A&P II - 11.3 Nervous Tissue - Neurons are classified on the basis of structure and function.

Autonomic ganglia

the autonomic ganglia house the neuron cell bodies of the second set of visceral motor neurons innervating peripheral effectors.

Multipolar neuron

these have two or more dendrites and a single axon. These are the most common neurons in the CNS. All motor neurons that control skeletal muscles are multipolar. The axons of multipolar neurons can be as long as those of unipolar neurons. The longest carry motor commands from the spinal cord to small muscles that move the toes.

Sensory neurons

unipolar neurons whose cell bodies are located in sensory ganglia in the PNS.

Interneuron

usually lie between sensory neurons and motor neurons. Interneurons receive sensory information from the PNS as well as input from other interneurons in the CNS. Interneurons are also responsible for higher function, such as memory, planning, and learning.

Nerve

a bundle of axons in the PNS.

Ganglion

a collection of neuron cell bodies in the PNS.

Efferent fibers

are axons that carry instructions from the CNS to peripheral tissues.

Sensory receptors

are either cells monitored by sensory neurons or processes of specialized sensory neurons.

Anaxonic neurons

are small and lack anatomical features that distinguish dendrites from axons; all the cell processes look alike. Anaxonic neurons are located in the brain and in special sense organs. Functions are poorly understood.

Exteroceptors

provide information about the external environment in the form of touch, temperature, or pressure sensations and the more complex senses of taste, smell, sight, equilibrium, and hearing.

Bipolar neurons

Bipolar neurons have two distinct processes--one dendritic process that branches extensively at its distal tip, and one axon00 with the cell body between the two. Bipolar neurons are rare but occur in special sense organs, where they relay information about sight, smell, or hearing from receptor cells to other neurons.

Afferent fibers

axons that carry sensory information to the CNS.

Unipolar neuron

in unipolar neurons, the dendrites and axon are continuous and the cell body lies of to one side. In such a neuron, an initial segment, the first portion of the axon, lies where the dendrites converge. The rest of the process, which carries action potentials, is usually considered to be an axon. Most sensory neurons of the peripheral nervous system are unipolar. Their axon may extend a meter or more, ending at synapses in the central nervous system. The longest extending from the tips of the toes to the spinal cord.

Visceral motor neurons

innervate all peripheral effectors other than skeletal muscles,--that is, smooth muscle, glands, cardiac muscle, and adipose tissue throughout the body. Visceral motor neurons in the CNS control a second set of visceral motor neurons located in the PNS.

Somatic motor neurons

innervate skeletal muscles. We have conscious control over the activity of these neurons. The cell body of a somatic motor neuron lies in the CNS, and its axon extends within a peripheral nerve to innervate skeletal muscle fibers at neuromuscular junctions.

Visceral sensory neurons

monitor internal conditions and the organ systems.

Interoceptors

monitor the digestive, respiratory, cardiovascular, urinary, and reproductive system and provide distension, deep pressure, and pain.

Somatic sensory neurons

monitor the outside world and our position within it.

Proprioceptors

monitor the position and movement of skeletal muscles and joints.