7: Nervous System Histology

A complete set of vocabulary flashcards based on the Nervous System Part 1 lecture, covering functional divisions, directional terms, histology, neuron components, and specific types of neuroglia.

Sensory input

Monitoring changes occurring both inside and outside the body using millions of sensory receptors.

Integration

The process where the nervous system processes and interprets input and decides what should be done each moment using stored memories and predictions.

Motor output

The response caused by the activation of effector organs, specifically muscles and glands.

Central nervous system (CNS)

The integration and control center of the nervous system, consisting of the brain and spinal cord.

Peripheral nervous system (PNS)

The communication pathways that link all body parts to the CNS, consisting of nerves, ganglia, and sensory receptors.

Sensory (afferent) division

The "input" division of the PNS that conveys nerve impulses from sensory receptors to the brain or spinal cord.

Motor (efferent) division

The "output" division of the PNS that conveys nerve impulses from the brain or spinal cord to effector organs (muscles and glands).

Somatic sensory nerves

Nerves that convey impulses from the skin, skeletal muscles, or joints to the CNS.

Visceral sensory nerves

Nerves that convey impulses from visceral organs within the ventral body cavity to the CNS.

Somatic nervous system

The "voluntary" nervous system composed of somatic efferents that allow conscious control of skeletal muscles.

Autonomic nervous system (ANS)

The "involuntary" nervous system composed of visceral efferents that automatically control cardiac muscle, smooth muscle, and glands.

Rostral

A directional term meaning towards the beak or snout; used specifically in the brain.

Caudal

A directional term meaning towards the tail; used specifically in the brain.

Excitability

The ability of cells within a tissue to respond to electrical impulses, such as nerve impulses or action potentials.

Neurons

Highly specialized nerve cells adapted to generate and conduct nerve impulses; characterized as being amitotic and having a high metabolic rate.

Neuroglia (glial cells)

Nonconducting cells that support, insulate, and protect neurons and maintain nervous system homeostasis.

Amitotic

A characteristic of neurons where they lose their ability to divide by mitosis during specialization and cannot be replaced if destroyed.

Dendrites

Short, highly branched processes that provide area for receiving signals and conduct graded potentials toward the cell body.

Cell body (soma)

The biosynthetic and metabolic center of the neuron; most are located in the CNS and make up the bulk of gray matter.

Nuclei

Small, isolated bundles of neuronal cell bodies located within the CNS.

Ganglia

Small, isolated bundles of neuronal cell bodies located within the PNS.

Gray matter

Tissue composed of neuron cell bodies and short nonmyelinated neurons; found on the brain's surface and the "H" region of the spinal cord.

White matter

Tissue composed mostly of myelinated axons; the white color is provided by the dense coating of fatty myelin.

Axon

A single, long process that conducts electrical impulses (action potentials) away from the cell body toward another cell.

Nerve fibers

A term used to describe long axons.

Myelin sheath

A whitish, fatty, segmented covering that protects and electrically insulates axons, increasing the speed of nerve impulse conduction.

Nodes of Ranvier

Small gaps of approximately $1\,\mu m$ of exposed axon located between segments of myelin; sites of condensed voltage-gated $Na^+$ channels.

Saltatory conduction

The fastest form of nerve impulse transmission where the electrical impulse jumps from node to node in myelinated axons.

Continuous conduction

A slower process of impulse transmission in unmyelinated axons where the action potential moves successively down every portion of the axon.

Neurotransmitters

Chemical messengers released by the terminal end bulb into the synapse to convert an electrical signal into a chemical one.

Tracts

Bundles of neuronal axons located in the CNS.

Nerves

Bundles of neuronal axons located in the PNS.

Mixed nerves

Nerves that contain both sensory (afferent) and motor (efferent) axons, conducting messages in both directions.

Interneurons

Also called association neurons, these CNS cells lie between motor and sensory neurons to shuttle impulses and integrate stimuli; they make up count for more than $99\%$ of all neurons.

Astrocytes

The most abundant CNS glial cells; they regulate the chemical environment, maintain the blood-brain barrier (BBB), and anchor neurons to blood vessels.

Oligodendrocytes

The myelinating glial cells of the CNS; a single cell can wrap its multiple flat processes around as many as $60$ axons.

Ependymal cells

Ciliated glial cells that line the central cavities of the CNS and produce, maintain, and circulate cerebrospinal fluid (CSF).

Microglial cells

The immune cells of the CNS that monitor neuronal health and transform into macrophages to phagocytize microorganisms or debris.

Satellite cells

PNS glial cells that surround neuronal cell bodies in ganglia; they function similarly to astrocytes in the CNS.

Schwann cells

The myelinating cells of the PNS that wrap their entire body around a single axon to create the myelin sheath.