L1: Muscle & Joint Basics (P2)

structure of an epiphysis

located at the ends of a long bone

• rounded, flared out

• covered by articular cartilage

function of an epiphysis

• forms articulations (in synovial joints)

• acts as an attachment area for muscles

structure of a diaphysis

refers to the shaft of a long bone

• it contains the medullary cavity (which houses bone marrow)

function of a diaphysis

• provides strength for movement

• supports BW

• attachment for (some) muscles

what are epiphyseal plates

refers to growth plates

• they’re a layer of hyaline cartilage

• are only present in children (in growing bones)

how does tendon attachment occur

1. near-parallel collagen fibers

   1. tendons are made of type 1 collagen

   2. these fibers run parallel to the direction of pull = inc tensile strength

2. blend into collagen of perisoteum

   1. fibers interweave into the collagen fibers of periosteum (fibrous outer layer of bone)

3. some fibers go deep into bone

   1. portion of fibers penetrate the bone matrix = sharpey’s fibers

what are sharpey’s fibers

collagen fibers that embed into bone

• they hold tendon/ligament to bone (so they don’t pull of)

• they help pass forces (from muscle → bone)

what are immovable joints

bones that are joined by dense CT

• they contain no synovial joint cavity

• where the edges of bones interlock

• provides stability + protection

• ex. skull sutures

what are fibrous joints

flat bones that are joined by fibrous tissue

• they resist tensile (pulling) forces

what are slightly moveable joints

bones connected by fibrocartilage w/ no joint cavity

• allows limited movement

• balance b/w stability and flexibility

what are syndesmosis joints

bones joined by interosseous ligament or fibrous sheet (membranes)

• maintains alignment b/w bones

what are highly moveable joints

bones separated by a joint cavity

• where the ends are covered w/ hyaline cartilage

• allows free, controlled movement

• ex. shoulder joint

what are synovial joints

• joint cavity filled w/ synovial fluid

• surrounded by a capsule

• they reduce friction = smooth, wide-range movement

• the most common joint type

what is hyaline cartilage

a firm but flexible matrix that..

1. resists compression

2. provides tough, flexible support

3. reduces friction b/w surfaces in joints

what is fibrocartilage

cartilage that is strong and tough that..

1. resists compression and tension

2. acts as a shock absorber

3. prevents bone-bone stress during heavy loading

location of the fibrous membrane

• surrounds entire joint

• inserts into the adjacent bones

function of the fibrous membrae

• contains bands of collagen which form ligaments (sometimes)

• resists strength (in multiple directions)

• holds bones together

• limits excessive movement

what is the synovial membrane

a double-layer of loose CT

1. thin layer of synoviocytes which produce synovial fluid

2. loose CT w/ BV which provide nutrition

structure of the synovial joint cavity

the space b/w articulating bones that is filled w/ synovial fluid

function of the synovial joint cavity

• allows near-frictionless movement

• separates articular surfaces

• reduces wear on joint surfaces

what are ligaments

bands of dense regular CT that have poor blood supply

function of ligaments

• joins bone-bone

• stabilizes joints (by creating strong attachments b/w bone and muscles)

• withstands tension (stretching) along fibers

• blends into the capsule of the joint it reinforces (typically)
  

types of ligaments (+ what are they)

1. extrinsic ligament - on the outside of the joint capsule (ext. support)

2. intrinsic ligament - within/around the joint capsule

similarities between ligaments / tendons

1. comprised of dense CT

2. alike in structure + function (generally)

differences between ligaments / tendons

1. L: bone-bone (connection) ; T: muscle-bone (attachment)

2. L: resist force ; T: transfer force

3. T have a higher collagen ratio and are aligned more longitudinally (straight down)

4. L: resist forces in multiple directions ; T: carry more unidirectional forces

structure/location of bursa

they’re fluid-filled sacs that are..

• positioned b/w bony prominences and soft tissue (ex. tendon, ligament, muscle or skin)

function of bursa

• reduces friction b/w bony prominences and overlying tendons (typically)

• cushions areas of repeated pressure

  • prevents wear/irritation

what is a labrum

a ring of fibrocartilage that..

• increases the depth of a joint (for increased congruency)

• acts as shock absorption

• guides movement (for smooth rotation)

what is a menisci

a crescent-shaped pad of fibrocartilage that..

• increases the depth of a joint (for increased congruency)

• acts as shock absorption

• guides movement (controls rolling + gliding)

what is an uniaxial joint

a joint that permits one movement pair (around 1 axis)

• ex. hinge, pivot

what is a biaxial joint

a joint that permits 2 movement pairs (around 2 axes)

• ex. condyloid, ellipsoid, saddle

what is a triaxial/multiaxial joint

a joint that permits 3 movement pairs/combined movement (around 3 axes)

• ex. planar, ball & socket

what is a hinge joint

a convex surface → concave surface

• it’s a uniaxial joint

• ex. knee, elbow

what movements does a hinge joint allow

flexion/extension

what is a pivot joint

when a rounded bone rotates within a ring of bone/ligament

• it’s a uniaxial joint

• ex. upper part of forearm

what movements does a pivot joint allow

rotation (spinning)

what is a condyloid/ellipsoid joint

an oval-shaped surface → oval-shaped depression

• it’s a biaxial joint

• ex. wrist

what movements does a condyloid/ellipsoid joint allow

1. flexion/extension

2. abduction/adduction

what is a saddle joint

a convex surface (one-way) → concave surface (one-way)

• it’s a biaxial joint

• ex. thumb

what movements does a saddle joint allow

1. flexion/extension

2. abduction/adduction

what is a planar joint

a triaxial joint (combined movement)

• ex. clavicle, fingers

what movements does a planar joint allow

1. shift anterior/posterior

2. can slightly pivot (minor rotation

what is a ball-and-socket joint

a spherical head → socket

• it’s a multiaxial joint

• ex. shoulder, hip

what movements does a ball-and-socket joint allow

1. flexion/extension

2. abduction/adduction

3. rotation

4. circumduction (rotation combining all the movements)

definition of origin

the place where the muscle ‘begins’

• usually attached proximally

• fixed, less moveable

definition of insertion

the point where the muscle ‘ends'

• usually attached distally

• moveable attachment

organization of skeletal muscle

1. parallel - large RoM, ex. rectus abdominis

2. convergent/divergent - broad origin that converge to a single tendon, ex. pectoralis major

3. pennate - feather-like, high force production

   1. unipennate - fibers attach to one side of the tendon

   2. bipennate - fibers attach to both sides of the tendon

   3. multipennate - multiple tendons w/ fibers arranged at several angles

4. circular (sphincter) - arranged in concentric rings to control opening/closing

ways that muscles attach

1. bone or cartilage (via tendons anchored by SF)

2. fascia (connective tissue sheets) to distribute force

3. dermis (overlying skin) - so movement of skin

4. to the muscle itself (circular arrangements) so they can control opening/closing of body openings

criteria for how the muscles are named

1. regions .. which help you place muscle location (ex. temporalis; after temporal region of skull)

2. orientation of muscle (ex. rectus; in a straight lin)

3. features (ex. biceps; 2 heads)

4. length, size or shape (ex. longus, minimus, trapezius)

5. level or depth (ex. superficialis; closer to surface)

6. origin/insertion points (ex. sternocleidomastoid)

7. function (ex. extensor digitorum; extends finger)

8. occupation .. historical/functional associations (ex. sartorius; cross-legged sitting posture)

what is the 1st muscle rule

movement is predicted by..

1. shape of joint (what movement; hinge joint = flex/extend only)

2. direction of muscle fibres (which movement; vertical fibres = pull vertically)

what is the 2nd muscle rule

muscle pull is guided by…

1. attachments of the muscle (a typical muscle contraction pulls in the insertion closer to the origin)

2. type of contraction

   1. isometric (tension w/o movement)

   2. eccentric (control movement)

   3. concentric (insertion → origin = movement)

what is the 3rd muscle rule

a muscle acts on all joints it crosses

• multi-joint muscles create multiple actions

• ex. hamstring; hip extension, knee flexion

what is the 4th muscle rule

one muscle cannot produce both movement pair actions

• cannot produce F/E at the same joint

• ex. biceps F elbow, triceps E elbow

what is the 5h muscle rule

in general, muscle innervation is by compartments

• nerve damage affects groups of muscles

what is the 6th muscle rule

if there are 2 muscles w/ the same action across the same joint.. then the muscle which is a 1-joint muscle will likely be stronger for that action

what is the 7th muscle rule

stretching a muscle is the entire opposite of the concentric contraction it produces

• concentric; biceps curl up

• stretching; elbow E = bicep stretching

what is the 8th muscle rule

strengthening a muscle should incorporate all of its actions

what is isotonic contraction

idea that the tension developed in the muscle remains almost constant while the muscle changes its length

what is concentric isotonic contraction

where the muscle shortens while producing force

• the joint moves in direction of the muscles action

• ex. bicep curls (biceps shorten, elbow F)

what is eccentric isotonic contraction

where the muscle lengthens while producing force

• the muscle acts as a brake to control movement

• ex. lowering dumbbell (biceps lengthen, elbow E in a controlled manner)

what is isometric contraction

where the tension generated is not enough to exceed the resistance of the object to be moved

• therefore th e muscle does not change in length

• ex. holding a plank

what is tension dependent on

1. sacromere length (too short = X, too long = X)

2. frequency of stimulation (inc. nerve signal speed = inc. contraction strength)

3. motor unit size (bigger = more force = more tension)

4. recruitment of motor units (more units = more force = more tension)