Divisions, Cells, and Structure of the Nervous System

Comprehensive vocabulary flashcards covering the divisions of the nervous system, glial cells, neuron classifications, and structural components of nerves and myelin.

Central nervous system (CNS)

The primary division of the nervous system consisting of the brain and spinal cord.

Peripheral nervous system (PNS)

The division of the nervous system consisting of the vast network of nerves and ganglia throughout the body, comprising everything outside the brain and spinal cord.

Neurobiology

The scientific study of the nervous system.

Sensory (afferent) division

The division of the peripheral nervous system that carries signals from nerve endings to the central nervous system.

Motor (efferent) division

The division of the peripheral nervous system that transmits information from the central nervous system to the rest of the body.

Somatic sensory

The subdivision of the sensory nervous system that carries signals from skin, bones, joints, and muscles.

Visceral sensory

The subdivision of the sensory nervous system that carries signals from the viscera of the heart, lungs, stomach, and bladder.

Somatic motor

The subdivision of the motor nervous system that allows voluntary movements of skeletal muscles.

Autonomic motor

The subdivision of the motor nervous system that provides "automatic" activities such as the control of blood pressure and heart rate.

Sympathetic division

The autonomic division that arouses the body for action, commonly referred to as "fight or flight."

Parasympathetic division

The autonomic division that exerts a calming effect on the body, commonly referred to as "rest and digest."

Neurons

The excitable, impulse-conducting nerve cells that handle the role of communication and perform the functional work of the nervous system.

Neuroglia

Supportive, non-excitable cells of the nervous system (also called glial cells, meaning "glue") that bind, support, and protect neurons, outnumbering them about $50$ to $1$.

Oligodendrocytes

Neuroglia of the central nervous system that form myelin sheaths around multiple nearby nerve fibers in the brain and spinal cord to speed signal conduction.

Ependymal cells

Neuroglia that line the spinal cord and cavities of the brain; some secrete cerebrospinal fluid, while others possess cilia that aid in fluid circulation.

Microglia

Phagocytic glial cells of the central nervous system that engulf microorganisms and cellular debris.

Astrocytes

Star-shaped cells that are the most abundant and versatile neuroglia in the central nervous system; they nourish neurons with glucose, attach them to blood vessels, provide structural support, and form the blood-brain barrier.

Schwann cells

Glial cells of the peripheral nervous system that wrap around peripheral nerve fibers to form the myelin sheath and neurilemma.

Blood-brain barrier (BBB)

A semi-permeable membrane formed by the feet of astrocytes joining with capillary endothelial cells that allows small molecules (oxygen, carbon dioxide, water) to diffuse into the brain while blocking larger molecules and most medications.

Gliomas

Highly malignant, rapidly growing brain tumors consisting of glial cells that retain the ability to undergo mitosis throughout life.

Interneurons

Neurons found exclusively in the central nervous system that connect incoming sensory pathways with outgoing motor pathways; they process and store information and make up about $90\%$ of the body's neurons.

Multipolar neurons

Neurons having one axon and multiple dendrites; the most common structural type of neuron, comprising most neurons of the brain and spinal cord.

Bipolar neurons

Neurons possessing two processes—one axon and one dendrite—with the cell body positioned in between; located in the retina of the eye and olfactory nerve in the nose.

Unipolar neurons

Neurons possessing a single process extending from the cell body that branches in a T shape; primarily found in sensory nerves of the peripheral nervous system.

Soma

The cell body of a neuron that serves as its control center and houses the nucleus.

Dendrites

Tree branch-like extensions of a neuron that receive signals from other neurons and conduct information toward the cell body.

Axon

A single extension of a neuron that carries nerve signals away from the cell body toward target cells.

Nodes of Ranvier

Evenly spaced gaps occurring along the myelin sheath of an axon.

Synaptic knob

The swollen terminal end of an axon branch that houses vesicles containing neurotransmitters.

Sciatic nerve

The nerve containing the longest axon in the human body, extending from the base of the spine to the big toe in each foot.

Myelin sheath

An insulating lipid-rich layer that encloses axons to accelerate nerve impulse conduction.

Neurilemma

The outermost layer of a Schwann cell in the peripheral nervous system containing its nucleus and cytoplasm; essential for peripheral nerve regeneration.