Topic 6 - Definitions

What is "Acetylcholine"?

A neurotransmitter used for communication between neurones.

What is "Actin"?

A protein filament forming thin filaments in myofibrils, made of two twisted chains.

What is "Actinomyosin bridge"?

A cross-bridge formed when a myosin head binds to an actin filament.

What is "Action potential"?

A temporary change in electrical potential across an axon membrane during nerve impulse transmission.

What is "Adenylate cyclase"?

An enzyme that converts ATP into cyclic AMP (cAMP).

What is "Adrenaline"?

A hormone released in stress that raises blood glucose by stimulating glycogenolysis.

What is "Afferent arteriole"?

The blood vessel supplying the glomerulus; it has a wider diameter than the efferent arteriole.

What is "All-or-nothing principle"?

The rule that any stimulus above threshold produces an action potential of the same size.

What is "Anisotropic (A) bands"?

Dark bands in myofibrils containing overlapping actin and myosin.

What are "Antagonistic muscles"?

Muscle pairs that work in opposite directions.

What is "Antidiuretic hormone (ADH)"?

A hormone that increases water reabsorption in the distal convoluted tubule and collecting duct.

What is "Ascending limb"?

The water-impermeable limb of the loop of Henle where sodium ions are actively transported out.

What is "Atrioventricular node (AVN)"?

A group of cells that delays excitation before passing it to the ventricles.

What is "Atrioventricular septum"?

Non-conductive tissue separating atria from ventricles.

What is "Autonomic nervous system"?

The involuntary motor system controlling glands and muscles, with sympathetic and parasympathetic divisions.

What are "Auxins"?

Plant hormones that control cell elongation.

What is "Axon"?

A long neurone fibre that carries impulses away from the cell body.

What is "Bundle of His"?

Conducting fibres that carry impulses from the AVN to the ventricles.

What is "Cell body"?

The part of a neurone containing the nucleus and organelles.

What is "Central nervous system (CNS)"?

The brain and spinal cord.

What is "Chemoreceptor"?

A receptor detecting blood pH changes and signalling the medulla oblongata.

What is "Cholinergic synapse"?

A synapse that uses acetylcholine as its neurotransmitter.

What is "Collecting duct"?

The nephron region that collects urine and has ADH-controlled water permeability.

What are "Cone cells"?

Photoreceptors detecting colour and high-intensity light with high visual acuity.

What is "Control mechanism"?

A self-regulating system with receptor, coordinator, effector, feedback and optimum point.

What is "Coordinator"?

A component that processes information from receptors and signals effectors.

What is "Cyclic AMP (cAMP)"?

A second messenger that activates protein kinase.

What are "Dendrites"?

Short branched extensions that receive nerve impulses.

What are "Dendrons"?

Extensions from the cell body that branch into dendrites.

What is "Depolarisation"?

A reduction in membrane potential where the inside becomes less negative.

What is "Descending limb"?

The water-permeable limb of the loop of Henle that loses water.

What is "Diabetes"?

A disorder where blood glucose regulation fails, including Type I and Type II.

What is "Distal convoluted tubule"?

A nephron segment regulating ions, pH and water reabsorption.

What is "Effector"?

A structure that carries out a response to a stimulus.

What is "Efferent arteriole"?

The vessel carrying blood away from the glomerulus, narrower than the afferent arteriole.

What is "Excitatory synapse"?

A synapse that increases the chance of an action potential.

What are "Fast-twitch muscle fibres"?

Fibres adapted for rapid, powerful, anaerobic contractions.

What is "Feedback mechanism"?

A system where effectors influence the original stimulus.

What is "Fovea"?

The retinal region with the highest cone concentration and visual acuity.

What is "Generator potential"?

A graded depolarisation in a sensory receptor cell.

What is "Glomerular filtrate"?

Fluid filtered into the renal capsule containing small soluble molecules.

What is "Glomerulus"?

A capillary network in the renal capsule adapted for ultrafiltration.

What is "Glucagon"?

A hormone that raises blood glucose via glycogenolysis and gluconeogenesis.

What is "Gluconeogenesis"?

The synthesis of glucose from non-carbohydrate sources.

What is "Glycogenesis"?

The formation of glycogen from glucose.

What is "Glycogenolysis"?

The breakdown of glycogen into glucose.

What is "Gravitropism"?

Plant growth in response to gravity.

What is "Homeostasis"?

Maintenance of a stable internal environment.

What are "Hormones"?

Chemical messengers released into the blood by endocrine glands.

What is "Hyperpolarisation"?

An increase in membrane potential making it more negative than resting.

What is "Hypothalamus"?

A brain region regulating temperature, water balance and autonomic control.

What is "H-zone"?

The lighter central region of an A band containing only myosin.

What is "Indoleacetic acid (IAA)"?

An auxin that promotes shoot elongation and inhibits root elongation.

What is "Inhibitory synapse"?

A synapse that hyperpolarises the postsynaptic neurone.

What is "Insulin"?

A hormone that lowers blood glucose by increasing glucose uptake and glycogenesis.

What is "Intermediate neurone"?

A neurone linking sensory and motor neurones in the CNS.

What is "Iodopsin"?

The light-sensitive pigment found in cone cells.

What are "Islets of Langerhans"?

Pancreatic cell clusters that secrete insulin and glucagon.

What are "Isotropic (I) bands"?

Light bands containing only actin filaments.

What is "Kinesis"?

A non-directional response altering movement speed or turning rate.

What is "Loop of Henle"?

A nephron loop creating a low water potential in the medulla.

What is "Medulla oblongata"?

A brain region controlling heart rate and breathing.

What is "Motor neurone"?

A neurone carrying impulses from the CNS to effectors.

What is "Myelin sheath"?

An insulating layer that increases impulse transmission speed.

What are "Myofibrils"?

Contractile fibres in muscle cells made of actin and myosin.

What does "Myogenic" mean?

Cardiac muscle that contracts without nervous stimulation.

What is "Myosin"?

A thick filament protein with projecting heads.

What is "Myosin binding site"?

A site on actin exposed during contraction for myosin attachment.

What is "Negative feedback"?

A mechanism that reverses changes to restore the optimum point.

What is "Negative tropism"?

Growth away from a stimulus.

What is "Nephron"?

The functional unit of the kidney.

What is "Nerve impulse"?

A self-propagating wave of depolarisation.

What is "Neuromuscular junction"?

A synapse between a motor neurone and a muscle fibre.

What are "Neurones"?

Cells specialised for rapid impulse transmission.

What are "Neurotransmitters"?

Chemicals that transmit signals across synapses.

What are "Nodes of Ranvier"?

Gaps in the myelin sheath allowing saltatory conduction.

What is "Optic nerve"?

The nerve carrying impulses from the retina to the brain.

What is "Optimum point"?

The most efficient operating level of a system.

What are "Osmoreceptors"?

Hypothalamic receptors detecting blood water potential.

What is "Osmoregulation"?

Regulation of blood water potential by the kidneys.

What is "Pacinian corpuscle"?

A pressure-sensitive mechanoreceptor.

What is "Parasympathetic nervous system"?

The division that slows activity during rest.

What is "Peripheral nervous system (PNS)"?

Nerves carrying impulses to and from the CNS.

What is "Phosphocreatine"?

A muscle phosphate store for rapid ATP regeneration.

What is "Phototropism"?

Plant growth in response to light.

What are "Plant growth factors"?

Hormone-like substances controlling plant growth.

What is "Polarisation"?

The resting membrane potential of an axon.

What is "Positive feedback"?

A mechanism that amplifies a change.

What is "Positive tropism"?

Growth towards a stimulus.

What is "Posterior pituitary gland"?

The gland that releases ADH.

What is "Postsynaptic neurone"?

The neurone that receives neurotransmitters.

What are "Pressure receptors"?

Receptors detecting blood pressure changes.

What is "Presynaptic neurone"?

The neurone that releases neurotransmitter.

What is "Protein kinase"?

An enzyme activated by cAMP that phosphorylates proteins.

What is "Proximal convoluted tubule"?

A nephron region for selective reabsorption.

What is "Purkyne tissue"?

Specialised fibres conducting impulses through ventricles.

What is "Receptor"?

A structure detecting a stimulus.

What is "Reflex"?

A rapid automatic response to a stimulus.

What is "Reflex arc"?

The neurone pathway of a reflex action.

What is "Refractory period"?

A period preventing further action potentials.