Signal Transmission in the Brain

Signals travel through the nervous system using both electrical and chemical means, specifically through nerve impulses and neurotransmitters.

Nerve impulses, also known as action potentials, are rapid electrical signals that travel along the axons of neurons.

Calcium plays a crucial role in neurotransmitter release. When an action potential reaches the synapse, it triggers the influx of calcium into the presynaptic neuron, leading to the release of neurotransmitters.

Potassium (K+) and sodium (Na+) are the primary ions involved in generating and maintaining the resting membrane potential and action potentials in neurons.

The resting membrane potential is the steady electrical potential difference across the plasma membrane of a neuron when it is not actively transmitting a signal.

The resting membrane potential is maintained by the unequal distribution of ions across the neuronal membrane, predominantly by the movement of potassium ions out of the cell through potassium channels.

The membrane is more permeable to potassium ions than sodium ions, allowing potassium to move out of the neuron more readily.

The resting membrane potential of a typical neuron is approximately -65 millivolts (mV). This means the inside of the neuron is negatively charged relative to the outside.

Electrical excitability in cells arises from the rapid movement of sodium ions into the neuron, changing the polarity of the membrane.

The sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into the cell, maintaining the resting membrane potential by restoring the ionic balance.

The brain is a very energy-consuming organ, requiring a significant amount of energy to maintain its electrical activity.

ATP, the energy currency of the cell, is essential for maintaining the electrochemical gradients across the neuronal membrane. Brain activity requires a large supply of ATP.

The resting membrane potential is primarily determined by the interplay of ion channels that selectively allow specific ions to pass through the membrane and the sodium-potassium pump that actively transports ions against their concentration gradient.

An action potential is a rapid, short-lasting electrical signal that travels down the axon of a neuron, conveying information over long distances.

A generator potential, also known as a graded potential, is a localized change in membrane potential that can trigger an action potential if it reaches a threshold.

A specific threshold level of depolarization must be reached for an action potential to be generated. This threshold is typically around -55 mV.

An action potential is an all-or-none event. Once the threshold is reached, an action potential will occur fully. There is no partial action potential.

If the depolarizing current is not strong enough to reach the threshold, the membrane will not reach the threshold and an action potential will not be generated.

The strength of the depolarizing current influences the firing rate of action potentials. A stronger current will lead to a higher firing rate.

The maximum firing rate of action potentials in a neuron is approximately 1000 action potentials per second.

Frequency coding refers to the use of the frequency of action potentials to encode the strength or intensity of a stimulus. A stronger stimulus will lead to a higher frequency of action potentials.

During the absolute refractory period, another action potential cannot be generated regardless of the strength of the stimulus.

The relative refractory period is a period of time after the absolute refractory period when a stronger than usual stimulus is required to generate an action potential.

Synaptic input from other neurons can influence the membrane potential of a neuron. Excitatory input depolarizes the membrane, making it more likely to fire an action potential.

Sodium channels are voltage-gated ion channels that open quickly when the membrane depolarizes. They remain open for about a millisecond before closing.

Action potentials propagate along the axon of a neuron at a rate of 0.1 to 100 meters per second.

The diameter of an axon influences the speed of action potential propagation. Larger axons have a lower resistance to current flow, allowing the signal to travel faster.

Saltatory conduction is a mechanism of action potential propagation in myelinated axons. The action potential jumps from one node of Ranvier to the next, speeding up the process.

Myelination greatly increases the speed of action potential conduction. Myelinated axons can transmit signals up to 100 meters per second, compared to unmyelinated axons.