W4 - Introduction to muscle and the lower limb Flashcards
What parts consitute the muscle-tendon unit (MTU)?
The muscle belly and tendon, that transmit force to the skeleton
What is the heirarchical strucutre of muscle?
- Muscle
- Fibre bundle
- Fascicle
- Fibre (cell)
- Myofibrils
- Filament
- Sarcomere
What are the three types of fascia fount in muscle?
- Epimysium
- Perimysium
- Endomysium
Which type of fascia surrounds a fibre bundle?
Epimysium
Which type of fascia surrounds a fascicle?
Perimysium
What type of fascia seprates muscle fibres (cells)?
Endomysium
What is the cell membrane of a muscle fibre (cell) called?
Sarcolemma
Describe the microscopic organisation of a muscle fibre
- Many nuclei
- Sarcoplasm - cytoplasm of the musclular cell, contataining glycogen and other fuels
- Mitochondria for cell metabolism
- Myofibril - contractile apparatus
- Membranous system - Sarcoplasmic retiulum and T tubule
What does the myofibril consist of?
Many sarcomeres
What is a sarcomere?
The contractile machinery of muscle
What is the Z line?
Stucture of the sarcomere
The point at which the thin actin fillaments join.
Found in the centre of the I band.
What is the I band?
Stucture of the sarcomere
The space not occuiped by the thick myosin fillament
What is the M line?
Stucture of the sarcomere
The point “line” the thick myosin fillaments connect. Positioned in the centre of A band/ H zone
What is the A band?
Stucture of the sarcomere
The space occupied by the thick myosin fillaments
What is the H zone?
The are not occupied by the thin actin fillament, it is occupied by the thick myosin fillament. Same area as M line. Central of A band.
What area is the sarcomere?
The sarcomere spans the area between both Z lines
Summarise the mechanism of contraction in the sliding fillament theory
- Action potential travels along the sarcolemma
- Action potential enters the cell at Transverse Tubule (TT) and triggers release of calcium into the cell
- Calcium binds to topomyosin, tropomyosin “unblocks” the actin fillaments
- Myosin heads bind with actin to form cross bridges and complete the power stroke - actin and myosin move closer together
- ATP fuels the pumping back of calcium into the SR which “re-sets” the system
How does the amount of force developed in a muscle relate to the number of cross bridges formed?
The amount of force developed in a muscle is directly propeortional to the number of cross bridges formed
How do sarcomeres want to change in length?
Sarcomeres always want to shorten - the external force dictates changes in muscle (or MTU) length
Describe the sliding fillament mechanic and the power stroke
- Lever movement of myosin head drive displacement of actin relative to myosin
- This also deforms internal elastic structures, developing force (~5 pN)
- Thick and thin fillaments “slide” relative to each other
What is the maximal force a muscle can generate?
40N cm2
How is muscle organised?
Hierarchically, allowing the mechanism of contraction when an action potential reaches the muscle
What are the 3 main mechanisms of contraction?
- Eccentric
- Concentric
- Isometric
What are girdles?
Parts of the appendicular skeleton that anchor the appendages to the axial skeleton
What are the three parts that make up the pelvic girdle?
2 Innominates (aka hip bones)
Sacrum
What are the three joints that the pelvic girdle is made from?
The pubic symphysis
The two sacroilliac joints
What type of joint is the Pubic symphysis?
Amphiarthroses
What type of joint are the sacroilliac joints?
Diarthorses
Gliding
What is an important feature of the pelvic girdles structure?
The pelvic girdle forms a fixed ring. It:
* Connects the trunk to the lower extremities
* Tranfers force
* Protects
What three bones make up the innominates?
- Illium - superior
- Ischium - “sitbones” - inferior/posterior
- Pubis inferior/anterior
Name important landmarks of the innominate
- Illiac crest
- Anterior superior illiac spine
- Anterior inferior illiac spine
- Posterior superior illiac spine
- Posterior inferior illiac spine
- Acetabulum
- Ischial tuberosity
Where is the hip joint located?
The hip joint joins the femoral head to the acetabulum of the innominate
What are the features of the hip joint?
- Ball and socket joint - articulation between the head of the femur and the acetabulum of the innominate
- Stable joint - Acetabulum forms a deep cup and there is a good bony fit
- Large loads - force transfer from the axial to the appendicular skeleton goes through the hip joint
What contributes to hip joint stability?
- Bony fit provides good stability, which is enhanced by the labrum that deepens the cup of the acetabulum
- Strong ligaments help to further stabilise the joint
- Muscles are less important for stability than at the shoulder and some other joints
What is the labrum?
Flat rim of fibrocartilage attached by its circumference to the margin of the acetabulum
It can be injured in sport
How does the labrum contribute to stability?
Helps to deepen the cup
What are the five ligaments key to stability of the hip joint?
- Transverse Acetabular ligament
- Ligamentum Teres/Teres femoris
- Iliofemoral ligament
- Pubofemoral ligament
- Ishiofemoral ligament
What is the Transverse Acetabular ligament?
What’s its function?
Flat band of fibres continuous with the labrum bridging the acetabular notch completing the acetabular ring
Prevents inferior displacement
What is the Ligamentum Teres/Teres Femoris
Connects the head of the femur to the acetabulum helping to reinforce the joint from within
What is the Illiofemoral ligament?
What is its function?
Anterior and blended with the capsule
Supports the hip in standing and resists: extension, internal and external rotation
What is the Pubofemoral ligament?
What is its function?
Medial anterior and lower portion of the capsule
Resists abduction, extension and external rotation
What is the Ischiofemoral ligament?
Posterior capsule
Resists adduction and internal rotation
Consider the hips mobility
How does it compare to the shoulder?
The hip has considerable range of motion in all three planes
The shoulder has greater ROM but lower stability
How many degrees of flexion does the hip joint have?
~130o
How many degrees of extension does the hip joint have?
~30o
How many degrees of abduction does the hip joint have?
~45o
How many degrees of adduction does the hip joint have?
~30o
How many degrees of lateral/external rotation does the hip joint have?
~50o
How many degrees of medial/internal rotation does the hip joint have?
~45o
The hip can also do circumduction
Circumduction is a combination of flexion, extension, abduction and adduction
What are the anterior muscles of the hip?
- Psoas Major (Illiopsoas)
- Illiacus (Illiopsoas)
- Pectineus
- Rectus Femoris
- Sartorius
What are the posterior muscles of the hip?
- Biceps femoris (Hamstrings)
- Semimembranosus (Hamstrings)
- Semitendinosus (Hamstrings)
- Gluteus maximus
- 6 deep external rotators
What are the medial muscles of the hip?
- Adductor brevis
- Adductor longus
- Adductor magnus
- Gracilis
What are the lateral muscles of the hip?
- Gluteus medius
- Glutues minimus
- Tensor fasciae latae
What actions are Psoas Major responsible for?
- Hip flexion (flexes the trunk if legs are fixed)
- Hip medial rotation
- Trunk side flexion
What action is Iliacus responsible for?
Hip flexion
What actions are Pectineus responsible for?
- Hip flexion
- Hip adduction
What actions are Rectus Femoris responsible for?
- Hip flexion
- Knee extension
Biarticular
What is a biarticular muscle?
A muscle that crosses two joints
What is the longest muscle in the body?
Sartorius
What actions are Satrorius responsible for?
- Hip flexion
- Hip lateral rotation
- Hip Abduction
Biarticular
