The Musculoskeletal System

• The musculoskeletal system connects bones and muscle fibers through connective tissue like tendons and ligaments.
• Muscles support and move bones by contracting to move the bones around a joint.
• Cartilage prevents bone ends from rubbing together in order to allow motion

Muscular System Functions

• Body movement (locomotion)
• Posture Maintenance
• Respiratory function is enabled by the diaphragm and intercostal contractions
• Communication occurs through expression
• Organs and vessels vasoconstriction and constriction
• Heartbeat
• Body heat Production (Thermogenesis)

Muscle Properties

• Contractility denotes a muscle's ability to shorten and generate pulling force.
• Excitability is the capacity of a muscle to respond to a stimulus using ions
• Extensibility is the capacity of a muscle to be stretched back to its original length.
• Elasticity is the capacity of a muscle to recoil to its original resting length after being stretched.

Muscle Types

• Skeletal muscles are attached to bones and characterized by long fibers
• Skeletal muscles make up 40% of body weight.
• Skeletal Muscle is responsible for the movement, expressions, posture, and respiratory function of the body
• Skeletal muscles are voluntary in action, and striated, multinucleate
• Smooth muscles are in the walls of hollow organs, blood vessels, iris, and glands
• Smooth Muscle functions to propel urine, and regulate pupils and blood flow
• Smooth Muscles are involuntary by the endocrine system and autonomic nervous systems
• Smooth muscles are also autorhythmic in some areas, non-striated, and mononucleate
• Cardiac muscle is responsible for heart movement/function
• Cardiac muscle is involuntary by the endocrine system and autonomic nervous system
• Cardiac Muscle is striated and mononucleate

Skeletal Muscle Keypoints

• Most skeletal muscles connect to at least two bones
• Muscles cross past the joint connected to the bone
• Muscles produce movement by generating tension

Origins Vs Insertions

• Origin refers to the muscle attachment point that moves the least during contraction, usually the proximal attachment.
• Insertion is the muscle attachment that moves that most during contraction, usually the distal attachment.

Types of Muscle Attachment

• Indirect muscle attachment is the most common, muscles attach to the periosteum.
• In indirect attachment, the epimysium extends beyond the muscle to form a tendon.
• Direct muscle attachment involves the epimysium adhering or fusing directly to the periosteum.

Skeletal Muscle Organisation

• Muscles are surrounded by epimysium
• Fascicles (bundles of muscle fibers) are surrounded by perimysium.
• Muscle fibers are surrounded by endomysium.
• Myofibrils are surrounded by the sarcolemma (cell membrane).
• Myofilaments comprise mainly actin & myosin.

Connective Tissue

• Epimysium: A thick layer of connective tissue that surrounds the entire muscle.
• Perimysium: Connective tissue that surrounds groups of muscle fibers (fascicles).
• Endomysium: A loose connective tissue surrounding individual muscle fibers.
• Collagen fibers from all three layers can create a flattened tendon-like structure called an aponeurosis

Classifying Skeletal Muscle Fibres

• Fibre classification does not apply to the whole muscle, but to individual fibers; muscles are mixed and can change
• Muscle fibers vary on whether they use an aerobic or anerobic pathway
• Muscle fibres depend on the amount of myoglobin they have to store oxygen (high/low)
• Muscles fibre efficiency is determined by how fast/slow they can decompose ATP with ATPase

Muscle Fibre types

• Slow-twitch fatigue-resistant muscle fibers are slow/oxidative/red.
• Slow muscle fibres have endurance capabilities
• Slow muscle fibres deliver strong, prolonged contractions.
• Slow fibre ATPase enzymes, abundance of mitochondria
• Slow fibres move slowly and also have slow contraction
• Slow muscle fibre contains abundant myoglobin, giving muscles a red color.
• Fast-twitch fatigable muscle fibers are fast/glycolytic/white.
• Fast twitch fibres are designed for short duration. high intensity contractions.
• Fast fibres fatigue rapidly and also contract for limited periods
• These fibres contain small amounts of myoglobin and white pigments
• Fast Muscle fibres are best suited for short bursts with high intensity

Joints

• They are the functional unit of the musculoskeletal system.
• Three main joint types are: fibrous, cartilaginous, and synovial.
• The degrees of mobility vary in each joint type.

Fibrous Joints

• Fibrous Joints contain connective tissue and cannot move
• Three variations of fibrous joints are: sutures, syndesmosis, gomphosis
• These types of joints contain no cavity, and are attached with connective tissue
• The sutures in skull bones connect by suture joints
• Sutures in fetal skulls are wide to allow a slight movement during child brith

Cartilaginous Joints

• Cartilaginous Joints connect by cartilage entirely
• These Joints can only move very slightly
• There is more movement compared to fibrous joints, and less compared to synovial joints
• There are two types of cartilaginous joints: Synchondroses and Symphyses
• Synchondroses uses hyaline cartilage (smooth/glassy feeling)
• Synchondroses is seen at either the e.g., dia/epiphyseal or the first sternocostal joint
• Symphyses uses fibrocartilage and is seen at e.g., pubic bones, vertebrae

Synovial Joints

• Synovial Joints have space between the adjoining bones.
• The cavity in Synovial Joints has synovial fluid
• the fluid cushions and protects the joint allowing it to move
• These Joints give greatest range of motion, however they are the weakest joints

Synovial Joints Elements

• Synovial Joints are made up of hyaline cartilage, tough fibrous capsule and synovial fluid
• Hyaline cartilage works to reduce friction
• Fibrous Joint capsules protect damage to the surrounding area
• Synovial membrane produces synovial fluid to lubricate the joint

Roles of Synovial Joints

• Bone Ends are covered in smooth hyaline (cartilage)
• Synovial fluid Cushions excessive bone pressure
• Joints allow the joint to move smoothly and without pain.
• They use 70% water
• They undergo compression under pressure and return back to their original structure when force is released
• The Joints are also known as articular cartilage

More About Synovial Fluid

• It is a viscous, yellowish translucent liquid, produced by the synovial membrane (synovium).
• Synovial fluid lubricates and reduces friction, therefore enabling bones to slide smoothly
• It resists compression, pulling forces and stress forces
• It is a non-Newtonian fluid and grows more viscous when the force is applied

Meniscus

• The articular cartilage in healthy synovial joints does not touch - separated bysynovial fluid
• In some joints there is a shock absorber made of cartilage called the meniscus (pl. menisci).

Cartilage

• They come in three forms which all provide support, flexibility and resistance to compression
  • E.g: hyaline, supports nasal/auditory/respiratory function
  • E.g: Elastic, the Eustachian tubes, epiglottis, and ear lobes
  • E.g: Fibrocartilage, in public symphysis

Tendons

• Tendons are made of fibrous connective tissue that connects muscles to bone
• Tendons can be used to connect muscles to additional parts of the body, such as the eyeball
• It operates by working to move or affect a structures like joints
• Their collagen fibres work to generally run aligned to long axis
• Tendons have high resistance to extension, however they remain relativley flexible

Ligaments

• A bone is connected to bone by a tissue called a ligament
• Ligaments exist to hold secure bone to joint/cartilage
• ligaments themselves are slightly stretchy, and allow slightly movement

Ligaments Composition

• Composed of primarily collagenous fibres
  • Fibre Spindle-shaped cells -- Ground A little ground substance (chondroitin sulphate
• There are two major types: -- White ligament with collegenous fibres -Yellow elastic tough ligaments (fibrocytes)

Bursar

• Bursae protect tendons and muscles that cross a bone
• Bursae contain lubricating liquid that acts as cushions.