Chapter 2 Cells and Structures: The Anatomy of the Nervous system

Motoneurons

(Motor Neurons) are large and have long axons reaching out to synapse on muscles, causing muscular contractions. Neuron that transmits neural messages to muscles or glands

Neuron

(Nerve cell) it is the basic unit of the nervous system, each is made of receptive extensions called dendrites, an integrating cell body, a conducting axon, and a transmitting axon terminal. Each neuron receives inputs from many other neurons, integrates those inputs, and then distributes the processed information to other neurons.

Unipolar neurons

(monopolar neurons) have a single extension, usually thought of as an axon, that branches into directions after leaving the cell body. One end is the input zone with branches like dendrites; the other, the output zone. Transmit touch information from the body into the spinal chord.

Neurons can be viewed as belonging to four functional zones:

1) Input zone 2) Integration zone 3) Conduction zone 4) Output zone

In addition to size, neurons are also classified according to three general shapes, each specialized for a particular kind of information processing:

1) Multipolar neurons 2) Bipolar neurons 3) Unipolar neurons

A synapses is typically composed of the following elements:

1) The specialized presynaptic membrane of the axon terminal of the presynaptic neuron 2) The specialized postsynaptic membrane on the dendrite or cell body of the postsynaptic neuron 3) The synaptic cleft, a gap that separates the presynaptic and postsynaptic membranes, which is tiny, measuring only 20-40nm

Synaptic Vesicle

A small spherical structure that contains molecules of neurotransmitter. microscopic hollow spheres that the presynaptic axon terminals contain. Each contains molecules of neurotransmitter.

Neurotransmitter receptor

A specialized protein, often embedded in the cell membrane, that selectively senses and reacts to molecules of a corresponding neurotransmitter or hormone.

Axon

Also called nerve fiber. A single extension from the nerve cell that carries action potentials from the cell body toward the axon terminals.

Cell Body

Also called soma. The region of a neuron that is defined by the presence of the cell nucleus.

Axon Terminal

Also called synaptic bouton. The end of an axon or axon collateral, which forms a synapse with a neuron or other target cell. Each axon terminal synapses onto another cell in order to transmit information.

Neurotransmitter

Also called synaptic transmitter, chemical transmitter, or transmitter. The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons.

Dendrite

An extension of the cell body that receives information from other neurons

What are the two types of cell stains that allow detailed study of the size and shape of neurons?

Golgi stains and Nissl stains

Multipolar Neurons

Have many dendrites and a single axon. They are the most common type of neuron.

immediate early genes (IEG)

Neurons that become more active express these. by using ICC to label the IEG product, researchers can identify brain regions that were active during particular behaviors being performed by the animal shortly before it was sacrificed.

Postsynaptic

Referring to the region of a synapse that receives and responds to neurotransmitter

Neuroplasticity

The ability of the nervous system to change in response to experience or the environment.

4) Output Zone

The part of a neuron at which the cell sends information to another cell Specialized swellings at the ends of the axons, called axon terminals, transmit the neurons signals across synapses to other cells. Where the neuron transfers information to other cells.

1) Input zone

The part of a neuron that receives information from other neurons or from specialized sensory structures. At dendrites, neurons receive information from other neurons. Dendrites may be elaborately branched, to accommodate synapses from many other neurons. neurons collect and process information, either from the environment or from other cells.

3) Conduction zone

The part of a neuron--typically the axon-- over which the action potential is actively propagated. A signal extension, the axon, conducts the neurons output information, in the form of electrical impulses, away from the cell body. Where information can be electrically transmitted over great distances.

2) Integration zone

The part of the neuron that initiates neural electrical activity. In addition to receiving additional synaptic inputs, the neurons cell body combines the information that has been received to determine whether or not to send a signal of its own where the decision to produce a neural signal is made.

Synaptic Cleft

The space between the presynaptic and postsynaptic neurons at a synapse.

Presynaptic membrane

The specialized membrane on the axon terminal of a nerve cell that transmits information by releasing neurotransmitter.

Postsynaptic membrane

The specialized membrane on the surface of a neuron that receives information by responding to neurotransmitter from a presynaptic neuron.

How heavy is the brain?

Three pounds

Santiago Ramon y Cajal

able to show that although neurons come very close together, they are not quite continuous with one another. showed that (1) the neurons and other cells of the brain are structurally, metabolically, and functionally independent (2) information is transmitted from to neuron to neuron across tiny gaps (synapses). (later became known as neuron doctrine).

Glial Cells

also called glia. Nonneuronal brain cells that provide structural, nutritional, and other types of support to the brain. provides a variety of support functions but also participate in information processing. neurons are much larger and produce more readily measured electrical signals than glial cells.

Horseradish peroxidase (HRP)

an enzyme found in the roots of horseradish. HRP is taken up into he axon at the terminals and transported back to the cell body, where it is readily visualized. Along the way, visible reaction products are formed--akin to footprints along a pathway.

Interneurons

analyze information gathered from one set of neurons and communicate with others. Nerve cell that is neither a sensory neuron nor a motor neuron. They receive input from and send output to other neurons

Immunocytochemistry (ICC)

capitalizes on the affinity of antibodies for specific proteins brain slices are exposed to antibodies that are selective for a particular protein of interest. After time is allowed for the antibodies to attach to molecules of the target protein, unattached antibodies are rinsed off and chemical treatments make the antibodies visible. This process reveals only those cells that were making that particular protein

Autoradiography

cells are manipulated into taking photographs of themselves.

Golgi stains

fill the whole cells, including details such as dendritic spines. This technique stains only a small number of cells, each which stands out in dramatic contrast to adjacent unstained cells. Useful for identifying the type and shape of cells in a region.

Bipolar neurons

have a single dendrite at one end of the cell and a single axon at the other end. They are especially common in sensory systems, like vision.

Presynaptic

located on the "transmitting" side of a synapse

How many Neurons does you brain contain?

nearly 100 billion. They work together to process large amounts of information with apparent ease.

Nissl Stain

outlines all cell bodies because the dyes are attracted to RNA distributed within the cell Allow for the measure of cell body size and the density of cells in particular regions.

Sensory neurons

specialized to gather sensory information and have very diverse shapes, depending on whether they detect light or sound or touch and so on. Nerve cell that is directly affected by changes in the environment such as light, odor, or touch.

synapses

the cellular location at which information is transmitted from a neuron to another cell. the brain may have as many as 10^15 synapses.

in situ hybridization

using radioactively labeled lengths of nucleic acids RNA or DNA, identifies neurons in which a gene of interest has been turned on.