Week 3

Question 1

How do neurons and wires conduct current?

Answer 1

Wires conduct current by electron flow in metal, while neurons conduct current by ion flow in fluid. Both are impeded by resistance.

Question 2

What is the time constant (τ) and how is it defined?

Answer 2

The time constant (τ) is the time it takes for the voltage to reach about 37% of its original value. It is defined as τ= R_M C_M.

Question 3

How do myelination and axon diameter affect conduction velocity?

Answer 3

Both myelination and increased axon diameter increase the space constant (λ), which in turn increases conduction velocity.

Question 4

What determines the membrane potential in neurons?

Answer 4

The membrane potential is determined by a balance of electrical and chemical forces, with a resting potential of -60 to -70 mV in mammalian neurons.

Question 5

What is the role of the sodium-potassium pump in neurons?

Answer 5

The sodium-potassium pump maintains the membrane potential by pumping 3 Na+ ions out and 2 K+ ions in, using ATP. This creates a high extracellular Na+ concentration and a high intracellular K+ concentration.

Question 6

What are the states of voltage-gated Na+ and K+ channels?

Answer 6

Na+ channels have three states: open, closed, deactivated. K+ channels have two states: open, closed.

Question 7

Describe the positive feedback cycle of an action potential.

Answer 7

Depolarization opens Na+ channels, causing further depolarization. K+ channels open more slowly, causing repolarization. This ensures unidirectional travel of the action potential due to the refractory period.

Question 8

How does temperature affect the speed of an action potential?

Answer 8

Higher temperatures facilitate faster action potentials by speeding up the dynamics of Na/K ion channel opening and closing.

Question 9

How does neuron diameter affect conduction velocity?

Answer 9

Increased neuron diameter increases the space constant (λ) but does not affect the time constant (τ). A larger space constant results in faster conduction.

Question 10

Why do squids have giant axons?

Answer 10

Squids have giant axons (up to 800 μm in diameter) to facilitate rapid signal transmission for jet propulsion, as they do not have myelin sheaths.

Question 11

What is saltatory conduction?

Answer 11

Saltatory conduction is the process where the action potential ‘jumps’ between nodes of Ranvier in myelinated neurons, increasing conduction speed.

Question 12

How does myelination affect the space constant (λ)?

Answer 12

Myelination increases the space constant (λ), allowing the ion current to travel further before decaying.

Question 13

How is conduction velocity measured in human peripheral nerves?

Answer 13

Conduction velocity is measured by stimulating a motor neuron at two sites, measuring the latency of evoked responses, and calculating the velocity based on time and distance.

Question 14

What are the effects of demyelination on nerve signals?

Answer 14

Demyelination reduces the amplitude and increases the latency of nerve signals, occurring in conditions like Multiple Sclerosis and Guillain-Barré syndrome.

Question 15

Who demonstrated that the human body can generate electrical current and when?

Answer 15

Emil Du Bois-Reymond in 1850 demonstrated that the human body can generate electrical current, marking the first demonstration of Electromyography (EMG).

Question 16

How can the principle used to detect electrical activity in muscles be applied to the heart?

Answer 16

The same principle can be used to detect electrical activity from the heart, resulting in an Electrocardiogram (ECG).

Question 17

Who made the first recordings of EMG and when?

Answer 17

Erlanger, Gasser, and Newcomer made the first recordings of EMG in the 1920s using a cathode ray oscilloscope and a triode vacuum tube amplifier.

Question 18

What is the sequence of events in muscle contraction?

Answer 18

1. Action potential (AP) stimulates the release of a neurotransmitter across the neuromuscular junction.
2. AP spreads across the sarcolemma and into the fiber along the T-tubules.
3. Causes release of calcium from the Sarcoplasmic Reticulum.
4. Calcium binds to muscle and causes cross-bridge cycling.

Question 19

What is a motor unit?

Answer 19

A motor unit consists of one alpha motor neuron and all the muscle fibers it activates.

Question 20

How is continuous smooth muscle contraction generated?

Answer 20

Continuous smooth muscle contraction is generated by the fusion of multiple twitches. Muscles generate extra force by recruiting more motor units and increasing the frequency of firing.

Question 21

What is Electromyography (EMG)?

Answer 21

EMG is a technique for recording the electrical activity of muscles using either needle electrodes inserted into the muscle or surface electrodes placed on the skin.

Question 22

How do action potentials from numerous motor units contribute to the EMG signal?

Answer 22

Action potentials from numerous motor units summate to produce the surface EMG signal.

Question 23

How does muscle fiber type affect EMG signals?

Answer 23

Fast muscle fibers have higher resting membrane potentials, greater density of sodium channels, and faster action potentials, generating larger electrical responses compared to slow muscle fibers.

Question 24

What is muscle wisdom?

Answer 24

Muscle wisdom refers to the reduction in motor unit firing rates to compensate for prolonged twitch duration during muscle fatigue.

Question 25

What are the two types of muscle fatigue?

Answer 25

1. High frequency fatigue: Caused by continuous high-frequency stimulation, recovers immediately after cessation.
2. Low frequency fatigue: Caused by intense exercise, takes hours/days to recover, likely due to reduced calcium release from the Sarcoplasmic Reticulum.

Question 26

What is the interpolated twitch technique?

Answer 26

The interpolated twitch technique measures the degree of motor unit activation during voluntary effort by superimposing an electrical stimulus onto a muscle during contraction and measuring the evoked twitch force.

Question 27

What is Acoustomyography (AMG)?

Answer 27

AMG measures the sounds generated by muscles during contraction. The amplitude of AMG declines during muscle fatigue, representing muscle force.

Question 28

How does ultrasound contribute to measuring muscle activity?

Answer 28

Ultrasound monitors changes in muscle length, indicating whether the muscle is lengthening (eccentric) or shortening (concentric) during contraction.

Question 29

What is the relationship between EMG and AMG during muscle fatigue?

Answer 29

The EMG/AMG ratio can be used to monitor changes in muscle control due to fatigue, as AMG represents muscle force and declines during muscle fatigue while surface EMG signals do not.