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EEOB Exam 2 (Questions + Answers) Solved

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Which word is incorrect in the following statement? Placental mammals (Placentalia) form a monophyletic group. Monotremata is an ancestral lineage that diverged from the basal node in mammals during the Jurassic. Marsupial (Marsupialia) and placental mammals are sister clades. - ️️ancestral ...

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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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