Final answer:
The extracellular space of cells is electrically neutral, but there is a slight difference in charge at the membrane surface that allows for the generation of electrical signals in neurons and muscle cells.
Step-by-step explanation:
The extracellular space of cells is electrically neutral, meaning it contains the same number of protons and electrons. However, there is a slight difference in charge right at the membrane surface, both internally and externally. This difference in charge is what allows neurons and muscle cells to generate electrical signals.
The cell membrane, also known as the plasma membrane, is a crucial component of all cells. It separates the cell's internal environment from the external surroundings and regulates the passage of substances in and out of the cell. The cell membrane itself does not have a constant overall charge, but it does exhibit a separation of charges across its structure.
Lipid Bilayer:
The primary structural component of the cell membrane is the lipid bilayer, composed of phospholipids. Phospholipids have a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
The arrangement of these phospholipids forms a bilayer with the hydrophilic heads facing outward towards the aqueous environments (both extracellular and intracellular), and the hydrophobic tails facing inward.
Proteins and Charges:
Proteins embedded in the cell membrane can contribute to the overall charge of the membrane.
Some proteins may have charges associated with them, and the distribution of charged amino acids in these proteins can affect the local charge environment.
Ion Channels and Pumps:
Integral membrane proteins, such as ion channels and pumps, are involved in the transport of ions across the membrane. These processes contribute to the establishment and maintenance of a membrane potential.
The movement of ions, particularly sodium (Na+), potassium (K+), and chloride (Cl-), can lead to changes in the local charge distribution.
Membrane Potential:
The separation of charges across the cell membrane results in a membrane potential. This potential is a voltage difference across the membrane.
The resting membrane potential of a typical animal cell is negative on the inside relative to the outside, with values around -70 to -90 millivolts.
Electrogenic Nature:
The cell membrane is electrogenic, meaning it can generate and maintain an electrical potential. This is crucial for various cellular processes, including the transmission of nerve impulses and muscle contraction.
In summary, while the cell membrane itself doesn't have a constant overall charge, the distribution of charges across its structure, along with the presence of charged ions and proteins, contributes to the establishment of a membrane potential. This membrane potential is essential for the functioning of cells and plays a role in various cellular processes.