The heart's electrical conduction pathway begins at the sinoatrial (SA) node and finishes with the Purkinje fibers.

The threshold potential of the action potential of SA node is achieved due to the slow influx of calcium ions.

Pacemaker cells in the SA node are autorhythmic (can generate own electrical impulses without external simulation). This primarily corresponds to prepotential phase shown in inset (b), because that’s the phase, at the end of which, the threshold for the next action potential is achieved.

Pacemaker cells in the SA node are autorhythmic (can generate own electrical impulses without external simulation). This primarily corresponds to the rapid depolarization phase shown in inset (b).

For inset (b), it’s possible that multiple action potentials can happen before one contraction cycle (or 1 peak in the contraction plot) is complete.

For inset (a), the duration of contraction is larger than the duration of excitation.

Skeletal muscle has a slightly higher magnitude for its resting potential than the cardiac muscle

For inset (a), it’s possible that multiple action potentials can happen before one contraction cycle (or 1 peak in the contraction plot) is complete.

Cardiac action potentials have a plateau phase, while neuronal action potentials do not.

The resting potential of the cardiac muscle has a higher magnitude than the resting potential of the neuron

The action potential of a neuron is considerably shorter in duration than the action potential of the cardiac muscle

Sodium ions play no role in the depolarization of the action potential shown in inset (b).

The refractory period in the action potential shown in inset (a) is due to the efflux of potassium ions and an influx of calcium ions.

The structure labeled

"Troponin" is shown situated directly on the myosin heads,

facilitating their attachment to actin.

“H zone" represents the region of

the sarcomere containing only thick filaments and the M line

Thick filaments consist of bundled myosin

molecules where the "Heads" project outwards, and these heads are

connected to the myosin "Tail" via a "Flexible hinge

region".

The thin filaments are shown to be

composed solely of actin subunits.

Each individual myosin molecule

illustrated possesses distinct "Actin-binding sites" and an

"ATP-binding site", both located on the heads.

The

"I band" is depicted as a region containing the Z line and portions

of the thick filaments extending from Z line.

When someone is running, the heart rate will be faster since there will be an increase in frequency of the heart’s contraction cycle (a.k.a cardiac cycle).

While running, the heart, our body’s muscular pump, will be pumping faster and hence the heart rate will be slower.

The type of muscle involved in the modulation of blood vessels diameter (shown in (c)), is (2) in inset (b). When someone exercises, vasodilation happens for thermoregulation.

When someone is running, the calf muscles in the legs are likely to belong to motor unit 2.

When someone is running, the calf muscles in the legs are likely belonging to motor unit 1.

The type of muscle involved in the modulation of blood vessels diameter (shown in (c)), is (2) in inset (b). When someone is running vasoconstriction happens for thermoregulation.

The structure called

‘Myelin’

encloses the

axon, which is responsible for passing signals from the neuron's cell body

towards the neuromuscular junction.

The resting membrane potential for all

three tissue types shown is identical and corresponds exactly to 0 mV before

stimulation.

The membrane potential at the peak of the

action potential approaches closer to the equilibrium potential of Na⁺, as Na⁺

permeability is highest at that point.

During the absolute refractory period,

another action potential can be generated, but only with a larger-than-normal

stimulus.

The repolarization phase is primarily due

to the opening of voltage-gated Na⁺ channels and the influx of Na⁺ ions into

the cell.

The sodium-potassium pump (Na⁺/K⁺ ATPase)

is responsible for returning the membrane to resting potential post hyperpolarization.

Hyperpolarization is only dependent on

the inactivation loop of sodium channels, which allows excess K⁺ to exit the

cell beyond the resting potential level.