The Musculoskeletal System Flashcards
What are the 3 muscle types?
- Cardiac
- Smooth
- Skeletal
Isometric contraction
= muscles contract but no shortening (no movement)
Concentric contraction
= muscles contract and shorted to lift weight
Eccentric contraction
= muscles contract but lengthen to control the lowering of the weight
At what point is muscle the strongest and why?
Mid-range
…because it’s the optimum point for the development of cross-bridges which allow strong contractions
What is muscle strength affected by?
- metabolic factors
- endocrine factors
- neural output
- psychological factors
- range of joints
- age
- gender
- muscle architecture
- biomechanical set up
Inner range
= muscle shortened
Mid-range
= mid-length of muscle
Outer range
= muscle lengthened
Skeletal muscle
- multinucleate and myofilaments precisely aligned and packaged by connective tissue
- contraction is under voluntary control
Cardiac muscle
- One nucleus, branching and connected by specialised junctions – intercalated discs
- Forms walls of the heart
Smooth muscle
- One nucleus, no striations
- Arranged in sheets and line walls of hollow organs
- Specialised for propelling substances along internal passaged (e.g.: urine in bladder, food in the gut)
Epimysium
covers whole muscle
Perimysium
surrounds muscle fascicles
Endomysium
surrounds muscle fibre
What does a thin filament consist of?
- two strands of actin subunits twisted into a helix
- two types of regulatory proteins (troponin and tropomyosin)
What does the thick filament consist of?
many myosin molecules whose heads protrude at opposite ends of the filament
What are thin myofilaments known as?
actin
What are thick myofilaments known as?
myosin
Describe a neuromuscular junction (synapse)
- Nerve fibre makes a functional connection with its target cell
- Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors
- Neurotransmitter (acetylcholine/ACh) release causes stimulation of muscle cell
Excitation
action potentials in the nerve lead to formation of action potentials in muscle fibre
Excitation-contraction coupling
action potentials on sarcolemma activate myofilaments
Contraction
tensing or shortening of muscle fibre
Relaxation
return of fibre to its resting length
Describe skeletal muscle contraction, initiation and execution
- action potential travels along a motor nerve to its ending on muscle fibres
- the nerve secretes acetylcholine (Ach)
- acts locally on the muscle fibre membrane to open Ach-gated cation channels
- allows large quantities of Na ions to diffuse to the interior of the muscle fibre membrane
- this action potential causes a local depolarisation, leading to the opening of voltage-gated Na channels, which initiates an action potential at the membrane
- the action potential depolarises the muscle membrane, causing the sarcoplasmic reticulum (SR) to release large quantities of Ca ions stored within the reticulum
- the Ca ions produce attractive forces to act between actin and myosin filaments, causing them to slide alongside each other leading to the contractile process
- after a fraction of a second, the Ca ions are pumped back into the SR by a Ca-membrane pump and remain stored in the SR until a new muscle action potential occurs
- the removal of Ca ions from the myofibrils causes muscle contraction to cease
What muscle adaptations are there to resistance training?
Muscle fibre hypertrophy
Neural activation
- recruit more motor units
- synchronous recruitment
What muscle adaptations are there to aerobic training?
- Muscle fibre type (more type 1 fibres)
- Capillary supply
- Myoglobin levels
- Mitochondrial function
- Storage of more glycogen and fat
- Adaptations of CV system
What are (6) adaptations due to immobilisation or stopping training?
- Rate of protein synthesis decreases
- Atrophy (loss of protein)
- Decreased neuromuscular activity
- Decreased flexibility
- Endurance decreases even after 2/52 inactivity
- Can recover if training resumed but the period of time is longer than that to lose adaptations
