Muscle Contraction Flashcards
Contraction model
-occurs due to shortening within the muscles
Actin and myosin
-contractile molecules that inhibit the process of shortening
Sliding filament model
Actin and myosin slide or move across each other forming a more compact unit
Cell structure
- cellular level
- sub cellular level
- molecular level
Cellular level
Cell structures:
- cell membrane: sarcolemma
- cell nuclei: many present, just under the membrane
- cell shape: long, threadlike, referred to as a fiber
Sub cellular level
- there are many specialized organelles present
- sarcoplasmic reticulum and myofibrils
Sub cellular level
Sarcoplasmic reticulum
- Specialized endoplasmic reticulum
- stores calcium needed for contraction
Sub cellular level
Myofibrils
- cylinder shaped organelles passing through cell length
- composed of myofilaments
Molecular level
-large molecular structures are present in the myofibrils that are responsible for the contraction process: actin and myosin
Molecular level
Actin myofilaments
- thin filaments composed of 3 parts: actin protein molecules, tropomyosin, troponin
- anchored or attached to Z lines (disks)
Molecular level
Myosin myofilaments
-thick filaments composed of long rods with globular heads
Molecular level
Sarcomere
- structural unit of myofibrils
- composed of overlapping myosin and actin myofilaments inside Z-lines
- many per myofibril; forming the contraction unit
- contains everything from z-disk to z-disk
Events of contraction
nerve stimulus, calcium release, calcium action
Events of contraction
nerve stimulus
-nerve impulse (action potential) passes along the muscle cell membrane to the sarcoplasmic reticulum
Events of contration
calcium release
-calcium is released from storage and diffuses into the cytoplasm and myofibrils
Events of contraction
calcium action
- calcium binds to the troponin molecule on actin myofilaments
- exposes the active sites, allowing interaction between actin and myosin
Actin-myosin interaction a
- linkages or crossbridges are formed between actin and myosin
- the myosin head moves and pulls on the actin
Actin-myosin interaction b
- the myosin head releases from one site on actin, resets and pulls on the actin at another site
- the process is repeated many times very rapidly, moving actin across the myosin
- this requires many atp molecules
Actin-myosin interaction c
- myosin “walking” down actin causes shortening of the sarcomere units
- as each sarcomere contracts, a myofibril shortens
Actin-myosin interaction d
-contraction ofthe myofibrils causes shortening of a whole muscle cell
Actin-myosin interaction e
-contraction of many muscle cells allows a whole muscle to move a body part
Whole muscle contraction
contraction strength
- in a whole muscle requires many motor units to be activated
- a motor unit is a nerve cell and all the muscle cells that it controls
- the ratio may vary from 1:50 to 1:500 in larger muscles
Whole muscle contraction
energy requirements
- many atp molecules are needed for formation of actin and myosin crossbridges during the contraction process
- main source of atp is from glucose molecules
- either aerobic or anaerobic metabolism of glucose produces the needed atp supplies during exercise
absolute strength
-the maximum force exerted with the whole body, or part of the body, irrespective of body size or muscle size
relative strength
-maximum force exerted in relation to body weight or muscle size
muscle cross-sectional area (MSCA)
-measure by taking the girth of the forearm
summation
-involves increasing the force of contration of the muscle fibers within the muscle
recruitment
-refers to increase in the number of muscle fibers contracting
multiple-motor unit summation
-relationship between increased stimulus strength and increase in the number of contracting motor units
treppe (staircase effect)
- occurs in muscles that have been rested for long periods and results in each slow contraction being stronger and stronger for a short period as the muscle warms up
- it is likely that this happens as more calcium becomes available to sustain the contraction process
Hip Psoas major (iliopsoas) 1
Origin: T12, L1-5 and illiac fossa
Insertion: lesser trochanter of femur
Action: flexes thigh
Hip
iliacus (iliopsoas) 2
Action: flexes and rotates thigh (medially)
Hip
gluteus maximus 3
Origin:outer iliac blade, iliac crest, sacrum, coccyx
Insertion: gluteal tuberosity of femur
Action: extends, abducts, rotates thigh laterally
Hip
gluteus medius and minimus 4
Action: abduct thigh and rotate it medially
Hip
tensor fascia latae 9
Action: flexes, abducts and rotates thigh
Thigh (quad group)
rectus femoris 11a
Origin: anterior inferior iliac spine
Insertion: tibial tuberosity by the patellar ligament
Action: flexes thigh
Thigh (quad group)
vastus lateralis 11c
Action: extend leg at knee
Thigh (quad group)
vastus medialis 11b
Action: extend leg at knee
Thigh (quad group)
vastus intermedius 11d
Action: extend leg at knee
Thigh
adductor longus 13
Action: adducts, flexes and rotates thigh
Thigh
sartorius 10
Action: flexes, rotates thigh, flexes leg
Thigh
gracilis 15
Action: adducts thigh; flexes leg
Thigh (hamstring group)
biceps femoris 18
Origin: ischial tuberosity, linea aspera of femur
Insertion: head of fibula, lateral condyle of tibia
Action: extend thigh; flexes leg
Thigh (hamstring group)
semitendinousus 16
Action: extend thigh; flexes leg
Thigh (hamstring group)
semimembranosus 17
Action: extend thigh; flexes leg
Leg
tibialis anterior 19
Origin: tibia, interosseous membrane
Insertion: metatarsal 1 and cuniform 1
Action: dorsiflexes and inverts foot
Leg
extensor digitorum 21
Action: extends toes
Leg
fibularis longus 22
Action: plantar flexes and everts foot
Leg
fibularis brevis 23
Action: plantar flexes and everts foot
Leg
gastrocnemius 24ab
Origin: condyles of femur
Insertion:calcaneus by the calcaneal tendon
Action: flexes leg; plantar flexes foot
Leg
soleus 24e
Action: plantar flexes foot
