Lecture 14: Overview of the Nervous System and Anatomy of a Neuron

There are two parallel and complementary systems that control and regulate the functions of our bodies, what are they?

1. The nervous system

2. The endocrine system

The Nervous System

The Endocrine System

What are the two major anatomical divisions of the nervous system?

Sensory (afferent) division

carries sensory signals from receptors to CNS (central nervous system)

Somatic sensory division

signals from receptors in skin, muscles, bones, and joints

Visceral sensory division

signals from viscera (heart, lungs, etc.)

Motor (efferent) division

carries signals from CNS to gland and muscle cells, the effectors (muscles)

Somatic motor division

signals to skeletal muscles

Visceral motor division (autonomic nervous system, ANS)

signals to glands, cardiac and smooth muscle

Sympathetic division

arouses body for action (“fight or flight”)

Parasympathetic division

prepares for energy intake, conservation

Enteric division

in wall of digestive tract; coordinates and controls digestive tract

Nerve cell (or neuron)

functional unit of the nervous system; carries out communicative role

What are the three fundamental physiological properties of neurons?

What are the three functional classes of neurons?

Which class of neurons is confined to the CNS and is the most abundant neuron type?

interneurons

Cell body of neuron (neurosoma or soma)

control center of neuron; contains nucleus, cytoplasm with organelles, and cytoskeleton

Dendrites

primary sites for receiving signals from other neurons; contain smaller protrusions called dendritic spines

Axon (nerve fiber)

Fiber specialized for rapid conduction of outgoing signals

• contains axoplasm and its membrane is the axolemma; may be surrounded by a myelin sheath

• axon branches into terminal arborization; each branch ending in axon terminal (terminal bouton, synaptic knob)

How are neurons classified?

Neurons are classified structurally by number of processes extending from cell body.

What are the different structure classes of neurons?

Neuroglia (glial cells)

supportive cells of the nervous system; there are six types

What are the CNS glia?

What are the PNS glia?

Myelin sheath

insulating layer around a nerve fiber

In PNS, ______ _____ wrap round a single nerve fiber, laying down many layers of its own membrane.

schwann cells

In CNS, __________ reach out to myelinate several nerve fibers in its vicinity.

oligodendrocytes

Myelin sheath gaps (nodes of Ranvier)

gaps or spaces between myelin segments

Internodal segments (internodes)

myelin-covered segments

Most nerve cells are ________.

unmyelinated

_________ depends on fiber diameter and presence or absence of myelin.

signal conduction speed

True or False: The fastest fibers are both large and myelinated; these are employed where speed is important.

True

The presence of myelin speeds ______.

conduction