Chapter 15 - Control and Coordination

endocrine gland

an organ that secretes hormones directly into the blood; endocrine glands are known as ductless glands

endocrine system

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

nerve impulses

a wave of electrical depolarisation that is transmitted along neurones

neurones 

a nerve cell; a cell which is specialized for the conduction of nerve impulses 

sensory neurone

a neurone that transmits nerve impulses from a receptor to the central nervous system (CNS)

intermediate neurone 

transmit impulses from sensory neurones to motor neurones

motor neurones

a neurone who cell body is in the brain, spinal cord, or a ganglion (a swelling on a nerve), and that transmits nerve impulses to an effector such as a muscle or gland 

myelin

insulating material that surrounds the axons of many neurones; myelin is made of layers of cell surface membrane formed by Schwann cells so that they are very rich in phospholipids and therefore impermeable to water and ions in tissue fluid 

node of Ranvier

a very short gap between Schwann cells where myelinated axons are not covered in myelin so are exposed to tissue fluid 

action potential

a brief change in the potential difference from -70mV to +30mV across the cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions 

potential difference

the difference in electrical potential between two points; in the nervous system, between the inside and the outside of a cell surface membrane such as the membrane that encloses an axon

resting potential 

the difference in electrical potential that is maintained across the cell surface membrane of a neurone when it is not transmitting an action potential; it is normally about -70mV inside and is partly maintained by sodium-potassium pumps

voltage-gated channel proteins 

a channel protein through a cell membrane that opens or closes in response to changes in electrical potential across the membrane 

action potential 

a brief change in the potential difference from -70mV to +30mV across the cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions 

depolarisation 

the reversal of the resting potential across the cell surface membrane of a neurone or muscle cell, so that the inside becomes positively charged compared with the outside 

threshold potential

the critical potential difference across the cell surface membrane of a sensory receptor or neurone which must be reached before an action potential is initiated 

repolarisation

returning the potential difference across the cell surface membrane of a neurone or muscle cell to normal following the depolarisation of an action potential 

refractory period

a period of time during which a neurone is recovering from an action potential, and during which another action potential cannot be generated 

saltatory conduction

movement of an action potential along a myelinated axon, in which the action potential ‘jumps’ from one node of Ranvier to the next

chemoreceptors 

a receptor cell that responds to chemical stimuli; chemoreceptors are found in taste buds on the tongue, in the nose and in blood vessels where they detect changes in oxygen and carbon dioxide concentrations 

receptor potential

a change in the normal resting potential across the membrane of a receptor cell, caused by a stimulus 

all-or-none law

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

synaptic cleft

a very small gap between two neurones at a synapse; nerve impulses are transmitted across synaptic clefts by neurotransmitters 

synapse

a point at which two neurones meet but do not touch; the synapse is made up of the end of the presynaptic neurone, the synaptic cleft and the end of the postsynaptic neurone 

neurotransmitter 

a chemical release at synapses to transmit impulses between neurones or between a motor neurone and a muscle fibre 

presynaptic neurone

a neurone ending at a synapse from which neurotransmitter is realeased when an action potential arrives 

postsynaptic neurone

the neurone on the opposite side of a synapse to the neurone in which the action potential arrives 

noradrenaline

a type of neurotransmitter, which is also released by cells in the adrenal glands as a hormone 

acetylcholine 

a type of neurotransmitter released by cholinergic synapses 

cholinergic synapses 

a synapse at which the transmitter substance is ACh 

voltage-gated calcium ion channel proteins

a channel protein in presynaptic membranes that responds to depolarisation by opening to allow diffusion of calcium ions down their electrochemical gradient 

receptor proteins

a protein on a postsynaptic membrane that is a ligand-gated channel protein opening in response to binding of a neurotransmitter 

acetylcholinesterase

an enzyme in the synaptic cleft and on the postsynaptic membrane that hydrolyses ACh to acetate and choline 

neuromuscular junction 

a synapse between a motor neurone and a muscle 

striated muscle

type of muscle tissue in skeletal muscles; the muscle fibres have regular striations that can be seen under the light microscope

sarcolemma

the cell surface membrane of a muscle fibre 

sarcoplasm

the cytoplasm of muscle cells

sarcoplasmic reticulum (SR)

the endoplasmic reticulum of a muscle fibre

transverse system tubules (T-tubules)

infolding of the sarcolemma that go deep into a muscle fibre and conducts impulses to the SR 

myofibrils

one of many cylindrical bundles of thick (myosin) and thin (actin) filaments inside a muscle fibre 

myosin

the protein that makes up the thick filaments in striated muscle; the globular heads of each molecule break down ATP (they act as an ATP-ase)

actin

the protein that makes up the thin filaments in striated muscle 

sarcomere

the part of a myofibril between two Z discs

tropomyosin

a fibrous protein that is part of the thin filaments in myofibrils in striated muscle; tropomyosin blocks the atttachment site on the thin filament for myosin heads so preventing the formation of cross bridges

troponin

a calcium-binding protein that is part of the thin filaments in myofibrils in striated muschle

sliding filament model

the mechanism of muscle contractions; within each sarcomere the movement of thin filaments closer together by the action of myosin heads in the thick filaments shortens the overall length of each muscle fibre

plant growth regulators

any chemical produced in plants that influences their growth and development (eg. auxins, gibberellins, cytokinins, ABA)

auxins

a plant growth regulator (plant hormone) that stimulates cell elongation

gibberellins

a plant growth regulator (plant hormone) that stimulates seed germination and regulates plant height (stem growth); a lack of gibberellin causes dwarfness

expansins

proteins in the cell walls of plants that loosen the attachment of microfibrils of cellulose during elongation growth

endosperm

a tissue in some seeds, such as barley, that is a store of starch and other nutrients

aleurone layer

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