Term
| Skeletal muscle is innervated by _______ whose cell bodies lie in the __________ of spinal cord (ventral horn motoneurons) or in _______________ of the brainstem. |
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Definition
| Neurons, ventral horn, cranial nerve nuclei |
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Term
| An axon that innervates a few muscle fibers is a more _______ controlled muscle. |
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Definition
| finely controlled muscles of fingers or in extraocular muscles. |
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Term
| The axon that innervates a several hundred muscle fibers is more ________ type of muscle or control? |
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Definition
| in more powerful limb muscles). |
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Term
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Definition
Collective term for the motor neuron and the muscle fibers it innervates.
A muscle may contain from a few to hundreds of motor units.
a. So, There is an inverse relationship between then number of muscle fibers that a single axon innervates and the number of motor units per muscle.
i. For example:
If a muscle has 1000 fibers and each axon that innervates it only innervates 10 muscle fibers, then 100 axons are required to completely innervate the muscle.
If each axon innervates 100 muscle fibers then only 10 are required to completely innervate the muscle. |
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Term
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Definition
Activation of the motor neuron causes depolarization of the axon terminals and release of the neurotransmitter. Causes excitation of muscle fiber.
a. ACh crosses the synaptic cleft and binds to its receptor on the muscle.
b. Binding of ACh to its receptor causes Na+ and K+ channels to open in the muscle membrane, which normally depolarizes the membrane beyond threshold and results in an action potential (AP) being produced.
c. In normal muscle, every AP in an alpha motor neuron results in an AP in the muscle. APs are conducted in both directions from the neuromuscular junction, down the length of the muscle membrane, the sarcolemma.
4. Activation of motor neuron causes all of the muscle fibers of the motor unit to be activated and to contract by a process known as "excitation-contraction" (E-C) coupling. |
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Term
| excitation-contraction" (E-C) coupling |
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Definition
| Activation of motor neuron causes all of the muscle fibers of the motor unit to be activated and to contract by a process. |
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Term
T or F
In normal muscle, every AP in an alpha motor neuron results in an AP in the muscle. |
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Definition
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Term
T or F
Each muscle fiber is actually a muscle cell? |
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Definition
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Term
Muscle fibers...Name where they are and what they do.
myofilaments
myofibrils
Sarcomeres |
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Definition
myofibrils- Muscle cells are subdivided into myofibrils, which are composed of many myofilaments (thin filaments and thick filaments).
myofilaments-Myofilaments are aligned in parallel to one another in a highly organized manner throughout the length of the fiber. The regularity of two types of myofilaments gives rise to the banding pattern characteristic of striated muscles when viewed side-on (longitudinally).
Sarcomeres- The bands are divisible into functional units. |
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Term
| The energy molecule needed for muscle contraction is... |
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Definition
ATP
Most of the ATP is produced by mitochondria which are abundant in highly aerobic types of muscle.
2. ATP can also be produced from glycogen stores within the muscle cell. ATP is synthesized in muscle from fuel molecules, especially carbohydrates and fats in the diet. |
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Term
| Muscle shortening, or contraction, occurs when... |
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Definition
| Ca++ ions are released from the sarcoplasmic reticulum (SR), allowing the contractile proteins (actin and myosin) to interact with one another. |
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Term
| Cessation of muscle contraction is dependent upon the breaking of actin-myosin cross bridges via... |
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Definition
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Term
| Force Production by Muscle depends upon... |
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Definition
-The length of the sarcomeres within a muscle (i.e., the length-tension relation). The degree of overlap between actin and myosin determines the number of cross-bridges that can be formed.
-determined by the number and frequency of motor unit firing. |
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Term
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Definition
Similar to spatial summation of graded potentials.
The excitation of additional motor units will increase the force generated by that muscle |
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Term
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Definition
Similar to temporal summation of graded potentials.
Increased frequency of individual motor unit firing will also increase force generation. |
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Term
| Fusion of individual twitches occurs at approximately what hz? |
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Definition
| 50 hz in fast muscles and at a lower frequency in slower contracting muscles. |
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Term
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Definition
| Muscle contraction is the activity of myosin ATPase (i.e., the rate at which cross bridges can cycle). Fast muscle has higher ATPase activity. |
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Term
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Definition
| Tthe motor unit is defined as the number of muscle fibers that are innervated by a single alpha motor neuron (ranges from <100 to >1500 muscle fibers per motor neuron). In general, the finer the control, the smaller the innervation ratio (ie. <100 muscle fibers per neuron). Both extraocular muscles and in intrinsic hand muscles (fine finger control) have small innervation ratios. |
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Term
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Definition
| fast-contracting, fast fatiguing |
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Term
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Definition
| fast-contracting, fatigue resistant |
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Term
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Definition
| slow contracting, non-fatigable |
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Term
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Definition
| fast-contracting, glycolytic |
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Term
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Definition
| fast-contracting oxidative and glycolytic |
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Term
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Definition
| slow-contracting, oxidative |
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Term
| Are smaller or larger motor units recruited first? |
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Definition
smaller motor units
Low resistance type S motor neurons have a lower threshold for synaptic activation.
As additional force is needed, additional units are recruited that are progressively larger, with greater force-producing capabilities.
Electrical stimulation of muscle results in a reversed recruitment order with larger fast fatiguing motor units being recruited first. |
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Term
| Neurogenic Disorders: Motor Neuron Disorders |
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Definition
1. Amyotrophic Lateral Sclerosis (upper and lower) Luke Gary’s disease
2. Motor Neuron Degeneration Following CVA
3. Poliomyelitis (aka Polio) |
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Term
| Myogenic Disorders: Disorders of the Neuromuscular Junction or Muscle |
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Definition
1. Myasthenia Gravis (MG) Muscle loses ACHT Receptors.
2. Botulism Poisoning and Use of Botulinum Toxin (Botox)
3. Muscular Dystrophy (jerry’s kids)
4. Myotonia |
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Term
| The Effects of Exercise on Muscle Fiber Types |
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Definition
The distribution of muscle fiber types can be altered to a certain extent by exercise.
1. High intensity exercise (i.e., weight training) results in conversion of some muscle fiber types to those with greater glycolytic capacity, but lower aerobic capacity. This type of exercise also causes increases in muscle strength as more contractile proteins are synthesized over time and packed within the muscle fibers (hypertrophy).
2. Endurance exercise (low intensity, high repetitions) results in increased aerobic capacity of the muscle, that is, increased ability of the muscle to utilize oxygen (more mitochondria and greater ATP production per muscle fiber). FG muscle fibers may be converted to FOG (more oxidative), but there is little change in the type SO muscle fibers. |
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Term
| Effects of Aging on the Neuromuscular System |
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Definition
1. Muscles become thinner (due to loss of muscle fibers with aging).
2. Strength decreases.
3. Movements become slower and less precise. The elderly can recruit motor units as effectively as younger subjects, therefore, the loss of strength is more due to changes within the muscle rather than in the nerve supply to muscle, although changes in both areas occur.
4. Twitch contraction speed is slowed with age (may be due to decrease in volume and Ca2+-pumping capacity of sarcoplasmic reticulum).
5. There is evidence of loss of motor neurons with age (i.e., 25-50% of neurons have died by old age). This provides a possible explanation for weakness associated with post-polio syndrome.
6. There is evidence of loss of normal mosaic pattern and evidence for collateral sprouting of intact motor neurons to innervate the denervated fibers in old age. Result is formation of giant MUs which produce larger than normal action potentials in the EMG recording. Motor units that are enlarged through collateral sprouting and reinnervation produce large twitch forces, thus reducing fine control of movement.
7. Conduction velocity is reduced with age due to segmental demyelination, remyelination (but not as heavy as original myelin sheath), decreased internodal length, and death of alpha motor neurons with large diameter axons.
8. Average rate of nerve regeneration is slower with increasing age.
9. Type II fibers (fast-contracting, FG and FOG) undergo the greatest atrophy (most likely due to disuse).
10. Despite degenerative changes in the neuromuscular system with aging, elderly subjects/patients do benefit from strengthening programs, with Type II fibers showing the greatest changes (e.g., increase in cross-sectional area). |
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