Neuronal Structure And Function

Question 1

Steps of Depolarization

Answer 1

1. The resting membrane potential across the plasma membrane is approximately -70 mV, with the interior of the cell negatively charged with respect to the exterior of the cell
2. The sodium potassium ATPase pump, pumps three sodium ions out of the cell and two potassium ions into the cell with the hydrolysis of one ATP molecule
3. A gradient is created with high sodium outside of the cell and high potassium inside the cell
4. Leak channels for potassium allow the ions to leak across the membrane down their gradient. Making the interior of the cell more negative than the exterior of the cell (cells are polarized)
5. In response to change in the membrane potential the sodium ion channels open and allow ions to flow down their gradient into the cell and depolarize the section of the membrane to -50mv
6. One threshold potential has a reach has been reached the channels are open fully but below the threshold they are closed and do not allow the passage of any ions through the channel
7. When the channels open so damn flows down its concentration gradient depolarizing the section of the membrane to about 35 mV before inactivating
8. Slightly depolarizing the neighboring section of the membrane and so on

Question 2

Steps of repolarization

Answer 2

1. Voltage gated sodium channels inactivate very quickly after they open
2. Voltage gated potassium channels open more slowly than sodium channels and stay open longer. As potassium leaves the cell down its concentration gradient membrane potential returns negative values overshooting the resting potential
3. Potassium leak channels in the NAK ATPase pump continue to function to bring the membrane back to resting potential

Question 3

Nodes of Ranvier

Answer 3

Voltage gated sodium and potassium channels are concentrated at the nodes the myelin sheath dramatically speeds the movement of action potentials by forcing the action potential to jump from node to node this rapid jumping conduction in myelinated axons is termed saltatory conduction

Question 4

Glial cell- Schwann cells

Answer 4

Found in the PNS. For Myelin to increase speed of conduction of action potentials along the axon

Question 5

Glial cell- oligodendrocytes

Answer 5

Location is in the CNS. They form myelin to increase speed of conduction of action potentials along an axon

Question 6

Glial cell- astrocytes

Answer 6

Location is in the CNS. They guide neuronal development and regulate synaptic communication via regulation of neurotransmitter levels

Question 7

Glial cell-microglia

Answer 7

Location in the CNS. They remove dead cells and debris

Question 8

Glial cell-ependymal cells

Answer 8

Found in the CNS. They produce in circulate cerebrospinal fluid.

Question 9

Equilibrium potential

Answer 9

The membrane potential at which the gradient does not exist. No net movement of ions across the membrane. For sodium the equilibrium potential is positive around 50 mV. Sodium ions are driven inward by their chemical concentration gradient but if the cells are too positive the positively charged ions are repelled so the electrical gradient drives them out. Potassium’s equilibrium potential is negative. The potassium ions are driven outward by their concentration gradient however if the interior of the cells to negative the positively charged ions can’t escape the attraction. The electrical gradient drives the potassium back in. The equilibrium potential for potassium is about -90 mV

The resting membrane potential is -70 mV. Since it is closer to potassiums eq. Pot, that means there are more potassium leak channels allowing potassium out.