Action potential propagation Flashcards
what is AP propagation
the movement of an action potential along the membrane of a single cell
motor neurons have what function?
send impulses to muscles to generate movement, initiate motor movement
describe motor neuron basic structure
cell body (soma), coming off of soma are small projections called dendrites
- on other side of soma is a long projection that extends called an axon
- axon hillock is where axon connects to cell body
- at end of axon, small branches called terminals
basic structure and function of bipolar neurons (interneuron)
have 2 projections- one single dendrite coming off one end/pole of cell body and one single axon coming off the other end/pole
- these are sensory in function and are involved in olfaction(smell) and vision
Sensory neurons are called ___ neurons, not ___
pseudounipolar
unipolar
describe structure of pseudounipolar neurons
dendrite on top and axon on bottom- appears to be a single projection coming off of cell body, but differentiated according to function
- top part is called peripheral axon (functions like axon & carries info up from projections down toward the cell body)
- bottom part called central axon (takes sensory info and sends it toward the CNS to be registered) –> info seems to bypass the cell body, cell body does not have a role in processing/integrating that info
describe multipolar (motoneurons)
have a few short intermediate dendrites coming off one end of cell body & one single axon coming off of other
- involved in neural pathways called through circuits, a long distance neural pathway (neural pathways called neural circuits)
bipolar neurons aka ___ neurons
interneurons
pseudounipolar neurons aka ___ neurons
sensory neurons
multipolar neurons aka ___ neurons
motoneurons
structure & function of nerve cell is closely related…
what is the zone of dendrites and soma
zone of impulse integration
- the part of the neuron that receives and processes incoming stimuli
- a nerve cell can receive multiple stimuli at any given time, not just one –> dendrites and soma integrate these multiple signals into one final signal, which travels to axon hillock…if final signal above threshold–>AP
structure & function of nerve cell is closely related…
what is the zone of axon hillock
zone of spike initiation
(spike is term for AP), AP travels along axon
structure & function of nerve cell is closely related…
what is the zone of axon
zone of impulse propagation
movement of AP across length of single cell
structure & function of nerve cell is closely related…
what is the zone of terminals
zone of impulse transmission
when AP gets to terminals, only option is to jump to another cell (movement of AP from one cell to another cell)
in a typical motor neuron, in what structures are voltage-gated Na+ and K+ channels found?
exclusively found in axon and terminals (absent in cell body & dendrites)
in a typical motor neuron, in what structures are ligand-gated channels found?
in dendrites and cell body
how are ligand-gated channels activated
by some sort of chemical messenger that binds to the channel, most common chemical messenger is a neurotransmitter
in a typical motor neuron, in what structures are mechanically-gated channels found?
what are these channels?
in dendrites and cell body
mechanically-gated channels are activated by a result of stretch of pressure or temp on the membrane
can an action potential be generated in cell body or dendrites of nerve cell?
no
explain why an action potential is not generated in soma or dendrites
all the stimuli that come in cause a grated potential- a change in membrane potential that is directly proportional to the strength of the incoming stimulus
ex: depolarizing stimulus of 10 mV will depolarize the membrane by 10 mV- but no action potential because no voltage-gated channels to be spontaneously activated
what is electrotonic spread
the movement of an electrical signal with progressive loss of strength
explain signal integration that happens at soma and dendrites (start with +10 depolarizing stimulus)
10 mV depolarizing stimulus comes into inner surface of membrane –> opens sodium channels, positively charged sodium builds up on inside of membrane, changing potential by 10 mV –> this signal then begins to move laterally along membrane, moves b/c there is a high concentration of positive charge at the point where the signal entered, so move from + to - by electrical attraction (this signal is due to sodium, in that exact spot, high conc of sodium, but everywhere else: low conc.
- so, once a signal is established, starts to move down its electrical gradient –> as sodium diffuses along inside of membrane, some of it will be pumped through the sodium pump and some will diffuse back out through random diffusion…so as signal moves, loses strength (electrotonic spread) 10 mV becomes 9…8…7…6…5
- however, soma can receive multiple stimuli at a time, so at the same time, another 10 mV depolarizing signal can be added…now have 15 mV depolarizing signal (soma and dendrites progressively add these signals to form one signal of resulting strength—> final strength of it determines where you get an AP at axon hillock or not)
- also, a negative 10 mV signal can come in –> opens potassium channels, K increases outward, inside of membrane more negative, hyperpolarization
- if + and - signals meet, come together and cancel each other out
positive signals/stimuli to the membrane are called ___ signals, involving what ion?
excitatory signals
positive stimuli open sodium channels, causing depolarization of membrane, takes it toward threshold –> AP
negative signals/stimuli to the membrane are called ___ signals, involving what ion?
inhibitory signals
negative stimuli open potassium channels, cause hyperpolarization, takes potential away from threshold –> prevent AP
thousands of ___ and ___ signals come together to either give an action potential or not
excitatory and inhibitory
neurons operate on ____, all action potentials are the same size
binary code
action potential generated at axon hillock, how much energy is released?
releases all stored energy of the membrane (stored energy results in 85 mV signal, this 85 mV begins to move down the axon)
does the AP have enough strength to get all the way to the terminal and jump to another cell (maintain its strength of 85 mV)?
specific type of axon called naked axon- the exposed membrane of the axon, the AP moves by electrotonic spread (progressive loss of strength)
- so the 85 mV moves down the membrane and loses strength as it goes..but not exactly
- as AP begins to move forward, immediately encounters area of membrane in front of itself that is still at rest, which means that area still has all of its stored energy present in the resting potential –> as soon as AP hits the resting part, the signal will be strong enough to be above threshold and will generate the AP in front of itself –> this continues all the way down the length of the axon continuously regenerating itself as it goes
in a naked axon, the AP moves by electrotonic spread in theory, but since membrane is continuous…
since membrane is continuous, the AP is continuously being exposed to the area in front of it still at rest (does not have to travel any distance, always in contact with area in front of it at rest)
so…the AP never really decays to any degree- 85 mV never really loses any strength- AP moves along membrane regenerating itself point by point all the way along the membrane, basically an infinite number of points, so you basically have a wave
an action potential is generated the ___, moves along membrane as a ___ __ ____, when it reaches terminal, this is its strength, __
axon hillock
wave of depolarization
just as strong as when it started
in addition to billions of neuron cells, there are also billions of support cells called ___, which serve a number of different functions
glial cells (neuroglia)
glial cells (neuroglia) are directly involved in facilitating ____ by synthesizing and secreting a substance called ___
the action potential along neurons
myelin
name 2 glial cells (neuroglia)
1- oligodendrocytes (in central NS- brain, spinal cord)
2- Schwann cells (in peripheral NS- cranial and spinal nerves that leave CNS and go to peripheral parts of body
name 2 other small types of glial cells (neuroglia)
1- astrocytes (in central NS)- provide nutrients, help recycle ions after AP generated, support connections between 2 neurons
2- microglia- maintain health and welfare of the NS, scavenge cellular debris
what is myelin and on what cells?
myelin is synthesized and incorporated into the cell membrane, membrane of Schwann cells and oligodendrocytes grows and expands and wraps around the axon in concentric layers to form myelin sheath
- this forms a myelinated axon, the myelin sheath is intermittent, occurs intermittently along axon, leaving some areas of axon exposed (nodes of Ranvier)
exposed areas of the membrane in the myelinated axon are called ___
the myelin axon part are is called ___
nodes of Ranvier
internode
what is myelin made out of?
myelin is almost pure lipid, myelin sheath almost pure lipid membrane
myelin sheath acts as an ___ on the axon
insulator
- lipids are non polar, not water soluble, and impermeable to anything that has a charge (sodium and potassium have a charge, Na+ and K+ currents cannot pass myelin sheath)
- membrane under myelin sheath cannot be depolarized or generate an AP b/c ion currents cannot pass –> can only generate AP on nodes of ranvier, jumps from node to node
what is saltatory conduction
action potential mechanism on myelinated axons
- AP generated on axon hillock of exposed node, current migrates along axon past the myelin sheath to the next exposed node and depolarizes that node, AP jumps node to node
which is faster- saltatory conduction or electrotonic spread
why?
saltatory conduction on myelinated axons is a faster mechanism of AP propagation than electrotonic spread on naked axons
the insulation of myelin sheath reduces the longitudinal distance of a membrane (AP on naked axon has to work against every point on that membrane b/c the points resist being activated), the myelinated axon only has to work against the exposed nodes, less work for it to do, so works faster
vertebrates mostly have ___ axons and invertebrates have ___ axons
vertebrates- myelin
invertebrates- naked
although invertebrates have naked axons, they move just as fast as us, how?
through axons of large diameter
- AP speed is directly proportional to axon diameter (larger the diameter –> faster AP will move)
what is the limitation of invertebrates having large diameter axons?
large diameter axons limit the # of neurons that can be packed in the space of the NS of the animal (individual neurons are large so invertebrates have fewer of them)
- their pathways are then limited in complexity, so their behaviors are also limited in complexity
- the exception is the octopus (giant head can pack lots of neurons, thus the smartest invertebrate)
advantage of myelin with small diameter axons is…
can shrink diameter of neuron without loss of speed (just as fast, if not faster) –> more complex pathways
