Animal Support Systems: Skeletons

• MODULE 1 focuses on support systems in animals.
• The objectives are to identify different types of skeletons, advantages, disadvantages, classify the human skeleton, explain the functions of the skeleton, understand bone structure, analyze the structure of joints, describe roles of bones and muscles, effects of diseases, common injuries, and the importance of exercise
• The environment and needs of an organism dictate the skeleton's design.
• The complexity of an organism is proportional to the complexity of its skeleton.

General Functions of the Skeletal System

• Support
• Protection
• Mineral storage
• Production of RBC and WBC
• Allows movement
• Hearing

Types of Skeletons

• There are three types: Hydrostatic, exoskeleton, and endoskeleton.

Hydrostatic Skeleton

• It is a fluid-filled coelom held under pressure.
• The function is to provide support for muscles and protection
• Movement is controlled by changing the shape of the body during crawling and burrowing.
• Examples include coelenterates, annelids, nematodes, jellyfish, earthworms, and roundworms.
• Disadvantages: No structural defense, restricted movement, confinement to watery areas, and inability to grow large.

Exoskeleton

• It is common in invertebrates, specifically arthropods.
• The exoskeleton is a chitin layer forming a non-living external structure without blood vessels or nerve tissue
• Muscles attach to the chitin layer for movement.
• The functions are support, protection, and to provide attachment points for muscles.
• Advantages: They create the structure of thin skeletons by joints, and are covered with a cuticle.
• Rigid skeletons limit mobility and growth
• Overcoming disadvantages: Segmented bodies/functional units (head, thorax, abdomen) and the process of moulting.

Endoskeleton

• It is common in vertebrates.
• The endoskeleton is a hard, mineralized structure inside the body.
• A soft endoskeleton is cartilage that that is softer due to fewer minerals, blood vessels, and nerves.
• A hard endoskeleton is bone.
• Mineral content determines the overall hardness of the endoskeleton structure.
• General functions: Support, protection, mineral storage, movement via muscle attachment points, and hearing.

Human Skeleton

• It has 206 bones.
• Functions: Support, body shape, protection of vital organs, movement , mineral storage, production of RBC and WBC, and hearing via ossicles
• Divisions: Axial and appendicular skeleton

Axial Skeleton

• Central axis: Skull, keeps body upright.
• Protection of internal organs: E.g., brain, spinal cord, heart, and lungs.
• It has three regions: Skull, vertebral column, and bony thorax.

Skull

• Flat bones with immovable joints, fused and interlocked via sutures.
• There are two sets of bones: Cranial and facial bones.
• The skull contains the foramen magnum, a hole at the bottom.
• Cranium bones: 2 parietal, 2 temporal, frontal, occipital, sphenoid, and ethmoid bones
• Facial bones: 15 irregular bones.

Vertebral Column

• Backbone or spine with bones and nerves surrounding the spinal cord
• Provides support, protection, attachment for ribs/muscles, absorbs shock, gives balance and flexibility.
• It contains 33 bones in five regions.
• Regions: Neck, chest, lower back, pelvic, and tail regions.
• The first disc is the atlas, and the second is the axis.

Structure of Vertebra

• Consists of the Spinal cord, Vertebral foramen,Facet of superior articular process, Facet for head of rib, Posterior, Spinous Process, Transverse Process, Vertebral Arch (Lamina, Pedicle), Anterior, and Body.

Bony Thorax

• Consists of the rib cage and sternum, comprised of bones and cartilage.
• Breathing occurs due to intercostal muscles.
• Protection and support are the primary functions.
• It is an attachment point for the back, chest, and shoulders, and enables breathing.
• It contains 7 pairs of true ribs, 3 pairs of false ribs, and 2 pairs of floating ribs.

Appendicular Skeleton

• It contains the girdles and limbs.
• It includes the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.
• Girdles connect the limbs to the axial skeleton.

Pectoral Girdle

• The pectoral girdle is the scapula and clavicle.
• The scapula extends to form the glenoid cavity.
• Functions: It attaches the upper limbs the axial skeleton and provides attachment points for muscles.

Upper Limbs

• Consists of the bones of the arm - humerus, radius, ulna, carpals, metacarpals, and phalanges.
• The scapula extends to form the glenoid cavity

Pelvic Girdle

• It consists of the ilium, ischium, and pubis, all fused.
• The front is the pubic symphysis, and the back is the sacrum.
• The point of fusion is the acetabulum socket.
• To form a ball and socket joint with the femur.
• Functions: Attach lower limbs to the axial skeleton, transmit weight of the upper body to the lower limbs, support and protect organs, and provide attachment point for muscles of the lower limbs.

Lower Limbs

• The femur is the largest and strongest
• Consists of the bones of the leg - femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.
• Functions: The lower limbs carry the weight of the body, provide stability via the fibula, support and provide balance, and enable movement.

Composition of Human Skeleton

• Cartilage
• Bone
• Ligaments
• Tendons

Cartilage

• It is found in isolated parts of the body, and is softer.
• Three types: Hyaline, elastic, and fibrous.
• Chondrocytes in a jelly-like matrix of collagen and elastin.
• Functions: Reduce friction, absorb shock, and form flexible structures.

Bone

• It is the hardest but also lightest tissue.
• It is supplied with blood vessels, nerves, and lymph vessels.
• Osteocytes in a matrix of collagen fibers and minerals.
• Two types: Compact and spongy bone.

Functions of Compact and Spongy Bone

• Compact bone: Forms the surface and shaft, is hard and dense, contains Haversian systems, and provides strength and support.
• Spongy bone: Is light, porous, thin plates of bone called trabeculae, resists stress, and forms erythrocytes and leukocytes in bone marrow.

Long Bone Structure

• They create strength and movement, such as the tibia, fibula, radius, and ulna
• Include the hyaline cartilage, spongy bone tissue, red bone marrow, epiphysis, compact bone tissue, periosteum, endosteum, yellow bone marrow, and diaphysis.

Types of Bones

• There are four types: Long, short, irregular, and flat.
• Long bones: Enable strength and movement, e.g., tibia, fibula, radius, ulna.
• Short bones: Absorb shock, spread load, allow movement in any direction, e.g., carpals and tarsals.
• Irregular bones: Shape and protection, e.g., facial and vertebral bones.
• Flat bones: Protection of vital organs, e.g., ribs, cranium, skull.

Ligaments

• They are composed of connective tissue.
• They are strong and resilient, connecting bones to bones.
• They form an articular capsule at joints.
• They hold bones together, directing bone movement.

Tendons

• They have collagen fibers, making them strong and inelastic.
• They stabilizes joints.
• They connect muscles to bone (stationary bone and movable bone.)
• Muscles work in pairs, one contracts as the other relaxes.

Antagonistic Muscles

• Work in opposite motions, when one contracts, the other relaxes.

Types of Joints

• Fibrous Immovable Joints: Skull, hips, ribs, exhibits zero movement
• Cartilagenous Partially Movable Joints: Vertebra, exhibits a little movement.
• Synovial Joint Freely Movable: Freely moveable

Types of Synovial Joints

• Ball & Socket :The head of one bone fits into the socket of another, movement in many directions, shoulder and hip.
• Hinge: Up/Down Left/Right movement along one plane, elbow.
• Gliding/Plane: Flat bones slide over one another, rotation is enabled, wrist and ankle.
• Pivot/Axis: Bones rotate around one another, rotation is enabled, skull and atlas.

The Breakdown of Muscles

• Includes the tendon, epimysium, deep fascia, blood vessels, perimysium, fascicle endomysium, blood capillary, sarcolemma, muscle fiber (cell), and myofibril.

Characteristics of Skeletal Muscle Tissue

• Characteristics: It forms skeletal muscles, striated, and controlled voluntarily.
• Functions: Enables movement, maintains posture and stability due to muscle tone, stabilizes joints, and generates heat.

Skeletal Muscle

• Consists of fascicles
• -The muscle is surrounded by Epimysium
• A fascicle is surrunded by Perimysium
• A muscle fibre (muscle cell) is surrounded by Endomysium

Structure of Muscle Fibers

• Muscle fibers are large, elongated, cylindrical muscle cells.
• Consist of Nucleus, Muscle Fiber, Light I Band, Dark A Band, Myofibril, Mitochondrion,and Sarcolemma
• Composition: Many nuclei and mitochondria under sarcolemma, sarcoplasm with stored glycogen & myoglobin, 2 sets of tubules (sacroplasmic reticulum & T-tubules), and myofibrils.

Structure of Myofibrils

• Parallel filaments forming an alternating pattern.
• Composition: Muscle fiber, light I band, myofibril, mitochondrion, sarcolemma, dark A band, sarcomere, thin (actin) filament, Z disc, H zone, thick (myosin) filament
• Alternating dark and light bands.
• Dark bands: Thick filaments of protein myosin .
• Light bands: Thin filaments of protein actin.
• Overlaps in some areas; H zone bisects dark bands, Z line bisects light bands.
• Sarcomere - between two Z lines.

Muscle Contraction

• The Z disc and I band gets smaller
• Thin filament (actin) slides over the thick filament (myosin)

Muscle Contraction Simplified

• Muscles contract when signals are sent to the nerves in the sarcolemma.
• Thin actin filaments slide past the thicker myosin filaments.
• This generates more overlaps of actin and myosin.
• The Z lines move closer to each other, shortening the sarcomere,
• The shortened sarcomere leads to the shortening of myofibrils, muscle fibers, and eventually the whole muscle.

Health Issues of the Musculoskeletal System

• Several health problems may arise, often due to vitamin deficiency, genetics, or accidents which causes damage.
• Rickets: Occurs due to lack of vitamin D and malnutrition, which caused softening of the bones, which further creates dental problems, deformities, and stunted growth.
• Osteomalacia: Lack of minerals in adults leading to softening of bones, bone pain, muscle weakness, and fractures.
• Osteoporosis: Loss of minerals from bones leading to loss of body density, fractures, pain, and curving.
• Osteoarthritis: Cartilage lining wears down, resulting in bones rubing each other leading to pain and stiffness.
• Rheumatoid arthritis: Inflammation of joints can occur, possibly due to over injury. Over time if left untreated Synovial membranes thicken due to inflammation, creating Synovial fluid which creates Swelling of joints, leading to Deformed joints.

Injuries to the Musculoskeletal System

• Fractures
• Slipped discs
• Sprain
• Dislocation
• Cramps