Introduction To Muscles Flashcards
Describe the connective tissue arrangement in skeletal muscle
Myofibres surrounded by endomysium
Myofibres grouped into fascicles surrounded by perimysium
Fascicles grouped into muscle surrounded by epimysium
What is the specific name for a muscle fibre membrane?
Sarcolemma
Describe a muscle fibre
Multinucleated (peripheral)
Sarcoplasm packed with myofibrils
Varying numbers of mitochondria
What are tendons?
Extensions of connective tissue that attach muscle to bone
How are tendons connected to bone?
Sharpey’s fibres
At rest, what is the general range of length of a sarcomere?
3.6-4.5 microns
Why are muscle fibres long?
Maximise distance of movement
How long is a (mostly) contracted sarcomere?
2microns
Describe the relationship between muscle extension and power of contraction?
Fully extended muscle = little power
Power increases as muscle shortens
As maximal shortening approaches, power decreases
When does the number of muscle fibres stop increasing?
After 24 weeks in utero
How can muscle size increase? (2)
Increase/decrease in diameter of individual fibres by adding new sarcomeres to existing cells (exercise)
During childhood and adolescence, new sarcomeres are added to the ends of fibres (length)
What happens to muscle as you age?
Muscle bulk and strength decrease with age
Describe type I muscle fibres (3)
Respires aerobically (lots of mitochondria)
Weaker contractile force
Endurance
Describe type II muscle fibres (3)
Respire anaerobically
Fatigue quickly
Strong contractile force
Why are tendons slow-healing?
Poor blood supply
What are the three types of tendons?
Cylindrical
Linear
Common
Describe cylindrical tendons
Closely-packed fibres
Produce an elevation/tubercle on bone
Describe linear tendons
Form fleshy attachments
May produce linear ridges (pectoralis major)
What does a common tendon do?
Attachment for 2 or more muscles
What are the three types of common tendon?
Intermediate
Raphe
Aponeurosis
What is an intermediate tendon?
“Wrapped around”
Allows muscles to act independently with different nerve supplies
What is a Raphe tendon?
Two muscles “sewn” together
What is an aponeurotic tendon?
Muscle regressed during development leaving connective tissue (tendon)
Why do we have synovial tendon sheaths?
Reduce friction where tendons lie close to each other or pass round bony prominences
Prevent bowstringing
What is a retinaculum?
Tough collagen sheets attached to bone under which tendons run
What adjectives are used to describe tendon/muscle attachments?
Proximal
Distal
What part of the nervous system innervates skeletal muscle?
Somatic (motor and sensory)
In skeletal organs, what measures length? (Sensory)
Muscle spindles
In skeletal muscles, what measures tension? (Sensory)
Tendon organs
What kind of motor neurons innervate skeletal muscle?
Alpha motor neurons
Are skeletal muscle motor neurons myelinated?
Yes
What neurotransmitter is released at the neuromuscular junction?
Acetylcholine
What is the name of the junction between the motor neuron and skeletal muscle fibre?
Motor end plate/neuromuscular junction
What is the range of the number of muscle fibres innervated by one alpha motor neuron?
20-2000
How is the motor unit arranged to allow even muscle contraction?
The fibres are not next to each other in the muscle
What does alternating between motor units allow?
Endurance
What does a strap muscle look like?
Muscle fibres arranged in parallel
Wide muscle-tendon attachment
What does a fusiform muscle look like?
Longer tendons
Larger in middle, slims towards ends/tendons
What does a fan-shaped muscle look like?
Large proximal attachment
Converges on distal attachment
What are pennate muscles built for?
Power
What is the structure of a bipennate muscle?
Two fleshy bellies
Central tendon
What kind of pennate muscle has only one fleshy belly?
Unipennate
What do agonist muscles do?
Initiate movement/contract
What is another name for an agonist muscle?
Prime mover
What does an antagonist muscle do?
Oppose movement/stretch
What do fixator muscles do?
Stabilise body/skeleton to give the most advantageous position for required movement
What do synergists do?
Act with prime movers to refine movement and control undesirable movement