Nerve cell dendrites

Neurons—Nervous system unit that includes the nerve cell, dendrites, and axons. 

The structural design of nerve cells is a striking example of dendritic architecture, which acts as a signal transduction system. Neurons are known to send out a series of long specialized processes that will either receive electrical signals (dendrites) or transmit these electrical signals (axons) to their target cells (Fig. 5.40). 

Raff It also seems to be true in nerve cells, in the formation of dendrites and axons. This seems to be a stochastic process. 

By immunohistochemistry, a- and p-synucleins are concentrated in nerve terminals, with little staining of somata and dendrites. Ultrastructurally, they are found in close proximity to synaptic vesicles. In contrast,y-synuclein is present throughout nerve cells in many brain regions. In rat, a-synuclein is most abundant throughout telencephalon and diencephalon, with lower levels in more caudal regions. P-Synuclein is distributed fairly evenly throughout the central nervous system, whereas y-synuclein is most abundant in midbrain, pons and spinal cord, with much lower levels in forebrain areas. 

Figure 1.1 Neurons (nerve cells) transmit information throughout the brain and the body. A typical neuron is shown here. Electrical impulses are received by the dendrites and transmitted to the next neuron via the axon. The myelin sheath insulates the axon and increases the speed at which electrical impulses can travel.

The nervous system consists of two main units the central nervous system (CNS), which includes the brain and the spinal cord and the peripheral nervous system (PNS), which includes the body s system of nerves that control the muscles (motor function), the senses (the sensory nerves), and which are involved in other critical control functions. The individual units of the nervous system are the nerve cells, called neurons. Nenrons are a nniqne type of cell becanse they have the capacity to transmit electrical messages aronnd the body. Messages pass from one nenron to the next in a strnctnre called a synapse. Electric impnlses moving along a branch of the nenron called the axon reach the synapse (a space between nenrons) and canse the release of certain chemicals called neurotransmitters, one of which, acetylcholine, we described earlier in the chapter. These chemicals migrate to a nnit of the next nenron called the dendrites, where their presence canses the bnild-np of an electrical impnlse in the second nenron. 

The cell body gathers the incoming action potentials from the dendrites and sends along a single action potential to the axon. The action potential travels the length of the axon until reaching the axon terminals. At this point, the nerve cell must pass the impulse to its neighboring cells. This communication from one neuron to another is accomplished by neurotransmission. 

Neurotransmitter Release. When the nerve cell is stimulated, an action potential is generated that travels the length of the cell from dendrite to cell body to axon. Once the action potential reaches the axon terminal, it causes the storage vesicles... 

Essentially all nerve cells have one or more projections termed dendrites whose primary function is to receive information from other cells in their vicinity and pass this information on to the cell body. Following the analysis of this information by the nerve cell, bioelectrical changes occur in the nerve membrane that result in the information being passed to the nerve terminal situated at the end of the axon. The change in membrane permeability at the nerve terminal then triggers the release of the neurotransmitter. 

A typical neuron consists of a cell body and an axonal projection through which information in the form of an action potential passes from the cell body to the axonal terminal. Information is received by the cell body via a complex array of dendrites which make contact with adjacent neurons. The structural complexity and the number of dendritic processes vary according to the type of nerve cell and its physiological function. For example, the granule cells in the dentate gyrus of the hippocampus (a region of the brain which plays a role in short-term memory) receives and integrates information from up to 10 000 other cells in the vicinity. 

In addition to the posts)maptic receptors, dopamine autoreceptors also exist on the nerve terminals, dendrites and cell bodies. Experimental studies have shown that stimulation of the autoreceptors in the somatodendritic region of the neuron slows the firing rate of the dopaminergic neuron while stimulation of the autoreceptors on the nerve terminal inhibits both the release and the synthesis of the neurotransmitter. Structurally, the autoreceptor appears to be of the D2 type. While several experimental compounds have been developed that show a high affinity for the autoreceptors, to date there is no convincing evidence for their therapeutic efficacy. 

Nerve cells (neurons) are easily excitable cells that produce electrical signals and can react to such signals as well. Their structure is markedly different from that of other types of cell. Numerous branching processes project from their cell body (soma). Neurons are able to receive signals via dendrites and to pass them on via axons. The axons, which can be up to 1 m long, are usually surrounded by Schwann cells, which cover them with a lipid-rich myelin sheath to improve their electrical insulation. 

There is a space that exists between neurons known as the synapse. The transmission of the nerve signal across this synaptic cleft is a chemical phenomenon. Molecules generically referred to as neurotransmitters are produced in the neuron and released from the axonal membrane into the synapse. They diffuse to the dendrites of the next nerve cell and combine with receptors. This combination of neurotransmitter (agonist) and receptor produces a response which results in the propagation of the nerve signal down the next neuron. We will discuss this activity in much more detail shortly. 

Neuronopathy. Neuronopathy refers to generalized damage to nerve cells, with the primary damage occurring at the nerve cell body. Axonal and dendritic processes die secondarily in response to loss of the cell body. Like other cells in the body, neurons die by one of two processes distinguished by their morphological and molecular features apoptosis and necrosis. (This division is overly simplistic there is much debate... 

Microwells defined in agarose were used to culture nerve cells. The dendrite growth of the nerve cells was studied in narrow tunnel-shaped channels in agarose. The tunnels were fabricated by photo-thermal etching the agarose [863]. 

Nerve cells Nerve cells, or neurons, consist of a cell body from which the dendrites and axon extend. The dendrites receive information from other cells the axon passes this information on to another cell, the post-synaptic cell. The axon is covered in a myelin membranous sheath except at the nodes of Ranvier. The axon ends at the nerve terminal where chemical neurotransmitters are stored in synaptic vesicles for release into the synaptic cleft. 

---