Nerve Impulses

Cell body function

• Contains organelles found in a typical animal cell

• Including nucleus and large amounts of rough ER

• Proteins and neurotransmitters are produced here

Dendrite function

Carry action potential/nerve impulses to surrounding cells

What are the nodes of ranvier?

• Gaps in the myelin sheath

• Exposed axon membrane

3 functions of Schwann cells

• Wrap around the axon to form the myelin sheath

• Carries out phagocytosis

• Nerve regeneration

Myelin sheath function

• Myelin sheath is lipid, so does not allow charged ions to pass through it

• Provides electrical insulation

Axon function

Carries nerve impulses away from the cell body

What root does a motor neurone extend through?

Ventral root

What root does a sensory neurone extend through?

Dorsal root

What matter is the interneuron located in?

Entirely grey matter

What value is membrane resting potential (when a neuron is not conducting an impulse)

-70mV

What value is threshold?

-55mV

What value is action potential

+40/30mV

What establishes a resting potential?

The sodium-potassium pump

Give 3 purposes of hyperpolarization/refractory period

• Ensures discrete impulses

  • An action potential cannot be immediately generated after another → Ensures action potentials are seperate 

• Ensures action potentials travel in one direction

  • Stops action potentials from spreading out in to 2 directions → which would prevent a response

• Limits number of nerve impulse transmission

  • Prevents over reaction to stimulus → therefore prevents overwhelming the senses

What is saltatory conduction?

When sodium ions diffuse laterally across the membrane, causing threshold to occur, as it makes part of the membrane slightly less negative

What are the 3 factors increasing the speed of an action potential?

• Myelination

• Larger axon diameter

• Increased temperature

Why does myelination increase speed of action potential?

Action potentials are only generated at nodes of ranvier, not the entire length of axon

Why does a wider axon diameter increase speed of action potential?

• Less leakage of ions

• Less internal resistance to the flow of ions

• Therefore action potentials travel faster

Why does a higher temperature increase speed of action potential?

• Ions have more kinetic energy so diffuse faster

• Enzymes involved in respiration work faster

• More ATP for active transport in the Na⁺/K⁺ pump