Exam 2 Flashcards
Which channel is most important for NM transmission?
Ligand channels
Which channel is most important for tactile sensation?
Mechanically gated channels
Which channel is most important for action potential transmission in the axon?
Voltage gated channels
What is the membrane’s potential determined by?
Differences in the concentrations of ions
What are the 2 types of gradients created by the different ion concentrations that determine membrane potential’?
Concentration gradients
Electrical gradients
What are the main ions that contribute to membrane potentials? Include their charge and their location of highest concentration
Na: + extracellular K: + intracellular Ca: + extracellular Cl: - extracellular Anions: - intracellular
What are anions made of?
Protein
PO4
What pump is the sodium gradient maintained through?
Na/K ATPase
How does the Na/K ATPase pump work?
It removes 3 Na in exchange for 2 K and contribute -4 mV to the membrane potential
What would happen if the balance of Na significantly differed form inside to outside?
The cell would shrink or swell
Which ion is the most important to be able to diffuse across the membrane? What is its equilibrium potential?
Potassium
-96.81 mV
Which ion is so tightly regulated it cannot diffuse through the membrane? What is its equilibrium potential?
Calcium
+137.04 mV
What is the resting potential for the neuronal membrane?
-70 mV
What does the membrane potential allow the neuron, dendrites, and axons to have?
Excitable membranes so they can transmit signals
Where is the trigger zone (Dr. Beasley’s favorite area)located?
At the axon hillock
What must happen in order to transmit an action potential?
You must reach the threshold to stimulate the axon
What is the membrane potential of the trigger zone?
Between -40 mV and -55 mV
Does a depolarization make the membrane potential more positive or negative?
Positive
Does a hyper polarization make the membrane potential more positive or negative?
Negative
What are the steps of action potential?
Threshold is reached, making depolarization self-generating via graded potentials
This triggers opening of the activation gates of the voltage gated Na channels, which are open for a predetermined amount of time until the inactivation gates close
Sodium rushes into the cell down its potential making the membrane on the inside more positive
This triggers neighboring voltage gated sodium channels to open propagating the action potential, but only in the direction of axon flow because of the absolute refractory period
The voltage gated potassium channels open and the potassium rushes out down its concentration gradient
The membrane becomes extra negative as too much potassium leaves the cell, which creates a hyperpolarized membrane potential
To reach the threshold potential to create a new action potential, you have to get from hyperpolarized membrane to the threshold at -40 to -55 mV
The Na/K ATPase pumps kick into high gear to get the Na out of the cell and the K back in returning the membrane to its resting membrane potential
What is the hyperpolarized membrane potential?
-80 to -90 mV
More simply put, what does the action potential consist of?
Depolarization, repolarization, hyperpolarization
Where does myelin live?
On the axons
What creates myelin in the CNS?
Oligodendrocytes
What is the ratio of oligodendrocytes to axons?
1:many
What creates myelin in the PNS?
Schwann cells
What is the ratio of Schwann cells to axons?
1: 1 myelinated
1: many unmyelinated
What does myelin do?
Protection of the axon
Electrically insulating fibers from one another
Increasing the speed of nerve impulse transmission
Which axons are affected first with spinal cord compression?
Large, heavily myelinated fibers
What is the last function lost with severe spinal cord compression/disease?
Tactile sensation/deep pain
What does the loss deep pain mean for prognosis for return to function?
It is 50:50 or less than 20% depending on time
Where do synapses occur?
Axon terminals
What happens as the action potential reaches the axon terminal?
The change in membrane potential opens voltage gated Ca channels
What does the calcium from a change in membrane potential cause?
Synaptic vessels to fuse with axon membrane and exocytosis of neurotransmitter into the synaptic cleft
Which variety are the receptors on the post synaptic membrane?
Ligand
What ion do the ligand receptors on the post synaptic membrane allowing into the post synaptic cell?
Na
What happens if enough Na enters the post synaptic cell?
It triggers the opening of the voltage gated Na channels and get triggering of an action potential
What happens with signals at the synapses?
You are taking an electrical signal, turning it into a chemical signal and then back to an electrical signal
What are the 3ways to remove neurotransmitters from the synaptic cleft?
Diffusion
Re-uptake
Degradation of enzymatic destruction
What is involved in re-uptake?
Active transport into presynaptic neuron
Active transport into astrocytes
What do excitatory post-synaptic potentials do?
Depolarizes membrane potential a little
What happens when the membrane potential depolarizes a little? Does this make the membrane more positive or negative?
Opens Na channels
Positive
What do inhibitory post-synaptic potentials do?
Hyperpolarizing the membrane potential a little
What happens when the the membrane potential hyperpolarizes a little? Does this make the membrane more positive or negative?
Opens Cl channels
Negative
What must a neurotransmitter do to be considered a neurotransmitter?
Substance must be present within presynaptic neuron
Substance must be released in response to presynaptic depolarization and must be Ca dependent
Specific receptors for the substance must be present on post-synaptic cell
Which would mimic the action of a neurotransmitter by binding to its receptor, agonist or antagonist?
Agonist
Who are the major excitatory neurotransmitters? What ion enters through their ligand gated channels?
Acetylcholine (Na)
Glutamate (Ca and Na)
Epinephrine, norepinephrine, dopamine, serotonin, and histamine
Who are the major inhibitory neurotransmitters? What ion enters through their ligand gated channels?
Gamma-amino butyric acid (GABA) (Cl)
Glycine (Cl)
Where are nicotinic receptors found?
Neuromuscular junction in preganglionic ANS
Who binds to nicotinic receptors?
Acetylcholine
Where are muscarinic receptors found?
Postganglionic parasympathetic nervous system
Who binds to muscarinic receptors?
Acetylcholine
What degrades acetylcholine?
Acetylcholinesterase
What neurotransmitter do we believe is responsible for excitotoxicity following head trauma?
Glutamate
What neurotransmitters are affected in tetanus?
GABA and Glycine
What nuerotransmitters are affected with strychnine toxicity?
Glycine
What are the neurotransmitters and receptors of the post-gnaglion neurons of the SANS?
Norepinephrine and epinephrine
Alpha and beta receptors
What neurotransmitter has agonist created to be anti-seizure medications?
GABA
Which neurotransmitters are often manipulated for behavior modification?
Serotonin, dopamine, and histamine
What nerve is involved in the patella reflex? Where does it live in the spinal cord?
Femoral nerve
L4 and L5