Ch. 37 Nervous System

Parts of a Neuron/Types of Neurons

100

What is the role of a dendrite on a nerve cell?

receive chemical signals/pick up stimuli

200

What is the benefit of the axon being myelinated?

Helps action potentials propagate down the axon faster

- can jump between nodes

300

Sensory neurons transmit electrical signals from _______ to the _____.

PNS (peripheral nervous system) to CNS (central nervous system)

(Work with sensory receptors to transmit signals about the presence of a stimulus) 

400

Motor neurons trasmit signals from the _______to the _______.

CNS (central nervous system) to the PNS (peripheral nervous system)

(Send signals to either glands or muscles to execute an instruction)

500

What do interneurons do?

integrate sensory information and/or motor commands

Electrical part/Action Potential

100

True or False. You can stop an action potential once it has started traveling down the axon.

Bonus: What exactly is an action potential?

False. All or none event.  There is no such thing as a partial action potential.

Bonus: It is a rapid, temporary, and localized change in the membrane potential.

200

True or False.  It is the type of action potential that determines whether or not inhibition or excitation of the post-synaptic cell occurs.

Bonus: What aspect of an action potential can be changed?

FALSE  - All action potentials for a given neuron are identical in magnitude and duration

Whether or not an action potential from upstream nerve results in inhibition (hyperpolarization) of post-synaptic cell or excitation (depolarization) of post-synaptic cell depends on what neurotransmitter is released

Bonus: Frequency may vary as a result of signal input

300

What happens during hyperpolarization?

• Sodium channels are now closed, but some potassium channels are still open
• K+ rushing out of the cell can hyperpolarize the cell (make it more negative than resting potential) before rest is re-established

400

What happens during depolarization?

*More details the more points earned*

Bonus: Why does Na+ want to get into the cell?

• Stimulus opens some gated sodium channels --> Na+ inflow through those channels depolarizes the membrane (makes it more positive)
• If depolarization gets positive enough (reaches threshold) it triggers an action potential
• Depolarization opens voltage-gated sodium channels (= more Na+ inflow = makes membrane potential more positive), while potassium channels remain closed

Bonus: Sodium is subject to both a concentration and charge gradient

500

What happens during the repolarization phase?

*More details the more points*

• Most sodium channels become inactivated, blocking Na+ inflow (no more positive ions flowing in)
• Most voltage-gated potassium channels open, permitting K+ outflow = positive flowing out  (K+ wants to get out now because of sudden charge gradient --> inside becomes positive due to influx of Na+)
• Both of these things cause the inside to become negative again

Chemical part/Synapse

100

What is the synapse?

Bonus: True or False.  Action potentials can cross the synapse.

junction btwn the nerve and next downstream thing (could be another nerve, muscle fiber, hormone secreting organ)

Bonus: False

200

What are three ways to increase the transmission of a signal across the synapse (can be excitatory or inhibitory)?

1) increase the amount of neurotransmitter production

2) decrease the amount of enzyme within the synapse

3) increase sensitivty of post-synaptic receptors (ex --> can be amount of receptors)

300

What happens when an action potential arrives at a synaptic terminal?

-The membrane is depolarized, which opens voltage-gated calcium channels.

- The opening of these voltage-gated channels triggers an influx of Ca2+.

400

What happens when there is an elevated Ca2+ concentration in the synaptic terminal?

Synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft

500

What do the neurotransmitters do? (ones that just got released into the synaptic cleft)

- They bind to ligand-gated ion channels on the post-synaptic membrane, which results in a change in the membrane potential

- whether it is depolarized (excitation) or hyperpolarized (innhibition) depends on the type of neurotransmitter

Misc.

100

The inside of a nerve cell is ________relative to the outside.

negative

200

Threshold potential is what? (voltage)

Bonus: What happens if threshold potential is exceeded at the axon hillock?

roughly -55 mV

Bonus: An action potential occurs + gets propagated down the axon

300

What is resting potential? (the voltage)

Bonus: What keeps a cell at resting potential?

Bonus: How is this potential created?

roughly -70 mV

Bonus: Sodium-potassium pumps

Bonus: 

1) Sodium-potassium pumps pump 3Na+ out for every two K+ allowed in

2) Sodium has a larger charge density compared to potassium, so the cell is negatively charged on the inside compared to the outside

400

An action potential starts at__________and gets propogated down______.

Bonus:  Can a action potential be progagated up and down and axon (both directions)? Why?

axon hillock, axon

No - can only go from axon hillock -->down axon --->to axon terminals

- Can't go backwards becayse sodium channels are deactivated.  There is a lag period where sodiunm channels cannot be reopened = only goes forward

500

Why is it important that chemicals are involved at the synapse and it is not just an electrical process?

- With having a chemical component, responses to signals can be modified in response to other signals (multiple signals can be taken into account)

In other words:

- don't want an uninterrupted pathway from input to ultimate synaptic target

- you want a break in the pathway so as to allow for modulation