Lecture 17 - Skeletal Muscle Flashcards
How do we generate the force to produce movement?
Skeletal muscle
What are the properties of muscle tissue?
Excitability, conducts electrical impulses, contractibility, extensibility, elasticity
What is excitability?
The property of muscle being sensitive or responsive to chemical, electrical, or mechanical stimuli
What is contractibility?
The ability of muscle to contract and develop tension or internal force against resistance when stimulated
What is extensibility?
The ability of muscle to be stretched back to its original length following contraction
What is elasticity?
The ability of muscle to return to it’s original length following stretching
What are agonist muscles?
Muscles that cause joint motion through a specified plane of motion when contracting concentrically
What are agonist muscles also known as?
Primary/prime movers
What are antagonist muscles?
Muscles located on the opposite side of a joint from an agonist that contract concentrically to perform the opposite joint motion of agonist muscles
What are agonist muscles also known as?
Contralateral muscles
What are synergist muscles?
Muscles that assist in action of agonists that assist in refined movement and reduce undesired motions
What are synergist muscles also known as?
Guiding muscles
What is the epimysium?
Connective tissue surrounding the entire muscle
What is the perimysium?
Connective tissue surrounding the bundles of muscle fibers (fascicles)
What is the endomysium?
Connective tissue surrounding individual muscle fibers
What is the sarcolemma?
The muscle cell membrane
What are myofibrils?
Threadlike strands within muscle fibers made up of actin and myosin
What is actin?
Thin filament made up of troponin and tropomyosin
What is myosin?
Thick filament
What is a sarcomere?
The smallest contractile unit of skeletal muscle
What is a motor unit?
A single motor neuron and muscle fibers it innervates
Why does the CNS alternate the motor units it recruits?
To reduce fatigue and distribute work load
What are the types of muscle contractions?
Isometric and isotonic
What is an isometric contraction?
A contraction where the muscle exerts force without changing length
What is an isotonic contraction?
A contraction where the muscle exerts force by changing length
What are the types of isotonic contraction?
Concentric and eccentric
What is a concentric contraction?
A contraction where the muscle shortens during force production
What is an eccentric contraction?
A contraction where the muscle length increases during force production
How does neural excitation move to muscle force?
Muscle activation dynamics (excitation contraction coupling) and muscle contraction dynamics
What is force output dependent on?
Muscle length, velocity, and activation of the muscle unit
Who is A.V. Hill?
Physiologist who studies the chemical and mechanical properties of muscle
What did A.V Hill conclude in his first experiment?
Multiple motor units combine to produce a usable force that can be increased by the nervous system by recruiting more motor units or increasing the frequency of action potentials
What did A.V. Hill observe about muscle mechanics in his first experiment?
That contraction begins with the twitch of a muscle fiber
What is a twitch?
A force produced by an isometric muscle response to an action potential in one or more motor units
What is the summation of twitches?
When the muscle is not allowed to relax between action potentials to the point of tetanus?
When does tetanus occur in humans?
50-60 Hz
What was A.V. Hill’s second experiment?
Force Length
How did A.V. Hill observe force length?
By measuring passive and active force
What did A.V. Hill observe about active length tension in his second experiment?
Active length tension relationships are directly related to sarcomere length
What happens when a sarcomere is too long?
It is unable to crossbridge
What happens when a sarcomere is too short?
It is unable to contract further because thin filaments hit each other
What did A.V. Hill observe about passive length tension in his second experiment?
Passive length tension is like a spring (non linear) due to connective tissue
What did A.V. Hill observe about muscles during unloading vs loading in his second experiment.
Hyesteresis, different length tension properties apply when loading and unloading tissue
Can active and passive tension be combined to produce force?
Yes
What was A.V Hill’s third experiment?
Force velocity relationship
