Chapter Four Anatomy of the Nervous System

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Chapter Four Anatomy of the Nervous System
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Starring

• Your Brain

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Research Methods

• Injection of dye into blood allows CAT
  (computerized axial tomography) scanner to take
  images of the brain
• Intentional brain damage
• points to behavioral impairment, e.g., damage to
  Brocas area associated with inability to speak
• intense magnetic field temporarily inactivates
  area
• electrode or chemicals used to damage specific
  area
• but, brain damage may not solely produce
  behavior impairment may be due to many factors

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• Figure 4.1  Computerized axial tomography (CT
  scanning). (a) A persons head is placed into the
  device and than a rapidly rotating source sends
  x-rays through the head while detectors on the
  opposite side make photographs. A computer than
  constructs an image of the brain. (b) A CT scan
  of a normal human brain. (Source Dan
  McCoy/Rainbow).

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Research Methods cont.

• Brain stimulation
• can evoke sensations, e.g., flashes of light
• less intense magnetic fields stimulate an area
• injected chemicals stimulate specific receptors
• but, sensations are in isolation and behaviors
  depend on coordination across brain areas

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Research Methods cont.

• Recording brain activity
• identifies area of brain associated with behavior
• PET (positron emission tomography) detects
  radioactive chemicals absorbed by most active
  cells
• rCBF (regional cerebral blood flow) measures
  increased blood flow by monitoring inert
  radioactive chemical
• fMRI (functional magnetic resonance imaging)
  detects release of oxygen in active cell -
  replaces PET and rCBF
• but, brain is always active and interpreting
  changing activity is a challenge
• also, different people use different areas for
  same task

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New Brain Research CNN Today Biological
Psychology, Volume I
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Research Methods cont.

• Correlating brain anatomy with behavior
• extensive practice on string instrument
  correlated with enlarged area of brain receiving
  sensations from left hand
• experienced taxi drivers have enlarged area of
  hippocampus related to spatial memory
• Albert Einstein had one area of brain larger than
  normal and had unusually high ratio of glia to
  neurons
• Caution samples are small correlation is not
  causation

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Structure of the Vertebrate Nervous System

• CNS brain spinal cord
• PNS nerves outside brain spinal cord
• somatic nerves that convey messages from sense
  organs to CNS from CNS to muscles and glands
• autonomic set of neurons that control heart,
  intestines, other organs
• sympathetic arousal, fight or flight,
  emergency
• parasympathetic relax and digest,
  non-emergency

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• Figure 4.5  The human nervous system. Both the
  central nervous system and the peripheral nervous
  system have major subdivisions. The closeup of
  the brain shows the right hemisphere as seen from
  the midline.

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Anatomical Terms for Directions

• Road map of nervous system uses technical terms
  to describe a three dimensional structure
• basic terms include, e.g., ventral, dorsal,
  lateral and medial
• permits clear communication among investigators

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• Figure 4.6 Terms for anatomical directions in the
  nervous system. In four-legged animals dorsal and
  ventral point in the same direction for the head
  as they do for the rest of the body. However,
  humans upright position has tilted the head
  relative to the spinal cord, so the dorsal and
  ventral directions of the head are not parallel
  to the dorsal and ventral directions of the
  spinal cord.

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The Spinal Cord

• Bell-Magendie Law
• the entering dorsal roots carry sensory info to
  brain and,
• the exiting ventral roots carry motor info to
  muscles and glands
• Dorsal root ganglia clusters of neurons outside,
  but near, the spinal cord on dorsal roots
  carrying sensory info
• Cut the spinal cord and brain loses motor control
  over parts of body served by that segment and
  below

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• Figure 4.7  Diagram of a cross section through
  the spinal cord. The dorsal root on each side
  conveys sensory information to the spinal cord
  the ventral root conveys motor commands to the
  muscles.

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Autonomic Nervous System

• Sympathetic prepares body for arousal
• increased breathing, increased heart rate,
  decreased digestive activity
• form chain of ganglia just outside spinal cord
• act as a single system in sympathy with one
  another
• short preganglionic axons and long postganglionic
  axons both release norepinephrine

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Autonomic Nervous System cont.

• Parasympathetic facilitates vegetative,
  nonemergency responses by the bodys organs
• increases digestive activity, activities opposing
  sympathetic system
• consists of cranial nerves and nerves from sacral
  spinal cord
• long preganglionic axons extend from the spinal
  cord to parasympathetic ganglia close to each
  internal organ
• shorter postganglionic fibers then extend from
  the parasympathetic ganglia in the organs
  release acetylcholine

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The Hindbrain (rhombencephalon)

• Medulla controls vital reflexes, e.g.,
  breathing, heart beat
• Pons area where many axons cross from one side
  of the brain to the other
• Reticular formation controls motor areas of the
  spinal cord output to cerebral cortex increasing
  arousal and attention
• Raphe system sends axons to much of the
  forebrain, increasing or decreasing the brains
  readiness to respond
• Cerebellum controls movement, balance and
  coordination
• damage impairs timing and difficulty shifting
  attention between auditory and visual stimuli

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The Midbrain (mesencephalon)

• Tectum (roof) includes superior colliculus and
  inferior colliculus, important routes for sensory
  information
• Tegmentum (covering, carpet) includes
• nuclei for third and fourth cranial nerves (eye
  movements)
• parts of reticular formation
• extensions of the pathways between the forebrain
  and the spinal cord or hindbrain
• Substantia nigra gives rise to dopamine path that
  deteriorates in Parkinsons disease

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• Figure 4.12  The human brain stem. This composite
  structure extends from the top of the spinal cord
  into the center of the forebrain. The pons,
  pineal gland, and colliculi are ordinarily
  surrounded by the cerebral cortex.

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The Forebrain (prosencephalon)

• Cerebral cortex outer portion of brain
• Thalamus center of forebrain and relay station
  for sensory info to/from cerebral cortex (except
  olfactory)
• Hypothalamus small area with widespread
  connections
• damage here affects sexual behavior temperature
  regulation, fighting, feeding, activity level
• sends messages to attached pituitary gland,
  altering release of hormones into bloodstream
• Limbic system borders the brain stem and mediates
  eating, drinking, sexual activity, anxiety and
  aggression

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• Figure 4.14 The limbic system is a set of
  subcortical structures that form a border (or
  limbus) around the brain stem.

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The Forebrain cont.

• Basal ganglia includes caudate nucleus, putamen,
  globus pallidus
• many connections with frontal cortex, where
  planning, memory and emotional expression arise
• Basal forebrain
• here the nucleus basalis is key part of brains
  system for arousal, wakefulness, and attention
  (intermediary between hypothalamus and cerebral
  cortex)
• Hippocampus
• located between thalamus and cerebral cortex
• critical for the formation of new memory
• connected to the hypothalamus by the fornix

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Figure 4.18

• Figure 4.18  The basal ganglia. The thalamus is
  in the center, the basal ganglia are lateral to
  it, and the cerebral cortex is on the outside.
  (Source After Nieuwenhuys Voogd vanHuijzen,
  1988)

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Cerebral Spinal Fluid and the Ventricles

• Cerebral spinal fluid assists in cushioning the
  brain
• fills the central canal, channel in the center of
  the spinal cord
• fills the ventricles, four cavities within the
  brain
• fills space between brain and meninges (membranes
  that surround the brain and spinal cord)
• meningitis is inflammation of meninges

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Cerebral Spinal Fluid and the Ventricles cont.

• Cerebral spinal fluid is clear fluid similar to
  blood plasma
• formed in choroid plexus
• flows from lateral to third to fourth ventricle
  to central canal or between meninges
• reabsorbed in arachnoid apace between meninges
  and brain and spinal cord

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Cerebral Spinal Fluid and the Ventricles cont.

• Hydrocephalus is blockage of flow of CFS
• increases pressure on the brain
• in infants this spreads the skull bones and is
  associated with mental retardation

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• Figure 4.20  The cerebral ventricles. (a) Diagram
  showing positions of the four ventricles. (b)
  Photo of a human brain, viewed from above, with a
  horizontal cut through one hemisphere to show the
  position of the lateral ventricles. Note that the
  two parts of this figure are seen from different
  angles. (Source After Woolf, 1991)

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Cerebral Cortex

• Contains grey matter, the outer surface of
  cerebral hemispheres
• White matter is formed by axons extending inward
  from cortex
• Neurons from each hemisphere communicate with
  each other through the corpus callosum and
  anterior commissure

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Cerebral Cortex cont.

• Contains six distinct layers of cells parallel to
  surface of cortex (laminae I - VI)
• a layer may be missing in a region, e.g., lamina
  IV is absent from the motor cortex
• lamina V is thickest in motor cortex
• Organized into columns of cells
• arranged perpendicular to the laminae
• cells within a given column have similar or
  related properties, e.g., may all respond to
  touch on palm of hand or foot

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Lobes of Cortex

• Occipital lobe posterior end of cortex
• contains primary visual cortex
• damage in one hemisphere causes blindness in
  opposite visual field
• Parietal lobe between occipital lobe and the
  central sulcus
• contains the primary somatosensory cortex which
  receives touch sensation, muscle-stretch and
  joint position information
• postcentral gyrus includes four bands of cells
  two receive light-touch information, one receives
  deep-pressure and one a combination of both

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Lobes of Cortex cont.

• Temporal lobe lateral portion of each
  hemisphere, near the temples
• essential for understanding spoken language
• contributes to perception of movement and face
  recognition
• damage may lead to Külver-Bucy syndrome
• Frontal lobe extends from the central sulcus to
  the anterior limit of the brain
• primary motor cortex controls fine movements
• prefrontal cortex important for working memory,
  delayed response tasks, planning of appropriate
  behavior for context

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How Do the Parts Work Together

• A brain area functions like a word in a sentence
• damage the amygdala and diminish fear (delete a
  word and you lose something)
• but, fear intensifies with pain and diminishes
  with a trusted friend (a word has richer meaning
  in context)
• no single brain area where information is
  integrated

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How Do the Parts Work Together

• Unified experience emerges from binding of
  separate parts
• Simultaneous neural activity may bind brain areas
• recognition of Mooney faces produced gamma waves
  30-80/second in various brain areas
• when cat sees and hears bird it has synchronized
  neural activity in occipital, parietal, and
  frontal areas
• Einsteins brain had larger than normal inferior
  parietal cortex, an area known to bind different
  aspects of perception, e.g., damage prevents
  binding color to shape

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How Do the Parts Work Together cont.

• But, why does synchronous activity produce
  binding?
• Overall, the cerebral cortex serves to elaborate
  sensory material