Lecture 5: Synapse and Nervous System

The nervous system is a network of billions+ nerve cells linked in a highly organized manner to form the __________ __________ of the body.

control system.

Nerve cells (neurons) carry electrical signals rapidly (and often over long distances) to relay messages from one __________ of the cell to the other.

side.

Most neurons release chemical signals (neurotransmitters) into __________ to signal between cells.

ECF.

Other neurons use __________ __________ to allow electrical signals to travel between cells.

gap junctions.

Glial cells provide __________ to the neurons.

support.

Glial cells do not participate in the __________ __________ of electrical impulses.

direct transmission.

Glial cells outnumber neurons by:

>10 to 1.

Neuron cell body contains the __________.

organelles.

Neuron dendrites collect __________ from the surrounding cells.

signals.

Neuron axon conducts the __________ __________ away from the cell.

action potential.

Axon __________ is where the axon leaves the cell.

hillock.

Axon hillock has a concentration of:

Na+ gated channels.

Axon hillock is the site where action potentials are __________ by graded potentials (if of sufficient magnitude).

initiated.

Axon terminal releases __________ __________ in response to action potential to influence other cells.

chemical messengers.

Axons convey information of a single __________.

modality.

Neurons are described using three terms:

1. direction of information flow.

2. anatomical distribution of information flow.

3. embryological origin of structure being innervated.

Neuroglia does not conduct __________ __________.

nerve impulses.

Neuroglia communicate to nerves and other glial cells via __________ __________.

chemical messengers.

Neuroglia serve as __________ __________.

connective tissue.

Neuroglia maintain the __________ __________.

extracellular environment.

Four types of neuroglia found in CNS:

astrocytes, oligodendrocytes, microglia, ependymal cells.

Two types of neuroglia found in PNS:

Schwann cells, satellite cells.

Astrocytes are the __________ and __________ support.

physical and chemical.

Astrocytes supply __________ to neurons.

fuel.

Astrocytes regulate __________.

K+

Astrocytes synthesize __________.

neurotransmitters.

Astrocytes form the __________.

BBB (Blood brain barrier).

Astrocytes act as a neural __________ __________.

scar tissue.

Myelin-producing cell in CNS:

oligodendrocytes.

Myelin-producing cells in PNS:

Schwann cells.

Microglia is found in __________.

CNS.

Microglia is an __________ __________ cell.

immune defense.

Action potentials are brief, rapid, large (100 mV) changes in membrane potentials during which the potential actually __________.

reverses (inside of the cell becomes more positive than the outside).

Action potentials only involve a __________ portion of the membrane.

small.

Action potentials are propagated in a non-__________ fashion.

non-decremental (they do not diminish in strength from the site of initiation as they travel).

Either an excitable membrane responds to a triggering event with a __________ action potential or it doesn’t respond at all.

maximal.

The graded potential describes local changes in potential that occur in varying degrees of __________.

magnitude.

Graded potentials are usually produced by a specific triggering event that causes gated ion channels to open in a __________ region of an excitable cell membrane.

specialized.

The magnitude of the initial graded potential is related to the magnitude of the __________ __________.

triggering event.

The stronger the triggering event, the more gated channels open, the more ions pass through, the greater the __________.

depolarization.

The longer the duration of the triggering event, the longer the duration of the __________ __________.

graded potential.

When a graded potential occurs locally, the remainder of the membrane remains at __________ __________.

resting potential.

The temporarily depolarized region during a graded potential is called the __________ __________.

active area.

The active area is relatively more __________ than the neighboring inactive area, which are still at resting potential.

positive.

Graded potentials die out over __________ __________.

short distances.

Ions leak through open channels during a graded potential, resulting in a loss of __________.

current (magnitude decreases with distance traveled).

Graded potentials have __________ signaling distance but are critical for body function.

limited.

Post-synaptic potentials, receptor potentials, end-plate potentials, pacemaker potentials, and slow wave potentials are all examples of:

graded potentials.

Voltage-gated Na+ channels have 2 gates:

activation gate and inactivation gate.

Configurations of voltage-gated Na+ channels:

three:

closed but can open

open (activated)

closed but can open (inactivated)

Both gates must be open to allow the flow of __________ into the cells.

Na+.

Inactivated configuration of voltage-gated Na+ channel:

closed but incapable of opening.

Activated configuration of voltage-gated Na+ channel:

open.

Voltage-gated K+ channel has __________ __________.

one gate.

Configurations of voltage-gated K+ channel:

two:
open (activated), and closed (inactivated).

At resting potential, both types of voltage-gated channels are __________.

closed.

At resting potential, no __________ or __________ can flow through voltage-gated channels.

Na+ or K+

At resting potential, Na+/K+ can leak into and out of the cell due to the __________ __________.

leak channels.

The neuron has very few __________ leak channels.

Na+

The neuron has many __________ leak channels.

K+.

The resting membrane is 75x more permeable to __________ than __________.

K+ > Na+

When a membrane begins to depolarize from a triggering event, a few voltage-gated __________ channels open.

Na+

When a membrane depolarizes, Na+ begins to move __________ the cell down its concentration and electrical gradient.

into.

Further depolarization of the membrane leads to more opening of voltage-gated Na+ channels (__________ feedback loop).

positive.

At threshold, enough Na+ gates have opened to set off the __________ feedback loop.

positive.

At threshold, Na+ __________ dominates the membrane.

permeability.

At threshold, Na+ rushes into the cell, making the inside of the cell more __________ than the outside.

positive (trying to approach +60 mV).

At +30 mV, Na+ channels close to the __________ state and potential starts to fall back to resting values.

inactivation.

When Na+ channels are triggered to open, the channel’s “closed but inactive” process is initiated, like a __________ response.

delayed.

At peak, the K+ channels begin to open slowly, __________ membrane permeability to K+.

increasing.

K+ rushes __________ of the cell down its concentration gradient and electrical gradients to return to __________ __________.

out; resting potential.

Na+ channels return to their initial __________ configuration.

closed (but capable of opening).

K+ channels slowly close, allowing a slight excess of K+ to leave the cell, causing a __________ __________.

transient hyperpolarization.

The __________ __________ is the period of time where a new action potential can not be initiated by normal events in a region that has just undergone an action potential.

refractory period.

__________ refractory period has complete unresponsiveness.

absolute.

During absolute refractory period, Na+ channels are in an __________ state.

activated (they can’t be opened more until resting potential is restored and gates return to the initial closed but ready state).

__________ refractory period can initiated an action potential but the triggering event must be considerably stronger.

relative.

Relative refractory period is due to slow __________ of K+ channels.

closing.

Relative refractory period is during __________ state, so to reach the threshold, a stronger trigger must be applied.

hyperpolarized.

By the time the refractory period is over, the __________ __________ has moved far enough away so as not to influence the initial site.

action potential.

The refractory period limits the __________ of action potentials.

frequency.

Refractory periods vary in __________ in different types of neurons.

length.

A single action potential involves only a small patch of total __________ __________.

surface membrane.

The action potential is initiated in one part of the cell membrane that results in self-perpetuating __________ along the rest of the fiber.

propagation.

Depolarization causes positive charges to spread through the cytoplasm away from the site of __________.

depolarization

The __________ __________ __________ causes membrane potential changes resulting in the opening of voltage-gated Na+ channels which causes further depolarization.

local current flow.

Once an action potential is triggered, the impulse is propagated along the length of the axon without further __________.

stimulation.

Two methods of propagation:

contiguous, saltatory.

Contiguous propagation spreads an AP down the entire __________ of an axon.

length.

Contiguous propagation axons lacks __________.

myelin.

AP jumps between nodes to conduct the AP down the axon in __________ propagation.

saltatory.

Saltatory propagation axon possesses __________.

myelin.

The speed of an action potential is dependent on fiber __________.

diameter.

Resistance hinders electrical charge movement (current) thus as diameter increases, resistance __________.

decreases.

Some signals need to move so fast that the size of the fibers would be too __________ to support.

large.

Myelin is composed primarily of __________.

lipids.

Myelin acts as an __________ to prevent the movement of ions across the myelinated portions of the membrane.

insulator.

Myelin is not part of the neuron itself, but from __________ __________ that wrap themselves around the axons.

support cells.

Myelin makes impulses travel __________ faster and consumes less energy.

50x.

Na+-K+ pumps only need to work at the __________ regions when myelin is present, therefore less ATP is consumed.

nodal.