NERVOUS COORDINATION
Responsible for the detection of stimulus, relay of impulse and stimulation of response. Allow for rapid changes in an organisms internal and external environment.
in a neurones resting state the outside of the membrane is positively charged compared to the inside due to there being more positive ions outside the cell. this makes the membrane polarised where the resting voltage is -70mV.
the resting potential is created and maintained by the sodium potassium pump and potassium ion channels.
the sodium potassium pump uses active transport to move three sodium ions out the neurone for every two potassium ions moved in (ATP required). because the membrane of the neurone isnt permeable the sodium ions cannot diffuse back in creating a electrochemical gradient. the sodium potassium pump also move potassium ions into the neurone.
potassium ion channels allows facilitated diffusion of potassium ions put of the neurone down their concentration gradient. when the cells at rest most the k+ channels are open meaning the membrane is permeable so some potassium ions may diffuse back out through the channels.
When a neurone is stimulated sodium ion channels open allowing for a rapid change in potential difference causing the membrane to become depolarised - this sequence is known as an action potential.
A stimulus excites the neutrons cell membrane opening the sodium ion channels increasing sodium permeability. Sodium ions are able to diffuse into the neurone down the electrochemical gradient making the inside of the neurone less negative
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
all or nothing principle is once a threshold is reach an action potential will always fire the same change in voltage, iff threshold isn’t reached then action potential won’t fire. Bugger stimulus don’t cause bigger action potential but instead causing them to fire more frequently
speed of conduction if affected by three different factors
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
synaptic transmission involves synapses, synaptic clefts, pre & post synaptic neurones and synaptic vesicles
when an action potential reaches the end of a neurone it causes neurotransmitters to be released into the synaptic cleft. they diffuse across to the post synaptic neurone to bind to specific receptors where they trigger another action potential which may cause a muscle contraction.
these impulses are in-directional as receptors are only available on the post synapctic neurone, meaning they are only available to travel in one direction
Cholinergic synapses are synapses that use Acetylcholine as their neurotransmitter. They're an important kind of synapse because they are so widespread in the body, passing on signals to muscle cells in all neuromuscular junctions.
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
neurotransmitters can be excretory or inhibitory. acetylcholine is a excitatory neurotransmitter as it depolarises the postsynaptic membrane making it it fire an action potential. GABA is an inhibitory neurotransmitter as it hyper polarise the postsynaptic neurone preventing it from firing a 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.
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.
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
there are 3 types of muscle. 1) smooth - contracts without conscious control 2) cardiac - contracts without conscious control in the heart ONLY 3) skeletal - type of muscle you move
Skeletal muscles are the most abundant tissue forum in the human body. More than 40% or our body is made up of skeletal muscles.
skeletal muscle attaches to the bones by tendons and appears stripy under a microscope. Skeletal muscles contract and relax to move bones at a joint. the bones of skeletons are incompressible and act as levers giving something for the muscle to pull against
muscles that work together in pairs are called antagonistic pairs. the contracting muscle is the agonist and the relaxing muscle is the antagonist. an example of this is the biceps and triceps. as your biceps contracts the triceps relax
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.
Muscle contraction involves myosin and actin filaments sliding over one another
myosin filaments have globular heads that are hinged so they can move back and fourth. the head contains a binding site for both actin and ATP
actin filaments have binding sites for myosin heads to form actin myosin sites. the protein tropomyosin is found between actin filaments allowing the myofilaments to slide over one another
when muscles are relaxing the actin myosin binding site is blocked by the protein tropomyosin. this means the myofilaments cant slide past each-other as the myosin heads cant bind to the actin filaments
A nerve impulse (action potential) arrives at the neuromuscular junction and depolarises the sarcolemma via the t tubules. Calcium ions (Ca2+) are released from the sarcoplasmic reticulum and diffuse across the sarcoplasmic reticulum into the muscle fibres triggering a muscle contraction. Calcium ions bind to tropopin (changing its shape), pulling the attached tropomyosin, exposing the myosin binding sites on the actin. Myosin head binds with the actin filaments, forming cross-bridges actin myosin cross bridge
calcium ions activate ATP on the myosin head which breaks down into ADP + Pi, providing energy needed for muscle contraction. Myosin head nods forward pulling the actin towards the centre of the sarcomere. another An ATP molecule binds to the myosin head, breaking the cross-bridge, the myosin head detaches from the actin filament. the myosin head then returns to its starting position at a different binding site further down the filament where a new cross bridge is formed and the cycle repeats
return to resting involves calcium ions moving back into the sarcoplasmic reticulum by active transport. The troponin molecules move back to their original shape and the tropomyosin blocks the actin binding sites. So the myofilaments cannot slide past each other because the myosin heads cannot bind to the actin. The actin filaments slide back to their relaxed position, lengthening the sarcomeres.
energy for muscle contraction is achieved in three ways, aerobic respiration. anaerobic respiration and PCr system
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