neurons

Question 1

motor neuron

Answer 1

• many short dendrite carry nerve impulse from CNS to cell body
• long axon carry impulse from cell body to effector cells

Question 2

sensory neuron

Answer 2

• one long dendron carry impulse from receptor to cell body
• axon carry impulse from the cell body to CNS

Question 3

relay neuron

Answer 3

• many dendrites carry impulse from sensory neuron to cell body
• axon carry impulses from cell body to motor neuron

Question 4

neuron cell membranes are polarized at rest

Answer 4

• when at rest the outside of the membrane is more positive than the inside so the membrane is polarized
• resting potential is the voltage across the membrane when resting and is 70mv
• resting potential is maintained by Na-K pumps and K ion channels
• for 3 Na exit the neuron 2 K ions enter with the help of ATP
• the Na-K move Na ions out but membrane isn’t permeable so they can’t diffuse in creating an electrochemical gradient and outside more positive than the inside
• Na-K pumps move K ions in and the membrane is permeable to these ions so they can diffuse out through K channels

Question 5

neuron cells depolarized when stimulated

Answer 5

• stimulus excites the neuron cell and Na ion channels open making the membrane more permeable to Na and diffuse in the membrane down their electrochemical gradient so inside is less negative
• depolarization, it threshold value reached more Na channels open
• at repolarization Na channels close and K channels open so more K leave the neuron down their electrochemical gradient and starts to return to resting potential
• hyperpolarization, K channels slow to close so there is overshoot of many K leaving and potential difference becomes more negative then resting potential
• ion channels are reset and the Na-K pumps returns membrane to resting potential until membrane excited by another stimulus

Question 6

ions diffusing sideways

Answer 6

• in an action potential some of the neuron diffuse sideways
• this causes Na ion channels in the next region to open so Na diffuse into that part
• wave of depolarization travels along the neuron
  -wave moves away from the refractory period because they can’t fire an action potential

Question 7

why are refractory periods important

Answer 7

• they act as a time delay between action potentials so that they don’t overlap but pass as discrete impulses
• make sure that action potentials are unidirectional

Question 8

myelinated neurons and action potentials

Answer 8

• in myelinated neuron depolarization only happens at the node
• the neuron’s cytoplasm produces enough electric charge to depolarize the next node, so impulse jumps from node to node and is called saltatory conduction
• in non-myelinated neurons, the impulse travels as a wave and travels the whole length of the neuron
• speed at which impulse moves in a neuron is called conduction velocity