In what ways are neurons similar to other cells how are they structurally different

Despite the specific molecular, morphological, and functional features of any particular nerve cell type, the basic structure of neurons resembles that of other cells. Thus, each nerve cell has a cell body containing a nucleus, endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria, and other organelles that are essential to the function of all cells (Figure 1.3). These features are best recognized using the high magnification and resolution afforded by the electron microscope. The distinguishing characteristic of nerve cells is their specialization for intercellular communication. This attribute is apparent in their overall morphology, in the specialization of their membranes for electrical signaling, and in the structural and functional intricacies of the synaptic contacts between them.

Figure 1.3

(A) Diagram of nerve cells and their component parts. (B) Axon initial segment (blue) entering a myelin sheath (gold). (C) Terminal boutons (blue) loaded with synaptic vesicles (arrowheads) forming synapses (arrows) with a dendrite (purple). (D) Transverse (more...)

A particularly salient morphological feature of most nerve cells is the elaborate arborization of the dendrites (also called dendritic branches or dendritic processes) that arise from the neuronal cell body. The spectrum of neuronal geometries ranges from a small minority of cells that lack dendrites altogether to neurons with dendritic arborizations that rival the complexity of a mature tree (see Figure 1.1). The number of inputs that a particular neuron receives depends on the complexity of its dendritic arbor: Nerve cells that lack dendrites are innervated by just one or a few other nerve cells, whereas those with increasingly elaborate dendrites are innervated by a commensurately larger number of other neurons.

The dendrites (together with the cell body) provide the major site for synaptic terminals made by the axonal endings of other nerve cells. The synaptic contact itself is a special elaboration of the secretory apparatus found in most polarized epithelial cells. Typically, the presynaptic terminal is immediately adjacent to a postsynaptic specialization of the contacted cell. For the vast majority of synapses, there is no physical continuity between these pre- and postsynaptic elements. Instead, the pre- and postsynaptic components communicate via secretion of molecules from the presynaptic terminal that bind to receptors in the postsynaptic specialization. These molecules must traverse the extracellular space between pre- and postsynaptic elements; this interruption is called the synaptic cleft. The number of synaptic inputs received by each nerve cell in the human nervous system varies from 1 to about 100,000. This range of inputs reflects a fundamental purpose of nerve cells, namely to integrate information from other neurons. The number of inputs onto any particular cell is therefore an especially important determinant of neuronal function.

The information from the inputs that impinge on the neuronal dendrites is integrated and “read out” at the origin of the axon, the portion of the nerve cell specialized for signal conduction to the next site of synaptic interaction (see Figures 1.1 and 1.3). The axon is a unique extension from the neuronal cell body that may travel a few hundred micrometers or much farther, depending on the type of neuron and the size of the species. Many nerve cells in the human brain have axons no more than a few millimeters long, and a few have no axons at all (see, for example, the retinal amacrine cell in Figure 1.1; in fact, amacrine means “lacking a long process”). These short axons are a defining feature of local circuit neurons or interneurons throughout the brain. Many axons, however, extend to more distant targets. For example, the axons that run from the human spinal cord to the foot are about a meter long. The axonal mechanism that carries signals over such distances is called the action potential, a self-regenerating wave of electrical activity that propagates from its point of initiation at the cell body (called the axon hillock) to the terminus of the axon. At the axon ending, another set of synaptic contacts is made on yet other cells. The target cells of neurons include other nerve cells in the brain, spinal cord, and autonomic ganglia, and the cells of muscles and glands throughout the body.

The process by which information encoded by action potentials is passed on at synaptic contacts to the next cell in the pathway is called synaptic transmission. Presynaptic terminals (also called synaptic endings, axon terminals, or terminal boutons) and their postsynaptic specializations are typically chemical synapses, the most abundant type of synapse in the nervous system (another type, called electrical synapse, is described in Chapter 5). The secretory organelles in the presynaptic terminal of chemical synapses are called synaptic vesicles, which are filled with neurotransmitter molecules. The neurotransmitters released from synaptic vesicles modify the electrical properties of the target cell by binding to neurotransmitter receptors, which are localized primarily at the postsynaptic specialization. Neurotransmitters, receptors, and the related transduction molecules are the machinery that allows nerve cells to communicate with one another, and with effector cells in muscles and glands.

How are neurons structurally different to other cells?

How are neurons similar to other cells how are they unique?

In what ways are nerve cells similar to other cells how are they different how does the special structure of a neuron relate to its function?

How are they structurally different neurons?