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The structure of the Nervous system

1. Introduction

  • Neuroanatomy informs us of how the brain is organised which informs us of the organisation of behavior.
  • We can study different levels of the nervous system from molecules to synapses to neurons to networks to maps and then systems and then the overall anatomy of the Central Nervous System.
  • Understanding the different levels of structure is important for understanding function.

2. Divisions of the nervous system

  • The nervous system can be divide into the forebrain, midbrain and hindbrain.
  • The hindbrain contains the medulla, pons and cerebellum.
  • The midbrain contains the inferior and superior colliculi.
  • The forebrain contains the diencephalon and telecephalon.
  • The diencephalon contains the thalamus and the hypothamalus.
  • The thalamus is used to direct incoming sensory information and receives instructions from the cortex about which sensory information to transmit.
  • The telencephalon contains the amygdala, hippocampus, basal ganglia, cerebral cortex and septum. 
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The structure of the Nervous system

1. Introduction

  • Neuroanatomy informs us of how the brain is organised which informs us of the organisation of behavior.
  • We can study different levels of the nervous system from molecules to synapses to neurons to networks to maps and ton systems and then the overall anatomy of the Central Nervous System.
  • Understanding the different levels of structure is important for understanding function.

2. Divisions of the nervous system

  • The nervous system can be divided into the forebrain, midbrain and hindbrain.
  • The hindbrain contains the medulla, pons and cerebellum.
  • The midbrain contains the inferior and superior colliculi.
  • The forebrain contains the diencephalon and telecephalon.
  • The diencephalon contains the thalamus and the hypothamalus.
  • The thalamus is used to direct incoming sensory information and receives instructions from the cortex about which sensory information to transmit.
  • The telencephalon contains the amygdala, hippocampus, basal ganglia, cerebral cortex and septum. 
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The structure of the Nervous system

3. Divisions/lobes of the cerebral cortex

  • Frontal: movement and high level cognition as Dum and Strick (2002) found that there are six spatially separate motor areas and all of these connect to the primary motor area.
  • Occipital: vision. Temporal: auditory processing. Parietal: spatial cognition.
  • The cerebral cortex is a thick sheet of brain tissue which is divided into two hemispheres.
  • The corpus calloscum is the structure that allows communication between the hemispheres.

4. The sulci and gyri

  • Gyri are the ridges and sulci are the furrows on the surafce of the cortex and divide different areas of the cortex.
  • The central sulcus divides the frontal and parietal lobe.
  • The precentral sulcus separates the rest of the frontal lobes from the motor strip.
  • The motor strip is needed for movement and is found between the central and precentral sulcus and running perpendicular from this is the superior frontal gyrus, superior frontal sulcus, middle frontal gyrus, inferior frontal sulcus and inferior frontal gyrus. 
  • Division based on function depends on what you define as function.
  • Division can be based on cytoarchitecture, gross or connectional anatomy. 
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The structure of the Nervous system

5. Changes in the Nervous System over the lifespan

  • Grey matter loss (dendrites and nerve cell bodies) from age 4 to 22 vs. white matter which is used for transmission of information rather than information processing.
  • Gotgay et al. (2004) used MRI to find that this occurs in basic areas, then areas for spatial orientation then areas for learning/attention/speech then areas for executive function and movement coordination.
  • Gotgay et al. (2004) also found that this has clinical implications as individuals with Autism have GM hyperplasia in the first two years of life.
  • Shaw et al. (2006) used T1 weighted MRI to find that cortical thinning of the prefrontal cortex is prolonged in highly intelligent individuals.

6. Neural networks

  • There is integration and distribution of information.
  • There is a distinction between convergence (e.g. receptors to optic nerves) and divergence (e.g. optic nerves to neurons).
  • There is also a distinction between serial and parallel processing.
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The structure of the Nervous system

7. Layers in the nervous system

  • Staining cell bodies, axons and dendrites lead to the discovery of six layers and each have there own specific inputs and outputs.
  • The six layers are: molecular, internal pyramidal, internal granual, external pyramidal, internal pyramidal and polymorphic.
  • The inputs are: association fiber (communication with another part of neocortex), commissural (communication with other hemisphere) and thalamocortical (from the thalamus).
  • The outputs are: association, commissural, corticospinal (to the spinal chord) and corticothalamic (to the thalamus).
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The structure of the Nervous system

8. Cortical columns

  • Information processing units with specific input.
  • Run vertically as there are dense connections with neurons that are above or below.
  • 110 neurons in each column across species and brain areas. 270 in primate visual area.
  • Mountcastle (1957) - change in properties as electrode runs across cortex - some to light and some to deep stimulation.
  • Hubel and Weisel (1977) - firing of V1 and mapping inputs from eyes = orientation selective.
  • Cats auditory cortex = columns for monoaural and binaural stimuli.
  • Woosley and Van der Loos found that whiskers = columns.
  • Goodhill and Carreira-Pepinan (2002) found that repeated presentation of a certain orientation = more neurons for that orientation. 
  • Brodman (1909) mapped cortex based on columnar organisations.
  • Purves et al. (1992) - just an incidental coincidence of activity dependent elaboration of synaptic connections. 
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Connectional anatomy within the Nervous system

1. Motor hierarchy

  • Main pathway runs from the prefrontal to premotor to primary motor areas then input sent to the spinal chord which causes a muscle to ellicit a certain action.
  • The prefrontal area is used for decision making and planning. The premotor transforms a goal into action. The primary motor ellicits an action by influencing muscles.
  • Subcortical structures are also involved - the basal ganglia and cerebellum have looped connections and receive and send projections to various levels of the motor hierarchy so modulate activity there.

2. Further evidence

  • Drum and Strick (2002) also found the same amount or more corticospinal neurons as in the primary motor cortex, in all parts of the premotor area: the ventral and dorsal premotor areas, rostral areas, ventral and dorsal cingulate and supplementary motor areas.

3. Divide and rule strategy 

  • Benefits if there is damage to one pathway.
  • Lesions: to prefrontal = no planning but still action and to primary motor = planning and intention but no action.
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