Nervous System

• Name 3 types of neurone

  • Sensory
  • Motor
  • Relay
• What is part of the CNS?

  • Brain
  • Spinal Cord
• CNS


  Central nervous system
• What is part of the PNS?

  • Nerves
• PNS


  Peripheral nervous system
• What does the CNS do?

  Controls and coordinates a bodies response to different stimuli
• A stimulus is a change to the envrionment
• Receptors are cells that detect stimuli
• A sensory neurone is a nerve cell that carries electrical impulses towards the CNS (central nervous system)
• A motor neurone carries electrical impusls away from the CNS towards the effctor
• An effector is part of the body that brings about response such as a muscle or a gland.
• Name 2 effectors

  • Muscle
  • Gland
• The cell body cotains the organelles
• Dendrons and dendrites are extensions of the cytoplasm where an impulse is received and carried towards the cell body.
• The axon is a a long extension that carries impulses away from the cell body.
• What type of cytoplasm does the axon contain?

  Axoplasm
• Schwann cells wrap around the axon and secrete myelin to form a myelin sheath
• Nodes of Ranvier are gaps between the myelin sheath.
• Myelin is lipid substance that acts as an electrical insulator
• How does an impulse move along the axon?

  • impulse cannot move through mylinated parts of the axon as ions are prevented from moving in and out.
  • Ions can only move in and out at the Nodes of Ranvier
  • So an impulse jumps from node to node which speeds up the rate of conduction.
• Axon terminals are found at the end of the neurone where the neurone 'synapses' with an effector
• The electrical impulse that passes along an axon is an electrical potential due to differences in charge because there is distribution of sodium and postassium ions either side of the axon membrane.
• Resting potential decribes the axon membrane when there is no impulse being transmitted and has a value of -70mV.
• Resting Potential: Describe what is happening at 1

  The sodium potassium pump actively transports sodium and potassium ions across the membrane. 3 sodium ions are moved out and 2 potassium ions are moved in. This uses ATP.

  
• Resting Potential: Describe what is happening at 2

  The voltage gated sodium ion channel is closed. The membrane is impermeable to sodium ions so these remain outside of the axon.

  
• Resting Potential: Describe what is happenig at 3

  The voltage gated potassium ion channel is open. The membrane is permeable to potassium ions so these move out of the axon down a concentration gradient by facilitated diffusion.

  
• Resting Potential: Describe what is happening 4

  Large negative ions (anions) are not able to move across the axon membrane so they remain inside the axon.

  
• Name 2 examples of large negative ions that remain in the axon

  • ATP
  • Protein
• What value is resting potential?

  -70mV
• What is resting potential?

  The electrical potential difference across the membrane of a neuron when it is not transmitting a signal.
• What is resting potential a measure of?

  Difference in potential (charge) between the inside and outside of the axon.
• Why is the inside of an axon less positive than the outside?

  • By active transport - 3 sodium ions out and 2 potassium ions in
  • Facilitated diffusion only allows the movement of potassium ions out
  • Large negative ions are only found inside the axon
• The inside of the axon is relatively negative compared to the outside because active transport moves 3 sodium ions out and 2 potassium ions in, facilitated diffusion only moves potassium ions out and large negative ions are only found inside the axon.
• At resting potential the axon membrane is polarised.
• At resting potential, the axon membrane is said to be what?

  Polarised
• Where do ions move in and out of axon?

  Nodes of Ranvier
• Why can ions only move in and out at the Nodes of Ranvier?

  Nodes of Ranvier are not myelinated
• Ions can move in and out of an axon at Nodes of Ranvier because there is no myelin.
• Resting potential is measure of the difference in potential between the inside and outside of the axon. -70mV means that the inside is less positive than the outside.
• Action potential occurs when an impulse is being transmitted.