Muscle Physio II Flashcards
When do Muscle Fibers adapt?
Considerably in response to demands placed on them
What are the Types of Muscle Fiber Adaptations?
- Muscle Hypertrophy
2. Muscle Atrophy
Describe Muscle Hypertrophy.
Anaerobic Hi intensity resistance training; Increase Myosin and Actin filaments; Influenced by Testosterone; Interconversion between Fast muscle types
Describe Muscle Atrophy.
Disuse, denervation, aging; Limited repair of muscle (limited stem cells: satellite cells)
What are Whole Muscles?
Groups of Muscle Fibers bundled together and their tendons attached to bones
When and where is Muscle tension produced?
As the contractile component tightens the series-elastic component; produced internally within sarcomeres
What system do the interactive units of skeletal muscles, bones and joints form?
Lever system (Bones: Levers, Joints: Fulcrum, Skeletal Muscle: Force)
What are the Primary Types of Contraction?
- Isotonic: Constant load, muscle change
- Isokinetic: Constant velocity, muscle fibers shorten
- Isometric: Constant muscle length, tension increases
- Concentric: Muscle shortens
- Eccentric: Muscle lengthens
What skeletal muscle does not attach to bones at both ends but still produce movement?
Tongue muscle
What is the Load-Velocity relationship?
Velocity of shortening related to loud
What is most of the energy converted to when muscles contract?
Heat
What are the 2 primary factors that can be adjusted to produce graded contractions?
- No. of muscle fibers contracting
2. Tension developed by each contracting fiber
What are the factors affecting the Contraction?
- Extent of Motor Unit Recruitment (No. of fibers contracting within muscle)
- Frequency of Stimulation, fiber length and thickness, extent of fatigue (Tension developed by each muscle fiber)
What is Twitch Summation?
Increase in tension accompanying repetitive stimulation of a muscle fiber
What is Tetanus?
Smooth, sustained contraction of max strength
What does Twitch Summation result primarily from?
Sustained elevation in cytosolic Ca2+ (muscle fiber restimulated before complete relaxation)
When does Tetanus occur?
Muscle fiber stimulated so rapidly that it cannot relax at all between stimuli
What happens after Tetanus?
Stimulation stops or fatigue sets in
How do Muscles respond to Stimulus Strength?
Strength of contractions increase with strength of stimulus until max contraction
When can Max Tension be developed?
At optimal Muscle Length
What happens when muscle length is less than Optimal Muscle length?
Too much overlap in sarcomere
What happens when muscle length is more than Optimal Muscle length?
Too little overlap in sarcomere
Describe the Withdraw Reflex.
- Thermal pain receptor in finger activated
- AP generated in Afferent pathway; impulses propagated to spinal cord
- Spinal cord = Integrating center:
- Excitatory interneurons (biceps)
- Inhibitory interneurons (triceps)
- Interneurons ascending to brain - 2 efferent pathways to antagonistic muscles
- Resultant flexion of elbow joint pulls hand away from stimulus
- Events beyond reflex arc
What do Muscle Receptors provide?
Afferent Info needed to control Skeletal Muscle activity
Why does the CNS need continual info regarding ongoing changes in muscle length and tension?
For effective control of motor output
What do Muscle Spindles monitor?
Muscle Length
What do Golgi tendon organs detect?
Changes in tension
What is the Stretch reflex?
Local -ve feedback mechanism to sense and resist changes in muscle length when an additional load is applied
How is the Muscle Spindle structured?
Consists of collections of specialised muscle fibers (intrafusal fibers)
What fiber is the secondary sensory endings?
Type II fiber
What fiber is the primary sensory endings?
Type Ia fiber
What does Alpha gamma coactivation contract?
Both intra and extrafusal muscle fibers
Describe the process of an Unstretched Muscle.
AP generated at constant rate
Describe the process of a Stretched Muscle.
Increased rate of APs due to activation of muscle spindle
Describe the process of a Slack Muscle.
No APs are fired because only Alpha motor neurons are activated, contracting only Extrafusal muscle fibers; Unable to signal further length changes
Describe the process of a Muscle maintained by muscle spindle tension.
Alpha-gamma coactivation: Both muscle fibers contract; Still can signal changes in length
What type of tone is a single unit smooth muscle?
Myogenic (pacemaker and slow-wave potentials)
How are Smooth Muscle contractions different from Skeletal Muscle?
- Modification of activity by ANS
- Arrangement of Thick and Thin Filaments
- Ca2+ dependent phosphorylation of myosin
How is the Arrangement of Thick and Thin Filaments in Smooth Muscles?
No troponin; Tropomyosin does not cover actin
What is the function of phosphorylated myosin?
Permits binding with actin
Describe the characteristic of Smooth Muscle.
Can still develop tension yet inherently relaxed when stretched (Stress relaxation response); Slow and Economical (Latch phenomenon)
Describe the features of the Cardiac muscle.
Clear length-tension r/s; Interconnected by gap junctions in intercalated discs; Innervated by ANS
Where does Control of motor contraction by NS?
- Motor cortex (Premotor and Primary)
- Brain stem
- Spinal cord
- Cerebellum
- Somatic and ANS (Somatosensory)
What alterations occur during skeletal muscle hypertrophy and atrophy?
Myonuclear number (in conjunction with changes in myofibrillar protein content and CSA, resulting in a constant ratio of cytoplasmic area to nuclear number
What is Sarcopenia?
Gradual muscle loss after the 4th decade of life
Who does Sarcopenia mostly impact?
Males after the age of 50
How much is the % of loss per year through inactivity?
1%
Which type of fiber is more severely affected?
Type II
What will loss of muscle protein affect?
Permanent; Affect activities of daily living and bone mass later in life; Affect Immune system, insulin absorption, blood sugar levels; Increase risk of type II diabetes
What can the maintenance of muscle mass throughout life do?
Metabolic syndrome may be ameliorated
What are the Causes of Sarcopenia?
- Motor neuron death
- Changes in testosterone status
- Changes in activity
- Changes in protein metabolism rate
- Mitochondria dysfunction
