TEST 3- Neuron Physiology

Pumps

Membrain proteins that maintain a concentration gradient by moving substances agaist their concentration gradient. Require cellular energy,

Neurons

_____ have sodium-potassium pumps and calcium pumps in their membranes

Channels

Protein pores in the membrane that allows ions to move down their concentration gradients (into or out of the cell)

Leak channels

Type of channel that is always open for contious diffusion (passive)

Chemicallu gated channels

Type of channel that is normally closed, but open when neurotransmitters bind

Voltage-gated channels

Type of channel that are normally closed, but open when the membrane charge changes

Resting state

The first state of voltage-gated Na+ channels where the activation gate is closed and the inactivation gate is open- the entry of Na+ is prevented

Activation state

The second state of voltage-gated Na+ channels where the activation gate is open (due to voltage change) and the inactivation gate is open allowing Na+ to move through the channel

Inactivation state

The third state of voltage-gated Na+ channels where the activation gate is open but the inactivation gate is closed-the entry of Na+ is prevented. This state lasts a short time- the channel quickly resets to resting state

Modality gated channels

normally closed, but open in response to a stimulus other than a chemical or a voltage; Found in membranes of sensory neurons that respond to changes in their in their enviroment

Receptive segment

functional segment of a neuron: Cl- chemically gated channels found in the dendrite and cell body

Initial Segment

functional segment of a neuron: voltage-gate Na+ and K+ channels found on the axon hillock

Conductive Segment

functional segment of a neuron: voltage-gates Na+ and K+ channels found on the axon and its branches; action potential involves depolarization adn repolarizati

Transmissive segment

functional segment of a neuron: voltage-gated Ca+ channels and Ca+ pumps within the synaptic knob

K+ diffusion is the most imortant factor in setting RMP

K+ diffues out of the cell

limited by the electrical gradient- the pull of the negative RMP on the positive ions

if K+ were the only ions that were leaked, RMP would be where the K+ concentrationa and electrical grafients are at equilibrium (-90mV)

Since there are a few Na+ leak channels, Na+ also influences RMP

Na+ diffuses in to the cell

This small Na+ leakage means RMP is less negative (-70mV)

Describe neurons at rest in regards to resting membrane potential.

it maintains the concentration gradient for these ions

What is the role of Na+/K+ pumps

Graded potentials

small short-lived changes in the RMP

depolarization or hyperpolarization

Graded potentials in reference to the recpetive segment vary in degree and direction of change of RMP, this means the differences can be large or small and they can cause _________ and _______

Excitatory postsynaptic potentials- EPSP

Inhibitory postsynaptic potentials-EPSP

Graded Potentials are also known as postsynaptic potentials.

What is the term for a postsynaptic potential that results in depolarization?

What is the term for a postsynaptic potential that results in hyperpolarization?

Na+ entry

EPSPs are depolarizations caused by ______

K+ exit or Cl- entry

IPSPs are hyperpolarizations caused by ____ exit or ____ entry

Summation

In the Initial segment, __________ of EPSPs and IPSPs occurs at the axon hillock

open

Action potential

If threshold is reached at axon hillock (initial segment)→ voltage gated channels_____ and an _________ is generated

Spatial Summation

summation at multiple locations recieve neurotransmitters simultaneously and genrate postsynaptic potentials

Temporal Summation

summution where a single neuron repeatedly releases neurotransmitters and produces multiple EPSPs within a very short period of time

If the threshold is reached in the intial segment(axon hillock) then an action potenial is generated and send down without any loss of intensity

If it is not reached, the voltage-gated channels stay closed, no action potential is genrated

the axon reacts to values greater than the threshold

What is the All or none law and which segment does it apply to

1) voltage-gated channels are closed

2) Na+ enters, voltage-gated Na+ channels open

3) Na+ enters the axon resulting in a positvie potential

4) Na+ channels close becoming inactive temporarily

Steps 1-4 repeat in adjaacent regions and the impulse moves toward the synaptic knob

Decribe the steps of depolarization in generating action potentials

1) depolarization opens the K+ channels, K+ diffuses out of the cell resulting in a negative membrane potential

2) Channels stay open longer, K+ exits making the cell more negative than RMP

3) channels stay closed and the RMP is reestablished

repeat in adjacent regions and the impulse moves toward synaptic knob

Describe the steps of repolarization in generating Action potentials

1) the unstimulated axon has a resting membrane potential of -70mV

2) graded potentials reach the inital segment and are added together (-70mV → -55mV)

3) Depolarization occurs when the threshold (-55mV) is reached; voltage-gated Na+ channels open and Na+ enters rapidly changing the charge to positive (-55mV → +30mV)

4) Repolarization occurs due to the closure of the voltage gated Na+ channels-inactivation state- and opening of voltage gated K+ channels. K+ moves out of the cell and the cell is nce again negative (+30mV→-70mV)

5)hyperpolarization occurs when the volatafe gated K+ channels stay open longer than the time needed to reach the resting potential (-70mV→ -80mV)

6) Voltage gated K+ channels are closed and the plasma membrane has returned to resting conditions by the activity of Na+/K+ pumps (-80mV→ -70mV)

What are the events of an action potential

Refractory period

When it is impossible or difficult to fire another action potential in the conductive segment

Absolute refactory period

type of refactory period when no stimulus can initiate another action potential; Na+ channels are open then inactivated

Relative refactory period

type of refactory period When some k+ channels are still open; cell is slightly hyperpolarized and further from the threshold

Unmyelinated

Continoud conduction occurs on___________ axons

Continuous conduction

Conduction form when the charge opens the voltage gated channels→ opens more channels sequentially

Myelinated

saltory conduction occurs on _________ axons

Saltory Conduction

conduction form where the action potential occurs only at neurofibril nodes; much faster and myelinated cells used less ATP to maintain resting membrane potential

Ca²⁺

in the transmissive segment motor neuron potential opens voltage gated ____ channels

synaptic vesicles

neurotransmitters

in the transmission segment Ca²⁺ binds to porteins associated with ________ and triggers exocytosis→ vesicles fuse woth membrane, ________ is released into the cleft

Graded potential

Smaller and local. Neuron’s receptive region due to ion flow through the chemically gated channels→ positive or negative changes. Have larger potential change to stronger stimulus

(graded potential or action potential)

Action potential

Nerurons conductive region (axon). Involve depolarization (Na+ in) then repolarization (K+ out)

Follows the all or none rule down the enire axon

(graded potential or action potential)

Faster

more

When motor nerves fire at a _____ frequency it causes muscles to generate _____ tension; Firing frequency can influence the type of transmitter released

Neurotransmitters

are synthesized by neurons and stored within the vesicles in the synaptic knob; released from vesicles when the action potential triggers calcium entry into the synaptic knob; bind to a receptor in a target cell; trigger a physiologic response in the target cell