What are neurons?
Neurons are cells that underlie the functions of the central nervous system, including the brain and spinal cord, and the peripheral nervous system consisting of ganglions and nerves outside the brain and spinal cord. Neurons vary in shape but they share the common characteristics of electrical excitability. Neurons process chemical and electrical signals and transmit these signals to neurons and other types of cells. [Learn more on Wikipedia...
]Neurons in the brain – illustration
Image credit: Benedict Campbell. Wellcome Images
What are dendrites, axons, synapses?
Neurons have several major compartments, including soma
, and axon
. The shapes of these compartments varies depending on the functionality of the neuron:
- The soma of the neuron houses the nucleus of the neuron, which contains the genetic materials. Processes including transcription and translation of genes, assembling and modification of proteins take place in the soma.
- The dendrites, a tree like compartment arise from the soma, receives input from extracellular space, including chemical or electrical signals from other neurons. The tree like structure of the dendrite enables the neuron to receive and integrate inputs from a relatively large neighborhood.
- The axon is a long and slender structure arises from the soma. It is the output structure of a neuron. The initial segment of an axon, where the axon connects to the soma, is the place where action potentials are most often initiated. The axon carries action potentials away from the soma and transmits signal to other cells.
- A synapse is a structure that permits the signal transduction from one neuron to the target cell (notice that the target cell could be the neuron itself). A chemical synapse consists of presynatpic terminal, postsynaptic terminal and synaptic cleft. When the Action potential reaches the presynatpic terminal, generally located on the end of an axon, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters then bind to the receptors on the postsynaptic terminal, generally located on the soma or dendrite of the target cell, which completes the signal transduction.
What are action potentials?
An action potential is a transient change in the membrane potential of a cell, which is generated by the flow of ions across the cell membrane. Action potential occurs in excitable cells including neurons and muscle cells. Different types of excitable cells emit action potentials with distinct shape and amplitude. Action potential is considered to play a central role in transmitting information between cells.
What are neurotransmitters?
Neurotransmitters are chemicals that transmit signals across synaptic cleft, the gap between a neuron and a target cell. Neurotransmitters are packed into small packages name vesicles. Vesicles are located in the presynapic terminal and are release into the synaptic cleft following the opening of voltage gated calcium channels, which is generally caused by an action potential. The neurotransmitters then bind to the receptors on the postsynaptic terminal. Different neurotransmitters bind to different receptors and may cause different responses (activation or inhibition) in the target cell.
What does the recording of a single neuron looks like what are spikes?
Using a microelectrode placed to the vicinity (extracellular recording) or inside a neuron (intracellular recording), one can measure the change of membrane potential of a neuron. Recoding of single neurons is an important technique in understanding neural activity. Single neuron recording has great temporal and spatial resolution; however recoding a large number of neurons simultaneously can be difficult.
What is a neural network?
A neural network is a circuit formed by a group of connected (physically or by neural signals) neurons that performs certain functionality. On a micro level, several connected neurons can perform sophisticated tasks such as mediate reflexes, process sensory information, generate locomotion and mediate learning and memory. More complex networks (macrocircuits) consist of multiple imbedded microcircuits. Macrocircuits mediate higher brain functions such as object recognition and cognition. [Learn more...
What are calcium channels and how does fluorescence imaging of neural activity work?
Calcium carries out many important physiological functions. Among other functionalities, calcium influx following an action potential causes the release of neural transmitters. Fluorescence dye labeled calcium can be injected into neural tissue. The changes of fluorescence recorded from the neural tissue are proved to be directly corresponding to neural activity (i.e. action potentials). Through calcium imaging one can study the neural activity of a population of neurons simultaneously, which is critical in uncovering the function of neural networks. [Learn more...