In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell. The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement. The negative resting membrane potential is created and maintained by increasing the concentration of cations outside the cell (in the extracellular fluid) relative to inside the cell (in the cytoplasm). When the membrane is at rest, K + ions accumulate inside the cell due to the activity of the Na/K pump, driving both ions against their concentration gradient. The difference in the number of positively charged potassium ions (K +) inside and outside the cell dominates the resting membrane potential ( Figure 35.10). Because ions cannot simply cross the membrane at will, there are different concentrations of several ions inside and outside the cell, as shown in Table 35.1. If the membrane were equally permeable to all ions, each type of ion would flow across the membrane and the system would reach equilibrium. This voltage is called the resting membrane potential it is caused by differences in the concentrations of ions inside and outside the cell. The difference in total charge between the inside and outside of the cell is called the membrane potential.Īccess multimedia content Resting Membrane PotentialĪ neuron at rest is negatively charged: the inside of a cell is approximately 70 millivolts more negative than the outside (−70 mV, note that this number varies by neuron type and by species). Voltage-gated ion channels regulate the relative concentrations of different ions inside and outside the cell. Ion channels that change their structure in response to voltage changes are called voltage-gated ion channels. These ion channels are sensitive to the environment and can change their shape accordingly. Some ion channels need to be activated in order to open and allow ions to pass into or out of the cell. Ion channels have different configurations: open, closed, and inactive, as illustrated in Figure 35.9. To enter or exit the neuron, ions must pass through special proteins called ion channels that span the membrane. The lipid bilayer membrane that surrounds a neuron is impermeable to charged molecules or ions. To understand how neurons communicate, one must first understand the basis of the baseline or ‘resting’ membrane charge. These signals are possible because each neuron has a charged cellular membrane (a voltage difference between the inside and the outside), and the charge of this membrane can change in response to neurotransmitter molecules released from other neurons and environmental stimuli. Nerve Impulse Transmission within a Neuronįor the nervous system to function, neurons must be able to send and receive signals. Just like a person in a committee, one neuron usually receives and synthesizes messages from multiple other neurons before “making the decision” to send the message on to other neurons. While humans use words and body language to communicate, neurons use electrical and chemical signals. Describe long-term potentiation and long-term depressionĪll functions performed by the nervous system-from a simple motor reflex to more advanced functions like making a memory or a decision-require neurons to communicate with one another.Explain the similarities and differences between chemical and electrical synapses.Explain the stages of an action potential and how action potentials are propagated.Describe the basis of the resting membrane potential.By the end of this section, you will be able to do the following:
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