Nervous

• Reflex arcs are rapid and autonomic, are involuntary actions and are for protection form harm
• Name 2 types of nervous system

  Central nervous system

  Peripheral nervous system
• CNS

  Central nervous system
• PNS

  Peripheral nervous system
• What is contained within the CNS?

  • Brain
  • Spinal cord
• What is contained within the PNS?

  Nerves
• White matter

  Contains myelinated axons, mylein is a lipid substance so appears white.
• Grey matter

  Contains unmyelinated cell bodies of relay and motor neurones
• Name 3 neurones

  • Sensory
  • Relay
  • Motor
• Sensory neurones

  Carry impulses towards the CNS
• Relay neurones

  Relays information from the sensory to motor neurones
• Motor neurons

  Carries impulses away from the CNS towards the effects
• Name 2 effectors

  Muscles

  Glands
• Dendrites

  Conduct impulses towards the cell body of the motor neurone
• Axon

  Conduct impulses away from the cell body of the motor neurone
• Schwann cells

  Support the axon and secrete mylein to form a myelin sheath
• Myelin

  Acts as an electrical insulator and is a lipid substance which wraps around the axon. It speeds up electrical impulse transmission by causing saltatory conduction.
• Node of Ranvier

  Are gaps between the myelin sheath
• Steps within a reflex arc

  • Stimulus
  • Receptors
  • Sensory neurone
  • Synapse
  • Relay neurone
  • Synapse
  • Motor neurones
  • Effector
  • Response
• Sensory neurone cell bodies create swellings - what are they called?

  Dorsal root ganglion
• Sensory neurones enter the spinal cord through the dorsal root
• Motor neurones leave the spinal cord through the ventral root
• What voltage is resting potential?

  -70mV
• What is the axon at resting potential called?

  Polarised - inside is more negative than the outside
• What occurs at resting potential?

  1. Sodium potassium pump actively transports 3 sodium ions out and 2 potassium ions in
  2. Voltage gated sodium ion channels are closed so they remain outside the axon
  3. Voltage gated potassium ion channels are open so potassium ions move out of the axon by facilitated diffusion
  4. Large negative ions remain in the axon as they are too big to leave
• What voltage is the membrane at axon potential?

  +40mV
• For depolarisation to occur and to produce an action potentia, threshold potential must be met
• What occurs at action potential?

  1. A stimulus causes a voltage change allowing voltage gated sodium ion channels to ope. Sodium ions move into the axon by facilitated diffusion. = Depolarisation
  2. Sodium diffuse with the axon to the next node of ranvier= local circuit
  3. An influx of sodium ions causes more sodium ion channels to open
  4. Saltatory conduction= action potential jumps from one node to the next
• What occurs repolarisation?

  1. At +40mV, voltage gated sodium ion channels close
  2. Voltage gated potassium ion channels open causing potassium ions to leave by facilitated diffusion
  3. Repolarisation occurs (+40 to -70)
  4. A potassium ion overshoot can occur which cause hyperpolarisation (membrane potential is below -70mV)
  5. The refractory period is the time axon is hyperpolarised
  6. Eventually voltage gated potassium ion channels close
  7. Resting potential is restored by the sodium potassium pump
• How does a refractory period prevent damage to the axon?

  • Prevents a new action potential being generated
  • Ensures an impulse travels in only 1 direction
  • Prevents overstimulation
• All or nothing theory

  • Action potential is always -40mV
  • Frequency of action potentials can chnage
• If an impulse doesn't reach threshold value, an action potential isn't generated and depolarisation doesn't occur.
• Synapses are junctions joining 2 neurones
• Describe how n impulse is transmitted across a synapse

  1. An action potential cause voltage gated calcium ion channels to open, calcium ions enter the presynaptic neurone by facilitated diffusion
  2. Synaptic vesicles contain neurotransmitters/acetylcholine which ove and fuse and fuse the presynaptic membrane
  3. Acetylcholine is released by exocytosis and infuses across the synaptic cleft
  4. Acetylcholine binds to receptors on the postsynaptic neurone
  5. Voltage gated sodium ion channels open and sodium ions ove into the postsynaptic neurone
  6. If theshold is reached, an action potential is generated
• Acetylcholine is broken down by acetylcholinesterase to prevent constant stimulation of the postsynaptic neurone