Chapter Fortyfour

(b) Specialized neurons

(a) Generalized neuron anatomy

Dendrites receive infor-mation from other neurons.

The cell body contains \ the nucleus and most cell organelles.

Base of axon (axon hillock) integrates information collected by dendrites and initiates nerve impulses.

The axon conducts nerve impulses away from the cell body.

Axon terminals synapse \ with a target cell._j

(a) Generalized neuron anatomy

The cell body contains \ the nucleus and most cell organelles.

Base of axon (axon hillock) integrates information collected by dendrites and initiates nerve impulses.

The axon conducts nerve impulses away from the cell body.

Axon terminals synapse \ with a target cell._j

Cell Body Diagram Axon Hillock

Target cell

44.2 Neurons (a) A generalized diagram of a neuron. (b) Neurons from different parts of the mammalian nervous system are specifically adapted to their functions.

Neurons with bushy dendrites collect information from many other cells.

Neurons with fewer dendrites process fewer inputs.

Target cell

44.2 Neurons (a) A generalized diagram of a neuron. (b) Neurons from different parts of the mammalian nervous system are specifically adapted to their functions.

the others, and is called the axon. Axons usually carry information away from the cell body. The length of the axon also differs among different types of neurons—some axons are remarkably long, such as those that run from the spinal cord to the toes.

Axons are the "telephone lines" of the nervous system. Information received by the dendrites can cause the cell body to generate a nerve impulse, which is then conducted along the axon to the cell that is its target. At the target cell—which can be another neuron, a muscle cell, or an endocrine cell— the axon divides into a spray of fine nerve endings. At the tip of each of these tiny nerve endings is a swelling, called an axon terminal, that comes very close to the target cell.

Where an axon terminal comes close to another cell, the membranes of both cells are modified to form a synapse. In most cases, a space only about 25 nm wide separates the two membranes. A nerve impulse arriving at an axon terminal causes an increase of chemical messenger molecules called neurotransmitters stored in the axon terminal to be released. The released neurotransmitters diffuse across the space and bind to receptors on the plasma membrane of the target cell. We will discuss this process of synaptic transmission in more detail later in the chapter.

Thousands of synapses impinge on most individual neurons. Integration of information in the nervous system is pos

Neurons with bushy dendrites collect information from many other cells.

Cerebellum

Axon

Dendrites Axon Cell body

Cerebellum

Axon

Some neurons branch over a broad area.

Some neurons provide local links to a small number of cells.

Cerebral cortex

Cell body

Some neurons provide local links to a small number of cells.

Some communicate long distances via long axons.

Neurons with fewer dendrites process fewer inputs.

Dendrites Axon Cell body

Some neurons branch over a broad area.

Cell body

Number Synapses Cerebral Cortex

Cerebral cortex

Some communicate long distances via long axons.

sible because a neuron can receive information (synaptic inputs) from many sources before producing nerve impulses that travel down its single axon to target cells.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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