CIE A Level: Control and Coordination

action potential

a brief change in the potential difference from -70mV to +30mV across the cell surface membrane of neurons and sarcolemma of muscle cells

troponin

a calcium-binding protein that is joined to the actin filaments and changes shape to move tropomyosin and expose myosin-binding sites on the actin filament

motor neuron

a cell that conducts impulses from the central nervous system to an effector such as a muscle or a gland

chemoreceptor

a cell that responds to chemical stimuli such as presence of food molecules near the tongue, odour-causing molecules in the nose, or oxygen and carbon dioxide concentrations in the blood

sensory neuron

a cell that transmits impulses from a receptor to the central nervous system

receptor potential

a change from the resting potential across the membrane of a receptor cell caused by a stimulus

neurotransmitter

a chemical released from the presynaptic terminal by exocytosis to transmit an impulse between neurons or from a motor neuron to a muscle

tropomyosin

a long fibrous protein that is joined to the thin actin filaments and blocks the attachment site for myosin heads, preventing cross-bridge formation

noradrenaline

a neurotransmitter found mainly in areas of the brain that are involved in governing autonomic nervous system activity. A hormone version is also released from the adrenal glands

gibberellin

a plant hormone that stimulates seed germination and general plant growth

synapse

a point at which two neurons meet but do not touch, made up of the presynaptic terminal, the synaptic cleft, and the postsynaptic neuron

receptor protein

a protein embedded in a membrane that changes shape in response to binding with a complementary ligand molecule, this can act as a ligand-gated ion channel or activate other proteins associated with the membrane

neuron

a specialised cell of the nervous system that conducts impulses

neuromuscular junction

a specialised type of synapse between a motor neuron's axon terminal and a muscle

aleurone layer

a tissue around the endosperm of seeds that synthesises amylase during germination

endosperm

a tissue in seeds, such as barley seeds, that stores starch

ligand-gated ion channel

a transmembrane protein containing a pore that opens or closes as it changes shape in response to a signaling molecule binding to it

voltage-gated ion channel protein

a transmembrane protein that opens or closes in response to changes in the electrical potential across a membrane

acetylcholine (ACh)

a type of neurotransmitter released by cholinergic synapses involved in reflex arcs and stimulation of skeletal muscle

node of Ranvier

a very short gap between Schwann cells where myelinated axons are not covered by myelin and are therefore permeable to ions in the surrounding tissue fluid

nerve impulse

a wave of electrical depolarisation that is transmitted along neurons

acetylcholinesterase

an enzyme embedded in the postsynaptic membrane and found in the synaptic cleft that hydrolyses ACh into acetate and choline which are taken back into the presynaptic terminal and reused

endocrine gland

an organ that secretes hormones directly into the blood

endocrine system

consists of all endocrine glands in the body together with the hormones they secrete

T-tubules

infoldings of the sarcolemma which go deep into the muscle fibre and conduct impulses to the sarcoplasmic reticulum

myelin

insulating material made of layers of cell membranes of Schwann cells that surrounds the axons of many neurons, making them impermeable to water and ions

saltatory conduction

movement of action potentials along a myelinated axon from one node of Ranvier to the next

all-or-none law

neurons and muscle cells only transmit impulses if the initial stimulus is sufficient to increase the membrane potential above the threshold potential

myofibril

one of many cylindrical bundles of actin and myosin filaments inside a muscle fibre

auxins

plant hormones (such as IAA) that stimulate cell elongation

expansins

proteins in the cell walls of plants that weaken hydrogen bonds between cellulose microfibrils allowing for cell elongation in response to IAA

sarcolemma

the cell surface membrane of a muscle fibre

threshold potential

the critical electrical potential across a cell surface membrane of a receptor or neuron which must be reached before positive feedback causes an action potential to be initiated

sarcoplasm

the cytoplasm of muscle fibres

potential difference

the difference in electrical potential between the inside and outside of a cell membrane

resting potential

the difference in electrical potential that is maintained across the cell membrane of a neuron at rest. It is about -70mV

sarcoplasmic reticulum

the endoplasmic reticulum in muscle fibres that release Ca2+ ions in response to an impulse arriving at the neuromuscular junction

sliding filament model

the mechanism via which thin actin filaments slide over thick myosin filaments causing sarcomeres to shorten. Hence, muscle fibres shorten and the muscle contracts

sarcomere

the part of a myofibril between two Z lines

myosin

the protein that makes up the thick filaments of sarcomeres in striated muscle

actin

the protein that makes up the thin filaments of sarcomeres in striated muscle

repolarisation

the return of the potential difference across the cell surface membrane of a neuron or muscle cell to normal (negative inside, positive outside) during an action potential

depolarisation

the reversal of the resting potential across the cell surface membrane of a neuron or muscle cell so that the inside becomes positive and outside becomes negative

presynaptic neuron

the specialised nerve cell ending at a synapse from which neurotransmitters are released when an action potential arrives at its axon terminal

postsynaptic neuron

the specialised nerve cell on the opposite side of the synapse from the neuron at which the action potential arrived

refractory period

the time during which a neuron is recovering from an action potential and another action potential cannot be generated

striated muscle

the type of muscle tissue in skeletal muscles with a striped pattern due to the arrangement of actin and myosin filaments within sarcomeres of the myofibrils

synaptic cleft

the very small gap between two neurons across which neurotransmitters diffuse