Organism response to change in internal/external environment

• Stimulus


  A change in the internal or external environment
• Receptor


  Detects a stimulus
• Coordinator


  Formulates a suitable response to a stimulus
• Effector


  Produces a response
• Receptors are specific to one type of stimulus
• Nerve cells


  Pass electrical impulses along their length
• Nerve impulse


  Specific to a target cell only because it releases a chemical messenger directly onto it, producing a response that is usually rapid, short-lived and localised
• Mammalian hormones


  Stimulate their target cells via the blood system, are specific to the tertiary structure of receptors on their target cells and produce responses that are usually slow, long-lasting and widespread
• Plant growth substances


  Plants control their response using hormone-like growth substances
• Flowering plants


  • Specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli
  • The effect of different concentrations of indoleacetic acid (IAA) on cell elongation in the roots and shoots of flowering plants as an explanation of gravitropism and phototropism
• Taxes and kineses


  Simple responses that can maintain a mobile organism in a favourable environment
• Reflex


  A protective effect, exemplified by a three-neurone simple reflex
• Pacinian corpuscle


  • Receptors respond only to specific stimuli
  • Stimulation of a receptor leads to the establishment of a generator potential
• Pacinian corpuscle


  Deformation of stretch-mediated sodium ion channels leads to the establishment of a generator potential
• Human retina


  • Differences in sensitivity to light, sensitivity to colour and visual acuity are explained by differences in the optical pigments of rods and cones and the connections rods and cones make in the optic nerve
• Myogenic stimulation


  Stimulation of the heart and transmission of a subsequent wave of electrical activity
• Sinoatrial node (SAN), atrioventricular node (AVN) and Purkyne tissue


  Roles in the control of heart rate
• Chemoreceptors and pressure receptors

  Roles in controlling heart rate
• Autonomic nervous system and effectors

  Roles in controlling heart rate
• Resting potential


  Established in terms of differential membrane permeability, electrochemical gradients and the movement of sodium ions and potassium ions
• Depolarisation and action potential

  Changes in membrane permeability lead to depolarisation and the generation of an action potential
• All-or-nothing principle


  The passage of an action potential along non-myelinated and myelinated axons, resulting in nerve impulses
• Refractory period


  Nature and importance in producing discrete impulses and in limiting the frequency of impulse transmission
• Factors affecting speed of conduction

  Myelination and saltatory conduction, axon diameter, temperature
• Synapse and neuromuscular junction

  Detailed structure
• Transmission across a cholinergic synapse

  1. Unidirectionality

  2. Temporal and spatial summation

  3. Inhibition by inhibitory synapses
• Comparison of transmission


  Across a cholinergic synapse and across a neuromuscular junction
• Students should be able to use information provided to predict and explain the effects of specific drugs on a synapse
• Skeletal muscles


  Act in antagonistic pairs against an incompressible skeleton
• Skeletal muscle structure


  Gross and microscopic structure, ultrastructure of a myofibril
• Muscle contraction


  • Roles of actin, myosin, calcium ions and ATP
  • Roles of calcium ions and tropomyosin in the cycle of actinomyosin bridge formation
  • Roles of ATP and phosphocreatine
• Slow and fast skeletal muscle fibres


  Structure, location and general properties
• Homeostasis in mammals involves physiological control systems that maintain the internal environment within restricted limits
• Importance of maintaining stable core temperature and blood pH

  In relation to enzyme activity
• Importance of maintaining stable blood glucose concentration

  In terms of availability of respiratory substrate and of the water potential of blood
• Negative feedback


  Restores systems to their original level, possession of separate mechanisms involving negative feedback controls departures in different directions from the original state, giving a greater degree of control
• Students should be able to interpret information relating to examples of negative and positive feedback
• Factors influencing blood glucose concentration

  Role of the liver in glycogenesis, glycogenolysis and gluconeogenesis
• Insulin action


  Attaching to receptors on the surfaces of target cells, controlling the uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of target cells, activating enzymes involved in the conversion of glucose to glycogen
• Glucagon action


  Attaching to receptors on the surfaces of target cells, activating enzymes involved in the conversion of glycogen to glucose, activating enzymes involved in the conversion of glycerol and amino acids into glucose