Lab Activity 21
The Brain
Portland Community College
BI 232
Brain Meninges: Dura Mater
• Continuous with the spinal meninges
• Dura mater: An outer and inner fibrous
connective tissue
• Outer later is fused to the periosteum of the
cranial bones (no epidural space)
• Between the layers are tissue fluids, blood
vessels and venous sinuses.
• Venous sinuses are large collecting veins.
• Venous sinuses drain into the internal jugular
veins
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Dural Folds
• The inner layer of dura mater that extends
into the cranial cavity.
• Provide additional stabilization and support
for the brain
• Contain the dural sinuses
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Dural Folds
• Falx cerebri projects between the cerebral
hemispheres in the longitudinal fissure
• Superior sagittal sinus & inferior sagittal sinus
• Tentorium cerebelli separates the cerebellar
hemisphere from the cerebrum
• Transverse sinus
• Falx cerebelli divides the cerebellar
hemispheres
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Brain Meninges:
Arachnoid & Pia Mater
• Arachnoid mater consists of the arachnoid
membrane and fibers of the arachnoid
trabeculae that attach to the pia mater
• Pia mater: attached to the surface of the
brain, anchored by processes of astrocytes
• Contains branches of cerebral blood vessels that
penetrate the surface of the brain.
• CSF is between these two membranes in the
subarachnoid space
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Ventricles
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CSF Circulation
• CSF is made from
tufts of blood
capillaries called
choroid plexuses
• CSF cushions and
provides buoyancy to
the brain.
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CSF circulation
• CSF flows through the
arachnoid granulations
under the dura mater
and returns to venous
sinuses returning the
fluid to the
cardiovascular system.
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Blood Supply to the brain
• Blood vessels supply
the brain with
nutrients and oxygen.
• The two main arteries
are the vertebral
arteries and internal
carotid arteries
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Blood Supply to the Brain
• The vertebral arteries
join to form the basilar
artery before
branching into the
arterial circle (circle
of Willis) that forms a
loop around the
pituitary gland.
• Joins with the internal
carotid arteries
anteriorly
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Brain Regions
• Forebrain
• Cerebrum
• Diencephalon
• Midbrain
• Corpora Quadrigemina
• Hindbrain
• Pons
• Medulla oblongata
• cerebellum
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Cerebrum
• Frontal lobe (many higher functions)
• Intellect, abstract reasoning, creativity, social awareness
and language
• Precentral gyrus = primary motor cortex
• Broca’s area is the motor speech area
• Parietal lobe
• Sensation (except smell), language
• Postcentral gyrus=primary somatic sensory cortex
• Wernicke's area involved in the formation of language
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Cerebrum
• Occipital lobe
• Primary vision cortex
• Shape, color and distance of an object are
perceived here
• Temporal lobe
• Primary auditory cortex, interprets impulses
sent from the inner ear
• Translates words into thought
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Precentral Gyrus:
(frontal lobe)
contains the
primary motor area
Central Sulcus
Postcentral Gyrus:
(parietal lobe)
contains the primary
somatosensory area.
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Cerebral Hemispheres
• Left hemisphere
involved with
language and
reasoning (Broca area
usually on left)
• Right hemisphere
involved in space and
pattern perceptions,
artistic awareness,
imagination
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Sulci & Gyri
• Sulci: Shallow depressions of the cerebral
cortex
Sulci
• Central sulcus is between the frontal and parietal
lobes
• Lateral sulcus is between the parietal lobes and
temporal lobes.
• Fissures: Deep grooves
• Longitudinal: separates cerebral hemispheres
• Transverse: separates cerebrum form the
cerebellum
• Gyri: The elevated ridges of the cerebral cortex
• Serve to increase the surface area
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Longitudinal
Fissure
Transverse
fissure
Transverse
Fissure
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Central
Sulcus
Lateral
Sulcus
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Diencephalon
Structures
• Thalamus
• Hypothalamus
• Epithalamus
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Diencephalon: Hypothalamus
• Pituitary gland: Attaches to the hypothalamus via
the infundibulum
• Mamillary bodies: Process olfactory sensations.
(smell to memory)
Pituitary gland
(not in this
picture) would
be hanging here
Mamillary
body
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Diencephalon: Hypothalamus
•
Major Functions:
1. Controls somatic motor activities at the
subconscious level
2. Controls autonomic function
3. Coordinates activities of the nervous and endocrine
systems
4. Secretes hormones
5. Produces emotions and behavioral drives
6. Coordinates voluntary and autonomic functions
7. Regulates body temperature
8. Coordinates circadian cycles of activity
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Diencephalon: Thalamus
• Relay station for sensory input
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Diencephalon: Epithalamus
• Superior to the third ventricle, contains the
pineal gland
Pineal gland
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Brainstem
3 Structures:
• Midbrain
Corpora
quadrigemina
(mesencephalon)
• Pons
• Medulla
oblongata
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Midbrain
Pons
Medulla
Corpora
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quadrigemina
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Midbrain
• Functions:
• Connects pons to cerebellum
• Superior colliculi: visual reflex centers
• Inferior colliculi: auditory reflex centers
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Brainstem: Pons
• Functions:
• Sensory and motor nuclei of Cranial nerves V,
VI, VII, and VIII
• Respiratory control:
• Apneustic center and pneumotaxic center to
modify the activity of the respiratory
rhythmicity center in the medulla
• Nuclei and tracts that process and relay
information to and from the cerebellum
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Medulla Oblongata
• Functions:
• Center for the coordination of complex
autonomic reflexes (heart rate, respiratory
rhythm, blood pressure)
• Control of visceral functions (vomiting,
swallowing)
• Decussation of pyramids: a crossover point for
the major motor tracts
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Cerebellum
• Functions:
• Coordination of
movements
• Adjustment of
postural muscles
Arbor Vita (white
matter that looks
like a leaf)
Vermis
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Cerebrum Vs Cerebellum cells
Cerebrum Slide
Cerebellum Slide
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Cerebral Cortex
• The superficial
layer/rim of gray
matter in the
cerebral
hemispheres
• Gray matter
consists of cell
bodies, dendrites,
and unmyelinated
axons.
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White Matter & Basal Nuclei
• White matter consists primarily of myelinated axons
• Is beneath the gray matter cortex
• Notice how it is the opposite arrangement from the spinal cord
(Spinal cord: white matter is on the outside and gray matter is
on the inside.)
• Corpus callosum: Connects the right and left hemispheres
• Basal nuclei: Islands of gray matter within the white
matter.
• Function: Involved in the subconscious control of skeletal
muscle tone and the coordination of learned movement
patterns
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White Matter
& Basal Nuclei
White Matter
Basal Nuclei
Corpus
Callosum
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Sheep Brain Dissection
• Follow instructions in book for the sheep
brain dissection.
• When finished discard brain in the container
provided.
Wash utensils and put back so other classes
can use the materials.
• ID structures on the brain models for next
week’s quiz.
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Cranial Nerves
• Nerves that originate from the brain rather
than the spinal cord
• Part of the peripheral nervous system (not
the central nervous system)
• CNs (except for XII) are in sequence from
anterior to posterior
• May contain one or more of the following:
• Sensory: receives neural input
• Somatic Motor: predominantly innervates muscles
• Mixed: have significant sensory and motor functions
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CN I: Olfactory Nerve
• Function:
• Sensory for smell
• Exiting foramen=cribriform
plate
• Origin forebrain
• Test: Have patient identify aromatic
substances like vanilla or coffee
• Symptoms of nerve damage:
Anosmia: diminished or absent
sense of smell
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CN II: Optic Nerve
•
•
Function:
•
Sensory for vision
•
Exiting foramen= optic canal
•
Origin=forebrain
Tests:
1. Eye chart
2. Check peripheral vision
3. Funduscopic exam
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CN II: Optic Nerve
• Optic chiasm: Fibers
from the nasal half of
each retina cross over to
the opposite side of the
brain.
• Symptoms of nerve
damage:
• Loss of vision (peripheral
or central)
• Abnormal funduscopic
appearance
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CN II: Optic Nerve Pathology
Papilledema. Note swelling of the
disc, hemorrhages, and exudates,
with preservation of the
physiologic cup.
Proliferative Diabetic
Retinopathy. Note the multiple
hemorrhages throughout the
retina.
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Cranial Nerves III, IV & VI
(Control Eye Movements)
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CN III: Oculomotor nerve
•
Function:
• Somatic Motor to extraocular
muscles (voluntarily move the eye)
• Parasympathetic (motor) to iris
and lens (pupillary constriction)
• Exiting Foramen= superior orbital fissure
• Origin= midbrain
•
Tests:
1. Check pupils for size, shape and equality
2. Shine light in each eye and check for pupil constriction
3. Have patient follow an object in all directions to check for symmetric eye
movements
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CN III: Oculomotor Nerve Injury
• Symptoms of nerve damage:
• Double vision (diplopia): The affected eye
turns outward when the unaffected eye
looks straight ahead
• The affected eye can move only to the
middle when looking inward and cannot
look upward and downward.
• Ptosis: eyelid droop
• Pupil may be dilated and sometimes fixed
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Oculomotor Nerve Injury
Right Eye
Injured
side
Normal
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side
Pupillary Reflex
Efferent
Afferent
Consensual reflex: Both pupils should constrict at the same time
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Originates in the midbrain
CN IV: Trochlear Nerve
• Function:
• Somatic motor to superior oblique muscle of the eye.
• Exiting foramen= superior orbital fissure
• Origin= midbrain
• Test: Check eye movements
• Symptoms of nerve damage:
• Outward rotation of the affected eye
• Vertical diplopia
Normal side
Injured side
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Originates in the pons
CN VI: Abducens Nerve
• Function:
• Somatic Motor to lateral rectus
muscle of the eye.
Exiting foramen=superior orbital fissure
Origin= pons
• Test: Check eye movements
• Symptoms of nerve damage:
• The affected eye will tend to be
deviated inward because of the
unopposed action of the medial rectus
muscle.
• Cannot move eyeball laterally beyond
the midpoint
Injured
side
Normal
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side
CN V: Trigeminal Nerve
3 Branches
1. Ophthalmic
2. Maxillary
3. Mandibular
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Originates in the pons
CN V: Trigeminal Nerve
•
Function:
• Somatic Motor (mandibular branch) to
muscles of mastication (chewing)
• Sensory (all branches)to face and cornea.
• Exiting foramen= Ophthalmic
branch=superior orbital fissure
• Maxillary branch= foramen rotundum
• Mandibular branch = foramen oval
• Origin= pons
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CN V: Trigeminal Nerve
Test: Have patient bite
down while you palpate
the masseter muscle
Test: Touch patient with an open
paperclip and ask “sharp or dull”
Test: Touch cornea with
a wisp of cotton. Patient
should blink
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CN V: Trigeminal Nerve
• Symptoms of nerve damage:
• Inability to firmly bite down (mandibular branch
only)
• Loss of sensation (each branch can be affected
independently)
• Loss of corneal reflex (may indicate brain stem
injury)
• Trigeminal Neuralgia (Tic Douloureux):
debilitating intermittent pain on one side of the
face
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Originates in the pons
CN VII: Facial Nerve
5 Branches
1. Temporal
2. Zygomatic
3. Buccal
4. Mandibular
5. Cervical
• Function:
• Somatic Motor to muscles of facial expression
• Parasympathetic (motor) to lacrimal and
salivary glands
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• Sensory taste to anterior 2/3 tongue
CN VII: Facial Nerve
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CN VII: Facial Nerve Testing
•
•
•
Exiting foramen= enters internal acoustic
meatus exits via stylomastoid foramen
Origin= Pons
Tests:
1. Check taste on anterior 2/3 of tongue by
having patient taste sugar, salt, sour and
bitter
2. Check symmetry of facial muscles:
• Close eyes, smile, whistle, puff out
cheeks (make funny faces)
3. Check tearing with ammonia fumes
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CN VII: Facial Nerve
• Symptoms of nerve damage:
• Mild weakness to total paralysis of facial
muscles (may include twitching),
• Drooping eyelid
• Drooping corner of the mouth
• Drooling or dry mouth
• Impairment of taste
• Excessive tearing in the eye or dry eye
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CN VII: Facial Nerve Injury
(Bell’s Palsy)
Normal
side
Injured
side
Paralyzed facial muscles
Patients can still feel their face because sensory is supplied by the
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trigeminal nerve
Originates in the medulla
CN VIII: Vestibulocochlear
• Function: Sensory
• Vestibular system for balance & equilibrium
• Cochlea for hearing
• Exiting foramen= internal acoustic meatus
• Origin= Pons-medulla border
• Tests:
• Auditory component of the nerve:
• Hearing test
• Vestibular control of balance and movement:
• Romberg test (tests equilibrium)
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CN VIII: Vestibulocochlear Tests
• Simple hearing test:
• Rub fingers together near the ear
and ask “right or left” If there
is lateralization (hearing louder
on one side) there is a problem
• Other hearing tests:
• Performed by an audiologist with special
equipment to determine tones, frequencies
and degree of hearing loss
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CN VIII: Vestibulocochlear Tests
Romberg Test
• Have patient stand with arms at side
and feet together
• Have patient stand with their eyes
closed
• Stand close to prevent falls
• Normally, they should maintain position
for 20 seconds with only minimal
swaying
• If they loose their balance, they have failed
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the equilibrium test.
CN IX: Glossopharyngeal
•
Function:
• Somatic Motor to muscles of pharynx
• Parasympathetic (motor) to salivary glands
• Sensory to pharynx and taste to posterior tongue
• Exiting foramen= Jugular foramen
• Origin= medulla oblongata
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CN IX: Glossopharyngeal
• Tests:
• Gag reflex: Touch each side of the throat with
the tongue depressor
• Evaluate swallowing movements
• Say AHH, and watch the palate
and uvula elevate.
• Evaluate taste on posterior 1/3 of tongue
• Symptoms of nerve damage:
• Loss of gag reflex
• Difficulty swallowing
• Loss of taste
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Originates in the medulla
CN X: Vagus Nerve
• Function:
• Somatic Motor to
muscles of pharynx
and larynx
• Parasympathetic
(motor) fibers of
the heart and other
viscera
• Sensory to pharynx
and larynx
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CN X: Vagus Nerve
• Test:
• Inspect palate
• Test gag reflex
• Symptoms of nerve damage:
• Loss of gag reflex
• Difficulty swallowing
• Hoarse voice
• Exiting foramen = Jugular foramen
• Origin = Medulla oblongata
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Originates in the medulla
CN XI: Accessory Nerve
• Function: Somatic Motor to sternocleidomastoid
and trapezius muscles
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CN XI: Accessory Nerve
• Exiting foramen = jugular
foramen
• Origin = medulla oblongata
• and spinal cord
• Test:
• Shrug shoulders against
resistance
• Turn head against
resistance.
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CN XI: Accessory Nerve
• Symptoms of
nerve damage:
• Weakness
• Uneven
shoulders
• Winged
scapula
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Originates in the medulla
CN XII: Hypoglossal Nerve
• Function: Somatic Motor to tongue
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Hypoglossal Nerve Injury
• Exiting foramen = hypoglossal
canal
• Origin = medulla oblongata
• Test:
• Ask patient to stick out tongue
• Symptoms of nerve damage:
• When paralyzed, the tongue will
point to the damaged side
Normal
side
Injured
side
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Lab Activities
• Identify cranial nerves on models
• You will be responsible for testing cranial
nerves in the upcoming weeks.
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The End
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