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Central Nervous System (CNS)
Lab 9, BIO 105
• CNS consists of brain and spinal cord
• Surface anatomy includes cerebral hemispheres,
cerebellum and brain stem
• Brain regions
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Cerebral hemispheres
Diencephalon
Brain stem (midbrain, pons, and medulla)
Cerebellum
BIOL 105—Lab 9---Gross Anatomy Brain
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Regions and Organization of the CNS
• Spinal cord
– Central cavity surrounded by gray matter
• Gray matter will become the processing part of
brain
– External white matter composed of
myelinated fiber tracts
• White matter is generally protective in nature
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• Brain
– Cerebral hemispheres and cerebellum
• Outer gray matter called cortex
BIOL 105—Lab 9---Gross Anatomy Brain
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Ventricles of the Brain
• Ventricles filled with cerebrospinal fluid (CSF)
• Lined by ependymal cells
• Connected to one another and to central canal of spinal
cord and to subarachnoid space
– Lateral ventricles--paired, C-shaped
– Third ventricle
– Fourth ventricle
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Cerebral Hemispheres
• 3 basic regions: cortex, white matter and basal
nuclei
• Surface markings increase surface area and thus
brain activity
– Ridges (gyri), shallow grooves (sulci), and deep
grooves (fissures)
– Longitudinal fissure separates two
hemispheres
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Cerebral Hemispheres
• Deep sulci divide the hemispheres into 5 lobes:
– Frontal
– Parietal
– Temporal
– Occipital
– Insula--function: associated with visceral
functions, integrates autonomic information
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Cerebral Hemispheres
Cerebral cortex—gray matter superficially, white
matter internally
• Site of conscious mind; conscious behavior involves
the entire cortex; no functional area acts alone
– Enables awareness, sensory perception, voluntary
movements, communication, memory storage,
understanding
• Each hemisphere concerned with contralateral
(opposite) side of body
– Lateralization or specialization of cortical function in each
hemisphere
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Functional areas
1. Motor areas—control voluntary movement
2. Sensory areas—conscious awareness of
sensation
3. Association areas—integrate information
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Cerebral Cortex--Motor Areas
• Frontal lobe--controls voluntary movement
– Primary (somatic) motor cortex
– Premotor cortex anterior
– Broca's area-speech musculature &
comprehension
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• Parietal lobes: somatosensory lobe and some
association areas
– Receives sensory information from skin and
proprioceptors of skeletal muscle, joints, and
tendons
– spatial discrimination; identification of body region
being stimulated
• Occipital lobe: visual lobe, includes association
areas
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• Temporal lobes: auditory lobes and includes
association areas
– Interprets information including pitch,
loudness, and location
– Stores memories of sounds and permits
perception of sound stimulus
• Wernicke’s area--can speak, but speech often
incoherent and makes no sense
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Networks of neurons that span wide areas of brain
BUT work together
• Limbic system:
• emotional or affective brain; gives emotional
responses to odors
• Example: skunks smell bad
• Reticular formation- governs brain arousal
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Reticular Formation: governs brain arousal
• includes RAS
• Reticular activating system (RAS)
– Sends impulses to cerebral cortex to keep
conscious and alert
– Filters out repetitive, familiar, or weak stimuli
– Inhibited by hypothalamic sleep centers, alcohol,
drugs
– Severe injury results in permanent
unconsciousness (coma)
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Diencephalon
• Consists of 3 structures
– Thalamus
– Hypothalamus
– Epithalamus (Pineal gland)
• Structures enclose third ventricle
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Thalamus-- Function
• Gateway to cerebral cortex-is the relay station for
brain
• Essential role in mediating sensation, motor
activities, cortical arousal, learning, and memory
• Sorts, edits, and relays ascending input
– regulation of emotion and visceral function
– help direct motor cortex
– Impulses for memory or sensory integration
– Impulses from visual and auditory centers
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Hypothalamus
• Located below the thalamus
• Primarily involved in hormone production
 Infundibulum—stalk that connects it to pituitary gland
Hypothalamic Function
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Controls autonomic nervous system
Controls endocrine system
Physical responses to emotions
Regulates body temperature, hunger, thirst
Regulates sleep-wake cycles
Biological clock
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Epithalamus or Pineal gland (body)
• secretes melatonin—helps regulate sleep-
wake cycle
• Helps regulate body cycles by monitoring length
of day via input from optic nerve
Choroid Plexus:
• produce CSF at constant rate;
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Brain Stem
• Consists of 3 regions
– Midbrain
– Pons
– Medulla oblongata
• Controls automatic behaviors necessary for survival
• Provides pathway for nerve tracts connecting higher
and lower brain centers
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Medulla Oblongata
• Most inferior portion of the brain stem; joins spinal cord
at foramen magnum
• Cardiovascular center
– Cardiac center adjusts force and rate of heart
contraction
– Vasomotor center adjusts blood vessel diameter for
blood pressure regulation
• Respiratory centers
– Generate respiratory rhythm
– Control rate and depth of breathing (with pontine
centers)
• Vestibular nuclei (pons and medulla)—mediate
responses that maintain equilibrium
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Medulla Oblongata
• Additional centers regulate
– Vomiting
Hiccupping
– Swallowing
Coughing
Sneezing
Pons
• Bulging brainstem area between midbrain and medulla
oblongata
• helps maintain normal rhythm of breathing
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Cerebellum
• Subconscious input from cortex, brain stem and
sensory receptors to allow smooth, coordinated
movements of skeletal muscles
• Arbor vitae—treelike pattern of cerebellar white
matter
• May compare actual with predicted movement
sequences and adjust movement accordingly
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– Meninges--3 protective connective tissue
membranes enclose brain and spinal cord
• Dura mater is outermost and strongest
layer
• Arachnoid mater is middle layer; has
spidery extensions which secure it to
innermost layer.
• Pia mater is innermost layer and clings
tightly to CNS.
Nervous System
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Cerebrospinal Fluid (CSF)
• Composition
– Watery solution formed from blood plasma
• Contains less protein and different ion
concentrations than plasma
– Constant volume
• Functions
– Gives buoyancy to CNS structures
• Reduces weight by 97%
– Protects CNS from blows and other trauma
– Nourishes brain and carries chemical signals
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Hydrocephalus
• Obstruction blocks CSF circulation or drainage
• Fontanelles at skull in newborn allow
enlargement of head
• Brain damage in adult due to rigid adult skull
• Treated by draining with ventricular shunt to
abdominal cavity
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Blood Brain Barrier
• Helps maintain stable environment for brain
• Separates neurons from most bloodborne
substances
• Selective barrier
– Allows nutrients to move by facilitated diffusion
– Metabolic wastes, proteins, toxins, most drugs, small
nonessential amino acids, K+ denied
– Allows any fat-soluble substances to pass, including
alcohol, nicotine, and anesthetics
• Absent in some areas, e.g., vomiting center and
hypothalamus, where necessary to monitor
chemical composition of blood
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• The BBB in adults consists of a complex cellular system
of a highly specialized basal membrane, a large number
of pericytes embedded in the basal membrane and
astrocytic end feet. Whereas the endothelial cells form
the barrier proper, the interaction with adjacent cells
seems to be required for the development of the
barrier. The brain endothelial cells differ from endothelial
cells from other organs in two important ways. First,
continuous tight junctions are present between brain
endothelial cells. These tight junctions prevent
paracellular movement of molecules. Second, there are
no detectable transendothelial pathways such as
intracellular vesicles. These properties of brain
endothelial cells provide a barrier between the blood and
the brain.
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1.
2.
3.
4.
5.
LABWORK (includes next slide)
Identify and describe the meninges and structures of the
brain stem.
Identify and describe the cerebellum and structures of
the diencephalon.
Identify and describe the structures of the cerebrum.
State the function of the cranial nerves.
Locate the following on diagrams, human brain models,
the sheep brain:
Ventral view: olfactory bulb, pituitary gland, mammillary
body, trigeminal nerve, pons, cerebellum, medulla oblongata,
oculomotor nerve, optic tract, optic chiasma, optic
nerve, cerebrum
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Midsagittal view: corpus callosum, thalamus,
hypothalamus, optic chiasma, pituitary gland, pons,
cerebellum, arbor vitae, corpora quadrigemina
(midbrain), pineal body, cerebral hemisphere.
On the human brain models, Locate the lobes of the
cerebrum, gyri, sulci, and fissures.
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Cranial Nerves
• Twelve pairs of nerves associated with brain and
visible on inferior surface
• Most mixed nerves; two pairs purely sensory
• Most innervate head and neck except the vagus
nerve
• Numbered (I through XII) and named from rostral
(forward) to caudal
“On old Olympus topmost top, a Finn and
German viewed some hops”
"On occasion, our trusty truck acts funny—very
good vehicle anyhow"
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I: The Olfactory Nerves (sensory)
– Sense of smell
II: The Optic Nerves (sensory)
• Vision; ability to see
III: The Oculomotor Nerves (motor)
– Fibers extend to most extrinsic eye muscles
– Controls pupil size, eye movement, iris, and most eye
muscles that move the eye
IV: The Trochlear Nerves (motor)
– Primarily controls eye movement
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V: The Trigeminal Nerves (mixed motor & sensory)
–
–
–
–
Largest cranial nerve; fibers extend from pons to face
Three divisions
Conveys sensory impulses from face, head & teeth
Some chewing muscles
VI: The Abducens Nerves (motor)
– Controls 1 eye muscle
VII: The Facial Nerves (mixed motor & sensory)
– Motor functions: muscles of facial expression,
lacrimal glands and salivary glands, ear
sensation
– Sensory function: taste
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VIII: The Vestibulocochlear Nerves (mainly
sensory; has some motor fibers)
• hearing and equilibrium (balance) receptors
• Formerly called the Auditory Nerve
IX: The Glossopharyngeal Nerves (mixed)
• Motor functions – swallowing, some neck
muscles
• Sensory functions - taste and general
sensory impulses from pharynx and
posterior tongue
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X: The Vagus Nerves (motor)
• Only cranial nerves that extends (beyond head
and neck region) to thoracic & abdominopelvic
cavities
• Most motor fibers are parasympathetic fibers
that help regulate activities of heart, lungs, and
abdominal viscera
• Sensory fibers carry impulses from thoracic and
abdominal viscera, baroreceptors,
chemoreceptors, and taste buds of posterior tongue
and pharynx
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XI: Accessory Nerves (motor)
– for neck and head movement (innervate
trapezius and SCM muscle)
– Formerly spinal accessory nerve
XII: Hypoglossal Nerves (motor)
– Tongue muscles for swallowing and speech
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XII: Hypoglossal Nerves (motor)
– Tongue muscles for swallowing and speech
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