2 3 17 Synaptic Plasticity 35 mins Facilitation Potentiation stim for a longer period of time duplicates result o residual Ca build up Depression first input the largest then it goes down Short in time like facilitation but opposite Long term Potentiation minutes to days Long term Depression minutes to days 2 8 17 Skeletal Muscle Synapses Sound localization Circuit example used by vertebrates for sound localization Lines represent peak of sound pressure Sound sources coming in from If sound is straight ahead sound waves right means it will activated at the same time hit right ear before left Only if 2 EPSPs arrive at the same time do they sum to reach threshold More sound from right ear then Neuron A will be the only one to sum inputs and reach threshold and neuron will fire So more sound from the right means more neurons from the left will fire o From left E will be the only one to fire Unbelievably efficienct this circuit is able to break up that 1 s difference into 45 seconds can detect 1 45 of a second Frequency is coded as position of the long membrane such that for given frequency you get a maximal vibration of that membrane the hair cell sits There s other mechanisms to tune up frequency sensitivity That frequency sensitivity projects itself onto nucleus so that s there s not just one array but thousands in parallel Each network is very systematically varied in frequency from the one in front and behind it With distance through the nucleus log There s not just one place encoding circuit but there is many of them tuned to a particular frequency and sounds The outputs of these five neurons go up to another brain center and composition of the sound How much power is in each band of frequency Skeletal Muscle Contraction is interaction between cross bridges interacting with thin filaments Cross bridge Cycling Neck head of myosin molecule Arbitrary how many steps there are Cross bridges purple Shaft Binding sites of actin Accessory proteins that attach myosin When a prt binds something it could change the conformation of protein n a conformational way 1 Myosin head is bound to Actin monomer 1 When the myosin head has nothing bound to it it has high affinity to bind actin When it binds actin the angle head is 45 If all cross bridges are in that state the muscle is in rigor 2 ATP binds to myosin head and myosin entirely loses its binding affinity to actin head detaches a RATE LIMITING STEP 3 Myosin head has ATPase and will hydrolyze it to ADP and P i a Step 3 4 is Ca dependent 4 The hydrolyzed ATP causes a conformational change in neck and myosin head has 90 angle gives precise distance between actin so myosin binds weakly to actin 2 a little more strongly than in step 2 5 The myosin binding to actin lowers the affinity for myosin holding onto P i so its released Power stroke where myosin slides over actin 6 Release of ADP rigor state again 2 types of schwann cells one myelinates axons other sit on top of nerve terminal Blue neural terminal Mitochondria and synaptic vesicles filled with Ach at crests of folds are nAChR nicotinic Ach receptor Inward current causes large EPSP aka Endplate Potential Excitation and Contraction coupling T tubules SR blue smooth ER of muscle 2 10 17 T tubule is continuous with the plasma membrane the lumen is continuous with the extracellular space V gated Cl K channels are in the t tubule membranes of animals Na channels in plasma membrane are not uniformly distributed but concentrates in rings around t tubule openings High concentration of Na channels Acts as current amplifier More inward current by T tubules Action potential going down fiber also go deep into fiber radially Triad Junction SR t tubule SR SR double walled membrane structure Wraps around each segment of muscle fiber Ring of t tubule in every sarcomere Lumen of SR is where a is sequestered Yellow t tubule Ca pumps or SERCA or ryanodine receptor Dihydropyridine receptor acts like Ca channel just V sensor undergoes structural change when membrane depolarizes Ca release channel has lost V sensitivty Ca comes out when open The two are linked through proteins Dihydropyrdine yanks the proteins and opens the Ca channel For every AP a burst of Ca comes out The rise in Ca is brief because Ca pumps constantly working to pump Ca back in 2 Ca buffering proteins in cytoplasm porvalbumin calmodulin Troponin tropomyosin regulated contraction through Ca Troponin complex has 3 types Troponin C Ca binds and moves troponin I out of the way to expose site to actin Troponin T binds to myosin Troponin I inhibits binds to actin blocks binding site on actin shifts over when TnC binds Ca Diagnositic tool ammunoassay for cardiac troponin is a standard test for cardiac infarction Troponin found in blood sign of muscle tissue dead Isometric contraction constant length If you stimulate short muscle you won t get much force as you stretch you get more and more force Overstretch it will fall off Muscle generates force by having overlap between thick and thin filaments A muscle contracts the muscle fibers generate force contraction with shortening or if too heavy will When the muscle contract against a heavy load Force length relationship curve L0 length at which you get maximal force at isometric contraction Upside down U shaped curve Muscles increase in size but sarcomeres are the same length When in resting position the average sarcomere length is at zero no matter the age Therefore sarcomeres must be added throughout growth to maintain this Load force No force no velocity Isometric contraction when force muscle is generating is the same as the load being opposed by the exact same force Lengthening is a negative change in When you contract a muscle and it shortens concentric elongates eccentric Properties Used to Classify Muscle Fibers 1 Whether ion channels in sarcolemma allow action potentials all or none twitch or not graded or tonic contractions Twitch 2 Rate of cross bridge detachment during contraction related to ATPase activity of myosin isoform Determines V0 How fast can the muscle build up force 3 Number of Ca2 pumps in SR determines rate of relaxation Shorter the Ca 4 Number of mitochondria and capillary density which determine capacity for oxidative phosphorylation and fatigue resistance Metabolic mechanisms 2 determines velocity of shortening and 3 determines rate of relaxation together determine twitch duration 2 13 17 Smooth Muscle Twitch fibers Humans have mostly 1 2S Type IS more active slow twitch