Chapter 11: Introduction to the Nervous System and Nervous Tissue Flashcards

Comprehensive vocabulary flashcards covering nervous system anatomy, neuroglia, electrophysiology, action potentials, synaptic transmission, neurotransmitters, and neuronal circuits based on Chapter 11 notes.

Central Nervous System (CNS)

The structural division of the nervous system consisting of the brain and spinal cord, responsible for integrating sensory information and coordinating responses.

Peripheral Nervous System (PNS)

The structural division of the nervous system consisting of cranial nerves, spinal nerves, and their branches that connect the central nervous system to the rest of the body.

Brain

The central organ of the nervous system located in the cranium, composed of about $100\text{ billion}$ neurons that regulate body functions.

Spinal Cord

The organ containing about $100\text{ million}$ neurons that merges with the brain at the foramen magnum, passes through the vertebral column, and enables communication below the head and neck.

Nerves

Bundles of long neuron axons packed with blood vessels and surrounded by connective tissue sheaths that carry signals between the CNS and the rest of the body.

Cranial Nerves

Twelve pairs of nerves originating from or traveling directly to the brain.

Spinal Nerves

Thirty-one pairs of nerves originating from or traveling directly to the spinal cord.

Sensory (Afferent) Division

The functional division of the PNS responsible for gathering information about the internal and external environments of the body.

Somatic Sensory Division

The division of the PNS sensory branch whose neurons carry signals from skeletal muscles, bones, joints, skin, and special sensory organs (vision, hearing, taste, smell, and balance).

Visceral Sensory Division

The division of the PNS sensory branch whose neurons carry signals from internal organs (viscera) such as the heart, lungs, stomach, intestines, kidneys, and urinary bladder.

Integrative Functions

Functions performed primarily by the brain in the CNS to analyze and interpret detected sensory stimuli and determine an appropriate response.

Motor (Efferent) Division

The functional division of the PNS whose neurons carry out motor responses by carrying signals away from the CNS to effectors.

Somatic Motor Division

The voluntary motor division of the PNS whose neurons transmit signals to skeletal muscles.

Autonomic Nervous System (ANS)

The visceral or involuntary motor division of the PNS whose neurons carry signals to smooth muscle, cardiac muscle, and glands.

Effectors

Organs, such as muscles and glands, that perform motor actions in response to signals from the motor division.

Neurons

Excitable, long-lived, generally amitotic cells responsible for sending and receiving signals in the form of action potentials.

Neuroglia

Supportive cells in nervous tissue that hold neurons together, protect them, maintain their environment, and retain the ability to divide by mitosis.

Cell Body (Soma)

The central, most metabolically active portion of a neuron ranging from $5$ to $100\,\mu m$ in diameter, containing organelles such as Nissl bodies, mitochondria, and nuclei.

Nissl Bodies

Abundant clusters of free ribosomes and rough endoplasmic reticulum found in the cytoplasm of a neuronal cell body.

Neurofibrils

Bundles of intermediate filaments in the neuronal cytoskeleton that extend into the dendrites and axon to support cell structure.

Dendrites

Short, highly branched processes that receive input from other neurons and transmit electrical impulses toward the cell body.

Axon

A long single process (nerve fiber) of a neuron capable of generating and conducting action potentials away from the cell body.

Axon Hillock

The cone-shaped area of the neuronal cell body from which the axon originates.

Axon Collaterals

Branches that extend off the main axon.

Telodendria

Fine terminal branches located at the end of an axon and its collaterals.

Axon Terminals

Swollen bulbous ends of telodendria (also called synaptic knobs) that communicate with target cells by releasing neurotransmitters.

Axolemma

The specialized plasma membrane surrounding an axon.

Axoplasm

The cytoplasm within an axon containing mitochondria, cytoskeleton, vesicles, and lysosomes, but lacking protein-synthesizing organelles.

Slow Axonal Transport

Passage of substances such as cytoskeletal proteins away from the cell body through axoplasm at a rate of $1\text{--}3\,mm/day$.

Fast Axonal Transport

ATP-dependent movement of vesicles and organelles along motor proteins in retrograde (up to $200\,mm/day$) or anterograde (up to $400\,mm/day$) directions.

Poliomyelitis

An infectious disease caused by poliovirus that reaches the spinal cord via retrograde axonal transport, causing deformity and paralysis.

Receptive Region

The functional region of a neuron consisting of dendrites and the cell body that receive signals from other neurons.

Conducting Region

The functional region of a neuron consisting of the axon that conducts electrical signals.

Secretory Region

The functional region of a neuron consisting of axon terminals that secrete neurotransmitters onto target cells.

Multipolar Neurons

Neurons featuring a single axon and two or more dendrites; comprises over 99% of all neurons.

Bipolar Neurons

Neurons featuring one axon and one dendrite, found mainly in special sense organs such as the retina and olfactory epithelium.

Pseudounipolar Neurons

Sensory neurons featuring a single short process splitting into a peripheral process and a central process, detecting touch, pressure, and pain.

Interneurons

Multipolar neurons located entirely within the CNS that relay and integrate signals between sensory and motor neurons.

Nuclei

Clusters of neuron cell bodies located within the Central Nervous System.

Ganglia

Clusters of neuron cell bodies located within the Peripheral Nervous System.

Tracts

Bundles of neuron axons located within the Central Nervous System.

Astrocytes

Star-shaped CNS neuroglia that anchor neurons and blood vessels, maintain the blood-brain barrier, regulate the extracellular environment, and repair damaged tissue.

Gliomas

Primary brain tumors arising from abnormally rapid cellular division of neuroglial cells.

Astrocytomas

The most common type of glioma, resulting from uncontrolled proliferation of astrocytes.

Oligodendrocytes

CNS neuroglia with flattened processes that wrap around the axolemmas of several axons to form myelin sheaths.

Microglia

Small CNS neuroglia that act as phagocytes to clean up cell debris, dead neurons, and pathogens following injury.

Ependymal Cells

Ciliated CNS neuroglial cells lining the cavities of the brain and spinal cord that secrete, monitor, and circulate cerebrospinal fluid.

Neurolemmocytes

PNS neuroglia (also called Schwann cells) that wrap around axons to form myelin sheaths and play a key role in axonal repair.

Satellite Cells

Flat PNS neuroglia that surround and support neuron cell bodies within ganglia.

Myelin Sheath

An insulating layer composed of lipid-rich repeating plasma membrane wrapped around an axon to speed up electrical impulse conduction.

Internodes

Myelinated segments of an axon ranging between $0.15$ and $1.5\,mm$ in length.

Myelin Sheath Gaps

Unmyelinated spaces along an axon between adjacent internodes (also known as Nodes of Ranvier).

Neurolemma

The outer edge of a myelinated PNS axon containing the neurolemmocyte cytoplasm, nucleus, and organelles.

White Matter

CNS tissue composed primarily of myelinated axons.

Gray Matter

CNS tissue composed primarily of neuron cell bodies, dendrites, and unmyelinated axons.

Wallerian Degeneration

Phagocytic breakdown and degeneration of the axon and myelin sheath distal to a site of axonal damage in the PNS.

Regeneration Tube

A cellular tube formed by neurolemmocytes and basal lamina that guides growing axon processes toward their target cell during PNS repair.

Resting Membrane Potential

The voltage or electrical potential difference across the plasma membrane of a resting neuron, measuring approximately $-70\,mV$.

Leak Channels

Transmembrane ion channels that are always open, allowing specific ions to continually leak across the membrane down their gradients.

Ligand-Gated Channels

Ion channels that open or close in response to a chemical (ligand) binding to the channel or an associated receptor.

Voltage-Gated Channels

Ion channels that open or close in response to changes in the membrane potential across the plasma membrane.

Mechanically Gated Channels

Ion channels that open or close in response to physical deformation of the membrane caused by pressure, stretch, or vibration.

Sodium-Potassium Pump

An active transport pump ($\text{Na}^+/\text{K}^+\text{ ATPase}$) that uses ATP to move three $\text{Na}^+$ ions out of the cell and two $\text{K}^+$ ions into the cell.

Depolarization

A change in membrane potential that makes the cytosol less negative relative to rest (moving toward or above $0\,mV$).

Repolarization

The movement of membrane potential back toward its negative resting level following depolarization.

Hyperpolarization

A change in membrane potential that makes the cytosol more negative than its normal resting membrane potential.

Local Potential

A small, graded, reversible, and decremental change in membrane potential generated over short distances across the plasma membrane.

Action Potential

A uniform, rapid, nondecremental sequence of depolarization and repolarization that propagates down the entire length of an axon.

Trigger Zone

The axon hillock and initial segment of an axon where local potentials summate to generate action potentials.

Threshold

The specific membrane potential ($-55\,mV$) required to open voltage-gated sodium channels and trigger an action potential.

Absolute Refractory Period

The timeframe after an action potential onset during which no stimulus can trigger another action potential because voltage-gated sodium channels are activated or inactivated.

Relative Refractory Period

The timeframe following the absolute refractory period during which an action potential can be fired only by a stronger-than-normal stimulus.

All-or-None Principle

The rule stating that an action potential occurs at maximum intensity if threshold is reached, or does not occur at all if threshold is not reached.

Continuous Conduction

Conduction along unmyelinated axons in which every sequential section of the axolemma must undergo depolarization to threshold.

Saltatory Conduction

Rapid conduction along myelinated axons in which action potentials 'jump' between unmyelinated myelin sheath gaps.

Type A Fibers

Large-diameter, heavily myelinated axons with the fastest conduction speeds (up to $120\,m/s$ or $250\,mi/h$), found in motor and muscle/joint sensory fibers.

Type B Fibers

Intermediate-diameter, mostly myelinated axons with moderate conduction speeds (up to $15\,m/s$ or $32\,mi/h$), found in visceral sensory fibers and ANS efferents.

Type C Fibers

Small-diameter, unmyelinated axons with the slowest conduction speeds ($0.5\text{--}2\,m/s$ or $1\text{--}5\,mi/h$), transmitting pain, temperature, and autonomic signals.

Multiple Sclerosis

An autoimmune disorder in which immune cells attack and destroy myelin sheaths in the CNS, impairing signal transmission.

Presynaptic Neuron

The neuron at a synapse that transmits signals from its axon terminal.

Postsynaptic Neuron

The neuron at a synapse that receives input at its dendrite, cell body, or axon.

Electrical Synapse

A synapse where axolemmas are joined by gap junctions ($3.5\,nm$ apart), allowing direct, instantaneous, and bidirectional electrical current flow.

Chemical Synapse

A synapse where neurotransmitters are released across a $20\text{--}50\,nm$ synaptic cleft to transmit unidirectional signals to target cell receptors.

Synaptic Cleft

The fluid-filled space ($20\text{--}50\,nm$) separating presynaptic and postsynaptic membranes at a chemical synapse.

Synaptic Delay

The short time gap (about $0.5\,ms$) required for neurotransmitter release, diffusion across the cleft, and receptor binding.

Excitatory Postsynaptic Potential (EPSP)

A small, local depolarization of a postsynaptic membrane caused by the opening of ligand-gated cation channels (such as $\text{Na}^+$ or $\text{Ca}^{2+}$).

Inhibitory Postsynaptic Potential (IPSP)

A small, local hyperpolarization of a postsynaptic membrane caused by the opening of ligand-gated $\text{K}^+$ or $\text{Cl}^-$ channels.

Neural Integration

The process by which a postsynaptic neuron combines all incoming excitatory and inhibitory inputs to determine whether an action potential will fire.

Temporal Summation

The accumulation of postsynaptic potentials occurring in rapid succession from a single presynaptic axon terminal within a short duration ($<15\,ms$).

Spatial Summation

The simultaneous accumulation of postsynaptic potentials originating from multiple presynaptic axon terminals at different locations on a postsynaptic neuron.

Ionotropic Receptors

Transmembrane neurotransmitter receptors that form ligand-gated ion channels, producing rapid and short-lived postsynaptic potentials.

Metabotropic Receptors

Receptors associated with G-proteins and second messengers (like cAMP) that produce slower, longer-lasting, and more varied postsynaptic effects.

Acetylcholine (ACh)

A neurotransmitter synthesized from choline and acetyl-CoA, active at neuromuscular junctions, the CNS, and ANS, and degraded by acetylcholinesterase.

Catecholamines

A subgroup of biogenic amine neurotransmitters synthesized from tyrosine, including norepinephrine, epinephrine, and dopamine.

Glutamate

The major excitatory neurotransmitter in the brain, synthesized from glutamine.

GABA (Gamma-Aminobutyric Acid)

The primary inhibitory neurotransmitter in the brain, synthesized from glutamate, which opens ligand-gated chloride channels.

Glycine

The primary inhibitory neurotransmitter in the spinal cord, synthesized from serine.

Substance P

A neuropeptide released from type C sensory afferent fibers that transmits pain and temperature perception.

Opioids

A group of neuropeptides (endorphins, enkephalins, dynorphins) that act as natural pain relievers and nervous system depressants.

Neuromodulation

The process by which neurotransmitters bind to metabotropic receptors to alter synaptic transmission strength or duration without direct excitation or inhibition.