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1 General Information about the brain : 1-The brain is considered as one of the most complex structures in the whole body, it contains hundred billions ( thousand of millions) neurons cells only,and if we have this no. multiplied by 3 we ll get the no. of supporting cells like glayl cells, oligodendrocyte, extracyte etc. 2- The brain weighs 2% of the body weight. And it utilizes 20% of the total energy expenditure. So you can imagine this small area of our body. this huge amount of cells.!! 3- acting to the complexity each neuron receives an average about ( ) information( input). Its such a huge amount of information s and this make it one of the most complex ever structure in the body. each neuron give only a single axon (output) that does not indicate that we give a single output. on the contrary, the output will branch, the axon will branch and also we came to so many cells How many languages(electrical signal) does the brain has? we have a very sophisticate brain, everything is going direct toward it, we are the most sophisticated creature on earth. In fact the brain is also bilingual : one of the major languages that the neural tissue communicate between each other is (action potential) nerve impulse-, the other one is the electro tonic graded potential. This discovery language of brain- is very important. from all of these scientist (physiology scientist ) take the Nobel prize because of action potential and graded potential researches, in 2000 they talk about mind reading : they can know any function, how the person talk,move, control himself, save his memory, how he think and solve problem. they win the Nobel prize in ( we will take it in 3 rd year ) Nobel prize given for 1- new discovery and 2- help patient to recover Sheet #12 Page 1

2 Action potential : The importance of action potential : 1- there is a lot of drugs that discovered and helped a lot of patients, the 1 st one is any chemical substance that end with caine, like lignocaine, procaine, xylocain, lidocaine and they are all act as local anesthesia. when you go to the dentist or when you have injured in a car accident as example. If they did not know about depolarization and the neurotransmission by the opening and voltage gated channels they cannot made the lignocaine, which block the Na voltage channel and prevent the transmission (this is the main function for the local anesthesia). If the injury was in the hand and I put local anesthesia, there will be a pain, but it will not reach the action potential so it will not go to the brain and the person will not feel the pain. and it s the same with your teeth and CPR when the heart is going to stop we will give him direct injection of local anesthesia in the heart, so I will reduce the heart rate and save the patient. 2- If I know the normal then I can diagnose the abnormal : when we do the EBG(electrical brain graph), ENG(Electroneurography),EMG(electromyography) we know the abnormal condition like cut in the nerve, paralysis of the muscle by recognize them from the normal. so we must know the normal. )ملخص( because: So the action potential is important 1- discovery of action potential has helped of diagnosis of so many disordered that is related to pathology in the brain, in the spinal cord and peripheral nerves in the muscles. 2- so many discovery of the drugs that work to block or enhance the channels that initiate action potential and that help thousands and thousands of people to recover. -action potential is the base to understand the physiology of many functions in the body. Sheet #12 Page 2

3 We have 4 different channels : (and their function ) 1- leakage channels : it open and close spontaneously like K+ which very abundant with less abundant Na+ channels, its responsible about resting membrane potential ( RMP). 2- voltage gated channel : change in the voltage of membrane, we have a very fast Na+ gated channel and the slow k+ gated channel, it s responsible of action potential (AP). there is activation and inactivation (we must know about them from previous lectures). 3- legend gated : on the opening gate there is a receptor for chemical substance like Acetylcholine, dopamine etc. it must sit (bind)on the gate, so the gate will open and ions will enter, and this is one of properties of the synapses and neuromuscular junction. 4- mechanically - gated channels : you distorted mechanically certain type of channels that will lead to opening or closing. Notes: 1- depolarization : Na+ influx 2- repolarization : K+ efflux Any word that end with caine (local anesthesia) its block the Na+ channels,the voltage gated type. its help in make the pain less and in healing. When I transmit the information like smell, vision, hearing and all the somatic sensation,which one of these sensation (where they special or somatic) need to be transmitted to the brain as fast as possible unless the body will suffer certain damage?? -The fastest type of nerve fiber will transmit the info in 120 m/s (it will reach the brain in friction of a sec. ) and the slowest fiber will transmit the info in 0.5 m/s. -The proprioception is the most important and the fastest info that can reach the brain in 120m/s, and it s the main reason for balance and equilibrium, reaction الفعل( )رده info move to the brain by 70m/s, the pain is one from the slowest info that reach the brain. -To reach the best conduction velocity to move the action potential as fast as we can which is 120m/s we increased the diameter of nerve and myelination!! Sheet #12 Page 3

4 - The 1 st time we record the action potential was in the squid and it has a large nerve 0.8 millimeter in diameter and sometimes reach 1 millimeter in big squid. but as a human we don t have this big diameter in our nerves, we don t have a signal nerve fiber alone,we have a 100s and 1000s of nerve fibers, some of them are large and some of them are small, some myelinated and some unmyelinated, some carry sensation and some carry motor activity. -So if we want to make them bigger we need a nerve with the size of the hand!!! and our body will be huge!!! So we must do myelination, note: unmyelinated(actually they are partially myelinated fibers ). The difference between myelinated and unmyelinated (Again; partially myelinated in fact ) nerve fibers: (for more info see Guyton the 12 th edition, p67- and lock to the slides) -There is no nerve fiber can move without myelination -the unmyelinated fibers is partially incomplete myelination, so there is no any nerve fiber can do his work without myelination. the only difference between them that is one layer is not complete --The different between myelination in the brain and in the peripheral : They are millions of axons of neurons and it must be covered (myelinated), the Schwann cells are found only in the body (peripheral nerves), in CNS we will see other type of cells known as oligodendrocyte its large and responsible in myelinating the axon. )ملخص(, body -So, we have different types of nerve fiber on our 1- there is very large in diameter heavily myelinated and its mainly for the equilibrium and balance and proprioception, its velocity is 120 m/s 2- and we have less diameter and less myelination until we reach to a partially myelinated (unmyelinated) they are slow and response for pain like abdominal pain which velocity is 0.5 m/s. The superficial pain is faster than the abdominal pain (cut your self, burns etc) is about m/s. Sheet #12 Page 4

5 In unmyelinated: June 27, 2012 [PHYSIOLOGY SHEET # 12] When the axon hillok decide to generate the action potential this happen step by step, each point will excite the next point, and for that the unmyelinated fiber there still conduction In myelinated: The Schwann cells have raping the axon until there is a gap between each cell and the other (nodes of Ranvier), for that, action potential will jump from one node of Ranvier to the other, so jumping make it much faster for the conduction of action potential, in addition usually heavy myelinated (large diameter- less internal resistance ) so the flow of ions is faster and the action potential will be faster. Why when you have myelinated fiber there is no point to point excitation and vice versa?? the action potential is a criteria of cell membrane, under the myeline there is cell membrane, so what make the action potential jump from node to another node? the Na+ pump under the myelined is few in number and the ions are freely movement in liquids, the Na+ enter the point that had the depolarization and that will effect the whole Na+ channels, but because of its few number under the Schwann cells (myeline) there is no action potential because it will not reach the threshold, so when it reach the node or Ranvier, thousands of Na+ pumps will open depolarization and threshold will reached so action potential will happend and so on. so there is jumping from one node to the other by passing all the myelinated period and for that there is faster production. When we talk about unmyelinated, distribution of Na+ channels equal, so the stimulation will be step by step. - In conclusion If we want to know how does the action potential work in one motor neuron, there is always stimulation or decision by the soma that action potential must be fired, once its fired it will propagates regenerated at a very same amplitude without need of any external form of energy, like dominoes. you just hit the first piece. the same at action potential, it needs only a stimulis enough to reach and fired the action potential then it will be spontaneous. and it will reach to the destination. Sheet #12 Page 5

6 Note:: action potential is a regenerative process. -If there is action potential (spreading along the axon of a neuron for example) and there is leakage of sodium,, there is leak to backward or no???? ((ya3ne 2el Sodium betwaza3 forward only wela forward and backward))?? The leak will be forward and backward..but Why there is no action potential in the backward region(it doesn t have an effect)?? Because this region is in the refractory period ((membrane resists any 2 nd stimulus))..((فترة الممانعه)) Refractory period divided into two parts:: 1. Absolute complete :: depolarization and the first one third of the repolarization. No matter how powerful you give a second stimuli will never be able record a second action potential. 2.Relative Refractory period: which involves the last two third of repolarization. If I stimulate with more powerful stimuli It will be able to initiate to second action potential. ** Why we have absolute in this period and why we have relative in the other period?? ((3al rasmeh 2eli bl slide!!!)) When we are in the process of depolarization and the beginning of repolarization.. the majority of the sodium channels are either opened or in the process of an inactivation that cause no matter how much you increase the stimuli will never find the freshly sodium channels that can open in response to your stimuli. When we come to the relative refractory period channels that has opened to begin depolarization has been inactivated and closed and ready to be opened but only when you give very strong stimuli. So the relative refractory period depend on the strength of stimuli. Its happened just with only Na channels,without K channels. -Look at the diaphragm!! Sheet #12 Page 6

7 Look at the slide that talk about action potential ( very important one)!!! Action potential (nerve impulse) : Regenerative Threshold Move along the axon Voltage gated channels Propagates All or none Amplitude above 100 mv Short duration Depolarizing then repolarizing Refectory period No summation Function: Carry info faithfully uncharged from one end of neuron to other, without decrement and in a pulse code Epilepsy: epilepsy compulsion in the brain) fit excessive action potential ( excessive discharge of old neurons because of = 1. Increase the temperature 2. Hypoxia 3. Myocardial infraction Sheet #12 Page 7

8 epilepsy:: excessive activation of the brain that cause intense stimulation to the muscles and the patient will be like a wood piece or like the bridge and the breathing is stopped because the respiratory muscle contracted without relaxation and the patient become bluish. Note:1- tonic phase:: too much contraction of the muscle. In the 2-Clonic phase (( contraction relaxation)): in this stage the patient can take breath. and this stage take about 1 min..((7akat 2eno synapse in the brain btet3ab 3shan heeek bt9eer hay 2el mar7aleh w 3ashan ma ymoot bsabab 2en8e6a3 2el oxygen in the first step,, because there is no breathing in the previous stage). The patient might be urinated, defecate and throw from the mouth (vomit) he might bite his tongue. Once piece of advice:: If you happen to see a patient with epilepsy in the market, university, or even hospital, we can t do anything for the patient. One common mistake that young physician do that they enter their hands into the mouth of the patient. Because when you enter your hand into his mouth in the clonic phase the patient will bite your fingers and break your bones and you will handicapped yourself. The only thing we can do : bring a pipe made from iron (not wood) covered by cloth and enters it (in mouth) then we convert it to open the cavities and the air way passages Hypocalcaemia Extracellular:: cause epilepsy **** why when we have low of calcium outside,it lead to cause epilepsy?? Sodium carry one positive charge and it is small,, but calcium carry two positive charge and its large.. that mean only needed percentage of sodium can enter and cause action potential =this occur in the normal case and normal level of calcium.. But when we have calcium much less than normal.. that allows sodium to enter with a huge percentage and cause 1000 action potential instead of 1 action potential that cause epilepsy. Note:: Hypercalcaemia = cause paralysis Sheet #12 Page 8

9 Lucture 2 Quick review AP Action potintial (5 major The Brain (3 major languages of the body (2 language) Def. + some info epilepsy (3 casues (3 phases (2 phases) Importance of AP (2 + review Channels(4 pumps) as fast as the info reach the brain (5 difference between myelinated & unmylinated how AP work in one motor neuron (4 AP slide (2major Refractory period (2 types) Am sry if there is any mistakes in the sheet,,,, hope the best to all of u :D Salameh AlHabashneh Sheet #12 Page 9