Download CNS – composed of the brain and spinal cord Cephalization

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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The Brain
Composed of wrinkled, pinkish gray tissue
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 almost 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
Paired lateral ventricles
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
Prominent gyri and sulci are the same in all human brains
and are anatomical landmarks
Have three basic regions: cortex, white matter, and basal
nuclei
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Major Lobes, Gyri, and Sulci of the Cerebral
Hemisphere
Deep 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
The precentral and postcentral gyri border the
central sulcus
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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 whose allows conscious control of precise, skilled, voluntary
movements. Their long axons project into the spinal cord forming the
massive pyramidal tracts (corticospinal tracts)
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 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)
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 loudness
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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