A&P 1 TEST 3 gantz

6.Why do we maintain a resting membrane potential? Put another way, why don't we create an electrical charge across the membrane when we want to send a signal? What would be the benefits if we did this?

25-40% of the energy used by your nervous system is used by Na+K+ ATPase ; can be up to 60% during intense activity Alternative way: Benefit: it would save energy; Drawbacks: its slower; you could have lag time so slower response as well Talk about how much it cost: you have to keep the Na+/K+ pump on which is so expensive, but this allows us to send stuff so much faster and respond to our environment. For example, if we didn't have these more expensive, faster responses we would fall over a ton.

Describe a nerve impulse, i.e. how do you generate an action potential? Include the role of graded potentials, action potentials, and myelination/saltatory conduction

A nerve impulse is an electrical signal that travels along an axon. There is a kind of stimulus that activates a graded potential. 1. The neuron is at a resting state. A stimulus, usually a graded potential is created first and is passed to the adjacent neuron and an action potential is started by depolarizing the cell. Depolarization only happens after the neuron reaches the threshold, -55mV 2. Depolarization: Sodium channels open letting sodium come into the inside of the - cell 3. Repolarization: cell is brought back to resting potential by opening K channels and closing Na channels 4. Hyperpolarization: is goes past the -70mV testing potential The more myelinated the cell the more efficient it is in sending signals because it is well insulated, but myelination comes at a great cost, so it is only done in cells that do a lot of signaling

What is axonal transport? What are the different types and what does each accomplish? Why is it necessary? What happens when axonal transport stops?

Axonal transport: essential for neuronal function;Axonal transport is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts (i.e. organelles) to and from a neuron's cell body, through the cytoplasm of its axon Anterograde movement: movement away from the cell body in the axon. Axons don't have a rough ER or a Golgi apparatus, so the axons rely on the this transport to provide the function of these organelles. Mitochondria, cytoskeletal elements, vesicle (which have material that can repair cell membranes and cell contents), neurotransmitters, and enzymes are moved into the axon. Retrograde movement: movement from the axon to the cell body. It mostly moves organelles back into the cell body to be degraded or recycled. It also carries signals from the axon to the cell body about the condition of the axons.

Why do we put so much effort into a complex nervous system? Include discussion of the biological importance of both basic and complex functions of the nervous system.

Basic functions: Motor(movement, tone, posture), sensory, autonomic (reflexes, organ function, etc) blood pressure, hydration. Higher function: cognition, emotion, consciousness Value: community building, learning patterns(animal behavior for hunting, seasons, avoiding predators. Later on, agriculture, crop rotations, cultivation and breeding programs, etc), being invested in others well being

What are the differences between action potentials and graded potentials? Please include both the underlying physiological differences and the locations in which they occur.

Graded potential(dendrites and cell bodys): incoming signals that have variable strength and usually travel short distance. As small patch of the membrane depolarizes. Depolarization spreads across the membrane through attraction of opposite charges. The current leaks across the membrane making the voltage decrease with the distance from the signal. This makes the signals short distance. Happens right next to where action potentials happen Action potential(axons): long distance signals that travel along the axon and always maintain the same strength. Action potential occurs once the graded potential depolarization spreads to the membrane in the axon, which causes a change in the membrane potential allowing the voltage-gated sodium channels to open at -55mV. Sodium rushes in to the axon and depolarizes it. Once it reaches somewhere between +30 and +40, the voltage-gated sodium channel closes and the voltage gated potassium channel opens somewhere between 0-40, which causes repolarization and the K flows out of the axon. The cell repolarizes then hyperpolarizes

6. Describe the physiological mechanism underlying chill coma in insects. Make a connection between this and human health.

Lower temperatures cause chemical reactions to occur slower.. The Na+K+ ATPase works more slowly, so ion leak across the cell happens faster than the Na+K+ ATPase and you lose the ability to maintain different concentrations, thus you lose the membrane potential so your neurons won't be able to fire. Insects have an adaptation in which they can bring more Na+K+ ATPase to make up for the slowed activity. Na+K+ ATPase dysfunction is the main culprit for migraines. Studying the neurophysiological adaptations to cold in locust has improved our understanding of how Na+ K+ ATPase functions under stress. Sodium and potassium ATPase can't keep up with ion leak across the membrane and can't maintain the resting membrane potential..

3. What does multiple sclerosis do to the nervous system? How does this affect nerve impulses and our ability to coordinate movements?(on 10/31 slides)

Multiple sclerosis attack and destroy myelin sheaths. Loss of coordination happens because the speed at which signals are being sent is drastically slowed. You have to put a lot more energy into nerve impulses because you have to turn on the Na/K to help stop more leakage.

Discuss the different types of neuroglia and their roles in the central nervous system. How do these fit in with the primary functions of the nervous system?

Neuroglia: smaller cells that support and protect neurons Astrocytes(CNS): cling to neurons and envelop capillaries, supporting neurons and anchor them to their nutrient supply; help establish connections between neurons, control chemical environment Microglial cells(CNS) part of the immune response in the CNS; sense when neurons are damaged and migrate toward them, convert to special type of macrophage when invading bacteria or viruses are present Ependymal cells: lining of cavities in CNS; ciliary action helps to circulate cerebrospinal fluid Oligodendrocytes(CNS): provide electrical insulator to neurons called myelin Satellite cells(PNS): protective role, similar to that of astrocytes Schwann cells: similar role as oligodendrocytes, providing myelin sheath to neurons

Do nerves suffer from surface area-to-volume ratio issues like muscle cells do? Why or why not?

No, because muscle cells are bundles of bundles and have to diffuse a long way to get to the middle. The largest neurons in the body are as thick as the smallest muscles in your body. Neurons can be huge cells, but they are not thick, just long so the length doesn't really affect the surface to volume ratio.

How is retrograde axonal transport used in gene therapy?

Retrograde transport: movement from the axon to the cell body. Virus can hijack this system to invade the nervous system. Researchers use viruses that are encoded with the corrected gene that will be transported into the nervous system.

Describe the three parts of communication through the nervous system (i.e. sensory input, integration, and motor output).

Sensory input: gathering information about environment, both inside and outside the body Integration: processing and interpreting all this information Motor output: a response generated because of sensory input and integration SIM

Why do we convert electrical signals to chemical signals in neurons? Include both benefits and negative effects of this conversion.(10/31)

Take an electrical signal from one end to the cell to another end of the cell, converting it to a chemical signal to cross the synapse, and switches it back to the electrical signal once it passes over the synapse. Steps: The axon terminal receives action potential, which causes voltage gated calcium channels to open and release calcium, which causes the release of neurotransmitters across the synapse. Neurotransmitters diffuse across synapse, binds to receptors, open ion channels to start a graded potential. Neurotransmitters are taken back up by presynaptic axon to use again or broken down by enzymes. Negative effects: this conversion is slower because you have to convert these electrical to chemical conversions. Typical synaptic delay is 0.3 to 5 milliseconds. Benefits: A chemical signal can be more complex than an electrical signal; electric singals can only be on or off while chemcial signals can be excitatory or inhibitory, so this makes it possible for you to inhibit or make something more sensative not just turning things on and off.

How do we discern severe stimuli from mild ones? What neurophysiological phenomenon is important in this distinction?

The frequency of an action potential signal. A stronger signal tells your brain how to interpret the stimulus; the action potential always changes at the same intensity, despite the signals strength. The strength just tells your brain how strong the stimulus is. For examples a weaker signal would come from a light slap when compared to mike Tyson wrecking your face with a punch (a stronger signal), which tells you brain that the punch is way worse that a light slap. This is how we differentiate stimuli.

Describe the competing interests between neuron size (thickness, not length) and rate of impulse conduction. Why do only a few of our neurons maximize speed? What types of neurons maximize speed of conduction and what types do not?

The thicker the axon=cost more to maintain=has faster conduction Neurons with myelinated axons maximize the speed of conduction. Also talk about how the energy expenditure of the Doubling the size of the axon cost 4 times the amount of energy used while only doubling the speed of conduction That is why we have only a hand=full of thick myelinated, because they cost so much but don't proportionately speed up

Most animals have nervous systems that function using pretty much the same basic principles. What does this suggest about the origin of the nervous system?

They have a common origin. There is pretty much only one way to solve the problem.

How do some diseases use axonal transport to their benefit?

They hijack retrograde movement to get from the body of the axon into the cell, which allows the diseases to invade the nervous system. Examples: Herpes Simplex, tetanus, rabies, and polio. There is a delay between the infection and the symptoms because of how long it takes to move into the CNS

Describe how we generate resting membrane potentials

We generate resting membrane potential by the use of sodium/Potassium pump, and maintain it by simple diffusion of Na+ and K+. The sodium Potassium pump; pumps ions against their concentration gradient, and maintains the charge inside the cell negative and the outside the cell positive. Our resting membrane potential is -70 mV. (Draw diagram)

Why is it likely that some dinosaurs had different methods than we do for axonal transport? Please include how the physical structure of neurons contributes to this problem (i.e. what about the size/shape/organization of neurons makes it so there is a problem in the first place).

Yes, they probably did have a different method as it would have a delay if they used our method since their neurons would have been extremely long.