Glossary
Actin
An abundant protein that forms actin filaments. Monomeric form is globular actin (G actin); polymeric form is filamenous actin (F actin)
Action potential
A rapid change in membrane potential that is self-propagating and allows long-distance signalling possible in the nervous system
Active transport
The movement of a molecule across a membrane against its concentration or electrochemical gradient using energy and a carrier protein
ADP (Adenosine 5'-diphosphate)
The resulting nucleotide after the hydrolyisis of the terminal phosphate of ATP
ATP (Adenosine 5'-triphosphate)
The principal carrier of chemical energy in the cell. Its hydrolysis releases a large amount of free energy
Cardiac muscle
Striated involuntary muscle of the heart. Simililar in structure to skeletal muscle (main difference being that cardiac muscle can branch)
Dihydropyridine receptor
A voltage-gated calcium release channel in the T tubule membrane which releases a little Ca2+ into the sarcoplasm and interacts with a ryanodine receptor upon stimulation of an action potential
Endoplasmic reticulum
A large membranous compartment in eukaryotic cells where lipids and proteins are synthesised. Can be rough (ribosome-studded) or smooth (ribosome-free)
Membrane
The lipid bilayer (with some proteins) that surrounds organelles and cells
Muscle fibre
A single muscle cell in a skeletal muscle that is composed of bundles of myofibrils
Myoblast
A mononucleated, undifferentiated muscle progenitor cell
Myofibril
A bundle of myofilaments in a muscle cell
Myofilament
The thick and thin filaments responsible for muscle contraction that form myofibrils. Made up mostly of actin and myosin
Myosin
The motor protein that makes up the thick filaments of the muscle cell
Neuron
A nerve cell that conducts signals in the nervous system. A motor neuron stimulates muscle fibres; a sensory neuron receives sensory input and transmits the information to the central nervous system
Neurotransmitter
A chemical messenger that is released at a synapse from a nerve cell and diffuses across the synaptic cleft and stimulates the post-synaptic cell
Neuromuscular junction
Specialised synapse between a motor neuron and a muscle cell
Plasma membrane
The membrane around a cell
Ryanodine receptor
A calcium-release channel in the sarcoplasmic reticulum membrane that release Ca2+ into the sarcoplasm upon coupling with a dihydropyridine receptor
Sarcolemma
The plasma membrane of a muscle fibre
Sarcomere
The contractile unit of a myofibril (delimited by the Z lines)
Sarcoplasm
The cytoplasm of a muscle fibre
Sarcoplasmic reticulum
The specialised smooth endoplasmic reticulum of a muscle fibre that regulates the calcium concentration in the sarcoplasm
Skeletal muscle
Striated voluntary muscle that is attached to bones
Smooth muscle
Non-striated involuntary muscle found in walls of hollow organs (except heart)
Titin
The lasrgest known protein that anchors the thin filaments to the Z line of a sarcomere
T (transverse) tubules
A tubular invagination of the sarcolemma that conducts action potentials into the sarcoplasm
Tropomyosin
A regulatory protein that blocks G actin binding sites of the thin filament
Troponin
A calcium-binding protein that controls the position on tropomyosin on the thin filament