Chapter 4: The Structure and Electrical Activity of Neurons

epilepsy

a condition characterized by recurrent seizures linked to abnormal electrical discharges

dendritic spines

small protrusions of the dendrites that greatly increase the cell’s surface area

axon collaterals

a branch that emerged from a single axon

teleodendria

smaller branches that divided from the axon collaterals

terminal button

the end of each teleodendrion

synapse

the space and connection between the surface of the terminal button and the corresponding surface of the neighboring dendritic spine

inhibitory synapses

synapses that decrease the neuron’s ability to pass information along to other neurons

excitatory synapses

synapses that increase the neuron’s ability to pass information along to other neurons

axon hillock

a distinctive enlargement that forms at the beginning on the neuron’s axon

neurotransmitters

chemical messages,

cell membrane

separates the cell from its surrenders and allows it to regulate the materials that enter and leave

nuclear membrane

surrounds the nucleus, which consists of genes, chromosomes, and the cells proteins that are stored and copied

endoplasmic reticulum (ER)

an extension of the nuclear membrane where the cell’s protein products are assembled

Golgi bodies

where the finished protein are packed and passed along to the cell’s transportation network

tubules

a system that carries proteins to their destination

microfilaments

tubules that form the cell’s structural framework

mitochondria

the structure that supplies the cell energy

lysosomes

saclike vesicles that transport incoming supplies and moves and stores wastes

extracellular fluid

water containing dissolved substances that separates and cushions neurons and glia

intracellular fluid

water containing dissolved substances inside a cell (also referred to as cytoplasm)

ions

molecules that carry a positive or negative charge

phospholipid

a molecule that forms the membrane bilayer

genes

segments of DNA that encode the synthesis of a particular proteins

chromosomes

the double-helix molecular structures that hold an organisms entire DNA sequence

nucleotide bases

the molecules of the genetic code (A,T,G, and C)

amino acids

the constituent molecules of the proteins

transcription

the process protein sysnthesis when a gene segment of the DNA unwinds to attract nucleotides that attach to form a strand of ribonucleic acid; created messenger (mRNA)

translation

the process protein sysnthesis when a particular sequence of nucleotide bases in the mRNA is transformed into a particular amino acid sequence.

codons

three consecutive nucleotide bases along an mRNA molecule that encodes one articular amino acid

polypeptide chain

a connection of amino acids connected with a peptide bond

gene methylation

a process that creates phenotypic plasticity without altering the base-pair nucleotide sequence of the genes or changing the genetic code

histone

supporting molecules of protein wrapped around chromosomes

histone methylation

a process in which DNA may be unspooled or be stopped from unspooling

mRNA modification

a process in which the mRNA message that produces the protein that a gene codes may be enabled or blocked

exocytosis

the process in which proteins remain within their membranes, and fuse with the cell membrane which allows it to be expelled into the extracellular fluid (usually as a neurotransmitter)

channels

holes through which substances can pass—different proteins with different-size channels allow different substances to enter or leave the cell

gates

some protein molecules have the ability to change shape—gates can change shape when another chemical binds to them, or in response to environmental conditions

gated channel

a channel that allows molecules to enter at some times but not at others

pumps

transports many substances across the cell membrane

transporter protein

a molecule that actively transports substances across the cell membrane

oscilloscope

an instrument that turns electrical fluctuations into visible signals

micrometers (µm)

one-millionth of a meter or one-thousandth of a millimeter

millivolts (mV)

one thousandth of a volt

milliseconds (ms)

one thousandth of a second

concentration gradient

describes relative differences in amount of substance at different locations in a container

diffusion

molecules spontaneously spread out from where they’re in concentrated areas to less concentrated areas

voltage gradient

the difference in charge between two regions that allows a flow of current if the two regions are connected

resting potential

-70mV the charge on the inside of the neuron

sodium-potassium pump (Na+ — K+ pump)

a protein molecule embedded in the membrane that shunts Na+ ions out of the cell and K+ ions into it

anions

negatively charged ions

cations

positively charged ions

graded potentials

slight decreases or increases in an axon’s membrane voltage

depolarization

a decrease in the voltage on the membrane

hyperpolarization

an increase in the voltage on the membrane

action potential

a brief but extremely large reversal in the polarity of the axon’s membrane that lasts for about 1ms

theshold potential

when the cell membrane is depolarized to about -50mV

voltage-sensitive channels

a class of gated sodium and potassium channels, and are sensitive to the membrane’s voltage; they close at the resting potential so ions cant pass through, and open at the threshold potential

absolutely refractory

when the axon membrane doesn’t respond with a new action potential because the sodium gates are insensitive during the depolarizing or repolarizing phase of the action potential

relatively refractory

when the axon membrane is stimulated during the hyperpolarization phase, but a new action potential can only be induced in the intensity of stimulation is higher than the one that initiated the first action potential

nerve impulse

the process in which repetitive action potential induces a change in the membrane voltage down the axon’s length

nodes of Ranvier

uninsulated regions between the myelinated segments that are richly endowed with voltage-sensitive ion channels

saltatory conduction

action potential pumps from node to node as a result of tiny gaps in the myelin sheath that are close enough that an action potential at one node can induce voltage-sensitive gates to open at an adjacent node

excitatory postsynaptic potentials (EPSPs)

increase the probability that an action potential will result

inhibitory postsynaptic potentials (IPSPs)

decrease the probability that an action potential will result

temporal summation

the relation between two EPSPs occurring close together or even at the same time

spatial summation

indicates that two separate inputs occurring very close to one another on the cell membrane and in time will sum

black propagation

the reverse movement of an action potential from the axon hillock into the dendritic field of a neuron