Chapter 11 Flashcards

Nervous System

Master controlling and communicating system of the body.

Sensory Input

Information gathered by sensory receptors about internal and external changes.

Integration

Processing and interpretation of sensory input.

Motor Output

Activation of effector organs (muscles and glands) produces a response.

Central Nervous System (CNS)

Brain and spinal cord of dorsal body cavity; interprets sensory input and dictates motor output.

Peripheral Nervous System (PNS)

The portion of the nervous system outside the CNS; consists mainly of nerves that extend from the brain and spinal cord.

Somatic sensory fibers

Convey impulses from skin, skeletal muscles, and joints to CNS.

Visceral sensory fibers

Convey impulses from visceral organs to CNS.

Motor (efferent) division

Transmits impulses from CNS to effector organs (muscles and glands).

Somatic nervous system

Somatic motor nerve fibers conduct impulses from CNS to skeletal muscle; conscious control of skeletal muscles.

Autonomic nervous system

Consists of visceral motor nerve fibers; regulates smooth muscle, cardiac muscle, and glands; involuntary nervous system.

Involuntary nervous system

Regulates smooth muscle, cardiac muscle, and glands.

Neuroglia (glial cells)

Small cells that surround and wrap delicate neurons.

Neurons (nerve cells)

Excitable cells that transmit electrical signals.

Astrocytes

Most abundant, versatile, and highly branched of glial cells in the CNS.

Microglial cells

Defensive cells in the CNS.

Ependymal cells

Line cerebrospinal fluid-filled CNS cavities.

Oligodendrocytes

Have processes that form myelin sheaths around CNS nerve fibers.

Satellite cells

Surround neuron cell bodies in PNS; function similar to astrocytes of CNS.

Schwann cells (neurolemmocytes)

Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers.

Neurons (nerve cells)

Large, highly specialized cells that conduct impulses.

Neuron Cell Body

Also called the perikaryon or soma; biosynthetic center of neuron.

Nuclei

Clusters of neuron cell bodies in CNS.

Ganglia

Clusters of neuron cell bodies in PNS.

Tracts

Bundles of neuron processes in CNS.

Nerves

Bundles of neuron processes in PNS.

Dendrites

Receptive (input) region of neuron; convey incoming messages toward cell body as graded potentials.

Axon terminal

Region that secretes neurotransmitters, which are released into extracellular space; can excite or inhibit neurons it contacts.

Anterograde

Away from cell body. Examples: mitochondria, cytoskeletal elements, membrane components, enzymes.

Retrograde

Toward cell body. Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins.

Myelin sheath

Composed of myelin, a whitish, protein-lipid substance; protects and electrically insulates axon and increases speed of nerve impulse transmission.

Myelinated fibers

Segmented sheath surrounds most long or large-diameter axons.

Nonmyelinated fibers

Do not contain sheath; conduct impulses more slowly.

Myelin sheath gaps

Gaps between adjacent Schwann cells; sites where axon collaterals can emerge.

White matter

Regions of brain and spinal cord with dense collections of myelinated fibers.

Gray matter

Mostly neuron cell bodies and nonmyelinated fibers.

Multipolar

Three or more processes (1 axon, others dendrites); most common and major neuron type in CNS.

Bipolar

Two processes (one axon, one dendrite); rare (ex: retina and olfactory mucosa).

Unipolar

One T-like process (two axons); also called pseudounipolar.

Sensory neurons

Transmit impulses from sensory receptors toward CNS; almost all are unipolar; cell bodies are located in ganglia in PNS.

Motor neurons

Carry impulses from CNS to effectors; multipolar; most cell bodies are located in CNS (except some autonomic neurons).

Interneurons

Also called association neurons; lie between motor and sensory neurons; shuttle signals through CNS pathways; most are entirely within CNS; 99% of body’s neurons are —-.

Resting Membrane Potential

The potential difference across the membrane of a resting cell, approximately -70 mV in neurons.

Voltage

A measure of potential energy generated by separated charge, measured in volts (V) or millivolts (mV).

Current

The flow of electrical charge (ions) between two points, which can be used to do work.

Resistance

Hindrance to charge flow; substances with high resistance are insulators, while those with low resistance are conductors.

Ohm’s Law

Gives the relationship of voltage, current, and resistance: Current (I) = Voltage (V) / Resistance (R).

Leakage (nongated) channels

Ion channels that are always open.

Gated channels

Ion channels in which part of the protein changes shape to open or close the channel; can be chemically, voltage, or mechanically gated.

Chemically gated (ligand-gated) channels

Open only with the binding of a specific chemical (e.g., a neurotransmitter).

Voltage-gated channels

Open and close in response to changes in membrane potential.

Mechanically gated channels

Open and close in response to physical deformation of receptors, as in sensory receptors.

Electrochemical gradient

The combination of electrical and chemical gradients that drives ion flow across a membrane.

Polarized

The state of a membrane when there is a charge difference across it.

Sodium-potassium pump (Na+/K+ ATPase)

Stabilizes the resting membrane potential by maintaining concentration gradients for Na+ and K+; pumps three Na+ ions out of the cell while pumping two K+ ions back in.

Graded Potentials

Short-lived, localized changes in membrane potential that are triggered by a stimulus that opens gated ion channels, resulting in depolarization or hyperpolarization.

Action Potentials

Brief reversal of membrane potential with a change in voltage of ~100 mV; the principal way neurons send signals over long distances.

Depolarization

Decrease in membrane potential (moves toward zero and above) making the inside of the membrane less negative; increases the probability of producing an impulse.

Hyperpolarization

Increase in membrane potential (away from zero) making the inside of the membrane more negative; decreases the probability of producing an impulse.

Resting state (Action Potential)

All gated Na+ and K+ channels are closed; only leakage channels are open, maintaining the resting membrane potential.

Threshold

The point at which depolarization must reach for an axon to "fire" and trigger an action potential. Typically between -55 to -50 mV.

All-or-None Phenomenon

An action potential either happens completely, or does not happen at all.

Refractory Period

Time in which neuron cannot trigger another AP because voltage-gated Na+ channels are open, so neuron cannot respond to another stimulus.

Absolute Refractory Period

Time from opening of Na+ channels until resetting of the channels; ensures that each AP is an all-or-none event and enforces one-way transmission of nerve impulses.

Relative Refractory Period

Follows the absolute refractory period; most Na+ channels have returned to their resting state, some K+ channels are still open, and the threshold for AP generation is elevated.

Continuous Conduction

Slow conduction that occurs in nonmyelinated axons.

Saltatory Conduction

Occurs only in myelinated axons and is about 30 times faster than continuous conduction; electrical signal appears to jump rapidly from gap to gap.

Group A Fibers

Largest diameter, myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints that transmit at 150 m/s (~300 mph).

Group B Fibers

Intermediate diameter, lightly myelinated fibers that transmit at 15 m/s (~30 mph).

Group C Fibers

Smallest diameter, unmyelinated fibers that transmit at 1 m/s (~2 mph); include ANS visceral motor and sensory fibers that serve visceral organs.

Synapse

Junctions that mediate information transfer from one neuron to another neuron, or from one neuron to an effector cell.

Presynaptic Neuron

Neuron conducting impulses toward the synapse; it sends information.

Postsynaptic Neuron

Neuron transmitting electrical signal away from the synapse; it receives information. In the PNS, this may be a neuron, muscle cell, or gland cell.

Axodendritic Synapse

Synapse between the axon terminals of one neuron and the dendrites of another.

Axosomatic Synapse

Synapse between the axon terminals of one neuron and the soma (cell body) of another.

Axoaxonal Synapse

Synapse from axon to axon

Dendrodendritic Synapse

Synapse from dendrite to dendrite

Somatodendritic Synapse

Synapse from soma to dendrite

Chemical Synapse

Specialized for the release and reception of chemical neurotransmitters.

Electrical Synapse

Neurons are electrically coupled; joined by gap junctions that connect the cytoplasm of adjacent neurons. Communication is very rapid and may be unidirectional or bidirectional.

Synaptic Cleft

Fluid-filled space separating the presynaptic and postsynaptic neurons.

Neurotransmitter

Chemical released at the synapse to transmit signals from one neuron to another.

Synaptic Vesicles

Small membrane-bound sacs in the axon terminal that contain neurotransmitters.

Voltage-gated Ca2+ channels

Channels that open when the action potential arrives at the axon terminal, allowing calcium ions to enter the axon terminal.

Synaptic Delay

Time needed for neurotransmitter to be released, diffuse across synapse, and bind to receptors. This is the rate-limiting step of neural transmission.

Gap Junctions

Connections that join neurons in electrical synapses.

Postsynaptic Potential

Graded potentials caused by neurotransmitter receptors that vary in strength.

EPSP

Excitatory postsynaptic potential; a local net graded potential depolarization.

IPSP

Inhibitory postsynaptic potential; binding to receptor opens chemically gated channels that allow entrance/exit of ions that cause hyperpolarization.

Temporal Summation

One or more presynaptic neurons transmit impulses in rapid-fire order.

Spatial Summation

Postsynaptic neuron is stimulated by a large number of terminals simultaneously

Synaptic Potentiation

Repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron.

Presynaptic Inhibition

Release of excitatory neurotransmitter by one neuron is inhibited by another neuron via an axoaxonal synapse.

Acetylcholine (ACh)

First identified and best understood neurotransmitter; released at neuromuscular junctions, and used by many ANS and CNS neurons.

Biogenic Amines

Neurotransmitters including catecholamines (dopamine, norepinephrine, epinephrine) and indolamines (serotonin, histamine).

Amino Acids (as neurotransmitters)

Glutamate, aspartate, glycine, GABA.

Peptides (Neuropeptides)

Strings of amino acids with diverse functions, e.g., Substance P, endorphins, gut-brain peptides.

Purines (as neurotransmitters)

Monomers of nucleic acids, e.g., ATP and adenosine.

Gasotransmitters

Gases such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) that act as neurotransmitters.

Endocannabinoids

Lipid-soluble neurotransmitters that act at the same receptors as THC.