Cerebral lateralization
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Cerebral Lateralization. Left hemisphere - categorical hemisphere specialized for spoken and written language, sequential and analytical reasoning (math and science), analyze data in linear way Right hemisphere - representational hemisphere

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Cerebral lateralization l.jpg
Cerebral Lateralization

  • Left hemisphere - categorical hemisphere

    • specialized for spoken and written language, sequential and analytical reasoning (math and science), analyze data in linear way

  • Right hemisphere - representational hemisphere

    • perceives information more holistically, perception of spatial relationships, pattern, comparison of special senses, imagination and insight, music and artistic skill

  • Highly correlated with handedness

    • 91% of people right-handed are left side dominant

  • Lateralization develops with age

    • females have more communication between hemispheres (corpus callosum thicker posteriorly)


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Cranial Nerves

  • 12 pair of nerves

    • arise from brain

    • exit through foramina leading to muscles, glands and sense organs in head and neck

  • Input and output ipsilateral except CN II and IV


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12 Cranial Nerves

  • How do you remember which nerve is which number?

    • Here is a G-rated mnemonic devices:

      • Old Opie occasionally tries trigonometry and feels very gloomy, vague, and hypoactive.

    • There are also several R-rated ones

  • Some cranial nerves are sensory, some motor, and some are both (mixed)?

    • Some say marry money but my brother says big butts matter more.


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CN1 Olfactory nerves

  • How many noses do you have?

  • Sensory, motor, or mixed?

  • Run from the nasal mucosa to the olfactory bulb.

  • Extend thru the cribriform plate.

  • Lesion to these nerves or cribriform plate fracture may yield anosmia – loss of smell.


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CN2 Optic Nerves

  • How many eyes do you have?

  • Sensory, motor, or mixed?

  • Begin at the retina, run to the opticchiasm, cross over, continue as the optictract and synapse in the thalamus.

  • Optic nerve damage yields blindness in the eye served by the nerve. Optic tract damage yields partial visual loss.

  • Visual defects = anopsias


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CN3 Oculomotor Nerves

  • “Eye mover”

  • Sensory, motor, or mixed?

  • Originate at the ventral midbrain.

  • Synapse on:

    • Extraocular muscles

      • Inferior oblique; Inferior, medial, and superior rectus

    • Iris constrictor muscle

    • Ciliary muscle

  • Disorders can result in eye paralysis, diplopiaor ptosis.


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How Do I know If the Nerve is Motor, Sensory or Mixed?

  • There are a couple that are in dispute. The book says one thing our notes say another. Yes, as they are primarily sensory or primarily motor. SO….for our test, let’s go with the silly sayings. For example, CN 8, vestibularcochlear, is predominately SENSORY anyway so it’s O.K . It memorize it that way.


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CN4 Trochlear Nerves

  • Controls the superior oblique muscle which depresses the eye via pulling on the superior oblique tendon which loops over a ligamentous pulley known as the trochlea.

  • Originates on the dorsal midbrain and synapses on the superior oblique

  • Sensory, motor, or mixed?

  • Trauma can result in double vision. Why?


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Trochlear Nerve

  • Eye movement (superior oblique muscle)

  • Damage causes double vision and inability to rotate eye inferolaterally


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CN5 Trigeminal Nerves

  • Sensory, motor, or mixed?

  • Biggest cranial nerve

  • Originates in the pons and eventually splits into 3 divisions:

    • Ophthalmic (V1), Maxillary (V2), &

      Mandibular (V3).

  • Sensory info (touch, temp., and pain) from face.

  • Motor info to muscles of mastication

  • Damage?


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CN5 Abducens Nerves

  • Sensory, motor, or mixed?

  • Runs between inferior pons and lateral rectus.


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Abducens Nerve

  • Provides eye movement (lateral rectus m.)

  • Damage results in inability to rotate eye laterally and at rest eye rotates medially


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CN7 Facial Nerves

  • Sensory, motor, or mixed?

  • Originates at the pons

  • Convey motor impulses to facial skeletal muscles – except for chewing muscles.

  • Convey parasympathetic motor impulses to tear, nasal, and some salivary glands.

  • Convey sensory info from taste buds on anterior

    2/3 of the tongue.

  • Facial nerve damage may yield Bell’s palsy, total ipsilateral hemifacial paralysis


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Branches of Facial Nerve

Clinical test: Test anterior 2/3’s of tongue with substances such as sugar, salt, vinegar, and quinine; test response of tear glands to ammonia fumes; test motor functions by asking subject to close eyes, smile, whistle, frown, raise eyebrows, etc.


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CN8 Auditory/Vestibulocochlear Nerves

  • Sensory, motor, or mixed?

  • Originates at the pons

  • 2 divisions:

    • Cochlear

      • Afferent fibers from

        cochlea in the inner ear

      • HEARING

    • Vestibular

      • Afferent fibers from equilibrium receptors in inner ear

      • BALANCE

  • Functional impairment?


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Glossopharyngeal Nerve

  • Swallowing, salivation, gagging, control of BP and respiration

  • Sensations from posterior 1/3 of tongue

  • Damage results in loss of bitter and sour taste and impaired swallowing


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CN9 Glossopharyngeal Nerves

  • Sensory, motor, or mixed?

  • Fibers run emerge from medulla and run to the throat.

  • Motor Functions:

    • Motor fibers to some swallowing muscles

    • Parasympathetic fibers to some salivary glands

  • Sensory Functions:

    • Taste, touch, heat from pharynx and posterior tongue.

    • Info from chemoreceptors on the level of O2 and CO2 in the blood. Info from baroreceptors on BP.

      • Chemoreceptors and baroreceptors are located in the carotid sinus – a dilation in the internal carotid artery.


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CN10 Vagus Nerves

  • Sensory, motor, or mixed?

  • Only cranial nerves to extend beyond head and neck.

    • Fibers emerge from medulla, leave the skull, and course downwards into the thorax and abdomen.

  • Motor Functions:

    • Parasympathetic efferents to the heart, lungs, and abdominal organs.

  • Sensory Functions:

    • Input from thoracic and abdominal viscera; from baro- and chemoreceptors in the carotid sinus; from taste buds in posterior tongue and pharynx


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Vagus Nerve

  • Swallowing, speech, regulation of viscera

  • Damage causes hoarseness or loss of voice, impaired swallowing and fatal if both are cut


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CN11 Accessory Nerves

  • Sensory, motor, or mixed?

  • Formed by the union of a cranial root and a spinal root.

    • CR arises from medulla while SR arises from superior spinal cord. SR passes thru the FM and joins with CR to form the accessory nerve. They then leave the skull via the jugular foramen.

    • Cranial division then joins vagus and innervates larynx, pharynx, and soft palate.

    • Spinal division innervates sternocleidomastoids and trapezius.


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CN12 Hypoglossal Nerves

  • Sensory, motor, or mixed?

  • Arise from the medulla and exit the skull via the hypoglossal canal and innervate the tongue.

  • Innervate the intrinsic & extrinsic muscles of the tongue.

    • Swallowing, speech, food manipulation.

  • Damage?


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Hypoglossal Nerve

  • Tongue movements for speech, food manipulation and swallowing

    • if both are damaged – can’t protrude tongue

    • if one side is damaged – tongue deviates towards injured side; see ipsilateral atrophy


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Cranial Nerve Disorders

  • Trigeminal neuralgia (tic douloureux)

    • recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose)

    • pain triggered by touch, drinking, washing face

    • treatment may require cutting nerve

  • Bell’s palsy

    • disorder of facial nerve causes paralysis of facial muscles on one side

    • may appear abruptly with full recovery within 3-5 weeks


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