Lecture 7 9/1/23 Flashcards
What are the two types of synapses?
-electrical synapse
-chemical synapse
What are the characteristics of electrical synapses?
-in smooth and cardiac muscle
-gap junctions allow free movement of ions
What are the characteristics of chemical synapses?
-majority in CNS and at NMJ
-release neurotransmitters
What are the characteristics of innervation?
-one nerve can innervate multiple muscle fibers
-each muscle cell only has one neuron
How does muscle contraction work in terms of action potentials?
-each muscle contraction is an all-or-nothing action potential
-the number of motor neurons firing determines the strength of the muscle contraction
What are the synaptic vesicles?
packets of acetylcholine neurotransmitters
What are the junctional folds of the post-synaptic membrane?
areas of increased surface area allowing for more receptors
What is the synaptic cleft?
the space where acetylcholine is released between the presynaptic terminal and the muscle cell
What type of ACh receptors are in skeletal muscle?
nicotinic receptors
What is the role of Ca2+ ions in neuro-muscular junctions?
-voltage changes associated with APs opens voltage-gated Ca2+ channels
-Ca2+ influxes into pre-synaptic terminal
-Ca2+ triggers vesicles to release ACh
What is the safety factor associated with NMJ?
-more than enough ACh and more than enough receptors
-ensures that muscle contraction occurs with every AP
Why is it important that there is a process to stop muscle contraction?
we only want one muscle contraction to occur per AP
How is muscle contraction stopped?
-acetylcholinesterase exists within synapse and breaks down ACh
-breakdown of ACh stops the muscle contraction
-choline is recycled for use in future APs and contractions
What is myasthenia gravis?
-condition in which there are not enough available ACh receptors
-leads to exercise fatigue
What are the two types of myasthenia gravis?
-immune-mediated: immune system attacks ACh receptors
-congenital: animal is not born with enough receptors
Why is the lack of NMJ safety factor important in myasthenia gravis?
-safety factor typically ensures that, as amount of ACh decreases, there are still enough receptors for the remaining ACh to find
-with fewer receptors, remaining ACh struggles to find receptors and carry out AP/contraction
Why is myasthenia gravis a dangerous condition in dogs?
-muscles controlling the esophagus and breathing functions are skeletal muscle in dogs
-can lead to difficulty breathing
-also results in animal not being able to properly swallow
-end result can be regurgitation, aspiration, and pneumonia
How can immune-mediated myasthenia gravis be treated?
suppression of the immune system to prevent it from attacking receptors
How can congenital myasthenia gravis be treated?
inhibition of acetylcholinesterase to prevent ACh breakdown
Why does inhibition of acetylcholinesterase treat myasthenia gravis?
it allows for acetylcholine to exist within the synaptic cleft for an extended time, increasing the likelihood it reaches the ACh receptors
What are the potential downfalls of acetylcholinesterase inhibition?
-can lead to increased weakness due to not having enough time to reset between APs
-can overstimulate parasympathetic nervous system
How can neurotransmitters function on a cell?
-excitatory/cause APs
-inhibitory/prevent APs
How do different neurotransmitters function with different ion channels?
-excitatory neurotransmitters will open channels that allow for influx of + ions or efflux of - ions
-inhibitory neurotransmitters will open channels that allow for influx of - ions or efflux of + ions
What is glycine?
an inhibitory transmitter, especially in the spinal cord/reflexes
What is the effect of tetanus?
-toxins bind irreversibly to glycine receptors
-animal has no muscle relaxation
-must wait for animal to regenerate new glycine receptors following infection
