Describe the formation and conduction of nerve impulses along the axon.

Nerve impulses are electrical signals that travel along the axon of a neuron. The formation and conduction of these impulses involve a series of complex processes.

When a neuron is at rest, it maintains a negative charge inside the cell compared to the outside. This is due to the uneven distribution of ions across the cell membrane, with more sodium ions outside the cell and more potassium ions inside. This difference in charge is known as the resting membrane potential.

When a stimulus is received by the neuron, it causes a change in the membrane potential, known as depolarization. This occurs when sodium channels open, allowing sodium ions to rush into the cell, causing the inside of the cell to become more positively charged.

This depolarization triggers an action potential, a rapid change in membrane potential that travels along the axon. The action potential is generated at the initial segment of the axon, known as the axon hillock, and travels down the length of the axon towards the axon terminals.

As the action potential travels along the axon, it is propagated by a process called saltatory conduction. This involves the rapid depolarization of one segment of the axon, which triggers the opening of voltage-gated sodium channels in the next segment, causing depolarization to occur there. This process continues down the length of the axon, allowing the action potential to travel quickly and efficiently.

At the axon terminals, the action potential triggers the release of neurotransmitters into the synaptic cleft, the small gap between the axon terminal of one neuron and the dendrite of another. These neurotransmitters bind to receptors on the dendrite of the receiving neuron, causing depolarization and the generation of a new action potential.

Overall, the formation and conduction of nerve impulses along the axon involve a coordinated interplay of ion channels, membrane potential changes, and neurotransmitter release, allowing for the rapid and precise transmission of information within the nervous system.

Formation of Nerve Impulses

1. Resting Potential: Neurons maintain an electrochemical gradient across their membranes, with the inside negative and the outside positive. This is known as the resting potential.

2. Depolarization: When a neuron receives a stimulus, sodium-potassium pumps in the membrane become permeable to sodium ions. Sodium ions flood into the neuron, causing the membrane potential to become less negative. If the depolarization reaches a threshold, an action potential is triggered.

Conduction of Nerve Impulses

1. Action Potential: The action potential is a rapid change in membrane potential. As the sodium influx continues, the membrane potential becomes positive. The sodium-potassium pumps then become permeable to potassium ions.

2. Repolarization: Potassium ions flow out of the neuron, making the membrane potential more negative again. This process is aided by the sodium-potassium pumps, which pump sodium ions out and potassium ions in.

3. Hyperpolarization: The membrane potential briefly becomes more negative than the resting potential. This is due to the delayed closing of the potassium channels.

4. Refractory Period: After an action potential, the neuron enters a refractory period. During this time, it is less excitable and cannot generate another action potential. This ensures a one-way transmission of the nerve impulse.

5. Saltatory Conduction: In myelinated axons, nerve impulses jump from node to node, rather than traveling smoothly along the entire membrane. This speeds up conduction.

Myelination

Myelination is a layer of insulation around the axons of some neurons. It is composed of Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. Myelination increases the speed and efficiency of nerve impulse conduction.