M1 | Neuronal Mechanisms for Information Transmission
M1 | Neuronal Mechanisms for Information Transmission
How neuronal signals encode information
Key Takeaways
The overall function of the nervous system is to organize and control behavior and regulate many internal functions.
Divisions of the nervous system
The nervous system has two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. Its function is to coordinate and transmit signals to the muscles and glands in order to produce movements and adapt the body to changes in the environment. The PNS relays information from peripheral receptors to the CNS and executes motor commands that are generated in the CNS. The PNS includes the nerves of the autonomic division, which innervate the internal organs, such as the heart, the smooth muscles of the body (e.g. blood vessels, intestines), and the exocrine glands (e.g. pancreas, adrenal medulla) and the spinal and cranial nerves of the somatic division, which innervate the skin, the joints, and the skeletal muscles.
Neurons
Key Takeaways
Neurons are considered the building blocks of the CNS, that is, they are its smallest functional units.
The nervous system is composed of cells, as is the rest of the body. Neural tissue contains two types of cells: nerve cells (neurons) and glial cells. Neurons have specializations that allow them to produce signals that communicate information. Glial cells are not directly involved in neuronal signaling but provide nutrition and support for neurons. Neurons are the basic signaling units of the CNS. The structure of a neuron can be thought of as having input (dendrites, cell body) and output components (axon, presynaptic terminals). Dendrites are outgrowths of the cell body that, like the cell body, receive signals from other neurons. Each neuron typically has multiple dendrites. The cell body maintains cell life; it contains the nucleus (genetic information) and ribosomes (protein synthesis). The cell body’s role in information transmission is to integrate and process signals. At the site of the axon hillock (initial segment), the cell body gives rise to the axon (nerve fiber). Typically, there is only a single axon per neuron. The axon hillock is the site at which electrical signals (action potentials) are generated. Conduction of action potentials along the axon provides the mechanism by which information is transmitted with high fidelity over long distances, from the axon hillock to the axon terminals. Axons can be very long. For example, cell bodies of motor neurons that innervate the muscles of the toes are located in the spinal cord whereas the axon terminals are located at the site of the muscles. Neurons use a combination of electrical and chemical signals to encode and transmit information. Neurons come in all different shapes and sizes. Many of the differences in form are related to differences in function. Sensory receptors are morphologically specialized to transduce mechan