Chapter 12: Neural Tissue

Vocabulary practice flashcards covering Chapter 12: Neural Tissue, including structural and functional divisions of the nervous system, neuron anatomy and classifications, neuroglia of the CNS and PNS, axonal transport, and nerve injury responses.

Neurons

The basic functional units of the nervous system that send and receive electrical signals.

Neuroglia (glial cells)

Supporting cells that support and protect neurons, provide a supportive framework, act as phagocytes, and regulate the interstitial fluid.

Central Nervous System (CNS)

The anatomical division consisting of the brain and spinal cord, containing neural tissue, connective tissues, and blood vessels, with approximately 86 billion neurons in the human brain.

Peripheral Nervous System (PNS)

The division that includes all neural tissue outside the CNS and enteric nervous system, functioning to deliver sensory information to the CNS and carry motor commands to peripheral tissues.

Enteric Nervous System (ENS)

A neural network inside the gastrointestinal system that senses gut content, processes sensory information, and promotes digestion and food movement without requiring CNS or ANS input.

Peripheral Nerves

Bundles of axons enveloped with connective tissues and blood vessels that carry sensory and motor information between the CNS and PNS.

Afferent Division

The functional division of the PNS that carries sensory information from sensory receptors to the CNS.

Receptors

Sensory structures that detect changes in the external or internal environment or respond to specific stimuli.

Efferent Division

The functional division of the PNS that carries motor commands from the CNS to peripheral effectors such as muscles, glands, and adipose tissue.

Effectors

Target tissues and organs—specifically muscles, glands, and adipose tissue—that respond to motor commands transmitted by the efferent division.

Somatic Nervous System (SNS)

The efferent component of the PNS that controls skeletal muscle contractions, including voluntary contractions and involuntary reflexes.

Autonomic Nervous System (ANS)

The efferent component of the PNS that governs subconscious actions, including contractions of smooth and cardiac muscles, glandular secretions, and adipose tissue.

Sympathetic Division

A branch of the autonomic nervous system that typically exerts stimulating effects on target organs.

Parasympathetic Division

A branch of the autonomic nervous system that typically exerts relaxing effects on target organs.

Perikaryon

The cytoplasm surrounding the nucleus within the cell body of a neuron.

Nissl Bodies

Dense regions of rough endoplasmic reticulum (RER) and free ribosomes in neurons that synthesize proteins and neurotransmitters, giving neural tissue a gray appearance (gray matter).

Neurofibrils

Bundles of neurofilaments that extend through the cytoskeleton to support the dendrites and axon.

Dendritic Spines

Fine processes projecting from dendrites that receive information from other neurons and account for up to 90% of a neuron's surface area.

Axon

A long cytoplasmic process that propagates electrical signals and action potentials to a target postsynaptic cell.

Axon Hillock

The thickened region of the neuron cell body that leads into the initial segment.

Initial Segment

The segment of the axon immediately following the axon hillock where electrical inputs can initiate an action potential.

Axolemma

The specialized cell membrane covering the axoplasm of the axon.

Axoplasm

The cytoplasm of the axon, containing neurofibrils, enzymes, and organelles.

Collaterals

Side branches that originate from a single axon, enabling communication with multiple targets.

Telodendria

Fine extensions located at the distal ends of an axon main trunk and collaterals.

Synaptic Terminals

The specialized distal tips of telodendria where synapses are formed with target cells.

Anterograde Flow

Axoplasmic transport that carries synthesized materials such as neurotransmitters and enzymes along neurotubules away from the cell body toward the synapse.

Retrograde Flow

Axoplasmic transport that carries debris, waste, and certain pathogens along neurotubules from the synapse back to the cell body.

Rabies Virus

A pathogen transmitted by infected saliva that binds peripheral nerve endings, travels via retrograde axonal transport to the spinal cord and brain, and causes fatal encephalitis.

Synapse

A specialized junction where a presynaptic neuron communicates with a postsynaptic cell across a narrow synaptic cleft.

Synaptic Cleft

The narrow extracellular space separating the presynaptic membrane from the postsynaptic membrane.

Synaptic Knob

The expanded bulbous region of an axon terminal that contains synaptic vesicles filled with neurotransmitters.

Neurotransmitters

Chemical messengers released at the presynaptic membrane that bind postsynaptic receptors and are subsequently degraded by enzymes and reassembled in the synaptic knob.

Anaxonic Neurons

Neurons that possess numerous dendrites but no distinguishable axon, found in the brain and special sensory organs.

Bipolar Neurons

Neurons characterized by two distinct processes—one dendrite and one axon separated by the cell body—found in special sensory organs for sight, smell, and hearing.

Unipolar Neurons

Sensory neurons whose dendrites and axon are continuous with the cell body positioned off to the side, featuring axons that can reach over 1 meter in length.

Multipolar Neurons

The most common structural class of neurons in the CNS, having multiple dendrites and a single long axon, including all skeletal muscle motor neurons.

Interneurons

Association neurons located entirely within the CNS (numbering around 20 billion) that distribute sensory information and coordinate processing, planning, and learning.

Ependymal Cells

Simple cuboidal epithelial glial cells lining the ventricles of the brain and central canal of the spinal cord that produce, circulate, and monitor cerebrospinal fluid (CSF).

Astrocytes

The largest and most numerous neuroglia in the CNS; star-shaped cells that maintain the blood-brain barrier, regulate interstitial fluid ions and neurotransmitters, provide structural framework, and repair damaged neural tissue.

Blood-Brain Barrier (BBB)

A protective barrier formed by astrocyte cytoplasmic feet wrapping around capillary endothelial cells to restrict the movement of toxins and pathogens into the CNS.

Oligodendrocytes

CNS neuroglia with sheet-like processes that wrap around axons to create insulating myelin sheaths, giving myelinated tracts a white appearance.

Microglia

Migratory phagocytes derived from lymphocytes that patrol CNS neural tissue to engulf cellular debris, waste products, and pathogens.

Gray Matter

Regions of the central nervous system dominated by unmyelinated structures, neuron cell bodies containing Nissl bodies, and dendrites.

White Matter

Regions of the central nervous system dominated by high concentrations of myelinated axons.

Satellite Cells (amphicytes)

PNS neuroglia that encapsulate neuron cell bodies in ganglia to regulate the exchange of nutrients and metabolic waste products.

Schwann Cells (neurolemmocytes)

PNS neuroglia that form the neurilemma and myelin sheath around a single internode segment of a peripheral axon.

Internodes

The myelinated segments of an axon covered by oligodendrocyte or Schwann cell membranes.

Nodes of Ranvier

Gaps between adjacent internodes along an axon where the axolemma remains exposed and where collateral branches can emerge.

Wallerian Degeneration

The process in the PNS where the axon segment distal to an injury degenerates while Schwann cells survive to form a cellular cord guiding regeneration.

Super Agers

Individuals older than 80 years with exceptional memory performance who maintain high levels of hippocampal neurogenesis compared to individuals experiencing cognitive decline or Alzheimer's disease.