Armondo hysteria and biology and medicine videos please make sure to subscribe join the forum and group for the latest videos please visit Facebook and once again please like and here you can also ask questions answer questions and please pose some interesting things including artworks and you can also change the quality settings to the highest one for better graphics and in this video we're going to let skeletal muscle contraction and so with this we begin with the neuron in nerve cell and this neuron is specifically what's called a somatic neuron and here we have a muscle fiber from a muscle and so a skeletal muscle will contract only when stimulated by a somatic motor neuron and so if we have a signal here that comes towards neuron this will this can cause the muscle fiber to contract now a somatic motor neuron can innervate between 3 - up to 1,000 muscle fibres and so when a neuron the neurons nerve fibers - next to a muscle fiber this is this complex is what we call a motor unit so it's where we have a nerve fiber and a muscle fiber so if you remember what a muscle fiber is if we have a bone here with a muscle attaching on it we have the tendon which attaches to the month up to the bone and here we have the actual muscle now the muscle contains many structures within it portions of the muscle known as fascicles and these fascicles then contain many muscle fibers and so here is where our muscle fiber is so now let's zoom into one motor unit here and see what kind of structures are around in the muscle fiber and also the end of this neuron that assists that assists in muscle contraction and so here we have the end bulb the axon terminal of the motor neuron and the axon terminal of the motor neuron the end bulb has many vesicles here and these vesicles contain your transmitters known as a seal choline so now we'll just stop there for now and look at the muscle fibers and so here we have a muscle fiber one muscle fiber and the muscle fiber contains many myofibrils so here we have the myofibrils and around this area within the muscle fiber we have also mitochondria which can provide ATP and we also have the many nucleus around the muscle fiber because the muscle fiber is multi nucleated the muscle fiber has a membrane called the sacral lemma which contains many receptors and ion channels now let's stop there for a bit and look specifically at the myofibrils so if you remember the myofibrils contain thin and thick filaments here in blue is a thin filament and red the thick filaments from one z line to another z line of the thin filaments is what we call a sarcomere and so we have this within each myofibril however in each myofibril you can say we also have what's called the t-tubule which runs around the myofibril and the t tubules surrounding it we have what's called a sacra plasmic reticulum abbreviated SR and these sacrificing reticulum contain calcium ions a closer look at the teacher teacher Byul because a teachable has an important role in skeletal muscle contraction the teacher bill essentially connects with the outer membrane and wraps around the myofibril and the teacher will contain special ion channels for calcium here showing orange surrounding the Cheechoo bill we have the sacral plasmic reticulum which contains calcium ions so surrounding it here we have the sacrifice reticulum specifically our what's called the terminal cistern cysts is turning which is part of the sequence of psycho plasma ticular and the terminal cisternae contains these calcium ions but these calcium ions they cannot go into the t-tubule because the ion channels the calcium ion channels are blocked and therefore they need to be opened for calcium to come out and here of course um beneath this teacher Buell or or within the myofibril we have the thin filaments and thick filaments and the thin filaments requires calcium in order to initiate muscle contraction but remember the calcium are still within the sacral plasmic reticulum so how do these calcium ions come out well let's have a look let's begin at the neuron the neurons involve the axon terminal where an action potential has arrived this action potential will cause these vesicles containing a silk Colleen to release acetylcholine at these acetylcholine will then bind up to the receptors in the sacral Emma let's have a closer look at this interaction between a silk : and the receptors in the sacral Emma so here we have the n-bomb the axon terminal of the motor neuron and here we have a vesicle containing acetylcholine here is our receptor for a silk calling on the sacral Emma a point to make which is pretty important is out outside in the extracellular fluid we have high concentrations of sodium and within the muscle the within them sacra inside the cell we have higher concentrations of potassium ions so what happens is when the vesicle containing a sealed choline releases acetylcholine out these are sealed colons will then bind onto this receptor which will cause the receptor to open when this receptor opens sodium ions can then come inside and when sodium comes inside this will open the voltage-gated channels which will then create an action potential these action potentials will then travel across the sacral mo where the action potential can then propagate down the cheap tea tube you'll when the action potential travels down the t-tubule it will cause these calcium ion channels which were previously closed to open up and it opens up because there's a change in voltage in the t-tubule which will cause the calcium channels to open and so when these calcium channels open calcium will then move out from the terminal cistern into the t-tubule will travel down and essentially go and bind onto the thin filaments and so essentially calcium and also ATP will help with muscle contraction and to understand how they help in muscle construction please click on the link for the sliding filament theory which will look at the contraction at a molecular level at a sarcomere level please like comment and subscribe and share