Resting potential, action potential, and signaling

Question 1

What is the approximate value of the ‘resting potential’?

Answer 1

[ ~-70 mV]

Question 2

What is the approximate amplitude, duration of an action potential?

Answer 2

[100 mV, 1 msec]

Question 3

What is an EPSP?

Answer 3

[excitatory post-synaptic potential; the neurotransmitter/receptor has caused a depolarization of the post-synaptic membrane]

Question 4

What is an IPSP?

Answer 4

[inhibitory post-synaptic potential; the neurotransmitter/receptor has caused a hyper-polarization of the post-synaptic membrane]

Question 5

What kinds of sensors are there?

Answer 5

[chemoreceptors, mechanical receptors, light receptors]

Question 6

what is transduction?

Answer 6

[in nervous system, conversion of some form of energy (activated sensor) into electrical energy, as a local (receptor) potential]

Question 7

Identify the differences between a local potential and an action potential?

Answer 7

[local potentials are graded (amplitude varies, dissipate in time and space across the membrane, and can be depolarizing or hyperpolarizing. Action potentials are all-or-none and move down the axon without decrement. A bunch of excitatory local potentials can add up to depolarize the soma enough so that it reaches threshold and creates an action potential]

Question 8

what is a processor?

Answer 8

[a neuron in a network that is past initial sensation, that integrates properties with other sensory inputs and other neurons that may be further away or closer to the sensory input]

Question 9

what is a receptive field?

Answer 9

[a description of the conditions under which a given neuron produces an action potential, aka, ‘spike’. It is usually fixed, but can be dynamic, and is the consequence of integrating its inputs. Often tied to a restricted region of a sensory surface (e.g., a patch of skin) that reflects the regions sampled by its inputs]

Question 10

What is an effector?

Answer 10

[Usually, a lower motor neuron, i.e., a neuron whose axon innervates muscle]

Question 11

What is a lower motor neuron?

Answer 11

[a neuron whose axon innervates muscle]

Question 12

What is an upper motor neuron?

Answer 12

[a neuron that controls the lower motor neurons; e.g., corticospinal neurons exert control over lower motor neurons of the ventral horn of spinal cord]

Question 13

What is behind the idea of a labelled line?

Answer 13

[That the activation of a particular neuron gives rise to a particular perception]

Question 14

What is a reflex?

Answer 14

[a simple behavior characterized by its stereotypy. It is usually triggered by a sensory input that drives a simple motor output, e.g., the knee jerk reflex is tripped by stretch of muscle spindle receptors wired to the primary afferent which then monosynaptically activates lower motor neurons innervating that muscle. In real life, reflexes function as autonomous pieces of behavior that are chained into adaptive bigger pieces of behavior, much like a single software routine in a much bigger computer program. Spinal reflexes require no upper motor neurons; they are autonomous at that level of the spinal cord]

Question 15

Why does the brain need so many processors?

Answer 15

[External stimuli are complex, making pattern recognition challenging (ask anyone involved in artificial intelligence). The Halle Barry cell was extracting invariant shapes specifying faces, and then that face. Just faces alone is difficult, because there’s probably a million variations impinging on the retina that are ‘faces’ and hundreds of millions that are not. This takes a significant amount of circuitry to solve]

Question 16

What is Hebb’s rule?

Answer 16

[The idea is simple enough… basically, a pre-synaptic event that causes a post-synaptic event (i.e., an action potential) will be strengthened. Forms the bases for conditioning in which erstwhile irrelevant stimuli paired with strong stimuli, now trigger the same reaction (think meat and bell with Pavlov’s dogs). We will continue this discussion later in the course] Pavlov was having a drink at the bar. He heard a bell and thought, time to feed the dogs.

Question 17

What does it mean, ‘membrane potential’?

Answer 17

[refers to a separation of charge across the membrane; due to differences in permeability between ions. This separation yields a ‘potential’ measured in volts that represents potential energy gained by letting these charges get back together. Alternatively, it’s the work done to keep these charges separated.]

Question 18

Do all cells have a membrane potential?

Answer 18

[Yes….it’s not just neurons… but neurons are best at exploiting membrane potential for signaling purposes.. also, only neurons and muscle cells produce action potentials large, local, quick shifts in membrane potential. A good guess for the membrane potential is -70 mV]

Question 19

If we could harness all of our neurons’ electrical energy, could we light up a city?

Answer 19

[have to be a very small city… we can only put out 15W…. kind of a dim bulb, so to speak]

Question 20

What is an action potential?

Answer 20

[a sudden, brief (1 msec) local shift of the neuron’s membrane potential by 100 mV. It is described as ‘all-or-none’ and is generated if the local membrane potential is sufficiently depolarized. Action potentials enable the neurons to communicate with each other]

Question 21

What is ‘spike’ threshold?

Answer 21

[The depolarization needed to trip a massive change in ion flow across the membrane which initiates a local action potential which quickly propagates down the neuron’s axon.]

Question 22

What is a synapse?

Answer 22

[the specialized junction between 2 neurons. It is ~.2 um across, and is usually portrayed as the junction between the axon terminal which releases neurotransmitter, and a dendrite on which receptors for the neurotransmitter reside]