Exam 2 Flashcards
What is Ohm’s Law?
I = V/R or in words, current equals voltage (membrane potential) over resistance (cell membrane)
Describe how nicotinic ACh receptors work
2 ACh bind the nACh-R sites on a negatively charged ion pore in the cell membrane. Positive ions flow in (mostly Na+) and depolarize the cell. This initial current can then open adjacent VG fast Na channels.
Where are nicotinic ACh receptors found? What is significant about this site?
Mainly in the skeletal muscles at the neuromuscular junction (NMJ). This is where our paralytics work.
Describe how muscarinic ACh receptors work…
ACh released from the vagus nerve binds a mACh receptor site on a GPCR. This activates the alpha protein which goes on to open the coupled K channel. This allows more K+ to leave the cell hyperpolarizing the cell.
Where are muscarinic ACh receptors found?
mACh-R are found in the SA and AV node of the heart. The right vagus nerve sends ACh to the SA node and the left vagus nerve sends ACh to the AV node.
How does atropine work to increase our heart rates?
It blocks mACh-R and inhibits them, which increases our heart rate as ACh inhibits our pacemaker cells.
Describe how pressure sensors in the vascular system relay the message ^MAP to the CNS
Pressure sensors on our smooth muscle cells in the vascular system are compressed and Na leak channels on these cell walls widen. This allows more Na into the cell and can generate an action potential to the CNS for processing.
How is VG Na channel opening an example of positive feedback when generating an action potential?
An initial stimulus/action potential causes fast NA channels to open in a resting cell. Na enters the cell, this depolarization leads to activation of adjacent VG Na channels. The signal is propagated along the length of the cell and can be bidirectional allowing for faster conduction of the signal.
What three things would decrease the rate of action potential propagation? (What about increase?)
- Narrow neuron (wide)
- Longer neuron (short)
- Less insulation or myelin (more myelination)
What’s the precursor to myelin again? Where is it found?
Sphingomyelin, in the cell wall
How does myelin insulate the neuron?
It wraps around the neuron and squeezes all the water out between layers. All lipid, makes an excellent insulator.
Where are most of the fast Na channels found in the myelinated neuron?
At the nodes of ranvier
How does saltatory conduction work?
The action potential spreads from one node to the next via myelin, which prevents leakage of the Na as it “covers up” Na/K ATPase pumps. This helps propagate action potentials really quickly.
What makes myelin? In the CNS? The PNS?
Glial cells. In the CNS oligodendrocytes specifically and schwann cells in the peripheral nervous system.
Which cells can generate more myelin in adults?
Schwann cells in the PNS. Oligodendrocytes are not good at doing this in adulthood!
How do diseases like Guillain Barre and Multiple Sclerosis lead to paralysis?
These are demyelinating diseases. There is a progressive loss of myelin from the neurons. This “uncovers” the Na/K pumps and lots of Na gets pumped out. The action potential will not be able to propagate to the next node.
What are connexins, where are they located.
These are proteins that form a tube with 6 connexins. They form at gap junctions and create a conduit between cells for Na current to flow through. This allows for rapid conduction of a signal.
Where is ACh excitatory and where is ACh inhibitory?
It is excitatory at skeletal muscle cells and inhibitory at pacemaker cells in the heart.
How does calcium impact membrane potential?
Ca is larger and positively charged and hangs out near sodium leak channels. It gets “in the way” and inhibits Na leakiness, which makes the inside of the cell more negative (decreases excitability).
What effect does hypocalcemia have on the ICF?
Low serum calcium makes the inside of the cell more positive as there is less to block Na leak channels and more Na gets into the cells.
Why would we give calcium to someone with hyperkalemia?
With hyperkalemia, less K wants to leave the cell (lower concentration gradient). By adding more Ca one could block more Na leak channels, lowering the membrane potential, which would “hold on to” k more
Describe how hypocalcemia leads to Trousseau’s tetany
Less calcium means more Na can “leak” into the cell, which increases the membrane potential, making the cell more excitable. This causes overactivity of the motor neuron which leads to increased contraction of the skeletal muscles
What are the three classes of neurons and what’s special about them?
A neurons are myelinated. B, lightly myelinated and C non-myelinated neurons.
What does a inhibitory post-synaptic potential do?
It makes the membrane potential more negative than normal.
What does an excitatory post-synaptic potential do?
It makes the membrane potential more positive than normal.
What occurs at the axon hillock?
There are four inhibitory connections here. Usually these are GABA receptors that increase Chloride permeability.
How does alcohol withdrawal lead to seizures?
Alcohol is a GABA1 agonist and therefore inhibits the neurons so the body doesn’t need to make as much of it’s own GABA. If one stops drinking the GABA receptors are no longer inhibited and there is not enough endogenous GABA left and the nervous system is overexcited
Where are Astrocytes located and what are they good at?
They are wrapped around capillaries in the NS to help maintain the BBB and are good at maintaining an electrolyte balance in the CNS
What are ependymal cells?
These are concentrated in the 3rd and 4th ventricles and form the choroid plexus which produces CSF.
What do Oligodendrocytes do?
They make myelin in the CNS
What do Schwann cells do?
They form myelin in the PNS
What are microglia responsible for?
Cleaning up debris, they are macrophages.
What are multipolar neurons and give an example
These are the “decision makers” an example are motor neurons
What are pseudounipolar neurons
These are typically found near the spinal cord. They are good at sensing.
What are bipolar neurons?
These are neurons that can send bidirectional messages. They are in the retina and optic nerve and are primarily for sensing
An example of nociceptors? Two examples of pressure receptors or “bend” receptors?
Free nerve endings (pain)
Pacinian corpuscle (pressure)
Meissner’s corpuscle (pressure)
What are some examples of stretch/pressure sensing receptors?
Golgi tendon apparatus
muscle spindles
How do pressure receptors sense?
They respond to pressure changes with edema caused by sodium shifts (which is followed by water)
How do nociceptors undergo adaptation?
They go through reverse adaptation. They become sensitized each time there is a pain response
Which sensory receptors undergo fast adaptation?
All of them, except free nerve endings
What does the sagittal plane bisect?
Left from right
What does the coronal plane bisect?
anterior from posterior
what does the horizontal plane bisect?
superior from inferior
What structures are in the telencephalon?
The outer portion of the brain, cerebral cortex and basal ganglia
What structures are in the diencephalon?
inner part of the brain (thalamus, hypothalamus) and 3rd ventricle
What structures are in the mesencephalon?
Midbrain
What part of the brain is responsible for speech?
Broca’s area
Which part of the brain is responsible for language comprehension?
Wernicke’s area
where is the somatosensory cortex?
in the anterior part of the parietal lobe
Where is the primary motor cortex?
in the posterior part of the frontal lobe
What makes up the white matter?
usually axons, myelinated axons, does the sending and receiving of messages
