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Skeletal and Muscular System Overview Cheat Sheet by

Goes through study guide with questions regarding both the skeletal and muscular system

Bony components of the skeletal system

What are the functions of the skeletal system?
Support, movement, protec­tion, mineral storage, electr­oly­te/pH balance, detox (absorb metals and foreign elements), and blood cell formation
What is osseous tissue and how is it formed­/ma­int­ained?
Osseous tissue is connective tissue with a hard extrac­ellular matrix. It is formed through ossifi­cation (end­och­ond­ral [cartilage model is replaced by bone] and intr­ame­mbr­anous [bone develops from mesenc­hymal sheet])
What are the different bone classi­fic­ations? (Think shape)
Irregular, flat, short, long, and sesamoid
What are the connective tissue membranes of bones?
Perios­teum, perfor­ating fibers, nutrient foramina, endosteum and articular cartilage
What are the microa­nat­omical structures of compact bone?
Osteons are the structural unit of compact bone, lamella are the rings of the calcified matrix (circu­mfe­rential are the external and internal surface of compact bone and inters­titial lamellae are found in between osteons), the central canal is at the core of the osteon and has the nerve and blood supply, perfor­ating canals extend from the marrow cavity to the periosteum providing blood supply, canaliculi connect neighb­oring osteocytes and capill­aries
What are the microa­nat­omical structures of spongy bone?
Trabeculae are the structural component of spongy bone (porous), it has layers of lamellae but NO osteons, often has bone marrow (yellow is fat and red is blood)
What charac­ter­istics of bone prevent breakage?
Trabecular organi­zation is meant to form along stress lines and resist stress with low mass. The structure of lamellae resist breakage because of their spiraling layers of calcified rings
Define bone apposi­tional growth
Bones widen and thicken (circu­mfe­rential lamellae are added)
Define bone elongation
growth at the epiphyseal plate
How does bone elongation occur?
Starts at the zone of reserve: matrix produc­tion. Second stage is the prolif­erative zone: mitosis takes place. Third is the zone of hypert­rophy: lipids, glycogen and alkaline phosph­atase accumu­late; the matrix calcifies. Fourth is the zone of calcif­ica­tion: chondr­ocyte cell death. Last is the zone of ossifi­cation: where the new bone is.
What is bone marrow? Where are the different marrows found?
It is soft, spongy tissue present in bone. Red marrow is typically found in the epiphysis of bone and yellow marrow is found in the medullary cavity of long bones.
What bones develop through endoch­ondral ossifc­ation?
All bones from the base of the skull down (aside from the clavicles)
What bones develop through intram­emb­ranous ossifi­cation?
Flat bones of the skull, the clavicles, and some of the facial bones
What are the functions of bone remode­ling?
Functions to respond to mechanical stress­/injury (maintain blood calcium and PO43-
What are the processes involved in bone remode­ling?
Resorp­tion- osteoclast activity Deposi­tion- osteoblast activity
What are bone fractures?
A broken bone due to trauma (high stress)
What are the processes involved in bone repair?
1. Hematoma formation (fracture hematoma) 2. Soft callus formation 3. Hard callus formation 4. Remodeling

Cartil­aginous Components of the Skeletal System

Hyaline Cartilage Charac­ter­istics
Most common cartilage with lots of tissue fluid
Elastic Cartilage Charac­ter­istics
Contains elastic and collagen fibers
Fibroc­art­ilage Charac­ter­istcs
Contains thick collagen fibers
Hyaline Cartilage Functions
Support, cushions, eases movement and is the template for bone growth
Elastic Cartilage Function
Provide flexible support (recoil)
Fibroc­art­ilage Functions
Resist compre­ssion and absorb shock

Bones of the Body

What are cranial bones? What are facial bones?
Cranial bones are the flat bones of the skull. Facial bones are any of the bones surrou­nding the mouth and nose and contri­buting to the eye socket
What is the vertebral column? What are the different types of vertebrae?
The vertebral column is the central axis of the skeleton, it provides muscle attach­ments, protects the spinal cord, and supports the trunk. The different types of vertebrae include cervical vertebrae (7), thoracic vertebrae (12), and lumbar vertebrae (5), included is the sacrum and the coccyx.
What are the curves of the spine?
Kyphosis- concave anteriorly Lordosis- concave poster­iorly
What bones make up the thoracic cage?
The sternum (manub­rium, body, and xiphoid) and 12 pairs of ribs (true are 1-7, false are 8-12, floating are 11-12)
What bones make up the brachium, antebr­achium, and the hand?
Brachium: humerus. Antebr­achium: ulna and radius. Hand: carpals (8), metaca­rpals (5), and phalanges (14)
What bones make up the pelvic girdle?
The hip bones (coxal, ossa coxae, pelvic, innomi­nate), the pelvis and articu­lates (ilium and ischium)
What bones make up the thigh, crura (leg), and feet?
Thigh: femur. Crura: tibia and fibula. Foot: tarsals (7), metata­rsals (5), and phalanges (14)

Functional Joint Classi­fic­ation

immobile (short fibers)
limited mobility (long fibers)
Freely movable

Structural Joint Classi­fic­ation

Bony (synar­thr­otic) joints
The space between two bones ossifies (hip, epiphyseal line, frontal bone)
Fibrous (synar­thr­otic) joints
Elements are connected by fibrous connective tissue (3 types: sutures [bind bones of the skull], gomphosis [anchors tooth root in socket], and syndes­mosis [bones attached via ligame­nts])
Cartil­aginous (ampia­rth­rotic) joints
Bones are attached via cartilage (synch­ond­roses [hyaline cartilage unites bone] and symphyses [fibro­car­tilage connects bone])
Synovial (diart­hrotic) joints
Bones are struct­urally complex

Synovial Joints

What are the charac­ter­ist­ics­/st­ruc­tures associated with synovial joints?
1. Joint (artic­ular) capsule- encloses the joint cavity and has a fibrous capsule and synovial membrane. 2. Synovial Fluid 3. Arti­cular cartil­age Accessory structures include tend­ons (joint stabil­iza­tion), liga­ments (reinf­orcing the capsule), and bursae (fluid filled fibrous sacs that ease friction in the joint)
What are the full structural classi­fic­ations of synovial joints?
Uniaxial diarth­rotic joints, biaxial diarth­rotic joints, multiaxial diarth­rotic joints, and sometimes nonaxial diarth­rotic joints
What are the full functional classi­fic­ations of synovial joints?
Pivot- uniaxial Hing­e­-un­iaxial Cond­yla­r­-bi­axial Sadd­le- biaxial Plane- biaxia­l/n­onaxial Ball and Socket- multiaxial

Muscle Function and Properties

Muscle Functions
Movement, postur­e/joint stabil­iza­tion, open & close passages, heat production
Properties of muscle tissue
Excita­tion, conduc­tivity, contra­cti­lity, elasti­city, and extens­ibility
Skeletal muscle
Striated, voluntary
Cardiac muscle
Striated, involu­ntary
Smooth muscle

Histology of Muscles

What are the structures of skeletal muscle fibers?
Sarcol­emma, sarcop­lasma, myofib­rils, t-tubules, sarcop­lasmic reticulum, glycogen, and myoglobin
What is the sarcol­emma?
plasma membrane of muscle cells (excit­able)
What is the sarcop­lasm?
the cytoplasm of muscle cells
What is the T-Tubule?
invagi­nations of sarcolemma
What is the function of a t-tubule?
Conduct nerve impulses throughout muscle
What is the sarcop­lasmic reticulum?
Elaborate smooth ER surrou­nding myofibrils
What is the function of the sarcop­lasmic reticulum?
store and release calcium

Structure of Myofibrils

What are myofib­rils?
the contra­ctile organelles of skeletal and cardiac muscle
What are the structures of myofib­rils?
Actin (thin filaments) and myosin (thick filaments)
What are sarcom­eres?
the functional unit of muscle
What protei­ns/­str­uctures make up a sarcomere?
Myofil­aments, z disks, m line, titin, a band, h band, and I band

Muscle Contra­ction

1. Cross-­bridge forms: myosin heads binds to actin
2. Myosin "­fle­xes­" and pulls on actin
3. Actin pulls Z disk towards each other

Muscle Relaxation

Nervous stimul­ation stops
SR absorbs calcium
Cross-­bridges no longer form
Muscle returns to resting length

Muscle Contra­ction Questions

What is excita­tio­n-c­ont­raction coupling?
The nerve sends the impulse, the impulse excites the muscle, so the muscle contracts
What is the sliding filament model?
thin filaments pulled past thick (filaments do not shorten
What happens to each element of a sarcomere during contra­ction?
I Band- narrows, H Zone- narrows A Band- unaffected Z Disk- unaffected
What are the roles of Ca+ and ATP during contra­ction?
Calcium binds the myosin heads to actin and ATP breaks the binding apart
What happens during relaxa­tion?
Cross-­bridges are no longer forming and the muscle returns to its resting length
What are the different types of muscle contra­ction?
Conc­ent­ric- muscle shortens (movement upwards) Ecce­ntr­ic- muscle is trying to contact but the load is too heavy (movement downwards) Isom­etr­ic- muscle remains contracted (0 movement)

Fascicle Arrang­ement

fascicles are parallel to each other (sarto­rius)
a bulging parallel muscle (biceps brachii)
go in a circle around something (orbic­ularis oris)
broad base to a narrow end, kinda like a triangle (pecto­ralis major)
attach to CT at an oblique angle; feather like

Muscle Growth & Atrophy

What is hypert­rophy and how does it occur?
muscle fibers get bigger, connective tissue develo­pment increases
What is atrophy and how does it occur?
number of myofibrils and sarcomeres decrease, reduced use

Muscle Attachment

What is the origin?
Where the muscle is less mobile
What is the insertion?
Where the muscle is more mobile
During normal movement what attachment moves toward the other?
Insertion moves toward the origin
What is a direct attach­ment?
It looks fleshy, kinda like muscle to muscle
What is an indirect attach­ment?
Aponeu­rosis and tendon
How do muscles attach?
CT sheaths fuse/fused sheaths attach to bone (at perios­teum)

Muscle Actions

Protra­ction, retrac­tion, elevation, depres­sion, and compre­ssion
Flexion, extension, adduction, abduction, dorsif­lexion, plantar flexion, and lateral flexion
Rotation, medial­/la­teral rotation

Muscle Intera­ctions

What is the agonist?
the prime mover, it is the muscle doing the action
What is the synergist?
the helper to the prime mover (produces the same action as the agonist)
What is the antago­nist?
muscle with the opposite action of the agonist
What is the fixator?
the muscles that stabilize the joint


What is the lever?
the "­bar­" (bone)
What is the fulcrum?
the point of movement (joint)
What is the effort?
the force exerted (muscle)
What is the load?
what is being moved
What are the benefits of lever systems?
moving a heavy load with less effort and moving a load farthe­r/f­aster
Describe mechanical advantages
the further the effort arm is from the joint, the better the mechanical advantage
How do you find the mechanical advantage?
effort arm/load arm Higher the number, the higher the advant­age

Lever System



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