Cell Communication, Nervous System, and Neurons

Question 1

Accommodation

Answer 1

Threshold stimulus is reached too slowly to trigger action potential

Question 2

Summation

Answer 2

Nervous system screens and aggregates signals

Spatial:
Multiple dendrites receive a signal at the same time

Temporal:
Adds up effects of signals received by single dendrite in quick succession

Question 3

What chemical and electrical gradient forces are the ions in a neuron at resting potential experiencing?

Answer 3

Resting potential is -60mV
Na+: chemical concentration into the cell and electrical gradient into the cell
K+: chemical concentration out of the cell and electrical gradient into the cell
Organic anions: chemical concentration out of the cell and electrical gradient out of the cell
Cl-: chemical concentration into the cell and electrical gradient out of the cell
Ca2+: chemical concentration into the cell and electrical gradient into the cell

Question 4

Electrical synapse

Answer 4

Rare, but occur when coordinated action is required from a group of cells (I.e. the cardiac muscle, or smooth visceral muscle)

Much quicker signal transmission, and signal propagation is bidirectional

Question 5

Which signals are short range and fleeting?

Answer 5

Somatic nervous system with neurotransmitters effecting very specific muscles

Question 6

Describe the transduction of a signal along your neurons

Answer 6

Input from environment reaches sensory receptors, physics information stimulates the sensory neurons and is translated to electrical signal that travels length of neuron. Chemical signal carries signal from one neuron to the next and then converts back to electrical signal

Question 7

What factors contribute to the nervous system’s perception about what stimuli is the most important?

Answer 7

Past experience, preconceived notions, evolutionary instinct

Question 8

Depolarization

Answer 8

Membrane potential reverses polarity so it is positive on inside and negative on outside due to sodium rushing inward

Question 9

Voltage gated Na+ Channels

Answer 9

Proteins change configuration when voltage across membrane reaches threshold, allowing Na+ to flow into cell

Positive feedback as more Na+ flows into cell, Na+ diffuses down axon and kicks off more depolarization

Question 10

What methods might a G-protein use as a second messenger system?

Answer 10

G-protein attached to receptor protein on inside of postsynaptic membrane

Alpha subunit breaks free when receptor stimulated and:

1. May activate separate specific ion channels
2. May activate another second messenger (cGMP)
3. May activate intracellular enzymes
4. May activate gene transcription

Question 11

Where does action potential originate in neuron

Answer 11

At axon hillock of signal strength is large enough

Question 12

How does neurotransmitter stop stimulating the post-synaptic cell?

Answer 12

Neurotransmitter may be destroyed by enzyme in matrix of synaptic cleft
May be directly absorbed by presynaptic cell via active transport
May diffuse out of synaptic cleft

Question 13

How is a neuron a concentration cell?

Answer 13

Neurons use an insulating membrane (cellular membrane) to separate two conducting solutions; the intracellular and extracellular fluids.

Uneven distribution of large amounts of Na+ outside of cell, and much higher amounts of K+ inside of the cell is responsible for a resting potential difference across the membrane (-70mV). Outside of cell- positive charge buildup

Question 14

Chemical communication systems in the body

Answer 14

1. nervous system: propagates neurotransmitters in short intercellular gaps (nervous system)
2. Local mediators: released for cells in general proximity (paracrine system)
3. Hormones: sustained long range signal molecules which move through the blood (endocrine system)

Question 15

Fatigue

Answer 15

Presynaptic cell unable to transmit action potential due to lack of neurotransmitters. Happens when cell fires too often

Question 16

How does post-synaptic cell receive action potential

Answer 16

Neurotransmitter diffuses across synaptic cleft and binds as a ligand to receptor protein, which causes increase in membrane permeability to ions, which then diffuse into the cell

Can function through a second messenger system, or direct change to protein permeability

Prolonged changes prefer a second messenger system (G-proteins commonly initiate)

Question 17

What causes the resting potential to be so negative inside a neuron?

Answer 17

K+\Na+ ATPase pumps K+ into cell and Na+ out of cell. Since membrane is very permeable to K+, it diffuses out of the cell, and Na+ cannot diffuse inward. Therefore, as K+ reaches closer to equilibrium in terms of concentration gradient, it brings the resting potential down by decreasing the number of positive ions in the cell. This yields a resting potential of -60mV

Question 18

What are the rates of diffusion of K+ and Na+ through leakage channels across the membrane?

Answer 18

Membrane is highly permeable to K+, but very impermeable to Na+, so diffusion of K+ out of cell is much faster

Question 19

Can a synapse have both inhibitory and excitatory stimuli?

Answer 19

A given synapse only inhibits or excites

Neurotransmitters can be excitatory or inhibitory depending on the type of receptor in the post synaptic membrane

Question 20

Discuss specificity of neurons to neurotransmitters

Answer 20

A single neuron usually secretes only one type of neurotransmitter, so it only has to produce one kind
A neuron may respond to multiple types of neurotransmitters if it’s dendrites have corresponding receptors

Over 50 neurotransmitters have been discovered, many for different parts of nervous system

Question 21

Frequency of firing

Answer 21

Number of times a signal gets received for a specific unit of time

Question 22

What signals are long range and sustained?

Answer 22

Endocrine hormone signals that travel through the blood stream

Question 23

Neurotransmitter

Answer 23

Chemicals that are often derived from amino acids are released into the synapse by a presynaptic neuron and attach to receptors on post-synaptic cell

Small vesicles filled with neurotransmitters rest just inside presynaptic membrane

Question 24

What are the structures in the Nervous System?

Answer 24

Brain, spinal cord, nerves, neural support cells, and sensory organs (eyes and ears)

Central Nervous System (CNS): brain and spinal cord
Peripheral Nervous System (PNS): nerves that signal voluntary movement and nerves that signal involuntary bodily functions

Question 25

Ca2+ voltage gated channels in presynaptic neuron

Answer 25

Channels activated when action potential arrives at synapse, allowing Ca2+ to flow into cell

Rush of Ca2+ causes neurotransmitters to be released into synaptic cleft through exocytosis

Question 26

Cell body

Answer 26

Contains organelles of neuron

Cytosol highly conductive and conducts signals immediately to axon hillock

Small dendrites transfer signals quickly to cel body

Question 27

What are ways a signal can become high intensity?

Answer 27

High frequency of firing
Large number of receptors that respond
Specific type of receptors that respond

High intensity signals trigger action potentials

Question 28

Relative refractory period

Answer 28

Only abnormally large stimulus will create action potential due to membrane hyperpolarization

Question 29



Answer 29

*basic structure of a neuron

Neurons are comprised of many dendrites (branches off of cell body), single cell body, one axon with many branches

Question 30

Stimuli to stimulate action potential

Answer 30

Total effects of all inputs exceeds threshold stimulus

Stimuli can be excitatory (depolarizing) or inhibitory (hyperpolarizing)

Question 31

Voltage gated K+ channels

Answer 31

Less sensitive to voltage changes than Na+, so take longer to open. As they open, most Na+ channels are closing and becoming inactivated. They allow K+ to rush out of cell

Cause repolarization -> hyperpolarization

Question 32

What are the benefits of having one long axon instead of multiple shorter ones?

Answer 32

Minimize error and maximize efficiency in signal transduction

Shorter axons with more synapses could slow down signal and introduce more possible sources of error

Question 33

What are two ways to modify an axon to make an action potential transduct faster?

Answer 33

Increase the diameter of the axon to allow freer flow of Na+ down the axon

Increase the amount of myelin at ion on the axon to decrease capacitance and therefore decrease the amount of Na+ that needs to rush into the cell to depolarize the cell membrane

Question 34

Chemical synapse

Answer 34

Space between two neurons that is crossed by neurotransmitters

Unidirectional and slower than electrical synapses

Example: motor end plate, or connection between neuron and a muscle

Question 35

Neuron

Answer 35

Smallest functional unit of the nervous system. Highly specialized cell capable of transmitting a signal from one cell to another through combination of electrical and chemical processes

Join to form higher level divisions of NS

Cannot divide

Uses mostly glucose and oxygen from blood, and depends on aerobic respiration

Question 36

What processes does the nervous system carry out to maintain homeostasis?

Answer 36

Sensing the environment, selecting and processing most significant information, communicating it to body, and coordinating a response

Question 37

What is their Nernst equation and how does it become negative?

Answer 37

EK = - RT/nF ln(K+ intracellular/ K+ extracellular)

Because K+ is greater intracellularly, the fraction is greater than 1, and the natural log becomes positive, then with the negative it becomes negative.

This means that for the concentration difference of K+ to equal out, there must be a negative voltage across the membrane, because positive actions are rushing out of the cell

Question 38

Resting potential

Answer 38

Electrical potential or voltage across the neuronal membrane at rest

Question 39

Axon

Answer 39

Long strand that carries a tip potential to other neurons

Contains lots of ion channels to sustain signal.

Carries signal to synapse, which passes signal to another cell

Question 40

What protein pumps potassium and sodium against concentration gradients to maintain gradient?

Answer 40

Na+/K+ ATPase: pumps three Na+ out for every two K+ it pumps in

Question 41

What ions are important to creating the resting potential of a neuron and what are their concentrations inside and outside of the cell?

Answer 41

Na+: greater concentration outside of the cell
K+: greater concentration inside of the cell
Cl-: greater concentration outside of the cell
Organic anions (proteins): greater concentration inside of the cell
Ca2+: greater concentration outside of the cell

Resting membrane potential around -60mV

Question 42

Absolute refractory period

Answer 42

Time in which no stimuli can stimulate action potential

Can occur due to Na+ channels being inactivated or due to the cell still being depolarized

Question 43

Excitatory postsynaptic potential and Inhibitory postsynaptic potential

Answer 43

Aka EPSP or IPSP

Firing of one or more synapses that creates a change in neuron cell potential that is either depolarizing or hyperpolarizing, respectively

Typically, around 40-80 synapses must fire simultaneously in same neuron for EPSP to create action potential

Question 44

Action potential

Answer 44

Mechanism by which a signal travels down the length of a neuron
Triggered by a depolarization above a threshold, all or none

Caused by opening of Na+ voltage gated channels at threshold which causes Na+ to rush into cell and move potential towards the equilibrium potential of 50mV for Na+.
Voltage gated K+ channels as Na+ channels begin to deactivate
Voltage gated Na+ channels inactivated and K+ channels from arise membrane
Voltage gated K+ channels close and membrane equilibrates to resting potential