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Summary Module 5.1.1: Homeostasis and neuronal communication
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OCR A Level Biology A Key concepts from homeostatic processes to neurones and action potentials.
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HOMEOSTATIS NEURONAL COMMUNICATIONCommunication Neurone structure
- Respond to internal + external environ, coordinate - Cell body – nucleus, cytoplasm, mito for neurot
- Cell signalling – molecule released, specific shape, - Dendrons – impulses towards, divide into dendrites
receptor on target cell complimentary shape - Axon – elongated nerve fibre, impulses away
Feedback Sensory – from receptor to relay/motor/brain
- Homeostasis = fluctuations over narrow range Relay – between neurones, short axon/dendron
- Sensory receptors monitor + detect internal changes Motor – from neurone to effector (muscle/glad)
- Effectors (muscle/gland) respond + change condition
Negative = detect by sensory, effectors restore optimum
Common E.g. blood sugar, temp, water balance
Positive = deviation from normal conditions amplified
Eg blood clotting, childbirth contractions
Thermoregulation
Maintain constant core body temp (optim enzyme)
> Exothermic chemical reactions
> Latent heat of vaporisation (evaporation cools) Myelinated neurone
> Radiation (between air, water, ground) - Myelin sheath = multiple membrane layers
> Convection (current), conduction (molec collision) - Schwan cells grow round axon many times
- Insulting layer = faster electrical impulse speed
Ectotherms - Nodes of Ranvier = impulse jumps between
- Use surroundings to heat, not control own temp
- Invertebrate animals, fish, amphibians, reptiles Sensory receptors
- Dark colours absorb ↑ radiation (cold climates) Specific to stimulus type, act as transducer
1) Mechanoreceptor = pressure in skin
Behavioural responses 2) Chemoreceptor = chemicals in nose
1) Bask in the sun, ↑SA = ↑ metabolic reactions 3) Thermoreceptor = heat in tongue
2) Conduction by pressing body against ground 4) Photoreceptor = light in eyes
3) Exothermic metabolic reactions, contractions
4) Shade, cool ground, low SA, prevent denaturing Pacinian corpuscle
- Pressure sensor in skin
Endotherms - Constant pressure = stop
- Metabolic processes to warm, mammals and birds responding as sodium ion
- Actively maintain stable core temp, -ve feedback channels remain open, no AP
- Anatomical adaptions - change SA:V, insulating fat
- Peripheral temp receptors in skin 1) Resting potential = Na channels closed
- Effectors in skin, muscles, vessels, liver 2) Pressure deforms rings + push against nerves
- Hypothalamus in brain = blood temp deep in body 3) Stretch mediated sodium channels, Na+ diffuse in
Heat loss curve = ↑ blood temp, impulses autonomic 4) Depolarised from Na+ forms generator potential
motor neurones to effectors + lower core temp 5) AP down neurone to CNS
Become too warm Generating impulses
1) Vasodilation – arterioles near surface dilate, ↑ Resting potential = polarised, pd -70mV (outside +ve)
radiation, conduction if against cool surfaces 1) Sodium/potassium pump (3Na out, 2K in)
2) Sweating – evaporates + blood below 2) Closed Na+ channels, open K+ channels (out)
3) Hair – erector pili muscles relax + lie flat 3) Large organic anions on inside of cell
Becoming too cold
1) Vasoconstriction – surface arterioles constrict,
2) Decrease sweating – still evaporation from lungs
3) Raise body hair – erector pili contract = insulates
4) Shivering – involuntary relax/contract muscles,
metabolic heat from exothermic reactions warms
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