NEUROMUSCULAR JUNCTION.ppt
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The neuromuscular junction is where a motor neuron synapses with a muscle fiber. When an action potential reaches the motor neuron terminus, acetylcholine is released into the synaptic cleft, binding to nicotinic receptors on the muscle fiber and triggering an end plate potential that generates an action potential if it exceeds threshold. Electrical stimulation can target different tissue types by manipulating parameters like phase duration and pulse frequency. It is used to induce motor contractions, control pain and edema, and enhance fracture healing. Precautions must be taken with certain health conditions and implant locations.
NEUROMUSCULAR JUNCTION.ppt
- 1. NEUROMUSCULAR JUNCTION AND EFFECT OF ELECTRICAL STIMULATION ON NERVES SYED MASOOD
- 2. NEUROMUSCULAR JUNCTION It is a junction between the terminal branch of the nerve fiber and muscle fiber. The membrane of nerve is called presynaptic membrane. The membrane of muscle fiber is called postsynaptic membrane. Space between two is called synaptic cleft.
- 5. THE NEUROMUSCULAR JUNCTION • Arrival of an action potential at the terminus of a presynaptic motor neuron induces opening of voltage-gated Ca2+ channels • subsequent release of acetylcholine, which triggers opening of the ligand-gated nicotinic receptors in the muscle plasma membrane • The resulting influx of Na+ produces a localized depolarization of the membrane • leading to opening of voltage-gated Na+ channels and generation of an action potential * * *
- 6. ACETYLCHOLINE – GENERAL INFO • Motor neuron transmitter at the neuromusccular junction (NMJ) in vertebrates • Present in brain (10% of synapses) • Packaged in high numbers in vesicles 1,000 to 10,000 molecules per vesicle at the NMJ • Like all small chemical transmitters Ach is synthesized and packaged into vesicles in the synapse • The NMJ pre-synaptic side is packed full of vesicles in the axon terminal • Many vesicles are released per action potential to ensure a large safety margin so that the muscle fiber (i.e. the postsynaptic cell) will depolarize to beyond threshold.
- 7. ACETYLCHOLINE – RECEPTOR • Officially called the nicotinic ACH receptor (nAChR) because nicotine binds to this receptor and activates it • ligand gated ion channel • has a depolarizing effect because Na+ is the dominant ion through these channels
- 8. ACETYLCHOLINE – RECEPTOR • generates an excitatory postsynaptic potential which at the NMJ (motor end plate) is often called an "end plate potential“
- 9. EPP - END PLATE POTENTIAL Aka Excitatory Junctional Potential (EJP) End plate potentials (EPPs) evoked by stimulation of a motor neuron are normally above threshold and therefore produce an action potential in the postsynaptic muscle cell.
- 10. POSTSYNAPTIC MEMBRANES AND ION CHANNELS Ligand gated ion channels – a review a. Resting K+ channels: responsible for generating the resting potential across the membrane b. Voltage- gated channels: responsible for propagating action potentials along the axonal membrane Two types of ion channels in dendrites and cell bodies are responsible for generating electric signals in postsynaptic cells. (c) Has a site for binding a specific extracellular neurotransmitter (d) Coupled to a neurotransmitter receptor via a G protein.
- 11. NEUROMUSCULAR BLOCKING AGENTS Ultra-Short: Succinylcholine chloride Short: Mivacurium chloride Intermediate: Rocuronium bromide, Vecuronium bromide, Atracurium besylate Long: Pancuronium bromide, curare, metocurine, Pipecuronium bromide, Doxacurium chloride
- 13. CURRENT FLOW Electron Flow (shown in red) Between the generators and electrodes To and from the generator Ion Flow (shown in yellow) Occurs within the tissues Negative ions flow towards the anode and away from the cathode Positive ions flow towards the cathode and away from the anode + + - -
- 14. ELECTRODES Purpose Completes the circuit between the generator and body Interface between electron and ion flow Primary site of resistance to current Materials Metallic (uses sponges) Silver Carbon rubber Self-adhesive
- 15. ELECTRODE SIZE Determines the Current Density Equal size Bipolar arrangement Approximately equal effects under exach
- 16. ELECTRODE ARRANGEMENTS Based on: Current Density Proximity to Each Other Anatomic Location (Stimulation Points)
- 17. CURRENT DENSITY Bipolar Technique Equal current densities Equal effects under each electrode (all other factors being equal) Monopolar Technique Unequal current densities At least 4:1 difference Effects are concentrated under the smaller electrode “Active” electrode(s) No effects under larger electrode “Dispersive” electrode Quadripolar Technique Two bipolar electrode arrangements Two independent electrical channels TENS is a common example “Active” “Dispersive”
- 18. ELECTRODE PROXIMITY Determines the number of parallel paths The farther apart the electrodes the more parallel paths are formed More current is required to produce effects as the number of paths increases
- 19. STIMULATION POINTS Motor Points Superficial location of motor nerve Predictably located Motor nerve charts Trigger Points Localized, hypersensitive muscle spasm Trigger referred pain Arise secondary to pathology Acupuncture Points Areas of skin having decreased electrical resistance May result in pain reduction Traumatized Areas Decreased electrical resistance (increased current flow)
- 20. PATH OF LEAST RESISTANCE Ion flow will follow the path of least resistance Nerves Blood vessels The current usually does not flow from electrode-to- electrode (the shortest path) The path of least resistance is not necessarily the shortest path
- 21. SELECTIVE STIMULATION OF NERVES Nerves always depolarize in the same order Sensory nerves Motor nerves Pain nerves Muscle fiber Based on the cross-sectional diameter Large-diameter nerves depolarize first Location of the nerve Superficial nerves depolarize first
- 22. PHASE DURATION AND NERVE DEPOLARIZATION Phase duration selectively depolarizes tissues Phase Duration Tissue Short Sensory nerves Medium Motor nerves Long Pain nerves DC Muscle fiber
- 23. ADAPTATIONS Patients “get used” to the treatment More intense output needed Habituation Central nervous system Brain filters out nonmeaningful, repetitive information Accommodation Peripheral nervous system Depolarization threshold increases Preventing Adaptation Vary output (output modulation) to prevent The longer the current is flowing, the more the current must be modulated.
- 25. MOTOR-LEVEL STIMULATION COMPARISON OF VOLUNTARY AND ELECTRICALLY-INDUCED CONTRACTIONS Voluntary Type I fibers recruited first Asynchronous Decreases fatigue GTO protect muscles Electrically-induced Type II fibers recruited first Synchronous recruitment Based on PPS GTOs do not limit contraction
- 26. MOTOR-LEVEL STIMULATION Parameters: Amplitude: Contraction strength increases as amplitude increases Phase duration: 300 to 500 µsec targets motor nerves: The shorter the phase duration, the more amplitude required Longer durations will also depolarize pain nerves Pain often limits quality and quantity of the contraction Pulse frequency: Determines the type of contraction
- 27. PULSE FREQUENCY Frequency determines the time for mechanical adaptation Lower pps allows more time (longer interpulse interverals) Label Range Result Low < 15 pps* Twitch: Individual contractions Medium 15-40 pps* Summation: Contractions blend High >40 pps* Tonic: Constant contraction * Approximate values. The actual range varies from person-to-person and between muscle groups
- 28. EFFECT OF PULSE FREQUENCY ON MUSCLE CONTRACTIONS 1 pulse per second Twitch Contraction The amount of time between pulses – the interpulse interval – is long enough to allow the muscle fibers to return to their original position 20 pulses per second Summation The amount of time between pulses allows some elongation of the fibers, but not to their starting point. 40 pulses per second Tonic Contraction The current is flowing so rapidly that there is not sufficient time to allow the fibers to elongate
- 29. ELECTRICAL STIMULATION GOALS Pain Control
- 30. PAIN CONTROL Sensory-level Motor-Level Noxious Level Target A-beta fibers Motor nerves A-delta Tissue C fibers Phase < 60 µsec 120 to 250 µsec 1 msec Duration Pulse 60 to 100 pps 2 to 4 pps Variable Frequency 80 to 120 pps Intensity Submotor Moderate to To tolerance Strong contraction
- 31. ELECTRICAL STIMULATION GOALS Edema Control and Reduction
- 32. EDEMA CONTROL Cathode placed over injured tissues High pulse frequency Submotor intensity Thought to decrease capillary permeability Do not use if edema has already formed
- 33. EDEMA REDUCTION Muscle contractions “milk” edema from extremity Electrodes follow the vein’s path Alternating rate targets muscle groups Elevate during treatment
- 34. ELECTRICAL STIMULATION GOALS Fracture Healing
- 35. FRACTURE HEALING Electrical current triggers bone growth Piezoelectric effect within the collagen matrix Alternating current Applied transcutaneously Similar to diathermy units (no heat production) Direct current Implanted electrodes
- 36. CONTRAINDICATIONS AND PRECAUTIONS Areas of sensitivity Carotid sinus Esophagus Larynx Pharynx Around the eyes Temporal region Upper thorax Severe obesity Epilepsy In the presence of electronic monitoring equipment Cardiac disability Demand-type pacemakers Pregnancy (over lumbar and abdominal area) Menstruation (over lumbar and abdominal area) Cancerous lesions (over area) Sites of infection (over area) Exposed metal implants