Response to Changes in Environment Flashcards
acetylcholine
a type of neurotransmitter that is used for communication between neurones
actin
a type of protein filament found in myofibrils. it forms thin filaments consisting of two long twisted chains
actinomyosin bridge
the cross-bridge formed when a myosin head attaches to the myosin binding site on an actin filament
action potenital
the temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse
adenylate cyclase
an enzyme that catalyses the conversion of ATP to cAMP
adrenaline
a hormone that is secreted by the adrenal glands under stressful conditions. it increases blood glucose concentration by activating enzymes involved in glycogenolysis
afferent arteriole
The blood vessel that stems from the renal artery and supplies blood to the nephron. It has a larger diameter than the efferent arteriole and divides into a complex system of capillaries, the glomerulus.
all-or-nothing
a principle that states that all stimuli above a certain threshold value will generate the same size of action potential, regardless of the strength of the stimulus
A bands
the darker bands in a myofibril, which consist of overlapping actin and myosin filaments
antagonistic muscles
pairs of muscles that work in opposite directions
ADH (antidiuretic hormone)
A hormone made by the hypothalamus and secreted by the posterior pituitary gland in response to a fall in blood water potential. It increases the permeability to water of the distal convoluted tubule and the collecting duct, allowing more water to be reabsorbed into the blood.
ascending limb
The limb of the loop of Henle that rises into the cortex. It is wider in diameter than the ascending limb and its walls are impermeable to water. Sodium ions are moved out of the ascending limb by active transport.
AVN (atrioventricular node)
A group of cells located between the atria that slow down the wave of excitation and pass it between the ventricles, along the bundle of His.
atrioventricular septum
a layer of non-conductive tissue between the right atrium and left ventricle of the mammalian heart
autonomic nervous system
A branch of the motor nervous system that carries nerve impulses to muscles and glands. It controls involuntary activities and has two divisions: the sympathetic nervous system and the parasympathetic nervous system.
