PHYL 141 Nervous Tissue Part 2 (Exam 3 Study Guide)

fluid outside cells; has an overall positive charge

extracellular fluid (ECF)

fluid in the tissues that fill the spaces between cells

interstitial fluid

fluid inside of the cell (cytoplasm); has an overall negative charge

intracellular fluid (ICF)

the difference in electrical charge between the outside and inside of the cell

membrane potential

the electrical charge of an undisturbed cell

resting membrane potential

-70 mV

resting membrane potential

the electrical impulse that goes through the axon once the threshold has been reached

action potential

changes in the membrane potential that cannot spread far from the site of stimulation; what starts an action potential

graded potential

The potential when there is an equal concentration of Na+ and K+ on both sides of the membrane; this results in there being no ion movement (e.g. potassium's equilibrium potential is -90 mV)

equilibrium potential

a gradient that is a combination of the electrical charges and concentration of a certain ion

(e.g. K+ has a positive gradient and has a high concentration inside the cell)

electrochemical gradient

ions that have a higher concentration in the extracellular fluid when the cell is at rest

overall positive charge

Na+, Cl-, Ca2+

ions that have a higher concentration in the cytosol when the cell is at rest

overall negative charge

K+, proteins

Na+ / Ca2+ would rush into the cell; the cell would depolarize and have a more positive membrane potential

What would happen if sodium / calcium ion channels opened in a resting neuron?

K+ would rush outside of the cell; the cell would repolarize or hyperpolarize and have a more negative membrane potential

What would happen if potassium ion channels opened in a resting neuron?

-55 mV to -60 mV

The threshold for action potential in millivolts

+30 mV to +40 mV

The peak membrane potential in millivolts

Channels that are always open; passive transport for ions to pass through freely due to diffusion; help a lot in maintaining/balancing the electrical charge the resting membrane potential

leak channels

Gated ion channels are active transport, need ATP, and can move ions from low to high concentrations. Leak channels are passive transport, do not require ATP (diffusion), and moves ions from high to low concentrations.

What is the difference between gated ion channels and leak channels?

When a certain ligand or chemical (usually a neurotransmitter in the case of a neuron) binds to a receptor on the postsynaptic cell, which opens up the gate

What stimuli triggers the opening of a chemically-gated / ligand-gated ion channel?

When there is changes in the membrane potential / voltage of a cell (e.g. graded or action potentials)

What stimuli triggers the opening of voltage-gated channels?

touch, pressure, vibration

Basically, when there is a physical distortion in the membrane surface

What stimuli trigger the opening of mechanically-gated channels?

When there is a difference in charge between the two sides of the plasma membrane

polarization

When the membrane potential of a cell becomes more positive (usually due to Na+ entering the cell) and results in an action potential

depolarization

When the membrane potential of a cell becomes more negative (usually due to K+ exiting the cell) and results in the action potential dissipating

repolarization

A result of the time lag waiting for potassium ion channels to close; too much K+ escapes and the cell becomes even more negative than its resting membrane potential

hyperpolarization

The membrane potential needed in order to trigger an action potential; a graded potential must reach this voltage in order to start an action potential

threshold

This explains that an action potential may or may not be triggered. If the threshold is not reached by the graded potential (even if by a hair's breadth), then there still will not be any action potential generated

all-or-none principle

Starts off with resting membrane potential
1. Graded potential reaches threshold—action potential is triggered
2. Depolarization—sodium ions rush in via sodium channels, making the cell more positive
3. Repolarization—too much positive ions in the cell, potassium ions are pushed out via potassium channels
4. Hyperpolarization—until resting membrane potential is restored, the potassium channels remain open and continue to lose positive ions until the cell has a negative charge

action potential phases

during depolarization; membrane potential becomes more positive

When do Na+ channels open? How does this affect the membrane potential?

during repolarization and hyperpolarization; membrane potential becomes more negative

When do K+ channels open? How does this affect the membrane potential?

When the action potential triggers the voltage-gated sodium ion channels. Na+ rushes in and makes the membrane potential more positive.

When does depolarization occur?

When the cell reaches its peak membrane potential (+30 to +40 mV). The Na+ channel is closed and the K+ channel is opened. K+ exits the cell and the membrane potential becomes more negative.

When does repolarization occur?

1. Action potential allows Na+ or Ca2+ to enter axolemma
2. Na+ or Ca2+ allows vesicles to be formed
3. Vesicles of neurotransmitters are released into the synaptic cleft
4. Neurotransmitters bind to receptors and open ligand-gated channels
5. Na+ rushes into postsynaptic neuron and creates another action potential

How do signals pass between presynaptic/postsynaptic neurons?

A synapse that releases acetylcholine (ACh)

Neuromuscular junction

cholinergic synapse

A synapse between two cells that are directly in contact due to gap junctions

Membrane potential of one cell affects the other; therefore faster

electrical synapse

A synapse that involves neurotransmitters and does not touch the other cell (synaptic cleft)

More independent; therefore, slower

chemical synapse

It is released at neuromuscular junctions involving skeletal muscle fibers

What role does ACh have in the somatic nervous system?

It is released at all neuromuscular and neuroglandar junctions in the parasympathetic division of the ANS (rest and digest, calming)

What role does ACh have in the autonomic nervous system?

boosts mood, regulates sleep patterns, and regulates appetite

What is the role of serotonin in the brain?

Fluoxetine (Prozac) blocks the serotonin reuptake channel, keeps serotonin in the synapse, person's response to serotonin is prolonged and amplified

Side effects: loss of appetite, mood issues, insomnia

How does fluoxetine affect serotonin?

It increases heart rate, alertness, and one's fight or flight response (sympathetic nervous system)

How does norepinephrine affect mood and mental status?

Synapses that release NE (norepinephrine or noradrenaline)

What is an adrenergic synapse?

It affects emotion and attention, pleasure, and the reward system (links stimuli with positive feelings)

Can cause addiction and impulsive behavior (e.g. gambling gene)

What are the functions of dopamine in the brain and human body?

Parkinson's is the death of cells that produce dopamine.

This results in tremors, hypokinesia, rigidity, dementia

How is Parkinson's disease related to dopamine?

Glutamate—primary excitatory neurotransmitter (helps brain work faster); important for learning and synaptic plasticity

GABA—primary inhibitory neurotransmitter (decreases brain activity); creates a calming effect and reduces anxiety

What are the effects of gamma-aminobutyric acid (GABA) and glutamate on the nervous system?

a neurotransmitter that makes postsynaptic cells more likely to fire an action potential by decreasing the distance between the original membrane potential and the threshold

excitatory neurotransmitter

a neurotransmitter that decreases the likeliness of an action potential occurring by increasing the distance to the threshold

inhibitory neurotransmitter

involves timing and frequency; only one presynaptic neuron and one postsynaptic neuron

temporal summation

involves the location, number of synapses, and type of neurotransmitter

usually involves multiple presynaptic neurons and one postsynaptic neuron

spatial summation