Unit 8 MSK pt. 1 Patho Flashcards
What is muscle fatigue and what can cause it?
A reversible condition in which an exercising muscle is no longer able to generate or sustain the expected power output.
Changes in Ca++ release from the sarcoplasmic reticulum may have a major impact on muscle function.
What is a Type 1 muscle fiber? (just definition)
A slow-twitch oxidative; Red muscle
What is a Type 2A muscle fiber? (just definition)
A fast-twitch oxidative-glycolytic; Red muscle
What is a Type 2 B/X muscle fiber? (just definition)
A fast-twitch glycolytic; white muscle
What are the characteristics of a Type 1 muscle fiber?
It is the slowest in development of maximum tension;
It is slow in Myosin ATPase activity;
It has the longest contraction duration;
fatigue resistance;
most used (Posture);
has numerous mitochondria
What are the characteristics of a Type 2A muscle fiber?
It is intermediate speed in development of maximum tension;
It is medium speed in Myosin ATPase activity;
It has a short contraction duration;
It is fatigue resistance;
Used in standing and walking;
has moderate mitochondria
What are the characteristics of a Type 2B/X muscle fiber?
It is the fastest in development in maximum tension;
It is fast in Myosin ATPase activity;
It has a short contraction duration;
It is easily fatigued;
Least used (Quick fine movements);
Few mitochondria
What does a motor unit consist of?
One motor neuron and all the muscle fibers it innervates
What are the three muscle types?
Skeletal
Cardiac
Smooth
What are that characteristics of skeletal muscles?
Skeletal muscles have large fibers, multinucleate cells that appear striped or striated under the microscope
What are the characteristics of Cardiac muscles?
Cardiac muscles fibers are also striated but they are smaller, branched, and uninucleate. Cells are joined in series by junctions called intercalated disk
What are the characteristics of Smooth muscle?
Smooth muscles fibers are small and lack striations
Skeletal muscles is composed of:
Connective tisse
Muscle fascicles
Blood vessels
Nerves
_______ are the basic functional unit of the muscle fiber.
Sarcomeres
What are each sarcomere composed of?
Contractile, structural, and accessory proteins.
Different components of the sarcomere are named based on their appearance under a light microscope and to name different areas and structures of the sarcomere
What are the contractile proteins?
Myosin and actin
What are the structural proteins?
M Line and Z disk
What are the Accessory Proteins?
Titin and Nebulin
These are giant accessory proteins. Titin spans the distance form one Z-disk to the neighboring M line. Nebulin, lying along thing filaments, attaches to a Z-disk but does not extend to the M-line
What do Titin and Nebulin do?
Titin provides elasticity and stabilizes myosin.
Nebulin help align actin
What are the components for the Myosin molecule?
Myosin tail, hinge region, and the myosin heads
What regulatory proteins are associated with the actin chain?
Tropomyosin and troponin
What are the roles of tropomyosin and troponin?
Tropomyosin covers the actin binding sites.
Troponin controls the positioning of tropomyosin over the binding site.
Describe the location and function of the T-tubule.
T-tubules allow action potential to move rapidly from cell surface to inferior to fiber to reach terminal cisternae simultaneously
What is the Sliding Filament?
With any contraction that takes place the myosin and actin do not change length but slide past each other
Muscle contracts——->Sarcomere shortens with contraction——> Muscle contraction: H zone and I band both shorten, while A band remains constant
What signal initiates the power stroke?
A calcium signal initiates the power stroke when myosin cross bridges swivel and push the actin filaments toward center of sarcomere.
How is ATP used during the contraction cycle?
ATP is used by myosin to convert energy into mechanical energy of crossbridge motion
Why does Rigor Mortis occur after death?
Metabolism stops and ATP supplies exhaust. Muscles are unable to to bind more ATP so they remain in a tightly bound rigor state, muscles freeze due to immovable cross bridges
The somatic motor division controls what?
Skeletal muscles
What are the characteristics of the somatic motor division?
These pathways have a single neuron where the cell body originates in the CNS and a single myelinated axon projects to a skeletal muscle.
These pathways are excitatory
The synapse of an alpha motoneuron on the muscle fibers is called:
Neuromuscular Junction (NMJ)
What does the neuromuscular junction consist of?
Axon terminals; motor end plates on the muscle membrane; Schwann cell sheaths
What is Motor End Plate?
A region of muscle membrane that contains high concentrations of ACh receptors
What is motor end plate potential (EPP)?
The addition of net positive charge (sodium influx exceeds potassium efflux) to muscle fiber and depolarizes the membrane.
EPP reaches threshold and initiates muscle action potential
If we have a high calcium ion concentration inside of the sarcoplasmic reticulum, what would happen?
The calcium ions get dumped in the cytoplasm (inside the muscle cell) they will bond to troponin proteins causing muscle contraction
If we have a low calcium concentration inside of the sarcoplasmic reticulum, what would happen?
The troponin move the tropomyosin back in the way of the myosin heads and we have no contraction (Relaxation)
What is the role of the autonomic motor neurons?
Controls smooth muscle, cardiac muscle, and many glands, and some adipose tissue
What are the divisions of the autonomic nervous system? How do these divisions interact with each other?
Sympathetic- Dominates during stressful situation (Fight or Flight)
Parasympathetic- Dominates during quite activities (Rest and Digest)
Homeostasis is maintained as the two autonomic branches cooperate with each other
Describe the autonomic control centers, and where they are located?
Hypothalamus: Temperature control, Water balance, Eating balance
Pons: Urinary bladder control, secondary respiratory center, Blood pressure control
Medulla: Blood pressure control, Respiratory center
Where in the CNS does the SNS and PSNS originate?
SNS: Thoracic and lumbar segments
PSNS: Brainstem and sacral segments
Where is the Ganglion location for the SNS and PSNS?
SNS: Close to spinal cord
PSNS: On or close to target
What are the pathways for the SNS and PSNS?
SNS: Short Preganglionic
Long postganglionic neurons
(Use ACh and norepinephrine)
PSNS: Long Preganglionic
Short postganglionic neurons
(Use AcH)
Compare and contrast the SNS and PSNS neurotransmitters and receptors on postganglionic neurons and target tissues?
SNS: Postganglionic neurons release norepinephrine onto alpha or beta-adrenergic receptors on target cell
PSNS: Postganglionic neurons release ACh onto muscarinic receptors on target cells
What ligand band binds to the Nicotinic receptors?
Two ACh molecules bind to the Nicotinic Cholinergic receptor
What is the role of Acetylcholinesterase (AChE)?
Breaks down to ACh- it deactivates it by degrading into Acetyl and choline
What impact might an AChE inhibitor medication or nicotine from smoking have on a neurotransmitter and/or receptor actions?
A continued presence of nicotine causes ion channels to remain open, so the muscle remains depolarized and is unable to contract again (paralysis)
What is Myasthenia Gravis?
An autoimmune disease that results in the loss of ACh receptors.
(The most common disorder of the NMJ)
What is Excitation-contraction coupling?
The process in which muscle action potentials are translated into calcium signals which initiate a contraction-relaxation cycle
What is the timing of Excitation-contraction coupling?
Action potential in the motor neuron–> Muscle action potential
–> Development of tension (contraction)
What is the difference between motor neuron action potential and muscle fiber action potential?
In a motor neuron action potential the resting state is -70 and the peak depolarization is +30
In a muscle fiber action potential the resting state is -80 and the peak depolarization is +20, with little hyper-depolarization
What is twitch in E-C coupling?
A single contraction-relaxation cycle
What is latent period in E-C coupling?
A short delay between muscle action potentials and muscle tension development
What is the role of phosphocreatine and creatine kinase as an energy source for a muscle action?
Phosphocreatine is the backup energy source of muscles. It’s a molecule whose high-energy phosphate bonds are created from creatine and ATP when muscles are at rest.
When muscles become active the high-energy phosphate group of phosphocreatine is transferred to ADP (creating more ATP to power muscle)
Would aerobic or anaerobic metabolism provide the most ATP?
Aerobic metabolism provides the most ATP
What substrate would be the preferred energy source for quick and efficient ATP production?
Glucose is the preferred energy source for quick efficient ATP production
The role of central vs peripheral fatigue and where they arise
Central fatigue is subjective to tiredness and desire to cease activity. (Arise in CNS)
Peripheral fatigue is associated with some neuromuscular diseases, probably not a factor in normal exercise. (Arise anywhere between NMJ and contractile elements of muscle)
What is strongest evidence that supports muscle fatigue?
Failure of EC coupling
Lactate accumulation is no longer a likely cause of fatigue
Describe length tension relationship
The tension generated by a muscle fiber is directly proportional to the number of cross bridges formed between the thick and thin filaments .
So if the contraction has very long sarcomere length, there would be decreased force.
If sarcomere is very short there would be too much overlap and prevents cross bridge formation
Optimum sarcomere length is normal resting length for skeletal muscles
What is motor unit? What is the benefit of asynchronous recruitment?
Motor unit is the basic unit of contraction in a intact skeletal muscle. It is composed of a group of muscle fibers that function together and the somatic motor neuron that controls them.
Asynchronous Recruitment is how the nervous system avoids fatigue. The nervous system modulates the firing rate of the motor neuron so that the different motor units take turns maintaining muscle tension
Isometric vs Isotonic muscle contraction
Isometric contraction- Contraction the creates force with moving load (muscle doesn’t shorten or lengthen)
Isotonic contraction- A contraction that creates force and moves load (Bicep curl)
Why smooth muscle myosin longer than skeletal muscle?
Smooth muscle have less myosin.
What is the role of calmodulin during smooth muscle contraction?
Calmodulin activates myosin light chain kinase (MLCK)
Calcium bind to calmodulin
What parts of the brain primarily control the autonomic nervous system?
Hypothalamus, Pons, Medulla
Describe the events at the neuromuscular junction.
Converts an acetylcholine into electrical signal in muscle fiber
What is excitation-contraction (E-C) coupling?
The process in which muscle action potentials are translated into calcium signals, these calcium signals in turn initiate a contraction-relaxation cycle
Summarize the events in a muscle contraction
Events at neuromuscular junction (converts acetylcholine into electrical signal in the muscle fiber)
⬇️
E-C coupling (muscle action potentials translated into calcium signals)
⬇️
Ca++ signal
⬇️
Contraction-relaxation cycle
↙️ ↘️
Muscle twitch Sliding filament theory
What is the enzyme that turns phosphocreatines to ADP?
Creatine kinase (CK)
What is one way the nervous system avoids fatigue in sustained contractions?
Asynchronous recruitment
The nervous system modulates the firing rate of the motor neuron so that different motor neurons take turns maintaining muscle tension.
What are the four contraction patterns of smooth muscles with examples.
1) Phasic smooth (relaxed) - esophagus
2) Phasic smooth (contracted) - intestine
3) Tonic smooth (usually contracted) - sphincter relaxes to allow material to pass
4) Tonic smooth (varied contraction) - vascular smooth muscle
What are single unit smooth muscle cells?
Muscles that are electrically connected by gap junctions and contract as a coordinated unit
What are multi unit smooth muscle cells?
Muscles NOT electronically linked and each cell function independently
