Neuron
or spinal cord are referred to as interneurons and make up the central nervous system. Other neurons, receptors, and afferent (sensory) neurons are specialized to receive signals from within the body or from the external environment and to transmit that information to the central nervous system. Efferent neurons carry signals from the central nervous system to the effector organs (muscles and glands) of the body. If an efferent neuron is connected to a muscle, it is also called a motor neuron.
central nervous system brain and spinal cord
The ability of a neuron to carry out its function of integration and propagation depends both upon its structure and its ability to generate electrical and chemical signals. While different neurons have different shapes, all neurons share the same signaling abilities.
The Structure of a Typical Neuron Neurons have many different shapes and sizes. However, a typical neuron in a vertebrate (such as a human) consists of four major regions: a cell body, dendrites, an axon, and synaptic terminals. Like all cells, the entire neuron is surrounded by a cell membrane. The cell body (soma) is the enlarged portion of a neuron that most closely resembles other cells. It contains the nucleus and other organelles (for example, the mitochondria and endoplasmic reticulum) and it coordinates the metabolic activity of the neuron. The dendrites and axon are thin cytoplasmic extensions of the neuron. The dendrites, which branch out in treelike fashion from the cell body, are specialized to receive signals and transmit them toward the cell body. The single long axon carries signals away from the cell body. In humans, a single axon may be as long as 1 meter (about 3 feet). Some neurons that have cell bodies in the spinal cord have axons that extend all the way down to the toes. Axons generally divide and redivide near their ends and each branch gives rise to a specialized ending called a synaptic knob (synaptic terminal). It is the synaptic terminals of a neuron that form connections either with the dendrites or cell body of another neuron or with effector cells in muscles or glands. Once an electrical signal has arrived at the end of an axon, the synaptic terminals release a chemical messenger called a neurotransmitter, which relays the signal across the synapse to the next neuron or to the effector cell.
axon long extension of a nerve cell down which information flows nucleus membranebound portion of cell containing the chromosomes organelle membranebound cell compartment mitochondria subcellular organelle that creates ATP used for energy-requiring processes in a cell endoplasmic reticulum network of membranes within the cell cytoplasm material in a cell, excluding the nucleus
Classifying Neurons by Shape Neurons can be classified according to the number of processes that extend from the cell body. Multipolar neurons are the most common type. They have several dendrites and one axon extending from the cell body. Bipolar neurons have two processes extending from the cell body, an axon and a single dendrite. This type of neuron can be found in the retina. Unipolar neurons are generally sensory (afferent) neurons that have a single process, which then divides into two. One of the two processes extends outward to receive sensory information from various areas of the body, while the other process relays sensory information towards the spinal cord or brain.
Electrical Signals in Neurons All living cells have a separation of charges across the cell membrane. This separation of charges gives rise to the resting membrane potential.
membrane potential electrical and chemical differences across a membrane leading to storage of energy and excitability
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