Skeletal & Muscular Systems

• Higher animals use skeletons and muscles to work together for locomotion.
• Muscles attach to the skeleton to form either a skeletal muscles system or musculo-skeletal system.
• The nervous system coordinates both systems.
• Animal bodies have a framework known as the skeleton.
• A skeletal system provides shape, support, protection, and movement power.

Endoskeleton

• Lyes inside the body and is found in some invertebrates like sponges and starfish.
• It's the complex skeleton of vertebrates
• Internal framework composed of bone and cartilage.
• Cartilage and bone articulate via joints, allowing movement by muscle contraction.
• The endoskeleton of vertebrates grows in correlation with the animal.

Human Skeleton Introduction

• Human endoskeleton has 206 bones connected by joints

Composition of Human Skeleton

Bones

• Rigid connective tissue forming the skeleton and limbs.
• Bone cells secrete a matrix with a collagen network.
• Bone cells include osteoblasts, osteocytes, osteogenic cells, and osteoclasts.

Ossification Requirements

• Hardening of bone matrix by osteoblast activity and calcium phosphate deposition (ossification or calcification).
• Requires vitamin D for calcium absorption.
• Milk provides proteins and minerals for hard, elastic bones.

Gross Anatomy of Bones

• Long bones contain a diaphysis and epiphysis.
• Diaphysis Description: Hollow, tubular and shaft between bone ends, holds the medullary cavity, which is filled with yellow marrow in adults.
• Diaphysis outer walls (cortex or cortical bone) consist of dense, hard compact bone which is a type of osseous tissue.
• Epiphysis Description: Wider section at bone ends, contains spongy bone.
• Epiphysis Description: Has red bone marrow in some long bones.
• Metaphysis Description: Site of growth with the epiphyseal plate when young and epiphyseal line when old.

Bone Tissue Structure

• Compact and spongy bone differ in density or packing
• Osteoblasts create bone.
• Osteoclasts break down bone.
• Osteocytes are mature bone cells.
• Equilibrium between osteoblasts and osteoclasts maintains bone tissue.

Compact Bone

• Made of packed osteons (Haversian systems) with a central osteonic (haversian) canal.
• Canal surrounded by concentric matrix rings (lamellae).
• Bone cells (osteocytes) reside in lacunae between matrix rings.
• Canaliculi (small channels) radiate from lacunae to the osteonic canal provide matrix passageways.
• Blood vessels interconnect osteonic canals via surface-connecting perforating canals.

Spongy (Cancellous) Bone

• It's lighter and less dense than compact bone.
• Consists of trabeculae (plates and bars) adjacent to cavities containing bone marrow.
• Canaliculi connect to adjacent cavities instead of a central canal for blood supply.

Bone Cells

• Bone cells make up less than 2% of bone mass, but are essential for bone function.
• Osteogenic cells develop into osteoblasts inside the endosteum.
• Osteoblasts formation inside the endosteum.
• Osteocytes Maintain mineral concentration of matrix while inside the matrix.
• Osteoclasts perform bone resorption along the endosteum.

Cartilage

• Flexible connective tissue that stands apart from bone.
• Primary cell type is chondrocytes instead of osteocytes.
• Chondrocytes comes from chondroblast and then produce the collagen extracellular matrix (ECM) and get trapped in it.
• Chondrocytes are in lacunae and obtain nutrients via diffusion, lacking blood vessels (avascular).
• Slow healing of cartilage is caused by the absence of proper blood supply.
• The cartilage's base substance contains chondroitin sulfate.
• Cartilage organization is less ordered than bone.
• The fibrous sheath that covers cartilage is called the perichondrium.
• Cartilage grows slowly through cell division, not size or mass increase.
• Articular cartilage relies on ECM's proteoglycan and collagen composition.
• Cartilage matrix remodeling responds to its tensile and compressive forces

Types of Cartilage

• Hyaline cartilage, fibrocartilage, and elastic cartilage are major types.

Hyaline Cartilage

• It's the most common cartilage type, is found on articular surfaces, rib tips, trachea rings, and skull parts.
• Predominantly collagenous, with a glassy texture.
• Bones Initially form as ossifying hyaline cartilage in embryos.
• Hyaline Cartilage is covered by perichondrium.
• Hyaline Cartilage does not have any nerves or blood vessels
• It's cells are rounded grouped in granular/homogeneous matrix
• They consist of translucent protoplasm

Fibrocartilage

• Contains lots of collagen fibers (types I and II).
• Grades into dense tendon and ligament tissue.
• White fibrocartilage combines fibrous and cartilaginous tissues.
• Flexibility and toughness are from fibrous tissue, elasticity from cartilaginous tissue.
• Unique cartilage with both type I and type II collagen
• Found in public symphysis, intervertebral discs, menisci, and the temporomandibular joint.

Elastic Cartilage

• It consists of elastin and collagen fibers network
• The main protein is elastin.
• Histologically similar to hyaline cartilage but contains many yellow elastic fibers in a matrix
• Great flexibility to withstand bending.
• Found in the epiglottis in the larynx.

Division of Human Skeleton

• Axial and appendicular skeletons exist in humans.

Axial Skeleton

• Protective in nature, containing skull, vertebral column, and rib cage bones.

Skull

• Cranium protects brain.
• It consists of 8 bones: occipital, two temporals, two parietals, sphenoid, ethmoid, and frontal bones.
• Consists of 14 facial bones: vomer, two inferior nasal conchae, two nasals, two maxillae, mandible, two palatines, two zygomatics, and two lacrimals.
• There are 6 auditory ossicles (malleus, incus, stapes) in each ear which transfers air vibrations into the inner ear as sound.
• Hyoid bone Description: Is a U-shaped throat bone is a U-shaped and provides tongue/oral cavity muscle attachments.

Vertebral Column

• Spine of 33 bones (26 after fusion) that protects the spinal cord.
• 7 cervical vertebrae are found in the neck.
• 12 thoracic vertebrae articulate in the chest.
• 5 lumbar vertebrae are the vertebrae in the lower back.
• 5 sacral vertebrae fuse to form the sacrum, articulating with the pelvic girdle.
• 4 coccygeal vertebrae are found in the tail.
• The atlas and axis vertebrae (top two cervicals) permit skull movement.
• Cartilaginous discs support/protect the vertebrae.

Ribcage

• Contains 12 pairs of bones.
• Protects the chest cavity, heart, and lungs.
• Semicircular bones connected to vertebrae dorsally, sternum ventrally.
• There are a total of 7 pairs of true ribs where costal cartilages join to the sternum anteriorly.
• There are a total of 5 pairs of false ribs, this means, the costal cartilages do not articulate directly with the sternum.
• The floating ribs are not connected to the sternum.

Appendicular Skeleton

• It consists of 126 bones, including arms, legs, and pectoral and pelvic girdles.

Pectoral Girdle

• Shoulder region, consists of the scapula and clavicle.

Upper Limb

• Humerus joints to the scapula by ball and socket joint.
• It consists of 30 bones (60 in both upper limbs).
• Radius and ulna are the bones below the humerus.
• Description: There are 8 carpals, 5 metacarpals, and 14 phalanges are small bones arranged in 5 rows.

Pelvic Girdle

• Hip bone consists of the ilium, ischium, and pubic bone.
• Coxal bone (hip bone) is a pair of bones joined to the sacrum of the vertebral column.
• Ilium Description: The largest part of the coxal bone, forming the upper part with a fan-like structure, and attaches to the vertebral column sacrum.
• Ischium Description: The posterior part of the pelvic girdle below the ilium providing support while sitting.
• Pubis Description: Lower anterior part of the pelvic girdle.
• Description: Pubic symphysis- The joint between the two hip bones in the middle portion containing fibrous cartilage.
• Hip joint's main role is to support body weight and facilitate force transmission from the axial skeleton to lower parts.

Lower Limb

• Consist of 30 bones (60 in both lower limbs).
• Femur Description: Largest bone in the leg which is connected to the pelvis.
• There are tibia and fibula, 7 tarsals, 5 metatarsals, and 14 phalanges below.

Joints

• Connect bones in the skeletal system.
• Can be classified on tissue type or movement degree.

Classification by Tissue Type

• Fibrous joints connected by fibrous tissue
• Cartilaginous joint connected by cartilage
• Synovial Joint articulating surfaces enclosed within a fluid-filled joint capsule.

Classification by Movement Degree

• Synarthrosis Joint, immovable
• Amphiarthrosis Joint, slightly movable.
• Diarthrosis Joint, freely movable.

Fibrous Joints

• Bones linked by a tough, fibrous tissue.
• These joints typically require strength and stability over range of movement.
• Includes sutures, gomphoses, and syndesmose.

Sutures

• Immovable joints (synarthrosis) between flat, plate-like skull bones.
• Limited movement until ~20 years, become fixed and immobile after that.
• These joints allow skull deformation during birth

Gomphoses

• Immovable joints where teeth articulate with sockets in the maxilla (upper teeth) or mandible (lower teeth).
• The tooth is bound into its socket by the solid periodontal ligament.

Syndesmose

• Slightly movable joints (amphiarthroses) made of bones with an interosseous membrane.
• The middle radioulnar joint and middle tibiofibular joint are examples of a syndesmosis joint.

Cartilaginous Joint

• Bones joined by either fibrocartilage or hyaline cartilage.
• There are 2 types: synchondroses and symphyses.

Synchondroses

• Bones connected by hyaline cartilage which is immovable (synarthrosis).
• Example: joint between diaphysis and epiphysis of a growing long bone.

Symphyses

• The bones are united by fibrocartilage, so they are slightly movable joints (amphiarthrosis).
• The pubic symphysis and intervertebral joints are examples.

Synovial Joint

• Contains fluid-filled joint cavity inside a fibrous capsule.
• Freely movable (diarthrosis) and most common.
• Sub-classified by shape and movement permitted: hinge joints, saddle joints, plane joints, pivot joints, condyloid joints, and ball and socket.
• Hinge Joint permits movement in one plane like flexion/extension from elbow, ankle, knee joints.
• Saddle Joint resembles a saddle on a horse's back and characterized by opposing articular surfaces with a reciprocal concave-convex shape in carpometacarpal joints
• Plane Joints the articular surfaces are relatively flat which allows the bones to glide over one another in the acromioclavicular joint and subtalar joint.
• Pivot Joints allows only rotation and is formed by a bony ligamentous ring which is in a bony pivot like proximal, distal radioulnar and atlantoaxial joints.
• Condyloid Joint has contains a convex surface which articulates with a concave elliptical cavity, which they are considered as ellipsoid joints such as in wrist joints.
• Ball and Socket Joint where the ball-shaped surface of one rounded bone fits into a cup-like depression to permit free movement as in the hip and shoulder joint.

Arthritis

• Is when the joint becomes swollen, painful and immovable

Arthritis Types

• Osteoarthritis breaks down joint cartilage and is the common form of arthritis
• Ankylosing spondylitis: Spinal arthritis in the lower back.
• Juvenile arthritis (JA): Attacks tissue surrounding joints; commonly affects those 16 or younger.
• Gout creates hard crystals of uric acid in joints.
• Psoriatic arthritis is a joint inflammation related to psoriasis.
• Rheumatoid arthritis causes immune system attacks on synovial membranes.

Clinical Effects

• Calcium deposits leading to inflexibility.

Treatment

• Artificial joint replacement or use of medicines is used.

Muscular System Introduction

• Muscles form muscular system in vertebrates.
• Muscles are made of muscular tissue.
• Each muscle cell has unique function to create force during shortens.
• Contraction force or pulling force helps to perform different functions.
• The muscular system partners with the skeletal system in movement.
• Humans have over 600 muscles contributing half of the body weight.
• Men and women usually have the same bones and muscles.

Muscular System Functions

• Movement of eyelids, tongue, and food within the alimentary
• Activity of internal heart and internal circulation.
• Excretion of excretions from the body
• Important substances are secreted in specific locations.
• They cause exchange in the body

Muscle Types

• Smooth, cardiac, and skeletal are the 3 types

Smooth Muscles

• Structurally simple
• They consists of long spindle shaped.
• They are uninucleated.
• Each muscle has cytoplasm
• The nucleus contains granular cytoplasm with elongated fibres called myofibrils.
• Blood vessels, digestive tract, and other organs contain these muscles.
• Smooth muscles are involuntary and perform autonomously.
• These muscles are controlled by the autonomic nervous system
• They contract slowly and can be used for long periods of time.
• It pushes food down the alimentary
• They helps in waste removal from urine
• It adjusts the blood's size
• They adjust pupil size for sufficient light entry.
• Smooth muscles cause erection of hairs.

Skeletal Muscles

• Attaches to the skeleton to enable movement.
• Under microscope skeleton muscles look striped, which are striated muscles called called so due to their striped appearance.
• It contains of protein filaments
• Light/dark bands exist and regulated voluntarily.
• striated voluntary muscles is what they are known as.
• Contractions occur due to the central nervous system.
• Under central nervous system control as they are able to rapidly go back to their normal position.
• Some attach directly to bone outer layers, others connecting to tendon tissue.
• Ligaments are connect bones together.
• Muscle contraction moves the stretched tendon and bone.
• Contraction is needed for at least two joints so movement occurs.
• Origin is the stationary attachment point and insertion is the moving attachment point.

Cardiac Muscles

• Construct only the muscular walls in the heart of vertebrataes.
• Uni- or bi-nucleated and branched to form contractile tissue meshwork connected by Intercalated Discs.
• The fibers will not separate.
• Heart walls handles high stress, without the risk of damage.
• Heart chambers contract due to the meshwork of heart muscle fibers, maintaining blood flow.
• Includes more mitochondria and the actin and myosin proteins to sustain continuous energy supply for the tissue of the heart.
• Contract and relax rhythmically in a heartbeat pattern
• It's regulated by the sino-atrial node (SAN), which is the pace maker.
• The impulse caused by the pace maker spreads through the heart, without involving the central nervous system

Structure of Skeletal Muscles

• Each muscle is has a 3 layers of connective tissue ("mysia") that provides structure and encloses the muscle with muscle compartment.
• Epimysium: Irregular connective tissue sheath around muscle, which allows a muscle to contract and move powerfully while maintaining its structural integrity.
• Perimysium: Irregular connective tissue sheath around fascicles inside, it enables specific movements via nervous system.
• Endomysium: Encases each muscle fiber which are involved in collagen and reticular fibers.
• Endomysium contains extracellular fluid and nutrients supplied by capillaries.
• Each muscle consists of aligned, elongated muscle fiber structures.
• Each fiber is a complete cell having sarcoplasm (cytoplasm) and surrounded by sarcolemma (outer membrane).
• Specialized sites of skeletal motor axons of the muscle fiber creates the NMJ (neuromuscular junction) where the muscle fiber first starts indicating to the motor neuron.
• Sarcolemma in the neuromuscular junction contains transmembrane proteins receiving electrical signals.

Composition of Muscle Fibers

• Each fiber consists of many contractile myofibrils.
• Fibrils are composed of a chain of sarcomeres which are the muscle tissue units that contract.
• Sarcoplasmic reticulum (SR) surrounds each myofibril .
• Sarcoplasmic reticulum (SR) Description: The ER that store,releases, and retrieves calcium ions (Ca++).
• Motor releases cause release of calcium ions (Ca++) from the Sarcroplasmic Reticulum.
• The sarcolemma has T-tubules to reach the SR, which means that the signals given from the motor neuron will reach the membrane of the SR.
• Z line separates the sarcomeres.
• Dark and light zones make up the sarcomeres.
• Striated muscles are made of sarcomere light and dark patterns.

Myofilaments and its Types

• Composed of microfilaments.
• Includes thick and thin filaments.

Thick Filament

• Composed of myosin.
• Myosin myofilaments contain a tail and functional heads.
• tails Description: Connect myosin myofilaments.
• heads Description: The active role is in muscle contraction and contains an actin-binding and ATP-binding part.

Thin Filament

• Six thin filaments surround the myosin.
• Composed of actin, tropomyosin, and troponin.
• Troponin consists of polypeptide.
• Troponin I (Tnl) binds to actin.
• Troponin T (TnT) binds to tropomyosin.
• Troponin C (TnC): Binds to calcium ions.
• Troponin and tropomyosin controls actin binding sites.

Overlapping Pattern of Thin and Thick Filaments

• Bands caused by overlapping filaments.
• I-bands (isotropic) possess a pair of I-bands which are outer areas on each sarcomere and it contains only active filaments.
• A-bands: (Anisotropic): The dark and are located outside to each and can be only located on I cells .
• H-bands: (Helle): Lightly staining A-band center zone it contains only the thick filaments.
• Thick filaments have cross bridges attached to the actin filaments.

Mechanism of Contraction of Skeletal Muscles

• Muscle contraction occurs when a muscle activates and becomes shorter.

Explanation: Huxley sliding filament theory

• Thin and thick filaments slide together during muscle contraction.
• The sliding over the filaments is the reason that the muscles get shorter and thicker.

Cross Bridge Cycle

• Nerves causes to release of calcium released (Ca++) from SR surrounding miofibrils, causing change in the troponin molecules, enabling the interaction with actin
• Head regions are attached to sites of actin forming cross links and releases in inorganic phosphate
• ADP is released and starts the stroke, and moving the filament in the mesomere
• ATP bounds to myosin head regions causing the removing of cross lines after hydrolysis to cause moving to trigger the new cross linking , stopping the creation, after the new signal occurs