Brain anatomy: cerebral hemispheres

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Brain anatomy cerebral hemispheres
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The cerebral hemispheres

• The cerebral cortex (consists of six lobes on
  each side
• frontal,
• parietal,
• temporal,
• occipital,
• insular, and
• limbic).
• the underlying cerebral white matter,
• the basal ganglia a complex of deep gray matter
  masses.

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Frontal lobe

• Prefrontal Personality
• And adaptation of the personality to events and
  experiences
• Foresight and imagination
• Sense of self

• frontal- main motor areas (originate movement
  that is co-ordinated elsewhere)

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Parietal lobe

• Principle sensory area
• Touch
• Proprioception
• Lesions cause sensory losses
• Involvement in cognition
• Receptive speech loss

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Temporal lobe

• Cognition
• Emotion
• Memory
• Links to the hippocampus and the limbic system
  are important to both of the above
• Wernickes area (tempero-parietal) special role
  in auditory association and speech comprehension

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• What might be involved in speech processing?

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Occipital lobe

• Vision
• Visual processing and visual association
• Involved in eye movement
• Hemianopia from damage
• Think what might be involved in visual processing?

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• The cortex is particularly well developed in
  humans and is responsible for many higher brain
  functions, including manual dexterity (eg to move
  the fingers individually so as to play the
  piano) conscious, discriminative aspects of
  sensation and cognitive activity, including
  language, reasoning, and many aspects of learning
  and memory.

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Anatomy

• The cerebral hemispheres make up the largest
  portion of the human brain.
• The cerebral hemispheres appear as highly
  convoluted masses of gray matter that are
  organized into a folded structure.
• The crests of the cortical folds (gyri) are
  separated by furrows (sulci) or deeper fissures.
• The folding of the cortex into gyri and sulci
  permits the cranial vault to contain a large area
  of cortex (nearly 2 1/2 square feet), more than
  50 of which is hidden within the sulci and
  fissures.

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Main Sulci Fissures

• The surfaces of the cerebral hemispheres contain
  many fissures and sulci that separate the
  frontal, parietal, occipital, and temporal lobes
  from each other and the insula.
• The lateral cerebral fissure (Sylvian fissure)
  separates the temporal lobe from the frontal and
  parietal lobes.
• The insula, a portion of cortex that did not grow
  much during development, lies deep within the
  fissure The circular sulcus surrounds the insula
  and separates it from the adjacent frontal,
  parietal, and temporal lobes.
• The hemispheres are separated by a deep median
  fissure, the longitudinal cerebral fissure.
• The central sulcus (the fissure of Rolando)
  arises about the middle of the hemisphere, and
  separates the frontal lobe from the parietal
  lobe.
• The parieto-occipital fissure separates the
  parietal lobe from the occipital lobe.

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Corpus Callosum

• The corpus callosum connects the two hemispheres
• It is a large bundle of myelinated and
  nonmyelinated fibers, that crosses the
  longitudinal cerebral fissure and interconnects
  the hemispheres.
• The corpus callosum serves to integrate the
  activity of the two hemispheres and permits them
  to communicate with each other.
• Most parts of the cerebral cortex are connected
  with their counterparts in the opposite
  hemisphere by axons that run in the corpus
  callosum.

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White Matter

• The white matter of the adult cerebral hemisphere
  contains myelinated nerve fibers of many sizes as
  well as neuroglia.
• Transverse (commissural) fibresinterconnect the
  two cerebral hemispheres (mainly the corpus
  callosum)
• Projection fibres connect the cerebral cortex
  with lower portions of the brain or the spinal
  cord.

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White matter continued

• Association fibres connect the various portions
  of a cerebral hemisphere and permit the cortex to
  function as a coordinated whole.

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Areas of the cerebrum

• Brodmann numbers to identify functions- down to
  individual sulci
• Question localisation now that we know more about
  connectionism and we have amore dynamic view of
  the brain works

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Primary Motor Cortex

• The primary motor projection cortex is located on
  the anterior wall of the central sulcus.
• These cells control voluntary movements of
  skeletal muscle on the opposite side of the body.

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Homunculus

• Map of motor control
• Reflects the body
• Sizes indicate the amount of brain needed for
  various functions
• Note vast area for the face- why?

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Primary Sensory Cortex

• The primary sensory projection cortex for sensory
  information received from the skin, mucosa, and
  other tissues of the body and face is located in
  the postcentral gyrus and is called the
  somatesthetic area,
• This area receives fibers that convey touch and
  proprioceptive (muscle, joint, and tendon)
  sensations from the opposite side of the body.
• A relatively wide portion of the adjacent frontal
  and parietal lobes can be considered a secondary
  sensory cortex because this area also receives
  sensory stimuli.
• The cortical taste area is located close to the
  facial sensory area.

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• How do areas compare on the homunculous?

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Primary Visual Cortex

• The primary visual receptive cortex is located in
  the occipital lobe.
• In primates, an extensive posterior portion of
  the occipital pole is concerned primarily with
  high-resolution macular vision
• the more anterior parts are concerned with
  peripheral vision.
• The visual cortex in the right occipital lobe
  receives impulses from the right half of each
  retina,
• The left visual cortex receives impulses from the
  left half of each retina. The upper portion of
  area 17 represents the upper half of each retina,
  and the lower portion represents the lower half.

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Primary auditory cortex

• The primary auditory receptive area is located in
  the superior temporal gyrus toward the lateral
  cerebral fissure.
• The auditory cortex on each side receives the
  auditory radiation from the cochlea of both ears,
  and there is point-to-point projection of the
  cochlea on the acoustic area.
• Wernicke's area (in the posterior third of the
  superior temporal gyrus in the dominant (usually
  left) hemisphere, is involved in high-order
  auditory discrimination and speech comprehension.

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Basal ganglia

• The term basal ganglia are masses of gray matter
  deep within the cerebral hemispheres.
• The term is debatable because these masses are
  nuclei rather than ganglia
• Anatomically, the basal ganglia include the
  caudate nucleus, the putamen, and the globus
  pallidus.Together they are called the corpus
  straitum
• Functionally, the basal ganglia and their
  interconnections and neurotransmitters form the
  extrapyramidal system.

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Extrapyramidal system

• Influences motor instructions sent to the
  periphery
• Has a role in stabilising the large and
  complicated systems that control movement
• Helps to direct action and interpret sensory
  information

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About the hemispheres

• Why have they evolved?
• Why do we need them?
• Why are they so big?