Central Nervous System (CNS)

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Central Nervous System (CNS)

• CNS consists of the brain and spinal cord
• Cephalization
• Evolutionary development of the rostral
  (anterior) portion of the CNS
• Increased number of neurons in the head
• Highest level is reached in the human brain

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Embryonic Development

• Neural plate forms from ectoderm
• Neural plate invaginates to form a neural groove
  and neural folds

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Regions and Organization of the CNS

• Adult brain regions
• Cerebral hemispheres
• Diencephalon
• Brain stem (midbrain, pons, and medulla)
• Cerebellum

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Cerebral hemisphere
Diencephalon
Cerebellum
Brain stem
Midbrain
Pons
Medullaoblongata

(d) Birth
Figure 12.3d
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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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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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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 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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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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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

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Diencephalon

• Three paired structures
• Thalamus
• Hypothalamus
• Epithalamus
• Encloses the third ventricle

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Cerebral hemisphere
Septum pellucidum
Corpus callosum
Interthalamic adhesion (intermediate mass of
thalamus)
Fornix
Choroid plexus
Thalamus (encloses third ventricle)
Interven- tricular foramen
Posterior commissure
Pineal gland (part of epithalamus)
Anterior commissure
Corpora quadrigemina
Mid- brain
Cerebral aqueduct
Hypothalamus
Optic chiasma
Arbor vitae (of cerebellum)
Pituitary gland
Fourth ventricle
Mammillary body
Choroid plexus
Pons
Cerebellum
Medulla oblongata
Spinal cord
Figure 12.12
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Thalamus

• 80 of diencephalon
• Superolateral walls of the third ventricle
• Connected by the interthalamic adhesion
  (intermediate mass)
• Contains several nuclei, named for their location
• Nuclei project and receive fibers from the
  cerebral cortex

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Dorsal nuclei
Medial
Lateral dorsal
Lateral posterior
Pulvinar
Anterior nuclear group
Medial geniculate body
Reticular nucleus
Lateral geniculate body
Ventral postero- lateral
Ventral anterior
Ventral lateral
Ventral nuclei
(a) The main thalamic nuclei. (The reticular
nuclei that cap thethalamus laterally are
depicted as curving translucent structures.)

Figure 12.13a
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Thalamic Function

• Gateway to the cerebral cortex
• Sorts, edits, and relays information
• Afferent impulses from all senses and all parts
  of the body
• Impulses from the hypothalamus for regulation of
  emotion and visceral function
• Impulses from the cerebellum and basal nuclei to
  help direct the motor cortices
• Mediates sensation, motor activities, cortical
  arousal, learning, and memory

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Hypothalamus

• Forms the inferolateral walls of the third
  ventricle
• Contains many nuclei
• Example mammillary bodies
• Paired anterior nuclei
• Olfactory relay stations
• Infundibulumstalk that connects to the pituitary
  gland

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Paraventricular nucleus
Dorsomedial nucleus
Anterior commissure
Fornix
Preoptic nucleus
Posterior hypothalamic nucleus
Anterior hypothalamic nucleus
Lateral hypothalamic area
Supraoptic nucleus
Ventromedial nucleus
Supra- chiasmatic nucleus
Mammillary body
Arcuate nucleus
Optic chiasma
Pituitary gland
Infundibulum (stalk of the pituitary gland)
(b) The main hypothalamic nuclei.
Figure 12.13b
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Hypothalamic Function

• Autonomic control center for many visceral
  functions (e.g., blood pressure, rate and force
  of heartbeat, digestive tract motility)
• Center for emotional response Involved in
  perception of pleasure, fear, and rage and in
  biological rhythms and drives