okay let's talk about nicotinic cholinergic receptors and answer the questions what are nicotinic receptors what are the two types of nicotinic receptors and what are the locations and functions of nicotinic receptors hello everyone my name is dr morton and i am the noted anatomist so what are cholinergic receptors well they're receptors that bind acetylcholine and there are two types nicotinic and muscarinic and we're going to focus on nicotinic receptors today now what are nicotinic receptors well they are ligand-gated ion channels ligand-gated because this term ligand is a molecule that binds to another molecule and early physiologists found that tobacco plants produced a molecule named nicotine and when put inside the body binds to a receptor and so early physiologists said well what do we call this receptor that nicotine binds and they said we'll call it a nicotinic receptor we found also that in normal physiology there was another molecule the very first neurotransmitter discovered that's called acetylcholine and acetylcholine also binds to this nicotinic receptor and it's called a so an acetyl colon acts as ligand it's called ligand-gated because when acetylcholine binds the nicotinic receptor opens like a gate it's called the ligand-gated ion channel because the ion sodium is in high concentration outside the cell so when a so when acetylcholine binds to the nicotinic receptor the gate opens and sodium goes from a high to a low concentration and rushes into the cell and this influx of positively charged ions causes a depolarization and excitation of the membrane and initiates an action potential ligand-gated ion channels there are two types of nicotinic receptors n m and n n and n because the letter m represents the location of this receptor which is in skeletal muscle and n because its location is on neurons as well as the adrenal medulla so let's start talking about the nm first they're located on the sarcolemma of a skeletal muscle fiber within the neuromuscular junction and when stimulated nm depolarizes the membrane and results in muscular contraction here's a motor neuron that's going to release acetylcholine there is a skeletal muscle specifically the could be the biceps or any muscle actually which possesses nm receptors and the space in between is called the synaptic cleft or the neuromuscular junction when the motor neuron releases acetylcholine and acetylcholine binds to the nm receptor the muscle contracts so stimulating nm results in muscle contraction and where do we find these nicotinic m receptors anywhere we have skeletal muscle from the frontalis to your extensor digitorum longus in this cross section of the spinal cord we see a somatic or lower motor neuron that's going to release acetylcholine into the neuromuscular junction and binds to the nicotinic receptor so let's now take the schematic and go into a little bit more detail there's the terminal axon for a somatic lower motor neuron and it's going to release acetylcholine and there's the side of a skeletal muscle cell and the synapse is the space in between also called the neuromuscular junction and in the synapse we find acetylcholine released by the terminal axon and an acetylcholine receptor or cholinergic receptor and in skeletal muscle specifically it is an n m receptor and when stimulated opens a gate and sodium rushes in depolarizing the sarcolemma the action potential spreads down the t tubule which then causes the sarcoplasmic reticulum to release calcium which binds to troponin and results in muscle contraction so a clinical correlation is the following here's a motor neuron with acetylcholine and a skeletal muscle fiber with a nicotinic muscle receptor and the condition is called myasthenia gravis which is an autoimmune disease where antibodies block or destroy the nicotinic muscle receptors so when a motor neuron releases acetylcholine the acetylcholine cannot bind to the nm receptors and as a result the depolarization of that motor end plate is hindered or completely stopped and results in muscle weakness and ultimately paralysis okay next we're going to talk about the nnn receptors and they're found in all peripheral autonomic nervous system ganglia so nnn receptors another way of saying this is they're found on the dendrites of the postganglionic sympathetic and parasympathetic neurons so there's a preganglionic autonomic nervous system neuron which will release acetylcholine there is a postganglionic autonomic nervous system cell body and you put them all together and it makes an autonomic ganglion and those dendrites possess a nicotinic n receptor and the space in between is a synaptic clef and when acetylcholine binds to that nicotinic end receptor it the ach is a ligand the gate opens sodium rushes in depolarizes the membrane and the action potential continues down the neuron so stimulation of nnn results in a continuation of the action potential so where is the locations of these nnn receptors well sympathetic ganglia like the sympathetic chain or pre-aortic ganglia like the celiac and inferior mesenteric ganglia or cranial nerve parasympathetic ganglia like pterygopalatine and submandibular ganglia or intramural ganglia like in the wall of an organ so there's the jejunum and if we zoom in and in and there's our box plexus that's where we find nnn receptors so nnn receptors are on all peripheral autonomic nervous system ganglia including the adrenal medulla so in this schematic we see a preganglionic sympathetic neuron synapsing in the adrenal gland specifically chromafin cells in the adrenal medulla so if we zoom in on that we see the preganglionic sympathetic neuron release acetylcholine that binds to a nicotinic n receptor on these chromophen cells which secrete a catecholamine like epinephrine into the blood stimulating nnn on the chromophant cells results in secretion of epinephrine now nnn receptors are located all throughout the central nervous system all throughout the brain so much so that it's too much to cover in this tutorial in conclusion there's a somatic motor neuron sympathetic pathways and parasympathetic pathways and m receptors are found on the sarcolemma within the neuromuscular junction and n receptors are found in the dendrites of postganglionic neurons in autonomic nervous system ganglia including chromaffin cells in the adrenal medulla and that my friends is a little overview of nicotinic cholinergic receptors in a nutshell [Music] um [Music] dude [Music] you