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Neurones and neural pathways

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Title: Neurones and neural pathways


1
Neurones and neural pathways
  • Unit 3
  • Behaviour, populations and Environment

2
Lesson Aims
  • To examine the functions of dendrites, the cell
    body, axons and myelin sheath
  • To learn about the post-natal development of
    myelination
  • To examine the function of neurotransmitters

3
Neurone Structure
  • Dendrites receive nerve impulses and pass
    towards cell body
  • Cell Body located in CNS. Contain nucleus, most
    of the cytoplasm and ribosomes required for
    protein synthesis
  • Axons single fibre which carries impulses away
    from cell body

4
Sensory Neurone
  • take messages from sensory receptors in the skin
    and the specialised sense organs - the nose,
    tongue and ears, to the brain

Cultured sensory neurone
5
Motor Neurone
  • has many dendrites protruding from the cell body
    which is end-on to the axon
  • Axon can be very long

6
Myelinated Axon
  • Fatty material
  • Insulating jacket around nerve fibre
  • Increases transmission rate of nerve impulses

7
Myelination
  • Development takes about 2 years after birth to
    complete
  • Hypothalamus in infants not fully myelinated so
    cannot control temperature
  • In Multiple Sclerosis (MS), there is patchy loss
    of myelin and this leads to delayed or blocked
    conduction of nervous impulses.

8
Synapse
  • Gap between an axon ending of one neurone
    (pre-synaptic) and dendrite or cell body of the
    next neurone (post-synaptic)
  • Act like switches and may allow or prevent
    signals passing from one neurone to the next
  • Many mitochondria provide the energy for active
    transport which helps maintain electrical
    potential and reabsorb neurotransmitters.

9
Neurotransmitters
  • Protein messengers which "jump across synapse
    between one neurone and the next to communicate
    impulses to the next neurone.
  • An impulse arriving at a synaptic terminal
    stimulates the synaptic vesicles to secrete their
    contents into the synapse.
  • If the number of excitatory signals exceeds the
    number of inhibitory signals, the neurone will
    "fire", carrying an impulse to the next synapse,
    but this only occurs if a certain threshold is
    reached

10
Acetylcholine
  • Neurotransmitter
  • Acetylcholine from a parasympathetic nerve in the
    heart will inhibit heart rate and volume.
    However, it promotes peristalsis in the
    alimentary canal.
  • Some acetylcholine receptors also respond to
    nicotine from cigarettes, often leading to
    tobacco addiction in those who smoke. They can
    also be blocked temporarily by anaesthetics
    called muscle blockers (relaxants)
  • To avoid repeated contractions from the same
    stimulus, acetylcholine is immediately destroyed
    by an enzyme called acetylcholinesterase

11
Noradrenaline
  • Neurotransmitter
  • normally produces effects such as increased heart
    rate, increased blood pressure, dilation of
    pupils, dilation of air passages in the lungs and
    narrowing of blood vessels in non-essential
    organs. This enables the body to perform well in
    stressful situations.
  • Is removed by being reabsorbed back into the
    pre-synaptic ending.

12
Converging pathway
13
Diverging pathway
14
The Facts You Need to Know
  • p17
  • from nerves are bundles of nerve fibres to
  • the same transmitter molecule .
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