Chapter 11 Part 2 Fundamentals of the Nervous System and Nervous Tissue

Voltage

potential energy generated by separate electrical charges

measure in volts or millivolts.

Potential

difference in voltage between two points

greater potential + greater difference

= greater voltage

Current

flow of electrical charge from one point to another.

Resistance

hindrance to charge flow

provided by substances current must pass through

Ohm's law

Describes mathematical relationship between voltage, current, and resistance

Current is equal to voltage divided by resistance.

Leakage channel

plasma membrane ion channel protein

always open.

Ligand-gated channel

plasma membrane channel protein

closed unless stimulated to open by binding of molecular chemical signal

Voltage-gated channel

plasma membrane channel protein

closed unless stimulated to open by electrical signal/current change.

Mechanically gated channel

plasma membrane channel protein

closed unless stimulated to open by pressure or force.

Electrochemical gradient

combination of chemical and electrical forces

Concentration gradient and charge

acts on membrane potential.

Resting membrane potential

potential difference in resting neuron across plasma membrane.

Polarized

Electrical condition

of plasma membrane

of resting neuron.

Sodium-potassium pump

carrier protein

uses ATP to actively transport sodium ions out of a cell and potassium ions into cell.

Depolarization

decrease in difference in charge across plasma membrane (membrane potential)

Hyperpolarization

increase in difference in charge across plasma membrane (membrane potential)

Graded potential

brief, short-distance electrical signal

occurs in cell body and dendrites

decays with distance.

Action potential

brief reversal of membrane potential in axon

acts in an all-or-none manner

total amplitude (change in voltage) = 100mV.

Nerve impulse

Another name for action potential.

Repolarization

restoration of internal negativity

of resting potential

of neuron

after graded or action potential has occurred

All-or-none phenomenon

activity of an action potential

either happens completely in a positive-feedback manner or not at all.

Propagated

Transmitted or spread.

Absolute refractory period

period immediately after firing of nerve fiber

cannot be stimulated to produce another action potential

no matter how great stimulus applied

because sodium ion voltage-gated channels are still open.

Relative refractory period

period immediately following firing of nerve fiber and absolute refractory period

most sodium ion channels have returned to resting state

some potassium channels are still open

repolarization is occurring

action potential can occur if stimulus is exceptionally strong.

Continuous conduction

Slow conduction that occurs in nonmyelinated axons

sodium and potassium channels regenerate action potential at each point along axon

voltage does not decay.

Multipe sclerosis

Autoimmune disease

immune system attacks and destroys myelin proteins.

Synapse

Junction between axon tip of sending neuron and dendrite or cell body of receiving neuron.

Presynaptic neuron

Neuron that sends electrical signal towards synapse.

Postsynaptic neuron

Neuron that sends electrical signal away from synapse.

Synaptic vesicles

Membrane-bounded compartments in axon terminals of neurons

synthesized neurotransmitters kept

Synaptic cleft

narrow gap

separates presynaptic neuron from postsynaptic cell.

Excitatory postsynaptic potential (EPSP)

slight local depolarization or graded potential.

Occurs on membrane of postsynaptic cell

Lowers electrical barrier by moving membrane potential closer to action potential threshold.

Inhibitory postsynaptic potential (IPSP)

Slight local hyperpolarization or graded potential.

Occurs on membrane of postsynaptic cell.

Raises electrical barrier by moving membrane potential further away from action potential threshold.

Summate

To add together

cumulative change in postsynaptic potentials toward reaching threshold.

Occurs across span of membrane (spatial summation).

Occurs over amount of time (temporal summation).

Temporal summation

Combined effect of EPSPs or IPSPs produced in rapid succession

Determines membrane potential of postsynaptic cell in chemical synapse

Phenomenon of neural integration

Spatial summation

Combined effect of EPSPs or IPSPs produced nearly simultaneously by different synapses

Determines membrane potential of postsynaptic cell

Phenomenon of neural integration

Acetylcholine (ACh)

neurotransmitter

enables learning and memory

triggers muscle contraction

Acetylcholinesterase

enzyme

breaks down acetylcholine in synaptic cleft.

Biogenic amines

Neurotransmitters derived from amino acids distributed in brain.

Catecholamines

Class of monoamine hormones and neurotransmitters containing catechol structure

Includes dopamine, norepinephrine, and epinephrine

Secreted by adrenal medulla and sympathetic neurons

Regulates sympathetic nervous system stress response (fight-or-flight)

Indolamines

Class of monoamine neurotransmitters containing indole ring structure

Synthesized from amino acid tryptophan

Includes serotonin (5-HT) and melatonin

Regulates sleep, mood, circadian rhythms, and emotional behavior