The Brain

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The Brain
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Some interesting brain facts

• Brain weighs 3 lbs
• However, it is completely immersed in liquid
  (cerebrospinal fluid) and, as a result, its
  effective weight is 3 ounces.
• Brain uses 20 of the bodys blood, 20 of its
  oxygen, and 70 of its glucose.
• 80 of the human brain is cortex
• Cortex is virtually absent in fish, reptiles, and
  birds
• 1/3 of the cortex is visible
• Cortex is 1/8 thick and, if spread out flat, is
  about the size of 1 sheet of newspaper (4 pages
  of a textbook)
• Localization of function vs. equipotentiality
  (mass action)
• Brocas area is in the frontal lobe when
  destroyed, patient cannot produce language, but
  can comprehend language Brocas aphasia
• Wernickes area is in the temporal lobe when
  destroyed patient cannot comprehend language, but
  can produce language Wernickes aphasia

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Direction in the brain

• We are symmetrical around our midline we have a
  left arm and a right arm, a left ear and a right
  ear, etc.
• Medial close to the midline
• Lateral farther from the midline closer to the
  side of the head

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Some brain structure terminology

• Sulcus (pl. sulci) any of the shallow grooves
  separating the convolutions (bumps, ridges) on
  the surface of the brain
• Fissure a very deep groove that, typically,
  separates major cortical structures
• Gyrus (pl. gyri) a convolution (bump, ridge) on
  the brain surface
• Commisures a fiber bundle that interconnects
  corresponding regions on each side of the brain
• White matter (mylinated axons) and gray matter
  (cell bodies)
• Cortical structures are specialized parts of the
  cortex.
• Everything else under the cortex, but above the
  brainstem, is referred to as a subcortical
  structure.

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Some brain organization terminology

• Hemispheres
• The two relatively symmetrical halves of the
  brain one on the left and one on the right
• Contralaterality
• The left hemisphere receives sensory input from,
  and sends motor messages to, the right side of
  the body vice versa for the right hemisphere
• Cerebral lateralization (hemispheric
  specialization)
• Instances in which one of the hemispheres is more
  responsible for a particular cognitive function
  than the other hemisphere
• Left hemisphere specialized for language and
  analytical thought
• Right hemisphere specialized for visual-spatial
  tasks, music, face recognition, and emotional
  states
• Cerebral dominance
• In 90 of human beings, the left hemisphere is
  specialized for language and these individuals
  are right-handed thus, the left hemisphere is
  said to be the dominant hemisphere

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Brainstem

• Medulla
• Vital involuntary functions
• Pons
• Sleep and arousal
• Reticular formation
• Sleep, arousal, attention
• Cerebellum
• Motor coordination
• Also involved in planning, memory, language, and
  emotion

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Another view of the brainstem
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Limbic System I Emotion and motivation

• Hypothalamus
• Regulates
• Glands
• Autonomic system
• Eating
• Drinking
• Sleeping
• Sexual activity
• Plays a role in emotion
• Amygdala
• Forms learned associations between objects and
  emotion, especially fear

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Limbic system II Cognitive functions

• Thalamus
• Sensory relay station
• Hippocampus
• Formation of new memories
• Basal ganglia
• Putamen, globus pallidus, caudate nucleus
• Motor behavior
• Habit learning

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Another view of both the limbic system and brain
stem
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Neglect Syndrome (Hemineglect)

• A patient with a stroke in the right hemisphere
  was asked to copy the model drawings
• Typical of neglect syndromes, the left side of
  the model is almost completely ignored

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Primary motor cortex and somatosensory cortex
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The Corpus Callosum

• Millions of myelinated axons connecting the
  brains hemispheres
• Provides a pathway for communication between the
  hemispheres
• If surgically severed for treatment of epilepsy,
  hemispheres cannot communicate directly

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Visual Processing

• Both eyes send information to both hemispheres
• Right half of the visual field goes to the left
  hemisphere
• Left half of the visual field goes to the right
  hemisphere

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Sperrys Split-Brain Experiment

• Split-brain subjects could not name objects shown
  only to the right hemisphere
• If asked to select these objects with their left
  hand, they succeeded but they could not say why
• The right side of the brain doesnt control speech

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Brain Change

• Plasticity
• A property of the brain that allows it to change
  as a result of experience, drugs, or injury
• Chemical signals guide growing connections.
• Experience fine-tunes neural connections.
• Critical periods
• Rats in special environments have heavier brains
  with more synaptic connections
• Change in the strength of connections underlies
  learning
• Hebbian learning fire together, wire together
• Neurogenesis production of new brain cells in
  the adult brain
• Brain reorganization in response to overuse or
  underuse
• Devoting more cortex to information that is
  pertinent for tasks at hand
• Blind people who read Braille have much larger
  areas of cortex devoted to receiving input from
  index fingers than do sighted individuals
• Brain reorganization in response to brain injury
• Much more likely to occur in the young
• Treatment for brain injury or disease
• Neural grafting, using stem cells