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Transcript of The Brain and Cranial Nerves Chapter 15. Human Anatomy, 3rd edition Prentice Hall, © 2001...
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The Brain and Cranial Nerves
Chapter 15
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Introduction to the Brain
• Weighs about 3 lbs. in adults
• Structures– Divided into 5 areas– Contains ventricles
• Functions– Controls the bare
necessities of life– Location for primal
drives and emotions– Intellectual thought,
imagination, perception, etc.
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Development of the Brain
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Human Anatomy, 3rd editionPrentice Hall, © 2001
3-4 Weeks
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Human Anatomy, 3rd editionPrentice Hall, © 2001
4 Weeks
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Human Anatomy, 3rd editionPrentice Hall, © 2001
5 Weeks
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Human Anatomy, 3rd editionPrentice Hall, © 2001
11 Weeks
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Human Anatomy, 3rd editionPrentice Hall, © 2001
A Child’s Brain
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The Adult Brain
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Adult Brain – Forebrain (Prosencephalon)
• Cerebrum (telencephalon)
• Thalamus, hypothalamus (diencephalon)
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Adult Brain – Midbrain (Mesencephalon)
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Adult Brain – Hindbrain (Rhombencephalon)
• Pons and cerebellum (metencephalon)
• Medulla oblongata (myelencephalon)
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Ventricles of the Brain• Lateral ventricles
– Separated by the septum pallucidum
– Connects to third ventricle
• Interventricular foramen
• Third ventricle – Connects to fourth
ventricle• Cerebral
aqueduct
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Ventricles of the Brain
• Fourth ventricle
– Connects to the subarachnoid space and spinal canal
• Cerebrospinal fluid circulates down through the ventricles and into the spinal cord.
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Protections and Coverings
• Cranial bones – strong support
• Cranial meninges – shock absorbers– Dura mater – 2
layers• Endosteal
(periosteal)• Meningeal
– Arachnoid
– Pia mater
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Blood-Brain Barrier• Astrocytes
– Secrete chemicals that maintain the BBB
– Absorb materials from blood
– Extract materials from brain
• Endothelial cells of capillaries form tight junctions– Lipid-soluble
compounds– Water-soluble
compounds
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebrospinal Fluid
• Composition– Proteins, glucose,
urea, salts – White blood cells
• Functions– Shock absorber– Medium of transport
for nutrients, gases, etc.
• Formed by the choroid plexus (“vascular braid”)
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Problems Associated with CSF
• Hydrocephalus
• Meningitis
• Headaches
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The Parts of the Brain
Forebrain
Cerebrum, Hypothalamus, Thalamus
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebrum – Gray & White Matter
• Outer layer – cerebral cortex– Gray matter
• Inner portion– White matter
• Projection tracts• Association tracts• Commissural
tracts (corpus collosum)
– Masses of gray matter
• Cerebral nuclei
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebral Cortex
• Gyri are separated by grooves (sulci)– Fissures – deeper
grooves• Longitudinal fissure
– Divides the cerebrum into cerebral hemispheres
• Central sulcus– Precentral gyrus– Post-central gyrus
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebral Lobes• Frontal lobe
– Decision-making, planning– Broca’s area– Primary motor cortex
• Parietal lobe– Speech comprehension, reading,
taste – Primary sensory cortex
• Occipital lobe– Visual cortex
• Temporal lobe– Wernicke’s area– Olfactory cortex– Auditory cortex
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Homunculus
Primary Motor Cortex Primary Sensory Cortex
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebral Nuclei
• Collections of cell bodies (gray matter)
• Mostly control the movement of skeletal muscles
• Examples– Caudate nucleus
– Amygdaloid body
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Limbic System• Functional unit• Emotional part of the
brain– Feelings of fear, loss,
love, rage, etc.
• Includes parts of several anatomical structures– Cerebrum
– Hypothalamus
– Thalamus
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Hypothalamus• Location – floor of the
third ventricle• Structure
– Mammillary bodies• Feeding reflexes
– Infundibulum
– Autonomic centers
– Nuclei
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Functions of Hypothalamus• Initiates primal drives
– Hunger, thirst, sex, rage, etc. – Controls “fight or flight” sympathetic
response.
• Sets emotional states (with limbic system)• Controls pituitary gland (“master gland” of
endocrine system)– Secretes “releasing factors” and “inhibiting
factors”– Infundibulum (“funnel”) funnels secretions to
the pituitary gland
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Thalamus and Epithalamus• Thalamus
– Superior brain stem– Relay station between
the body and cerebral cortex
– Emotion (limbic system)
– Integrates visual & auditory reflexes
• Epithalamus– Roof of third ventricle– Contains pineal body
• Secretes melatonin– Contains choroid plexus
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Midbrain
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Midbrain (Mesencephalon)• Cerebral peduncles –
on anterolateral surface– Motor neurons from
cerebral cortex to pons and spinal cord
– Sensory neurons to the thalamus
• Corpora quadrigemina– Superior colliculi
receive visual information
– Inferior colliculi receive auditory information
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Nuclei of Midbrain• Substantia nigra
secretes dopamine– Modifies muscle tone
& motor activity– Parkinson’s disease
• Red nucleus – highly vascularized– Integrates
information from cerebrum & cerebellum
– Maintains muscle tone & posture
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Hindbrain
Cerebellum, Pons, & Medulla Oblongata
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebellum
• 2nd largest structure of the brain
• Separated from cerebrum by transverse fissure
• Divided into 2 lateral hemispheres– Vermis = “worm-
shaped”
• Cortex – gyri & sulci
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cerebellum• Arbor vitae• Cerebellar nuclei
– Within arbor vitae• Cerebellar peduncles
– Inferior– Middle– Superior
• Functions – controls subconscious movements in skeletal muscle– Coordination, posture,
balance
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Pons• Pons = “bridge”
– Consists of white fibers with scattered nuclei
• Functions– Controls respiration
rate (with medulla)
– Contains nuclei for several cranial nerves
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Medulla Oblongata• Continuation of spinal cord• Forms the base of the
“brain stem”• Pyramids
– Just above the spinal cord
– Large tracts cross from one side to the other
• Contains reflex centers– Cardiac center,
vasomotor center, respiratory rythmicity center
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Cranial Nerves
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Introduction to the Cranial Nerves• 12 pairs• Leave the skull
through foramina• Types
– Mixed– Sensory– Motor
• Part of the somatic nervous system– Some fibers of the
ANS bundled with those of the cranial nerves
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve I – Olfactory Nerve• Sensory• Function – smell
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve II – Optic Nerve• Sensory• Function – vision
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Nerves Controlling Extrinsic Eye Muscles (III, IV, VI)
• Cranial Nerve III – oculomotor nerve– Motor
– Function – controls raising of upper eyelid, movements of eyeball
– Parasympathetic fibers to lens and pupil
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Nerves Controlling Extrinsic Eye Muscles (III, IV, VI)
• Cranial Nerve IV – trochlear nerve– Motor– Function –
movements of eyeball
• Cranial Nerve VI – Abducens– Motor– Function –
movements of eyeball
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Craniel Nerve V – Trigeminal Nerve
• Mixed• Sensory fibers receive
information from cornea, scalp, forehead, face, teeth
• Motor fibers to the muscles of mastication (control chewing)
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve VII – Facial Nerve• Mixed• Sensory fibers
– Taste from anterior 2/3 of the tongue
• Motor fibers – Facial expression
• Parasympathetic fibers to:– Lacrimal glands
• Tears – Submandibular and
submaxillary salivary glands
• Salivation
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve VIII – Auditory Nerve (Vestibulocochlear Nerve)• Sensory
• Function – hearing and balance
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve IX – Glossopharyngeal Nerve
• Mixed
• Sensory fibers – Taste and touch from
posterior l/3 of the tongue and pharynx
• Motor fibers to pharyngeal muscles– Swallowing
• Parasympathetic fibers to the parotid gland – salivation
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve X – Vagus Nerve
• Mixed
• Sensory fibers from external ears (hearing), rear of tongue (taste), viscera
• Motor fibers to the muscles of the pharynx and larynx (motor)
• Parasympathetic fibers to viscera
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Human Anatomy, 3rd editionPrentice Hall, © 2001
Cranial Nerve XI – Spinal Accessory NerveCranial Nerve XII – Hypoglossal Nerve
• XI – Spinal accessory nerve
– Motor to trapezius and sternocleidomastoid muscles
– Function – head movements
• XII – Hypoglossal nerve– Motor to muscles of
tongue– Function – speech and
swallowing
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Cranial Nerves“On old Olympus’ towering top, a Finn and
German viewed a hawk.”