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Structure and Function of the musculoskeletal system.pdf

Fibroblasts - cells producing the matrix for skin, tendons and ligaments. 

Chrondrocytes - cells producing the matrix for cartilage. 

Osteocytes - cells producing the matrix for bone. 

Collagen fibers: 

Type I - tendons, ligaments, bone, skin. 

Type II - cartilage. 

Type III - blood vessel walls. 

Mechanical properties depend on fiber types and fiber arrangements. 

- 기계적 특성은 콜라겐 섬유의 type와 배열에 의존함. 

Collagen 

Collagen molecule  - a triple helix of three extended protein chains wrapped around one another.  

Numerous rodlike collagen molecules cross-link together to form unextendable collagen fibrils.  

Collagen fibrils are striped because of the regular repeating arrangement of the collagen molecules within the fibril. 

Collagen fibers 콜라겐 섬유

Strength of collagen is 50% strength of bone.  

Under tension, collagen fibers first elongate slightly and then become increasing stiff until failure.  

Collagen fibrils have  the tensile strength of steel.  

- 뼈 강도의 50%는 콜라겐의 강도임.

- 장력하에서 콜라겐 섬유는 약간 늘어나고 손상때까지 점차 단단해짐. 

- 콜라겐 피브릴은 철의 장력강도를 가짐. 

Elastic Fibers 탄력섬유

Elastin - polypeptide chains cross-linked together to form rubberlike, elastic fibers.  

Elastin molecule uncoils when the fiber is stretched and spontaneously recoils when the stretching force is relaxed. 

- 엘라스틴-폴리펩티드 사슬은 고무상 탄성을 가짐. 

- 엘라스틴 분자는 섬유가 늘어날때, 스트레칭 힘이 이완될때 .....

Elastic fibers 

Weak and brittle fibers.  

At low loads they strain greatly and can increase ~200% in length before failure. 

- 엘라스틴 섬유는 약하고 깨지기 쉬운 섬유

- 엘라스틴 섬유는 파열전 200%까지 늘어날 수 있음. 

Tendon structure

􀃎 Tendon

􀃎 Tendon sheath:

􀁺 Synovium - lubricant producing tissue.

􀁺 Synovial fluid - lubricant fluid.

- 건, 건초, 활막, 활액으로 구성...

Tendons and Ligaments

􀃎 At certain points, ligaments surround parts of the tendon sheath to act as:

􀁺 Pulleys – retinaculae that keep tendons attached to joints when muscles contract

􀁺 Tendon guides – retinaculae that restrict lateral tendon movement

􀃎 Ligament attachments allow tendons to work around corners, as in the fingers and toes.

Tendons

􀃎 Tendons connect muscle to bone to create movement.

- 힘줄은 근육과 뼈를 연결하고 힘을 만드는 구조임. 

Collagen in Tendons

􀃎 Tendons comprise parallel bundles of collagen fibers, with few elastic fibers and ground substance.

- 힘줄은 콜라겐 평행다발로 구성되어 약간의 탄력섬유와 기질로 구성됨. 

Tendon and Muscle

􀃎 Muscle fiber wrapped in endomysium

􀃎 Fibers bundled into fascicles (up to 200 fibers) wrapped in perimysium

􀃎 Fasciculi bundled together and interspersed with blood vessels and nerves in muscle and wrapped in epimysium

􀃎 Epimysium and perimysium tissues taper at each end to form tendons

- 근섬유는 근내막으로 둘러싸여 있음. 

- 근주막에서 200개의  fascicle를 둘러싸고 있음. 

- 근외막에서 근육은 혈관과 신경을 둘러싼 다발..

- 근외막과 근주막은 ....

Cartilage: 3 types

1) Hyaline cartilage

􀁺 Solid matrix, cells (chrondrocytes) densely clustered

􀁺 present in the growth plates at the end of bones and on the articular surfaces of joints. Also present in the respiratory tract (e.g. trachea).

- 초자연골 solid maxtix, chondrocyte가 촘촘하게 무리지어 있음.

- 뼈의 끝에 성장판에 존재함. 그리고 활액관절면의 끝에 존재함. 또한 기관지에 존재함.

2) Fibrocartilage

􀁺 solid matrix, cells widely interspersed among collagen fibers

􀁺 present in intervertebral discs

- 섬유성 연골

-  solid matrix, 세포는 콜라겐 섬유사이에 산재함.

- 추간판에 흔히 존재함.

3)Elastic cartilage

􀁺 solid matrix, cells in small groups between many elastic fibers

􀁺 present in ears, nose, epiglottis etc

- 탄성 연골

- solid matrix, 세포는 많은 탄력섬유 사이에 존재함.

- 귀, 코, epiglottis에 존재

Bone

􀃎 Adult human skeleton has 206 bones.

􀃎 Babies born with ~ 300 bones but fusion occurs as a child develops.

􀃎 99% of bodies calcium is in bone.

􀃎 80% of bone tissue by weight is minerals.

􀃎 Longest bone (femur)

􀃎 Smallest bone (stapes)

􀃎 Males have slightly thicker and longer legs and arms

􀃎 Females have a wider pelvis and a larger pelvic cavity

- 성인 뼈는 206개

- 아이는 300개가 넘는 뼈로 태어나고 성인이 되면서 fusion 되면서 206개로 발달함. 

- 칼슘은 뼈에 99% 존재함

- 체중에 의한 뼈조직의 80%는 미네랄임.

- 대퇴골은 가장 긴 뼈임, stapes는 가장 작은 뼈임.

- 남성은 뼈가 팔과 다리에서 두껍고 약간 길다.

- 여성은 골반이 좀더 넓다. 

Bone groups

􀃎 Axial skeleton (80 bones)

􀁺 skull (29 bones)

􀁺 thorax (25 bones)

􀁺 vertebrae (33 bones)

􀁺 Auditory ossicles

􀁺 Hyoid bone

􀃎 Appendicular skeleton (126 bones)

􀁺 pectoral girdle (4 bones)

􀁺 upper extremity (60 bones)

􀁺 lower extremity (60 bones)

􀁺 and pelvic girdle (2 bones)

- 뼈그룹

- 골격을 만드는 뼈는 80개

- 두뇌뼈는 29개

- 흉곽뼈는 25개

- 척추뼈는 33개

- 귀뼈, 설골

Long bones

􀃎 Round bones comprising:

􀁺 diaphysis - shaft

􀁺 epiphyses - 2 expanded ends

Bone Structure and Growth

􀃎 Ossification - processes of bone formation.

􀁺 Osteoblasts - cells that form the bone matrix. They transform into

􀁺 Osteocytes - cells isolated inside the mineralized bone matrix.

􀁺 Osteoclasts - cells important to bone remodeling.

- 골화 - 뼈형성의 과정

- osteoblast - 세포는 뼈조직을 만듬

Types of Bone

􀃎 Cancellous (spongy) bone - less dense bone tissue found at the epiphyses of the long bones and in axial bones, such as the skull. 30-90% porosity.

􀃎 Cortical (compact) bone - tissue with high proportion of bone. 5-30% porosity.

Anisotropy

􀃎 All bone is anisotropic (i.e. its mechanical property changes when loads are applied in different directions).

Bone: Mechanical properties

􀃎 Most important properties are strength and stiffness of bone.

􀃎 Fractures occur when the bone is loaded to failure.

􀃎 Compression fractures are commonest in cancellous bone (e.g. fractured skull)

􀃎 Bending and torsional fractures are commonest in cortical bone (e.g. broken tibia).

Speed of loading to fracture.

Human Muscles

􀃎 Muscular system is 50% of total human body weight.

􀃎 >600 skeletal muscles, which enables the human body to move and stand erect.

􀃎 Skeletal muscles are arranged in overlapping intricate layers:

􀁺 Superficial muscles

􀁺 Deep muscles

- 근육계는 인체 체중의 총 50%

- 인체에는 600개 넘는 근육이 있고, 직립하고 인체를 움직이는 역할을 수행함

- 골격근은 겹쳐지는 복잡한 층으로 배열되어 있음. 

- 표층 근육과 심측근육으로 분류함. 

Skeletal muscle

􀃎 Skeletal muscle is striated (striped), and excludes cardiac and smooth muscle.

􀃎 Skeletal muscle is under voluntary control.

􀃎 Each muscle is a separate organ.

􀃎 Each muscle is attached to bone by tendons that cross one or more joints.

􀃎 Generally, skeletal muscles generate moments about joints.

- 골격근

Muscle fibers

􀃎 Long, cylindrical cells containing multiple nuclei.

􀃎 Most of the fiber volume is occupied by the contractile elements - myofibrils.

􀃎 Myofibrils show a banding pattern (transverse striation) of thick myofilaments (myosin) and thin ones (actin).

􀃎 The contractile unit of the myofibril is called the sarcomere.

- 근섬유

- 길고, cylindrical cell

- 액틴필라멘트와 마이오신 필라멘트로 연결된 구조. 근절

Structure of Skeletal Muscle

􀃎 Skeletal muscle is covered by a fascia called the epimysium.

􀃎 The epimysium penetrates and subdivides the muscle into muscle fiber bundles called the fascicles (fasciculi).

􀃎 Each fascicle is covered by connective tissue called the perimysium.

􀃎 Each individual muscle fiber is covered by connective tissue called the endomysium.

􀃎 Connective tissue provides pathways for nerves and blood vessels + contributes to the mechanical properties of the muscle.

- 근외막은 근육을 싸고 있음.

- 근주막, 근내막이 있음. 

Skeletal Muscle Structure

􀃎 Actin & Myosin filamentary protein molecules form the sarcomeres, and these bundle to form myofibrils, which bundle to form muscle fibers.

􀃎 Longest fibers ~30 cm long, 0.05-0.15 mm wide, and contain several thousand nuclei.

Motor Units

􀃎 Motor unit - group of muscle fibers innervated by branches of the same efferent neuron.

􀃎 Functional unit of the muscle.

􀃎 Motor units are small in muscles requiring precise control (e.g. eye muscles), and large in coarse acting muscles (e.g. gastrocnemius muscle).

􀃎 Motor units work in an “all-or-none” way.

􀃎 Progressive contraction occurs because of recruitment of motor units.

운동단위

- 운동단위는 같은 원심성 뉴런의 가지에 의해서 지배되는 근육그룹

- 근육의 기능적 단위

- 운동단위는 정확한 움직임조절이 필요한 근육에서는 작고, 큰 동작에서는 큼. 

- 운동단위는 all or none 방식으로 작동함

- 진행적 수축은 운동단위의 동원때문에 일어남. 

Sarcomere and Contraction

Muscle Action

􀃎 Actin & Myosin filamentary protein molecules interact to create movement.

􀃎 The Myosin head firmly attaches to the Actin filament.

􀃎 When the Myosin head swivels it pulls the Actin filament forward.

􀃎 Many Myosin head swiveling simultaneously, or nearly so, pull the entire thin actin myofilament.

근절과 수축

- 액틴과 미오신은 상호작용하여 움직임을 창조함

- 미오신 헤드는 액틴필라멘트에 단단하게 부착하여 노를 젓는 것처럼 움직임. 

Muscle fibers

􀃎 Slow twitch fibers (type 1) – S fibers, fatigue resistant, red fibers, slow myosin, contraction times from 100-120 msecs.

􀃎 Fast twitch fibers (type II) – white fibers, fast myosin, contraction times from 40- 45 msecs., subdivided into:

􀁺 FR fibers (type IIa) –aerobic, fatigue resistant

􀁺 FF fibers (type IIx) – type IIb, anaerobic, fatigable

􀃎 Average person has 50% type 1, 25% type IIa, 25% type IIx

􀃎 Elite distance runners have more type I fibers

􀃎 Elite sprinters have more type IIx fibers

􀃎 Exercise can convert type I and IIx fibers to type IIa fibers

근섬유

- slow twitch 섬유는 근피로 저항, 붉은색, 근수축 시간이 100~120msecs

- fast twitch 섬유는 흰색, 근수축 시간이 40-45msecs

Muscles and Aging

􀃎 Loss of muscle mass begins around age 25 years 

􀃎 By age 50 there is a 10% loss of skeletal muscle mass

􀃎 By age 80 there is a 50% loss of skeletal muscle mass

􀃎 Most loss is loss of muscle fibers and fast fibers atrophy at a higher rate than slow fibers

􀃎 In aged muscle up to 30% of fibers have morphed into something between a fast and slow fiber

􀃎 Muscle fibers are never regained

􀃎 Muscle bulk can be increased with weight training and this thickens the muscle fibers

- 근육질량의 감소는 25세이후 시작됨

- 50세에 골격근량은 10% 감소

- 80세에 골격근량은 50% 감소

- 근섬유 소실의 대부분은 fast fiber에서 일어남.

- 나이든 근육...

Muscle Junctions

􀃎 Myotendinal junction - area where tendon fibers insert into muscle connective tissue and also into bone matrix (Sharpey’s fibers).

􀃎 Neuromuscular junction - motor endplate where nerve fibers connect with myofibrils. In leg muscle one neuron innervates several hundred to >1000 muscle fibers. In finger muscles one neuron innervates one to a few muscle fibers.

Musculotendinous Unit

􀃎 Skeletal muscles anchor to the skeleton via either a:

􀁺 Tendon – narrow cord of connective tissue

􀁺 Aponeurosis – broad band of connective tissue

Skeletal Muscle Innervation

􀃎 Nerves (neurons) connect from the brain and spinal cord to muscles.

􀃎 Efferent nerves carry motor instructions for contraction to the muscles.

􀃎 Afferent nerves carry sensory information to the brain.

􀁺 Proprioceptive feedback - muscle tone.

􀁺 Kinesthetic feedback - muscle + joint status.

􀃎 Mixed nerves carry a mix of both sensory and motor neurons (e.g. median nerve).

Properties of Skeletal Muscle

􀃎 Isometric (static, eccentric) contraction – when the muscle force is less than the external load the muscles contract to change muscle tone without changing length. This increases postural stability.

􀃎 Isotonic (dynamic, concentric) contraction - when muscle force is greater than the external load the muscle contracts in length. This produces movement at joints.

􀃎 Static contraction is prone to rapid fatigue.

􀃎 Dynamic contraction increases blood flow through muscles which slows fatigue.

Muscle Organization at Joints

􀃎 Agonist muscle - the muscle directly engaged in contraction (e.g. in flexing the elbow the biceps brachii is the agonist).

􀃎 Antagonist - the opposing muscle in relaxation (e.g. in flexing the elbow the triceps is the antagonist).

- 주동근과 길항근

Joints

􀃎 A joint is the union of 2 or more bones. 3 types of joint are found in the body.

􀁺 Synovial joint (diarthrodial joint) - no tissue between the articular surfaces. Most of the body joints are this type.

􀁺 Fibrous joint - fibrous tissue bridge between bones (e.g. skull).

􀁺 Cartilagenous joint - cartilage bridge between bones (e.g. intervertebral disc in spine).

Structure of a Synovial Joint

􀃎 Joint capsule - fibrous capsule around the joint.

􀃎 Synovial membrane - membrane lining the joint capsule and surrounding the synovial cavity. This tissue secretes the lubricating synovial fluid.

􀃎 Synovial cavity (joint cavity) - cavity containing synovial fluid + bone ends

􀃎 Articular cartilage (hyaline cartilage) - cartilage covering articular surfaces of the bone ends.

Joint degeneration

􀃎 Cartilage does not have a good capillary blood supply.

􀃎 Cartilage has a poor ability to repair and regenerate itself.

􀃎 With age, overuse and/or disease, such as arthritis, the articular cartilage degenerates and bone ends make more direct contact, causing inflammation and pain.

Intervertebral Disc Structure

􀃎 Nucleus pulposus - incompressible watery gel contained within an elastic sac.

􀃎 Annulus fibrosis - fibrocartilage lamellae arranged in layers around the nucleus. Fiber orientation varies from layer to layer.

􀃎 End plates - hyaline cartilage end plates protect each end of the disc.

􀃎 Motion segment - 2 vertebrae either side + intervertebral disc.

Bone and Muscle Loss in Space

􀃎 In space, astronauts will experience a deterioration in their musculoskeletal system:

􀁺 1 to 2 % loss of bone mass each month.

􀁺 Up to 20% loss of skeletal muscle mass within 2 weeks if the astronaut does not exercise:

􀂋 Visiting astronauts (< 2 weeks) exercise 30 minutes/day

􀂋 Space station astronauts exercise 2 hours/day

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