Exam 4 Flashcards
What are alpha motoneurons?
They are lower motoneurons that innervate extrafusal fibers in muscles.
What is the difference between big alpha motoneurons and small alpha motoneurons?
Big ones take a lot more signal to fire than small ones.
Small ones tend to have smaller motor units.
What are motor units?
Alpha motor neuron + all the muscle fibers it innervates.
What is the usefulness of a small motor unit? What about a big motor unit?
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.
What happens if a muscle is innervated by a new type of alpha motor neuron?
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.
What leads to a stronger motor force?
Either incorporating larger motor units and/or more motor units leads to a stronger muscle force.
What are slow muscle fibers?
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.
What are fast-fatigue-resistant muscle fibers?
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.
What are fast-fatigable muscle fibers?
White meat.
Lots of glycolysis due to their high glycogen stores.
Fastest muscle fiber but it tires quickly.
Largest motor force.
Largest fiber size.
What is the muscle spindle?
It is in the bulge of muscles and is used for a myotatic reflex. It gives information on muscle length.
What makes up a muscle spindle?
Gamma motor neurons.
Ia axons.
Intrafusal fibers.
What is the significance of Ia axons in the muscle fibers?
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.
What does it mean that the muscle spindle is monosynaptic?
No interneurons are invovled. The Ia axons directly innervate the alpha motor neurons.
How is the muscle spindle activated?
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.
What is a purpose of the stretch reflex?
To maintain posture.
What is the Golgi Tendon Organ?
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.
What do Ib axons do in the Golgi Tendon Organ?
They are a little slower than Ia axons but they connect to inhibitory interneurons which inhibit alpha motor neurons so that the muscle relaxes.
What are central pattern generators?
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.
What are the spinal segments?
Spinal segments: Cervical (C) 1-8 Thoracic (T) 1-12 Lumbar (L) 1-5 Sacral (S) 1-5
How do you tell the difference between the dorsal horns and ventral horns?
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.
What are the muscle excitation steps?
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.
What are the muscle contraction steps?
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.
What are the muscle relaxation steps?
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.
Describe what happens to muscles after death.
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.
What is flaccid paralysis?
Muscles being limp and being unable to move.
What is spastic paralysis?
The muscles contracting but unable to relax. This also prevents movement.
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.
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.
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.
What is accute flaccid myelitis?
Similar to polio but has a 2 year cycle.
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.
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.
What is proprioception?
The sense of knowing where one’s body is in space.
Where does proprioception come from?
Golgi Tendon Organ
Muscle Spindle
Others (especially in joints)
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.
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.
