Muscle and Neuron Physiology Flashcards
What are the three types of muscle tissue?
skeletal muscle, smooth muscle, cardiac muscle
What is the difference between striated and smooth muscle?
striated: most muscles have a mix of large diameter and small diameter muscle fibers… alternating light and dark bands which give it that striated look.
smooth: not involved in voluntary contractions. not attached to skeleton. keep in mind that cardiac muscle IS striated though but is INVOLUNTARY.
What is a muscle fiber?
a muscle fiber is a muscle cell.
skeletal muscle fibers develop from embryonic myoblasts.
Name the three connective tissues that bind together and cover skeletal muscle?
epimysium: sheath that surrounds each skeletal muscle.
perimysium: subdivides each whole muscle into numerous, visible bundles of muscle fibers.
endomysium: delicate layer of CT that separates the individual muscle fibers within each fascicle.
Where are the epimysium, perimysium and endomysium located?
epimysium located is the outermost layer surrounding the entire muscle
perimysium is the next layer within, and surrounds the muscle fascicles themselves
endomysium is the innermost layer surrounding bunnies of individual muscle fibers that compose a fascicle
What is actin, myosin and troponin/tropomyosin? Which of these is the thin filament, which is the thick?
The sarcomere consists of actin (thin) myofilaments and myosin (thick) myofilaments. It is the relationship of troponin and tropomyosin that dictates when the skeletal muscle will contract.
How do actin and myosin interact to cause a muscle contraction?
A cross bridge forms when the myosin binds to the actin, actin strands are pulled toward the H-zone, the H-zone disappears.
Hence the events occurring in muscular contraction are H-zone disappears, I-band reduces in width, The width of A band is unaffected and M-line and Z-lines come closer. Sarcomere shortens.
What is a sarcomere? Describe the parts of a sarcomere: A line, Z line, I band etc…
A sarcomere is a boundary line. It is the smallest portion of a muscle that can contract. Sarcomeres join end to end to form the myofibrils.
I band: lighter regions (includes a darker A band region), each of two I bands include a Z disk and extend to end of myosin myofilaments. I bands contain only actin (why they are light colored).
A band: darker-staining band in center of each sarcomere. A band contains both actin and myosin overlapping, except in the center of the A band. In the center of A band is the H Zone.
H zone: contains only myosin. Middle of each H zone has a dark line called the M line.
M line: M line consists of delicate filaments that hold myosin in place.
Titin: gives muscle ability to stretch, and to recoil.
Why is calcium important in muscle contraction?
Well, once Ca++ diffuses out of the sarcoplasmic reticulum (channels opened by actions potentials triggering voltage gated Ca++ channels to open) and into the sarcoplasm surrounding the myofibrils, Ca++ can will now bind to the troponin molecules of the actin myofilaments. Binding Ca++ to troponin causes the tropomyosin to move, which exposes active sites on the actin. Myosin heads then bind to the exposed active sites on actin to form cross-bridges. Muscles contract when cross-bridges move.
What will occur if calcium does not bind to troponin/tropomyosin.
First of all, a muscle cannot contract until the tropomyosin moves to uncover the active sites. Tropomyosin is a long fibrous protein that lies in the groove along the actin strand. It covers the active sites on the actin. The active sites can be thought of as receptor sites for the myosin head.
Troponin prevents tropomyosin from uncovering the actin active sites in a relaxed muscle. Troponin also binds Ca++
(pg 279 textbook)
Ca++ which is stored in the sarcoplasmic reticulum, is key for contraction. (pg 288) Once Ca++ rapidly diffuses out of the sarcoplasmic reticulum due to action potentials carried into the muscle fiber via the T tubules causing voltage gated Ca++ channels in the terminal cistern to open…
***Ca++ binds to troponin molecules of the actin. Binding Ca++ to troponin causes the tropomyosin to move, which exposes the active sites on the actin. The myosin heads then bind to the exposed active sites on actin to form cross bridges. Muscles contract when cross-bridges move.
The heads of the myosin myofilaments bend (power stroke), causing actin to slide past the myosin. As long as Ca++ is present, the cycle repeats.
Why is ATP important in muscle contraction?
ATP is important in muscle contraction because one ATP molecule is required for each cross-bridge cycle. The myosin head stores energy from ATP breakdown that happened during the previous cycle. Myosin head will remain in resting position until the muscle fiber is stimulated by a motor neuron (Ca++ has to bind to the troponin and expose active sites too, then myosin heads bind to them).
Binding of ATP causes the myosin head to detach from the actin. Breakdown of the ATP by the myosin head supplies energy for the recovery stroke.
To summarize…
ATP molecules on myosin heads are broken down to ADP and P, which releases energy needed to move the myosin heads.
ATP is also required to detach the myosin heads from the active sites for the recovery stroke.
ATP is also needed for the active transport of Ca++ into the sarcoplasmic reticulum from the sarcoplasm. (pg 292)
So, you need ATP in place (in advance) for the power stroke and you need one “on the fly” for the recovery stroke.
What would happen if ATP was not available for muscle contraction?
Need ATP for power stroke. ATP is already attached but hydrolyzed to get into that “position.” (chicken or egg question)… The energy released during ATP hydrolysis changes the angle of the myosin head into a “cocked” position. The myosin head is then in a position for further movement, possessing potential energy, but ADP and Pi are still attached. If actin binding sites are covered and unavailable, the myosin will remain in the high energy configuration with ATP hydrolyzed, but still attached.
Where is ATP produced?
ATP is produced from the mitochondria in a basically “reverse photosynthesis” kind of fashion, converting sugar into glucose and combusting with oxygen to make new, energy-rich ATP molecules.
https://www.youtube.com/watch?v=QImCld9YubE
What are the parts of a neuromuscular junction?
Remember, each muscle fiber (cell) is in contact with a motor neuron branch from the brain or spinal cord. A neuromuscular junction consists of: (pg 280)
1) axon terminals (presynaptic, cleft, motor-end plate aka post-synaptic membrane
2) area of the muscle fiber sarcolemma they innervate
What is a neurotransmitter?
Signal molecules that control the effectors. In an axon, the axon endings have many synaptic vesicles which store the signal molecules produced by the neuron aka neurotransmitter.
ex. acetylcholine, epinephrine, norepinephrine
What is a twitch…tetanus?
(pg 294) muscle twitches are all-or-none events when the stimulus frequency is very low, allowing for adequate rest. Muscle fibers stimulated at greater frequencies first display:
wave summation, then
(muscle fibers stimulated more frequently)
incomplete tetanus, then
(merging of more and more muscle twitches)
complete tetanus
(muscle fiber stays completely contracted with no relaxation)
What would happen if the cell does not produce acetylcholinesterase?
this enzyme (-ase denotes it’s an enzyme) keeps acetylcholine from accumulating within the synaptic cleft, otherwise the buildup of this neurotransmitter would constantly stimulate the motor-end plate and produce continuous contraction in the muscle fiber. This enzyme ensures that one presynaptic action potential yields only one action potential at the motor plate.
What is stored in the synaptic vesicles?
Pg 392/393
Neurotransmitter is stored in synaptic vesicles, which can be found in the endings of axons. Example of neurotransmitter would be acetylcholine.
Why is oxygen important in muscle contraction?
It is important for aerobic metabolism, in which O2 is absorbed in mitochondria along with pyruvate to form ATP. ATP is essential for muscle contraction, not to mention life in general.
What role does myoglobin and creatine phosphate have in muscle tissue?
myoglobin is important for oxygen storage, and is found in muscle. Important because oxygen is needed in the synthesis of ATP and aerobic respiration.
pg. 302 under creatine kinase
creatine phosphate’s role in muscle tissue is used when muscle fibers accumulate extra ATP during rest. This extra ATP is utilized in muscle fibers to transfer a phosphate from the ATP to a small protein synthesized by muscle fibers called creatine. The transfer of the phosphate creates the molecule creatine phosphate, this molecule acting like a “bank” for “high-energy” phosphate.
What is a motor neuron?
A motor neuron is a specialized nerve cell responsible for stimulating muscle contraction. Most origination brain/spinal cord and extend to muscle fibers through nerves. Whole muscles are generally supposed by several motor neurons. pg. 275
What causes rigor mortis?
mentioned on pg 290
shortly after a person dies, Ca++ diffuses out of the sarcoplasmic reticulum and the body becomes very still and rigid.
To understand correctly remember, before cross-bridges cycle when a person is alive, Ca++ binds to troponin and tryopomyosin (the chain blocking the active sites) moves out of the way so that the myosin heads can attach to the active sites on the actin. It takes one ATP for the heads to attach, cock their heads, and slide the actin past the myosin (power stroke). It takes ANOTHER ATP for the recovery stroke.
Knowing that, when someone dies, Ca++ floods out of the sarcoplasmic reticulum into muscles. Because of this influx of Ca++, tropomyosin moves out of the way and because your body still has some short-term ATP, so the ATP binds to the myosin, myosin cocks into position, and contracts the muscle. Will continue to contract until ATP stores are depleted. When no more ATP is available, the contracted muscle will stay that way because it does not have another ATP in order to relax.
To sum up, you need:
Ca++
ATP
What is oxygen debt?
If anaerobic respiration continues for a long time, lactic acid builds up in the muscles. Presence of lactic acid in the muscles causes pain and stiffness. Lactic acid can be broken down when an appropriate quantity of O2 reaches the cell. The quantity of O2 required to breakdown lactic acid into carbon dioxide and water is referred to as the OXYGEN DEBT. This additional quantity of O2 supplied to the muscles, comes from the increased rate of breathing that accompanies physical activity.
What causes muscle fatigue?
pg 302
fatigue is a temporary state of reduced work capacity. Without fatigue, muscles would be worked to the point of severe damage. multiple things cause fatigue:
- acidosis and ATP depletion due to increased ATP consumption or decreased ATP production.
- oxidative stress
- local inflammatory reactions
What would occur if calcium was unavailable during the action potential?
know all about calcium ions (pg 383)
if calcium is unavailable during an action potential something like hypocalcemia would be expected… where a person has lower than normal Ca++ levels in their blood. Because normal levels of Ca++ are required to keep voltage gated Na+ channels closed, hypocalcemia allows for their spontaneous opening. Thus, this condition would exhibit symptoms of nervousness and uncontrolled skeletal muscle contraction.
How is troponin affected by muscle fatigue?
muscle fatigue through the body’s use of anaerobic respiration when enough O2 not available that aerobic respiration usually provides. Supplements the process but results in breakdown of glucose to lactate and protons, more protons results in a lowering of pH. This results in Ca++ ability to bind to troponin, which is needed for tropomyosin to move out of the way. This interference results in a weak cross-bridge formation.
in other words, a low pH or acidosis would affect Ca++ ability to bind to troponin.
What happens to the length of the I band, H zone and A band during a muscle contraction?
When contracted:
I band: percentage of this are DECREASES
A band: percentage of this area INCREASES with the disappearance of the H-Zone (stays THE SAME in size though, so really there is NO change)
H zone: completely disappears
REMEMBER, when muscle is relaxed:
H Zone is thick filaments only
A band is where thick and thin filaments overlap
I band is thin filaments only
How does the resting length of the sarcomere affect tension production?
MUSCLE TENSION IS DEPENDENT ON MUSCLE LENGTH
the length of the sarcomere determines the DEGREE OF OVERLAP between myosin and actin.
the more the overlap, the greater the # of cross bridges, which form when myosin heads attach to actin.
the greater the # of cross bridges in the myofibril, the greater the amount of tension and the force of muscle contraction.
Define each term and know what they look like in a graph:
Contraction period, relaxation period, simple twitch, wave summation, cmplete tetanus, latent period and incomplete tetanus
tetanus.
for these terms, see graph image located on question part of this card
latent period (or phase): the gap between the time of stimulus to the motor neuron and the beginning of contraction
contraction period (or phase): commences once Ca++ is released from the sarcoplasmic reticulum and cross-bridge cycling occurs.
relaxation period (or phase): is much longer than the contraction phase because the concentration of Ca++ in the sarcoplasm decreases SLOWLY due to the active transport into the sarcoplasmic reticulum.
^^^PG 292 in textbook
For the following terms, see below attached image:
Simple twitch: the response of a muscle fiber to a single action potential along its motor neuron.
Wave summation: muscle fibers stimulated at greater frequencies first display wave summation, then incomplete tetanus, then complete tetanus. (treppe is the precursor to wave summation). Wave summation is caused by repeated stimuli. Rate of stimulus delivery increases and there is less and less time for the fiber to relax.
Incomplete tetanus: when there are periods of incomplete relaxation between summated stimuli.
Complete tetanus: there is NO relaxation between stimuli
What is lactic acid and how does if cause muscle fatigue?
Lactic acid is produced by skeletal muscle cells at all times, but especially during exercise, and is broken down or used to make new glucose, a product of anaerobic respiration when your muscles are fatigued and can’t get enough ATP to power muscle. Glucose undergoes glycolysis, the first step in anaerobic respiration - where glucose molecule is broke down into two molecules of pyruvic acid. Pyruvic acid is then converted to a molecule called lactate (almost synonymous with lactic acid). Although many factors contribute, the buildup of lactic acid and the corresponding drop in pH (acidosis) accounts for weak cross-bridge formation by interfering with Ca++ ability to bind to troponin.
What is an aponeurosis?
Aponeurosis is an extremely delicate, thin sheath-like structure, which attaches muscles to the bones whereas tendons are tough, rounded cord-like structures which are extensions of the muscle. Normally, tendons allow the attachment of the muscle from its originating bone to the bone on which it ends. An aponeurosis has the property of recoiling and hence, it functions like a spring; whenever the muscle expands or contracts, it bears all the extra pressure and tension. Likewise, a tendon has capacity for a lot of endurance to stretching and they allow the proper contraction of the muscle by providing strength and support. Aponeurosis is a white, transparent sheath, a flat structure like a sheet whereas a tendon is a white, shiny and glazed, rope-like tough structure.
page 275 in text
What is a motor unit and how does recruitment effect motor units?
pg 293
Recruitment is the amount of force in a whole muscle while “summation” is the amount of force in an individual muscle fiber.
Increasing force in a whole muscle depends on the TOTAL NUMBER of muscle fibers contracting.
A motor unit consists of a single motor neuron and all the muscle fibers it innervates. Motor units in different muscles contain different numbers of muscle fibers. Recruiting more motor units allows for the muscle to generate more force.
Note that delicate and precise movements call for many small motor units.
What are slow and fast twitch fibers?
pg 299
slow-twitch fibers (type 1) contract more slowly, have a better-developed blood supply, have more mitochondria, and are more fatigue-resistant than fast-twice muscle fibers. Breakdown ATP slowly. Aerobic respiration. Contain large amounts of myoglobin. Myoglobin is great for O2 STORAGE. Therefore, these muscle fibers perform for longer periods of time.
fast-twitch muscle fibers (type 2) response rapidly to nervous stimulation. Cross bridges form more rapidly, but less developed blood supply. Very little myoglobin, fewer mitochondria. Large deposits of glycogen and are well adapted for anaerobic respiration. Contract rapidly for a shorter time and fatigue quickly.
In humans, more of the upper limbs contain fast-twice fibers whereas the back and lower limbs contain more slow-twitch fibers.
What are myofibrils?
Pg 276
Myofibrils are bundles of protein filaments. Each muscle fiber has numerous myofibrils in its sarcoplasm. Not to be confused with MYOFILAMENTS which are ACTIN and MYOSIN. These myofilaments make up a myofibril.
Describe the characteristics of smooth, cardiac and skeletal.
Smooth: no striations, centrally single located nuclei per cell, involuntary, walls of hollow organs, blood vessels, eyes, glands, and skin.
Cardiac: striated, intercalated disks, centrally single located nuclei per cell, involuntary, heart.
Skeletal: striated, branched, multiple nuclei, voluntary AND involuntary (reflexes), attached to bones.
What is the importance of creatine phosphate?
the importance of creatine phosphate happens when a phosphate is transferred from extra ATP that’s accumulated during periods of rest. The phosphate from the ATP is transferred to a small protein synthesized by muscle fibers called creatine. This transfer creates the molecule creatine phosphate.
FUNCTION: this molecule acts like a “bank” for “high-energy” phosphate. When ATP levels start to drop in a contracting muscle fiber, the enzyme creatine kinase will transfer a phosphate from creatine phosphate to ADP, immediately making ATP.
Describe the parts of the neuromuscular junction?
pg 280
neuromuscular junction AKA synapse
parts are:
axon terminals
area of innervated muscle
presynaptic terminal: also just called the axon terminal
synaptic cleft: the space between the presynaptic terminal and the muscle fiber
motor end-plate aka postsynaptic membrane: muscle plasma membrane in the area of the junction
synaptic vesicles: small, spherical sacs located in the presynaptic terminal
acetylcholine: the neurotransmitter found within the synaptic vesicles
Define isometric, concentric and eccentric contractions.
Isometric contraction: a muscle produces increasing tension as it remains at a constant length, ex. postural muscles
Concentric contraction: are isotonic contractions in which tension in muscle is great enough to overcome the opposing resistance, and the muscle SHORTENS. (biceps brachiI)
Eccentric contraction: (think extend) are isotonic contractions in which tension is maintained in a muscle, but the opposing resistance is great enough to cause the muscle to INCREASE IN LENGTH. (descending a flight of stairs)
pg 298
What roles do the T-tubules play in muscle contraction.
T-tubules are inward folds of the sarcolemma. At regular intervals along the muscle fiber, the sarcolemma forms T-tubules by projecting and extending into the interior of the muscle fiber. The tubules carry electrical impulses into the center of the muscle fiber so that EVERY CONTRACTILE UNIT OF THE MUSCLE FIBER CONTRACTS IN UNISON
pg 276
Understand the ways ATP is generated in a muscle cell and when each way is used.
4 main pathways to ATP production in skeletal muscle.
- adenylate kinase quickly converts ADP to ATP. Only generates a few seconds of ATP.
- Creatine kinase uses banked phosphate from creatine phosphate for immediate ATP, depleted within 5-6 seconds.
- Anaerobic respiration used for short-term, intense exercise, up to 40 additional seconds of ATP.
- Aerobic respiration: produces ATP for hours of exercise.
How are muscle fibers more specialized to get more oxygen supply?
Well, T-tubules carry only ELECTRICAL SIGNALS or IMPULSES into the center of the muscle fiber… so, GOOD GUESS!!
Its actually that skeletal muscles have a rich supply of blood vessels. An artery and either one or two veins extend together with a nerve through the CT layers of skeletal muscles. Numerous branches of the arteries supply the extensive capillary beds surrounding the muscle fibers and blood is carried away from the capillary beds by branches of the veins.
pg 275
Describe the difference between slow twitch and fast twitch muscle fibers.
sprinter: explosive strength - more fast twitch fibers
when trained, they become big and heavy.
FAST TWITCH or TYPE 2 muscle fibers, produce more force, have more potential for growth.
marathoner: endurance - more slow twitch fibers
slow twitch, not as reactive and speedy, but can last for HOURS.
SLOW TWITCH or TYPE 1 muscle fibers, produce less force.
average person has about 50/50
Describe the difference between white muscle fibers and red muscle fibers.
Fast-twitch fibers appear whitish because relatively low blood supply (also because they are low in myoglobin which is dark-colored)/
Slow-twitch fibers appear reddish because they have well-developed blood supply and a large amount of myoglobin.
Human muscles exhibit both types of muscle fibers, although the # varies per muscle group. Upper limbs contain more fast-twitch while lower limbs contain more slow-twitch
What are ligands?
A ligand is any substance that can bind to a target protein, such as a neurotransmitter. It is a generic term.
https://www.youtube.com/watch?v=NXOXZ-kaSVI
Understand why receptor specificity is important.
Specificity is important because certain receptors require certain ligands in order to active/deactivate. Example: ligand-gated receptor - ligand acetylcholine binding to nicotinic receptors to allow sodium to enter the cell and create an electrochemical gradient, resulting in depolarization. It is a communication system.
https://www.youtube.com/watch?v=WORIhbaRABg
List the three properties that contribute to the electrical properties of the cell.
Ion channels - specifically 1. ligand-gated and 2. voltage-gated channels (responsible for membrane permeability and resting membrane potential), polarized plasma membrane creates a 3. resting membrane potential (due to K+ inside the cell and Na+ outside the cell).
pg. 312 under chapter 9.4 excitability of muscle fibers (also read action potentials, next heading, great summary) also pg. 287 is a great resource to see the events that occur at the neuromuscular junction.
- ligand-gated ion channels (pg 282)
- voltage gated ion channels (pg 282)
- resting membrane potential (pg 282)
Know the concentration gradients for sodium, chloride and potassium ions.
https://www.youtube.com/watch?v=Jk_9IhHVOTk
awesome ninja nerd video
sodium more prevalent on outside of cell, potassium more prevalent on inside of cell. There are leaky channels for both ions however, but they move from high to low, down their concentration gradients. Na+ moves from outside to inside, but hardly at all, very slowly… because Na+ isn’t very permeable. K+ moves from high to low (from inside cell to outside cell) and is much more permeable than Na+. There are also Na+/K+ ATPase pumps which pumps Sodium outside the cell and K+ inside the cell.
pg 383 and 384 in text
Hyperpolarization
Cl- (chloride) entry into the cell can cause hyperpolarization. K+ exit from the cell can also cause hyperpolarization. Hyperpolariztion is always inhibitory. Depolarizing is always excitatory.
Chloride higher outside the cell. Moving down it’s concentration gradient inside the cell can cause the cell to hyper polarize. Cl- (chloride is negative)
Depolarization
Sodium:
principle way cell depolarizes is through Na+ entering the cell and making the inside more positive.
Potassium:
If K+ becomes high outside the cell, the intracellular K+ won’t travel down its concentration gradient to go outside the cell, as it normally would. Instead, it will stay inside the cell and that can contribute to the cell becoming more positive on the inside.
How will the sodium/potassium pump maintain concentration gradients across the cell membrane?
pg 380 in text
all along the neuron axon, the SODIUM POTASSIUM PUMPS actively pump K+ against its concentration gradient into the cell while simultaneously pumping Na+ against its concentration gradient out of the cell. Three Na+ are transported out of the cell and two K+ are transported into the cell for every ATP molecule used.
Understand why the selective permeability of the membrane is important.
Membrane permeability is important to maintain homeostasis of the cell.. normal concentration differences must exist in order for certain processes to happen ex depolarization of the cell, synapses, etc.
pg 69 and 70
How will a molecule being lipid soluble effect its ability to diffuse across the membrane? How about a molecule that is
water soluble?
A molecule that is water soluble (hydrophilic) will NOT be able to to pass through the phospholipid bilayer. Requires some sort of transport. Example: protein channels - sugars and ions enter this way.
Lipid soluble material (hydrophobic molecules) can easily slip through the hydrophobic lipid core of the membrane. Substances such as the fat-soluble vitamins A,D,E, and K readily pass through the plasma membranes in the digestive tract and other tissues.
What is the cause of the electrical charge across the cell membrane?
A resting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential, or simply the resting potential.
The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.
In a resting neuron, there are concentration gradients across the membrane for Na+ and K+. Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential.
How does the overall charge of the inside of the cell compare to the charge outside the cell?
Overall charge of the inside of the cell is more negative than the outside of the cell. When RMP becomes more positive and reaches threshold, depolarization occurs. Hyperpolarization occurs when the cell becomes even more negative on the inside.
Define equilibrium potential
It is the voltage amount that exactly offsets the chemical concentration gradient.
K+ equilibrium potential: -90mv
Na+ equilibrium potential: 60mv
Understand the term resting membrane potential.
Charge difference across the cell membrane; neurons and muscle fibers have specialized components to utilize this charge. Like a sprinter in starting blocks - ready to respond at a moments notice.
RMP results of three factors
- Concentration of K+ is higher inside the cell than outside
- Concentration of Na+ is higher outside the cell than inside
- Plasma membrane is more permeable to K+ than it is to Na+
Understand the characteristics of a leak channels.
of leak channels determines a plasma membrane’s permeability to different types of ions. So, we could say that the plasma membrane is much more permeable to K+ than Na+ because there are much more K+ leak channels than there are Na+ channels.
Leak ion channels AKA NONGATED ion channels…
are ALWAYS OPEN and responsible for permeability of the plasma membrane to ions with the plasma membrane is at REST.
Understand how ligand-gated channels function.
Ligand-gated ion channels open by the binding of a specific molecule to the receptor site of the ion channel. Specific molecule (ligand - general term) can be a neurotransmitter or hormone. When it binds, the ion channel opens or closes.
Example: neurotransmitter acetylcholine released from the presynaptic terminal of a neuron is the ligand that binds to a ligand-gated Na+ channel in the membrane of a muscle fiber. As a result, the Na+ channel opens allowing Na+ to enter the fiber. These channels exist for Na+, K+, Ca++, and Cl-. Common in nervous and muscle tissue (and glands).
Know why a voltage-gated channel will open/close.
These channels open/close in response to a small voltage change across the plasma membrane. When a cell is stimulated, the permeability of the plasma membrane changes because GATED ION CHANNELS will open/close. The movement of ions in or out of the cell changes the charge difference across the plasma membrane, which IN TURN, can cause voltage-gated ion channels to open or close.
Na+ and K+ voltage gated channels are most numerous in electrically excitable tissues, but voltage gated Ca++ channels also exist, and are especially abundant in smooth/cardiac muscle.
How will the dual gates in a voltage-gated channel allow them to open and close?
Each voltage-gated channel has two gates called ACTIVATION gates and INACTIVATION gates. When the plasma membrane is at rest, the activation gates of the voltage gated Na+ are closed and the inactivation gates are open.
Because the activation gates are closed, Na+ cannot diffuse through the channels. At threshold, the change in membrane potential causes many of the activation gates to OPEN, and Na+ can diffuse through the Na+ channels into the cell.
Voltage-gated K+ channels have ONE GATE. They open WAAAAAAY slower than the Na+ gates. Both Na+ and K+ gates open at same time when graded potential reaches threshold.
Depolarization occurs because MUCH MORE NA+ DIFFUSES INTO THE CELL THAN K+ DIFFUSES OUT OF IT - AND THIS IS PARTLY DUE TO THE GATES. 2 Sets for Na+, 1 set for K+. Na+ gates open fast and there are more of them, K+ gates open very very slowly.
What is a local potential?
It’s called local because it only happens in the immediate area of the plasma membrane where the ion channel is opened. It’s also known as “graded” because it may vary in amplitude.
Action potentials are not local because the opening of voltage-gated ion channels depolarizes the membrane, which then stimulates the opening of adjacent voltage-gated ion channels. Like tipping dominos, the action potential causes more action potentials successively and distally along the axon.
Understand what can cause a local potential.
light, heat, mechanical disturbance, chemical signal.
chemical stimulus most common
ligand-gated channel. ligand attaches, ion channel opens. ions rush into cell. High to Low.
Small change in voltage - local potential. Multiple can converge at the trigger zone and consolidate to activate the action potential. Can be “graded” meaning they vary in magnitude - can be strong or weak.
Define threshold potential.
pg 284
Threshold potential is when the inside of the cell becomes more positive (depolarization) to the point that the membrane potential triggers an action potential - when MANY voltage-gated Na_ channels open rapidly for a brief time.
What is the threshold potential for a neuron?
about -55 mV
When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold.
Understand the significance of the all-or-none principle.
Action potentials occur according to the “all-or-none” principle, which means that all action potentials are identical for a given excitable cell. Meaning the rules apply no matter what, if depolarization reaches threshold (if it exceeds threshold by a lot or a little, doesn’t matter) all of the permeability changes for an action potential occur without stopping. You either flip the trigger switch or you don’t. All or nothing.
What effect will depolarization have on the cell’s potential? (Increase, decrease or remain unchanged?)
Depolarization makes the inside of the cell more positive than the extracellular, or outside part of the cell. The cell’s potential will decrease.
What effect will repolarization and hyperpolarization have on the potential of a cell?
During depolarization the MP or (membrane potential, NOT RMP BECAUSE IT’S NOT RESTING) soars to +30mv. At +30mv the repolarization phase is triggered, Na+ gates are closed and K+ gate opens, K+ RUSHING out of cell to ECF.
Hyperpolarization: So much K+ has left the cell that the RMP reaches -80mv to -90mv, it s hyper polarized. Ions are on the WRONG side of the fence though, and need to switch even though a RMP has been reached. This hyperpolarizing is good though because it allows the cell to rest, called the REFRACTORY period. The leak channels will restore the ions back to their original composition.
*CHECK WITH PROFESSOR TO SEE IF THIS IS CORRECT
Know what type (and direction) of ion movement will cause hyperpolarization, depolarization and repolarization.
Hyperpolarization: Either through K+ exit from cell or Cl- entry.
Depolarization: Na+ entry into the cell
Ca++ generates action potentials in cardiac cells
Extracellular Ca++ keeps voltage-gated Na+ channels closed until neuron generates an action potential.
When K+ stays inside the neuron cell instead of normally diffusing out of the cell’s leak channels due to its concentration gradient, the cell becomes depolarized.
Repolarization: Na+ movement into the cell stops. K+ movement out of the cell increases.
Know the steps that occur during an action potential.
pg 285 (see illustration)
- Resting membrane potential
Voltage-gated Na+ channels are closed. Some K+ channels are closed. K+ diffuses down its concentration gradient through the open K+ leak channels, making the inside of the cell negatively charged compared to the outside. - Depolarization
Voltage-gated Na+ channels are open. Na+ diffuses down its concentration gradient through the open voltage-gated Na+ channels, making the inside of the cell positively charged compared to the outside.
Simple: opening of voltage-gated Na+ channels.
*At the apex of the action potential (graph - see pg 284) voltage-gated K+ channels open.
- Repolarization
Voltage-gated Na+ channels are closed, and Na+ movement into the cells stops. More voltage-gated K+ channels open. K+ movement out of the cell increases, making the inside of the plasma membrane negatively charged compared to the outside once again.
pg 286
Action potentials occur in one area of the plasma membrane and then travel (propogate) along the plasma membrane. An action potential produced at one location in the plasma membrane stimulates the production of an action potential in the neighboring section of plasma membrane. The depolarization of the membrane in one action potential location triggers the opening of nearby voltage-gated Na+ channels. Note that a single action potential does not actually move along the plasma membrane. Rather, an action potential in an adjacent location, which in turn stimulate the production of another and so on, and so on. LIKE A ROW OF DOMINOES! Each domino falls but no single domino travels the length of the row.
Understand the graph of an action potential.
pg 284 in textbook
What would happen if the various ion channels could not open?
An action potential would not occur.
What are an ascending and a descending pathway?
pg 476 and 477 - EXCELLENT CHART
Ascending: sensory info from the periphery is transmitted via action potentials along sensory pathways or tracts to the brain.
Descending:
What is a nerve composed of?
A collection of many axons bundled together outside the brain and the spinal cord.
Name the different types of neuroglial cells and their functions?
CNS - there are 4:
1. Astrocytes: Cover surfaces of neurons, blood vessels, and Pia mater of brain/spinal cord. Provide structural support and play a role in regulating what substances from the blood reach neurons (BBB - blood-brain-barrier)
2. Ependyal cells: Ciliated, lining ventricles of brain and central canal of spinal cord to help move CSF fluid. Other ependymal cells exist on surface of choroid plexus, secreting CSF.
3. Microglia: Phagocytic cells of the CNS.
4. Oligodendrocytes: Extensions from these cells form part of the myelin sheaths of several axons within the CNS.
PNS - there are 2:
1. Schwann cells: form the myelin sheath of an axon within the PNS.
2. Satellite cells: surround neuron cell bodies within ganglia, provide support/nutrition AND PROTECT FROM HEAVY METAL POISONS like LEAD and MERCURY.
Which types of neuroglial cells are found in the CNS?
astrocytes
ependymal cells
microglia
oligodendrocytes
Which type of neuroglial cells are found in the PNS.
Schwann cells
satellite cells
What is a plexus?
A plexus is a bundle of nerves outside the brain and the spinal cord.
What comprises the CNS and the PNS?
CSN comprised of brain and spinal cord
PNS comprised of receptors, nerves, ganglia (mini brains), plexuses
ascending pathways picture from textbook
descending pathways - picture from textbook
if the term ends in “spinal” that means it is usually originating from the brain and DESCENDING to the spine…
that alone tells you that it is a DESCENDING PATHWAY
what division would you find the parasympathetic and sympathetic nervous systems?
visceral motor division
Schwann cell anatomy
in response to an injury at the axon, the muscle
will either atrophy or hypertrophy
