Nervous Tissue Overview and Classifications

Vocabulary practice flashcards covering nervous system organization, neuron structure and classifications, CNS and PNS neuroglia, myelination, and nervous tissue collections from Chapter 12.

Nervous System

A network of neurons and neuroglia found in two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System (CNS)

The nervous system division consisting of the brain and spinal cord that processes incoming sensory information and sends signals to stimulate muscles to contract or glands to secrete.

Peripheral Nervous System (PNS)

The nervous system division consisting of all nervous tissue outside of the CNS, including nerves, ganglia, enteric plexuses, and sensory receptors.

Sensory (Afferent) Division

The division of the nervous system that carries signals from sensory receptors to the CNS.

Somatic Sensory Division

The division that carries sensory signals from receptors in the skin, muscles, bones, and joints to the CNS.

Visceral Sensory Division

The division that carries signals from thoracic and abdominal organs (such as the heart, lungs, stomach, and bladder) to the CNS.

Interneuron

An association neuron located entirely within the CNS between sensory and motor neurons that integrates incoming sensory information and activates motor neurons.

Motor (Efferent) Neurons

Multipolar neurons that function to carry action potentials away from the CNS through cranial or spinal nerves to effectors such as muscles and glands.

Sensory (Afferent) Neurons

Neurons that conduct signals from sensory receptors to the central nervous system.

Nissl Bodies

Granules of rough endoplasmic reticulum (RER) in the cytoplasm of a neuron's cell body that help regenerate damaged neurons in the PNS.

Neurofibrils

A type of cytoskeleton found within a neuron.

Dendrites

Projections emerging from the neuronal cell body that act as the receiving portion of the neuron and contain receptor sites for chemical messages.

Axon

A long cylindrical projection (nerve fiber) that emerges from the axon hillock of the cell body and propagates nerve impulses to another neuron, muscle fiber, or gland.

Axon Terminals

The divided ends of an axon that form a synapse (junction) to the next cell.

Multipolar Neurons

Neurons consisting of several dendrites and one axon emerging from the cell body; the most common structural type in the CNS, including interneurons and motor neurons.

Bipolar Neurons

Neurons consisting of one main dendrite and one axon; found in olfactory cells, the retina, and the inner ear.

Unipolar Neurons

Neurons where dendrites and a single axon are fused together to form a continuous structure off the cell body; they act as sensory neurons carrying signals from skin and organs to the spinal cord.

Neuroglia

Supportive glial cells that act as glue holding the nervous system together, protecting neurons, and forming a framework for nervous tissue.

Oligodendrocytes

CNS neuroglia with arm-like processes that wrap around nerve axons to form and maintain the myelin sheath, speeding up signal conduction.

Ependymal Cells

Simple cuboidal epithelial neuroglia with cilia on the apical surface that line the internal cavities of the brain (ventricles) and spinal cord to secrete and circulate cerebrospinal fluid (CSF).

Microglia

CNS neuroglia developed from white blood cells (monocytes) that concentrate in areas of damage, wander through the CNS looking for debris, and perform phagocytosis.

Astrocytes

The most abundant CNS glial cells; they cover brain surfaces and non-synaptic regions, form the blood-brain barrier via perivascular feet, regulate blood flow and chemical environment, absorb excess neurotransmitters/ions, and secrete nerve growth factors.

Schwann Cell

PNS neuroglia (neurolemmocyte) that envelopes nerve axons, winds repeatedly around them to produce myelin, and assists in the regeneration of damaged fibers.

Satellite Cells

Flat glial cells in the PNS that surround neurosomas in ganglia, providing electrical insulation and regulating the chemical environment of neurons.

Myelin Sheath

An insulating layer around a nerve axon formed by oligodendrocytes in the CNS and Schwann cells in the PNS during myelination.

Neurilemma

The thick, outermost coil of the myelin sheath in the PNS that contains the cytoplasm and most organelles of the Schwann cell.

Nodes of Ranvier

Gaps in the myelin sheath along the length of an axon.

Unmyelinated Nerve Fibers

Nerve fibers lacking wrapped myelin sheaths; in the PNS, Schwann cells hold $1$ to $12$ of these small fibers within surface grooves.

Ganglion

A cluster of neuronal cell bodies located in the peripheral nervous system (PNS), including cranial and spinal nerves.

Nucleus (CNS)

A cluster of neuronal cell bodies located in the central nervous system (CNS).

Nerve

A bundle of axons located in the peripheral nervous system (PNS).

Tract

A bundle of axons located in the central nervous system (CNS).

White Matter

Nervous tissue consisting mainly of myelinated axons.

Gray Matter

Nervous tissue containing cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia.