Chapter 4: Excitable tissue

Question 1

Unipolar neurons

Answer 1

Have one process, with different segments serving as receptive surfaces and releasing terminals.

Question 2

Bipolar neurons

Answer 2

Have two specialized processes: a dendrite that carries information to the cell and an axon that transmits information from the cell.

¨Bipolar cell of retina

Question 3

Pseudounipolar cells

Answer 3

Some sensory neurons are in a subclass of bipolar cellls called pseudounipolar cells. As the cell develops, a single process splits into two, both of which function as axons - one going to skin or muscle and another to the spinal cord.

Question 4

Multipolar cells

Answer 4

Have one axon and many dendrites.

Motor neurons, hippocampal pyramidal cells with dendrites in the apex and base, and cerebellar Purkinje cells with an extensive dendritic tree in a single plane.

Question 5

Membrane potential

Answer 5

The voltage difference across the cell membrane of a neuron; it is the difference between the electrical potential in the cytoplasm of the cell and the electrical potential in the extracellular space.

The membrane potential results from the separation of positive and negative charges across the cell membrane.

Question 6

Resting membrane potential

Answer 6

Represents an equilibrium situation at wich the driving force for the membrane-permeant ions down their concentration gradients across the membrane is equal and opposite to the driving force for these ions down their electrical gradients.
The resting potential of neurons is usually -70 mV. Because there are more open K+ channels than Na+ at rest, membrane permeability to K+ is greater.

Question 7

Na/K ATPase

Answer 7

K+ higher inside tha outside the cell
Na+ higher outside than inside
*This concentration difference is established by Na/K ATPase. The outward K+ concentration is regulated by selective channels, and also the inward Na+ is regulated by selective channels.

Question 8

Action potential

Answer 8

1- In response to a depolarizing stimulus, some of the voltage-gated Na+ channels open and Na+ enters the cell and the membrane is brought to its threshold potential

2- the voltage-gated Na+ channels overwhelm the K+ and other channels. The entry of Na+ causes the opening of more voltage-gated Na+ channels and further depolarization, setting up a positive feedback loop.

3- The rapid upstroke in the membrane potential ensues

4-

Question 9

K+ normal value (plasma levels)

Answer 9

3.5–5.0 mEq/L