Lecture 5/6 Flashcards
Exam 2
How does the diameter of a nerve affect speed?
Larger diameter = faster
smaller=slower
How does length of nerve affect speed
Longer neuron = longer time, slower
Name of the insulation of the nerve
Myelin Sheath
How does myelination affect speed of a neuron?
Myelinated = faster
demyelinated = slower
What is the “Soma”?
neuron cell body
Where are dendrites located on a neuron and what are their function?
small branching projections off the soma
receive signals from other neurons
Where is the axon of a neuron and what is its function?
Long projection off the soma that sends signals
Where is the axon hillock and what is its function?
Area where the axon extends from the soma
functions to keep the brakes on the nervous system with GABA receptors
What is the name of the area on axon between myelination
node of ranvier
What cell forms the myelin sheath?
Schwann cell
Myelination allows ________ electrical propagation
faster
What is the term for the “jumping” of signals underneath the myelin sheath?
Saltatory conduction
How does extracellular Ca++ result in a calming effect on excitable cells?
Ca++ tries to enter Na+ leak channels, but too large to fit and blocks Na+ from leaking into the cell. The blocking of Na+ leak channels slows rate of depolarization, delaying AP from firing.
How does chloride affect the nervous system?
chloride puts the brake on the nervous system.
How would hypocalcemia affect cell excitability?
Cell would be more excitable. Vrm would be more + because cell becomes more permeable to Na+ because there is less Ca++ to block Na+ leak channels.
How many connexin to form a connexon?
6
How many connexons form a gap junction?
2
What is a connexon?
Formed of 6 connexin proteins, aligns with neighboring cell connexon which allows a channel for ions to move freely between the two cells. Allows for rapid conduction
What is a downside to gap junctions and what is an example?
movement of ions can go both ways, which can sometimes be bad.
ex. rogue pacemaker cells in the heart can fire signals in abnormal direction
What are the demyelinating disease examples given in lecture?
MS-multiple sclerosis
Optic Neuritis
Guillain-Barré (after COVID from antibodies)
What are some causes of demyelinating diseases?
genetics
infection
autoimmune (vaccines)
hyperactivity
polyneuropathies
Why does demyelination cause impaired signal firing?
Demyelination opens space that Na/K ATPase pumps can move and fill. VG Na+ and K+ channels don’t move/regenerate. So all the sodium ends up getting pumped out of the cell by the Na/K pumps stopping it from traveling further down the neuron
How does myelination speed up the rate of AP?
In the nodes on Ranvier, between the myelin sheaths, there is a high density of VG-Na and VG-K channels leaving little space for Na/K ATPase pumps. Not enough Na/K pumps to pump out the sodium, so the sodium travels to the next node to be pumped out, which causes the depolarization to continue down the axon.
What are supporting cells of the nervous system called?
Glial cells
What are the different types of glial cells?
CNS: oligodendrocytes
PNS: Schwann cells
which are better at regenerating? Schwann cells or oligodendrocytes?
schwann cells. the PNS is better at remyelinating than the CNS
Do myelinated neurons require more or less local anesthesia?
More
Gap junctions are an example of what type of cell signaling?
Direct coupling
Do all action potentials look alike?
No, some action potentials may take longer to reach threshold.
Stimulus strength may reach threshold faster and have larger initial spike.
Cardiac action potentials have a plateau phase
What are the signs of hypocalcemia?
- Trousseau sign - tetany of skeletal muscles
- Chvostek sign
(increased activity of motor neurons)
How does calcium treat hyperkalemia?
- If more [K+] in ECF → Vrm more (+)
- Give Ca++ → blocks Na+ channels → decreases Vrm (-) back to normal
What are the types of stimuli?
Sub-threshold, threshold, supra-threshold
How does pressure affect action potential in pressure receptors?
Turns pressure into action potential to send back to the nervous system
Action potential depends on the amount of pressure: a lot of pressure - fast action potentials; little pressure - no or slow action potentials
How do pressure receptors turn pressure into action potential?
Pressure → pressure sensitive Na channels get wider → Na+ enters cell → ICF (+) → action potential → nervous system
______ is given for excessive depolarization in the heart
Mg2+
- reduces electrical activity
- smaller than Ca2+
What affects how fast action potentials spread?
- Length of nerve (longer distance takes longer)
- Diameter of nerve (Wider = Faster; Less resistance)
- Insulation of the nerve (Myelin Sheath) - faster AP
How do Schwann cells create myelination?
Schwann cell: grows and wraps itself in a spiral around neuron, each layer is compacted and water that was initially in the cell gets squeezed out → becomes good insulator once water is squeezed out (mostly lipid)
What are the benefits of myelination?
- Decreases energy requirement (less Na/K+ pump ATP activity)
- speeds up action potential
Nodes of Ranvier are dense in ________
Fast (V-G) Na+ channels
________ prevents injury and ischemia of cells
Myelination
Gap junctions communicate via simple diffusion of ions, primarily _____
Na+
How do gap junctions work in the myocardium?
- Has a lot of channels because wants action potential to spread quickly (low resistance)
- Pacing system in heart has delays, or a pause from few gap junctions → higher resistance → harder to spread AP from one cell to another
How do gap junctions work in the smooth muscle?
gap junctions that allow neighboring smooth muscles to act as a unit
Chemical synapses take ______ than electrical synapses
longer
Ach is _______ in the heart & _______ in the skeletal muscle
Inhibitory
Excitatory
Chemical synapse requires a _______ connection between 2 cells
close
Presynaptic (sending) vs. postsynaptic (receiving) terminals
What stimulates a nicotinic receptor?
binding of 2 ACh (acetylecholine)
Where are nicotinic receptors located?
skeletal muscle
Where are muscarinic receptors located?
heart, smooth muscle, lungs
What type of receptor is the muscarinic receptor?
GPCR
What type of channel is coupled with the muscarinic receptor?
K+
The vagus nerve works through what kind of receptor?
muscarinic
Does the muscarinic receptor cause polarization or depolarization?
polarization/hyperpolarization
muscarinic receptor when activated opens K+ channels that allow K+ to leave the cell, causing polarization
How does muscarinic activity keep our HR in check?
HR if unchecked fires approx 100-110bpm. Vagus nerve constantly releasing ACh. Muscarinic activity decreases Vrm to make it take longer for AP to reach threshold, resulting in a lower HR.
Why are they called muscarinic receptors?
They respond to a compound called “muscarine” found in the rainforest
muscarinic receptors __________(increase or decrease) __________ permeability
increase K+ permeability
- activated by the alpha subunit on mACh-R
Vagal stimulation causes our heart rate to increase or decrease? why?
decrease
Vagal stimulation causes increased ACh. ACh binds to muscarinic receptors which increase K+ permeability leading to hyperpolarization of pacemaker cells
Antimuscarinic drugs increase or decrease heart rate? How?
Increase
blocks the binding of ACh on muscarinic receptors
decreases K+ permeability making Vrm more positive/depolarized.
_______ is a common antimuscarinic drug
atropine
______ opens chloride channels in neurons to hyperpolarize cells
GABA
Propagation of an action potential can be a ______ process
2-way
The ______ connects the end of the neuron and the receptor for neurotransmitters on the skeletal muscle
Neuromuscular junction (NMJ)
nACh Channels/Receptors are specific for which ions?
(+) ions - mainly Na+ in; a little K+ can leak out, some Ca++ can enter ICF too
- net influx of (+) ions (depolarization) opens up fast Na+ channels
Paralytics work at the _______
NMJ
nACh channels are _______ electrical activity
stimulating; depolarization
mACh-R channels are _______ electrical activity
suppressing; hyperpolarize
Muscarinic receptors are found in the ____ of the heart
Nodes
__________ come into contact with the pacing structures in the heart
Vagus nerves
The _____ vagus nerve affects the SA node
Right
The _____ vagus nerve affects the AV node
Left
______ is the neurotransmitter that allows the vagus nerve to talk to the heart
ACh
mACh-R antagonize ______ in the heart
Beta receptors
