The muscular system is responsible for movement of the body, maintaining posture, joint stabilisation and heat production (Sendic, 2023).

Muscle Categories

Cardiac

Location -

. Heart

Structure - 

. Visceral pericardium

. Inner endocardium

. Tubular

. Myofibril Chains

. Repeating sarcomeres comprised of actin myofilaments

. Cardiomyocytes - Containing many mitochondria

. Sarcolemma - Intracellular + extracellular barrier

Function - Involuntary (ANS*)

. Rhythmic contractions - Sinoatrial node regulated

. Controls varying cardiac output, meeting peripheral tissue metabolic needs

(Cardiac output is determined by contractile forces of muscle cells and rhythmicity)

 (Sadava.D, et al., 2016)

Smooth

Location -

. Digestive tract 

. Urinary tract

. Respiratory system

. Vascular system

Structure -

. Non-striated,

. Thick + thin filament

. Homogenous

. Proteins (actin, myosin)

. Calcium containing sarcoplasmic reticulum

. Fusiform shape

Function - Involuntary (ANS*)

. Propulsion of food bolus

. Regulates vascular resistance - Blood flow + pressure

. Regulates urine flow

. Controls pregnancy contractions + sperm propulsion

. Regulation of bronchiole diameter

. Dilation + constriction of the pupil

(Hafen, 2023)

Skeletal

Location -

. Attached throughout the entire anatomy
. Connected to bone structures by tendons

Structure - 

. Striated sarcomere

. Multiple tissues - Lymphatics / epimysium / perimysium

. Blood vessels + contractile muscle fibres 

. Contractile elements - actin + myosin

Function - Voluntary (SNS*)

. Enables movement - excitation/contraction 

. Respiratory mechanics

. Provides structure for posture and balance

. Protects vital organs

. Storage of amino acids

. Maintains thermostasis

. Energy source during starvation

(Sadava.D, et al., 2016)

Sliding Filament Hypothesis

 

 

Muscle contraction occurs when contractile actin and myosin proteins interact. Within muscle cells, these protein molecules are organised into sarcomeres; actin (thin filaments) and myosin (thick filaments)(Krans, 2010). These filaments lie parallel to each other. Once a muscle contraction is triggered the actin and myosin filaments slide past each other, shortening the length of the sarcomere.

 

Antagonistic Pairs

Phases of Cycling

  • Flexion: upward rotation phase, the hamstrings (semimembranosus and biceps femoris) are the agonist that contract bending the knee to lift the pedal. During this phase, the quadriceps (vastus medialis, rectus femoris and vastus lateralis) are the antagonist, relaxing and lengthening to allow for this  movement.
  • Extension: Power phase, the quadriceps are the agonist that contract to extend the knee and push the pedal down. During this phase, the hamstrings are the antagonist that relax and lengthen.

Then during recovery, the flexion phase repeats. These phases overlap, allowing for smooth controlled cycling movements, protecting the knee joint by balancing contraction forces on either side of the knee  (Lee, 2021). 

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