Chapter 1 Nerve Cells and Nerve Impulses

The Structure of a Neuron Neuron cells are similar to other cells of the body but have a distinctive shape Figure 1.3 Neurons, stained to appear dark Note the small fuzzy-looking spines on the dendrites. Photo courtesy of Bob Jacobs, Colorado College

Nervous System - brain - spinal cord neuron: - primary units of the nervous system - nerve cell: - cell body - dendrites axons 2008 McGraw-Hill Co., Inc. All rights reserved

A Vertebrate Motor Neuron Figure 1.4 The components of a vertebrate motor neuron The cell body of a motor neuron is located in the spinal cord. The parts are not drawn to scale; a real axon is much longer in proportion to the soma. © Cengage Learning

Dendrites Branching fibers with a surface lined with synaptic receptors responsible for bringing information into the neuron Some also contain dendritic spines that further branch out and increase the surface area of the dendrite The greater the surface area of the dendrite, the more information it can receive

Dendritic Spines Figure 1.6 Dendritic spines Many dendrites are lined with spines, short outgrowths that receive incoming information. Source: From K. M. Harris and J. K. Stevens, Society for Neuroscience, “Dendritic Spines of CA1 Pyramidal Cells in the Rat Hippocampus: Serial Electron Microscopy with Reference to Their Biophysical Characteristics.” Journal of Neuroscience, 9 (1989), pp. 2982–2997. Copyright © 1989 Society for Neuroscience. Reprinted by permission.

Cell Body/Soma Contains the nucleus, mitochondria, and ribosomes Responsible for the metabolic work of the neuron Covered with synapses on its surface in many neurons

Axons Thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles Maybe have a myelin sheath, an insulating material that contains interruptions in the sheath known as nodes of Ranvier Presynaptic terminals at the end points of an axon release chemicals to communicate with other neurons

Afferent, Efferent, and Intrinsic Afferent axon: refers to bringing information into a structure Efferent axon: refers to carrying information away from a structure Interneurons or intrinsic neurons are those whose dendrites and axons are completely contained within a single structure

Motor and Sensory Neurons A motor neuron Has its soma in the spinal cord Receives excitation from other neurons Conducts impulses along its axon to a muscle A sensory neuron Is specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound, etc.)

Nervous System (cont.) Glial cells: - support neurons and transport nutrients - produce the myelin sheath - influence the transmission of messages from one neuron to another across synaptic gaps 2008 McGraw-Hill Co., Inc. All rights reserved

Nervous System (cont.) Myelin sheath and synaptic transmission: - white fatty coating on axon - multiple sclerosis 2008 McGraw-Hill Co., Inc. All rights reserved

The Blood-Brain Barrier A mechanism that surrounds the brain and blocks most chemicals from entering The immune system destroys damaged or infected cells throughout the body Because neurons in the brain generally do not regenerate, it is vitally important for the blood brain barrier to block incoming viruses, bacteria, or other harmful material from entering

Blocking Sodium Channels Local anesthetic drugs block sodium channels and therefore prevent action potentials from occurring Example: Novocain and Xylocaine

Nervous System (cont.) Neural transmission: - ions - cell membrane: - semi-permeable - polarized - depolarization - action potential - all-or-none principle 2008 McGraw-Hill Co., Inc. All rights reserved

The transmission of a nerve impulse. The following are the answers to questions 1–4: The answer is b. Outside. The answer is a. Inside. The answer is d. Negatively charged. The answer is c. Positively charged. The following is how the figure should be labeled: b. Resting potential a. Threshold c. Depolarization d. Repolarization e. Hyperpolarization