Your SlideShare is downloading. ×
Cell Physiology: Synaptic Transmission
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Introducing the official SlideShare app

Stunning, full-screen experience for iPhone and Android

Text the download link to your phone

Standard text messaging rates apply

Cell Physiology: Synaptic Transmission

1,710
views

Published on

Part Two of Cell Physiology

Part Two of Cell Physiology

Published in: Education

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
1,710
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
62
Comments
0
Likes
1
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Cell PhysiologyCell Physiology Neuromuscular and Synaptic Transmission,Neuromuscular and Synaptic Transmission, Skeletal Muscle, Smooth MuscleSkeletal Muscle, Smooth Muscle Lectured by Bien Eli Nillos, MDLectured by Bien Eli Nillos, MD
  • 2. Neuromuscular and SynapticNeuromuscular and Synaptic TransmissionTransmission  An action potential in the presynaptic cellAn action potential in the presynaptic cell causes depolarization of the presynapticcauses depolarization of the presynaptic terminalterminal  As a result of the depolarization, CalciumAs a result of the depolarization, Calcium enters the presynaptic terminal causingenters the presynaptic terminal causing release of neurotransmitter into therelease of neurotransmitter into the synaptic cleftsynaptic cleft
  • 3. SYNAPSE Presynaptic cell Postsynaptic cell Synaptic cleft
  • 4.  Neurotransmitter diffuses across theNeurotransmitter diffuses across the synaptic cleft and combines with receptorssynaptic cleft and combines with receptors on the postsynaptic cell membraneon the postsynaptic cell membrane  Cause change in its permeability to ionsCause change in its permeability to ions and a change in its membrane potentialand a change in its membrane potential
  • 5. SYNAPSE Presynaptic cell Postsynaptic cell
  • 6. Neuromuscular JunctionNeuromuscular Junction  Synapse between axons of motor neuronsSynapse between axons of motor neurons and skeletal muscleand skeletal muscle  Acetylcholine – neurotransmitter releasedAcetylcholine – neurotransmitter released from the presynaptic terminalfrom the presynaptic terminal  Nicotinic receptor – found at theNicotinic receptor – found at the postsynaptic terminal, specific for Achpostsynaptic terminal, specific for Ach  Choline acetyltransferase – catalyzes theCholine acetyltransferase – catalyzes the formation of Ach from acetyl coenzyme Aformation of Ach from acetyl coenzyme A and choline in the presynaptic terminal.and choline in the presynaptic terminal.
  • 7.  Depolarization of the presynaptic terminalDepolarization of the presynaptic terminal opens Calcium channels.opens Calcium channels.  Calcium uptake causes release of AchCalcium uptake causes release of Ach into the synaptic cleft.into the synaptic cleft.  The nicotinic Ach receptor is also a Na+The nicotinic Ach receptor is also a Na+ and K+ ion channel (e.g. ligand-gatedand K+ ion channel (e.g. ligand-gated channel)channel)  Because the channels opened by AchBecause the channels opened by Ach conduct both Na and K ions, theconduct both Na and K ions, the postsynaptic membrane potential ispostsynaptic membrane potential is depolarized.depolarized.
  • 8. SYNAPSE Presynaptic cell Postsynaptic cell Ca Ca + - ++ --
  • 9.  Once the end plate is depolarized, localOnce the end plate is depolarized, local currents cause depolarization and actioncurrents cause depolarization and action potentials in the adjacent muscle tissue.potentials in the adjacent muscle tissue.  Action potentials in the muscle areAction potentials in the muscle are followed by contraction.followed by contraction.  Ach is degraded to acetyl-CoA andAch is degraded to acetyl-CoA and choline bycholine by acetylcholinesteraseacetylcholinesterase on theon the muscle end plate.muscle end plate.
  • 10. SYNAPSE Presynaptic cell Postsynaptic cell Ca Ca + - ++ -- + + + - - - -
  • 11.  Myasthenia gravis – caused by antibodiesMyasthenia gravis – caused by antibodies to the ACh receptorsto the ACh receptors  Characterized by skeletal muscleCharacterized by skeletal muscle weakness and fatigability resulting from aweakness and fatigability resulting from a reduced number of ACh receptors on thereduced number of ACh receptors on the muscle end plate.muscle end plate.  Treatment with AChE inhibitors preventsTreatment with AChE inhibitors prevents the degradation of ACh and prolongs thethe degradation of ACh and prolongs the action of ACh at the muscle end plate.action of ACh at the muscle end plate.
  • 12. Summation at SynapsesSummation at Synapses  Spatial summation – occurs when twoSpatial summation – occurs when two excitatory inputs arrive at a postsynapticexcitatory inputs arrive at a postsynaptic neuron simultaneously. They produceneuron simultaneously. They produce greater depolarization.greater depolarization.  Temporal summation – occurs when twoTemporal summation – occurs when two excitatory inputs arrive at a postsynpaticexcitatory inputs arrive at a postsynpatic neurons in rapid succession; they add inneurons in rapid succession; they add in stepwise fashion.stepwise fashion.
  • 13. NeurotransmittersNeurotransmitters  NorepinephrineNorepinephrine  EpinephrineEpinephrine  DopamineDopamine  SerotoninSerotonin  HistamineHistamine  GlutamateGlutamate  GABAGABA  GlycineGlycine
  • 14. The Skeletal MuscleThe Skeletal Muscle  Skeletal muscles are composed ofSkeletal muscles are composed of masses of fibers, each an individual cell.masses of fibers, each an individual cell.  Muscles are composed of muscle fibers;Muscles are composed of muscle fibers; fibers are composed (in part) of myofibrils;fibers are composed (in part) of myofibrils; and myofibrils are composed ofand myofibrils are composed of myofilaments.myofilaments.
  • 15.  Each muscle fiber contains about 1000Each muscle fiber contains about 1000 myofibrils that are 1 m in diameter and runmyofibrils that are 1 m in diameter and run the length of the fiber.the length of the fiber.  Myofibrils have no membrane, beingMyofibrils have no membrane, being simply surrounded with cytoplasm.simply surrounded with cytoplasm.  The cross-striations of the myofibrils areThe cross-striations of the myofibrils are serially repeating units calledserially repeating units called sarcomeressarcomeres
  • 16.  A sarcomere is bounded on each end by aA sarcomere is bounded on each end by a disc, called thedisc, called the Z disc or Z lineZ disc or Z line..  Each sarcomere contains an anisotropicEach sarcomere contains an anisotropic (doubly refractive, therefore dark in phase(doubly refractive, therefore dark in phase microscopy) band bounded by twomicroscopy) band bounded by two isotropic (singly refractive, therefore light)isotropic (singly refractive, therefore light) bands. Thebands. The anisotropicanisotropic band is called theband is called the A bandA band; the; the isotropicisotropic bandband is called theis called the II band.band.
  • 17.  In the center of the A band, there is aIn the center of the A band, there is a lighter region known as the H zone orlighter region known as the H zone or HH band.band.  The myofibrils are composed ofThe myofibrils are composed of proteinaceous structures calledproteinaceous structures called myofilamentsmyofilaments..  These filaments are referred to as theThese filaments are referred to as the thickthick filaments andfilaments and thinthin filamentsfilaments
  • 18.  Thick filamentsThick filaments are made up of severalare made up of several hundredhundred myosinmyosin moleculesmolecules  myosin moleculemyosin molecule has ahas a tail regiontail region that isthat is rodlike, androdlike, and head regionhead region, with two globular, with two globular subunits projecting out at approximatelysubunits projecting out at approximately right angles with the filamentright angles with the filament
  • 19.  Note:Note: The thick filament is studded withThe thick filament is studded with projections except at its center, whichprojections except at its center, which contains only myosin tails. Note thatcontains only myosin tails. Note that myosin molecules at opposite ends of themyosin molecules at opposite ends of the thick filament are oriented in oppositethick filament are oriented in opposite directions–sort of like a bundle of unsorteddirections–sort of like a bundle of unsorted golf clubsgolf clubs
  • 20.  EachEach thin filamentthin filament contains three proteincontains three protein molecules:molecules: actin, troponin, andactin, troponin, and tropomyosintropomyosin
  • 21.  T tubule is anT tubule is an invagination of theinvagination of the muscle membrane,muscle membrane, forms a ring aroundforms a ring around every myofibril;every myofibril;  The position of the TThe position of the T tubule with respect totubule with respect to the sarcomere isthe sarcomere is somewhat speciessomewhat species specificspecific
  • 22.  TheThe sarcoplasmic reticulumsarcoplasmic reticulum isis made up of tubules that runmade up of tubules that run parallel to the sarcomeres fromparallel to the sarcomeres from T tubule to T tubuleT tubule to T tubule  The sarcoplasmic reticulum is aThe sarcoplasmic reticulum is a sack with its ends expandedsack with its ends expanded (the(the cisternaecisternae) adjacent to the) adjacent to the T tubules and with narrow,T tubules and with narrow, longitudinal channelslongitudinal channels connecting these expansions,connecting these expansions, one at each endone at each end
  • 23. The Sliding Filament TheoryThe Sliding Filament Theory Step 1: ACh released from presynaptic cleftStep 1: ACh released from presynaptic cleft Step 2: Muscle cell (postsynaptic) isStep 2: Muscle cell (postsynaptic) is depolarizeddepolarized Step 3: Depolarization propagates to theStep 3: Depolarization propagates to the Transverse TubuleTransverse Tubule Step 4: Depolarized T-tubules triggerStep 4: Depolarized T-tubules trigger release of Calcium from sarcoplasmicrelease of Calcium from sarcoplasmic reticulumreticulum
  • 24.  Step 5: calcium binds to troponin, the positionsStep 5: calcium binds to troponin, the positions of troponin and tropomyosin are altered on theof troponin and tropomyosin are altered on the the thin flament and myosin then has access tothe thin flament and myosin then has access to its binding site on actinits binding site on actin  Step 6: Myosin hydolyzes ATP and undergoes aStep 6: Myosin hydolyzes ATP and undergoes a conformational change into a high-energy state.conformational change into a high-energy state. The head group of myosin binds to actin formingThe head group of myosin binds to actin forming a cross-bridge between the thick and thina cross-bridge between the thick and thin filaments.filaments.  Step 7: The resulting relaxation of the myosinStep 7: The resulting relaxation of the myosin molecule entails rotation of the globular head,molecule entails rotation of the globular head, which induces longitudinal sliding of thewhich induces longitudinal sliding of the filaments.filaments.
  • 25.  Step 7: The energy stored by myosin isStep 7: The energy stored by myosin is released, and ADP and inorganicreleased, and ADP and inorganic phosphate dissociate from myosinphosphate dissociate from myosin  Step 8: When the calcium level decreases,Step 8: When the calcium level decreases, troponin locks tropomyosin in the blockingtroponin locks tropomyosin in the blocking position and the thin filament slides backposition and the thin filament slides back to the resting state.to the resting state.
  • 26. ENDEND