Final answer:
Adequate extracellular calcium levels are critical for nerve impulse transmission and muscle contraction because calcium regulates membrane permeability to sodium ions and acts as a second messenger in various cellular signaling processes.
Step-by-step explanation:
It is necessary to have adequate calcium levels in the extracellular fluid for neurons to properly send signals to effectors because calcium plays a key role in the regulation of nerve impulses and muscle contractions. When the calcium ion concentration is at a normal level, it aids in maintaining the proper permeability of neuronal membranes to sodium ions. This is crucial for the generation of action potentials, which are the electrical signals that propagate along neurons to transmit information.
Calcium also acts as a second messenger in various cellular processes. For instance, it is involved in the release of neurotransmitters at synapses and in the contraction of muscles following the excitation of nerve cells. If extracellular calcium levels are too low, this can increase the membrane permeability to sodium, potentially leading to hyperexcitability and convulsions. Conversely, if calcium levels are too high, the decreased permeability to sodium can cause reduced responsiveness and lead to muscular and neural dysfunction.
The Role of Calcium in Neuronal Function
The balance of calcium ions is maintained by ion pumps that use ATP to transport calcium out of cells. This low internal concentration of calcium is disrupted when ligand-gated calcium channels open, allowing the influx of calcium from higher concentrations in the extracellular fluid into the cell, thereby initiating the various responses associated with increased intracellular calcium levels. These responses depend on the cell type but generally include essential processes like muscle contraction, secretion of hormones like insulin, and the propagation of nerve impulses.