Phys Resting membrane potential Exam #1

What are voltage gated ion channels

- are activated by changes in the electrical membrane potential near the channel - at rest, its closed

How do you code for intensity of an action potential?

- by the frequency - more signals happening over short periods of time

Describe the role of calcium ions in the chemical synapse.

- facilitates the release of transmitter form the pre-synaptic terminal 1) an action potential depolarizes the axon terminal 2) the depolarization opens voltage-gated Ca2+ channels, and Ca2+ enters the cell ( calcium ions are more concentrated the extracellular fluid than in the cytosol, so they move into the cell) 3) calcium entry triggers exocytosis of synaptic vesicle contents 4) neurotransmitter diffuses across the synaptic cleft and binds with receptors the postsynaptic cell 5) neurotransmitter binding initiates a response in the postsynaptic cell

What is the relative refractory period?

- follows absolute refractory period, only exceptionally strong stimulus could stimulate an AP -threshold for AP generation is elevated (inside of membrane more negative than resting state) - most Na+ channels have returned to their resting state -some Ka+ channels still open -repolarization is occurring

Graded potentials may?

- hyper polarize the membrane -depolarize the membrane to the threshold voltage -initiate an action potential -be called EPSPs or IPSPs

Explain chemically-gated ion channels

- if the Na+ channel opens up, it goes down its gradient - when Na+ comes in, it goes more positive (depolarization) -if the K+ opens up, it goes out, down its chemical gradient, and the interior goes more negative (hyper polarization) - can be all over the place/ but considering them at the dendrites (receiving the signal)

Describe the anatomy of a typical multipolar neuron, then indicate the functions of each region

- most common - located in CNS (brain and spinal cord) - have 3 or more processes attached to the cell bodies - 1 process is the axon( which conducts electrochemical impulses aka action potentials) between cells -the remaining processes are dendrites (receiving incoming signals) - Schwann cells attach to the axons of your neurons, twist around them, leaving myelin sheath which speeds up acton potentials as they move down - leaves tiny gaps called nodes of Ranvier - these notes play an important role in the transmission of electrical signals along the axon

List and describe the components of a reflex control.

- neural pathway that controls an action reflex. - an integrating center makes the decision to respond to a change. a chemical or electrical signal to the target cell or tissue then initiates the response. long-distance reflex pathways involve the nervous and endocrine systems and cytokines. Receptor: Responds to stimulus (change in external/internal environment); Distal end of dendrites, sensory structure; Initiate impulse via local depolarization (graded potential) (site os stimulus action) Sensory neuron: Receptor to axon termination in CNS; Transmits afferent impulse Integration center :Sensory impulse to motor impulse; Direct (monosynaptic) or polysynaptic region in CNS Motor neuron:n Efferent impulses from integration center to effector Effector: muscles and glands

Glial cells do what?

- provide structural and metabolic support and help maintain homeostasis of the brain's extracellular fluid - help maintain homeostasis of the brain's extracellular fluid - provide structural & metabolic support -guide neurons during growth and repair

Why doesn't the local current flow backwards and trigger an action potential in the other direction?

- when a section of axon depolarizes, positive charges move by local current flow into adjacent sections of the cytoplasm. - there is a short period of time called a refractory period, when the ion channels are considered to be inactive, which prevents an action potential from turning back on itself

The absolute refractory period of an action potential does what?

- when voltage-gated Na+ channels open, neuron cannot respond to another stimulus -time from opening of Na+ channels until resetting of the channels -ensures that each AP is an all-or none event -enforces one-way transmission of nerve impulses ensures one-way travel down an axon, allows a neuron to ignore a second signal sent that closely follows the first, and prevents summation of action potentials

What is the refractory period?

-a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation -Short period Of time after an impulse travels, when a neuron cell membrane cannot be stimulated to carry an impulse *THE PERIOD OF TIME AFTER AN ACTION POTENTIAL WHEREBY THE NERVE OF MUSCLE WILL BE UNRESPONSIVE TO STIMULATION FOR THE NEXT ACTION POTENTIAL.

Describe the events that occur at a synapse.

1) an action potential arrives at the synaptic terminal 2) calcium channels open, and calcium ions enter the synaptic terminal 3) vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron 4) Neurotransmitter molecules diffuse across the synaptic cleft 5) The neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing ion channels there to open

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

1) concentration gradients ( how steep is that sodium or potassium gradient) - the only gradient that truly matters is the K+ gradient 2) leak channels

List 3 means by which the activity of neurotransmitter is terminated

1) enzymes inactivate them 2) can be returned to axon terminals for reuse or transported into glial cells 3) can diffuse out of the synaptic cleft

Each synapse has two parts, what are they?

1) the axon terminal of the presynaptic cell 2) the membrane of the postsynaptic cell

Distinguish between afferent and efferent neural signals in the nervous system

AFFERENT: sensory nerves -carry nerve impulses from sensory stimuli TOWARDS the CNS and brain " like smelling a smelly sock" EFFERENT: motor nerves - carry neural impulses AWAY from the CNS and towards muscles to cause movement " wanting to get rid of the scent of the smelly sock"

Distinguish between types of control pathways for maintaining a "set point" for homeostasis :extrinsic (reflex) controls, intrinsic (local) controls, and review the types of feedback loops (negative and positive)

AN INTRINSIC controlled system is inherent in an organ; the organ is capable of maintaining homeostasis within itself. For example, the heart can control its own heart rate. - a cell or tissue senses a change in its immediate vicinity and responds - stimulus and response restricted to a specific region of the body (involves paracrine or autocrine signals) EXTRINSIC CONTROL SYSTEMS (nervous and endocrine systems) exist outside of the organs they control; these systems can override intrinsic systems. For example, although the heart controls its own rate, a slamming door will prompt the nervous system to increase the heart rate externally. - coordination of the response lies outside of the stimulus area -involves a long pathway -nervous involvement or endocrine involvement

Compare and contrast action and graded potentials

Action potentials are a result of a neuron sending information down an axon. It creates an impulse or explosion of electrical activity that is created by depolarization. Depolarization is when there is a decrease in membrane potential and the inside of the membrane becomes less negative than the resting membrane potential (-70mV). When it reaches -55mV, the neuron fires an action potential. This is called the threshold, which is always -55mV. You can't increase or decrease an action potential. It is all or nothing. This is where the action potential will generate. They are also caused when different ions cross the neuron membrane. Sodium ions rush into the neuron because there are way more sodium ions outside than inside, as well as inside being negative. This makes the neuron more positive and depolarized. Potassium channels take a little longer to open but when they do, potassium goes out of the cell and reverses depolarization. The resting membrane potential (-70mV) is obtained again, however, potassium channels stay open a little longer causing hyper polarization. Eventually the ions go back to the resting membrane potential at -70mV. Graded potentials open in response to a stimulus, like the opening of a mechanically gated channel.However, they vary depending on the duration and strength of the stimulus. They occur in the dendrites and cell body and the ions involved are usually Na+, Cl-, and Ca2+. They are either depolarization or hyper polarization and short-lived. They also can be excitatory or inhibitory. An inhibitory potential mess the neuron less likely to have an action potential because it makes it more negative. An excitatory potential makes the neuron more likely to have an action potential by making the membrane less negative. Unlike action potentials, they do not have to reach threshold. A larger stimulus causes a larger depolarization. There is no minimum level required to initiate graded potentials. The initial stimulus strength is indicated by frequency of a series of action potentials.

Ch.5- #17 Describe how a resting membrane potential (RMP) is established, including a description of the ions responsible for the production of the potential and their relative concentration. Include sodium (Na+) and potassium (K+) leakage channels, in your description.

Before a neuron can conduct an electrical signal, a resting membrane potential must be established with a positive charge outside the cell and a negative cell inside the cell. When the cell is at RMP, the activation gates of the voltage-gated Na+ ion channels are closed and the inactivation gates are open. Voltage-Gated K+ channels are closed. Depolarization is initiated by a stimulus which makes the membrane potential more positive, (from -70mV going down), causing the voltage-gated Na+ ion channels to start to open. As threshold (-55mV) is reached, many sodium channels open. Na+ ions diffuse across the membrane causing depolarization. Voltage-gated K+ ion channels also begin to open, but more slowly. Therefore depolarization occurs because more Na+ ions diffuse into the cell than K+ ions diffuse out. As the membrane potential approaches maximum depolarization, the inactivation gates of the voltage-gated sodium ion channels begin to close and the diffusion of sodium ions decreases.The K+ ion channels remain open and K+ ions continue to diffuse out of the cell. The increased K+ ion permeability lasts slightly longer than the time required to bring the membrane potential back to its resting level. The extra K+ ions rushing out causes the membrane potential to become slightly more negative than the resting value (hyper polarization). After the voltage-gated K+ ion channels close, the sodium potassium pump kicks out 3Na+ and brings in 2 K+ ion which brings the RMP back to -70mV. The uneven distribution of ions influence the cell membrane. There are more concentration of Na+, Cl- and Ca2+ outside the membrane and more concentration of K+ inside the cell membrane. The resting membrane potential is more permeable to K+ than to Na+ and Ca2+ because there are many more leak channels than Na+, which makes K+ the major ion contributing to the RMP and also establishes electrical disequilibrium. 2 ways that affect RMp is the concentration gradient and the leak channels. One of the ways it can be established is by the sodium potassium pump, which uses ATP to transport 3 Na+ out of the cell and 2 K+ inside the cell. The sodium potassium pump establishes an electrochemical gradient Although both sodium and potassium ions are positively charged, the negate-inside membrane potential is maintained because the sodium potassium pump doesn't pump the same number of each in. Na+ goes down a chemical and electrical gradient. Neurons contain a variety of gated ion channels that alternate between open and closed states, depending on the intracellular and extracellular conditions.

Distinguish between & describe the following types of chemical messengers (cytokines), paracrine, autocrine, neurotransmitter, hormone, neurohormone.

CYTOKINES: are among the most recently identified communication molecules. control cell development, cell differentiation, & the immune response - communication proteins -act as both local and long distance signals -can function as both autocrine and paracrine signals -signals not produced by specialized cells -have a broad spectrum of target cells PARACRINE: is a chemical that acts on cells in the immediate vicinity of the cell that secreted the signal. - a form of cell signaling in which the target cell is close to the signal releasing cell AUTOCRINE: if a chemical signal acts on the cell that secreted it - a form of signaling in which a cell secretes a hormone,or chemical messenger that binds to autocrine receptors on the same cell, leading changes in the cell NEUROTRANSMITTER: when a neurocrine molecule diffuses from the neuron across a narrow extracellular space to a target cell and has a rapid effect - synthesized in the cell body or in the axon terminal - long distance communication - neurons also use electric signals for propagation -have a rapid effect -neuro-hormones released directly into blood -chemicals secreted by neurons that diffuse across a small gap to the target cell HORMONE: are chemical substances that act like messenger molecules in the body. after being made in one part of the body, they travel to other parts of the body where they help control how cells and organs do their work. NEUROHORMONE: when a neurocrine released by a neuron diffuses into the blood for distribution -any hormone that is produced not by an endocrine gland but by a specialized nerve cell & is secreted from nerve endings into the blood stream or directly to the tissue or organ whose growth or function it controls

What are leak channels

Channel proteins that are open all the time -Channels that remain open at resting membrane potential and thus DO NOT require depolarization to open them. contribute to maintenance of the RMP. Impose a barrier to depolarizaion that must be exceeded in order for a cell to reach the threshold for firing an action potential.

Are in most neurons and respond to a variety of ligands, such as extracellular neurotransmitters and neromodulaters or intracellular signal molecules.

Chemically-gated ion channels ( mostly closed, but only open in response to a chemical binding into it, a neurotransmitter binds, and makes it open up)

What type of conduction takes place in unmyelinated axons?

Continuous conduction

What happens during an action potential?

During an action potential, there is a brief reversal in membrane potential as the interior of the cell becomes positive (depolarization) and then returns to negative resting potential (repolarization). The action potential is the electrical signal generated by neurons that is used in long distance communication.

Explain how an excitatory postsynaptic potential (EPSP) and an inhibitory postsynaptic potential (IPSP) are generated in a post-synaptic neuron.

EPSP: occurs when the summation of potentials is strong enough to reach the threshold of activation - caused by depolarizing current through the postsynaptic membrane - cell is moving towards firing an action potential - occurs when ion channels allow negatively charged ions to move out & positively charged ions to move in - think of them as small action potentials that aren't strong enough on their own to reach the activation of a full action potential, meaning that enough positively charged ions have to flow into the postsynaptic membrane to open the ligand-gated ion channels. IPSP - less likely to generate an action potential - caused by hyper polarizing current through the postsynaptic membrane -Cell is moved farther away -from firing an Action Potential. Occurs when more negatively charged ions are added to an already negatively charged receptor cell. The same is true with an IPSP but in the opposite direction. Positive ions are leaving which is causing the cell to dip below its resting state, making it farther away from threshold and making it less likely to cause an action potential.

Describe the production, fast axonal transport, storage location and function of neurotransmitters in a typical multipolar neuron

FAST AXONAL TRANSPORT: goes in 2 directions, these motor proteins alternately bind and unbind to the microtubules with the help of ATP FORWARD: moves vesicles and mitochondria from the cell body to the axon terminal BACKWARD: transport returns old cellular components from the axon terminal to the cell body for recycling NEUROTRANSMITTER: when a neurocrine molecule diffuses from the neuron across a narrow extracellular space to a target cell and has a rapid effect - synthesized in the cell body or in the axon terminal - long distance communication - neurons also use electric signals for propagation -have a rapid effect -neuro-hormones released directly into blood -chemicals secreted by neurons that diffuse across a small gap to the target cel

What do components of electrochemical gradient dictates for Na+ and K+ in resting cell?

For Na+, the electrical component causes Na+ to want to go inside the cell, and the chemical component causes the Na+ ions desire to flow also inside the cell, due to differences in gradient concentration, since there is less Na+ concentration inside and more outside, sodium wants to flow from area of high solute to low solute concentration. For K+, the electrical component causes K+ to go inside the cell, and the chemical component causes K+ to go OUT of the cell, also due to differences in gradient concentration, since there is more K+ ions inside than outside the cell these ions want to flow from areas of high solute to low solute concentration.

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.

During an action potential, activation of voltage-gated sodium and potassium channels occurs at different rates. What is the effect of this difference on ion flow across an axon membrane?

Initially, Na+ flows into the cell followed by K+ flowing out of the cell

The falling phase of the action potential is due primarily to

K+ flow out of the cell only

What is the major determinant of resting membrane potential?

K+ ions

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

Myelinated vs Unmyelinated axons

MYELINATED speeds up the acton potential - you only have voltage-gated channels in the small regions where there is no myelin -so the current jumps from node of Ranvier, to node of Ranvier - if covered in myelin sheath, the impulse is faster limits the amount of membrane in contact with the extracellular fluid - as an action potential passes down the axon from trigger zone to axon terminal, it passes through alternating regions of myelinated axon and nodes of ranvier. -NONMYELINATED - the progression of the axon goes a little slower - not covered by myelin sheath, slower - has low resistance to current leak because the entire axon membrane is in contact with the extracellular fluid and has ion channels through which current can leak * myelin sheath is considered an electrical insulated, its purpose is to speed the transmission of nerve impulse.

In which type of axon will velocity of action potential conduction be the fastest?

Myelinated axons with the largest diameter

When voltage-gated Na+ channels of a resting neuron open

Na+ enters the neuron and the neuron depolarizes

Describe the organization of the nervous system

Neurons (specialized cells of the nervous system) send signals along thin fibers called axons and communicate with other cells by releasing chemicals called neurotransmitters at cell-cell junctions called synapses. Glial cells are non-neuronal cells that provide support and nutrition in the nervous system. In humans, the nervous system consists of the central and peripheral nervous systems. The central nervous system of humans contains the brain, spinal cord, and retina. The peripheral nervous system consists of sensory neurons, clusters of neurons called ganglia, and nerves connecting them to each other and to the central nervous system.

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Compare and contrast the 2 forms of summation: temporal and spatial summation.

Temporal summation occurs when a single pre-synaptic neuron fires many times in succession, causing the post-synaptic neuron to reach its threshold and fire. Spatial summation occurs when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire.

Explain why action potentials are self-propagating.

The axon hillock is where action potentials begin. A stimulus is applied to the axon hillock and usually this stimulus is called a "graded potential". The positive stimulus of the graded potential is enough to trigger an action potential in the axon hillock. The local current flow keeps moving into the next segments, where the previous ones have went back to its resting membrane potential. This continues until the action has propagated all the way down to the axon. A neuron cannot fire a second action potential during the refractory period, when the inner membrane voltage falls below and then returns to resting potential. The action potential is propagated along the axon in only a single direction because the refractory period prevents the membrane from reaching its threshold too quickly after an action potential and firing an action potential in the reverse direction.

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.

What characterizes depolarization the first phase of the action potential

The membrane potential changes from a negative value to a positive value

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

What is the function of the myelin sheath?

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

Describe the role of sodium ions and sodium channels in generating an action potential.

The opening of voltage-gated sodium ion channel gates leads to the rapid diffusion of sodium ions into the cell (down their electrochemical gradient). As these positively charged ions enter the cell, the membrane potential becomes positive for a brief period (depolarization). At the peak of the action potential, the sodium ion channels inactivate.

What is a postsynaptic neuron?

The postsynaptic neuron is the one that receives the neurotransmitter and may undergo an action potential (and become a presynaptic to the next nerve cell)

What is a presynaptic neuron?

The presynaptic neuron terminal is the one that releases a neurotransmitter in response to an action potential. a neuron from the axon terminal of which an electrical impulse is transmitted across a synaptic cleft to the cell body or one or more dendrites of a postsynaptic neuron by the release of a chemical neurotransmitter.

Ch.5 - #18 Describe the roles of the sodium-potassium (Na-K) active transport pump and equilibrium potentials for Na+ and K+ in the establishment of the membrane potential.

The sodium potassium pump, establishes the resting membrane potential by using ATP to pump out 3 Na+ ions and bring in 2K+ ions.

The plasma membrane is much more permeable to K+ than to Na+ why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open.

Respond to changes in the cell's membrane potential. Play an important tole in the initiation and conduction of electrical signals along the axon.

Voltage-gated ion channels

What would happen to a neuron if it was exposed to tetrodotoxin? Be specific regarding its effect on the ability of a neuron to communicate.

When TTX binds to the sodium ion channels, it effectively prevents sodium ions from entering the channel. This would prevent the cell from depolarizing and block the cell from generating an action potential. Since the action potential is the signal that neurons use in cell-to-cell communication, the ability of a neuron to communicate would be inhibited.

A neuron has a resting potential of -70 mV and a threshold voltage of -50 mV. There are currently three active synapses on the neuron's dendrites, each located the same distance from the axon. The potential changes are + 40 mV at synapse 1, + 20 mV at synapse 2, and -10 mV at synapse 3. These synaptic potentials diminish by 50% by the time they reach the trigger zone. Will this neuron produce an action potential at this time? Explain. (Hint: Draw a graph of the voltage changes.)

Yes. At the trigger zone, all potentials have halved and will sum as follows: +20mV (originated at synapse 1), + 10mV (originated at synapse 2), -5mV (originated at synapse 3) sum to produce a total potential change of +25mV. The neuron required a minimum change of +20 mV (-70 mV + 20 mV = -50 mV), so it will produce an action potential.

Ion concentrations are first significantly affected after

a few thousand action potentials

Which two properties determine the conduction velocity in a mammalian neuron? a) axon diameter and the leak resistance of the membrane b) myelination and voltage-gated Na+ channel concentration c) the leak resistance of the membrane and myelination d) the voltage-gated K+ ion channel concentration and axon diameter

a)

Why is an action potential conducted in only one direction, from axon hillock to an axon terminal? a) the membrane channels upstream are refractory and cannot open b) second messengers activate channels sequentially c) the channels are progressively easier to pen down the length of the axon d) the number of voltage-gated ion channels increases along the length of the axon

a)

Would the following reflexes have positive or negative feedback? a) glucagon secretion in response to declining blood glucose b) increasing milk release and secretion in response to baby's suckling c) urgency in emptying one's urinary bladder d) sweating in response to rising body temp.

a) negative b) positive c) negative d) negative

Information coming into the central nervous system is transmitted along_____ neurons.

afferent and sensory

What is saltatory conduction?

allows for faster conduction of a nerve impulse because impulses jump from node to node

Which of the following is the most common location where action potentials originate?

axon hillock

The minimum amount of stimulus required to depolarize an excitable membrane and generate an action potential is known as the a) gate b) threshold c) base potential d) limiting potential

b)

Voltage- regulated channels are located a) on the neuron cell body only b) in the membranes of dendrites, in the membranes of axons, and on the neuron cell body c) in the membranes of dendrites only d) in the membranes of axons only e) within the cytosol only

b)

why do voltage-gated channels open?

because of a change in membrane potential nearby

To increase the amount of neurotransmitter released onto a postsynaptic cell, the presynaptic cell would have to? a) send action potentials with higher voltage (higher amplitude) b) send action potentials with longer durations c) send action potentials with higher frequency d) do nothing;no change is possible since the all-or none law is in effect

c)

What happens if a graded stimulus is of sufficient strength to reach threshold at the trigger zone? a) the cell becomes more permeable to Cl- b) the graded stimulus moves through the cell more quickly c) an action potential occurs d) the membrane is hyper polarized

c)

Which of the following will best increase the conduction rate of action potentials? a) decrease the diameter of the axon, decrease the resistance of the axon membrane to ion leakage b) decrease the diameter of the axon, increase the resistance of the axon membrane to ion leakage c) increase the diameter of the axon, increase the resistance of the axon membrane to ion leakage d) increase the diameter of the axon, decrease the resistance of the axon membrane to ion leakage

c)

The ion necessary to initiate the release of acetylcholine into the synaptic cleft is

calcium

What are the 2 unique signals we can produce in a neuron?

chemically gated channels and affects the membrane potential locally, so when the neurotransmitter binds, its not going to affect the next channel, unless theres another neurotransmitter that opens up that channel (usually happens at the dendrites) 1) GRADED POTENTIALS can be excitatory, inhibitory, depolarization, hyper polarization -the further away the source, the less intense it will be -their size or amplitude is directly proportional to the strength of the triggering event - a large stimulus causes a strong graded potential, and a call stimulus results in a weak graded potential - decrease in strength as they spend out from point of origin, act only short distances - chemically gated/ ligand channels affect these 2)ACTION POTENTIALS are always going to be excitatory, and that turns into action, the firing of the action potential -long distance signals - quick reversal of membrane potential with a change in voltage of ~100 mV -depolarization, depolarization - always be excitatory - do not diminish in strength, are rapid, brief, and act over long distances - originates mostly on axon hillock -principle way neurons send signals

The total amount of neurotransmitter released at the axon terminal is directly related to? a) the amplitude of the action potential b) the length of the axon c) the amplitude of the graded potential d) the total number of action potentials

d)

What initiates exocytosis of synaptic vesicle contents in an axon terminal? a) binding of a ligand to its receptor on the post-synaptic cell membrane b) closing of voltage- gated K+ channels c) the mechanisms for this is not yet known d) opening of voltage-gated Ca2+ channels

d)

What would happen to the membrane potential if a cell suddenly becomes more permeable to Na+?

depolarize

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment

The rising phase of the action potential is due to what?

due to increased Na+ permeability.

If a signal from a sending neuron makes the receiving neuron more negative inside a) the sending neuron becomes more negative inside b) the reaching neuron immediately generates an action potential c) the sending neuron becomes more positive inside d) the receiving neuron is more likely to generate an action potential e) the receiving neuron is less likely to generate an action potential

e)

The voltage-gated Na channels of the axon have a _______activation gate and a _______inactivation gate.

faster, slower

Neurons contain a variety of what?

gated ion channels that alternate between open and closed states

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron?

ion channels in the plasma membrane of the receiving neuron open

Why do a ligand-gated channel close?

it can't be open all the time, because we wouldn't be able to maintain our membrane potential effectively - the neurotransmitters unbind, it closes and no more ions can pass through

Are found in sensory neurons and open in response to physical forces such as pressure.

mechanically gated ion channels

In order to signal a stronger stimulus, action potentials become

more frequent only

Spatial summation refers to

multiple graded potentials reaching the trigger zone one after the other

The primary problem in hyperkalemia is?

neurons are hyper excitable because their resting potential is closer to threshold and neurons respond too quickly to smaller graded potentials

A molecule that carries information across a synaptic cleft is a

neurotransmitter

The substance released at axon terminals to propagate a nervous impulse is called a(n) ________.

neurotransmitter

why do ligand-gated channels open?

neurotransmitter (ligand binds)

The gaps between adjacent Schwann cells on an axon are called

nodes of Ranvier

In response to binding a neurotransmitter, a postsynaptic cell can

open chemically gated ion channels, causing graded potentials known as fast synaptic potentials, close ion channels via G proteins and second messenger systems, producing slow responses, and regulate protein synthesis and affect the metabolic activities of the postsynaptic cell

What is suprathreshold?

refers to an intensity level above threshold

Immediately after an action potential passes along an axon, it is not possible to generate a second action potential; thus, we state that the membrane is briefly

refractory

What type of transport occurs when microtubules guide motor proteins as they move vesicles toward the cell body at speedup to 400 mm/day?

retrograde fast axonal transport

Having less channels impacts the rate of diffusion?

slows it down

During the relative refractory period, an initial threshold-level depolarization is usually not sufficient to trigger an action potential. Why?

some Na+ channels have returned to their resting position and K+ channels are still open, so Na+ entry is offset by K+ loss

The region where the axon terminal meets its target cell is called the

synapse

The small space between the sending neuron and the receiving neuron is the

synaptic cleft

How is the RMP generated?

t rest, positively charged sodium ions are at a higher concentration outside the cell, while positively charged potassium ions are at a higher concentration inside the cell. Sodium and potassium ions diffuse across the membrane while the cell is at rest. The rate at which this movement happens is dependent upon the permeability of the membrane to these two important ions. At rest, the electrical potential is negative, because positively charged potassium ions "leak" down their electrochemical gradient at a greater rate. This "drain" of positive charge from inside the cell causes the interior to become negative.

When several IPSPs arrive at the axon hillock rapidly in sequence from a single dendritic location, hyperpolarizing the postsynaptic cell more and more and thus preventing an action potential, this is an example of

temporal summation

When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs?

temporal summation( the summation of graded potentials that closely follow each other sequentially)

The ability of a neuron to respond rapidly to a stimulus and fire an action potential is called?

the cell's excitability

Tetrodotoxin is a toxin that blocks voltage-gated sodium channels. What effect does this substance have on the function of neurons?

the neuron is not able to propagate action potentials

why do ions move through the cell?

they move down their electrochemical gradient

When calcium ions enter the synaptic terminal, they cause?

vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron

What is the function of a synapse?

when an impulse reaches the axonal terminals the synaptic vesicles rupture and release the neurotransmitters into the synaptic cleft. The neurotransmitters then diffuse across the synaptic cleft and bind to the membrane receptors of the next neuron. This explains initiate an action potential.

What is repolarization?

when you reset everything back to -70mv (RMP)