Nervous System - Biology

The soma is the cell body of the neuron (D). The soma is the site of neuron metabolism and protein synthesis.

The dendrites of the neuron (A) receive incoming action potential signals. The axon (B) sends the action potential outward from the soma to the axon terminal (C). Vesicles of neurotransmitter are released from the axon terminal to the dendrites of other nearby neurons. Neurons can have numerous dendrites, but will only have one soma and one axon.

The cerebellum is responsible for maintaining balance and coordination.

The medulla oblongata is responsible for maintaining subconscious body functions, such as heart rate and breathing. The cerebrum is responsible for higher level functions such as movement and memory. The thalamus mediates survival instincts, including hunger, thirst, and sexual instinct.

The central nervous system is composed of the brain (including the cerebrum and brain stem) and spinal cord. Cranial and spinal nerves branch directly off of these structures, but are considered part of the peripheral nervous system.

The nervous system is used to conduct electrical signals throughout the body. These signals stimulate various functions, frequently causing muscles to contract or carrying sensory signals to the brain. The brain and spinal cord are key components for organizing and interpreting these signals.

Neurons are the cells responsible for conducting electrical impulses. The impulses themselves are known as action potentials.

Glial cells provide support for the nervous system. Different types of glial cells perform different functions, such as myelination of axons, immune activity, and the production of cerebrospinal fluid. The cerebellum is a region of the brain responsible for balance and coordination. Since the cerebellum is a part of the nervous system, its structure is primarily composed of neurons. Mitochondria are organelles found in most eukaryotic cells. They generate ATP, which provides energy to the cell. Their function is not inherently linked to the nervous system.

Glial cells provide support for neurons. Schwann cells, oligodendrocytes, astrocytes, and ependymal cells are a few examples of glia. Schwann cells and oligodendrocytes provide myelination for neurons. Astrocytes play a key role in supporting the blood-brain barrier, while epedymal cells are responsible for secreting and circulating cerebrospinal fluid.

Blood vessels provide oxygenated blood and nutrients necessary for proper neuronal function. Connective tissue is a large component of the dura surrounding the brain itself, but it doesn't provide support for neurons themselves. Similarly, epithelial cells help structurally support the blood-brain barrier, but do not interact directly with neurons. Mitochondria are not a cell type, but are an organelle found within neurons.

The three structural regions of the neuron include the cell body (or soma), dendrites, and axon. The dendrites receive electrical inputs and stimulation and transfer incoming information to the cell body, or soma. Signals accumulate in the soma before triggering the threshold for conducting an action potential down the axon. The axon then interfaces with the dendrites of another neuron, or with the membrane of a neighboring muscle cell.

Cell walls are not found in human cells, including neurons. Though flagella can be found in certain human cells and somewhat resembles the long, narrow structure of an axon, the two are functionally very different. Neurons do not have flagella.

The cell body (or soma) contains the nucleus of the neuron, as well as other organelles. Most basic cell processes, such as transcription and translation, take place in the cell body. For example, ribosomes synthesize neurotransmitters in the cell body. The neurotransmitters are then packaged in vesicles and transported to the axon terminal.

The axon of the neuron is responsible for conveying electrical signals away from the cell body, while the dendrites convey electrical signals toward the cell body. The axon terminal is located most distal from the cell body and marks the end of the axon. Neurotransmitters are stored and released from the axon terminal. The synapse is not technically a part of the neuron structure, but is instead the small space between the axon of one neuron and the dendrites of another.

The axon is the long extension of the nerve cell body that transmits nerve impulses to other cells. Neurotransmitters are stored at the end of the axon and released into the synapse to communicate with other neurons and cells.

Dendrites are generally not as long as axons, and are responsible for receiving the nerve impulses rather than transmitting them. Flagella are not related to nerve cells, as nerve cells do not need to travel from one place to another and have no use for motility. Action potentials are the electrical signals that travel down the axons from the cell body to the axon terminal. The synapse is the space between the axon terminal of one neuron and the dendrites of another.

The cauda equina is the batch of spinal nerves that run down through the inferior end of the vertebral column. It is located in the area of the lumbar vertebral column. Cervical and thoracic nerves are located toward the upper part of the vertebral column. The dura mater is the connective tissue covering that surrounds the central nervous system. Cranial nerves come off the brain, and are part of the central nervous system.

The olfactory nerve is the first of 12 cranial nerves and is associated with a sense of smell. The optic nerve is associated with vision, the trigeminal nerve is associated with sensation of the head and face, and the facial nerve is associated with control of the facial muscles.

The vast majority of neurons are myelinated (by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system) in order to allow for saltatory conduction, which greatly increases conduction speed. This occurs as the action potential "leaps" from one node of Ranvier to the next node of Ranvier rather than having to pass down the entire length of the axon.

The soma is the cell body of the neuron (D). The soma is the site of neuron metabolism and protein synthesis.

The dendrites of the neuron (A) receive incoming action potential signals. The axon (B) sends the action potential outward from the soma to the axon terminal (C). Vesicles of neurotransmitter are released from the axon terminal to the dendrites of other nearby neurons. Neurons can have numerous dendrites, but will only have one soma and one axon.

Vesicles of neurotransmitter are located at the axon terminal of the presynaptic neuron. Upon stimulation, they are released into the synapse and flow across the gap between neurons. Neurotransmitters attach to receptors located on the postsynaptic membrane after being released into the synaptic cleft. This allows the action potential to continue on to the next neuron.

In the neuron, dendrites respond to the chemical neurotransmitters released by other local neurons. These dendrites have receptors in their membranes that bind specific neurotransmitters and produce electrical signals as a result of this binding. Binding of a neurotransmitter can either excite or inhibit the neuron, influencing its ability to transmit a signal.

A hormone is a chemical that is synthesized by one group of cells, secreted, and then carried in the bloodstream to other cells whose activity is influenced by reception of the hormone. An electrolyte is a solutution that conducts electricity and generally contains ions. Enzymes are proteins that speed up chemical reactions. Proteins are organic molecules composed of amino acids that are necessary for growth and repair of tissues.

A neurotransmitter is a chemical agent that relays messages from one nerve cell to the next. An enzyme is a protein that causes other substances to change. Enzymes regulate the rate of chemical reactions. An electrolyte is a substance that, when dissolved, forms electrically charged particles. Ions have lost one or more electrons and have a positive charge, or gained one or more electrons and have a negative charge. In aqueous solutions, ions are called electrolytes because they permit the solution to conduct electricity. Interleukin is a type of protein that enables communication among cells active in inflammation or the specific immune response.

Vesicles containing neurotransmitters must bind to the membrane at the axon terminal in order to release their contents into the synapse. This binding is dependent upon an influx of calcium ions that occurs with an action potential. The other ions listed are important for other parts of the action potential, but it is calcium that is crucial for this particular step.

Voltage-gated potassium ion channels are responsible for bringing the membrane potential back to or below resting the potential. This is achieved when these channels open, which can only happen at very positive voltages (hence voltage-gated), and as the potassium ions rapidly leave the cell, the cell repolarizes to a negative potential.

The dendrites receive the messages sent from other neurons. Neurotransmitters are released into synaptic clefts between two neurons and bind receptors on the postsynaptic neuron's dendrites. Axons are nerve fibers that carry electrical impulses away from the cell body of a neuron. The nodes of Ranvier are unmyelinated spots on myelinated axons that facilitate conduction of a nerve impulse down an axon.

The effect of acetylcholine is terminated by acetylcholinesterase breaking down acetylcholine. If acetylcholinesterase is inhibited, the degradation of acetylcholine would not occur, and the effects of acetylcholine will be prolonged.

GABA is only found in the brain and has an inhibitory function. Although glycine is also inhibitory and found in the central nervous system, it's mainly concentrated in the spinal cord and brainstem. Glutamate and acetylcholine are also found in the central nervous system, but are excitatory. Norepinephrine is excitatory and associated with the adrenal glands, not the central nervous system.