Compare & Recall: High-Yield Physiology Tables for NEET PG

• Glucose and sodium move together, hence known as symport. 
• Na+ moves from high concentration to low concentration following concentration gradient, glucose moves against it due to its high amount in intestinal cells. 
• To classify as an active transporter,at least one substance must move against the concentration gradient. In Na-K-ATPase, both sodium and potassium move against it, while in SGLT, sodium moves along the gradient, and glucose moves against it. 
• When a large amount of glucose is absorbed from the cell, sodium concentration within it also rises. Na+ inside the cell must be removed to bring glucose inside the cell. 
• SGLT is thus dependent upon the NA-K-ATPase pump. 
• The secondary active transporter is always dependent on the primary active transporter. 
• If the primary active transporter is blocked, glucose absorption from the lumen to the cell is also blocked.

• Calcium entry triggers contraction during action potential. Subsequently, calcium evacuation is necessary for myocardial cell relaxation.
• The movement of calcium from inside to outside the cell is uphill transport since concentration of extracellular calcium is higher than the intracellular.
• To transport calcium against the concentration gradient, a molecule moving with the concentration gradient is needed.
•  Evacuating calcium from the cell can lead to intracellular sodium accumulation. To prevent this, sodium must be removed first with the assistance of Na-K-ATPase.
• NCX is dependent upon Na-K-ATPase to function.
• If Na-K-ATPase is blocked by ouabain or digitalis, NCX will stop to function which increases the accumulation of calcium inside the cell which will lead to increased force of contraction of the myocardial cell. 

• Tau (τ) should be long.
• Neurons are given two successive stimulations.
• First stimulation of local voltage is +5mV, gradually decreasing over time.
• If a second stimulation of +5mV occurs before the decrease.
• Summation of these 2 stimulations happens with a long time constant.
• If the neuron's threshold is 10mV, it can produce an action potential.
• With a short time constant, a 5mV decreases to 0; if a stimulus is given, no summation occurs. 
• In contrast, with a long time constant, giving a second stimulus results in summation.
• If two stimuli are given over time in the same area, requiring a long time constant for summation, it is termed temporal summation. 

• Lambda (λ) should be long.
• For spatial summation, two neurons are required to give simultaneous simulations. The local potential of these neurons will move towards the initial segment. 

• If their length constant is long enough, these potentials will reach the initial segment and add up with each other. 
• If the length constant is short, the local potential will move towards theinitial segment but won’t be able to add up with each other.
• Therefore, the Spatial summation occurs when stimuli are applied simultaneously, but in different areas, with a cumulative effect on membrane potential. 
• Spatial summation uses multiple synapses acting simultaneously.

• The Sarcotubular system in skeletal muscle forms are triadic junctions. 

• In the myocardium, there is a dyadic junction between the L tubule and T Tubule. 

• The calcium channel present is CaV1.1 and just opposite it is the RyR1 channel. 

• The Ca channel present is CaV 1.2 type channel and the opposite is the RyR2 Channel. 

AP → Depolarization of T. tub.

↓

DHPR: activation

↓

DHPR interaction RyR1

(Mechanical) 

↓

RyR opening

↓

Ca++ influx within cytoplasm

↓

Contraction

• An action potential on the muscle membrane signifies the entry of sodium ions into the cell.
• This will lead to the depolarization of the T Tubule the DHPR channel on this channel will get activated. 
• The DHPR will change its confirmation and the extent to one of its arms and this arm will interact with the RyR channel mechanically. 
• Twisting of the RyR channel will open it, enabling a significant influx of calcium from the cisternal region into the cytoplasm.

AP → Depolarization

↓

Activation of DHPR

↓

Opening of DHPR

↓

ECF Ca++ enters into cell

↓ ⊕

RyR2 channel

↓

RyR2 opening

↓

Ca++ entry into cytoplasm

↓

Contraction

• In the myocardium, during an action potential, the Na+ channels reaching the membrane surface lead to progressive depolarization.
• This depolarization will travel through the T Tubules activating the DHPR channel. 
• Even though the channel is DHPR in the myocardium is of different sub-variety, In the cardiac muscle, this channel will open up itself. 
• Calcium from the extracellular fluid will enters the cytoplasm through this channel. 
• The amount of calcium is inadequate for full contraction. 
• Ca+ from the extracellular fluid which is already inside the cell will stimulate the RyR2 channel, and because of its stimulation further calcium will enter the cytoplasm. 

• Electro-mechanical coupling occurs between DHPR and RyR.

• Electrochemical coupling occurs between DHPR and RyR.

• The source of calcium in skeletal muscle contraction is Cisternal calcium.

• There are two sources of calcium for myocardium:
• 20% from ECF extracellular fluid (essential source of Ca+). 
• 80% from the Sarcoplasmic reticulum.