Knowledge-19 NCO

• the stimulation of sensory receptors leads to generation of action potential in neurone. Synapses enables signals to be transmitted chemically between two neurons or a neuron and a muscle.
• Myelinated motor neurons :

  The central nervous system is made up of the brain and spinal cord.

  • the motor neurons transmit impulses from the CNS to muscles or glands.
  • the cell body contains the nucleus.
  • a long thin axon protrudes , which is surrounded by myelin sheath
  • there are gaps in the sheath called nodes of Ranvier.
  • the axon terminates in a gland or muscle.
• myelinated:

  • occurs along the long axons within the nervous system.
  • action potential jumps along axon at nodes of Ranvier.
  • faster transmission
  • wider axon
• Non-myelinated:

  • occurs in neuronal body cells and dendrites
  • Action potential occurs throughout / along the whole length of the axon.
  • slower transmission
  • narrower axon.
• Myelinated axons can have action potentials jump between nodes of Ranvier this is called saltatory conduction.
• Nerve impulses are generated and transmitted along a neurone.
• Resting potential (first step of nerve impulse):

  • the neurone is not transmitting an impulse. The cell is polarized : the inside is negatively charged and the outside is positively charged. This electrochemical gradient is maintained by the active transport of sodium ions out of the cell and potassium ions into the cell by differential membrane permeability for these ion.