Lec 17
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| Importance of myelination? | Function: speed up propaganda velocity by 25x
- Lower energy expenditure
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| How is info coded? Pain coding? | - Frequency of Action Potential
- Frequency of nerve impulses
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| Axon | - Longer & myelinated fibers
- Branches in cells, nerve, gland, muscle
- 1 branch = 1 muscle fiber
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| Synapse | functional connections between neurons, between neurons & other cells – muscle & glands or between muscle cells
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| 2 types of synaptic transmissions | Electrical synapse
Chemical Synapse
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| Electrical synapse | -Minimal delay of impulse transmission (fast)
-Bidirectional transmission of impulse
-Stimulate 1 cell, all will stimulate together
-Location: cerebellum
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| Chemical Synapse | -Unidirectional transmission
-Longer delay of transmission 0.5-4ms
-Presynaptic terminal & presynaptic membrane
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| Sarcolemma | muscle membrane
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| Synaptic clef | -30-40nm
-Membranes do not touch (gap)
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| Quanta | # of neurotransmitter vesicles released per Action Potential
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| Neurotransmitters packed in vesicles | Acetylcholine (Ach)
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| Release of Ach | voltage regulated Ca++ gates high Ca++ concentration & activate enzyme
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| Simultaneous opening of Ach-regulated Na+ & K+ gates | -Na+ out & K+ in
-Membrane starts depolarizing (more Na+)
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| More AP | more Ach released
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| ^ frequency of AP | ^ Quanta = ^ EEP
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| Characteristics of EPP | - No overshoot
- May go only up to 0mV
- Graded --> No all-or-none response
- Conducted decrementally along endplate
- Very long duration
- No refactory period
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| EPP may be summed | - 1AP : 1EPP
- 1 EPP : 1 ATP
- On average EPP is approximately 70mV
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| How can we relax muscle? | Acetylcholinesterase (key enzyme)
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| Acetylcholinesterase (key enzyme) | Ach diffuses into the interstitial fluid
-Breaking down to Choline & Acetate
-Reabsorbed into presynaptic terminal
-ATP will be used to combine choline & acetate
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| Nerve gas | inactivates acetylcholinesterase –-> Spastic paralysis
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| Curare | competitively binds to Ach receptors of post synaptic membrane
– flaccid paralysis because it binds to neuro cell receptor blocked. Allowing no contraction.
- Post-synaptic neuromuscular blockade
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| Botulinum Toxin | prevents release of vesicles (Botox )
-Presynaptic blockade
-Ach not released --> muscle cannot contract
-Flaccid paralysis
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| Skeletal muscle Function | - Force production for movement, locomotion
- Force production for breathing
- Force production for postural support
- Pumping venous blood towards heart
- Heat production during cold stress
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| 4 principle characteristics of skeletal muscle | -Excitability
-Contractility
-Extensibility
-Elasticity
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| Excitability | ability to respond to stimuli
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| Contractility | ability to contract & produce a force
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| Extensibility | ability to be stretched without rupture/tear
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| Elasticity | ability to shorten/extend & return back to original shape (rubber band)
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| How muscle respond to stimuli | contract
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| Muscle connective tissue | Epimysium
Perimysium
Endomysium
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| Epimysium | envelops individual muscles from outside providing structural integrity for whole muscle
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| Perimysium | envelopes several hundred muscle fibers forming fascicles (200-300 fibers)
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| Endomysium | envelopes each muscle fiber individually
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