Safety margin at single neuromuscular junctions
Joze V Trontelj1, Marjan Mihelin, Adnan Khuraibet
1Institute of Clinical Neurophysiology, University Medical Center, Zaloska 7, SI-1525 Ljubljana, Slovenia. joze.trontelj@kclj.si
Muscle & Nerve. Supplement
|July 13, 2002
Summary
Jitter measurements reveal that neuromuscular junctions maintain high safety factors across various stimulation rates. Some normal junctions and those with myasthenia exhibit facilitation at higher rates, improving synaptic function.
Area of Science:
- Neuroscience
- Physiology
Background:
- Neuromuscular junctions (NMJs) are critical for muscle activation.
- Synaptic function and safety factors are key to reliable neuromuscular transmission.
Purpose of the Study:
- To investigate synaptic function at normal neuromuscular junctions (NMJs) using jitter measurements.
- To characterize the impact of varying stimulation rates on NMJ transmission safety factors.
- To compare facilitation patterns in normal NMJs versus those in myasthenia.
Main Methods:
- Axonal microstimulation was employed to measure jitter at 115 normal NMJs.
- Stimulation rates varied from 0.5 Hz to 50 Hz to simulate different workloads.
- Jitter patterns and synaptic facilitation were analyzed across different stimulation frequencies.
Main Results:
- Jitter was lowest at 0.5 Hz and increased with stimulation rates up to 50 Hz.
- The majority of normal NMJs demonstrated a high safety factor for neuromuscular transmission.
- A subset of normal NMJs and most myasthenia NMJs showed facilitation at higher rates (10-20 Hz).
Conclusions:
- Normal neuromuscular junctions maintain a robust safety factor over a wide range of physiological discharge rates.
- Synaptic facilitation can enhance the safety factor, particularly in conditions like myasthenia or in normal NMJs with higher baseline jitter.
- Jitter measurement is a valuable tool for assessing synaptic function and safety margins at the NMJ.
Related Concept Videos
01:29Neuromuscular Junction And Blockade
The site of chemical communication between a motor neuron and a muscle fiber is called the neuromuscular junction (NMJ). The end of the motor neuron at the NMJ divides into a cluster of synaptic end bulbs. The cytoplasm of these bulbs consists of synaptic vesicles enclosing acetylcholine molecules, the principal neurotransmitter released at the NMJ. The region opposite the synaptic bulb that ends in the muscle fiber is called the motor end plate, which has acetylcholine receptors. Within the...
01:19The Neuromuscular Junction
The nervous system consists of complex motor neuron circuits, including upper motor neurons originating from the cerebral cortex and lower motor neurons starting in the spinal cord, coordinating both voluntary and involuntary movements. Among these, somatic motor neurons activate skeletal muscles and are classified into alpha, beta, and gamma types. Alpha neurons are vital for voluntary movement coordination, while gamma neurons adjust muscle spindle sensitivity, and the function of beta...
01:24Generation of Action Potential in Skeletal Muscles
Every cell in the body maintains a membrane potential due to an uneven distribution of positive and negative charges across its plasma membrane. The membrane potential is measured in millivolts and quantifies the difference in charge across the membrane.
Like neurons, muscle cells are also regarded as excitable due to their capacity to change in response to stimuli, primarily due to voltage-gated ion channels embedded in their plasma membranes, which get activated by alterations in the cell's...
Like neurons, muscle cells are also regarded as excitable due to their capacity to change in response to stimuli, primarily due to voltage-gated ion channels embedded in their plasma membranes, which get activated by alterations in the cell's...
01:29Relaxation of Skeletal Muscles
The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
01:20Motor Unit Stimulation
When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
01:22Somatic Spinal Reflexes
Somatic spinal reflexes are rapid, involuntary muscular responses to external stimuli that involve the somatic musculature and the spinal cord.
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...