nerve (Motor Portion-Autonomic Subdivision)
- For parasympathetic control of various thoracic & abdominopelvic viscera, preganglionic ANS motor neurons of dorsal motor nucleus of vagus project axons to synapse w/ postganglionic ANS neurons in visceral ganglia from where axons project to visceral organs
- Function: Vagal drive to viscera -> “vegetative rest/digest” functions
Vagus Nerve (Sensory Portion)
- Dendritic ends of unipolar sensory neurons are associated w/:
1. Pharynx, palate & larynx
2. Pinna of ear, ear canal
3. Aortic arch & aortic body of baro- & chemoreceptors respectively
4. Thoracic & abdominopelvic viscera - Their cell bodies reside in superior & inferior ganglia of Vagus, projecting axons to solitary nucleus/ spinal trigeminal nucleus
4 Functions of Vagus Sensory Portion
- Transmit gustatory info from epiglottis & pharynx
- Transmit touch, temperature, pain info from throat area & ears
- Transmit baroreceptor info from aortic arch & chemoreceptor info from aortic body
- Transmit sensory info from thoracic & abdominopelvic viscera
(Spinal) Accessory Nerve (Cranial Nerve 11)
- Motor nerve
- Motor neurons of spinal accessory nucleus (C1-C5) -> foramen magnum, then -> jugular foramen w/ 9 & 10
- Motor fibers innervate sternocleidomastoid & trapezius muscles
- Sensory fibers (muscle proprioception) exit nerve before it arrives at brain stem
- Function: Head & shoulder movement
Hypoglossal Nerve (Cranial Nerve 12)
- Motor nerve
- Controls muscles of tonge during speech/swallowing
Hypoglossal Nerve (Motor Portion)
- Motor neurons of hypoglossal nucleus innervate tongue muscles & 2 throat muscles
- Function: speech & swallowing
Hypoglossal Nerve (Sensory Portion)
Dendritic ends of sensory neurons carrying muscle proprioception info exit cranial nerve 12 & travel w/ cervical spinal nerves -> mesencephalic nucleus
