Neurones

• Motor Neurone

  • Transport nervous impulse from sensory or relay in CNS (brain or spinal cord) to an effector e.g. muscle or gland
  • Cell body in CNS
  • Dendrites: Thin cytoplasmic process, transmit to body
  • Axon
  • Transmit away
  • Long
  • Terminal branch (end in synaptic bulbs)
  • Synaptic bulbs
  • Vesicles containing neurotransmitter molecules
  • Pass impulse to effector cells
  • Cause effector cell response (e.g. muscle contraction or gland secretion)
  • Myelinated motor neurone has myelin sheath made of Schwann cells around axon
  • Gaps between Schwann cells are nodes of Ranvier
• Sensory Neurones

  • Transmit impulse from receptors in sense organs
  • To relay or motor neurones in CNS
  • Same basic structure as motor
  • Long dendron and short axon
  • Dendrites
  • In sense organ as receptors
  • Transmit impulse to cell body (located away from dendrites)
  • Dendron
  • Axon
  • Transmits impulse away from
  • To CNS
  • Synaptic knobs at terminal branch ends
• Nerve

  • Structure
  • Axon bundle surrounded by connective tissue
  • Similar to electrical cable with lots of electrical wires in it
  • Sensory nerve contains only sensory neurone axons
  • Motor nerve contains only motor neurone axons
  • Mixed nerve contains both sensory and motor axons
  • Reflex Arc
  • How neurones organised
  • Automatic, innate, protect from harm
  • Neurone sequence rapidly transmitting impulses to cause reflex response
  • Cell-Signalling: Stimulus > Receptor > Communication > Effector > Response > Pathway
• Myelination

  Myelinated

  • Enclosed by insulating myelin sheath
  • Made mostly of phospholipids (80% lipid + 20% protein)
  • Formed by Schwann cells that wrap whole axon length
  • Spiral round, enclosing axon in many plasma membrane layers
  • Spaces between cells are Nodes of Ranvier; every 1-3mm
  • Speeds nerve impulse transmission
  • Action potentials, only occur at Nodes of Ranvier
  • Jump node to node
  • Impulse conduction is saltatory conduction

  Unmyelinated

  • Action potentials have to occur along whole length
  • Conduction speed much slower than myelinated
  • Wider diameter also effects speed
  • Faster, less ion leakage + resistance
  • Peripheral fibre severed
  • Myelin sheath provides track regrowth
  • Unmyelinated fibres + myelinated mammalian CNS axons do not regenerate