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A2 Biology 1.1

OCR biology - communication and heat control and nerves

What is a stimulus + examples? Any change in the environment that causes a response. External = loud noise, change in temperature or light intensity. Internal = change in blood glucose conc, blood salt conc, pH, temperature, water potential in blood, blood pressure
What is a response? A change in behaviour or physiology as a result of a stimulus, that reduces stress
What is sensitivity? The ability of an organism to detect and respond to stimuli
What is cell signalling? Communication between cells along communication pathways (may/may not pass through coordination centre). Functions: coordinates organ activity, regulates cell growth, division, organisation, allows sensitivity
What are the types of cell signalling + how do they differ? Types:1) hormonal- cells in endocrine gland secrete hormone into blood, carried all over body only binds to complementary receptor on target cell, longer-term response 2) neuronal- electrical impulses along neurones, neurotransmitters across synapse, fast
What are the features of a good communication system in the body? Covers whole body, fast and specific communication, allows long and short-term responses
What is homeostasis? The maintenance of the internal environment at a constant state WITHIN NARROW LIMITS despite external changes, requires negative feedback mechanism
What is negative feedback? Where a change in a condition stimulates a response that reverses the change to recreate optimum steady state, involved in homeostasis. Sensory receptors e.g. chemoreceptors detect stimulus, cell signalling along communication pathways to effector cells..
Continued Which generate a response based on stored information that recreates the optimum steady state e.g. liver + muscle cells. Return to norm is detected by receptors so corrective mechanism is switched off.
What is an example of negative feedback? Blood glucose conc. Too high= pancreas secretes insulin, glucose channels increased uptake of glucose by liver/muscle cells, excess -> glycogen in liver. Too low= pancreas secretes glucagon, glycogen -> glucose
What is positive feedback? Where a change in a condition stimulates a response that increases the change - destabilises the system, not involved in homeostasis, can be dangerous
What is an example of positive feedback being useful? Oxytocin-neurotransmitter+hormone, hypothalamus. Initiates uterine contractions, impulse to anterior PG to secrete more, impulses are more frequent+intense, cervix stretches. Stimulate mechanreceptors in nipple=AG=SM in mammary gland contract= lactation
What is an example of positive feedback being harmful? Hypothermia - condition where body temperature drops below 35 degrees c. Low temperature = less movement and slower metabolism, less exergonic reactions generate heat, body temperature drops further
What is an ectotherm? An organism that relies on external sources of heat to regulate body temperature, therefore body temperature fluctuates with external temperature, e.g. amphibians, fish, reptiles
What are the advantages of being an ectotherm? Less heat energy needs to be produced, therefore; 1) less food needs to be consumed, so they can survive for long periods without eating, 2) a larger proportion of energy obtained from food via respiration can be used for growth
What are the disadvantages of being an ectotherm? some can't inhabit cold climates, some are less active or inactive in cold climates/ winter, some have to warm up in the morning before being active which creates a high risk of predation
How do ectotherms influence their body temperature? Behaviour: orientate body so larger/smaller SA is exposed to sun eg locusts, hide in a burrow eg lizards, bask in the sun eg snakes. Physiology: horned lizards expand and contract rib cage to change SA, locusts increase breathing movements for evaporation
What is an endotherm? An organism that can use internal sources of heat to maintain a stable core body temperature e.g. by varying the rate of exergonic reactions in the liver
What is thermoregulation? The maintenance of stable body temperature, controlled by the thermoregulatory centre in the hypothalamus, negative feedback
What are peripheral thermoreceptors? Receptors in the skin that monitor body temperature in the extremities
What are the advantages of being an endotherm? Body temperature remains fairly constant regardless of external temperature which is essential for enzymes and metabolism, they can inhabit cold climates, they remain active in cold climates
What are the disadvantages of being an endotherm? A smaller proportion of the energy gained from food can be used for growth, and they must consume a large volume of food
What physiological responses occur when an endotherm is too hot? Sweat glands secrete more sweat, panting- latent heat of vaporisation, water evaporates. Vasodilation- SM in sphincters relax, more blood enters true capillaries, heat radiates. Hepatocyte metabolism slows. Arrector pili muscles relax, no shivering
What behavioural responses occur when an endotherm is too hot? Move into the shade, burrow underground, orientate body so smaller SA is exposed to sunlight, less active, spread out limbs
What physiological responses occur when an endotherm needs to warm up? Arrector pili muscles contract-hairs on end, trap insulating air. Vasoconstriction-SM contracts, sphincters close, less radiation. Skeletal muscle sponaneous contractions. Faster hepatocyte metabolism, exergonic. No panting, less sweating
What behavioural responses occur when an endotherm needs to warm up? Bask in the sunlight, orientate body so larger SA exposed to sunlight, move around more, or roll up in ball if very cold
What is hyperthermia? Condition where core body temperature exceeds 40 degrees c. Excessive sweating causes dehydration, salt deprivation (stroke and cramps)
What is hypothermia? Condition where core body temperature falls below 30 degrees c. Positive feedback mechanism. Results in: vasoconstriction ,cell death, frostbite, gangrene
Describe structure/function of a sensory neurone Transmits APs from sensory receptors in PNS to CNS, cell body in PNS, long Dendron, short axon, dendrites, myelin sheath is made of schwann cells and has nodes of ranvier (1-3mm, 2-3micrometers long)
Describe structure/function of a relay neurone Transmits APs from sensory to motor neurones, cell body in CNs, short axon and dendrites, myelin sheath made up of oligodendrocytes and no nodes of ranvier.
Describe structure/function of a motor neurone Transmits action potentials from CNS to effectors in the PNS e.g. muscle, gland. Cell body in CNS, axon and dendrites, myelin sheath made up of schwann cells with nodes of ranvier
What is common to all neurones? Long cells, cell body contains nucleus + lots of ribosomes + mitochondria, plasma membranes contain lots of gated ion channels and Na/K pump to mantian a potential difference across membrane
What is an axon, a dendron and a myelin sheath? Axon - part of neurone conducts an AP away from cell body. Dendron - part of sensory neurone transmits an AP from sensory receptors to cell body. Myelin sheath - fatty layer insulates neurones from surrounding electrical activity, speeds up tranmission
What are sensory receptors? Receptors that detect stimuli in the environment, they are energy transducers because they convert different forms of energy into electrical energy
Give examples of sensory receptors Light intensity/wavelength=rods + cones, retina. Volatile chemicals=olfactory cells, nasal cavity. Soluble chemicals=taste buds, tongue, epiglottis, hard palate. Vibrations=sound receptors,cochlea. Length of muscle fibres=proprioceptors.Pascinan corpuscle
What is resting membrane potential and how is it maintained? In resting state, membrane is polarised, -70mV, more negative on inside wrt out. Na/K pumps actively transport 3Na+ ions out of cell for every 2K+ ions in, some K+ ions diffuse out leaky membrane, cytoplasm has organic anions, K+, Na+ ion channels closed
How is an action potential formed? 1) cell is in resting state. 2) sensory receptors - ligand-gated Na+ ion channels. 3) if membrane potential reaches threshold=voltage gated open, AP. 4) at +40mV, membrane repolarises. 5) hyperpolarisation. 6)return to resting state
Define an action potential? A depolarisation of the plasma membrane where mp reaches +40mV due to the influx of Na+ ions through voltage-gated channels, all or nothing response, transmitted along an axon
What is the absolute refractory period? From depolarisation to just after the peak, 1-2ms long. Plasma membrane can't be stimulated because Na+ ion channels are inactivated or already open.
What is the relative refractory period? From repolarisation to resting state, 3-4ms long. A stronger-than-normal stimulus is required to elicit an AP. K+ ion efflux opposes depolarisation caused by Na+ influx through recovered ion channels.
What is the function of the refractory period? Allows cells and proteins to recover from activation, allows restoration of the correct concentrations of Na+ and K+ ions on both sides of membrane, prevents action potentials from travelling backwards
How is an AP transmitted along a neurone? Na+ ions that have entered the neurone through voltage-gated channels diffuse along neurone down conc gradient, forming local currents. Memrbane further along neurone reaches threshold potential, voltage gated channels open, influx of Na+, AP travels
What factors increase the speed at which APs travel along a neurone? High temperature - ions have more KE so diffuse more quickly. Large axon diameter - less resistance, ions diffuse quicker. Myelin sheath + nodes of ranvier - salutatory conduction.
What are the benefits of myelin sheath with nodes of ranvier? Saltatory conduction is faster and more metabolically economical - fewer ions diffuse across membrane therefore sodium potassium pumps need less energy to restore resting membrane potential
What are the properties of a myelinated neurone? Schwann cells are wrapped around individual neurones - sheath consists of several layers of cytoplasm and membrane, nodes of ranvier, APs jump between nodes, longer cells, speed of transmission 100-120m/s, faster responses to stimuli.
What are the properties of a non-myelinated neurone? Several neurones are enshrouded in a loosely-wrapped schwann cell, no nodes of ranvier, action potential travels as a wave, controls breathing + digestion, slower repsonses to stimuli, 2-20m/s speed, shorter cells.
Describe the amplitude/ frequency of APs All APs have the same amplitude(+40mv) but the frequency depends on the intensity of a stimulus, frequency is interpreted by brain.
What is a synapse, a neurotransmitter and a cholinergic synapse? A junction between 2+ neurones, 20nm wide. A chemical that diffuses across synaptic cleft to transmit a signal from pre-synaptic to post-synaptic neurone. A synapse that uses acetylcholine neurotransmitter
What are the properties of a presynaptic knob? Many vesicles of neurotransmitter, many voltage gated Ca2+ ion channels, many ribosomes/ mitochondria/SER
How is an action potential transferred from a presynaptic to a postsynaptic neuron in a cholinergic synapse? AP reaches presynaptic membrane. Depolarisation opens voltage-gated ca2+ ions, influx of ions. Ca2+ ions binds to channels on memrbanes of vesicles containing ACh. Vesicles dock to plasma membrane + fuse, release ACh via exocytosis.
ACh diffuses across synapse, binds to receptors on 2 polypeptides of a 5-subunit Na+ ion channel, opens, influx of Na+, EPSP. Summation. ACh -> choline + ethnaoic acid, enter presynaptic neurone via endocytosis, -> ACh, repackage into vesicles
What is an EPSP? A graded depolarisation of the postsynaptic membrane
What are the methods of summation? Temporal - a persistent, low-level stimulus generates successive APs in a particular neurone, lots of neurotransmitter enters 1 synapse ina short period of time. Spatial - APs in several neurones means lots of neurotransmitter released into 1 synapse.
Why/how is acetylcholine broken down? Acetylcholine is hydrolysed by ACE - prevents continuous sitmulation of ACh receptors and continuous formation of action potentials, which can cause paralysis.
What is the function of the synapse? Prevents APs travelling backwards - vesicles of neurotrnamistter only in presynaptic knob. Acclimatisation - if a stimulus is repeated enough times, presynaptic knob runs out of vesicles of neurotransmittter, fatigued, no longer responds, useful
Filters out low-level, unwanted signals. allows small EPSPs to be summated. flexibility: 1 neurone diverges to multiple e.g. reflex arc, multiple neurones converge to 1 postsynaptic neurone
Created by: 11043



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