Question

In: Anatomy and Physiology

What would happen if at rest, there was no concentration gradient for Na+ or K+? You...

  1. What would happen if at rest, there was no concentration gradient for Na+ or K+?
  2. You have a muscular dysfunction that lacks T-tubules.  How might this affect muscle contraction?
  3. You have a muscular dysfunction that lacks sarcoplasmic reticulum.  How might this affect muscle contraction?
  4. You have a muscular dysfunction that lacks voltage-gated channels.  How might this affect muscle contraction?
  5. You have a muscular dysfunction that lacks chemically-gated channels.  How might this affect muscle contraction?
  6. If tropomyosin is never moved off actin, what would be the result?
  7. If you died, why would you develop rigor mortis?
  8. All of the motor units in the fingers were very large (many muscle fibers per motor unit.  How would this affect function?
  9. If the calcium (Ca++) pumps did not function how would this affect muscles?
  10. What would be an issue if all skeletal muscles relied on anaerobic metabolism instead of aerobic?
  11. Oh no! All of the muscle fibers in your legs are fast glycolytic.  How would this affect how your legs function?

Solutions

Expert Solution

A resting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential, or simply the resting potential. The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.

In a resting neuron, there are concentration gradients across the membrane for Na+ and K+. Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential.

Membrane potential is a potential gradient that forces ions to passively move in one direction: positive ions are attracted by the ‘negative’ side of the membrane and negative ions by the ‘positive’ one.

There are two things required for establishing a membrane potential: (1) ion concentration gradient across the membrane, and (2) selective ion channels in the membrane.

The concentration gradient causes the ion to move from the compartment with the higher ion concentration to the compartment with the lower ion concentration.

Na+/K+-pump is an electrogenic transmembrane ATPase located in the outer plasma membrane of cells. The Na+/K+-ATPase pumps 3 sodium ions out of cells while pumping 2 potassium ions into cells. Both cations move against their concentration gradients.

There is an ionic imbalance between the inside and outside of a cell, with K+ concentration high inside the cell and low outside, while the Na+ concentration is low inside the cell and high outside. The cell membrane is differentially permeable to K+ and Na+, being more permeable to K+ than to Na+ in the resting state. Thus, there is a continuous tendency to loose K+. To maintain this ionic gradient, the cell membrane has a Na+/K+ pump which requires a source of energy, ATP.

If there is no concentration gradient for Na+ or K+, across the plasma membrane, the ratio of the extracellular to intracellular concentration terms becomes 1. Hence, there will be no potential difference across this membrane, even if the channels for the ion were fully open and ions will diffuse according to membrane potential only.


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