1. conduct ions very rapidly (1 million ions/sec/channel)

2. Recognize & select among specific ions (Na,Ca,K)

3. Open & Close in response to specific electrical, mechanical, or chemical signals: gated channels

T/F: A non-gated channel produces an RMP.

TRUE

What is gated channel opening regulated by?

For gated channels, what fluctuates depending on the condition being met?

Gates fluctuate between open & closed states

If gated channels are open they are ________, if they are closed they are __________.

If gated channels are open they are activated, if they are closed they are inactivated.

T/F: There is no difference in the probability  of a channel opening therefore, gated channels are normally open unless shut by the appropriate stimulus.

FALSE 

There is a no difference in the probability  of a channel opening therefore, gated channels are normally open closed unless shut opened by the appropriate stimulus. 

Some channels are frequently _______ open at rest and _______ in response to a stimulus.

Some channels are frequently open  at rest and closed in response to a stimulus.

What do voltage gated channels open/close in response to? What is this associated with?

voltage changes associated with a movement of a charged region of the channel through the electric field of the membrane.

What drives voltage gated channels between the open/closed states?

Changes in the membrane voltage that tend to move the charged region back and forth through the electric field.

What type of channel can enter a refractory period after activation? What is this due to?

-Voltage-gated channel

-Probably due to a conformational change in the channel: inactivation

Intracellular application of enzymes can remove the refractory period without affecting _____channel activation

voltage-gated Na channel

What type of channel is inactivated by Ca influx, an increase in intracellular Ca either binds to an intracellualar site that changes the channels confirmation, or the Ca activates an intracellular enzyme that inactivates channel by protein dephosphorylation?

Voltage gated Ca channels

What is a stimulus gated stretch-activated channel?

A mechanically gated channel that open/closes in response to physical/chemical stimulation (Pacinian corpuscle)

What must be appropriately stimulating to cause a neuron channel to open in stimulus gated stretch-avticated channels? Then, how is the energy transferred?

lemellae.

The energy associated with membrane stretch is thought to be transferred to the channel through the cytoskeleton.

What type of channel opens/closes in response to neurotransmitters (NTs)/extracellularly applied chemicals? Give examples of these NTs.

Ligand-Gated Channels

ACh, Seratonin, dopamine

Do NTs enter the cell? What is there role?

NO. They act as a key to open a door and allow simple ions to enter the neuron (K, Na, Ca)

What occurs after a ligand-gated ch. is exposed to a high concentration of ligands?

The channels enter a refractory state: "desensitization"

What type of channel is found in cell somas, responds to intracellular molecules, and internally regulates neurons by activity w/in the neuron?

Messenger-Activated Channels

What is the basis for NS functioning and depends on rapid changes in the electrical potential difference across neuron membranes?

neuron signaling

What makes an electric potential possible?

Ion channels and the flow of ions across the plasma membrane

Where are ion channels found? What two types of cells in particular?

In many cells, however, nuerons and muscle cells have a rich variety and high density of membrane ion channels.

What is a resting membrane potential (RMP) and what is the basis of membrane signaling?

a steady state that is often disturbed

What is the most common RMP and what is another RMP for some neurons?

-70mV and -80mV

What is the RMP of a vertebral photoreceptor and why?

-40mV due to leakage of Na into the cell

How is an RMP generated?

a cell with a semi-permeable membrane  is selectively permeable to K+ with a solution of KCl on either side, only the K+ ion can cross the membrane.

What characteristics do glial cells have in relation to K+?

They regulate K+ and therefore, when glial cells are at rest, they are selectively permeable to K+

What ions are inside the cell and what ones are outside the cell?

K+ and anions are inside the cell and Na+, Ca2+ and Cl- are outside the cell.

For every _______ there is a ________.

For every + there is a -

T/F: there is chemical neutrality on both sides of a membrane

TRUE

What produces extra cations outside the cell and extra anions inside the cell?

K+ diffuses down its cencentration gradient out of the cell then, the concetration gradient decreases and an electrical gradient appears (+outside, - inside) causing this.

What produces an electrostatic attraction?

when K+ charges that have left the cell are attracted to the - charges inside the cell that were left behind.

When are two opposing forces working on each K+ ion? Name the two forces.

When the electrical gradient is formed and the K+ is being attracted back into the cell by the - anions along the inside of the membrane. There is one chemical force and one electrical force.

What will occur when an equilibrium potential is reached and the electrical gradient is balanced?

The K+ concentration inside the cell will equal that outside the cell

T/F: Once an equilibrium is established it will remain so with no Energy expenditure.

TRUE

What are the roles of action potentials (APs)?

1. conduct information (signals) long distances

2. release chemical transmitters (synaptic transimission)

What must be used to relay messages (via transmitters) from one neuron to another?

a synapse

What is an AP?

a booster system that allows electrical conduction over long distances; an all or none response; has a set amplitude

Will a stronger stimulus evoke more APs?

No, larger ones.

What are localized graded potentials?

play an essential role in specialized regions and spread short distances; the bigger the stimulus, the larger the graded potential

What is the potential of a cell due to?

Uneven distribution of electrical charges across the membrane; the norm is -65mV

What are receptor potentials?

changes in membrane potential brought about by sensory stimuli of sensory nerve terminals (specialized to respond to a particular type of stimulus)

What are synaptic potentials?

changes in membrane potential in a specialized region of a neuron that is designed to receive info from another neuron.

Are graded potentials localized/decremental? How far do they travel?

YES. 1-2mm

What are the roles of graded potentials?

Enable  neurons to perform their integrative function and initiate APs.

What are regenerative APs?

Occur only when stimulation (voltage change caused by stimulation) reaches threshold (-55mV); does not occur if stimulation is sub-threshold

What does threshold mean?

The potential at which an AP is generated 50% of the time.

What type of AP has a large amplitude, is conducted rapidly, and short duration (1-5ms)?

Regenerative AP

T/F: The size of AP is non-decremental because the size doesn't change.

TRUE

___________ is an important part of integration.

Summation

Why do regenerative APs usually arise?

Due to input from different sources

T/F: APs travel along long distances with  attenuation.

FALSE

...with NO attenuation

What do the steps in the generation of an AP involve?

activation of voltage-gated channels (Na, K)

What are the steps in the generation of an AP?

1. initial signal

2. disturbance of RMP

3. At threshold, voltage dependent Na+ channels open which causes a large increase in the permability of the membrane to Na+

4. Ions flow in direction of concentration gradient/electrical gradient

5. At -55mV, Na+ gates begin to inactivate

6. K+ gates activate at the peak of AP voltage which remain open and do not inactivate

7. Repolarization- time limited increase in Na influx; increase in K+ permability

T/F: K+ gates have a slower onset of opening

FALSE

Na+ gates do.

What ends during repolarization because voltage returns to resting level therefore, the voltage dependent condition is no longer met.

The increase of K+

What is the fastest firing of an AP?

400-500 AP/second

OR

150 m/s (for myelinated axons)

What occurs during the absolute refractory period?

Na inactivation: no amount of stimulation will reopen channels

What occurs during the relative refractory period?

A stronger than normal stimulus is required to elicit an AP because the threshold is higher

1. can have repetative firing due to long lasting depolarization

2. there is an upper limit on AP firing frequency

What is the upper limit on AP firing frequency?

1000Hz (1KHz)

What needs to occur for AP conduction?

What is saltitory conduction?

When AP conduction jumps from node to node where Na/K channels are clustered

The _______ diameter axon has a faster rate of conduction. What is this measured as?

-larger.

-conduction velocity.

What is the input/output rate of an unmyelinated axon?

0.5-10 m/s

What increases AP conduction?

myelination

What are characteristic of myelinated axons?

1. AP generation only occurs at the nodes; it's interrupted at the nodes

2. protective coating & provide nutrition for the neuron

3. Important in vertebrate evolution

4. produced by Schwann cells (PNS) and oligodendrocytes in the CNS

T/F: Oligodendrocytes myelinate one axon and Schwann cells myelinate several axons.

FALSE

opposite

What are demyelinating diseases?

MS- a loss of myelination-> loss of AP conduction

Alcoholism

Diabetes