Why is nervous tissue excitable

Oligodendrocytes and Schwann cells are involved in myelin formation around axons in the CNS and peripheral nervous system, respectively. Astrocytes, which are found throughout the brain, are further subdivided into two Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. This div only appears when the trigger link is hovered over.

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Clinical Sports Medicine Collection. Davis AT Collection. Davis PT Collection. This immunosuppressive drug acts by sequestering lymphocytes in the lymph nodes, thereby limiting their access to the CNS. Neurons are secretory cells, but they differ from other secretory cells in that the secretory zone is generally at the end of the axon, far removed from the cell body.

The apparatus for protein synthesis is located for the most part in the cell body, with transport of proteins and polypeptides to the axonal ending by axoplasmic flow. Thus, the cell body maintains the functional and anatomic integrity of the axon; if the axon is cut, the part distal to the cut degenerates Wallerian degeneration. Orthograde transport occurs along microtubules that run along the length of the axon and requires two molecular motors, dynein and kinesin Figure 4—4.

Orthograde transport moves from the cell body toward the axon terminals. Synaptic vesicles recycle in the membrane, but some used vesicles are carried back to the cell body and deposited in lysosomes. Some materials taken up at the ending by endocytosis, including nerve growth factor NGF and some viruses, are also transported back to the cell body.

A potentially important exception to these principles seems to occur in some dendrites. In them, single strands of mRNA transported from the cell body make contact with appropriate ribosomes, and protein synthesis appears to create local protein domains. Axonal transport along microtubules by dynein and kinesin.

A hallmark of nerve cells is their excitable membrane. Nerve cells respond to electrical, chemical, or mechanical stimuli. Two types of physicochemical disturbances are produced: local, nonpropagated potentials called, depending on their location, synaptic, generator, or electrotonic potentials; and propagated potentials, the action potentials or nerve impulses. Action potentials are the primary electrical responses of neurons and other excitable tissues, and they are the main form of communication within the nervous system.

They are due to changes in the conduction of ions across the cell membrane. The electrical events in neurons are rapid, being measured in milliseconds ms ; and the potential changes are small, being measured in millivolts mV. The impulse is normally transmitted conducted along the axon to its termination. Nerve tissue is in fact a relatively poor passive conductor, and it would take a potential of many volts to produce a signal of a fraction of a volt at the other end of a meter-long axon in the absence of active processes in the nerve.

Instead, conduction is an active, self-propagating process, and the impulse moves along the nerve at a constant amplitude and velocity. The process is often compared to what happens when a match is applied to one end of a trail of gunpowder; by igniting the powder particles immediately in front of it, the flame moves steadily down the trail to its end as it is extinguished in its wake.

Excitable Tissue: Nerve. After studying this chapter, you should be able to:. Name the various types of glia and their functions. Name the parts of a neuron and their functions. Describe orthograde and retrograde axonal transport. Describe the changes in ionic channels that underlie the action potential.

List the various nerve fiber types found in the mammalian nervous system. Describe the function of neurotrophins. Only gold members can continue reading.

Bipolar neurons possess a single dendrite and axon with the cell body, while unipolar neurons have only a single process extending out from the cell body, which divides into a functional dendrite and into a functional axon.

When a neuron is sufficiently stimulated, it generates an action potential that propagates down the axon towards the synapse. If enough neurotransmitters are released at the synapse to stimulate the next neuron or muscle, or gland , a response is generated.

The second class of neural cells are the neuroglia or glial cells, which have been characterized as having a simple support role. Recent research is shedding light on the more complex role of neuroglia in the function of the brain and nervous system. Astrocyte cells, named for their distinctive star shape, are abundant in the central nervous system. Microglia protect the nervous system against infection and are related to macrophages.

Oligodendrocyte cells produce myelin in the central nervous system brain and spinal cord while the Schwann cell produces myelin in the peripheral nervous system Figure 4. The most prominent cell of the nervous tissue, the neuron, is characterized mainly by its ability to receive stimuli and respond by generating an electrical signal, known as an action potential, which can travel rapidly over great distances in the body. A typical neuron displays a distinctive morphology: a large cell body branches out into short extensions called dendrites, which receive chemical signals from other neurons, and a long tail called an axon, which relays signals away from the cell to other neurons, muscles, or glands.

Many axons are wrapped by a myelin sheath, a lipid derivative that acts as an insulator and facilitates the transmission of the action potential. Human Development and the Continuity of Life. By the end of this section, you will be able to: Identify the classes of cells that make up nervous tissue Discuss how nervous tissue mediates perception and response.

Figure 4. The dendrites transfer the nerve impulse to the soma. The axon carries the action potential away to another excitable cell. The cells of nervous tissue are specialized to transmit and receive impulses. Previous Next. Order a print copy As an Amazon Associate we earn from qualifying purchases. We recommend using a citation tool such as this one.

Authors: J. Gordon Betts, Kelly A.