Module 2 - book ver. Flashcards
nerve cells
neurons
two basic subdivisions of the nervous system
central and peripheral
the CNS consists of
the brain and the spinal cord
the PNS consists of
the nerves and most of the sensory organs
the CNS communicates with the rest of the body through ?
nerves attached to the brain and spinal cord
bundles of thousands of individual neurons all wrapped in a tough, protective membrane
nerves
how do nerves perform like cable wires?
nerve fibers transmit messages through the nerve, from a sense organ to the brain or from the brain to a muscule or gland
information from the senses are gathered from the environment by specialized cells of the PNS called
sensory neurons
movements are accomplished by the contraction of muscles controlled by
motor neurons in the PNS
neurons that lie entirely within the CNS, in between sensory and motor neurons
interneurons
types of interneurons
local and relay
type of interneurons that form circuits with nearby neurons and analyze small pieces of information
local
type of interneurons that connect circuits of local interneurons in one region of the brain with those in other regions
relay
the information-processing and information-transmitting element of the nervous system
neurons
basic structure of the neuron
soma, dendrites, axon, and terminal buttons
contains the nucleus and much of the machinery that provides for the life processes of the cell
soma (cell body)
serve as important receivers of messages from other neurons
dendrites
dendrites receive neural messages that are transmitted across the -?
synapse
the small space between the terminal buttons of the sending cell and a portion of the somatic or dendritic membrane of the receiving cell
synapse
how does neural communication travel in one direction?
from the terminal button to the membrane of the other cell
a long, slender tube, often covered by a myelin sheath
axon
true or false. the outer surface of the axon carries information from the cell body to the terminal buttons and carries an electrical message
true
the basic message an axon carries; a brief electrical event that starts at the end of the axon next to the cell body and travels toward the terminal buttons
action potential
true or false. the action potential varies in size and duration
false. the action potential is always of the same size and duration
little knobs at the end of axon branches
terminal buttons
when an action potential traveling down the axon reached the terminal buttons, they secrete a chemical called -?
neurotransmitters
chemicals that either excites or inhibits the receiving cell and thus helps to determine whether an action potential occurs in its axon
neurotransmitters
FYI. an individual neuron receives information from the terminal buttons of axons of other neurons, and the terminal buttons of its axons form synapses with other neurons
okie!
true or false. a neuron may receive information from dozens or even hundreds of other neurons, each of which can form a large number of synaptic connections with it
true
true or false. terminal buttons can form synapses on the membrane of the dendrites or the soma
true
an active process that propels substances along microtubule “tracks” that run inside the length of the axon
axoplasmic transport
transport from the soma to the terminal buttons; this form of transport is accomplished by molecules of kinesin
anterograde axoplasmic transport
protein that attaches to the item being transported down the axon, then walks down a microtubule, carrying the cargo to its destination
kinesin
transport from the terminal buttons to the soma; dynein (instead of kinesin), carries the substances in this form of transport
retrograde axoplasmic transport
defines the boundary of the neuron; consists of a double layer of lipid molecules
cell membrane
the interior of the neurons contains a matrix of strands of protein that gives the neuron its shape
cytoskeleton
bundles of thirteen protein filaments arranged around a hallow core; the thickest among the three kinds of protein strands that make up the cytoskeleton
microtubules
a jellylike, semiliquid substance that fills the space outlined by the membrane
cytoplasm
a round or oval structure found in the soma
nucleus
responsible for the production of ribosomes
nucleolus
small structures that are involved in protein synthesis
ribosomes
consists of long stands of DNA
chromosomes
molecule that receives a copy of the information stored at the genes
mRNA (messenger ribonucleic acid)
proteins are produced through a two-step process:
transcription and translation
wherein information from DNA is transcribed into a portable form (mRNA)
transcription
wherein the ribosomes use the information from the mRNA and create proteins
translation
special protein molecules that act as catalysts; cause a chemical reaction to take place without becoming part of the final product themselves
enzymes
a network on internal membranes consisting of endoplasmic reticulum Golgi apparatus, and lysosomes
endomembrane system
endoplasmic reticulum that contains ribosomes; the protein produced by the ribosomes that are attached here are destined to be transported out of the cell or used in the membrane
rough
endoplasmic reticulum that provides channels for segregation of molecules involved in various cellular processes; lipid molecules are also produced here
smooth
a special form of smooth endoplasmic reticulum where some complex molecules are assembled; also serves as a wrapping or packaging agent
Golgi apparatus
the process wherein the membrane-wrapped product (using membrane produced by the Golgi apparatus) migrates to the inside of the outer membrane of the cell, fuses with the membrane, and bursts (spilling its contents into the fluid surrounding the cell)
exocytosis
produced by the Golgi apparatus; small sacs that contain enzymes that break down substances no longer needed by the cell (these products are then recycled or excreted)
lysosomes
provides cells with adenosine triphosphate (ATP), an immediate source of energy; its inner membrane is wrinkled, and the winkles make up a set of cristae where many of the biochemical steps that are involved in the extraction of energy from the breakdown of nutrients occur; “power plants” of neurons
mitochondria
true or false. neurons constitute only about half the volume of the CNS
true
supporting cells of the central nervous systems
glial cells (astrocytes, oligodendrocytes, and microglia)
general function of glial cells
- hold neurons in place (“nerve glue”)
- controlling supply of nutrients and some of the chemicals neurons need in order to exchange messages with other neurons
- insulate neurons from one another so that neural messages dont get scrambled
- destroy and remove the carcasses of neurons that are killed by disease or injury
“star cell”; provide physical support to neurons and clean up debris within the brain; produce some chemicals and help to control composition of the fluid surrounding neurons by actively taking up or releasing substances; involved in providing nourishment to neurons
astrocytes
thought that nutrients passed from capillaries to the cytoplasm of the astrocytes and then through the cytoplasm to the neurons
Camillo Golgi
astrocytes receives glucose from capillaries and break it down to -, which they release into the extracellular fluid that surrounds neurons so that neurons may take it up and transport it to their mitochondria to use it for energy
lactate
the chemical produced during the first step of glucose metabolism
lactate
true or false. although neurons receive some glucose directly from the capillaries, they receive most of their nutrients from astrocytes
true
true or false. oligodendrocytes surround and isolate synapses, limiting the dispersion of neurotransmitters that are released by the terminal buttons
false. astrocytes, not oligodendrocytes
process wherein certain astrocytes contact a piece of debris from a dead neuron, they push themselves against it, finally engulfing and digesting it
phagocytosis
what do astrocytes do when there is a considerable amount of injured tissue to be cleaned up?
they divide and produce enough new cells to perform phagocytosis. once they tissue has been broken down, a framework of astrocytes will be left to fill in the vacant area, and a specialized kind of astrocyte will form scar tissue
glial cells that provide support to axons to produce the myelin sheath
oligodendrocytes
insulates most axons from one another; a tube surrounding the axon; consists of a series of segments; 80% lipid, 20% protein
myelin sheath
a small portion of uncoated axon between myelin sheath segments
nodes of Ranvier
oligodendrocytes produce up to - segments of myelin
50
smallest of the glial cells; act as phagocytes; protect the brain from invading microorganisms; primarily responsible for the inflammatory reaction in response to brain damage
microglia
supporting cells of the peripheral nervous system
Schwann cells
1 myelin sheath segment=
1 Schwann cell wrapped many times around the axon
true or false. a Schwann cell provides myelin for only one axon, and only part of it surround the axon
false. its true that a Schwann cell provides myelin for only one axon, but it is the entire Schwann cell that surrounds the axon, not only part of it
if a nerve suffers damage, what do Schwann cells do?
they aid in the digestion of the dead and dying axons, then they arrange themselves in a series of cylinders that act as guides for regrowth of the axons (though distal portions of the severed axons die, the stumps grows sprouts which spread in all direction–if one of these sprouts encounters a cylinder provided by a Schwann cell, the sprout will grow through the tube quickly; this reestablished connections with the muscles and sense organs they previously served)
during development, axons have two modes of growth:
- continue to elongate
2. stop elongating
how do astrocytes differ from Schwann cells in tackling injuries?
although both have new sprouts forming, the scar tissue produced by astrocytes are impenetrable by the budding axons. should a sprout penetrate the barrier, there is no reestablishment of the original connection
difference between oligodendrocytes and Schwann cells?
the chemical composition of the myelin protein they produce
what happens in the immune system of someone with multiple sclerosis?
the myelin protein produced by oligodendrocytes are attacked (while the myelin of the PNS is spared)
the barrier that exists between the blood and the fluid that surrounds the cells of the brain; selectively permeable
blood-brain barrier
- constitue the blood-brain barrier
the walls of the capillaries of the brain
function of the blood-brain barrier
- makes it easier to regulate the composition of the extracellular fluid (which the brain depends on from transmission of messages within itself)
- prevents chemicals that could possibly interfere the transmission of information from reaching the brain
true or false. the blood-brain barrier is uniform throughout the nervous system
false. in several places, the barrier is relatively permeable
part of the brain that controls vomiting; area where the blood-brain barrier is weaker, allowing neurons in the region to detect the presence of toxic substances in the blood, stimulating the area to initiate vomiting
area postrema
overview of communication within the neuron (in the instance of painful stimulus)
- dendrites are stimulated by a noxious stimulus, sending messages down the axon to the terminal buttons (which are located in the spinal cord)
- terminal buttons of the sensory neuron release a neurotransmitter that excites the interneuron, causing it to send messages down its axon
- the terminal buttons of the interneuron release a neurotransmitter that excites the motor neuron, which sends messages down its axon
- the axon of the motor neuron joins a nerve and travels to a muscle
- when the terminal buttons of the motor neuron release their neurotransmitter, the muscle cells contract, causing the organ to move in response to the stimulus
what do inhibitory synapses do?
excitation in the motor neurons are counteracted by inhibition supplied by the brain (which calculates the risks of the response; neural circuits send information to the spinal cord that prevents the response–an axon from a neuron in the brain reaches the spinal cord, where its terminal buttons form synapses with an inhibitory interneuron. when the neuron in the brain becomes active, its terminal buttons excite this inhibitory interneuron, which releases an inhibitory neurotransmitter that decrease the activity of the motor neuron, blocking the response/reflex)
very small sensors that can be inserted into a neuron to record changes in electrical activity across the axon membrane
microelectrodes
the difference in charge across the membrane of an axon
membrane potential
membrane resting potential
-70mV (more negatively charged inside the axon than outside)
the message conducted along the axon can be measured as -?
an electrical event
when the inside of an axon becomes more negative relative to the outside, it is
hyperpolarized
when the inside of the axon becomes more positive, it is
depolarized
a set point for depolarization to trigger the main electrical event in the axon (action potential)
threshold of excitation
a burst of rapid depolarization followed by hyperpolarization; begins at the point where the soma meets the axon and propagates like a wave all the way to the end of the terminal buttons, informing the terminal buttons to release neurotransmitters into the synapse
action potential
much of what is currently known about electrical potentials in the axon came from studies of the -
giant squid axon
how large is the giant squid axon?
0.5mm in diameter
the electrical charge across the membrane potential is the result of a balance between two opposing forces:
diffusion and electrostatic pressure
the process whereby molecules distribute themselves evenly throughout the medium in which they are dissolved
diffusion
in diffusion, molecules diffuse from regions of - concentration to regions of - concentration
high; low
substances that split into two parts (each with an opposing electrical charge) when dissolved into water are called
electrolytes
the charged particles into which electrolytes decompose
ions
two basic types of ions
cation and anion
the force exerted by the attraction/repulsion between ions
electrostatic pressure
fluid within cells
intracellular fluid
fluid surrounding cells
extracellular fluid
fact! the forces of diffusion and electrostatic pressure contributed by the ions in the intracellular and extracellular fluid give rise to the membrane potential
yay!
the four important ions
organic anions (A-), chloride ions (Cl-), sodium ions (Na+), and potassium ions (K+)
ions dominantly found in the intracellular fluid
organic anions (A-) and potassium (K+)
ions dominantly found in the extracellular fluid
chloride (Cl-) and sodium (Na+)
true or false. organic anions (A-) can pass through the membrane of an axon
false
explain why K+ remains inside the membrane despite high concentration within the membrane?
although the force of diffusion pushes it out, electrostatic pressure pushes it in as the outside of the membrane is positively charged. (the same concept goes for chloride)
explain why Na+ remains high in concentration outside the cell despite the two forces favoring it to go inside
as it is high in concentration outside the axon, diffusion pushes it into the membrane, and because the inside is negatively charged, electrostatic pressure attracts the ion to enter as well. however!! since it is unnatural to have Na+ inside the axon for a long time, it must be pumped out by the sodium-potassium pump
consists of a large number of protein molecules embedded in the membrane; driven by energy provided by molecules of ATP produced by the mitochondria; exchange Na+ for K+
sodium-potassium pump
the sodium-potassium pump pumps out - sodium ions for every - potassium ions they push in
3; 2 (remember: more Na+ comes out than K+ comes in)
how much energy does the sodium-potassium pump take up?
up to 40% of a neuron’s metabolic resources
contain passages that can open or close; allows specific ions to flow in or out when open
ion channels
the permeability of a membrane to a particular ion at a given moment is determined by -
the number of ion channels are are open
consists of a series of changes in opening and closing of ion channels and the resulting distribution of ions
action potential
summarize the steps involved in generating an action potential
- the threshold of excitation is reached and sodium channels in the membrane open, allowing Na+ to rush in. the influx produces a rapid change in the membrane potential from -70mV to +40mV
- when the action potential reaches its peak, the sodium channels become refractory; no more Na+ can enter the cell
- voltage-dependent potassium channels open, letting K+ ions to move freely through the membrane; however, as the inside of the axon is positively charged at this time, the forces of diffusion and electrostatic pressure force K+ outside. this outflow of cations causes the resting potential to return
- once the resting potential occurs, sodium channels reset so that another depolarization can cause them to open again
- the membrane actually overshoots its resting value and only gradually returns to normal as the potassium channels finally close. eventually, sodium-potassium transporters remove the Na+ ions that leaked in and retrieve the K+ ions that leaked out
the opening of sodium channels are triggered by -
depolarization; reduction of the membrane potential
channels that are opened by changes in the membrane potential
voltage-dependent channels
when channels become blocked and cannot open again until the membrane reaches resting potential again they are -
refractory
states that an action potential either occurs or does not occur, and, once triggered, it is transmitted down the axon to its end
all-or-none law
true or false. action potentials in axons control the strength of muscular contractions and represent the intensity of a physical stimulus
true
true or false. a high rate of firing causes a strong muscular contraction, and a strong stimulus causes a high rate of firing
true
the principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which the axon fires
rate law
the only place where a myelinated axon comes into contact with the extracellular fluid; unmyelinated areas of an axon
node of Ranvier
the transmission of an action potential where it seems to be hopping from node to node
saltatory conduction
describe saltatory conduction
because myelinated segments of the axon do not allow the inflow of extracellular sodium, the action potential slides through it until it can regenerate at a node of Ranvier, where the axon is exposed to extracellular fluid (allowing for the opening of the needed channels)
the decrease in the size of the electrical disturbance being conducted in saltatory conduction
decremental conduction
the advantages of saltatory conduction
- myelinated axons expend much less energy because sodium-potassium channels are not constantly operating
- faster because the passive conduction of myelin segments
primary means of communication between neurons; the transmission of messages from one neuron to another across a synapse
synaptic transmission
the terminal buttons of the sending cell
presynaptic cell
the membrane of the receiving neuron
postsynaptic cell
brief depolarizations or hyperpolarization; increase or decrease the rate of firing of the axon of the presynaptic neuron
postsynaptic potentials
chemical that attaches to a binding site
ligand
naturally occurring ligands
neurotransmitters
junctions between the terminal buttons at the ends of the axonal branches of one neuron and the membrane of another
synapse
many synapses occur on - or on -
the smooth surface of a dendrite; dendritic spines
small protrusions that stud the dendrites of several types of large neurons in the brain
dendritic spines
a specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction.
presynaptic membrane
the membrane that receives a signal (binds with a neurotransmitter) from the presynaptic cell and responds via depolarization or hyperpolarization
postsynaptic membrane
where is the presynaptic membrane located?
at the end of the terminal buttons
where is the postsynaptic membrane located?
on the neuron that receives the message
the pre- and postsynaptic membranes face each other across the this; a gap that varies in size from synapse to synapse
synaptic cleft
two prominent structures located in the cytoplasm of the terminal button
mitochondria and synaptic vesicles
responsible for transporting material between the soma and terminal button
microtubules
two types of synaptic vesicles
small and large
synaptic vesicles that contain molecules of the neurotransmitter; consists of around 10,000 lipid molecules into which are inserted about 200 protein molecules
small
protein that fills vesicles with the neurotransmitter
transport proteins
protein that is involved in the release of neurotransmitters and recycling of the vesicles
trafficking proteins
synaptic vesicles are found in greatest numbers around the here; the region from which the neurotransmitter is released
release zone
synaptic vesicles that contain one of a number of different peptides
large
where are small synaptic vesicles produced?
in the Golgi apparatus located in the soma, and are carried by fast axoplasmic transport to the terminal button. some are also produced from recycled material in the terminal button
where are large synaptic vesicles produced?
only in the soma
describe the release of neurotransmitters
- a number of small synaptic vesicles located in the presynaptic membrane fuse with the membrane then break open, spilling their contents into the synaptic cleft
- the release zone of the presynaptic membrane contains voltage-dependent calcium channels. when the membrane of the terminal buttons is depolarized by an arriving action potential, the calcium channels open
three pools of synaptic vesicles
release-ready, recycling, and reserve
synaptic vesicle pool that are docked against the inside of the presynaptic membrane, ready to release their contents when an action potential arrives
release-ready
synaptic vesicle pool that constitute 10-15% of the total pool of vesicles
recycling
synaptic vesicle pool that make up the remaining 85-90% total pool of vesicles
reserve
when synaptic vesicles release most or all of their neurotransmitters, the fusion pore closes, and the vesicles break away from the presynaptic membrane and get filled again
kiss-and-run
Large pieces of the membrane of the terminal button fold inward, break off, and enter the cytoplasm
bulk endocytosis
binding sites of special protein molecules located in the postsynaptic membrane
postsynaptic receptors
opened by the postsynaptic receptors, these channels permit the passage of specific ions into our out of the cell
neurotransmitter-dependent ion channels
a neurotransmitter-dependent ion channel that is equipped with its own binding site
ionotropic receptor
receptors that activate a chain of chemical events when a ligand binds to it
metabotropic receptor
metabotropic receptors are located in close proximity to -, another protein attached to the membrane
G protein
the nature of postsynaptic potentials are determined by -
the characteristics of the particular type of ion channel postsynaptic receptors open
most important source of excitatory postsynaptic potentials
sodium channel
increase the likelihood of a postsynaptic action potential occurring; depolarization; when sodium channels open
excitatory postsynaptic potential
decrease the likelihood of a postsynaptic action potential occurring; hyperpolarization; when potassium channels open
inhibitory postsynaptic potential
- serve to neutralize EPSPs
the opening of chloride channels
an extremely rapid removal of neurotransmitter from the synaptic cleft by the terminal button
reuptake
accomplished by acetylcholinesterase (AChE) that destroys molecules of the neurotransmitter by breaking it down into its constituents; postsynaptic potentials are terminated in this way acetylcholine (ACh) & neurotransmitters that consist of peptide molecules
enzymatic degradation
how many molecules of ACh does one molecule of AChE break apart each second?
5,000
a disease in which the immune system destroys ACh receptors, reducing the amount of information conveyed from the ACh system to the muscles
myasthenia gravis
the interaction of the effects of excitatory and inhibitory synapses on a particular neuron
neural integration
receptors that respond t the neurotransmitter that they themselves release
autoreceptors
what do autoreceptors do?
regulate internal processes, including the synthesis and release of the neurotransmitter; they are part of a regulatory system that controls the amount of neurotransmitter that is released
what are other types of synapses?
axoaxonic, dendrodendritic, and electrical
synapses that alter the amount of neurotransmitter released by the terminal buttons of the postsynaptic axon; do not contribute directly to neural integration; can produce presynaptic modulation (presynaptic inhibition or facilitation)
axoaxonic synapse
if the activity of the axoaxonic synapse - the release of neurotransmitter, the effect is called -
decreases; presynaptic inhibition
if the activity of the axoaxonic synapse - the release of neurotransmitter, the effect is called -
increases; presynaptic facilitation
synapses between dendrites
dendrodendritic synapses
(type of synapse) membranes meet and almost touch, forming a gap junction. the membranes on both sides of a gap junction contain channels that permit ions to diffuse from one cell to another; when changes in the membrane potential of one neuron induces changes in the membrane of the other
electrical synapse
what are some other forms of chemical communication?
neuromodulators and hormones
chemicals release by neurons that travel farther and are dispersed more widely than are neurotransmitters, modulating the activity of many neurons in a particular part of the brain; most are peptides; affect general behavioral states
neuromodulators
chains of amino acids
peptides
hormones secreted by the cells of - or by cells located in various organs
endocrine glands
fact! cells that secrete hormones release these chemicals into the extracellular fluid. the hormones are then distributed to the rest of the body through the bloodstream. hormones affect the activity of cells that contain specialized receptors located either on the surface of their membrane or dep within their nuclei
thanks for letting me know!
cells that contain receptors for a particular hormone
target cells
what do peptide hormones do?
stimulate metabotropic receptors located in the membrane. the second messenger that is generated travels to the nucleus of the cell, where it initiates changes in the cell’s physiological processes
what do steroid hormones do?
since they are soluble in lipids, they pass easily through the cell membraned and travel to the nucleus, where they attach themselves to receptors located there, which stimulates said receptors to direct the machinery of the cell to alter it protein production
fact! presence of steroid receptors in terminal buttons and around the postsynaptic membrane of some neurons influence synaptic transmission rapidly
noice!
