Exam II Flashcards
Action potentials would never begin if it weren’t for ONE major difference between the response of voltage-gated sodium and potassium channels to depolarization – what is that difference? Note – name only ONE difference – no credit will be given for answers which list all of the differences!
K+ channels open with a delay. In excitable cells, such as neurons, the delayed counterflow of potassium ions shapes the action potential. The best-known flow of K+ is the outward current following depolarization of the membrane. This occurs through the delayed rectifier channel, which, activated by the influx of Na+, counteracts the effect of that cation by allowing the discharge of K+. By repolarizing the membrane in this way, the channel restricts the duration of the nerve impulse and participates in the regulation of repetitive firing of the neuron.
What electrical property of myelin allows it to speed up action potentials
The resistance of myelin. By acting as an electrical insulator, myelin greatly speeds up action potential conduction.
Why do action potentials generally not begin in the dendrites of a neuron, but rather in the cell body or axon hillock?
Voltage gated Na+ channels are not usually in the dendrites.
What did the discovery of miniature excitatory postsynaptic potentials tell researchers about the mechanism of neurotransmitter release?
This told researchers about how neurotransmitters are released in vesicles.
In what parts of a neuron are peptide neurotransmitters and small molecule amino acid neurotransmitters generally synthesized?
Small molecule neurotransmitters are generally synthesized in the synaptic terminal while peptide neurotransmitters are generally synthesized in the cell body.
Briefly describe an experiment that would map the receptive field of a somatosensory neuron in the cortex which displays an antagonistic center-surround form. What apparatus would you use, how would you use it, what results would you obtain and how would you interpret them?
(1) Record from a single cell in S1.
(2) Stimulate area of skin.
(3) Observe _ in action potential frequency in S1 cell at center of receptive field.
(4) Observe _ in action potential frequency at edge of receptive field.
In the spinal cord, neuronal circuits exist which might explain how the brain is able to suppress the sensation of pain. The neurotransmitter that mediates this suppression is enkephalin. On which cell does enkephalin act to suppress pain transmission?
The sensory receptor neuron (nocioceptor). It does so by presynaptic inhibition.
Fill in the blank: Phantom Limb Syndrome is an example of the brains use of
__________________ lines to perceive sensory information
Phantom Limb Syndrome is an example of the brains use of LABELLED lines to perceive sensory information.
Describe THREE differences between rod and cone photoreceptors
(1) Speed (rods have a slow response; cones have a fast response)
(2) Number of opsins expressed (color sensitivity)
(3) Size (rods are longer than cones)
(4) More cones in fovea and more rods in periphery
Briefly describe the response of horizontal cells when light hits the retina and how they communicate this response to other neurons in the retina.
The horizontal cells hyperpolarize. They inhibit neighboring photoreceptors:
(1) Illumination -> (2) Center photoreceptor hyperpolarization -> (3) Horizontal cell hyperpolarization -> (4) Surround photoreceptor depolarization
Describe TWO ways in which the receptive fields of retinal ganglion cells differ from the receptive fields of neurons in layers 1-3 and 5-6 of the primary visual cortex?
(1) V1 neurons are sensitive to bars, not spots
(2) V1 neurons can be binocular
(3) V1 neurons have orientation selectivity
Describe the loss of vision in each eye that would result from complete destruction of the fibers that travel from the LGN to the left visual cortex. Use diagrams if you wish
Loss of visual field seen by left eye (nasal side): right hand side of left eye visual field is lost. This is because contralateral side is affected. The LEFT visual cortex is for RIGHT hand vision. So the nasal side of the left eye is affected which is the right hand side of vision.
Loss of visual field seen by the right eye (temporal side): right hand side of right eye visual field would be lost. This is because the ipsilateral side is affected. So the temporal side of the right eye is affected which is the right hand side of vision.
Describe the difference(s) in function between neurons in the dorsal and ventral visual pathways of the cortex (i.e. what do the neurons in each pathway analyze?).
Dorsal Pathway (V1 -> V2 -> MT) detects motion–“where” things are.
Ventral Pathway (V1 -> V2 -> V4) detects form and color–“what” things are.
What is the function of the three bones of the middle ear?
To transmit vibration of tympanic membrane to the cochlea or oval window by acting as levers.
What is meant by a “tonotopic” organization of the properties of neurons in the auditory cortex?
Neurons are arranged in order of the frequencies that they are most sensitive to.
Describe how the displacement of the hair bundle of a receptor cell in the cochlea results in a change in its membrane potential
Tip link stretches when bundle is moved which opens channel and so K+ enters and the cell depolarizes.
What makes up a “motor unit”?
One motor neuron and all the muscle fibers that it innervates.
What two diseases indicate that damage to the basal ganglia results in abnormal motor planning and execution
Huntingtons Disease and Parkinsons Disease.
In what structure outside of the cerebral cortex do you find somatotopic maps of the body surface
Cerebellum.
You obtain the sequence of an unusual channel that is found in the postsynaptic membrane of a cell that you are studying. . Your colleague reviews the channel’s sequence and she makes two predictions…….
a) That this is an excitatory neurotransmitter-gated channel activated by glutamate.
b) That the channel will be blocked by intracellular calcium ions.
Describe how you would test both of your colleague’s predictions using patch clamp technology. Make sure that you address the following explicitly in your answer.
a) What configurations of the patch clamp would you use? (it may take more than one to provide a full test of both predictions)
b) What would be in the solutions that are inside or outside the patch for each test, and what Vm would you clamp at?
c) Sketch the recordings of current expected for each experiment – as well as an interpretation in terms of how the recordings might confirm the predictions. Be sure to label any graphs of the electrical recordings
(A) “Outside Out” Configuration and “Inside Out” Configuration. They both will be clamped at Vrest or Vthreshold. For the inside-out configuration, glutamate will be inside the pipette. For the outside-out configuration, glutamate will be outside the pipette.
(B) High Na+ and Low K+ in the extracellular fluid in bath (so outside of patch). Low Na+ and High K+ in the intracellular fluid in pipette (inside of patch). No calcium inside patch.
(C) When you add glutamate to bath, it opens the channels and you observe blips in the inward current. This shows excitation. When you add Ca2+ to the bath, the channels close and there are no blips in the inward current.
Action Potentials vs Graded Potentials
Graded potentials decay with distance because current leaks out of axon. Action potentials regenerate because of active and passive current flow.
Speed of action potentials in myelinated vs unmyelinated fibers
The speed of action potential conduction is much slower in unmyelinated vs myelinated axons because in advance of an action potential, passive current instantaneously spreads. Myelin insulates the axonal membrane, reducing leakage of passive current and reducing membrane capacitance. In unmyelinated axons, channels have to be open at every point of the axon.
Whole cell recording
The membrane patch within a pipette is disrupted by briefly applying strong suction so that the interior of the pipette is continuous with the cell cytoplasm to measure electrical potential and currents from the entire cell.
Inside-out Patch
The tip of the pipette is exposed to air so that the vesicle opens to yield a small patch of membrane with its former intracellular surface exposed.
ADVANTAGE: measurement of single channel currents with the ability to change medium of intracellular surface.
Outside-out Patch
The pipette is retracted while still in whole-cell configuration so that a membrane patch is produced that has the extracellular surface exposed.
ADVANTAGE: measurement of channel activity due to influence of extracellular chemical signals.
3 Major Structural Features of Channels
(1) Pore through which ions travel
(2) Selectivity filter in the pore which only allows certain ions to move through the channel
(3) Gate which opens or closes the pore in response to some stimulus
Electrical synapse
Gap junction proteins (connexons) connect the pre-synaptic and post-synaptic membranes. There is direct flow of electrical curent and small molecules occurs between the cells due to cytoplasmic connectivity. They are only excitatory and cannot be amplified. No neurotransmitters involved.
Chemical synapse
No contact occurs between pre-synaptic and post-synaptic membranes. No direct flow of electrical current occurs between the cells. Instead, transmission occurs via the release of neurotransmitters by the pre-synaptic cell to activate ion channels in the membrane of the post-synaptic cell. They can be excitatory, inhibitory, or amplified.
Excitatory Synapse
Sodium or calcium selective. Postsynaptic resting membrane potential rises beyond threshold.
Inhibitory Synapse
Potassium or chlorine selective. Postsynaptic resting membrane potential falls below threshold to suppress action potentials.
2 Types of Glutamate Receptors
(1) AMPA receptor is ionotropic so it binds glutamate and triggers conformational change to open ion channel so sodium can flow inside.
(2) mGluR receptor is metabotropic so it is a GPCR: upon ligand binding, G protein binds GTP after changing conformation and triggers alpha subunit to be released to bind to other protein to release signal.
Kinase
Kinase is an enzyme that mediates phosphorylated. By phosphorylating, a negative charge causes conformational change.
