Neuronal synapses (chemical) (video) | Khan Academy
Found where neurons meet skeletal muscles b. Endorphins are ______. Select one: Radically different in function from neurotransmitters. The function of the ______ is to carry information to and from all parts of the body. a. soma d. endorphins .. a. found where neurons meet skeletal muscles. The effect of alcohol is to enhance the effect of ______, which causes the general inhibition of the nervous system associated with getting drunk. Endorphins are ______. A. found where neurons meet skeletal muscles B. less powerful than.
That makes it look a little bit more realistic, although the whole thing is not very realistic. And this is also going to be a bilipid membrane. You get the idea, but let me just do it to make the point clear. So there are also these calcium ion pumps that are also subsets of ATPases, which they're just like the sodium potassium pumps. You give them one ATP and a calcium will bond someplace else and it'll pull apart the phosphate from the ATP and that'll be enough energy to change the confirmation of this protein and it'll push the calcium out.
Essentially, what was the calcium will bond and then it'll open up so the calcium can only exit the cell. It's just like the sodium potassium pumps, but it's good to know in the resting state, you have a high concentration of calcium ions out here and it's all driven by ATP.
A much higher concentration on the outside than you have on the inside and it's driven by those ion pumps. So once you have this action potential, instead of triggering another sodium gate, it starts triggering calcium gates and these calcium ions flood into the terminal end of this axon. Now, these calcium ions, they bond to other proteins. And before I go to those other proteins, we have to keep in mind what's going on near this junction right here. And I've used the word synapse already-- actually, maybe I haven't.
The place where this axon is meeting with this dendrite, this is the synapse. Or you can kind of view it as the touching point or the communication point or the connection point. And this neuron right here, this is called the presynaptic neuron.
Let me write that down. It's good to have a little terminology under our belt. This is the post-synaptic neuron. And the space between the two neurons, between this axon and this dendrite, this is called the synaptic cleft. It's a really small space in the terms of-- so what we're going to deal with in this video is a chemical synapse. In general, when people talk about synapses, they're talking about chemical synapses. There also are electrical synapses, but I won't go into detail on those.
This is kind of the most traditional one that people talk about. So your synaptic cleft in chemical synapses is about 20 nanometers, which is really small. If you think about the average width of a cell as about 10 to microns-- this micron is 10 to the minus 6.
This is 20 times 10 to the minus 9 meters. So this is a very small distance and it makes sense because look how big the cells look next to this small distance. So it's a very small distance and you have-- on the presynaptic neuron near the terminal end, you have these vesicles. Remember what vesicles were. These are just membrane bound things inside of the cell. So you have these vesicles. They also have their phospobilipid layers, their little membranes. So you have these vesicles so these are just-- you can kind of view them as containers.
I'll just draw one more just like that. And they can train these molecules called neurotransmitters and I'll draw the neurotransmitters in green.
So they have these molecules called neurotransmitters in them. You've probably heard the word before. In fact, a lot of drugs that people use for depression or other things related to our mental state, they affect neurotransmitters.
I won't go into detail there, but they contain these neurotransmitters. And when the calcium channels-- they're voltage gated-- when it becomes a little more positive, they open calcium floods in and what the calcium does is, it bonds to these proteins that have docked these vesciles. So these little vesicles, they're docked to the presynpatic membrane or to this axon terminal membrane right there. It's an acronym, but it's also a good word because they've literally snared the vesicles to this membrane.
1. How does muscle tissue contribute to homeostasis?
So that's what these proteins are. And when these calcium ions flood in, they bond to these proteins, they attach to these proteins, and they change the confirmation of the proteins just enough that these proteins bring these vesicles closer to the membrane and also kind of pull apart the two membranes so that the membranes merge. Let me do a zoom in of that just to make it clear what's going on. So after they've bonded-- this is kind of before the calcium comes in, bonds to those SNARE proteins, then the SNARE protein will bring the vesicle ultra-close to the presynaptic membrane.
So that's the vesicle and then the presynaptic membrane will look like this and then you have your SNARE proteins. And I'm not obviously drawing it exactly how it looks in the cell, but it'll give you the idea of what's going on.
Your SNARE proteins have essentially pulled the things together and have pulled them apart so that these two membranes merge. And then the main side effect-- the reason why all this is happening-- is it allows those neurotransmitters to be dumped into the synaptic cleft. So those neurotransmitters that were inside of our vesicle then get dumped into the synaptic cleft.
This process right here is called exocytosis. It's exiting the cytoplasm, you could say, of the presynaptic neuron. These neurotransmitters-- and you've probably heard the specific names of many of these-- serotonin, dopamine, epinephrine-- which is also adrenaline, but that's also a hormone, but it also acts as a neurotransmitter.
Norepinephrine, also both a hormone and a neurotransmitter. So these are words that you've probably heard before. But anyway, these enter into the synaptic cleft and then they bond on the surface of the membrane of the post-synaptic neuron or this dendrite. Let's say they bond here, they bond here, and they bond here. So they bond on special proteins on this membrane surface, but the main effect of that is, that will trigger ion channels.
So let's say that this neuron is exciting this dendrite. So when these neurotransmitters bond on this membrane, maybe sodium channels open up. So maybe that will cause a sodium channel to open up.
So instead of being voltage gated, it's neurotransmitter gated. So this will cause a sodium channel to open up and then sodium will flow in and then, just like we said before, if we go to the original one, that's like this getting excited, it'll become a little bit positive and then if it's enough positive, it'll electrotonically increase the potential at this point on the axon hillock and then we'll have another neuron-- in this case, this neuron being stimulated.
So that's essentially how it happens. It actually could be inhibitory. You could imagine if this, instead of triggering a sodium ion channel, if it triggered a potassium ion channel.
If it triggered a potassium ion channel, potassium ion's concentration gradient will make it want to go outside of the cell. So positive things are going to leave the cell if it's potassium. Remember, I used triangles for potassium. And so if positive things leave the cell, then if you go further down the neuron, it'll become less positive and so it'll be even harder for the action potential to start up because it'll need even more positive someplace else to make the threshold gradient.
I hope I'm not confusing you when I say that. How is excitation of the sarcolemma coupled to the contraction of a muscle fiber? D A Cellular membranes become leaky after death.
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- Neuronal synapses (chemical)
D Myosin ATPase activity allows the contraction cycle to repeat indefinitely. E Muscles contract until proteolytic enzymes from the lysosomes digest crossbridges. A neuromuscular junction NMJ A is the synapse of a motor neuron with a muscle fiber.
B includes the synaptic end bulbs of the muscle fiber. C includes the motor endplates of the motor neuron. E All of the above are correct. Place the events at the neuromuscular junction NMJ in the order in which they occur: Which of the following acts on the NMJ to block stimulation of muscle contraction? How do muscle fibers produce ATP? A from creatine phosphate B through anaerobic cellular respiration C through aerobic cellular respiration D A and B are correct.
Anaerobic cellular respiration A converts glucose to pyruvic acid and ultimately to lactic acid. B can produce energy for seconds of contractions. B occurs in the mitochondria. C requires O2, which can be obtained from hemoglobin or myoglobin. D is required for muscle activities lasting longer than one minute. E All of these are correct. A a single muscle fiber is controlled by through a single neuromuscular junction.
B a single motor neuron controls a single muscle fiber. C the strength of a muscle contraction depends on the number of motor units stimulated. D the strength of a muscle contraction depends on the size of the motor units stimulated.
E a motor unit consists of a somatic motor neuron and the skeletal muscle fibers it controls. Which of the following is true of a twitch contraction? A A During a twitch, all fibers in a motor unit respond to an action potential in a motor neuron.
D During its relaxation period, an action potential moves across the sarcolemma and T tubules. Wave summation in a muscle fiber A occurs when additional stimuli arrive before the fiber has relaxed after the initial stimulus.
B usually result in subsequent contractions that are stronger than the 1st. C may result in muscle fiber tetany. Motor unit recruitment A occurs when the number of motor units involved in muscle contraction decreases. B contributes to the production of smooth rather than jerky movements.
C promotes muscle fatigue. D prevents sustained contraction of a muscle group. E inhibits fine adjustments to muscle strength. Muscle tone A is maintained by conscious control from the autonomic division of the nervous system. B blocks muscle contractions not needed for movement of the body. C is a property of skeletal, but not, smooth muscle tissue.
D results from involuntary contractions of alternating small groups of motor units. E increases when motor nerves to a muscle group are damaged. Isotonic contractions A generate low muscle tension but allow little change in muscle length. B generate high muscle tension but allow little change in muscle length. C are used to move objects or to move the body.
D are important in maintaining posture. E are concentric if the length of the muscle increases during the contraction.
Slow oxidative muscle fibers A are the muscle cells most involved in short-term activity such as sprinting. B are the largest and most powerful of the skeletal muscle fiber types. C contract rapidly and generate ATP anaerobically. D resist fatigue and contain large amounts of myoglobin.
What is the relationship of exercise to skeletal muscle fibers? B Strength training exercises can induce production of more filaments in FG fibers. C Exercise does not change the number of skeletal muscle fibers.
Cardiac muscle tissue E A is autorhythmic. B contains branched cells that are connected by intercalated discs. D maintains contractions for longer periods of time than skeletal muscle tissue. Smooth muscle tissue A may be stimulated to contract by hormones. B has briefer contractions than skeletal muscle tissue. D A and C are correct. A Skeletal muscle tissue retains its mitotic ability and ability to regenerate throughout life.
B Smooth muscle fibers of the uterus and arterial walls have regenerative capacity. C Cardiac muscle tissue has limited regenerative capacity. D Most body tissues have more regenerative capacity than the muscle tissues.
E Healthy cardiac muscle fibers may undergo hypertrophy to compensate for damaged cells. Which of the following is NOT true of the effect of aging on muscular tissue? A Fibrous connective tissue and adipose tissue replace skeletal muscle tissue as age increases. B Skeletal muscle strength tends to decrease as age increases.
C Exercise has little effect on delaying or reversing age-related loss of skeletal muscle function. D The ratio of slow oxidative fibers to other skeletal muscle types increases with age. E The loss of skeletal muscle tissue may be related to decreased physical activity with age. Choose the answer from the column on the right that best matches the description or term on in the column on the left.
Myofibrils disuse or denervation. Which of the following is true? A Muscles pull on bones; they do not push bones. B The end of the muscle attached to the bone that moves least is the origin of that muscle. C The end of the muscle attached to the bone that moves most is the insertion of the muscle.
D The main movement that occurs when the muscle contracts is the action of the muscle. A A The origin of a muscle on a limb is usually proximal to it insertion.
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B A muscle must cover the limb or other body part it moves. C Muscles crossing one joint have more complex actions than those crossing two joints. A lever A is a rigid structure that moves about a fixed point. B provides mechanical advantage when a small effort can move a large load. C that provides a mechanical advantage decreases the speed and distance needed to move a load. A first class lever A may be represented as FEL.
B extends a bowed head on the vertebral column. C allows a ballerina to stand on her toes. D allows the forearm to flex on the arm. E is the least common lever system in the body. A third class lever A is the most common lever system in the human body.
B may be represented as FLE. C always produce a mechanical advantage. D favors force over speed. E favors force over range of motion. Which of the following may be the basis for the name of a muscle? Muscles of facial expression A generally originate from bones of the facial skull. B generally insert on the skin. C are innervated by the facial VII nerve.
Which of the following is NOT an extrinsic muscle of the eye? Which of the following is NOT a muscle of the abdominal wall? Which of the following muscles is used in breathing? Which of the following penetrates the diaphragm? Which of the following elevates the scapula? Which muscle is the primary abductor of the arm? Which of the following flex the forearm at the elbow? Four year old Parker has been going to the health club with his dad.
Today he is showing the trainers his big muscle. Parker flexes his forearm at the elbow and a bulge appears. Which of the following flex the wrist? The general activities of the hand depend on the functions of intrinsic hand muscles and include A pinching B free motion C power grip D precision handling E All of the above are correct.
Lower limb muscles function in A maintaining stability. C moving the body. Which muscle extends the thigh at the hip joint and laterally rotates the thigh? Which muscle does NOT flex the thigh? B Which of the following muscles is NOT part of the quadriceps femoris? The calcaneal Achilles tendon is formed by the fusion of the tendons of the A gastrocnemius B soleus C plantaris D A and B are correct. The gastrocnemius A is the prominent, superficial muscle of the calf. B everts the foot.
C dorsiflexes the foot. D extends the knee. Which of the following is NOT an intrinsic muscle of the foot? What is RICE therapy?Skeletal Muscle Microscopic Anatomy- Fibers and Fibrils
A an initial treatment for most sports injuries B a combination of rest, ice, compression and elevation C a therapy that should generally be used for weeks after an injury D A and B are correct. The most common type of lever in the human body arranges its F fulcrum, load and effort in this order: Fulcrum, Effort, Load G. The nervous system E A works with the endocrine system to maintain homeostasis.
B communicates with the body via action potentials. C is responsible for thoughts and behaviors. D initiates voluntary movements. Which of the following correctly describes a function of the nervous system? The central nervous system A excludes the cranial and spinal nerves, ganglia and sensory receptors.
B is the source of thoughts and emotions. C is the destination of action potentials from motor neurons. The peripheral nervous system B A includes the brain and spinal cord.
B may be divided into somatic, autonomic and enteric nervous systems. C is only involved with unconscious involuntary activities. The somatic nervous system A provides motor signals and conscious control to skeletal muscles.
B includes sympathetic and parasympathetic divisions. C regulates the gastrointestinal tract. D is dependent on the autonomic system for control. E includes motor neurons to smooth muscles. Neurons A are electrically excitable cells. B vary greatly in size. C have a perikaryon enriched with the organelles for protein synthesis.
B A A dendrite is a nerve fiber that receives impulses from other neurons. B Most neurons have many axons and one dendrite. C An axon sends an impulse to another neuron or to an effector cell. D Slow axonal transport moves axoplasm in only one direction.
E Fast axonal transport uses microtubules to move materials in two directions. Which of the following is true of a synapse? A The presynaptic neuron carries a nerve impulse away from a synapse. B The postsynaptic neuron carries a nerve impulse toward a synapse. C A synapse is the site of where two neurons or a neuron and an effector meet. D The presynaptic neuron releases chemical messengers called hormones.
E The synapse of a neuron and a gland is called a neuromuscular junction. Neuroglia A comprise about one-half of the tissue in the CNS. B retain mitotic potential but do not conduct nerve impulses. C support and protect neurons. Astrocites A support neurons in the peripheral nervous system. B form the blood-brain barrier. C regulate growth, migration and interconnection of neurons in the adult brain. D form myelin on central nervous system neurons.
E maintain the blood-cerebrospinal fluid barrier. Which neuroglia cells produce myelin? Gray matter A consists of neuron cell bodies, neuroglia and unmyelinated nerve fibers. B is found at the periphery of the spinal cord. C may be found in clusters called ganglia in the central nervous system.
D may be found in clusters called nuclei in the peripheral nervous system. Which of the following statements is correct? E A Ion channels in neuron plasma membranes block electron flow across those membranes.
B Action potentials allow cells to communicate over short distances only. C Graded potentials allow cells to communicate over either long or short distances. D The electrical current in living cells is the flow of electrons across a plasma membrane. E Neurons exhibit differences in electrical voltage across their plasma membranes. Graded potentials A arise when ion movement causes a minor change in the resting membrane potential. B usually propagate down the length of an axon. C occur when voltage-gated channels open.
D are most often observed in axons. E are usually associated with ion movement through leakage channels. Action potentials A arise slowly and are observed primarily in dendrites and cell bodies. B arise when a stimulus is strong enough to open mechanically-gated ion channels.
C occur in three phases: D vary in size depending on the strength of the initial stimulus. E allow an impulse to travel over long or short distances. Leakage channels restore resting membrane potential. Draw an action potential voltage vs time plot. Which of the following is true of nerve impulse conduction? A Saltatory conduction occurs on unmyelinated axons.
B Continuous conduction occurs on myelinated axons.