Download Central Nervous System (CNS) CNS – composed of the brain and

Central Nervous System (CNS)
CNS – composed of the brain and spinal cord
Cephalization
Elaboration of the anterior portion of the CNS
Increase in number of neurons in the head
Highest level is reached in the human brain
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I take
exception to
that!
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The Brain
Surface anatomy includes cerebral hemispheres,
cerebellum, and brain stem
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Embryonic Development
During the first 26 days of development:
Ectoderm thickens forming the neural plate
The neural plate invaginates, forming the neural folds
Superior edges fuse forming neural tube which detaches
from the ectoderm and sinks deeper
Neural tube differentiates into the CNS
Brain forms from neural tube (rostrally) as well as spinal
cord (posterior/dorsally)
Neural crest cells give rise to some neurons destined to
reside in ganglia
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Embryonic Development
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Figure 12.1
Brain Development: Primary Brain Vesicles
The anterior end of the neural tube expands and
constricts to form the three primary brain vesicles
Prosencephalon – the forebrain
Mesencephalon – the midbrain
Rhombencephalon – hindbrain
Remainder of neural tube becomes the spinal cord
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Neural Tube and Primary Brain Vesicles
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Figure 12.2a, b
Secondary Brain Vesicles
In week 5 of embryonic development, secondary
brain vesicles form
Telencephalon and diencephalon arise from the
forebrain
Mesencephalon remains undivided
Metencephalon and myelencephalon arise from the
hindbrain
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Secondary Brain Vesicles
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Figure 12.2c
Adult Brain Structures
Fates of the secondary brain vesicles:
Telencephalon – cerebrum: cortex, white matter,
and basal nuclei
Diencephalon – thalamus, hypothalamus, and
epithalamus
Mesencephalon – brain stem: midbrain
Metencephalon – brain stem: pons
Myelencephalon – brain stem: medulla oblongata
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Adult Neural Canal Regions
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Figure 12.2c, d
Adult Neural Canal Regions
Adult structures derived from the neural canal
Telencephalon – lateral ventricles
Diencephalon – third ventricle
Mesencephalon – cerebral aqueduct
Metencephalon and myelencephalon – fourth
ventricle
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Adult Neural Canal Regions
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Figure 12.2c, e
Space Restriction and Brain Development
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Figure 12.3
Space Restriction and Brain Development
Flexures: midbrain and cervical, which bend the
forebrain toward the brain stem
Cerebral hemispheres: grow posteriorly and
laterally and envelop the diencephalon and
midbrain
Continued growth causes the surface to crease
and fold producing convolutions thus increasing
the surface area
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Basic Pattern of the Central Nervous System
Spinal Cord
Central cavity surrounded by a gray matter core
External to which is white matter composed of
myelinated fiber tracts
Brain
Similar to spinal cord but with additional areas of
gray matter
Cerebellum has gray matter in nuclei
Cerebrum has nuclei and additional gray matter in
the cortex
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Basic Pattern of the Central Nervous System
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Figure 12.4
Ventricles of the Brain
Continuous with one another and with the central canal of the
spinal cord
Filled with cerebrospinal fluid and lined with ependymal cells
C-shaped reflects the pattern of cerebral growth
Septum pallucidum separates lateral ventricles via the
interventricular foreamen
Third ventricle connected to the fourth ventricle via the cerebral
aquaduct
Fourth ventricle is continuous with the central canal of the
spinal cord
Fourth ventricle is also continuous with the fluid filled space
surrounding the brain (subarachnoid) via lateral and medial
apertures.
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Ventricles of the Brain
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Figure 12.5
Cerebral Hemispheres
Form the superior part of the brain and make up
83% of its mass
Contain ridges (gyri) and shallow grooves (sulci)
Contain deep sulci called fissures
Are separated by the longitudinal fissure
Transverse fissure separates the cerebral
hemispheres from the cerebellum
Have three basic regions: cortex, white matter, and
basal nuclei
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Major Lobes, Gyri, and Sulci of the Cerebral
Hemisphere
Prominent sulci divide the hemispheres into five
lobes:
Frontal, parietal, temporal, occipital, and insula
These are named for the cranial bones under which
they lie
Central sulcus – separates the frontal and parietal
lobes.
Bordered by the precentral gyrus (anteriorly)
and the postcentral gyrus (posteriorly)
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Brain Lobes
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Figure 12.6a–b
Major Lobes, Gyri, and Sulci of the Cerebral
Hemisphere
Parieto-occipital sulcus – separates the parietal and
occipital lobes
Lateral sulcus – outlines the temporal lobe and
separates the parietal and temporal lobes
Insula: buried within the lateral sulcus and forms
part of the floor of the cerebral hemispheres
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Cerebral Cortex: Our “conscious mind”
The cortex – superficial gray matter; accounts for
40% of the mass of the brain.
Gray matter: neuron cell bodies, dendrites,
associated glia, blood vessels
It enables sensation, communication, memory,
understanding, and voluntary movements
Each hemisphere acts contralaterally (controls the
opposite side of the body)
Cerebral cortex has been extensively mapped
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Functional Areas of the Cerebral Cortex
The three types of functional areas are:
Motor areas – control voluntary movement
Sensory areas – conscious awareness of sensation
Association areas – integrate diverse information
All neurons here are interneurons not sensory & motor
neurons
Each hemisphere is chiefly concerned with the sensory and
motor functions of the opposite side of the body
Each side has specialization and is not necessarily bilateral
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Functional Areas of the Cerebral Cortex
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Figure 12.8a
Functional Areas of the Cerebral Cortex
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Figure 12.8b
Cerebral Cortex: Motor Areas (Voluntary Movement)
Lie in the posterior part of the frontal lobes:
Primary (somatic) motor cortex
Premotor cortex
Broca’s area
Frontal eye field
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Primary Motor Cortex (Brodmman’s Area #4)
Located in the precentral gyrus of the
frontal lobe of each hemisphere
Pyramidal cells:
allow conscious control of
precise, skilled, voluntary
movements.
Their long axons project into the
spinal cord forming the massive
pyramidal tracts (corticospinal
tracts)
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Primary Motor Cortex (Brodmman’s Area #4)
The entire body is represented spatially in the
primary motor cortex of each hemisphere (this
type of mapping is called somatotopy)
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Premotor Cortex (Brodmman’s Area #6)
Located anterior to the precentral gyrus in the frontal lobe
Controls learned, repetitious, or patterned motor skills
Coordinates movement by sending impulses to the primary
motor cortex
Involved in the planning of movements
Controls voluntary movements that depend on sensory feedback
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Broca’s Area: Brodmann Area #44 & 45
Broca’s area
Located anterior to the inferior region of the premotor area
Present in one hemisphere (usually the left)
A motor speech area that directs muscles of the tongue
Is active as one is planning to speak
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Frontal Eye Field: Brodmann’s Area #8
Frontal eye field
Located anterior to the premotor cortex and
superior to Broca’s area
Controls voluntary eye movement
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Sensory Areas
Primary somatosensory cortex
Somatosensory association cortex
Visual and auditory areas
Olfactory, gustatory, and vestibular cortices
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Sensory Areas
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Figure 12.8a
Primary Somatosensory Cortex: Brodmann’s Area #1-3
Located in the postcentral gyrus of parietal lobe
Receives info. from sensory receptors in the skin and
proprioceptors in the skeletal muscles, joints, tendons
Neurons identify the body region being stimulated (spatial
discrimination)
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Primary Somatosensory Cortex: Brodmann’s Area #1-3
Body is represented
spatially: contralaterally
and upside down
The amount of sensory
cortex devoted to a given
body region is related to
the degree of sensitivity
in that region, and not the
body size (e.g. face, lips,
fingertips)
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Somatosensory Association Cortex: Brodmann’s Areas 5 &7
Located posterior to the primary somatosensory cortex
Integrates sensory information relayed from the primary
somatosensory cortex to produce an understanding of the object
being felt
Determines size, texture, and relationship of parts
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Visual Areas: Brodmann’s Areas 17-19
Primary visual (striate) cortex
Seen on the extreme posterior tip of the occipital lobe
Most of it is buried in the calcarine sulcus
Receives visual information from the retinas
Visual association area
Surrounds the primary visual cortex
Interprets visual stimuli (e.g., color, form, and movement)
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Auditory Areas: Brodmann’s Areas 41-43
Primary auditory cortex
Located at the superior margin of the temporal lobe
Receives information related to pitch, rhythm, and volume
Auditory association area
Located posterior to the primary auditory cortex
Stores memories of sounds and permits perception of sounds
Wernicke’s area
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Olfactory Cortex: Brodmann’s Areas: 28 & 34
Located in the medial aspect of the temporal lobe dominated by
the uncus
Afferent fibers from smell receptors in the superior nasal
cavities send impulses along olfactory tracts and relay them to
the olfactory cortex
The O.C. is part of the primitive rhinencephalon
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…and the other corteces
Gustatory cortex (located in the insula)
Deep to the temporal lobe
Taste
Visceral sensory area (also in the insula)
Located just posterior to the gustatory cortex
Perception of visceral sensations
Vestibular (equilibrium) cortex
Located in the posterior part of the insula
Balance
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Multimodal Association Areas
Information flows from sensory neurons to
Primary sensory cortex to
Sensory association cortex to
Multimodal association cortex
Gives meaning to the information
Stores it in memory
Decision making area
Relay decisions to premotor cortex and then the motor
cortex
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Prefrontal Cortex (Anterior Association Area)
Located in the anterior portion of the frontal lobe
Most complicated cortical region
Involved with intellect, cognition, recall, and
personality
Necessary for judgment, reasoning, persistence,
and conscience
Matures slowly, dependent on positive/negative
feedback
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Posterior Association Area
Region encompassing parts of: temporal, parietal,
and occipital lobes
Involved in recognizing patterns, surroundings,
bringing different sensory inputs into a whole
Brings conscious attention to an area in space or to
an area of one’s own body
Problems here can result in a smelly, half naked
lady!
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Language Areas
Located in a large area surrounding the left (or
language-dominant) lateral sulcus
Major parts and functions:
Wernicke’s area –sounding out unfamiliar words
Broca’s area – speech preparation and production
Lateral prefrontal cortex – language
comprehension and word analysis
Lateral and ventral temporal lobe – coordinate
auditory and visual aspects of language
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Lateralization of Cortical Function
Lateralization – each hemisphere has abilities not shared
with its partner
Cerebral dominance – designates the hemisphere dominant
for a given task
Left hemisphere – controls language, math, and logic
E.g. Dad buys half a cow for conversation sake
Right hemisphere – controls visual-spatial skills, emotion,
and artistic skills
Most “righties” are left cerebral dominant, while most
“south paws” are right cerebral dominant.
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Cerebral White Matter
Located deep to the cortical grey matter
It is responsible for communication between the
cerebral cortex and lower CNS center, and within
areas of the cerebrum
Consists of deep myelinated fibers and their large
tracts
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Cerebral White Matter
Tracts are classified according to the direction in which they run
Types include:
Commissures – connect corresponding gray areas of the two hemispheres.
E.g. corpus collosum
Fibers run horizontally
Association fibers – connect different parts of the same hemisphere
E.g. connect adjacent gyri
Long fibers can connect different cortical lobes
Fibers run horizonatally
Projection fibers – enter the hemispheres from lower brain or cord centers
Tie the cortex to the rest of the nervous system and to the body’s receptors
and effectors
E.g. corona radiata: fan like projection of fibers from the brain stem to
the cortex
Fibers run vertically
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Fiber Tracts in White Matter
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Figure 12.10a
Basal Nuclei
Masses of gray matter found deep within the
cortical white matter
The corpus striatum (striped appearance) is
composed of three parts
Caudate nucleus
Lentiform nucleus – composed of the putamen and
the globus pallidus
Fibers of internal capsule running between and
through caudate and lentiform nuclei
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Basal Nuclei
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Figure 12.11a
Basal Nuclei
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Figure 12.11b
Functions of Basal Nuclei
Nuclei of the corpus striatum receive input from
the entire cerebral cortex
The basal nuclei project signals to the premotor
and prefrontal cortices (logic and reasoning of a
movement and how to best execute it)
And influences muscle movements
(subsequently directed by the primary motor
cortex)
Precise function of basal nuclei is still elusive
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Diencephalon
Central core of the forebrain
Surrounded by the cerebral hemispheres
Consists of three paired structures – thalamus,
hypothalamus, and epithalamus
Encloses the third ventricle
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Diencephalon
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Figure 12.12
Thalamus
Paired, egg-shaped masses that form the
superolateral walls of the third ventricle
Connected at the midline by the intermediate mass
Contains four groups of nuclei – anterior, ventral,
dorsal, and posterior
Nuclei project and receive fibers from the cerebral
cortex
Thalamus, thyroid, thymus
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Thalamus
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Figure 12.13a
Thalamic Function
Afferent fibers from all senses and all parts of the body
converge and synapse in the thalamus
Impulses of similar function are sorted out, edited, and
relayed as a group (e.g. “The Hot Bowl of Soup”)
All inputs ascending to the cerebral cortex pass through the
thalamus
Mediates sensation, motor activities, cortical arousal,
learning, and memory
Thalamus is the “gateway” to the cerebral cortex
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Hypothalamus
The hypothalamus links the nervous system to the endocrine
system via the pituitary gland (hypophysis).
Located below the thalamus, it caps the brainstem and forms the
inferolateral walls of the third ventricle
Extends from the optic chiasma to the posterior margin of the
mammillary bodies
Main visceral control center of the body
Vital for homeostasis
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Hypothalamus Associated Structures
Mammillary bodies
Small, paired nuclei bulging anteriorly from
the hypothalamus
Involved with recognition memory
Relay station for olfactory pathways
Infundibulum – stalk of the hypothalamus; connects
to the pituitary gland
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Hypothalamic Nuclei
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Figure 12.13b
Hypothalamic Function
Autonomic control center: controls autonomic nervous system.
Regulates cardiac and smooth muscle
Regulates gland secretion
Influences blood pressure, heartbeat rate, digestive tract motility, eye pupil
size
Emotional response center
Body temperature regulation
Regulates the feeling of hunger and satiation
Regulation of water balance and thirst
Sweating, shivering
Regulation of food intake
Center for pleasure, fear, rage
Regulates release of antidiuretic hormone causing kidneys to retain water
Regulates sleep wake cycle
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Endocrine Functions of the Hypothalamus
Releasing hormones control secretion of hormones
by the anterior pituitary gland
E.g. The supraoptic and paraventricular nuclei
produce ADH and oxytocin
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Epithalamus
Most dorsal portion of the diencephalon; forms
roof of the third ventricle
Pineal gland – extends from the posterior border
and secretes melatonin
Melatonin – a hormone involved with sleep
regulation, sleep-wake cycles, and mood
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Epithalamus
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Figure 12.12
Brain Stem
Consists of three regions – midbrain
(mesencephalon), pons, and medulla oblongata
Similar to spinal cord but contains embedded
nuclei
Controls automatic behaviors necessary for
survival
Provides the pathway for tracts between higher and
lower brain centers
Associated with 10 of the 12 pairs of cranial nerves
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Human Brain: Ventral Aspect
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Figure 12.14
Brain Stem
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Figure 12.15a
Brain Stem
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Figure 12.15b
Brain Stem
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Figure 12.15c
Midbrain (Mesencephalon)
Located between the diencephalon and the pons
Midbrain structures include:
Cerebral peduncles – two bulging structures that
contain pyramidal motor tracts descending toward
the spinal cord
Cerebral aqueduct – hollow tube that connects the
third and fourth ventricles
Various nuclei
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Midbrain Nuclei
Corpora quadrigemina – four domelike protrusions
of the dorsal midbrain (superior and inferior
colliculi)
Superior colliculi: visual reflex centers
Inferior colliculi: auditory relay (startle reflex)
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Midbrain Nuclei
2 pigmented nuclei:
Substantia nigra – pigmented from melanin
Precursor of dopamine released here. Disorders here, e.g.
Parkinson’s disease
Red nucleus – largest nucleus of the reticular formation
Controls some movements of the shoulder & upper arm
Red coloration due to high degree of vascularization
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Pons
Bulging brainstem region between the midbrain and the medulla
oblongata
Forms part of the anterior wall of the fourth ventricle
Formed of tracts coursing in 2 directions
Deep projections: connect higher brain centers and
spinal cord
Superficial projections relay between the motor cortex
of the cerebrum and the cerebellum
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Medulla Oblongata
Most inferior part of the brain stem
Along with the pons, forms the ventral wall of the
fourth ventricle
Contains a choroid plexus of the fourth ventricle
Pyramids – two longitudinal ridges formed by
corticospinal tracts
Decussation of the pyramids – crossover points of
the corticospinal tracts
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Medulla Oblongata
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Figure 12.16c
Medulla Nuclei
Inferior olivary nuclei – gray matter that relays
sensory information on the state of stretch of
muscles and joints to the cerebellum
Cochlear nuclei: auditory relays
Vestibular nuclear complex – synapses that
mediate and maintain equilibrium
Nucleus gracilis and caneatus: where somatic
sensory information ascends from the spinal cord
to the somatosensory cortex
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Medulla Nuclei
Involved in autonomic reflex center involved in
homeostasis
Cardiovascular control center – adjusts force
and rate of heart contraction
Respiratory centers – control rate and depth of
breathing
Additional centers – regulate vomiting,
hiccuping, swallowing, coughing, and sneezing
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The Cerebellum
Located dorsal to the pons and medulla
Protrudes under the occipital lobes of the cerebrum
Makes up 11% of the brain’s mass
Provides precise timing and appropriate patterns of
skeletal muscle contraction subconsciously
E.g. coordination
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The Cerebellum
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Figure 12.17b
Anatomy of the Cerebellum
Two bilaterally symmetrical hemispheres
connected medially by the vermis
Contains folia – transversely oriented gyri
Fissures subdivide each hemisphere into three
lobes – anterior, posterior, and flocculonodular
Neural arrangement – gray matter cortex, internal
white matter, scattered nuclei
Arbor vitae – distinctive treelike pattern of the
cerebellar white matter
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Cerebellar Peduncles
Three paired fiber tracts that connect the
cerebellum to the brain stem
All fibers in the cerebellum are ipsilateral
Superior peduncles connect the cerebellum to the
midbrain
Middle peduncles connect the pons to the
cerebellum
Inferior peduncles connect the medulla to the
cerebellum
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Cerebellar Processing
Cerebellum receives impulses of the intent to
initiate voluntary muscle contraction
Proprioceptors and visual signals “inform” the
cerebellum of the body’s condition
Cerebellar cortex calculates the best way to
perform a movement
A “blueprint” of coordinated movement is sent to
the cerebral pre-motor cortex
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