Anatomy and Embryology of Skeletal Muscle Flashcards
List 3 types of muscle
- Skeletal
- Cardiac
- Smooth
Describe characteristics of skeletal muscle
- Striated
- voluntary,
- controlled by somatic nervous system,
- cells multinucleated,
- un-branched.
Describe characteristics of cardiac muscle
- Striated
- involuntary
- controlled by autonomic nervous system
- single (branched) cells joined by intercalated disk
Describe characteristics of smooth muscle
- Non-striated
- involuntary
- controlled by autonomic nervous system,
- spindle-shaped single cells
List the three separate layers of connective tissue that hold muscle fibres in position in skeletal muscle
- Epimysium
- Perimysium
- Endomysium
What is epimysium?
tough outermost layer surrounds the entire muscle (epi = upon)
What is perimysium?
surrounds bundles of muscle fibres to create a fascicle (peri = around)
What is endomysium?
surrounds each muscle fibre within the fasciculus (endo = within) – between fibres
What is also embedded in CT in skeletal muscle?
Blood vessels and nerves
List the diff muscle shapes with e.g.s
- Digastric e.g. omohyoid
- Multipennate e.g. deltoid
- Convergent e.g. pectoralis major
- Quadrate e.g. rectus abdominis
- Thin parallel e.g. Sartorius
- Unipennate e.g. extensor digitorium longus
- Bipennate e.g. rectus femoris
- Flat parallel with aponeurosis e.g. EO
- Fusiform e.g. biceps
- Circular e.g. Orbicularis occuli
How do muscles gen force?
- only by contracting
- only pull (not push),
- only move in 1 direction
What are antagonistic muscles?
- work in pairs
- if muscle doing 1 action, need another to bring back to original pos
- muscle that bends the joint (dec the joint angle) = flexor muscle
- muscle that straightens the joint (inc the joint angle) = extensor muscle
List 2 types of muscle contraction
- Isotonic
2. Isometric
What is isotonic contraction and list 2 types
= cause the muscle to change length as it contracts
- Concentric
- Eccentric
What is concentric contraction and give e.g.?
muscle shortens during force production
lifting a heavy weight,
What is eccentric contraction and give e.g?
- Muscle produces force but length increases
- controlled lowering of the heavy weight raised
What is isometric contraction?
Muscle exerts force without changing length – no movement of muscle
Give e.g.s of isometric contraction
- Pulling against immovable object
- pushing against a wall.
- grip
- maintain posture.
- holding a heavy weight steady, neither raising nor lowering it.
Using deltoid as an e.g. describe the diff muscle contractions
- isometric - holding arm out straight - deltoid in steady pos
- concentric - raise arm up using force - deltoid shortens
- eccentric - lower arm down using gravity - deltoid lengthens
Give e.g. of antagonistic muscles
- flexors = biceps (concentric - raise forearm)
- extensor = triceps (eccentric - bring forearm back down)
List diff types of muscle in movement
- Agonist/Prime mover
- Antagonist
- Synergist
- Fixator
What is the agonist?
- muscle(s) that provides the major force to complete the movement.
- Because of this aka ‘prime movers’
- not always the muscle that is shortening (contracting concentrically).
- e.g. In a bicep curl the bicep is the agonist on the way up when it contracts concentrically, and on the way down when it contracts eccentrically - prime mover in both cases.
What is antagonist?
- muscles that oppose agonist.
- During elbow flexion, bicep = agonist, tricep = antagonist.
- While agonist contracts - causing the movement, antagonist typically relaxes so as not to impede agonist
- another function can be to slow down/stop a movement. e.g. if weight in bicep curl was v. heavy, when being lowered from top position, antagonist tricep would produce a sufficient amount of tension to help control the movement as weight lowers to prevent damage to elbow joint
What is the synergist?
- muscle(s) that stabilises a joint around which movement is occurring, which in turn helps agonist function effectively.
- also help to create the movement.
- In bicep curl, synergists = brachioradialis + brachialis which assist biceps to create the movement + stabilise elbow joint.
What is a fixator?
- muscle(s) that stabilises the origin of agonist through isometric contraction + the joint that the origin spans (moves over) in order to help agonist function most effectively.
- In bicep curl = rotator cuff muscles, the ‘guardians of the shoulder joint’.
- majority of fixator muscles are found working around hip + shoulder joints.
Do muscles perfom just one type of moevemt?
No - The same muscle can act as prime mover, antagonist synergist/fixator under diff cond/actions
What can also act as prime mover?
- Gravity can be a prime over pushing arm down
– upper arm adduction muscles to antagonise that action
What are striations and what causes them?
= alternating light and dark bands that appear across the length of the fibre
- Organisation of thick and thin filaments + division into sarcomeres causes skeletal muscle to have this striated appearance
List 2 major filament types of myofibrils
- thick filaments composed of myosin
2. thin filaments composed of actin
How are myofibrils div?
Into sarcomeres - contractile units
What is diff between myofibre and myofibril?
A myofibre is filled with many myofibrils
Describe sarcomere org
- Z line, 1/2 I band, A band (contains M line + H zone), 1/2 I band + Z line
- Each sarcomere has a complete A-band and two half I bands
What is the A band?
Thick myosin filaments (but also contains actin)
What is I band?
Only actin filaments
What is H zone?
In the centre of the sarcomere, portion of the myosin filament with no overlap of the actin
What is M line?
- attachment site for the thick filaments.
- in the center of the A band and, thus, in the center of the sarcomere.
What are Z lines?
div each sarcomere
