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NERVOUS COORDINATION - Coggle Diagram

- - - - myelination involves the myelin sheath which is a electrical insulator, it is made by a type of cell called a shwann cell. Between the sheaths are the nodes of ranviers
      - In a myelinated neurone, depolarisation only happens at the nodes of ranvier. The neurone cytoplasm conducts enough electrical charge to depolarise the next node so it jumps from node to node (saltatory conduction). In a non myelinated neurone the impulse travels as a wave at a much slower pace
      - axon diameter is important to speed of conduction, axons with a bigger diameter are quickly as there is less resistance to the flow of ions
      - temperature, as temperature increases speed of conduction increases because ions diffuse faster, only up to 40 degrees as after enzymes start to denature
  - - - If the potential difference reaches the threshold more sodium ion channels open so more ions are able to diffuse into the neurone
        
        At a potential difference of around +30 the sodium channels close and potassium ion channels open. Membrane is more permeable to k+ so they diffuse out the neurone down their concentration gradient getting the membrane slowly back to resting potential
        
        K+ Channels are slow to close so there is a slight overflow of k+ ions out the neurone so potential difference becomes more negative than resting potential
        
        The ion channels reset, the na/k pump returns the membrane to its resting potential by pumping sodium ions out and potassium in
        
        Waves of depolarisation are when sodium ion channels in the next region of the neurone open and sodium ions diffuse into that part, this causes a wave to travel along the neurone
        
        The refractory period acts as a time delay between one action potential and the next. Makes sure action potentials don’t overlap and it limits the frequency at which nerve impulses can be transmitted
- - - - aerobic respiration is where most ATP is generated via oxidative phosphorylation. works best for long periods of low intensity exercise
      - anaerobic respiration is where ATP is made rapidly by glycolysis. the end product pyruvate is converted to lactate by lactate fermentation. this builds up quickly in muscles causing fatigue. anaerobic respiration is good for fast high intensity exercise.
      - the PCr system is ATP-phosphocreatine system. ATP is made by phosphorylating ADP by adding a phosphate taken from PCr. the ATP PCr system generates energy quickly and is anaerobic and its a-lactic (doesn't form lactate). ADP + PCr -> ATP + Creatine
      - slow twitch muscle fibres contract slowly and work for a long amount of time so good for endurance ie maintaining posture (high concentration found in the back and calves). they have lots of mitochondria and blood vessels to supply the muscles with O2 for aerobic respiration. slow twitch muscles fibres are also have lots of myoglobin which stores oxygen
        
        fast twitch muscle fibres are good for short bursts of energy due to quick contraction and that they easily tire. high proportions are found in the legs, arms and eyes. energy is released via anaerobic respiration using glycogen, they also have stores for PCr so energy can be generated fast. they have few myoglobin
- - - - in skeletal muscles there are highly specialised muscle fibres. Each fibre contains nuclei, mitochondria (ATP for contraction) and sarcoplasmic reticulum (contains calcium ions). The cell membrane of a muscle fibre is the sarcolemma. Parts of the sarcolemma fold inwards across the fibres and stick into the sarcoplasm (cytoplasm of muscle cell). These folds are tranverse tubules and help spread electrical impulses through the sarcoplasm.
      - a network of internal membranes called sarcoplasmic reticulum runs through the sarcoplasm; which stores and releases calcium ions for muscle contraction. muscle fibres also contain lots of mitochondria - these are multinucleate and have lots of myofibrils
        
        myofibrils contain bundles of thick and thin myofilaments that move over each-other to contract. they are made of myosin (thick and dark) and actin (thin)
        
        a myofibril is made up of many short units called sarcomeres. the end of sarcomeres are marked with a Z line and in the middle of each sarcomere there is a M line. around the M line there is the H zone which consist of myosin filaments
      - sliding filament theory is where myosin and actin filaments slide over one another to make sarcomeres contract. the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
- - - - how do they work? 1) action potential arrives causing the depolarization of axolemma and opening the calcium ion channels 2) calcium ions diffuse into the synaptic knob 3) influx of calcium ion in knob causes synaptic vesicles to fuse with the presynaptic membrane 4) vesicles release neurotransmitters into synaptic cleft by exocytosis 5) neurotransmitters diffuse across synaptic cleft where they bind on receptors on post 6) binding causes sodium ion channels to open 7) influx of na+ into post synaptic membrane causes depolarisation and an action potential is generated
      - a neuromuscular junction is a specialised cholinergic synapse between a motor neurone and muscle cell. neuromuscular junctions use ACh, which binds to nicotinic cholinergic receptors.
        
        the difference between a neuromuscular junction and a cholinergic synapse is that neuromuscular junctions are; only excitatory, links neurones to muscle, the action potential ends here, only motor neurones are involved, Acetylcholine binds to receptors on the membrane of the muscle fibre, clefts in post synaptic membrane. a cholinergic synapse can be excitatory or inhibitory, links either neurones to neurones or neurones to other effectors, another action potential may be generated along the post-synaptic neurones, Acetylcholine binds to receptors on membrane of post-synaptic neurone.
    - - summation at synapses occur if a stimulus is weak and is unable to meet the threshold. spatial summation is when many presynaptic neurones connect to one postsynaptic neurone to meet the threshold and trigger an action potential. temporal summation is where there's a quick-fire of two or more action potentials arriving at the same time from one presynaptic neurone so more neurotransmitters are released into the cleft making an action potential more likely to occur as the threshold is met.
      - drugs can affect synaptic transmission
        
        Curare Drugs are used for complete blockage of action potential transmission at some synapses they bind to acetylcholine receptors and block their activation. The receptors are not stimulated even when abundant acetylcholine is present in the synaptic cleft. examples are atracurium and pancuronium,. These are the non-depolarizing muscle reactants, as they prevent the depolarization of post-synaptic cells.
        
        Morphine inhibits synaptic transmission of pain signals by activating meu-receptors. Meu-receptors cause increased K+ efflux out of the cell and decreased influx of Ca and Na+. The cell becomes hyperpolarized and the synaptic transmission is blocked
        
        Alcohol plays a role in the transmission of inhibitory synaptic signals. It mimics the action of inhibitory neurotransmitter GABA, bi binding to GABAA receptors. As a result, the inhibitory effect of GABA is enhanced. The post-synaptic neuron becomes hyperpolarized due to this action