EEOB 4550 Exam 2 Questions With 100% Correct Answers.
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EEOB 4550
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EEOB 4550
What does the change in membrane voltage depend on? - ️️depends on the ion
channels opened, not the neurotransmitter
some neurotransmitters can have both excitatory and inhibitory effects; depends on the
ligand gated channels in postsynaptic cell and the ion channels determining EPSP or
IPS...
EEOB 4550 Exam 2
What does the change in membrane voltage depend on? - ✔️✔️depends on the ion
channels opened, not the neurotransmitter
some neurotransmitters can have both excitatory and inhibitory effects; depends on the
ligand gated channels in postsynaptic cell and the ion channels determining EPSP or
IPSP
When are large axons used? - ✔️✔️rapid responses- cockroach startle/escape
response; sensory filiform hair receptors on back synapse to giant axon that goes to
thoracic region and then synapses with motor neurons in legs to allow quick escape
when they sense movement behind them
coordinated responses- squid mantle propulsion; stellate ganglion in brain synapse to
axons of varying size- large axon down the center and shorter axons going to the closer
regions, they all arrive at the same time since the larger axon has a faster conduction
velocity; allows for coordinated movement (squid axon is 800 micrometers while
mammalian is only 2 micrometers)
Why is the speed of an action potential important? - ✔️✔️resting potential, action
potential increase in membrane voltage, and action potential duration are about the
same in all organisms, but action potential speed varies greatly
speed is a limiting factor; things need to be processed in biologically relevant time and
propagation speed limits how big an organism can be and how complex
faster conduction allows for larger size
humans would not have developed their size or complexity without the speed we have
in action potentials
On what two properties of a neuron does the speed of an action potential depend? -
✔️✔️length constant and time constant
fastest action potential = small tau and large lambda
lamda (amplitude)- the distance at which delta Vm is reduced to 37% of the original Vm;
increased lambda means increased distance and increased speed
tau (slope)- time required for voltage change to reach 63% of its final value; want to
minimize tau; decreased tau means increased change in Vm and increased speed
How do invertebrates increase the speed of conduction? - ✔️✔️large diameter axons
,as diameter increases, speed increases
affects the cable properties (tau and lambda) of the axon- increases lambda and
decreases tau
tau is controlled by the change in resistance
- Rm decreases because larger diameter means more ion channels (Rm proportional to
1/D)
- Ri decreases because as you move away there is less attraction (emf) but as the
diameter increases the attraction of ions to other ions down stream increases and there
is more room for the charge to move (less friction) (Ri is proportional to 1/D2)
- Capacitance increases as diameter increases which is in the wrong direction but it
does not have as big of an effect as resistance
lambda is also affected change in resistance
- lambda is proportional to Rm/Ri
- Rm is is proportional to 1/D and Ri to 1/D2
- substitution gets you that lambda is proportional to D2/D which equals D, so diameter
increases, lambda increases
- conduction velocity can be increased by increasing rm or decreasing Ri since lambda
is proportional to Rm/Ri
- Ri is decreased in large axons
drawback to large axons in invertebrates - ✔️✔️take up more space
energetically expensive
How do vertebrates achieve high conduction velocity? - ✔️✔️myelinated to increase
conduction velocity
increases conduction velocity because of its effects on tau and lambda
- tau decreases because capacitance decrease: there is increased distance between
ICF and ECF so the ability to store charge in the membrane decreases because of the
increased separation of charge across a wider membrane
- lambda increases because Rm increases- there is no ion flow across the membrane
where there is myelin so Rm is high (and lambda proportional to Rm/Ri)
Oligodendrocytes - ✔️✔️CNS glial cells; send out branch of plasma membrane and
wraps around axons, cytoplasm is squeezed out so only the phospholipid bilayer
remains, forms a layer of liquid insulation
Schwann cells - ✔️✔️PNS glial cells; one cell wraps its entire self and cytoplasm is
squeezed out
, Nodes of Ranvier - ✔️✔️gaps between adjacent bands of myelin (where ion channels
are located)
What consequences does myelination have for the vertebrate nervous system? -
✔️✔️allows for faster neural processing and larger body size
if vertebrates lacked myelin they would require much larger organs in nervous system
(spine would need to be diameter of entire body) and it would be much more
energetically expensive because more tissue would require more energy and nutrients
effects of demyelinating disease: multiple sclerosis (MS) causes demyelination which
means there is no longer increased Rm, tau increases, lambda decreases and the
action potential just stops
saltatory conduction - ✔️✔️the jumping of action potentials from node to node; opening
and closing of ion channels exclusively at Nodes of Ranvier
speeds the arrival of the impulse at the nerve terminal in comparison with slower
process of unmyelinated axons
action potential is initiated, it goes down stream and reaches more Na+ channels at
nodes, does not decrease in velocity as does unmyelinated
What events occur at a synapse to produce post synaptic potentials (PSPs)? - ✔️✔️1.
membrane voltage is depolarized by an action potential
2. voltage-gate calcium channels open (intracellular Ca2+ is low so it enters the cell)
3. neurotransmitter is released (Ca2+ mobilizes vesicles of NT and triggers fusion to the
axonal membrane which causes the release of NT into the synaptic cleft)
4. NT binds to receptors on postsynaptic neuron
5. NT binds to ligand-gated ion channels which initiates a voltage change
6. movement of ions through channels generates a graded potential
7. Neurotransmitter is removed from the synaptic cleft three ways
- enzyme degradation
- reuptake of NT back into cell to be recycled
- diffuse away from cleft
Na+ channel - ✔️✔️EPSP, increases likelihood of AP because it depolarizes cell
(makes it more positive because positive charge is entering cell)
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