Exam 2 Worksheet Answers Flashcards
(155 cards)
1
Q
what are the two primary functional divisions of the nervous system
A
CNS and PNS
2
Q
how do the CNS and PNS differ
A
The two systems differ both anatomically and functionally. Looking at anatomy first, the CNS is composed of the brain and the spinal cord while the PNS is composed of the cranial nerves and the spinal nerves. The PNS can be further subdivided into the sensory (afferent) and motor (efferent) divisions. Both divisions are still composed of cranial and spinal nerves, but the nerves in each division are carrying different information (sensory or motor). Looking at function, the CNS is responsible for integration of information and contains regulatory control centers while the PNS is responsible for communication between the CNS and the rest of the body. Information from sensory nerves of the PNS will travel to the CNS where that information is integrated and a decision is made to perform an action. That action is sent to the appropriate muscles or glands on efferent nerves in the PNS.
3
Q
neuron characteristics of excitability
A
Excitability is the property of the neuronal membrane that allows it to generate local and transient or large and long lasting changes in membrane potential in response to a chemical signal. The chemical signal is often in the form of a neurotransmitter binding to a chemically gated ion channel. Opening these channels allow ions to flow across the membrane and change membrane potential. Voltage-gated ion channels also give the neuron excitability, they also allow the cell to change its permeability to different ions and thus alter membrane potential
4
Q
neuron characteristic of conductivity
A
Conductivity is the property of the neuron that allows current to move (propagate) along the membrane. This property allows graded potentials to travel from the dendrites to the axon hillock or the action potential to travel along the axon.
5
Q
neuron characteristic of secretion
A
Secretion is the property of neurons that allows them to release neurotransmitters under controlled conditions at the axon terminals. This response is controlled by the electrical activity of the neuron. If an action potential invades the axon terminal then vesicle fusion can occur. However, in the absence of an action potential, no vesicle fusion events will occur.
6
Q
function of dendrites
A
Dendrites are short processes that branch off the cell body creating a ‘dendritic tree’. A neuron may have one dendrite or many, depending on its role in the nervous system. Axons from other neurons will form synapses with the dendrites, thus the dendrites are the major receptive region for input into the neuron. Increasing the number of dendrites will increase the amount of information a given neuron will receive.
7
Q
function of axon
A
The axon is a singular process emanating from the cell body and is the main structure the neuron will use to communicate (i.e. send action potential) with other cells. Although there is only one axon per neuron, the axon can branch extensively, creating axon collaterals that will increase the number of cells that neuron can form synapses with. The initial part of the axon is called the axon hillock; this region is continuous with the cell body and is the site of action potential generation in a typical multipolar neuron. The terminal end of the axon is the axon terminal (also called synaptic terminal, synaptic knob, synaptic bulb) and will form the presynaptic side of a synapse with another neuron’s dendrite, a muscle cell, or a gland cell.
8
Q
function of synaptic vesicles
A
Synaptic vesicles are small lipid bilayer membrane sacs that cluster in the axon terminals. These vesicles contain neurotransmitters. Following a depolarization of the axon terminal by an action potential, synaptic vesicles will fuse with the membrane of the axon terminal and release there packaged neurotransmitters into the synaptic cleft.
9
Q
function of neurofilaments
A
Neurofilaments are a type of intermediate filament that is specific for neurons. Much like other intermediate filaments, neurofilaments are critical in providing tensile strength throughout the neuron, including the dendrites and axon. These proteins allow the cell to maintain its structure, and without these filaments the cell would not be able to function properly
10
Q
what are the two types axonal transport
A
fast and slow axonal transport
11
Q
what proteins are involved fast axonal transport
A
Fast axonal transport occurs in both an anterograde (cell body toward axon terminal) and retrograde (axon terminal to cell body) fashion. To keep cargo moving in the right direction specialized motor proteins (called kinesins and dyneins) attach to the cargo being moved and ‘walk’ down the microtubule scaffold that is present in the axon. Anterograde fast axonal transport will move substances including mitochondria, cytoskeletal elements, membrane components, and enzymes.
These substances are important for the neuron to maintain normal function. Retrograde fast axonal transport generally moves used up organelles that are going to the cell body to be recycled. However, sometimes signaling molecules can also move to the cell body via this mechanism and may signal for new protein synthesis to happen in the nucleus.
12
Q
what proteins are involved in slow axonal transport
A
Slow axonal transport only moves substances in an anterograde (from the cell body to the axon terminal) fashion. This process, moves similar kinds of substances including enzymes and cytoskeletal elements, but also moves axoplasm (the cytoplasm within the axon)
13
Q
what are the three structural classes of neurons
A
pseudounipolar, multipolar, and bipolar
14
Q
multipolar neuron
A
Multipolar neurons are the most common in the nervous system and the major neuron type of the CNS
15
Q
bipolar neuron
A
Bipolar neurons have two extensions from the cell body, one is a fused dendrite and the other is the axon. Bipolar neurons are rare and seen only in sensory organs
16
Q
pseudounipolar neuron
A
Pseudounipolar neurons have one process leaving the cell body forming the axon; however, at one end of this process, receptive endings are present and act like dendrites taking in sensory information. Pseudounipolar neurons are found mainly in the PNS, where their cell bodies can be found in ganglia located adjacent to the spinal cord
17
Q
What are the three connective tissue wrappings in a nerve?
A
The connective tissue wrappings in a nerve are very similar to those that you would find in the muscle. The epineurium surrounds the outside of the nerve creating a protective sheath. Inside the nerve, fascicles are again present. The fascicles are surrounded by a perineurium. Inside each fascicle are many axons of individual neurons. Filling in the space around each axon is the endoneurium. So the 3 connective tissue wrappings in order from superficial to deep would be the epineurium, perineurium, and endoneurium
18
Q
If a person has a brain tumor, is it more likely to have developed from neurons or from glial cells? Why
A
A brain tumor is most likely to develop from glial cells. The major reason for this is that neurons are generally amitotic and, outside of a few special regions, are not capable of cell division. Glial cells, however, are constantly dividing like many other cells outside the brain. Cancers (including brain tumors) result directly from hyperactivity of cell division. As a result glial cells are the only cell in the nervous system that are capable of acquiring mutations of cell division that would allow them to divide at a higher rate and create pathologies like brain tumors. In early childhood, while the brain is completing development, brain tumors may originate from dividing neurons
19
Q
Which specific type of glial cells ensheaths (wraps around) axons in the CNS
A
In the CNS, oligodendrocytes are responsible for myelination of axons. Each oligodendrocyte sends out many branches from its cell body. Each branch will wrap around a small section of an axon and create a myelin sheath (insulating cover) for that region of the axon. One oligodendrocyte can help myelination many different axons, but is not responsible for completely myelinating the axon of one individual neuron.
20
Q
Which specific type of glial cells ensheaths (wraps around) axons in the PNS
A
In the PNS, Schwann cells are responsible for myelination of axons. Each individual Schwann cell will myelinate a small region of a neuron. The entire cell is involved in wrapping each section of axon, with the organelles and cytoplasm pushed to the periphery to allow for the tight membrane wrappings. Many Schwann cells are needed to myelinate a single axon, and each Schwann cell is participating in myelinating only one axon
21
Q
What is the function of the myelin sheath?
A
The myelin sheath serves two important functions. The first is to provide protection for the axon. The second is to provide insulation; this property is directly related to the speed of conduction of action potentials down the axon. The insulation of the myelin provides an increased resistance at the membrane and inhibits electrical current from escaping. This property allows generated potentials to travel quickly under regions of myelination without much decay in the potential amplitude.
22
Q
How does myelination of axons occur in the PNS?
A
In the PNS myelination occurs when a Schwann cell begins to envelop an axon. The Schwann cell will then begin to rotate around the axon wrapping its plasma membrane around the axon in concentric layers. As the number of layers increases the wrappings get tighter and the cytoplasm and organelles of the Schwann cell are forced out to the periphery. This creates a many layer thick sheet of plasma membrane tightly wrapped around the axon. This arrangement provides the protection and insulation described above
23
Q
How does the process of nerve regeneration occur in the PNS
A
Nerve regeneration can be observed in the PNS under some conditions. Large-scale damage from injuries where many axons are severed or axons are severed close to their cell bodies in the spinal cord will inhibit regeneration. However, smaller injuries such as severing a single axon can be recovered from. The process of regeneration begins with breaking down the axon distal to the site of injury and removing any debris via phagocytosis. When the path is clear of debris, the axon will form a growth process or growth cone that will begin to look for chemical signals telling it which way to grow. The target tissue and Schwann cells will release chemical signals trying to attract the axon. As the axon grows, Schwann cells will form a regeneration tube to help guide the axon to the target
24
Q
The portion of the nervous system that conducts impulses from the skin, joints, skeletal muscles, and special senses is the _________ division
A
somatic sensory
25
Which statement best describes the distinguishing features of neurons?
a) A person is born with all of the neurons they will ever have
b) Most neurons formed in fetal development last a lifetime, but some brain regions in adults can generate new neurons
c) Neurons are constantly dying and being replaced throughout all regions of the brain
d) Stem cells in the brain become glia, which can later become neurons if there is a need for them to do so.
b) Most neurons formed in fetal development last a lifetime, but some brain regions in adults can generate new neurons
26
Based on structure, the most common type of neuron is the ______ neuron
multipolar
27
The glial cell that myelinates and insulated axons within the CNS is the
oligodendrocyte
28
define ion channels
An ion channel is any integral membrane protein that allows ions to pass passively between the extracellular and intracellular space. These proteins do not require energy and they do not control the direction of ion flow. The leak channels that establish resting membrane potential are considered ion channels.
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define receptor
A receptor is an integral membrane protein that produces a physiological change in a cell following a stimulus. There are two classes of receptors – ionotropic receptors and metabotropic receptors.
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inotropic receptors
Ionotropic receptors are ion channels that require a stimulus to open. The stimulus comes in the form of the binding of a neurotransmitter to a receptive region on the integral protein.
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metabotropic receptors
Metabotropic receptors, or G-protein coupled receptors, are also integral membrane proteins that are not directly coupled to ion channels. These receptors are coupled to G-proteins that can interact with other intracellular proteins. Once activated the G-protein initiates an intracellular cascade that results in the activation of a second messenger. Different G-protein coupled receptors will couple to different G-proteins that can go on to activate different second messengers. The key benefit of utilizing a metabotropic receptor is that the signal becomes amplified within the cell. This amplification of signal means that a single neurotransmitter binding event can result in large changes in cell physiology that can have long term effects
32
major difference between ion channels and receptors
One of the major differences between ion channels and receptors is how they are activated. Receptors must have a neurotransmitter binding event in order to become activated. In the case of ionotropic receptors, once the neurotransmitter binds the protein behaves just like an ion channel. Because of this you can say that an ion channel can be a type of receptor, but not all receptors are ion channels (i.e. metabotropic receptors)
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3 mechanisms ion channels use to open and close
conformational change, structural change, and blocking gate
34
conformational change
where a single region of the pore changes shape allowing for ion flow
35
structural change
where the entire pore region changes shape
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blocking gate
where a specialized protein responds to cues and closes the pore region from the intracellular side
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the gating mechanisms used to allow channels to respond to different stimuli
The decision to open or close an ion channel is made by the gating mechanism specific to the type of channel. There are four different types of gating for ion channels. Ligand gating is observed when the ion channel contains a receptive region for a specific chemical (ligand), like a neurotransmitter. Once a ligand binds, the ion channel undergoes a conformational change allowing the pore region to pass ions. This is a common gating mechanism we will see throughout the nervous system. Another common gating mechanism is voltage gating. Ion channels that are voltage gated contain a series of charged amino acids that respond to voltage changes across the plasma membrane. When the membrane potential changes, voltage gated ion channels undergo a conformational change and open their pore region. Ion channels can also be gated by phosphorylation. This mechanism is common for G-protein coupled receptors. An activated second messenger can phosphorylate the ion channel triggering a conformational change and opening of the pore region. A final mechanism that is common in sensory receptors is the stretch or pressure gate. In this mechanism physical deformation of the plasma membrane causes a structural change in the ion channel which will allow the ion channel to open
38
What are the 4 “rules” to be considered a neurotransmitter?
There are many molecules that are active in the nervous system. In order to correctly classify them neuroscientists have established a series of ‘rules’ for a molecule to be considered a neurotransmitter. First, it must be synthesized and released from a neuron. Second, the substance should be released from nerve terminals in a chemically or pharmacologically identifiable form. Third, the substance should reproduce at the postsynaptic cell the same events that are seen following presynaptic electrical stimulation. In other words, the molecule that is released from the neuron must behave the same following normal physiological release and when it is introduced into the synapse experimentally. Finally, there must be an appropriate mechanism for termination of action.
Note that neurotransmitters can have very different chemical structures. Some are simple amino acids, others are chains of amino acids (“peptides”), some are derivatives of amino acids (indolamines, catecholamines), and even a gas can be classified as a neurotransmitter (nitric oxide)
39
Which function of the plasma membrane is directly affected by the opening of ion channels?
selective permeability
40
How would you classify an integral membrane protein that binds a ligand and results in the immediate opening of an ion channel?
inotropic receptor
41
current
Current (I) is the flow of electrical charge from one point to another point and is measured in amperes (A).
42
resistance
Resistance (R) is the hindrance to change flow by substances through which current must pass and is measured in ohms (Ω). In a cell, resistance most often takes the form of closed ion channels. These integral membrane proteins are directly responsible for resisting the flow of ions across the cell membrane
43
voltage
Voltage (V) is the potential energy generated by separated electrical charges and is measured in volts (V). A potential difference for a cell can be referred to as the membrane potential and represents the difference in charge on the intercellular and extracellular sides of the membrane
44
how are current, resistance, and voltage related?
These properties are related to each other by Ohm’s Law, which states that current is equal to voltage divided by resistance (I =V/R). In this relationship current is directly proportional to voltage, but inversely proportional to resistance
45
What are the major functions of the plasma membrane, and which of these functions are important for establishing excitable membranes?
There are 5 major functions of the plasma membrane: 1) to create a mechanical barrier, 2) selective permeability, 3) establish and electrochemical gradient, 4) facilitate cell-to-cell communication, 5) facilitate intercellular cell signaling.
Three of these functions are critical for establishing excitable membranes. The first is the mechanical barrier, which maintains the physical separation between intracellular and extracellular environments. The second is selective permeability, which allows ions to move between intracellular and extracellular spaces only when integral membrane proteins open selective channels. The third function is the electrochemical gradient, which dictates the direction ions will move when ion channels open.
46
What is a membrane potential?
The membrane potential is the electrical disequilibrium (imbalance) that exists between the extracellular fluid and intracellular fluid of a living cell. The membrane potential exists because of the uneven distribution of electrical charges between these two spaces, separated by the plasma membrane
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what is the resting membrane potential
The resting membrane potential is simply the membrane potential for a given cell at rest. The specific value of the resting membrane potential can vary, ranging from -50 to -100 mV.
48
How can you have a membrane potential if the human body is electrically neutral?
The human body is eclectically neutral because the intracellular space has equal numbers of positive and negative charges, and the extracellular space has equal numbers of positive and negative charges. Thus, each space is neutral. However, the intracellular and extracellular spaces are not electrically neutral with each other; the mechanical barrier created by the plasma membrane creates an imbalance in charge across the plasma membrane is what creates the membrane potential
49
What is an electrical gradient?
An electrical gradient is the unequal distribution of charge across a given area that facilitates the movement of a changed particle toward an area of opposite electrical charge.
50
What is a chemical gradient?
A chemical (or concentration) gradient is the unequal distribution of chemicals across a given area that facilitates the movement of a chemical from and area of higher concentration to and area of lower concentration.
51
What is the electrochemical gradient?
The electrochemical gradient is the combination of the electrical and chemical gradients for a specific ion. Ions will have both a chemical and electrical property that will dictate its electrochemical gradient. The two gradients that make up the electrochemical gradient will establish how an individual ion will move when selective ion channels open in the membrane.
52
What is the equilibrium potential?
The equilibrium potential is defined as the membrane potential that exactly opposes a given concentration gradient for a given ion. In other words, the equilibrium potential exists where the forces driving the electrical gradients of an ion are directly opposed to the forces driving the chemical gradient of the same ion. We can use the Nernst equation to calculate the equilibrium potential of a given ion assuming we know the extracellular and intracellular concentrations of that ion.
53
How does the equilibrium potential of individual ions contribute to the resting membrane potential of a cell?
At rest, the cell will be permeable to both potassium and sodium due to the presence of leak channels. Given that we have to consider the movement of 2 different ions, the Nernst equation will not be helpful in calculating resting membrane potential. To calculate the resting membrane potential (RMP), we must use the Goldman-Hodgkin-Katz (GHK) equation which considers the concentration and permeability of each ion. An easy way to think about the calculation of resting membrane potential is to first think about the equilibrium potential of each ion. The equilibrium potential of potassium is -90mV and the equilibrium potential of sodium is +30mV. So, if at rest the membrane is permeable to both of these ions, then the RMP must be some value between -90mV and +30mV. Given that there is a much larger number of potassium leak channels, there is also a much greater permeability of the cell to potassium. Since potassium has a greater permeability, the equilibrium potential of potassium will have a greater influence over the RMP. We know by using the GHK equation that the RMP for most neurons is around -70mV. This value reflects the greater permeability of potassium relative to sodium. If the permeability of the two ions changed, then the RMP would also change.
54
What is the primary function of Na+/K+ pumps and leak channels in maintaining the resting membrane potential?
The resting membrane potential is a function of the activity of the Na+/K+ ATPase and the flow of ions (in particular potassium) through leak channels. The passive diffusion of ions through leak channels causes the ionic imbalances, and the active transport of ions by the Na+/K+ ATPase maintains the ionic imbalance.
The most important leakage channels are those that are selective for potassium. The movement of potassium in and out of the cell through these channels directly establishes the resting membrane potential. Potassium is drawn out of the cell due to its chemical gradient, but the net effect of this movement is a slight membrane hyperpolarization which attracts the positively charged potassium ions back into the cell.
The Na+/K+ ATPase is an active transport pump that extrudes 3 sodium ions and brings in 2 potassium ions with every cycle. The movement of these ions by the pump maintains their unequal distribution across the plasma membrane and thus maintains the electrochemical gradient of each ion
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What tissue types have excitable membranes and why do these cell types display these properties?
Muscle and nervous tissue have excitable membranes. The development of excitable membranes in these tissue types allows them to rapidly respond to changes in the environment and rapidly communicate. Our ability to take in sensory information from the environment, integrate that information, and produce a rapid and appropriate response is only possible due to the development of excitable membranes in muscle and nervous tissue.
56
According to Ohm’s Law, current is
Directly related to voltage and inversely related to resistance
57
If there were no sodium leak channels, the resting membrane potential of a neuron would be
more negative
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A depolarization is when the inside of a neuron becomes__________relative to the resting membrane potential.
less negative
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Under normal physiological conditions the Na+/K+ ATPase transports __________.
Na+ out of and K+ into the cell
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What property of ion channels allows them to limit the type of ion that can pass through the plasma membrane when open?
Selective permeability
61
What is the difference between a chemically gated channel and a voltage-gated channel? How are they gated? Where are they located?
The major difference between a chemically gated ion channel and a voltage gated ion channel is how they are gated or opened. Chemically gated channels are opened following the binding of a chemical (most commonly a neurotransmitter). This binding causes a conformational change in the receptor opening the channel through which ions can pass. These types of ion channels are located in the dendrites and the neuronal cell body where axon terminals from other neurons are present. Voltage gated channels are opened following a change in membrane potential. The change in membrane potential causes the protein to undergo a conformational change that opens the channel allowing ions to pass. These types of channels are located in the axon hillock, throughout the axon, and in the axon terminals.
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Which functional segments of a neuron contain chemically gated channels? Which functional segments contain voltage-gated channels?
The receptive segments o f a n e u r o n (dendrites and cell body) contain chemically gated channels. The axon hillock (trigger zone), conductive region (axon) and terminal, contain voltage-gated channels. The selectivity of voltage-gated channels will change in the different segments: voltage-gated sodium and potassium channels are found along the axon and terminal, while voltage gated calcium channels are located only in the terminal.
63
Describe the 3 states of the voltage gated sodium channel. What factors mediate the transitions between each state? How does the anatomy and physiology of the voltage gated sodium channel contribute to the positive feedback loop seen in the rising phase of the action potential?
The voltage gated sodium channel will always exist on one of three states: closed (resting) state, open (activation) state, inactive (inactivation) state. The movement through these states is unidirectional, such that the channel will only move from open to inactive to closed and back to open. The channel cannot go directly from inactive back to open. The reason the voltage gated sodium channel can exist in these three states is the presence of two (2) separate channel gates, an activation gate and an inactivation gate. The activation gate is the gate the responds to the change in voltage across the membrane, and thus is the gate that will open first. Opening this gate moves the channel from
the closed state to the open state. Once the activation gate opens, there is a fixed period of time before the inactivation swings into the channel and blocks the flow of ions. As the cell begins to repolarize, the activation gate closes again and the inactivation gate is removed. Following this transition the channel is back in the closed state and is ready to complete another cycle.
The positive feedback loop seen during the rising phase of the action potential results from the initial threshold depolarization of the membrane opening voltage gated sodium channels by opening the activation gate; incoming sodium through these opened channels further contributes to the depolarization, which opens more sodium channels and continues the loop. It is the inactivation gate that puts a limit on how long this loop can continue. Once a sodium channel opens, it is only a matter of time before the inactivation gate swing in and block the flow of ions
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What is the significance of the threshold membrane potential in the initial segment of a neuron?
The threshold membrane potential is the level of membrane depolarization where that depolarization becomes self- generating and the sodium channel positive feedback loop drives the exponential change in membrane potential. The existence of the threshold is dictated by the high concentration of voltage gated sodium channels at the axon hillock and the strong electrochemical gradient of sodium. This threshold potential is also responsible for the ‘all or none’ nature of the action potential. If a stimulus reaches threshold potential, an action potential is generated, but if the stimulus is sub-threshold, then no action potential is generated.
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Where are graded potentials and action potentials generated?
Graded potentials: Dendrites and cell body (where you have synapses)
- Action potentials: axon hillock (where you have a high concentration of voltage gated sodium channels)
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What channels do you need for graded potentials and action potentials?
Graded potentials: chemically gated ion channels (neurotransmitter binding)
- Action potentials: voltage gated ion channels (sodium first, and then potassium)
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direction of voltage change in graded potentials and action potentials
Graded potentials: positive (depolarization) or negative (hyperpolarization)
- Action potentials: positive (depolarization) and then negative (repolarization)
68
Amount & degree of voltage change in graded potentials and action potentials?
Graded potentials: relatively small amount and dependent on magnitude of the stimulus (more neurotransmitter released, more chemically gated ion channels opened, larger graded potential)
- Action potentials: relatively large change (complete change in polarity from -70mV to +30mV), but degree does not change (all action potentials will have the same shape and magnitude)
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duration of event in graded potential and action potential
Graded potential: short (will decay with distance)
| Action potential: long, travel the complete distance of the axon though propagation
70
change in intensity of graded potentials and action potentials
Graded potentials: amplitude of events will decrease over distance (no means of regeneration)
Action potentials: amplitude of events will always be the same
71
How does depolarization and repolarization occur in the conductive segment of a neuron?
Once you have generated an action potential it needs to be propagated down the axon. This is accomplished by the flow of current down the axon. Once the action potential is initiated and the depolarization phase begins, that local current that is generated in the axon hillock is attracted toward the more negative regions of the axon (i.e. down the axon toward the axon terminals). This causes voltage gated sodium channels in this more distal part of the axon to open allowing that region of membrane to become depolarized. In this manner, a wave of depolarization can travel down the axon, with each more distal region of the axon opening voltage gated sodium channels in response to the depolarization of the more proximal region. All of these axon segments also contain voltage gated potassium channels that will facilitate the repolarization phase. Just as repolarization followed depolarization when the action potential was generated at the axon hillock, this cycle of changes in membrane potential will be repeated all the way down the axon. You can think of action potential propagation as a wave of depolarization followed by a wave of repolarization all the way to the axon terminals.
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How does conduction of an action potential in an unmyelinated axon and myelinated axon differ?
In an unmyelinated axon the conduction of an action potential is relatively slow because the process of
depolarization and repolarization must be constantly repeated all the way down the axon. If you did not have a continuous wave of depolarization and repolarization down the axon, the signal would be lost as the current generated by an action potential decayed (similar to a graded potential). In a myelinated axon, the process of action potential propagation can take breaks under the myelin sheath. When myelin is present there is an increase in membrane resistance from the myelin that inhibits current from leaving the axon, and the only direction current can flow is down the axon. Due to this increased membrane resistance, the action potential can move passively under the myelin sheath with very little change in amplitude. When the leading wave of depolarization from the action potential emerges at the node of Ranvier, the voltage gated sodium channels that are concentrated there will open, initiate an action potential at that site, creating a large current that will flow inside the axon to the next node.
73
When a neuron exits its absolute refractory period, its voltage gated sodium channels are changing from:
Inactivated state to resting state
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In a myelinated axon, the greatest concentration of voltage-gated ion channels is in the
Nodes of Ranvier
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During the relative refractory period of the action potential
It is possible to generate an action potential with a large stimulus
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The speed of propagation of an action potential in an axon is increased by
Creating myelin sheath around segments of the axon
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The threshold value of the membrane potential is important to action potential generation because
It is the point where depolarization becomes self-generating
78
Compare and contrast the chemical and electrical synapse? What are some of the anatomical similarities and differences? What are some of the physiological similarities and differences?
Looking at anatomy first, the electrical and chemical synapses are similar in that they connect a presynaptic and postsynaptic cell together. The two types of synapses differ in their overall structure. The electrical synapse contains gap junctions between the presynaptic and postsynaptic cell that creates a physical connection and congruency between the cytoplasm of the two cells. The chemical synapse is composed of a presynaptic cell (axon terminal) and a postsynaptic cell (dendritic spine) with an empty space between them called the synaptic cleft. The presynaptic cell contains synaptic vesicles full of neurotransmitters and the postsynaptic cell membrane is studded with chemically gated ion channels.
The electrical synapse is relatively uncommon in humans, while the chemical synapse is the most common type of synapse in the human body.
Looking at physiology, the two types of synapses are very different. At an electrical synapse when gap junctions open ions are able to flow from the cytoplasm of one cell to the cytoplasm of the connected cell. This orientation allows for very fast communication and a depolarizing signal can travel extremely fast through these types of synapses as there is no synaptic delay in this type of synapse. At a chemical synapse, an electrical signal must be converted to a chemical signal and then back to an electrical signal. An action potential will arrive at the axon terminal of the presynaptic cell causing the release of a neurotransmitter. The movement of the neurotransmitter across the synaptic cleft takes time, given that the movement is by passive diffusion. Once the neurotransmitter binds to its postsynaptic chemical gated ion channel, ions can move into the postsynaptic cell and an electrical graded potential is generated. There is a built in delay in this process that is called synaptic delay, making the chemical synapse slower. Although this type of synapse is slow in comparison to the electrical synapse, it is also much more flexible and can be modified at many different steps making it critical for complex human behavior.
79
What are three mechanisms by which neurotransmitters can be removed from the synaptic cleft
The three mechanisms are degradation (enzymatic degradation), re-uptake, and diffusion away from the synapse. Acetylcholine is the only neurotransmitter that is broken down by enzymatic degradation via the enzyme acetylcholinesterase. Reuptake is a common mechanism for removal of a neurotransmitter from the synaptic cleft. Reuptake transporter proteins are localized on the presynaptic membrane and act to remove neurotransmitter from the synaptic cleft. Once the neurotransmitter is back inside the presynaptic terminal it is either broken down by enzymes or transported back into a synaptic vesicle. Diffusion away from the synapse is common for many peptide neurotransmitters where there are no specialized proteins in the synapse that degrade or transport these compounds
80
How is an EPSP graded potentials generated in the receptive segment of a neuron?
An EPSP is generated on the receptive segment of a neuron (dendrite or cell body) following the release of an excitatory neurotransmitter (such as glutamate) from a presynaptic neuron. The excitatory neurotransmitter is released into the synaptic cleft and moves passively toward the postsynaptic neuron. The postsynaptic membrane is littered with chemically gated ion channels that are selective for sodium. Once the neurotransmitter binds, the channel is opened and sodium can enter the cell. The influx of sodium causes a membrane depolarization that generates a graded potential. Given that this graded potential will be depolarizing, we call it an excitatory postsynaptic potential or EPSP.
81
How is anIPSP graded potentials generated in the receptive segment of a neuron?
An IPSP is generated on the receptive segment of a neuron (dendrite or cell body) following the release of an inhibitory neurotransmitter (such as GABA) from a presynaptic neuron. The inhibitory neurotransmitter is released into the synaptic cleft and moves passively toward the postsynaptic neuron. The postsynaptic membrane is studded with chemically gated ion channels that are selective for either potassium or chloride. Once the neurotransmitter binds the channel is opened and ions can move across the membrane. If the channel is selective for potassium, then potassium ions will flow out of the cell following its electrochemical gradient (leaving the inside more negative). If the channel is selective for chloride, then chloride ions will flow into of the cell following its electrochemical gradient, bringing more negatively charged ions in (leaving the inside more negative). The influx of chloride or the efflux of potassium will cause a membrane hyperpolarization that will generate a graded potential. Given that this graded potential will be hyperpolarizing we will call it an inhibitory postsynaptic potential or IPSP.
82
Why is calcium so important for neurotransmission?
Calcium is so important because it is the ‘go’ signal in neurotransmission. When the action potential reaches the axon terminal the depolarizing wave opens the voltage gated calcium channels allowing calcium to enter the terminal. Once in the terminal the calcium ions will bind to a protein on synaptic vesicles. This binding is the critical step, facilitating the fusion of the synaptic vesicle with the plasma membrane of the axon terminal. Without calcium there would be no binding, no synaptic vesicle fusion and therefore no neurotransmitter release. Without neurotransmitter release there cannot be neurotransmission.
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What are the two types of summation of graded potentials?
The two types of summation in the neuron are temporal summation and spatial summation. The two types are similar in that they are both mechanisms that influence the probability of a neuron firing an action potential, both integrate IPSPs and EPSPs, and both involve combining or integrating the effect of multiple synaptic events (graded potentials).
Remember the distance for the site of graded potential generation can also influence summation. A synapse closer to the axon hillock will have a greater influence of action potential generation when compared to a similar graded potential that is generated in the distal dendrites. The magnitude (amplitude) of the graded potential will decrease with distance.
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temporal summation
Temporal summation is observed when the frequency of stimulation to a single axon is modulated. Under normal conditions low frequency stimulation of a neuron by a single axon is insufficient to induce an action potential. However if the frequency of stimulation to that axon is enhanced the generated graded potentials will begin to fuse together pushing the membrane potential at the axon hillock closer to threshold (assuming the input is excitatory). Temporal summation can also be observed with IPSPs, in which case the neuron would be less likely to fire and action potential when the frequency of IPSPs increases.
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spatial summation
Spatial summation is observed when the simultaneous release of neurotransmitters is observed at multiple synapses located on different areas of the postsynaptic neuron. A graded potential generated at one synapse may be unable to affect membrane potential at the axon hillock, but if many synapses generate graded potentials of similar magnitude at the same time, the net effect can cause the cell to reach threshold potential. In spatial summation the number of excitatory or inhibitory inputs is important. If there are more IPSPs generated compared to EPSPs then the cell will be less likely to fire an action potential, and vice versa
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what are two major types of neurotransmitter receptors
The two major types of neurotransmitter receptors are ionotropic receptors (chemically (ligand) gated ion channels) and metabotropic receptors
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inotropic receptors
The actions of ionotropic receptors are direct and the effects are immediate. Once a neurotransmitter binds to one of these receptors, an ion channel is opened; this happens because the site of chemical binding is located on the same protein that makes up the ion channel. When that chemical binds the protein changes shape, the ion channel opens, and ions start to move resulting in either a depolarization or hyperpolarization
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metabotropic receptors
The actions of metabotropic receptors are indirect and the effects are slow. When a neurotransmitter binds, a signaling cascade is initiated. The integral membrane protein portion of the receptor is bound to a protein (called a G-protein), which is activated by neurotransmitter binding. This activated protein can go on to interact with other proteins and enzymes causing a series of changes in the physiology of the neuron. These activated proteins can also lead to opening of ion channels; however, these ion channels were never involved with the initial binding of the neurotransmitter and their activation is a slower, multistep process
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When a nerve impulse reaches the synaptic terminal
Calcium enters the cell by voltage gated channels, facilitating vesicle fusion
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When glutamate opens a chemically gated ion channel allowing sodium to enter the postsynaptic cell, the result is an
EPSP
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The main mechanism by which acetylcholine (ACh) is cleared from the synapse is
degradation by an enzyme
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Which statement best describes temporal summation?
two stimuli occurring repeatedly and quickly at the same synapse
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What are the five major functions of skeletal muscle?
The five major functions of skeletal muscle are 1) produce movement, 2) maintain posture and body position, 3) provide protection and support, 4) maintain body temperature (shivering), 5) storage and movement of materials (sphincters and peristalsis of the GI tract).
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skeletal muscle characteristic excitability
Excitability of muscle tissue is its ability to receive and respond to electrical stimulation. This property is most obviously seen at the neuromuscular junction
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skeletal muscle characteristic of contractility
Contractility of muscle tissue is the ability of muscle tissue to shorten forcibly when stimulated. At the molecular levels this is best seen when actin and myosin filaments interact following nerve stimulation actively shortening the sarcomere.
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skeletal muscle characteristic of conductivity
Conductivity of muscle tissue is its ability to allow electrical signals to move and spread along a membrane. This property is best observed during excitation-contraction coupling, when an action potential is generated in the sarcolemma and then travels down T-tubules.
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skeletal muscle characteristic of extensibility
Extensibility of muscle tissue is the ability of muscle to extend and stretch. This can be seen during isometric contractions during a cycle of concentric and eccentric contraction
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skeletal muscle characteristic of elasticity
Elasticity of muscle tissue is the ability of muscle tissue to recoil and resume resting length after stretch. This can be seen following the contraction period of the muscle twitch when the muscle enters the relaxation period and returns to its resting length.
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endomysium
The endomysium is the connective tissue between individual muscle fibers (cells).
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perimysium
The perimysium is the connective tissue surrounding and defining the borders of a fascicle. The fascicle is a group of muscle fibers.
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epimysium
The epimysium is the connective tissue surrounding the whole muscle creating an ‘overcoat’ or barrier separating each muscle from surrounding muscles.
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the endomysium, perimysium, and epimysium relationship
These three connective tissue layers are continues with each other and help to keep the muscle from bursting open or distorting in shape during contraction. In addition, these tissues help contribute to the elasticity of the muscle and provide routes of entry for nerves and blood vesicles.
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If a muscle is contracted, what happens to the following in the sarcomere: (a) width of the A band, (b) width of the H zone, (c) relationship of the Z discs, and (d) width of the I band?
Following contraction:
- The A band will not change in width
- The H zone will disappear as the thin filaments slide over the thick filaments and begin to occupy this region.
- The Z-discs will move closer together as they are pulled toward the M line by movement of the thin
filaments.
- The I band will decrease in width due again to the movement of the thin filaments toward the M line
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Place the following gross anatomic and microscopic structures in order from largest to smallest: fascicle, myofibril, myofilament, muscle, and muscle fiber
Muscle, fascicle, muscle fiber, myofibril, myofilament
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Compare and contrast the thick and thin myofilaments
Thick and thin myofilaments are both composed of many individual molecules (actin or myosin), are found in all 3 types of muscle tissue, and are critically important for muscle contraction.
Thick filaments are composed of bundles of myosin molecules with the myosin tails creating the shaft of the filament and the globular myosin heads pointing toward the edge of the filament. The myosin heads have ATPase activity that facilitates crossbridge cycling. Although the myosin heads will move during muscle contraction, the thick filament as a whole remains stationary.
Thin filaments are composed of globular actin that come together to make filamentous actin (F-actin). Two F- actin strands twist around each other to form the thin filament. Each G-actin molecule in the thin filament has a myosin head binding site where actin and myosin will interact. In addition to actin, the thin filaments also contain tropomyosin and troponin. Tropomyosin helps stabilize the thin filament structure and block the myosin binding site during rest. Troponin is a calcium sensing protein that can induce a conformational change in tropomyosin following calcium binding, initiating the crossbridge cycle.
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A skeletal muscle can be several inches long. The characteristic of muscle tissue that allows an impulse to travel down the entire length of the cell membrane is:
conductivity
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The structure responsible for attaching muscle to bone is a:
tendon
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The membranous network that wraps around myofibrils and holds relatively high concentrations of calcium is known as the:
sarcoplasmic reticulum
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A skeletal muscle cell contains hundreds to thousands of _________, which are complex organelles not found in other cell types outside muscle
myofibrils
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Which region of the sarcomere contains only thick filaments in cross section?
H zone
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What is a triad, and what role does it play in excitation-contraction coupling?
A triad is composed of two terminal cisterna and one T-tubule. Triads are found at the border of the A and I bands covering the regions where thick and thin filaments begin to overlap. During excitation-contraction coupling the action potential driven depolarization will travel down the T-tubule and cause a conformational change in voltage sensing proteins located in its membrane. The voltage sensitive proteins are physically connected to calcium channels located in the membrane of the terminal cisterna; when the voltage sensitive proteins are activated by depolarization, they change shape and pull open the calcium channels of the sarcoplasmic reticulum, allowing calcium to enter the sarcoplasm. Once calcium has entered the sarcoplasm, it can interact with troponin and initiate actin and myosin binding. Thus, the triad is the region directly responsible for linking the depolarization of the sarcolemma with the initiation of sarcomere shortening and muscle contraction.
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What are the three phases on neuromuscular transmission?
The three phases of neuromuscular transmission are: 1) Neuromuscular junction stimulation, 2) excitation- contraction coupling, and 3) crossbridge cycling
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What two events are linked in the physiologic process called excitation-contraction coupling?
Excitation-contraction coupling directly links the events of neuromuscular junction stimulation with crossbridge cycling. During these linked events an electrical signal travels down an axon and is converted to a chemical signal via acetylcholine release. This chemical signal is transduced back into an electrical signal via the
acetylcholine receptors on the motor end plate. The new electrical signal, if strong enough, can initiate an action potential within the muscle cell, which will travel down the sarcolemma, invade the T-tubule and result in calcium release from the terminal cisterna. The released calcium will then initiate crossbridge cycling and sarcomere shortening.
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Provide a description of the events of excitation-contraction coupling.
Excitation-contraction coupling begins when acetylcholine begins to bind to postsynaptic acetylcholine receptors (AChRs), initiating a local, transient membrane depolarization. As more AChRs becomes activated, the change in membrane potential begins to summate creating a wave of depolarization. The wave of depolarization travels to adjacent regions of the sarcolemma where voltage gated sodium and potassium channels are located. When the depolarization reaches these channels they open and the rapid movement of ions initiates an action potential. The action potential is propagated by voltage gated sodium channels down the sarcolemma and invades the T- tubules. Once inside the T-tubules the depolarization induced by the propagating action potential can activate voltage sensitive proteins that are physically attached to calcium channels on the terminal cisterna. Once the calcium channels are open calcium will rush into the sarcoplasm and can being to bind to troponin allowing for actin and myosin molecules to interact and crossbridge cycling to begin.
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What is the function of Ca2+ in skeletal muscle contraction?
Calcium will bind to troponin allowing it to cause a conformational change in tropomyosin. This conformational change will expose the myosin binding sites of the thin filament allowing for crossbridge cycling to begin.
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Describe the four processes that repeat in crossbridge cycling that result in the sarcomere shortening.
The four steps in crossbridge cycling are 1) crossbridge formation, 2) the power stroke, 3) crossbridge detachment, 4) cocking the myosin head.
During crossbridge formation an ADP and inorganic phosphate (Pi) are bound to the myosin head. When tropomyosin is moved, the myosin binding sites on actin are exposed; the myosin heads can bind to actin and create a crossbridge
During the power stroke, the myosin head rotates toward the M line, sliding the actin filament over top and thus shortening the sarcomere. ADP and the inorganic phosphate (Pi) are released from the myosin head
During crossbridge detachment ATP binds to the now unoccupied myosin ATPase site and the bond between actin and myosin is broken.
Finally, during the cocking of the myosin head the ATP is hydrolyzed to ADP and an inorganic phosphate (Pi) and the myosin head returns to its resting state or ‘cocked’ position
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What causes the release of the myosin head from actin? What resets the myosin head?
The myosin head is released from actin by the binding of ATP to the unoccupied ATP binding site. The myosin head is reset following the hydrolysis of ATP to ADP and an inorganic phosphate (Pi).
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How do acetylcholinesterase and Ca2+ pumps function in the relaxation of a muscle?
Acetylcholinesterase facilitates muscle relaxation by breaking down acetylcholine in the synaptic cleft. Once acetylcholine is broken down it can no longer activate acetylcholine receptors. If these receptors remain inactivated the motor end plate will not become depolarized.
Ca2+ pumps expressed in the membrane of the terminal cisternae are constantly working to remove calcium from the sarcoplasm. By decreasing the availability of calcium these pumps limit the amount of actin and myosin crossbridges that can be formed, given that crossbridge cycling is calcium dependent.
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Nicotine is a potent agonist (activating ligand) of skeletal muscle ACh receptors, what effect would this compound have on the motor end plate?
local transient depolarization
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which structures are reservoirs that store acetylcholine
synaptic vesicles
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one power stroke involves
a myosin head pulling a thin filament toward the center of the sarcomere
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a drug, like nerve gas, that inhibited acetylcholinesterase (AChE) would result in
enhanced stimulation of the muscle due to decreased ACh breakdown
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when a muscle relaxes
cross bridges stop forming and muscle elasticity returns the muscle to rest length
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features of smooth muscle tissue
cells are non-striated, contain a single nucleus (uninucleate) and have a fusiform shape
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features of skeletal muscle tissue
cells are striated, long and cylindrical in shape, and contain many nuclei (multinucleate)
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features of cardiac muscle tissue
cells are striated, short and branched, and have intercalated discs that connect them
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what are three anatomical or physiologic differences between skeletal muscle and cardiac muscle
Cardiac muscles have intercalated discs and skeletal muscles do not
- Skeletal muscles have many nuclei per cell and cardiac cells have one or two per cell.
- Skeletal muscles have discrete neuromuscular junctions that connect them to a single neuron;
cardiac cells are innervated by the autonomic nervous system and contract as a group to make strong fluid contractions
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What are three anatomical or physiologic differences between skeletal muscle and smooth muscle?
Skeletal muscles are striated and smooth muscles are non-striated.
- Smooth muscles are under involuntary control and skeletal muscles are under voluntary control
- Skeletal muscles are controlled by motor units allowing for tight control of muscle contraction,
while smooth muscles receive signals through large synapses called varicosities that stimulate many cells simultaneously
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Where is smooth muscle located in the human body
Smooth muscle tissue is located in the walls of the hollow organs of the body. This includes blood vessels, the airways, the lining of the digestive tract and linings of the reproductive and urinary systems. There is also smooth muscle in the skin, allowing hairs to stand on end
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How are contractile proteins in smooth muscle cells arranged
Thick and thin filaments are arranged diagonally across the cell in a crisscross pattern. This pattern continues in a spiral down the long axis of the cell creating the appearance of the stripes spinning around a barbershop pole.
Due to this arrangement, when the smooth muscle cells contracts to creates a twisting motion as it bunches up in the center.
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How does the neural control of cardiac and smooth muscle differ from skeletal muscle?
There are two main differences we talked about. The first is that only skeletal muscle cells have discreet neuromuscular junctions allowing for the formation of motor units. The second difference is that nervous stimulation to skeletal muscles is always excitatory, but in smooth and cardiac muscle nervous stimulation can be either excitatory or inhibitory
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What characteristics of smooth muscle contraction are responsible for the energy efficiency of this muscle tissue type?
Smooth muscle cell contractions are slow in initiation and long in duration. This activity is the result of very slow myosin ATPase activity. This slow enzymatic activity will slow down the crossbridge cycling and allow the cell to remain in a contracted state for longer periods without the addition of new ATP molecules. The smooth muscle cell is very efficient with the ATP it generates (by aerobic cellular respiration) and is considered to be fatigue-resistant
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What are the junctions between cardiac muscle cells called
Intercalated disks
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what structure contributes to the striated appearance of cardiac muscle
sacromeres
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Which of the following bodily functions would be controlled by smooth muscle?
constriction of lung airways
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I am controlled by visceral motor neurons, my cells are fusiform in shape and my contractions are long and energy efficient, what muscle type am I?
smooth
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What events are occurring on both the cellular and molecular levels within a muscle during the 3 phases of a muscle twitch?
The first phase of the muscle twitch is the latent period. During this period all of the events of neuromuscular junction stimulation occur and excitation-contraction coupling begins. The actin-myosin crossbridges are forming, but no contraction has started yet.
The second phase of the muscle twitch is the contraction period. This period begins as soon as the muscle shows measurable signs of contraction. The crossbridges are active and cycling, calcium is present in the sarcoplasm and the muscle moves toward peak contraction. If the contraction is isotonic the muscle will shorten, but if it is isometric the muscle will not change in length.
The third phase of the muscle twitch is the relaxation period. During this period the muscle is beginning to relax. Calcium is no longer leaving the terminal cisterna and is rapidly pumped back into storage. The crossbridges are detaching, and the myosin binding sites on the thin filaments are blocked by the return of tropomyosin to its resting position
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What is motor unit recruitment?
Motor unit recruitment is a mechanism through which muscles can create graded responses by directly modifying
the strength of stimulation. When stimulating a nerve, which is made up of many motor axons, a small stimulus will activate either none or very few motor neurons and thus activate a small number of muscle fibers. However, as the stimulus strength is increased more axons within the nerve will be activated. As more axons are activated more motor units will be activated and more muscle fibers will begin to contract. At some point, a maximum stimulus will be reached where additional increases in stimulus strength will not generate a stronger contraction. This results from the fact that there are a finite number of motor units that can be activated for a specific muscle.
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what is the size principal
The size principal results from the observation that muscles are made up of different sized muscle fibers. One motor unit is going to activate one size of muscle fiber. Small muscle fibers are the most excitable and will be recruited first. Large muscle fibers are less excitable and thus require a stronger stimulation to become activated. By establishing this gradient of muscle fiber sizes, each of which can be controlled by a specific motor neuron, an individual muscle can perform many tasks from delicate surgery to weight lifting.
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What happens to a single motor unit during wave summation?
Wave summation is also a mechanism that allows our muscles to perform graded responses where the frequency of stimulation can change muscle contraction. As the frequency of stimuli to a single motor unit is increased, the amount of tension generated in the muscle fiber will also increase. This response is most directly related to the accumulation of calcium in the sarcoplasm. At high frequency (greater than 40 stimuli per second), there will no longer be any visible relaxation of the muscle and the contractions will appear to fuse into a complete contraction or tetanus.
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What is the function of skeletal muscle tone?
Skeletal muscle tone is most important in the maintenance of posture and joint stabilization. Muscle tone is regulated by sensory receptors within the muscle (called muscle spindle receptors) that monitor the stretch of a muscle. These sensory receptors send signals via sensory axons into the central nervous system, which interprets the information and then sends instructions back to the muscle to contract or relax, thus maintaining the proper tone.
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When you flex your biceps brachii while doing “biceps curls,” what is the type of movement? How is that movement different from trying to lift a car?
Bicep curls are an example of isotonic (‘same tension’) muscle contraction. During isotonic contraction the muscle can overcome the load or weight that it has been asked to move and will shorten (concentric isotonic) or lengthen (eccentric isotonic). When trying to lift a car your biceps are still contracting, but now they are undergoing isometric (‘same measure’) contraction. In isometric contraction the muscle is trying to move, but cannot overcome the load that has been placed on it and thus it maintains the same length. In isometric contractions the myosin heads can be said to be ‘spinning their wheels’ because even though they are constantly forming new crossbridges, no sarcomere shortening is occurring.
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Events of excitation contraction coupling, such as the release of calcium from intracellular stores, occur during the ______ period of muscle twitch.
latent
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The increase in muscle tension that occurs with an increase in the intensity (voltage) of a stimulus is called:
recruitment
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Which of the following best describes complete tetanus?
Sustained contraction in which individual twitches are not apparent
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ATP is made immediately available in muscle tissue through which unique phosphate-containing molecule?
Creatine phosphate. This molecule will enter a reaction with ADP. Through the enzymatic properties of creatine kinase, one phosphate will be taken from creatine phosphate and added to ADP. The result of this reaction is one molecule of creatine and one molecule of ATP.
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What are the various means for making ATP available in a 1500-meter race (exercise lasting around 5 minutes)?
At the beginning of a 1500-meter race, you will be using predominantly aerobic cellular respiration to generate ATP. The muscles are working hard but oxygen is still flowing to the muscles, and the slower production of ATP is able to keep up with muscle demand. However, as you enter the last 100 meters of the race you will begin to increase your speed and enter a high-intensity, short-duration sprint. During this period, you will switch t o a combination of direct phosphorylation and anaerobic cellular respiration. Both of these processes occur without oxygen and although they are less efficient, they are much faster at producing ATP, which will be helpful for the last 15 seconds of your race
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Name the three types of skeletal muscle fibers. Explain how a fast-twitch fiber differs from a slow-twitch fiber, and how an oxidative fiber differs from a glycolytic fiber.
The three muscle fiber types are slow oxidative fibers, fast oxidative fibers, and fast glycolytic fibers. The speed of contraction classifies a fiber as fast or slow twitch, and this property is directly related to the type of myosin ATPase the muscle fiber contains. Fast twitch fibers have fast ATPase activity, and slow twitch fibers have slow ATPase activity.
The major pathway used by the muscle fiber to form ATP is how we classify a fiber as oxidative or glycolytic. An oxidative fiber will rely only on aerobic cellular respiration (oxygen dependent) for ATP generation. A glycolytic fiber will rely mostly on anaerobic cell respiration (glycolysis) or direct phosphorylation to produce ATP.
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Which muscle fiber type is slow contracting and fatigue-resistant? What is the advantage of this muscle fiber type?
Slow oxidative fibers are slow-contracting and fatigue-resistant. These muscle fibers have the advantage of producing sustained contraction without fatigue for long periods of time (hours) because they have high oxygen carrying capacity (high myoglobin concentrations) and slow ATPase activity. These metabolic features allow for a long sustained muscle contraction with low ATP consumption. Muscles that keep us walking upright (anti- gravity muscles) would contain a lot of these types of fibers.
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What anatomical changes occur in a skeletal muscle fiber when it undergoes hypertrophy?
During hypertrophy, skeletal muscle cells will increase in size by adding more myofibrils and myofilaments. The net effect of this activity is an increase in skeletal muscle size. In addition to this primary change, you will also see an increase in the number of mitochondria, larger glycogen stores, and an increased capacity to produce ATP (an increase in anaerobic threshold).
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What changes in skeletal muscle accompany aging?
During the aging process muscles decrease in size and power. This results from both a decrease in muscle cell number and a decrease in the number of myofibrils per cell. Capillaries decrease in number and myoglobin concentration decreases. One of the largest problems is the decreased ability of the muscles to repair themselves after injury. Decreased numbers of satellite cells make cellular repair difficult or impossible. As a result, connective tissues are used to repair muscles instead resulting in weaker and less elastic muscle tissue.
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For a sprint lasting 60 seconds, ATP is supplied initially by:
The phosphagen system (direct phosphorylation)
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The top long distance runners probably have ______ proportion of slow muscle fibers in their legs compared to average runners.
higher
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Glycolysis is an:
Anaerobic process that occurs in the cytosol
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With increased age, skeletal muscles show:
A decrease in the number of myofibrils
