A Flashcards
A-band
or anisotropic band
The region of a muscle sarcomere where the thick filaments occur
Absolute Refractory Period
The period during and immediately following an action potential in which an excitable cell cannot generate another action potential, no matter how strong the stimulus
Absolute Temperature
A measure of temperature in kelvins, where 0 k (absolute zero) is the temperature at where there is no atomic or molecular movement. 1 unit on the Kelvin scale equals 1 degree on the Celsius scale. 0 K = -273 degrees Celsius.
Acclimation
see also acclimatization
A persistent but reversible change
in a physiological function that occurs as a
result of an alteration in an environmental
parameter, such as temperature or photoperiod.
Acclimation usually occurs as a result
of an experimental manipulation
Acclimatization
see also acclimation
A reorganization of physiological
functions that occurs as a result of complex
environmental changes, such as season
or altitude
Accommodation
The process by which an eye
changes its focal length. Accommodation allows the eye to produce a focused image of
objects at different distances.
Acetyl CoA
An activated form of acetate that
serves as the entry point for carbon into the
TCA cycle.
Acetylcholine A
Neurotransmitter found in
most animal species in many types of neurons, including motor neurons and the autonomic ganglia of vertebrates.
Acetylcholinesterase
An enzyme that catalyzes the breakdown of acetylcholine into choline and acetate.
Acid
see also base
A chemical that donates a proton
Acidosis
A decrease in pH arising through respiration
(respiratory acidosis) or metabolism
(metabolic acidosis)
Acrosome
A vesicle in sperm that contains digestive
enzymes that enable the sperm to
penetrate the outer layers of an ovum
Acrosome Reaction
The exocytosis of the enzymeladen
acrosomal vesicle of sperm in response
to contact with the ovum
Actin
see also myosin
G-actin is a monomeric protein that can
be polymerized to construct filamentous actin
(F-actin). Actin is the basis of both cytoskeletal microfilaments (composed of the
α-actin isoform of G-actin) and skeletal thin
filaments (composed of the β-actin isoform
of G-actin)
Actinomyosin
The combination of actin and
myosin, joined by a cross-bridge
Action Potential
A relatively large-amplitude, rapid change in the membrane potential of an excitable cell as a result of the opening and closing of voltage-gated ion channels; involved in transmitting signals across long
distances in the nervous system
Activation Energy (E_A)
The energetic barrier that must be reached before a reactant can be transformed into a product
Activation Gate
see also inactivation gate
One of the two gates that open
and close voltage-gated sodium channels
Active Site
A region of an enzyme that binds the substrate and undergoes conformational
changes to catalyze the reaction.
Active State
The phase of a cross-bridge cycle in
which myosin is attached to actin and generating force.
Active Transport
(see also facilitated diffusion, passive
transport)
Protein-mediated movement of a substance across a membrane with the utilization of some form of energy. Primary active transport uses ATP. Secondary active transport uses an electrochemical gradient.
Acuity
The ability to resolve fine detail of a
stimulus.
Acute Response
The rapid phase of response to
an external or internal change in conditions,
usually within seconds to minutes.
Adaptation
Used in two contexts in physiology:
(1) a change in the genetic structure of a population as a result of natural selection;
(2) a reversible change in a physiological parameter that provides a beneficial response to an environmental change. Evolutionary and comparative physiologists prefer to use only the first definition.
Adaptive Immune System
The components of the immune system that deal with specific pathogens, in contrast to the innate immune system, which deals with pathogens more generally. Central to the adaptive (or acquired) immune system is receptors that bind to specific molecular motifs, initiating an immune response.
Adenine
A purine nitrogenous base component
of nucleotides, including nucleic acids.
Adenosine
A nucleoside composed of adenine and the sugar deoxyribose, important as a signaling molecule.
Adenosine Diphosphate (ADP)
A nucleotide composed of the nucleoside adenine with two phosphate groups, with a single high-energy phosphodiester bond.
Adenosine Triphosphate (ATP)
A nucleotide composed of the nucleoside adenine with three phosphate groups, with two high-energy phosphodiester bonds.
Adenylate Cyclase (adenylyl cyclase)
The enzyme that converts ATP to cyclic AMP.
Adequate Stimulus
The stimulus modality to which a sensory receptor is the most sensitive.
Adhesion Plaque
A membrane protein complex that anchors thin filaments to the membrane.
Adipose Tissue
A tissue composed of fat cells (adipocytes) that produce and store lipid.
Adrenal Gland
A gland near the kidney, which in mammals is composed of an outermost layer (the adrenal cortex) and an inner layer (adrenal medulla).
Adrenergic Receptor
A G protein–linked cell membrane receptor that binds norepinephrine preferentially, with a lower affinity for epinephrine.
Adrenergic Receptors
Receptors for the catecholamines
norepinephrine and epinephrine.
Aerobic
Occurring in, or depending on, the
presence of oxygen.
Aerobic Dive Limit
The maximum length of a dive prior to any increase in blood lactate levels.
Aerobic Scope
The ratio of the maximal aerobic metabolic rate to the basal metabolic rate, typically in the range of 3–10.
Aerofoil
A surface, teardrop shaped in profile,
that moves through air to generate lift. An
aerial version of a hydrofoil.
Afferent
see also efferent
Leading toward a region of interest.
Afferent Arteriole
An arteriole that enters the
glomerulus of a kidney tubule.
Afferent Division
The part of the peripheral nervous system that conducts sensory information from sensory receptors and organs toward the central nervous system.
Afferent Neuron
see also sensory neuron
A neuron that conducts a signal from the periphery to an integrating center.
Affinity
see also K_m
A measure of the degree of attraction
between a ligand and a molecule that binds
the ligand.
Affinity Constant (or Ka)
Reciprocal of the dissociation
constant.
After-Hyperpolarization Phase
A prolonged hyperpolarization
following an action potential.
Aglomerular Kidney
A derived form of kidney, with tubules that lack a glomerulus, found in many lineages of marine fish.
Agonist
A substance that binds to a receptor
and initiates a signaling event. May include
both the natural endogenous ligand as well
as pharmaceutical agents that mimic the natural substance.
Albumen
A protein found in eggs that cushions
the embryo.
Albumin
A binding globulin (carrier protein) that is one of the primary proteins of vertebrate plasma; makes a major contribution to blood osmotic pressure.
Aldosterone
Mineralocorticoid hormone secreted
by the adrenal cortex. Its main function
is to alter the levels of Na+ and K+ in the
urine, secondarily affecting water transport.
Alkaloids
A large group of compounds derived from plants that have pharmacological effects
in animals.
Alkalosis
see also metabolic alkalosis, respiratory alkalosis
The condition of being alkaline.
Allantoic Membrane
One of four membranes in
an amniote egg.
Allantoin
An intermediate in nucleotide breakdown
and uric acid synthesis; an important form of nitrogenous waste for some animals.
Allatostatin
A neuropeptide hormone in arthropods
that inhibits the corpus allatum from secreting juvenile hormone.
Allatotropin
A neuropeptide hormone in arthropods
that stimulates the corpus allatum to secrete juvenile hormone.
Alleles
Different forms of the same protein that
are encoded by the same gene but differ
slightly in primary sequence.
Allelochemical
A chemical produced by one species that affects the growth, survival, or reproduction of other species.
Allometry (or allometric scaling)
The pattern seen when comparing structural or functional parameters in relation to body size.