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Neurobiology > Exam 4 > Flashcards

Exam 4 Flashcards

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1
Q

What are alpha motoneurons?

A

They are lower motoneurons that innervate extrafusal fibers in muscles.

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2
Q

What is the difference between big alpha motoneurons and small alpha motoneurons?

A

Big ones take a lot more signal to fire than small ones.

Small ones tend to have smaller motor units.

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3
Q

What are motor units?

A

Alpha motor neuron + all the muscle fibers it innervates.

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4
Q

What is the usefulness of a small motor unit? What about a big motor unit?

A

Small motor units are used for fine motor control, like the fingers.
Big motor units are used to move big and stable muscles, like the legs muscles.

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5
Q

What happens if a muscle is innervated by a new type of alpha motor neuron?

A

The muscle fiber will change to the type of fiber its original target was. This is due to the change in signaling frequency by the alpha motor neuron.

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6
Q

What leads to a stronger motor force?

A

Either incorporating larger motor units and/or more motor units leads to a stronger muscle force.

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7
Q

What are slow muscle fibers?

A

Make up dark meat.
They have a slower frequency of twitches.
Uses a lot of ox phosphorylation due to the number of mitochondria, myoglobin, and blood flow they have.
Small motor force.
Small fiber size.

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8
Q

What are fast-fatigue-resistant muscle fibers?

A 
White meat. 
Lots of glycolysis is done due to their high glycogen stores.
Not as fast as fast-fatigable. 
Intermediate muscle fibers. 
Intermediate motor force. 
Intermediate fiber size.
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9
Q

What are fast-fatigable muscle fibers?

A

White meat.
Lots of glycolysis due to their high glycogen stores.
Fastest muscle fiber but it tires quickly.
Largest motor force.
Largest fiber size.

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10
Q

What is the muscle spindle?

A

It is in the bulge of muscles and is used for a myotatic reflex. It gives information on muscle length.

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11
Q

What makes up a muscle spindle?

A

Gamma motor neurons.
Ia axons.
Intrafusal fibers.

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12
Q

What is the significance of Ia axons in the muscle fibers?

A

Ia axons have the most myelin and the biggest axon diameter. Thus, they are the fastest axons. They quickly give information of muscle length to alpha motor neurons.

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13
Q

What does it mean that the muscle spindle is monosynaptic?

A

No interneurons are invovled. The Ia axons directly innervate the alpha motor neurons.

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14
Q

How is the muscle spindle activated?

A

When the muscle is stretched (such as in the knee jerk reflex). The Ia axons tell the alpha motor neurons to contract the muscle.

When the alpha motor neurons activate the muscle to contract, the gamma motor neurons activate to contract the muscle spindle so that it doesn’t go slack.

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15
Q

What is a purpose of the stretch reflex?

A

To maintain posture.

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16
Q

What is the Golgi Tendon Organ?

A

In the conjunction between the muscle and the tendon, it communicates through Ib axons how hard the muscle is pulling on the bone and muscle tension. It makes sure that muscle is not being overloaded.

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17
Q

What do Ib axons do in the Golgi Tendon Organ?

A

They are a little slower than Ia axons but they connect to inhibitory interneurons which inhibit alpha motor neurons so that the muscle relaxes.

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18
Q

What are central pattern generators?

A

They make a rhythmic firing motion. They are controlled by interneurons so that the brain doesn’t have to control rhythmic motions. For example, it is used for walking.

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19
Q

What are the spinal segments?

A 
Spinal segments:
Cervical (C) 1-8
Thoracic (T) 1-12
Lumbar (L) 1-5
Sacral (S) 1-5
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20
Q

How do you tell the difference between the dorsal horns and ventral horns?

A

When looking at a cross-section of the spine, the gray matter that reaches the ends of the dorsal horn, and the gray matter that doesn’t reach the ends is the ventral horn.

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21
Q

What are the muscle excitation steps?

A

Alpha motor neuron has an action potential.
Ca2+ comes into the alpha motor synapses and triggers ACh release.
ACh binds to nicotinic muscle ACh receptors.
The sarcolemma surrounding the muscles has an action potential.

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22
Q

What are the muscle contraction steps?

A

The action potential triggers T tubule Ca2+ channels to open.
This is the small amount of extracellular calcium in the steps.
The Ca2+-gated Ca2+ channels of the sarcoplasmic reticulum open and release a lot of Ca2+ into the myofibrils.
Ca2+ binds to troponin.
Troponin and tropomyosin move exposing myosin head binding spots on the actin.
The myosin head binds to the actin filament.
The myosin head jerks the filament.

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23
Q

What are the muscle relaxation steps?

A

ATP binds to the myosin head and causes a conformational change that disengages it from the actin filament.
ATP hydrolyzes and the myosin head returns to its beginning position.
ATP-driven Ca2+ pumps in the sarcoplasmic reticulum puts the Ca2+ back in the sarcoplasmic reticulum.
Thus tropomyosin covers the binding spot for the myosin head on the actin filament again.

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24
Q

Describe what happens to muscles after death.

A

The twitch as the muscles use up their last ATP.
They go flaccid after ATP stores are depleted.
They become stiff and go into rigor mortis and the sarcoplasmic reticulum breaks down and releases its Ca2+ stores. The myosin heads can’t detach because there is no more ATP.
The muscles go flaccid again after the actin filaments break down.

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25
What is flaccid paralysis?
Muscles being limp and being unable to move.
26
What is spastic paralysis?
The muscles contracting but unable to relax. This also prevents movement.
27
What happens in Familial hypokalemic periodic paralysis (FHPP) where T-tubules are broken and there is lower extracellular K+?
Without the T-tubule Ca2+ channel opening, the sarcoplasmic Ca-gated Ca2+ channel can't be open. This leads to flaccid paralysis. With less extracellular K+, there is a bigger diffusion force. Thus, the electrical pull has to be more negative to pull equally with the diffusion force. Thus, the resting potential is lower.
28
What happens in Brody disease when the Ca2+ pump in the sarcoplasmic reticulum is non-functional?
Ca2+ can't go back into the sarcoplasmic reticulum and the muscle will keep contracting. There is still ATP so the muscle will relax but as the Ca2+ is still there, it will just contract again. This leads to spastic paralysis and fatigue.
29
What does the polio virus target? What does this lead to?
Polio infects and kills lower motor neurons. This can lead to paralysis. People can die if polio affects their respiratory or cardiac muscles. The muscles don't all into atrophy as some alpha motor neurons that survive will take over for those who died. This can lead to less fine motor control as the motor units will be bigger now.
30
What is accute flaccid myelitis?
Similar to polio but has a 2 year cycle.
31
What is the difference between multiple sclerosis and Guillian-Barre syndrome?
In MS, the oligodendrocytes are attacked and it tends to be longer term. In GB, the Schwann cells are attacked and it tends to be short-term.
32
What is possible cause of ALS?
Mutations in repair systems for proteins + mRNA. These kill alpha motor neurons. There is a lack of reorganization as the alpha motor neurons are killed so quickly.
33
What is proprioception?
The sense of knowing where one's body is in space.
34
Where does proprioception come from?
Golgi Tendon Organ Muscle Spindle Others (especially in joints)
35
What are the advantages and disadvantages of elastic braces/body sleeves?
Advantage: Provide support. Enhance input of some proprioception. Don’t need as much proprioception because the brace is taking care of some of that. Disadvantage: Makes muscles weaker. Lose some sense of proprioception because you are not practicing that sense. Basically, the body leans too hard on the brace and could lose some skills on its own.
36
Describe how cholinesterase inhibitors that inhibit AChE affect muscles.
With AChE gone, ACh is not broken down as quickly and hangs out in the synaptic cleft longer. The muscle can get overexcited as there is now a lot more signal than normal. However, muscles can get desensitized to extra ACh so while at first twitches occur, then flaccid muscles and paralysis occur because they are no longer reacting as well to normal amounts of ACh.
37
How do AChR antagonists like curare affect muscles?
These block AChR so the muscle cannot get signal. This will cause flaccid paralysis.
38
If there is a lower threshold for muscle voltage-gated Na+ channels, how would that affect muscle signaling?
There could be a higher Na+ influx as the channel is open longer before the voltage-gated K+ channels open. This could result in more contraction and spastic paralysis. There could be a loss of fine motor control as the muscles will be more easily excited.
39
What would happen if the Ca2+ channels on the alpha motor neuron doesn't open as it does in Lambert-Easton myasthenic syndrome (LEMS)?
Too little because with less Ca2+ influx in the alpha motor neuron, fewer SNARE proteins are activated and bring the vesicle to the membrane. With less ACh released, there is a lower signal and a smaller motor response.
40
Botulinium toxin prevents SNAREs from working. What effect does this cause at the NMJ?
if fewer SNAREs are properly activated to bring vesicles to the membrane then less ACh is released to activate the muscle resulting in a smaller motor response.
41
What would happen in ACh synthesis was disrupted as it is in triethylcholine?
It inhibits ACh synthesis which means that less will be in the vesicles and there will be a lower quantal content and neurotransmitter release. The muscle won’t be able to respond as strongly.
42
Why do individuals whose sarcoplasmic reticulum Ca-gated Ca2+ channel has a bigger Ca2+ influx need more ATP?
They need extra ATP to pump back the Ca2+ released back into the sarcoplasmic reticulum. There is more than usual so more ATP is needed.
43
What are the three types of muscles?
Skeletal, cardiac, and smooth.
44
What is the difference between flexors and extensors?
Flexors=muscles that close a particular join. | Extensors=muscle that open a particular joint.
45
What are muscle antagonists?
Antagonists are muscles that work against each other. | Like flexors and extensors.
46
What are muscle synergists?
Synergists are muscles that work with each other, moving the joint in the same way.
47
What are proximal muscles?
Proximal=muscles of the shoulder, elbow, knee, and pelvis for locomotion.
48
What are distal musles?
Distal=muscles involving the digits, hands, and feet.
49
What are axial muscles?
Axial=trunk muscles for balance and posture.
50
What is the sliding filament theory?
The actin and myosin filaments slide past each other. The actin filaments slide and head closer to the middle of the muscle and the sarcomere shortnes. The muscle, therefore, gets shorter and it has tension that can pull the bone.
51
What is a dermatome?
Dermatome=area of skin innervated to the left and right of the dorsal root.
52
Why does the injury of a single spinal segment not result in loss of all sensation in that area?
Not all sensation is lost when a particular dermatome is cut because the dermatomes overlap.
53
What are 3 ways to have more motor force like when needing to hold onto something tighter?
Activating more motor units. Increasing firing rates Activating bigger alpha neurons.
54
What is reciprocal inhibition?
Reciprocal inhibition=when one set of muscles is activated, its antagonistic muscles are relaxed.
55
What is the flexor withdrawal reflex?
Flexor withdrawal reflex=moving a flexor away from an aversive stimulus.
56
What is the crossed-extensor reflex?
Crossed-extensor reflexes=when flexors in one limb are activated, extensors in the other limb are activated. Basically reciprocal inhibition but the opposite in the other limb.
57
What is one of the main reasons muscle fatigue sets in?
The glycogen stores in the muscle stores are depleted. They can't do glycolysis. Happens during vigorous exercise.
58
Why are fast twitch fibers able to twitch faster than slow fibers?
Fast-twitch fibers have an enzyme that cleaves ATP on myosin heads faster than the enzyme used in slow-twitch fibers.
59
What is sarcolemma?
Sarcolemma=excitable membrane around muscle fibers.
60
Imagine someone slides into the front of your lower right leg. Walkthrough what all happens to stabilize you.
Flexor withdrawal reflex excites muscles to pull your right leg away from the obstacle in your path. Reciprocal inhibition will occur to relax antagonistic muscles in the right leg. The crossed extensor reflex is activated to activate the opposite muscles and relax similar muscles in the other limb.
61
What are the strategizing areas of the brain?
Prefrontal cortex, basal ganglia, area 5 and are 7.
62
What does the prefrontal cortex do?
Strategizing area. Also involved in abstract thought, making decisions, inhibiting movement, and anticipating consequences.
63
What does area 5 do and where is it?
Parietal cortex. | Uses touch information to inform motor decisions.
64
What does area 7 do and where is it?
Parietal lobe. | Using visual information to inform motor decisions.
65
What is the basal ganglia made up of?
Caudate Putamen Globus pallidus
66
What are the inputs to the basal ganglia?
Frontal cerebrum like the prefrontal cortex Subthalamus Substantia nigra of the midbrain.
67
What are the outputs of the basal ganglia?
VLo of the thalamus to area 6 SMA.
68
What happens to the basal ganglia at rest?
The globus pallidus is spontaneously active at rest and it is inhibiting the VLo area of the thalamus which connects to area 6. So, at rest, the basal ganglia is inhibiting movement.
69
What is the direct input pathway of the basal ganglia?
Putamen inhibiting the globus pallidus which frees the VLo from inhibition. Allows area 6 to be activated. The putamen can be excited by either the substantia nigra or the frontal cerebrum.
70
What is the indirect pathway for the basal ganglia?
The subthalamus excites the globus pallidus so that even more inhibitory signal is sent. Leads area 6 to be more inhibited.
71
What would happen if the subthalamus had a lesion?
There would be more movement because the globus pallidus could not be excited as easily and inhibit the VLo more.
72
What would happen if the substania nigra had a lesion?
The putamen would not be as easily excited and thus it would not inhibit the globus pallidus as much to stop sending inhibitory signals to the VLo. This would result in less movement.
73
What would happen in the basal ganglia if the frontal cerebrum had a lesion?
The putamen would not be as easily excited and thus it would not inhibit the globus pallidus as much to stop sending inhibitory signals to the VLo. This would result in less movement.
74
What would happen if the frontal cerebrum, putamen, and GPi had a lesion?
The VLo would be free from all input and possible inhibition. This would result in more movement.
75
What functions is the basal ganglia involved in related to movement?
The basal ganglia is thought to be involved in habit learning because the information loops and gradually builds over time.
76
What is population coding and where does it happen?
It happens in area 4. It is not that one neuron activates one muscle. The neurons in that set and neighboring sets activate and their collective vote signals for a certain movement to happen. This is population coding and it helps to smooth out movements.
77
What is area 6 PMA?
The lateral premotor area (PMA) connects with reticulospinal neurons to activate proximal muscles.
78
What is area 6 SMA?
The medial supplementary motor area (SMA) controls the distal motor units directly.
79
Which motor cortex area is the primary one?
Area 4. Area 4 is the boss of area 6.
80
What are mirror neurons?
Neurons in area 6. Area 6 also has mirror neurons that activate when seeing or hearing someone make a movement. The best learning from mirror neurons comes if you have experience doing the action that you are watching someone do.
81
What does it mean that area 6 is active before a movement is initiated?
Area 6 is activated before a movement is initiated and it needs permission to release that command to the muscles.
82
What are the outputs from the cerebellum?
The pons and cerebellum activate the VLc of the thalamus which actives area 4 of the motor cortex.
83
What is the function of the cerebellum?
Involved most in involuntary movement and balance. Takes the plan from the strategizing areas so it knows what the goal is and it brings that to fruition. The cerebellum responds and adjusts when things go off track.
84
What is the corticospinal tract?
``` Lateral spinal tract. Main one. Goes straight through the cortex. Decussates in the brain at the pyramidal tract. Involved in voluntary movement. ```
85
What is the rubrospinal tract?
``` Lateral spinal tract. Back up for corticospinal. Involved in voluntary movement. Stops at the red nucleus in the midbrain. Decussates in the brain at the pons. ```
86
What is the vestibulospinal tract?
Ventromedial spinal tract. Controls balance. Has some input from the inner ear and cerebellum. Mostly subconscious.
87
What is the tectospinal tract?
Ventromedial spinal tract. Comes from the midbrain. Gets visual input from the superior colliculus and auditory input from the inferior colliculus. Decussates in the brain after leaving the superior colliculus. Controls proximal muscles.
88
What is the pontine reticulospinal tract?
Ventromedial spinal tract. Enhances anti-gravity muscles. Keeps you up while gravity wants to weigh you down. No decussation.
89
What is the medullary reticulospinal tract?
Ventromedial spinal tract. No decussation. Liberates the anti-gravity muscles.
90
What is the dorsomedial lemniscal medial pathway?
Sends information about touch sensations and proprioception. Afferent tract. Decussates in the midbrain.
91
What is the spinothalamic tract?
Communicates information about temperature and pain. Decussates at the spinal cord. In the ventral portion of the spinal cord. Afferent tract.
92
Where does muscle strength come from?
``` Recruiting more motor neurons. Lower threshold for motor neurons. Changing recruiting order. Synchronziation. Lower motor neurons reorganization. Increasing firing rate. ```

Neurobiology (5 decks)

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