Bio 436 lecture 4 (concepts)

How do we distinguish between strong and light stimuli, i.e. a gentle tap vs a hard slap?

Frequency of APs in a single neuron and the activation of more receptors; light touch = infrequent action potentials; rough touch + more frequent action potentials

What two major "conditions" dictate the speed at which AP's travel down the length of an axon?

1. Myelination of axon (range = 1-120 m/s) 2. Diameter of axon (range - 1/2-20 µm)

Know the sequence of events of an action potential What is threshold

1. RMP = -70mV 2. Threshold = -50mV 3. Depolarization = -50mV to +30mV ~ Na into cell 4. Repolarization = +30mV to -70mV ~K out of cell 5. Hyperpolarization = -70mV to -80mV ~K out of cell (locked state of VGNa)

Know the difference between absolute and relative refractory periods- what is different about each

Absolute refractory period: membrane cannot produce another AP bc Na+ channels are inactivated (locked) Relative refractory period: occurs when voltage- gated K+ channels are open, making it harder to depolarize to threshold. Stimulus of greater intensity can elicit a second response.

When a neuron signals another cell is there one or many action potentials?

According to two different quizlets, there are many action potentials.

Are action potentials all or non- what does this mean?

Action potentials are all or nothing because they will not happen if they do not reach threshold (-50mV); if a nerve is at rest the amplitude on one action potential will be the same all along the nerve independent of the stimulus strength.

Why is a membrane potential important?

Because it makes sure the neurons can spontaneously depolarize and conduct action potentials for no damn reason. According to someone's quizlet it's an alternative source to atp

Know the concentrations of NA and K on the inside and outside of most cells (average resting membrane potential in humans ~ - 70mV)

Intracellular: Na= 12mM K= 150 mM Extracellular Na=145mM K=5mM

How does the brain distinguish between stimulus intensities?

It differentiates the strengths of stimuli based on the number of AP the stimulus produced; does not necessarily mean that it is recruiting more neurons; the stimulus strength (current input in to the nerve either experimentally by injecting a large current or in real life by response of touch receptor) triggers different frequency of action potentials

How does a cell establish a membrane potential?

Membrane potentials change because membranes become more or less permeable to ions, which is usually from an ion channel being opened.

What is the name of the equation which allows us to calculate an equilibrium potential for any individual ion?

Nernst Equation: ENA = (RT/ZF) ln [(Na out)/(Na in)] R= 2 cal/˚K-mole T = 293˚K (20˚C) Z = valency = +1 F = 23,062 cal/mole-Volt *2.303 convert to log10* ENA = 0.06 log [(Na out)/(Na in)]

What is important inside of cells for the establishment of a membrane potential?

Potassium and negative charged components

What is different between sensory/afferent and motor/efferent neurons? Are both found in nerves

Sensory/ afferent neurons conduct impulses in CNS Motor/ Efferent neurons carry impulses out of CNS. (Somatic and autonomic)

What ions are most involved?What channels?

Sodium and potassium, and the Na and K channels. The potassium channel stays open after polarization to lead us to hyperpolarization (leaky channel).

Describe a neuron. What is a nerve?

Starts with the dendrites and goes to the cell body then down the axon, which is covered in the myelin sheaths (dont forget nodes of ranvier), then down to the axon terminal. "Nerves" are bundles of neurons

What is a membrane potential?

The difference in charge from one side of the membrane to the other side. The inside of a cell is usually -75mV so the resting membrane potential is said to be -75mV; is the alternative form of energy instead of ATP so that ATP can be used for something else

What are similaritis and differences between the gated Na channel and the gated K channel

There are more K+ channels, K channels are leaky, there are less Na channels and they are not as leaky so less sodium will diffuse in than K+ diffusing out.

What is the importance of a myelin sheath?

To increase the speed at which impulses moves along the length of an axon

How do cells signal one another?

With neurotransmitters

Do all cells have membrane potentials?

yes