Summary: Biologische Grondslagen: Cognitie

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• 1 Thema 1

• 1.1.1 Structure and Function of the Neuron

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• What contains the cell body and what is it involved in?

  The cell body contains the nucleus (and other organelles), which contains the genetic code which is involved in protein synthesis of certain neurotransmitters.

• How does communication by an axon work?

  The terminal of an axon flattens out into a disc-shaped structure. It is here that chemical signals enable communication between neurons via a small gap (synapse). The two neurons forming that synapse are reffered to as presynaptic (before the synapse) and postsynaptic (after the synapse), reflecting the direction of information flow.

• What is an action potential and how does it works?

  When a presynaptic neuron is active, an electrical current (action potential) is propogated down the length of the axon. When the action potential reaches the axon terminal, chemicals (neurotransmitters) are released into the synaptic cleft.

• What is a synaptic potential and how does it work?

  Neurotransmitters bind to receptors on the dendrites or cell body of the postsynaptic neuron and create a synaptic potential, which is conducted passively (without creating an action potential). 
  
  It is important to note that each postsynaptic neuron sums together many synaptic potentials, which are generated at many different and distant dedritic sites.

• What is the range of the two potentials?

  Passive conduction tends to be short range because the electrical signal is impeded by the resistance of the surrounding matter. 
  
  Active conduction enables long-range signalingsignaling between neurons by the propogation of action potentials.

• What is the function of myelin?

  Myelin is a fatty substance that is deposited around the axon of some cells (especially those who carry motor signals). It blocks the normal Na+/K+ transfer and so the action potential jumps, via passive conduction, down the length of an axon at the points at which the myelin is absent (called 'nodes of Ranvier').
  
  Destruction of myelin is found in multiple sclerosis.

• How is a synaptic potential created?

  The electrical signal initiates a sequence of events leaing to the release of neurotransmitters into the synaptic cleft. Protein receptors in the membrane of the postsynaptic neurons bind to the neurotransmitters. Many of the receptors are transmitter-gated ion channels. This sets up a localized flow of Na+, K+ or Cl-, which creates the synaptic potential.

• How do neurons code information?

  The amplitude of an action potential does not vary, but the number of action potentials propogated per second varies along a continuum. This rate of responding ('spiking rate') relates to the informational code carried by that neuron.

• 1.1.2 The Gross Organization of the Brain

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• What is white/gray matter and its location?

  Gray matter consists of neuronal cell bodies and its located at the cerebral cortex and the subcortex. 
  
  White matter consists of axons and support cells ('glia'). Its located beneath the cerebral cortex.   
  White matter tracts may project between different cortical regions within the same hemisphere (association tracts), may project between different cortical regions in different hemispheres (commmissures: corpus collosum) or may project between cortical and subcortical structures (projection tracts).

• What are the terms of referencing locations by the brain?

  1. Anterior and posterior refer to directions toward the front and the back of the brain.
  
  2. Superior/dorsal and inferior/ventral refer to directions towards the top and the bottom of the brain.
  
  3. Lateral and medial refer to directions toward the outer surface and the center of the brain.