LO5 of Unit 1 – Muscular System
Muscular System
Learning outcomes
By the end of this section, you will be able to:
5.1 Â Â Â Â Â Describe the characteristics and functions of the three types of muscle tissue
5.2 Â Â Â Â Â Describe the basic structure of skeletal muscle
5.3 Â Â Â Â Â Identify and locate the anterior and posterior skeletal muscles
5.4 Â Â Â Â Â Describe the structure and function of the pelvic floor muscles
5.5 Â Â Â Â Â Describe different types of muscle action
5.6 Â Â Â Â Â Identify joint actions brought about by specific muscle group contractions
5.7 Â Â Â Â Â Describe skeletal muscle fibre types and their characteristics
5.1
Types of muscle tissue
There are more than 600 muscles in the body, and they come in all shapes and sizes, performing many different functions. The smallest muscle called the stapedius is found in the ear (2mm long) and the largest is the gluteus maximus, located in the bottom.
Our muscles do everything from pumping blood to moving food through the intestines, helping you run, jump and lift heavy objects. Many muscles function at a subconscious level, performing functions without you thinking about them, such as those that control the heart beating or the movement of digested foodstuffs through the intestines.
There are three types of muscles tissue:
- Smooth
- Cardiac
- Skeletal
Smooth
Located in various bodies, such as the blood vessels, digestive tract, airways, lungs and reproductive system.
Smooth-looking in appearance. It lacks myofibrils and sarcomeres, and actin and myosin are scattered.
Non-striated
Contracts in a wave-like fashion called peristalsis propelling materials such as blood along the vessels and food along the digestive tract.
Is involuntarily in its action, meaning it requires no conscious thought to activate.
[IMAGE 1]
Example of smooth muscle
Cardiac
- Found only in the heart
- Striated (striped with light and dark areas) in appearance, with organized myofibrils and sarcomeres, are similar to skeletal muscle.
- Contracts without neural stimulation (i.e. is involuntary). The heart has its pacemaker.
- Contains a large number of mitochondria and abundant stores of myoglobin.
- Cardiac muscle cells are almost dependent on aerobic metabolism to maintain contraction.
- Does not readily fatigue.
[IMAGE 2]
Example of cardiac muscle
Skeletal
- Striated in appearance
- Skeletal muscles only shorten in one direction.
- Are mainly voluntarily (consciously organized by the brain, such as when jumping or lifting)
- Fibres have different contraction (twitch) speeds operating both aerobically and anaerobically.
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Skeletal muscle performs the following six functions:
- Produces skeletal movement
- Maintains posture and body position
- Supports soft tissue (organs)
- Maintains body temperature
- Stores nutrient reserves
- Guards entrances and exits (urinary tract)
[IMAGE 3]
Example of skeletal muscle
5.2
The basic structure of skeletal muscle
Epimysium
A dense layer of connective tissue that surrounds a skeletal muscle.
Fascicle
A single bundle of muscle fibres. Many fascicles make up a muscle.
Tendon
Strap or cord-like collagenous structure that attaches muscle to bone.
Perimysium
The connective tissue that divides the skeletal muscle into a series of compartments.
Each compartment contains a bundle of muscle fibres.
Endomysium
The connective tissue that surrounds the individual muscle fibre.
Muscle fibre
An individual muscle cell.
Myofibril
Long cylindrical threads composed of numerous myofilaments.
[IMAGE 4]
Global structure of muscle
5.3
Skeletal muscle names and locations
Anterior view
Deltoids anterior      Â
Pectoralis major
Biceps brachii           Â
Abdominal muscle group
- Rectus Abdominis    Â
- External oblique (Not in picture, located posterior to the external oblique)
- Internal oblique
Quadricep muscle group
- Rectus femoris         Â
- Vastus intermedius  Â
- Not in view, located posterior to the rectus femoris
- Vastus lateralis        Â
- Vastus medialis        Â
Adductor longus
Tibialis anterior
[IMAGE 5]
Anterior view of muscles
Posterior view
Deltoid posterior          Â
Trapezius (upper, mid & lower)
Rhomboids     (upper & lower)
Not in view, located anterior to the trapezius
Triceps brachii
Latissimus dorsi        Â
Gluteus medius
Gluteus maximus     Â
Hamstring muscle group
Biceps femoris           Â
Semitendinosus                    Â
Semimembranosus  Â
Adductor Magnus
Gastrocnemius (Not in view, located anterior to the gastrocnemius)
Soleus
[IMAGE 6]
Posterior view of muscles
5.4
Function of the pelvic floor
The pelvic floor or pelvic diaphragm comprises a small group of muscles and connective tissue underneath the pelvis. These muscles function like a muscular sling, spanning from the pubis toward the coccyx.
The pelvic floor comprises several muscles and is organized into superficial and deep muscle layers.
- Superficial layer – The superficial muscle layer and the muscles relevant to the anal canal function are the external anal sphincter, perineal body and possibly the puboperineal muscles.
- Deep layer – The deep pelvic floor muscles consist of pubococcygeus, iliococcygeus, coccygeus and puborectalis muscles.
Function
The pelvic floor muscles function to support the pelvic organs such as the bladder and the intestines, which are essential for maintaining continence. They can become damaged in women during pregnancy and birth.
- To support the organs of the pelvis (bladder, bowel, etc) and the abdominal contents
- Continence mechanism to the urethral, anal and vaginal orifices (in females)
- To assist in stabilisation of the spine by maintaining intra-abdominal pressure
[IMAGE 7]
Pelvic floor labelled diagram
5.5
Muscle roles and types of muscle contractions
Muscle roles
Muscles have been classified according to their role during exercise. There are four different roles that a muscle can fulfil during movement. These roles are:
Prime mover — the primary muscle contracting to move the joint.
Antagonist – the opposing muscle to the prime mover.
Fixator – holds other joints still (origin end) to allow the prime mover muscle to function.
Synergist – works in synergy with the prime mover to stabilize the joint’s movement.
[IMAGE 8]
Muscle roles
Example
When performing a dumbbell bicep curl the prime mover would be the biceps brachii muscle, and the antagonist is the triceps brachii muscle. The synergist muscles are the brachioradialis and brachialis, which help the biceps create the movement and stabilize the elbow joint. The rotator cuff muscles stabilize or fixate the shoulder joint to allow the prime mover to function at the elbow joint.
[IMAGE 9 / Video 1]
Example
Types of muscle contractions
Isometric – muscle contracting (under tension) but no joint movement; can elevate blood pressure
Isotonic – changes in length, joint movement, shortening and lengthening,
Concentric – muscle is shortening under tension during the lifting phase of the movement, occurs during acceleration movements
Eccentric – muscle is lengthening under tension, occurs during deceleration movements
Example: contraction types in the squat exercise
The quadriceps muscles in the thigh contract eccentrically during the movement’s downward phase.
If there is a pause at the bottom of the squat and no movement occurs, the quadriceps muscles are contracting isometrically.
During the squat movement’s upward phase, the quadriceps are contracting concentrically.
[Video 2]
Example
5.6
Muscle actions
Muscles are attached to bones via their tendon(s). Understanding a muscle’s function and moving the bones makes it useful to know the muscle’s location and attachment points. A muscle’s start point is referred to as the ‘origin’ and is usually considered the most proximal end, relative to the axial skeleton. On the other hand, the endpoint is the muscle’s ‘insertion’ point and is mostly the distal attachment point close to the axial skeleton.
Muscle: Biceps Brachii
Location: Upper anterior arm
Muscle origin: Scapula
Muscle insertion: Radius
Joint action(s):
- Flexion of the elbow
- Flexion of the shoulder
- Supination of the forearm
[IMAGE 10]
Muscle: Triceps Brachii
Location: Upper posterior arm
Muscle origin: Humerus and scapula
Muscle insertion: Ulna
Joint action(s):
- Extension of the elbow
- Extension of the shoulder
[IMAGE 11]
Muscle: Deltoid
Location: lateral aspect of the shoulder area
Muscle origin: Scapula and clavicle
Muscle insertion: Humerus
Joint action(s):
- Shoulder abduction
- Shoulder flexion
- Shoulder extension
- Shoulder horizontal flexion
- Shoulder horizontal extension
[IMAGE 12]
Muscle: Latissimus Dorsi
Location: Large, flat muscle on the back
Muscle origin: Lower 6 thoracic, lumbar vertebra and Ilium
Muscle insertion: Humerus
Joint action(s):
- Shoulder extension
- Shoulder adduction
[IMAGE 13]
Muscle: Trapezius
Location: Large superficial back muscle
Muscle origin: Base of skull, cervical and thoracic vertebrae
Muscle insertion: Clavicle and scapula
Joint action(s):
- Shoulder girdle elevation
- Scapula retraction
- Shoulder girdle depression
[IMAGE 14]
Muscle: Rhomboids
Location: Located on your upper back underneath the trapezius muscle
Muscle origin: Upper thoracic vertebra
Muscle insertion: Scapula
Joint action(s):
- Scapula retraction
[IMAGE 15]
Muscle: Erector Spinae (not all muscles are shown)
Location: Located on your upper back underneath the trapezius muscle
Muscle origin: Sacrum, Ilium, costals and spine
Muscle insertion: Costals, vertebrae and occipital bone
Joint action(s):
- Extends the spine
[IMAGE 16]
Muscle: Pectoralis Major
Location: Extends across the upper part of the chest
Muscle origin: Sternum and clavicle
Muscle insertion: Humerus
Joint action(s):
- Shoulder horizontal flexion
- Shoulder adduction
- Shoulder extension from full flexion
- Shoulder flexion from full extension
[IMAGE 17]
Muscle: Rectus abdominis
Location: Located in the front of the trunk
Muscle origin: Pubis
Muscle insertion: Sternum
Joint action(s):
- Flexion of the spine
- Lateral flexion of the spine
[IMAGE 18]
Muscle: Internal Oblique
Location: Located on the lateral side of the abdomen deep to the external oblique
Muscle origin: Ilium, costals
Muscle insertion: Pubis, linea alba
Joint action(s):
- Rotation the spine to the same side (i.e. right internal oblique rotates the trunk to the right)
- Lateral flexion of the spine to the same side
[IMAGE 19]
Muscle: External Oblique
Location: Located on the lateral side of the abdomen superficial to the internal oblique
Muscle origin: Costals
Muscle insertion: Ilium, pubis
Joint action(s):
- Rotation the spine to the opposite side (i.e. right external oblique rotates the trunk to the left)
- Lateral flexion of the spine to the same side
[IMAGE 20]
Muscle: Transversus Abdominis
Location: A broad, muscular sheet found on the lateral sides of the abdominal wall deep to the external oblique
Muscle origin: Costal margin, lumbar fascia, anterior two-thirds of iliac crest and lateral half of inguinal ligament
Muscle insertion: Aponeurosis of the posterior and anterior rectus sheath
Joint action(s):
Plays a significant role in increasing the intra- abdominal pressure
[IMAGE 21]
Muscle: Transversus Abdominis
Location: A broad, muscular sheet found on the lateral sides of the abdominal wall deep to the external oblique
Muscle origin: Costal margin, lumbar fascia, anterior two-thirds of iliac crest and lateral half of inguinal ligament
Muscle insertion: Aponeurosis of the posterior and anterior rectus sheath
Joint action(s):
Plays a significant role in increasing the intra- abdominal pressure
[IMAGE 22]
Muscle: Gluteus Maximus
Location: Located on the pelvis (buttocks)
Muscle origin: Ilium, sacrum
Muscle insertion: Femur and ilium and ilio- tibial (IT) band
Joint action(s):
- Hip extension
- Hip lateral rotation
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[IMAGE 23]
Muscle: Gluteus Medius
Location: Located on the lateral pelvis
Muscle origin: Ilium
Muscle insertion: Femur
Joint action(s):
- Hip abduction
[IMAGE 24]
Muscle: Gluteus Medius
Location: Located on the lateral pelvis
Muscle origin: Ilium
Muscle insertion: Femur
Joint action(s):
- Hip abduction
[IMAGE 25]
Muscle: Iliopsoas (consisting of two muscles)
Location: Located toward the front of the inner hip
Muscle origin: Lumbar spine and Ilium
Muscle insertion: Femur
Joint action(s):
- Hip flexion
[IMAGE 26]
Muscle: Adductor Longus
Location: Located in the inner thigh
Muscle origin: Pubis
Muscle insertion: Femur
Joint action(s):
- Hip adduction
- Hip flexion
[IMAGE 27]
Muscle: Adductor Magnus
Location: Located in the inner thigh
Muscle origin: Ischium
Muscle insertion: Femur
Joint action(s):
- Hip adduction
- Hip extension
[IMAGE 28]
Muscle: Biceps femoris (part of the hamstring muscle group)
Location: Located in the posterior thigh (the most lateral of three hamstring muscles)
Muscle origin: Ischium and femur
Muscle insertion: Lateral tibia and fibula head
Joint action(s):
- Hip Extension
- Knee flexion
[IMAGE 29]
Muscle: Semimembranosus (part of the hamstring muscle group)
Location: Located in the posterior thigh
Muscle origin: Ischium
Muscle insertion: Tibia (medial side)
Joint action(s):
- Hip extension
- Knee flexion
[IMAGE 30]
Muscle: Semitendinosus (part of the hamstring muscle group)
Location: Located in the posterior thigh
Muscle origin: Ischium
Muscle insertion: Tibia (medial side)
Joint action(s):
- Hip extension
- Knee flexion
[IMAGE 31]
Muscle: Rectus femoris (part of the quadriceps muscles)
Location: Located in the anterior thigh
Muscle origin: Ilium
Muscle insertion: Tibia tuberosity via the patella tendon
Joint action(s):
- Hip flexion
- Knee extension
[IMAGE 32]
Muscle: Vastus Medialis (part of the quadriceps muscles)
Location: Located in the anterior thigh (medial)
Muscle origin: Femur
Muscle insertion: Tibia tuberosity via the patella tendon
Joint action(s):
- Hip flexion
- Knee extension
[IMAGE 33]
Muscle: Vastus Intermedius (part of the quadriceps muscles)
Location: Located in the anterior thigh (deep to rectus femoris)
Muscle origin: Femur
Muscle insertion: Tibia tuberosity via the patella tendon
Joint action(s):
- Hip flexion
- Knee extension
[IMAGE 34]
Muscle: Vastus Lateralis (part of the quadriceps muscles)
Location: Located in the anterior thigh (lateral)
Muscle origin: Femur
Muscle insertion: Tibia tuberosity via the patella tendon
Joint action(s):
- Hip flexion
- Knee extension
[IMAGE 35]
Muscle: Soleus
Location: Located in the posterior lower leg deep to gastrocnemius
Muscle origin: Tibia and fibula
Muscle insertion: Calcaneus (heel bone)
Joint action(s):
- Ankle plantarflexion
[IMAGE 36]
Muscle: Gastrocnemius
Location: Located in the posterior lower leg deep to gastrocnemius
Muscle origin: Femur
Muscle insertion: Calcaneus (heel bone)
Joint action(s):
- Ankle plantarflexion
- Knee flexion
[IMAGE 37]
5.7
Muscle fibre types
Not all muscle fibres are alike. There are three major types of fibres based on their twitch (a period of contraction followed by a period of relaxation), characteristics or speed of contraction: The three categories are:
- Slow-twitch
- Intermediate twitch
- Fast-twitch
Fibre type characteristics
Genetics determines the number of each fibre type. A preponderance of one or the other fibre types in muscles may improve performance in certain sports activities. For example, having a high number of fast-twitch fibres could make a faster sprinter, or an increased number of slow-twitch fibres might make an athlete better at endurance activities. However, many factors lead to elite performances, but having genetics on your side is a good start.