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physiology - 3 Questions

1
Physiology
An unstable membrane potential that will spontaneously depolarize is a property of which type of muscle?
1. Cardiac only
2. Cardiac and smooth
3. Skeletal and smooth
4. Skeletal and cardiac

📝 Explanation:

The type of muscle that exhibits an unstable membrane potential that will spontaneously depolarize is cardiac muscle.

Cardiac muscle cells, which are responsible for the contraction of the heart, have an intrinsic ability to contract rhythmically without the need for external stimulation. This is due to their unique property of automaticity, which is mediated by the presence of the sinoatrial (SA) node and the subsequent propagation of electrical impulses throughout the heart via the conduction system. The SA node, often referred to as the "natural pacemaker" of the heart, generates action potentials spontaneously and sets the heart rate.

The cardiac action potential involves a series of ionic currents across the cell membrane that result in the depolarization and repolarization of the membrane. During the resting phase, the membrane potential is maintained at a negative value (around -90 mV) primarily due to the efflux of potassium ions (K+). When the SA node initiates an action potential, voltage-gated sodium (Na+) channels open, allowing an influx of sodium ions that leads to depolarization. Following this, calcium (Ca2+) and more sodium ions enter the cell through voltage-gated calcium (CaV) and sodium (Nav) channels, while potassium ions efflux through various types of potassium (K+) channels, contributing to the plateau phase and repolarization of the membrane.

The spontaneous depolarization of cardiac muscle cells is essential for the coordinated contraction of the heart, which is critical for maintaining blood circulation in the body. This property is not typically found in skeletal muscles, which require an external signal from motor neurons to contract, nor in smooth muscles, which are controlled by the autonomic nervous system and hormones.

2
Physiology

What is the typical osmolality of intestinal chyme?
1) Isotonic with blood (~300 mOsm/L)
2) Hypotonic (<300 mOsm/L)
3) Hypertonic (>300 mOsm/L)
4) Varies greatly depending on the composition of ingested food
E) Is not relevant for nutrient absorption

📝 Explanation:

The osmolality of intestinal chyme can vary widely depending on the type and quantity of food consumed. It can range from isotonic to hypertonic or hypotonic relative to blood. The intestinal mucosa plays a critical role in adjusting water and ion transport to maintain the osmolality of the blood and facilitate the absorption of nutrients.

3
Physiology

What is the significance of the ponto-genital occipital spikes seen in REM sleep?
1) They indicate deep sleep
2) They indicate the onset of dreaming
3) They are associated with eye movement
4) They are markers of REM sleep

📝 Explanation:

Ponto-genital occipital spikes, or PGO waves, are characteristic of REM sleep and are thought to be associated with the onset of dreaming, as they often coincide with rapid eye movement and increased brain activity during this phase.

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