axon

Examples of axon in the following topics:

• Nerve Impulse Transmission within a Neuron: Action Potential

  • Once the signal reaches the axon terminal, it stimulates other neurons.
  • The speed of conduction of an action potential along an axon is influenced by both the diameter of the axon and the axon's resistance to current leak.
  • A node of Ranvier is a natural gap in the myelin sheath along the axon .
  • Nodes of Ranvier are gaps in myelin coverage along axons.
  • The action potential is conducted down the axon as the axon membrane depolarizes, then repolarizes.

• Neurons

  • The cell body contains a specialized structure, the axon hillock, that integrates signals from multiple synapses and serves as a junction between the cell body and an axon: a tube-like structure that propagates the integrated signal to specialized endings called axon terminals .
  • Neurons usually have one or two axons, but some neurons, like amacrine cells in the retina, do not contain any axons.
  • Along these types of axons, there are periodic gaps in the myelin sheath.
  • A bipolar neuron has one axon and one dendrite extending from the soma.
  • Each multipolar neuron contains one axon and multiple dendrites.

• Glia

  • Glia guide developing neurons to their destinations, buffer ions and chemicals that would otherwise harm neurons, and provide myelin sheaths around axons.
  • Oligodendrocytes form myelin sheaths around axons in the CNS .
  • One axon can be myelinated by several oligodendrocytes; one oligodendrocyte can provide myelin for multiple neurons.
  • This is distinctive from the PNS where a single Schwann cell provides myelin for only one axon as the entire Schwann cell surrounds the axon.
  • Oligodendrocytes form the myelin sheath around axons.

• Visual Processing

  • The myelinated axons of ganglion cells make up the optic nerves.
  • Within the nerves, different axons carry different parts of the visual signal.
  • Some axons constitute the magnocellular (big cell) pathway, which carries information about form, movement, depth, and differences in brightness.
  • Other axons constitute the parvocellular (small cell) pathway, which carries information on color and fine detail.

• Signal Summation

  • Summation, either spatial or temporal, is the addition of these impulses at the axon hillock .
  • All these inputs are added together at the axon hillock.

• Synaptic Transmission

  • Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal.
  • When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated Na+ channels.
  • The synaptic vesicles fuse with the presynaptic axon terminal membrane and empty their contents by exocytosis into the synaptic cleft.
  • This pseudocolored image taken with a scanning electron microscope shows an axon terminal that was broken open to reveal synaptic vesicles (blue and orange) inside the neuron.

• Excitation–Contraction Coupling

  • Electrical signals called action potentials travel along the neuron's axon, which branches through the muscle, connecting to individual muscle fibers at a neuromuscular junction.
  • The end of the neuron's axon is called the synaptic terminal; it does not actually contact the motor-end plate.
  • Because neuron axons do not directly contact the motor-end plate, communication occurs between nerves and muscles through neurotransmitters.
  • Neurotransmitter release occurs when an action potential travels down the motor neuron's axon, resulting in altered permeability of the synaptic terminal membrane and an influx of calcium.

• Spinal Cord

  • Myelinated axons (the part of neurons that send signals) compose the "white matter," while neuron and glial cell bodies (neuronal "support" cells) compose the "grey matter."
  • Axons and cell bodies in the dorsal (facing the back of the animal) spinal cord convey mostly sensory information from the body to the brain.
  • Axons and cell bodies in the ventral (facing the front of the animal) spinal cord primarily transmit signals controlling movement from the brain to the body.
  • A cross-section of the spinal cord shows grey matter (containing cell bodies and interneurons) and white matter (containing axons).

• Muscle Tissues and Nervous Tissues

  • Projections from the cell body are either dendrites, specialized in receiving input, or a single axon, specialized in transmitting impulses .
  • Astrocytes regulate the chemical environment of the nerve cell, while oligodendrocytes insulate the axon so the electrical nerve impulse is transferred more efficiently.
  • The neuron has projections called dendrites that receive signals and projections called axons that send signals.
  • Also shown are two types of glial cells: astrocytes to regulate the chemical environment of the nerve cell, and oligodendrocytes to insulate the axon so the electrical nerve impulse is transferred more efficiently.

• Vertebrate Axis Formation

  • Wnt is also involved in the dorsal-ventral formation of the central nervous system through its involvement in axon guidance.
  • Wnt proteins guide the axons of the spinal cord in an anterior-posterior direction.