Anatomy of the Nervous System

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Anatomy of the Nervous System
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Introduction
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Directions and Planes of Section
There are a number of special words that are used
to describe the position and direction of brain
structures. These words help describe the
location of structures relative to other
structures. For example, we can say that the
frontal lobe is "rostral" to the occipital lobe.
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The brain is often cut ("sectioned") into pieces
for further study. These slices are usually made
in one of three planes the coronal plane, the
horizontal plane or the sagittal plane.
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Triune Brain Model (Paul Maclean)

• Consider the brain as three structures, the outer
  one being added to the inner ones during
  evolution- evolution from primitive to more
  complex

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1) R-Complex

• Brain stem and cerebellum
• R-complex behaviors are automatic, have a
  ritualistic quality, and are highly resistant to
  change.
• Autonomic functions Digestion, circulation,
  breathing
• Behaviors Establishing home territory,
  reproduction and social dominance.

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2) Limbic system

• Related to physiological needs eating, drinking,
  sex,
• Fight or flight responses Fear, anger,
  aggression
• Memory
• Expression and mediation of emotions and
  feelings, including emotions linked to
  attachment. These protective, loving feelings
  become increasingly complex as the limbic system
  and the neocortex link up.
•  

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3) Neocortex

• Seat of Higher Functions
• Movement (motor planning)
• processing of sensory information (perceptions)
• Language,
• Thinking/Intelligence
• Higher Level Emotions
• Consciousness
• Personality

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• It is known that all 3 layers of the brain
  interact
• In any given situation, one particular layer may
  be dominant while the rest of the brain acts in
  support.

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Localization versus Mass Action

• While there is no clear consensus as to which is
  correct, we will use the localization perspective
  as a simpler way to illustrate the brain
• Another way to think about it is that our more
  primitive functions are housed in the lower
  brain and more complex ones in the higher
• We will work from the lower CNS to the higher

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I) The Spinal Cord

• Continues to become the brain stem
• Conveys information into and out of the CNS
• It is a segmented structure, on each structure on
  each side, a sensory nerve, and a motor nerve

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Bell Magendie Law

• the entering dorsal roots carry sensory
  information and the exiting ventral roots carry
  motor information to the muscles and glands
• Cell bodies of motor neurons are located inside
  the spinal cord

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Disorders involving Spinal Cord Damage

• Spinal Cord Injury
• Complete Spinal Cord Injury Usually the loss of
  sensation and motor ability associated with a
  complete spinal cord injury caused by bruising,
  loss of blood to the spinal cord, or pressure on
  the spinal cord cut and severed spinal cords are
  rare. Generally, complete spinal cord injuries
  result in total loss of sensation and movement
  below the site of the injury.
• What I do is based on powers we all have inside
  us the ability to endure
• the ability love, to carry on, to make the best
  of what we have
• and you dont have to be a Superman to do
  it."  

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Incomplete Spinal Cord Injury An incomplete
spinal cord injury does not result in complete
loss of movement and sensation below the injury
site. A variety of patterns exist to classify
such injuries, depending on the location and
extent of the injury Amyotrophic lateral
sclerosis (ALS, Lou Gehrigs Disease) a disease
of the nerve cells in the brain and spinal cord
that control voluntary muscle movement. - ALS
affects approximately 5 out of every 100,000
people worldwide.- In about 10 of cases, ALS is
caused by a genetic defect. In the remaining
cases, the cause is unknown- There are no known
risk factors, except for having a family member
who has a hereditary form of the disease.
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Stephen Hawking

• With spinal cord injuries, individuals have their
  higher functions intact (thinking,
  consciousness), in contrast to individuals in a
  coma, or chronic vegetative state

• I am quite often asked How do you feel about
  having ALS? The answer is, not a lot. I try to
  lead as normal a life as possible, and not think
  about my condition, or regret the things it
  prevents me from doing, which are not that many.
• I have been lucky, that my condition has
  progressed more slowly than is often the case.
  But it shows that one need not lose hope.

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II) The Brain Stem (Medulla, Pons, Cerebellum)

• Also referred to as the hindbrain, the posterior
  part of the brain
• Majority of functions associated with this area
  are autonomic functions

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Medulla

• just above the spinal cord, and is regarded as an
  enlarged, elaborated extension of the spinal cord
• Controls breathing, heart rate, vomiting,
  salivation, coughing, and sneezing
• Contains the decussation of the pyramids-
  crossing of the corticospinal tracts

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• Cranial nerves a set of nerves that control
  sensory and motor information in the head,
  through which the medulla does a great deal of
  its work
• Large doses of opiates are fatal because they
  suppress activity of the medulla

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Pons

• Lies anterior and ventral to the medulla
• Portion of the hindbrain that helps connect the
  cerebral cortex with the brainstem

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• Reticular formation included in the pons and
  the medulla includes descending and ascending
  portions
• Descending portion controls the motor areas of
  the spinal cord
• Ascending sends output to much of the cerebral
  cortex-selectively increasing arousal and
  attention
• Medial Pontine Reticular formation REM sleep

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Cerebellum

• large hindbrain structure with a great many deep
  folds
• Long been know for its role in movement,
  balance, and coordination
• More recently implicated in implicit memory

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Coma/Terry Schiavo

• Typically limited activity in the cortex and/or
  areas of the brain-stem
• Questions regarding consciousness arise
• Resolution was that the feeding tube was removed

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III) Midbrain Subcortical structures
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Diencephalon

• Thalamus center of the forebrain the sensory
  gateway to the brain-only exception is olfactory
  information, which does not flow through it
• Lateral geniculate nucleus visual information
• Medial geniculate nucleus auditory

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Limbic system

• a number of interlinked structures, which form a
  border around the brain stem
• Fight or flight response
• Play major role in motivation and emotional
  behaviors-eating, drinking, and sexual activity

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Hypothalamus

• small area near the base of the brain, ventral to
  the thalamus
• the brain of the brain autonomic functions,
  eating, drinking, sexual behavior, aggression,
  and temperature regulation.
• Endocrine system through the pituitary gland
  synthesizes and releases hormones into the
  bloodstream
• Central structure of the limbic system, hence,
  the other areas of the limbic system vie for
  control/influence of the hypothalamus

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Amygdala

• most associated with fear /stress
• emotions, particularly emotional learning
• Aggression
• Emotional memory

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Hippocampus

• large structure between the thalamus and the
  cortex
• The Case of HM
• 27 year old assembly line worker who had suffered
  from untreatable and debilitating temporal lobe
  seizures for many years. Surgeon removed medial
  portion of the temporal lobes bilaterally (only
  right lobes removal is shown on the figure on
  the right).
• H.M.s seizures were improved, but there was a
  devastating side effect he suffered friom a
  severe anterograde amnesia, or, he could no
  longer form long-term memories.

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The case study of HM

• Every day is alone in itself, whatever enjoyment
  I have had, and whatever sorrow Ive hadRight
  now, Im wondering. Have I done or said anything
  amiss? You see, at this moment everything looks
  clear to me, but what happened just before?
  Thats what worries me. Its like waking from a
  dream I just dont remember, (Milner, 1970, p.
  37)

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Milner (1957) Could HM learn Mirror Writing?
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Memory Systems

• Explicit/Implicit memory which can function
  independent of one and other
• Explicit memory conscious recollection- facts,
  events, specific stimuli
• Implicit memory perceptual, stimulus-response
  learning and motor learning- unconscious
• Neurogenesis occurs here
• Depression-stress-cell death

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Nucleus Accumbens

• Olds Milner (1954)
• Rats who received electrical stimulation
• of the brain would return to the area
• where they received it!
• Routtenberg Lindy (1965) the rats
• suffering from starvation were forced to make
• a choice between obtaining food and water or
• electrical brain stimulation- picked brain
  stimulation and some died of starvation!

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The Pleasure Center Dopamine - classified
as a catecholamine- involved in movement,
reinforcement, frontal lobe(STM, planning,
problem solving)- Cocaine and Methylphenidate(Ri
talin) block reuptake of Dopamine-Etiology of
Schizophrenia- Role in Addiction/Learning
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Basal Ganglia

• a group of subcortical structures lateral to the
  thalamus, including the caudate, putamen, and
  globus pallidus
• heavily connected with the frontal areas of the
  cortex, involved in planning sequences of
  behavior

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Parkinsons Disease

• Parkinson's disease (PD) is a chronic,
  progressive disorder of the nervous system. A
  chronic disorder continues for long periods of
  time, usually many years. Parkinson's disease
  affects a person's muscular coordination.
  Symptoms of PD include tremor (shaking), rigidity
  in some muscles, slow movements, and problems
  with maintaining normal posture.
• Degeneration of neurons in the substantia nigra
  (DA), which sends axons to the Basal Ganglia

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Huntington's disease

• An inherited disease that causes the progressive
  breakdown (degeneration) of nerve cells in the
  brain. Huntington's disease has a broad impact on
  a person's functional abilities and usually
  results in movement, thinking (cognitive) and
  psychiatric disorders.
• HD is a familial disease, passed from parent to
  child through a mutation in the normal gene. Each
  child of an HD parent has a 50-50 chance of
  inheriting the HD gene. If a child does not
  inherit the HD gene, he or she will not develop
  the disease and cannot pass it to subsequent
  generations
• Caused by degeneration of neurons in the caudate
  nucleus and the putamen
• A specific group of inhibitory neurons- GABA

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IV) The cortex
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Ventricles

• four fluid filled cavities in the brain
• CSF a clear fluid similar to blood plasma which
  cushions the brain against mechanical shock when
  the head moves and helps support the weight of
  the brain

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Cerebral Cortex

• Consists of two hemispheres, each organized to
  receive sensory information from contralateral
  side of the body
• Corpus callosum Neurons in each hemisphere
  communicate with neurons in the corresponding
  part of the other hemisphere through two bundles
  of axons, this structure, and the smaller,
  anterior commissure

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Hemispheric specialization - Relative
specialization, not absolute

• Left Hemisphere
• Expressive speech
• Receptive language
• Language (general)
• Complex motor functions
• Vigilance
• Paired associate learning
• Liaison to consciousness
• Ideation
• Conceptual similarities
• Temporal analysis
• Analysis of detail
• Arithmetic
• Writing
• Calculation
• Finger naming
• Right-left orientation
• Sequential processing

• Right Hemisphere
• Spatial orientation
• Simple language comprehension
• Nonverbal ideation
• Picture and pattern sense
• Performancelike functions
• Spatial integration
• Creative associative thinking
• Facial recognition
• Sound recognition
• Nonverbal paired associate thought
• Tactile perception
• Gestalt perception
• Picture processing
• Intuitive problem solving
• Psychic experiences
• Humorous thoughts
• Simultaneous processing

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• The cortex contains six layers, or laminae
  layers of cell bodies that are parallel to the
  surface of the cortex and separated from each
  other by layers of fibers.
• Cells of the cortex are also organized into
  columns groups of cells with similar
  properties, arranged perpendicular to the
  laminae- the cells within a given column have
  similar or related properties and many
  connections to one and other
• i.e. Occipital lobe is organized into groups that
  process form, movement, and color
• We can distinguish 50 or more areas of the
  cerebral cortex based on differences in the
  thickness of the 6 laminae and on the appearance
  of cells and fibers within each laminae- for
  convenience, we have divided it into four lobes

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Sensation versus perception

• Sensation process by which our sensory receptor
  and CNS receive and represent information from
  our environment

• Perception Processing of organizing and
  interpreting sensory information
• The Cortex is involved in our perceptions

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The Occipital lobe

• Located at the posterior (caudal) end of the
  cortex
• The main target for the axons of the thalamic
  nuclei that receive input from the visual
  pathways
• Most posterior is the primary visual cortex
  (striate cortex),
• Herbert Livingstone color, form, movement are
  all carried by different pathways!?processed in
  parallel simultaneously but in different parts of
  the brain unified experience
• cortical blindness Total loss of vision in all
  or part of the visual field due to bilateral
  OCCIPITAL LOBE (i.e., VISUAL CORTEX) damage or
  dysfunction. Anton syndrome is characterized by
  the psychic denial of true, organic cortical
  blindness. (Adams et al., Principles of
  Neurology, 6th ed, p460)

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Temporal lobe

• the lateral portion of each hemisphere, near the
  temples
• Primary cortical target for auditory
  information-Primary auditory cortex
• Memory!!!!!- Pennfield- stimulated brains and
  all those who reported experiences (8), only
  occurred in the temporal lobe
• The God lobe- Spirituality

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The Parietal Lobe

• lies between the occipital lobe and the central
  sulcus, which is one of the deepest grooves in
  the surface of the cortex
• The area just posterior to the central sulcus,
  the postcentral gyrus, or the primary
  somatosensory cortex, is primary target for touch
  sensations and information from muscle stretch
  receptors and joint receptors
• The parietal lobes monitors all the information
  about eye, head, and body positions and passes it
  on to other brain areas that control movement
• Tactile Agnosia patients are unable to
  recognize objects which they feel

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The strange journey ofEinsteins brain

• He refused to turn them over, was fired, and took
  them with him wherever he went
• From time to time he sent pieces to
  neuroscientists (i.e. Marian Diamond)
• Ultimately, he returned the remainder of his
  brain to the pathology department at the
  University Medical Center at Princeton

• April 18th, 1955, Einstein died- left explicit
  instructions that he be cremated and his ashes
  scattered in secret
• He did not like being idolized and did not want
  to have idolization of his body to continue after
  his death
• The pathologist responsible for his autopsy,
  Thomas Stolz Harvey, removed his brain and eyes
• Gave his eyes to Einsteins opthalmologist-rumor
  is they are still in a safe deposit box in NYC!

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The Frontal Lobe

• extends from the central sulcus to the anterior
  limit of the brain-mist recently developed part
  of the brain
• Prefrontal cortex the most anterior portion of
  the frontal lobe and it receives information from
  all sensory systems-each sensory system projects
  to different cells in the prefrontal cortex
• Implicated in the functions of working memory and
  attention
• Expressive Language Brocas asphasia

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The Frontal Lobe

• Contains the primary motor cortex
• The amount of tissue on the precentral gyrus that
  is dedicated to the innervation of a particular
  part of the body is proportional to the amount of
  motor control needed by that area, not just its
  size. For example, much more of the motor strip
  is dedicated to the control of speech (tongue,
  lips, jaw, velum, pharynx, and larynx) than to
  the trunk.

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The Frontal Lobe (cont.)The Executive functions
Personality controversy

• Phineas Gage an efficient and capable foreman
  was injured on September 13, 1848, when a tamping
  iron was blown through the frontal region of is
  brain. He suffered the following change in his
  personality according to the physician J. M.
  Harlow, who attended to him. He is fitful,
  irreverent, indulging at times in the grossest
  profanity (which was not previously his custom),
  manifesting but little deference to his fellows,
  impatient of restraint or advice when it
  conflicts with his desires, at times
  pertinaciously obstinate yet capricious and
  vacillating, devising many plans for future
  operation which no sooner are arranged than they
  are abandoned in turn for others appearing more
  feasible. His mind was so radically changed so
  that his friends and acquaintances said that he
  was no longer Gage

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ADHD and the Brain

• Some studies have suggested a decrease in
  activity in the frontal lobes
• Ritalin is commonly used as a treatment
• Disinhibition

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Putting it all together!!!
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• emergence of a unified experience from the
  functioning of these separate parts is a most
  complex question
• The binding problem how does visual, auditory,
  and other areas of your brain influence on and
  other to produce a combined perception of a
  single object
• The idea of association areas in the brain has
  not fared well in terms of experimentation
• The most agreed upon answer to this question is
  that it is a combination of localization and mass
  action-individualized parts do seem to play roles
  in specific functioning but conscious experience
  is the result of these parts working together
  with other parts in a system
• Binding of perception depends on precisely
  simultaneous activity in various brain regions
• Synchrony among the distant parts of the cortex
  may depend on coordination by the inferior
  parietal cortex

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THE BIOLOGICAL ESSENCE OF INTELLIGENCE

• Einsteins Brain
• A greater number of glial cells in the and
  differences in the Parietal Lobe
• Inferior parietal lobe was 15 larger than
  normal visuospatial cognition, mathematical
  thought, and imagery of movement
• Heritability Estimates of Intelligence range
  from .40-.80
• Variations in a widely distributed network
  throughout the brain appear to predict individual
  differences in intelligence
• Important to note Conclusions with respect to
  the underlying neural architecture of higher
  cognitive functions is speculative!

• Volume (12-31 of variance) the most
  significant and frequently detected increases are
  observed in
• Frontal/Prefrontal lobe verbal Executive
  functions
• Parietal lobe visuo-spatial functions
• Temporal lobe verbal task demands
• Hippocampus encoding and retrieval of
  information
• Cerebellum the automaticity of being.

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• Larger Corpus Callosum more efficient
  inter-hemispheric information transfer- benefits
  the integration and processing of information
• PET Scans Intelligence and glucose metabolism
  are negatively correlated- more intelligent
  individuals use their neurons more efficiently!

• 2. Cerebral Tissue
• Grey Matter
• Estimate of the density of neurons,- Number of
  neuronal/glial cells dendritic expansions-
  efficiency of information processing
• Majority of data suggest higher intelligence is
  correlated with increased grey matter-
  prefrontal/frontal cortex
• White Matter
• Estimate of of axons and degree of myelination-
  enhanced facilitation of neuronal transmission