Physiology Quiz 2 (1/2) Flashcards Preview

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Flashcards in Physiology Quiz 2 (1/2) Deck (42):
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Synapse

Site at which an impulse is transmitted from one cell to another

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Types of synapses

Electrical
Chemical

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Ephaptic communication

Two excitable cells communicating by direct passage of electrical current between them (aka electrical synapses)

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Chemical synapses

A spike at the presynaptic membrane causes a release of neurotransmitter which attaches to receptors on the post synaptic membrane and causes depolarization

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Characteristics of chemical synapses

Synaptic delay of .5-1 msec
Transmission is unidirectional
Pharmacological agents can interfere.

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Characteristics of electrical synapses

No synaptic delay
Transmission is bidirectional
Pharmacological interference will not occur

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Neuromuscular junction

Chemical synapse between a motor nerve and muscle cell(s)

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Benzodiazepines*

Eg. Valium
Anti-anxiety for Pre-surgery
Blocks synaptic transmission*
Overuse can lead to too much transmission along nerve*

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What happens when the spike arrives at the alpha motor nerve ending?

1. Sudden large increase in calcium conductance at the presynaptic ending
-calcium diffuses inward
-attaches to enzymes, activating them
2. Activated enzymes cause the vesicles containing neurotransmitter to release into cleft
-Ach is neurotransmitter in neuromuscular junctions
3. Ach diffuses across cleft
4. Ach attaches to cholinergic receptor on post synaptic membrane
5. Causes end plate potential (EPP)
6. Potentials will sum and when threshold is reached, the cell fires an action potential

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Synaptic delay due to...

Time it takes for chemicals to get across synapse

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Neurotransmitter at neuromuscular junction

Acetylcholine (Ach)

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Two types of cholinergic receptors

Nicotinic
Muscarinic

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Nicotinic receptors

Found on muscle, attach to nicotine or Ach

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Muscarinic receptors

Found on organ tissue (ie. cardiac tissue)

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Atropine

Used to block poisons
Used in surgical settings to interfere with fluid production in lungs

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Nicotinic cholinergic type receptors

Cholinergic receptors on muscle

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Characteristics of nicotinic cholinergic receptors

Can attach to Ach
Can attach to nicotine

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End plate potentials (EPP)

Depolarizations of the postsynaptic membrane surface that are conduced electronically.
-large numbers of EPPs will occur when the nerve fires a spike
-Hesse must sum to cause a spike in the muscle membrane

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What happens every time an alpha motor nerve cell fires?

An excess of Ach is released

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Is it important to terminate the action of Ach at the neuromuscular junction?

Yes- for normal activity, muscles need to contract and relax
Eg. Lungs-muscles need to both contact and relax in order for you to breathe

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How termination of Ach is achieved

Broken down by acetylcholinesterase or by less specific cholinesterases

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Where is Ach-ase located?

On surface of postsynaptic membrane

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Where are cholinesterases located?

In extra cellular fluid in synaptic cleft

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What happens to Ach when it is attached to a receptor and the EPP is initiated?

It detaches

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Three possibilities for Ach molecule after it detaches from postsynaptic membrane

1. Attaches to another receptor
2. Attaches to acetylcholinesterase on the membrane and is destroyed
3. Attaches to a cholinesterase in the synaptic cleft and is destroyed

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Is an Ach molecule more likely to attach to another receptor or to an esterase as it detaches?

More likely to attach to another receptor (1500 receptors/square micron) than an esterase (2600 esterases/square micron) but as it attaches and detaches, it will eventually run into an esterase

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What is Ach broken down into?

Acetyl CoA + choline

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What I acetylcholinesterase CoA used for?

Metabolism

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What is choline used for?

Actively transported back into nerve terminal and utilized again to manufacture Ach

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When Ach is manufactured in the cell body, how does it travel to the nerve terminal?

Antegrade axoplasmic transport by microtubules

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Succinylcholine

Attaches to nicotinic cholinergic receptors and initially activates then blocks (does not detach from site)
Used for: Relaxing muscles during surgery or when using a breathing machine (ventilator). It is also used to induce anesthesia or when a tube must be inserted in the windpipe.

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Tubocurarine

This attaches to nicotinic cholinergic receptors and blocks them. (No muscle rigidity, just relaxes)
Used for: a diagnosis agent for myasthenia gravis, and also to facilitate the intubation after induction of anesthesia in surgical procedure

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Alpha-neurotoxins

Block nicotinic cholinergic
preventing synaptic acetylcholine (ACh) from opening the ion channel.

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Loss of inner action of motor end plate

Can happen in trauma where nerve is cut
Can also happen when the nerve has undergone mechanical or toxic insult sufficient to stop the motor nerve from functioning

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What happens when the motor nerve input to the motor end plate is lost?

Skeletal muscle develops high sensitivity to Ach
-thought to be due to a spread of receptors beyond the motor end plate
-cause unknown

35

Fasciculations

Low level uncoordinated contractions "quivering" of skeletal muscle

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mEPPs

(Miniature end plate potentials) small depolarizations that occur at the end plates without any activation of the alpha motor neuron
-thought due to spontaneous release of Ach
-some evidence that they are the tonic influence that nerves exert upon muscle to maintain it in a healthy state.
-another idea-they are releasing a chemical compound (probably a combo of both)

37

Botulism

Caused by ingesting food contaminated with spores of clostridium botulinum which attacks and destroys cholinergic nerve terminals creating acute denervation of motor end plates of muscle.
-respiration stops
-used in Botox injections

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Myasthenia gravis

Autoimmune process which destroys nicotinic cholinergic receptors
-most common in females
-facial muscles fatigue when eating is usually first complaint
-long process, patient eventually dies

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Treatment for myasthenia gravis

Give anti-cholinesterase drugs
-increases concentration of Ach for more activation of receptors

40

Osteophytes

Inappropriate growth of bone to stabilize joints

41

How does compression affect axoplasmic transport?

Slows it down