Anatomy PDF - Skeletal System

D 1. **Skeletal system** Definition Types Structure of a bone Bone features Bone microscopic structure Types of endoskeleton Parts of axial skeleton Structure of Skull and face Function of skull Backbone Function of vertebrae Function of vertebrae column Thoracic cage Appendicular...

D 1. **Skeletal system** Definition Types Structure of a bone Bone features Bone microscopic structure Types of endoskeleton Parts of axial skeleton Structure of Skull and face Function of skull Backbone Function of vertebrae Function of vertebrae column Thoracic cage Appendicular skeleton Shoulder girdle Clavicle structure of clavicle Scapula Structure of scapula Upper Limb Structure of humerus Ulna and radius Carpels Definition: Forms the body framework Give supports protection Shape and storage of nutrients. 3 **Types** of skeletal system are exoskeleton, hydro skeleton and endoskeleton. **Endoskeleton** Is found between the body among animals and classified into bone and cartilage. bones are static strong and high vascular living structures. types of bones are **long, shorts, irregular, flat and sesamoid.** long bone consists of a shaft and two extremities they are longer than their width. example are femur and tibular. The other types of bone have no shafts or extremities and are of diverse shapes and sizes. Examples: short born - carpel, irregular bone - skull bone flat bone are the ribs and sternum sesamoid bone -patella or knee cap **[Structures of bone]** Bones have a shafts (called diaphysis Which is composed of compact bone and Central medullary canal containing yellow bone marrow) and two extremities or epiphysis consists of an outer Sscovering or compact bone with spongy bones inside. The diaphysis and epiphysis are separated by epiphyseal cartilages which ossify when growth is complete. See structure of a long bone **[Feature of a bone]** :i t is completely covered by vascular membrane called **periosteum,** it contains bone cells (osteoblasts and osteoclast,) it has **hyaline cartilage to prevent damage at bone to bone conta**ct it has blood supply. **[microscopic structure of bone ]** **[-]**the bone consists of **calcium salts** (mainly calcium phosphates - 65%) which form the great hardness -the remaining materials are living organic materials called **Osteoid** which composed mainly of collagen. **-bone cells** responsible for bone formation are osteoblasts which later mature into osteocytes. osteoblast and chondrocytes (cartilage foaming cells) developed from the same parents fibrous tissue cells. **[osteoblast]** :this bone forming cells secrete both the organic and organic component of bone they are present in deeper layer of periosteum and center of ossification in of immature bones. **[osteocytes]** : these are the mature bone cells that monitor and maintain bone tissue and are numbered by tissue in the canaliculi that radiate from the central canal. **Osteoclast :their function is reabsorption of bone to maintain the optimal shape. this takes place at the bone surface under the periosteum to maintain the shape of bonds during growth and remove excess callus from the bone during healing of fracture.** **Types of endoskeleton** :**axial skeleton and appendicular skeleton.** **Axial skeleton consists of skull, vertebrate column, ribs and the sternum** **[Skull]: rest on the upper end of the vertebra column and its bony structures is divided into two parts: the cranium and the face or calvaria.** **[Cranium] is formed by a number of flat and irregular bones that protect the brain. the bones of the cranium are frontal bone parietal bone, temporal bone occipital bone, sphenoid bone and ethmoid bone.(~~Postef~~)** ***See structures of skull and face*** **[Face]:** the skeleton of the face is formed by 13 bones in addition to the frontal bone. they include : two zygomatic , one maxilla, two nasal, two lacrimal, one vomer, two palatine , two inferior conchae and one mandible bone. **[Fontanels of the skull]** At birth ossification of the cranium suture is incomplete. The skull bones do not fuse earlier to allow for molding of the baby\'s head during childbirth where three or more bones meets. the two largest are the anterior Fontanel, not fully ossified until the child is between 12 to 18 months old and the posterior fontanel usually ossifies 2 to 3 months after birth. **[functions of the skull]** The cranium protects the brain The eye socket protect the eyes and give attachment to the muscles, the temporal bone protect the delicate structures of the inner ear, the sinus gives resonance to the voice, the maxilla and the mandible provide alveolar ridges in which the teeth are embed, the mandible controlled by muscles of the lower face allows chewing. **[Vetebral coulom or backbone]** they are 33 to 34 in number and begins from the foreman Magnum and extends to the tail. the bones of the vertebral column are divided into five, they are :7 clavicle, 12 thoracic, 5 lumber, 5 sacral and 3 to 4 coccyx. **[features of typical vertebra]** They possess the following 5 features: body or centrum, vertical or neural arch called spine, neural canal, transverse process and transverse foremen. (See structure of a vertebrae column) **[Functions of the vertebral column ]** they provide strong body protection for the spinal cord, they allow the passage of spinal nerves , blood vessels, and lymph, they allow movement of the whole column, they provide support to the skull. It act as a shock absorber. **[Thoracic cage or thorax]** **[It]** is made up of the sternum and anteriorly and 12 pairs of ribs forming the lateral bony cage. **[The sternum or breastbone]** this is a flat bone which could be felt just under the skin. the manubrium is the uppermost section and articulates with the clavicle at the sternoclavicular joints and with the first two pairs of ribs. the xiphoid process is the inferior tip of the bone which gives attachments to the diaphragm, muscle of the anterior abdominal wall. structure of the thoracic cage **[ribs]** they are 12 pairs of ribs that form the walls of thoracic cage which articulate posteriorly with the vertebral column. the ribs are classified into typical ribs or true ribs, atypical ribs or false ribs and floating ribs. typical ribs are 7 pairs of ribs which articulate directly with the sternum (first to seventh ribs) false ribs are the next three pairs of ribs and articulate indirectly to the sternum. floating ribs at the lowest two pairs of ribs. they are called floating ribs because they do not join with the sternum at all. **[appendicular skeleton ]** The appendicular skeleton consists of the shoulder girdle with the upper limbs and the pelvic with the lower limbs. **[shoulder girdle]** consists of two clavicle and two scapulars. **[Clavicle]** or collar bone this is an s-shaped long bone. it\'s a articulates with the manubrium of the sternum and the external clavicular joint and forms the acromonoclavicular joints with the acromion process of the scapula. ***structure of the clavicle*** **[scapular or shoulder blade]** is a flat triangular shaped bone which lies on the posterior chest wall. it has a glenoid cavity which with the head of the Humorous forms the shoulder joints. at the posterior surface it has a rough ridge called spine. *structure of scapula* **[Upper Limb]** [ ] *structure of the humerus* it is the bone of the upper arm. the head sits within the glenoid cavity of the scapula forming the shoulder joints. **[ulna and radius]** these are two bones of the fore arm. the ulna is longer than and medial to the radius. they articulate with the humerus at the elbow joints with the carpal bones of the wrist joint. **[Carpels or wrist bone]** There are eight carpel bones arranged in two rows of four from outside inwards. they are proximal row : which includes the scaphoid, lunacte, triquetrum, and pisiform. distal row: includes the trapezium, trapezoid , capitate and hamate. *Structure of carpel or wrist bone* **[Pelvic girdle and lower limbs]** **[t]**he pelvic girdle is formed from two hip bones. each hip bone consists of three fused bones, the helium is ischium and the pubis on its lateral surface. there is a depression, the acetabulum which forms the hip joint. **[pelvis]** the pelvis is formed by the hip bones, the sacrum and the coccyx it is divided into upper and lower parts by the brim of the pelvis, consisting of the proximity of the sacrum. **[Differences between male and female pelvis]** the shape of the female pelvic allows for the passage of the body during childbirth in comparison with the male pelvic which has a lighter bones and shallower and more rounded. **[lower limbs]** the lower limbs consist of the following 6 bones: the femur, tibia, fibula, patella or knee cap, tarsal or ankle bone, metatarsal or bone of the foot **[joints ]** a joint is the site at which any two or more bones articulate or come together [classification of joints] there are three classifications of joint namely fibrous joints, cartilagenous joint and synovial joints. **[Fibrous joints]** these are tough fibrous materials which do not move. Examples are the skull bone, tooth. in the mandible, the tibia and fibular and held together along their shaft. **[Cartilagenous Joints ]** are formed by a part of tough fibrocartilage between the bones that act as a shock absorber. The Joint may be immobile, some permit limited movements. Examples are: the link between the diaphysis and epiphyses, vertebrae, pubic symphysis. **[synovial joints]** **[s]**ynovial joints are classified by the presence of space or capsule between the articulating joint which is lubricated with small amounts of fluids called synovial fluid, hence the name synovial joint. **[features of syno joints]** they are coated with hyaline cartilage, they have capsular ligament that holds the bone firmly together, they have synovial membrane that secretes synovial fluid. **[types of synovial joints]** **Ball and sockets :** the head of one bone is lall shaped and articulate with the cup-shaped socket of another bone. It allows a wide range of movement which include flexion, extension, adduction, abduction, rotation and circumduction. **Example**s are shoulder and hip joints **[Hinge joints:]** They allow only flexion and extension. Examples are knee and ankl. **[gliding joints:]** these joints only permit sliding against each other example are joints between carpel bones and wrist bones. **[pivot joints :]** this joints allows a bone or a limb to rotate. one bone fits into a hoop-shaped ligament that hold it close to another bone and allow it to rotate. example: head. **Musculoskeletal system** **Continuation : Muscles** Muscle, is a specialized tissue in the body that is responsible for producing movement, maintaining posture, and generating heat. Muscles are composed of muscle fibers, which are long, slender cells capable of contracting in response to stimulation. This contraction is what enables muscles to produce force and cause movement. Types of muscle cells 1\. Skeletal muscle 2\. Cardiac muscle 3\. Smooth muscle  Fig 1. Different muscle cells 1\. Skeletal Muscle: is the muscle that is attached to the bone and aids with movement, breathing (the diaphragm) etc. Structure of skeletal muscle Appearance: Striated (striped) due to the regular arrangement of actin and myosin filaments in sarcomeres. Cell Shape: Long, cylindrical, and multinucleated. Control: Voluntary control, meaning their contractions are consciously controlled by the somatic nervous system. Organization: Composed of bundles of muscle fibers (fascicles) encased in connective tissue. Function of skeletal muscle - Movement: Responsible for voluntary movements such as walking, lifting, and facial expressions by attaching to bones via tendons. - Posture: Helps maintain posture and body position. - Heat Production: Generates heat through muscle contraction, contributing to body temperature regulation. - Location: Found attached to bones throughout the body. 2\. Cardiac Muscle: this is the muscle of the heart that aids in pumping of blood Structure of the cardiac muscle Appearance: Striated like skeletal muscle, but with a more branched and interconnected structure Cell Shape: Short, branching cells with a single central nucleus (sometimes two). Cells are connected by intercalated discs, which contain gap junctions and desmosomes for communication and mechanical stability. Control: Involuntary control, meaning it contracts without conscious thought, controlled by the autonomic nervous system and intrinsic pacemaker cells. Intercalated Discs: Specialized structures that allow synchronized contraction of the heart muscle by facilitating the rapid transmission of electrical impulses. Functions of cardiac muscle - Pumping Blood: Responsible for the contraction of the heart, pumping blood throughout the body. - Rhythmic Contraction: The heart's rhythmic contractions are driven by pacemaker cells, ensuring consistent blood flow. - Location: Found exclusively in the heart, making up the bulk of the heart\'s walls (myocardium). 3\. Smooth Muscle: this is the muscle of everything else in the body that do not include skeletal or cardiac muscle. They line blood vessels and other organs of the body. Structure of smooth muscle Appearance: Non-striated (smooth) because actin and myosin filaments are not arranged in a regular pattern like in skeletal and cardiac muscle. Cell Shape: Spindle-shaped or eye shaped (tapered at both ends) with a single central nucleus. Control: Involuntary control, regulated by the autonomic nervous system and hormones. Organization: Cells are usually arranged in sheets or layers that contract in a coordinated fashion. Function of smooth muscle - Movement of Substances: Controls the movement of substances through hollow organs (e.g., intestines, blood vessels) by contracting and relaxing. - Regulation: Regulates the diameter of blood vessels (vasoconstriction and vasodilation), controls airflow in the lungs, and moves food through the digestive tract (peristalsis). - Location: Found in the walls of hollow organs such as the stomach, intestines, blood vessels, bladder, and uterus, as well as in the respiratory, urinary, and reproductive systems. Summary of Differences: Fig 2. **The structure of the muscle**  Fig 3. Diagram of the structure of the muscle Whole Muscle: is covered with epimysium, the outermost layer of connective tissue that surrounds the entire muscle. This sheath helps protect the muscle from friction against other muscles and bones and allows it to slide smoothly during movement. Fascicles is covered with perimysium. Each fascicle is wrapped in a layer of connective tissue known as the perimysium. Fascicles are the building blocks of muscles, containing multiple muscle fibers. Muscle Fibers: Each individual muscle fiber within a fascicle is encased in a thin layer of connective tissue called the endomysium. This layer provides support and separates muscle fibers from one another, as well as carrying small blood vessels and nerves. Beneath the endomysium is the sarcolemma, which is the cell membrane of the muscle fiber. The sarcolemma plays a crucial role in transmitting electrical impulses that trigger muscle contraction. Myofibrils: are long, cylindrical structures that run the length of the muscle fiber. They are composed of repeating units called sarcomeres, which are the smallest functional units of muscle contraction. Sarcomeres: Each myofibril is divided into sarcomeres, which are organized in a series, except in smooth muscles where it arranged haphazardly. Sarcomeres contain the actin (thin) and myosin (thick) filaments whose interaction causes muscle contraction. Striations: The arrangement of sarcomeres gives skeletal and cardiac muscle their striated (striped) appearance, as the alternating bands of actin and myosin align with each other. **Physiology of muscle contraction** Neuromuscular Junction Activation: A nerve impulse (action potential) travels down a motor neuron to the neuromuscular junction, the point where the nerve meets the muscle. The action potential triggers the release of the neurotransmitter acetylcholine (ACh) from the neuron into the synaptic cleft. Acetylcholine binds to receptors on the muscle cell membrane (sarcolemma), leading to depolarization of the membrane. Excitation-Contraction Coupling: The reaction causes the Na+ K+ channel to open and an influx of Na+ ions into the and causes the K+ ions to go outwards. This process is called depolarization. This causes the potential energy across the cell to change and the action potential spreads along the sarcolemma and down the T-tubules, which are invaginations (holes) of the membrane that penetrate into the muscle cell. The action potential triggers the sarcoplasmic reticulum (SR), a specialized organelle that stores calcium ions, to release calcium into the cytoplasm of the muscle cell. Calcium binds to the troponin on the thin filaments (actin), causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin. Cross-Bridge Cycle: With the myosin-binding sites exposed, the myosin heads bind to actin, forming cross-bridges.The myosin head pivots, pulling the actin filament towards the center of the sarcomere. This action shortens the muscle fiber, generating force. After the power stroke, ATP binds to the myosin head, causing it to release the actin. The myosin head then hydrolyzes the ATP into ADP and inorganic phosphate (Pi), which re-cocks the myosin head, readying it for another cycle. Relaxation: When the nerve impulse stops, the acetylcholine stops its realease to the synaptic cleft and an enzyme called acetylcholinesterase with breaksdown the remaining acetyl choline in the synaptic cleft, so there is nothing to bind to the acetylcholine receptors which stops the the depolarization and repolarizarion takes place. The positively charged cell returns to a negatively charged cell as Na+ goes back to the outside and K+ returns to the inside of the cell, which changes the action potential. The sarcoplasmic reticulum will now stop the release of Ca2+ from binding to the troponin. As calcium levels drop, the troponin-tropomyosin complex returns to its original position, blocking the myosin-binding sites on actin, which causes the muscle to relax. Fig 2. A sarcomeres (functional and contractile unit of the muscle  Fig 3. Excitation contraction coupling Fig 4. Cross bridge cycle  Fig 5. The physiology of muscle contraction