generating nerve impulses take 2

• describe the length of the fibres in a sensory neuron?

  Long dendron, short axon
• Describe the length fo fibres in the relay neurons?

  Short dendrites, the axon can be long or short
• Describe the length of the fibres in the motor neurons?

  Short dendrites, long axons
• describe the location of the sensory neurons?

  Cell body and dendron are outside of the spinal cord; the

  cell body is located in a dorsal root ganglion
• Describe the location of relay neurons?

  Entirely within the spinal cord or central nervous system
• Describe the location of the motor neurons.

  Dendrites and the cell body are located in the spinal cord; the axon is outside of the spinal cord
• Describe the function of sensory neurons?

  Conduct Impluses to the spinal cord
• Describe the function of relay neurons?

  Interconnect the sensory neuron with the appropriate motor neuron
• Describe the function of the motor neuron?

  Conduct impulses to an effector- a muscle, or gland
• what are the three types of channels in a neurone membrane?

  Sodium potassium pumps

  Potassium gates

  Sodium gates (Some are voltage controlled)
• how many potassium go into a neurone membrane, and how many sodium go out?

  3 sodium go out, and 2 potassium go in
• what is the resting potential of a neuron?

  -70 millivolts
• are sodium gates open, or closed when the neuron is at rest?

  closed
• What quantities of sodium and potassium are either entering or exiting when a neuron is at rest?

  3 sodium out, and 2 potassium in
• what is the partial charge of a neuron's outside when it is at rest, and why?

  It is positive, there are lots of positive Sodium and some positive potassium ions outside of the neuron
• Why is the inside of a neuron negative when it is at rest?

  There are lots of big negative proteins inside, and less positive ions.
• why is a resting neuron described as polarised?

  The sodium channels are closed
• in a resting neuron, are the Na/K pumps open or closed?

  they are open
• What type of transport occurs in a Na/K pump in a resting neuron?

  Active transport
• What is the ion movement in a Na/K pump on a resting neuron?

  3 sodium out, and 2 potassium in
• Are Potassium pumps open in a resting neuron?

  Yes
• What type of transport occurs in a potassium pump?

  Passive facilitated diffusion
• which ions move in a potassium channel and how?

  Potassium ions move out
• Are sodium channels open in a resting neuron?

  No
• does any transport of ions occur in a closed sodium channel of a resting neuron?

  No
• how is an action potential generated?

  By opening sodium channels, this is called depolarisaiton
• if there is a small stimulus, what happens to sodium gates?

  A few open, allowing few sodium ions to pass into the neuron.
• Why is a small stimulus not enough to generate an action potential?

  The depolarisation must pass -50 millivolts
• what happens if there is a big stimulus?

  enough sodium ions pass into the neuron, reaching the threshold of -50 millivolts. Because of this, more Sodium channels open as they are voltage-gated. The inside of the cell becomes positively charged at 40 millivolts.
• what are the steps to repolarise a neuron?

  Potassium diffuses out of the cell. The potential difference makes the cell hyperpolarised (negative 75 millivolts).

  Sodium/potassium pump starts to work to restore original concentrations.
• why is it impossible to restimulate the cell if it has been hyperpolarised?

  during hyperpolarisation, the neuron's membrane potential drops below the resting potential; this occurs because of the constant efflux of potassium ions through the voltage-gated channels or the influx of chloride ions. In this state, the membrane potential is further from the threshold potential of -50 Millivolts making it difficult to initiate another action potential.