The Central Nervous System

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• The Central Nervous System

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Objectives

• 1. Name the major regions of the adult brain.
• 2. Name and locate the ventricles of the brain.
• 3. List the major lobes, fissures, and functional
  areas of the cerebral cortex.
• 4. Describe the location of the diencephalon, and
  name its subdivisions and functions.
• 5. Identify the three major regions of the brain
  stem, and note the functions of each area.
• 6. Describe the structure and function of the
  cerebellum.
• 7. Locate the limbic system and the reticular
  formation, and explain the role of each
  functional system.
• 8. Describe how meninges, cerebrospinal fluid,
  and the blood-brain barrier protect the CNS.
• 9. Describe the formation of cerebrospinal fluid,
  and follow its circulatory pathway.

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Regions and Organization of the CNS

• Spinal cord
• Central cavity surrounded by a gray matter core
• External white matter composed of myelinated
  fiber tracts

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Regions and Organization of the CNS

• Brain
• Similar pattern with additional areas of gray
  matter
• Nuclei in cerebellum and cerebrum
• Cortex of cerebellum and cerebrum

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Cortex of gray matter
Central cavity
Migratory pattern of neurons
Inner gray matter
Outer white matter
Cerebrum
Cerebellum
Gray matter
Region of cerebellum
Central cavity
Inner gray matter
Outer white matter
Gray matter
Brain stem
Central cavity
Outer white matter
Inner gray matter
Spinal cord
Figure 12.4
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Ventricles of the Brain

• Connected to one another and to the central canal
  of the spinal cord
• Lined by ependymal cells

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Ventricles of the Brain

• Contain cerebrospinal fluid
• Two C-shaped lateral ventricles in the cerebral
  hemispheres
• Third ventricle in the diencephalon
• Fourth ventricle in the hindbrain, dorsal to the
  pons, develops from the lumen of the neural tube

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Lateral ventricle
Septum pellucidum
Anterior horn
Posterior horn
Inferior horn
Interventricular foramen
Lateral aperture
Median aperture
Third ventricle
Inferior horn
Lateral aperture
Cerebral aqueduct
Fourth ventricle
Central canal
(b) Left lateral view
(a) Anterior view
Figure 12.5
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Cerebral Hemispheres

• Surface markings
• Ridges (gyri), shallow grooves (sulci), and deep
  grooves (fissures)
• Five lobes
• Frontal
• Parietal
• Temporal
• Occipital
• Insula

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Cerebral Hemispheres

• Surface markings
• Central sulcus
• Separates the precentral gyrus of the frontal
  lobe and the postcentral gyrus of the parietal
  lobe
• Longitudinal fissure
• Separates the two hemispheres
• Transverse cerebral fissure
• Separates the cerebrum and the cerebellum

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Precentral gyrus
Central sulcus
Postcentral gyrus
Frontal lobe
Parietal lobe
Parieto-occipital sulcus (on medial surface of
hemisphere)
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse cerebral fissure
Cerebellum
Pons
Medulla oblongata
Fissure
Spinal cord
(a deep
sulcus)
Gyrus
Cortex (gray matter)
Sulcus
White matter
(a)
Figure 12.6a
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Central sulcus
Frontal lobe
Gyri of insula
Temporal lobe (pulled down)
(b)
Figure 12.6b
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Anterior
Longitudinal fissure
Frontal lobe
Cerebral veins and arteries covered
by arachnoid mater
Parietal lobe
Right cerebral hemisphere
Left cerebral hemisphere
Occipital lobe
Posterior
(c)
Figure 12.6c
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Left cerebral hemisphere
Transverse cerebral fissure
Brain stem
Cerebellum
(d)
Figure 12.6d
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Cerebral Cortex

• Thin (24 mm) superficial layer of gray matter
• 40 of the mass of the brain
• Site of conscious mind awareness, sensory
  perception, voluntary motor initiation,
  communication, memory storage, understanding
• Each hemisphere connects to contralateral side of
  the body
• There is lateralization of cortical function in
  the hemispheres

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Functional Areas of the Cerebral Cortex

• The three types of functional areas are
• Motor areascontrol voluntary movement
• Sensory areasconscious awareness of sensation
• Association areasintegrate diverse information
• Conscious behavior involves the entire cortex

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Motor Areas

• Primary (somatic) motor cortex
• Premotor cortex
• Brocas area
• Frontal eye field

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Motor areas
Sensory areas and related association areas
Central sulcus
Primary motor cortex
Primary somatosensory cortex
Premotor cortex
Somatic sensation
Frontal eye field
Somatosensory association cortex
Brocas area (outlined by dashes)
Gustatory cortex (in insula)
Taste
Prefrontal cortex
Wernickes area (outlined by dashes)
Working memory for spatial tasks
Executive area for task management
Primary visual cortex
Working memory for object-recall tasks
Vision
Visual association area
Solving complex, multitask problems
Auditory association area
Hearing
Primary auditory cortex
(a) Lateral view, left cerebral hemisphere
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
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Primary Motor Cortex

• Large pyramidal cells of the precentral gyri
• Long axons ? pyramidal (corticospinal) tracts
• Allows conscious control of precise, skilled,
  voluntary movements
• Motor homunculi upside-down caricatures
  representing the motor innervation of body regions

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Posterior
Motor
Anterior
Motor map in precentral gyrus
Toes
Jaw
Primary motor cortex (precentral gyrus)
Tongue
Swallowing
Figure 12.9
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Premotor Cortex

• Anterior to the precentral gyrus
• Controls learned, repetitious, or patterned motor
  skills
• Coordinates simultaneous or sequential actions
• Involved in the planning of movements that depend
  on sensory feedback

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Brocas Area

• 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 prepares to speak

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Frontal Eye Field

• Anterior to the premotor cortex and superior to
  Brocas area
• Controls voluntary eye movements

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Sensory Areas

• Primary somatosensory cortex
• Somatosensory association cortex
• Visual areas
• Auditory areas

• Olfactory cortex
• Gustatory cortex
• Visceral sensory area
• Vestibular cortex

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Primary Somatosensory Cortex

• In the postcentral gyri
• Receives sensory information from the skin,
  skeletal muscles, and joints
• Capable of spatial discrimination identification
  of body region being stimulated

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Posterior
Sensory
Anterior
Sensory map in postcentral gyrus
Genitals
Primary somato- sensory cortex (postcentral gyrus)
Intra- abdominal
Figure 12.9
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Somatosensory Association Cortex

• Posterior to the primary somatosensory cortex
• Integrates sensory input from primary
  somatosensory cortex
• Determines size, texture, and relationship of
  parts of objects being felt

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Visual Areas

• Primary visual (striate) cortex
• Extreme posterior tip of the occipital lobe
• Most of it is buried in the calcarine sulcus
• Receives visual information from the retinas

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Visual Areas

• Visual association area
• Surrounds the primary visual cortex
• Uses past visual experiences to interpret visual
  stimuli (e.g., color, form, and movement)
• Complex processing involves entire posterior half
  of the hemispheres

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Auditory Areas

• Primary auditory cortex
• Superior margin of the temporal lobes
• Interprets information from inner ear as pitch,
  loudness, and location
• Auditory association area
• Located posterior to the primary auditory cortex
• Stores memories of sounds and permits perception
  of sounds

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OIfactory Cortex

• Medial aspect of temporal lobes (in piriform
  lobes)
• Part of the primitive rhinencephalon, along with
  the olfactory bulbs and tracts
• (Remainder of the rhinencephalon in humans is
  part of the limbic system)
• Region of conscious awareness of odors

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Gustatory Cortex

• In the insula
• Involved in the perception of taste

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Visceral Sensory Area

• Posterior to gustatory cortex
• Conscious perception of visceral sensations,
  e.g., upset stomach or full bladder

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Vestibular Cortex

• Posterior part of the insula and adjacent
  parietal cortex
• Responsible for conscious awareness of balance
  (position of the head in space)

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Primary motor cortex
Cingulate gyrus
Premotor cortex
Central sulcus
Corpus callosum
Primary somatosensory cortex
Frontal eye field
Parietal lobe
Somatosensory association cortex
Prefrontal cortex
Parieto-occipital sulcus
Occipital lobe
Processes emotions related to personal and social
interactions
Visual association area
Orbitofrontal cortex
Olfactory bulb
Primary visual cortex
Olfactory tract
Fornix
Calcarine sulcus
Uncus
Temporal lobe
Primary olfactory cortex
Parahippocampal gyrus
(b) Parasagittal view, right hemisphere
Motor association cortex
Primary motor cortex
Primary sensory cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8b
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Multimodal Association Areas

• Receive inputs from multiple sensory areas
• Send outputs to multiple areas, including the
  premotor cortex
• Allow us to give meaning to information received,
  store it as memory, compare it to previous
  experience, and decide on action to take

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Multimodal Association Areas

• Three parts
• Anterior association area (prefrontal cortex)
• Posterior association area
• Limbic association area

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Anterior Association Area (Prefrontal Cortex)

• Most complicated cortical region
• Involved with intellect, cognition, recall, and
  personality
• Contains working memory needed for judgment,
  reasoning, persistence, and conscience
• Development depends on feedback from social
  environment

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Posterior Association Area

• Large region in temporal, parietal, and occipital
  lobes
• Plays a role in recognizing patterns and faces
  and localizing us in space
• Involved in understanding written and spoken
  language (Wernickes area)

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Limbic Association Area

• Part of the limbic system
• Provides emotional impact that helps establish
  memories

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Lateralization of Cortical Function

• Lateralization
• Division of labor between hemispheres
• Cerebral dominance
• Designates the hemisphere dominant for language
  (left hemisphere in 90 of people)

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Lateralization of Cortical Function

• Left hemisphere
• Controls language, math, and logic
• Right hemisphere
• Insight, visual-spatial skills, intuition, and
  artistic skills
• Left and right hemispheres communicate via fiber
  tracts in the cerebral white matter

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Cerebral White Matter

• Myelinated fibers and their tracts
• Responsible for communication
• Commissures (in corpus callosum)connect gray
  matter of the two hemispheres
• Association fibersconnect different parts of the
  same hemisphere
• Projection fibers(corona radiata) connect the
  hemispheres with lower brain or spinal cord

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Commissural fibers (corpus callosum)
Longitudinal fissure
Superior
Lateral ventricle
Association fibers
Basal nuclei
Caudate
Corona radiata
Putamen
Globuspallidus
Fornix
Internal capsule
Thalamus
Gray matter
Third ventricle
White matter
Projection fibers
Pons
Decussation of pyramids
Medulla oblongata
(a)
Figure 12.10a
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Basal Nuclei (Ganglia)

• Subcortical nuclei
• Consists of the corpus striatum
• Caudate nucleus
• Lentiform nucleus (putamen globus pallidus)
• Functionally associated with the subthalamic
  nuclei (diencephalon) and the substantia nigra
  (midbrain)

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Fibers of corona radiata
Caudate nucleus
Thalamus
Lentiform nucleus Putamen Globus pallidus
(deep to putamen)
Tail of caudate nucleus
Corpus striatum
Projection fibers run deep to lentiform nucleus
(a)
Figure 12.11a
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Anterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn of lateral ventricle
Caudate nucleus
Putamen
Lentiform nucleus
Globus pallidus
Thalamus
Tail of caudate nucleus
Third ventricle
Inferior horn of lateral ventricle
(b)
Posterior
Figure 12.11b (1 of 2)
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Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn of lateral ventricle
Caudate nucleus
Lentiform nucleus
Thalamus
Third ventricle
Inferior horn of lateral ventricle
(b)
Figure 12.11b (2 of 2)
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Functions of Basal Nuclei

• Though somewhat elusive, the following are
  thought to be functions of basal nuclei
• Influence muscular control
• Help regulate attention and cognition
• Regulate intensity of slow or stereotyped
  movements
• Inhibit antagonistic and unnecessary movements