Introduction to biological psychology

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Introduction to biological psychology
Topic 2 Structure and function of neurones
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Properties of Neurones

• In common with other cells
• Cell membrane
• Nucleus containing DNA, the genetic blueprint
  for the structure and function of the cell
• Organelles and machinery for translating genetic
  code into proteins (Golgi apparatus, endoplasmic
  reticulum, ribosomes)
• Therefore structural and metabolic proteins
  (e.g. enzymes)
• Metabolic machinery enabling glucose oxidation
  to provide energy

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Neuronal Specialisation
Excitability of the membrane
Dendrites network of fine processes derived
from cell body
Synapse connection between two neurones
Axon hillock site of action potential generation
Axon elongated neural process, specialised for
rapid signal transmission over long distances
Myelination fatty sheath round axon
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Membrane potentials

• The neuronal cell membrane is differentially
  permeable to intracellular and extracellular
  chemical constituents.
• Some ions can pass through the membrane easily,
  others can pass through, but with difficulty,
  others cannot pass through at all
• As a result of this differential permeability to
  ions, there is an uneven distribution of charge
  across the membrane
• This difference is the membrane potential
  the resting membrane potential of neurones is
  around 70mV
• The main ions contributing to the membrane
  potential are positively charged sodium (Na) and
  potassium (K), and negatively charged chloride
  (Cl-) and proteins (A-).

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Membrane potential
Outside Cell
Inside Cell
A-
K
K
Na
Na
Cl-
Cl-
Resting Potential approx -70 mV
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Changes in membrane potential

• Incoming signals cause changes in the dendritic
  membrane potential, by altering the permeability
  of the membrane to ions

• Increasing the permeability to sodium (Na)
  causes the membrane potential to become less
  negative (depolarisation)

• Increasing the permeability to chloride (Cl-)
  causes the membrane potential to become more
  negative (hyperpolarisation)

Inside Cell
Outside Cell
A-
K
K
Na
Na
Cl-
Cl-
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Signal transmission in dendrites
Na

• Changes in charge diffuse passively along the
  membrane from the point of origin
• Relatively slow
• Decay over distance

At any one point the membrane potential is
determined by the sum of all the individual
depolarising and hyperpolarising events
originating nearby
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The axon hillock
Axon hillock - the point where the axon leaves
the cell body

• Specialised for the generation of action
  potentials
• When the net depolarisation at the axon hillock
  reaches the threshold potential (around 50mV),
  an action potential is generated

• The action potential then propagates the
  electrical signal along the axon

No action potential
Still no action potential
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The action potential

• An electrical spike caused by reversal of
  membrane polarity
• Mediated by rapid changes in membrane
  permeability to sodium and potassium

• All-or-none phenomenon
• an action potential is always the same size
• Does not decay over distance
• an action potential is the same size when it
  reaches the terminal as it was when it left the
  axon hillock.

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Conduction velocity in axons
Comparison of different classes of primary
afferent axon
A-alpha fibre A-beta fibre A-delta fibre C fibre
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The synapse
Vesicles containing neurotransmitter
Neurotransmitter released into synaptic cleft
Postsynaptic receptors
Neurotransmitter reuptake sites
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Neurotransmitters

• Synthesised in the neurones, close to the site
  of release
• Stored on the terminal until required for
  release
• Released into synaptic cleft in response to an
  action potential
• Binds to receptors in post-synaptic membrane
• Causes changes in membrane potential
• Excitatory receptors cause depolarisation
• Inhibitory receptors cause hyperpolarisation

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Examples of neurotransmitters
Type Transmitter Action Amino
acid Glutamate Excitatory (NMDA-type, AMPA-type
receptors) GABA Inhibitory (A-, and B-type
receptors) Monoamines Dopamine Excitatory (D1
D5 receptors) Inhibitory (D2, D3 D4
receptors) Noradrenaline Excitatory (subtypes
of alpha- beta-receptors) Inhibitory
(subtypes of alpha- beta-receptors) Serotonin
Excitatory (5HT-1, 5HT-2 5HT-3 receptors)
( 5-hydroxytryptamine 5HT) Inhibitory
(some subtypes of 5HT-1 receptors) Others Acetyl
choline Excitatory (muscarinic some nicotinic
receptors) Inhibitory (subtypes of nicotinic
receptors)
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Synaptic transmission
Presynaptic neurone Synaptic cleft
Postsynaptic neurone
Chemical Neurotransmitter
Electrical Action potential
ElectricalChange in membrane potential
neurotransmitter release
neurotransmitter release
receptors
receptors
receptors
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Neurotransmitter-receptor interaction
Receptor
Excitation or Inhibition
Changes in membrane potential
AMJ Young, Jan, 2000 C\0_TEACH\PS103\lec2-sli.ppt
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Receptor pharmacology
Neurotransmitter Binds to receptor and evokes
excitation or inhibition
Agonist Binds to receptor and evokes the same
response as the native transmitter.
Antagonist Binds to receptor and does not evoke
any response.
Prevents the native transmitter or any agonist
from binding to the receptor
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Drugs affecting synaptic transmission
Action potential Neurotransmitter Change in
membrane potential
Reuptake and/or breakdown of neurotransmitter
neurotransmitter release
receptors
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Actions of therapeutic drugs
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Drugs acting atneurotransmitter receptors
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Drugs affecting membrane potentials
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Drugs affecting neurotransmitter synthesis and
storage
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Drugs affecting neurotransmitter release
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Drugs affecting reuptake and breakdown of
neurotransmitters