Neurotransmission

Question 1

What is known as the length constant? (lambda)

Answer 1

The distance a graded potential will move along a neuron.

Question 2

Equation for length constant. Include what each variable means.

Answer 2

lambda= square root of: r_m / (ri + r_o)

r_m= leakiness of neuron’s membrane to ions. Myelin makes this value higher. Think of Rm as the RESISTANCE.

Ri is internal resistance, and Ro is the resistance outside the cell parallel to it.

Question 3

Where does a PSP travel, and what happens to it as it does?

Answer 3

It travels towards the axon hillock. It degrades and gets smaller as it travels towards it.

Question 4

Myelinated axons have higher what?

Answer 4

Higher membrane resistance (Rm), and Higher length constant value

Question 5

Explain in detail the benefit of myelin, and what happens at the node of ranvier. What does the myelin do extra?

Answer 5

Unlike in unmyelinated axons, CONDUCTION ALONG A MYELINATED AXON DOES NOT REQUIRE ACTION POTENTIAL PRODUCTION ALONG THE ENTIRE AXON. It only requires action potentials at the nodes of ranvier. During the myelinated portions, the Na+ just diffuses down. The resistance in the myelinated area is so high, that APs just aren’t going to happen during those.

Question 6

What happens with multiple sclerosis? Treatment does what?

Answer 6

Inflamation damages myelin sheaths. This either slows and eventually stops the action potential. You can also get cross-talk between axons, abnormal pulse generation, and sensitivity. Treatments use K+channel blockers to delay repolarization of neurons and cause longer APs.

Question 7

How do local anesthetics work?

Answer 7

Block Na+ channels locally to prevent initiation or conduction of APs. Prevents transmission of pain signals from reaching the brain.

Question 8

Depolarization of nerve terminal causes what to happen?

Answer 8

Causes opening of voltage-gated Ca++ channels at the terminal.