(24) Intro to Upper Limb, Skeletal Muscles, & Posterior Shoulder Region

upper limb

Shoulder + arm + forearm + hand

shoulder

region containing the pectoral/shoulder girdle (articulated clavicle & scapula)

arm

region containing the humerus

forearm

region containing the radius and ulna

hand

region containing the wrist, palm, & digits

wrist

contains the carpal bones

palm

contains the metacarpals

digits

contains the phalanges

tension

force that is transmitted through a cable-like structure anchored at both ends; a pulling force

*muscles function by exerting this on their attachment sites

muscles cause motion by

pulling on attachments

contractile elements of muscle

sarcomeres

elastic elements of muscle

tendons & elastic filaments

active tension

activation of contractile elements; something a muscle does.

-Motor neuron tells muscle to contract → contractile elements shortens

passive tension

resistance of elastic elements to being stretched; something that happens to a muscle

-External force stretches muscle → elastic elements resist stretching

Sarcomere

contractile element made of thick and thin filaments. there are many within a muscle.

contraction

production of active tension caused by interactions between overlapping filaments; sarcomeres shorten

types of contraction

concentric, isometric, eccentric

-Differ based on what happens to length of muscle

concentric contraction

contraction that causes a muscle to decrease in length to produce movement.

-muscle pulls on a body segment & causes it to move closer to another

isometric contraction

contraction that occurs when a muscle is not allowed to change length to resist movement.

-prevents another force (gravity, opposing muscle pull) from moving a body segment by taking advantage of the elastic elements of a muscle (they stretch out to compensate so that sarcomeres within a muscle can shorten without causing a muscle to change in length)

eccentric contraction

contraction that occurs as a muscle increases in length (due to some other force acting on the muscle) to slow down/control an opposing movement.

-prevents another force from moving a body segment too quickly

-muscles increase in length even though sarcomeres shorten

Active Tension

strength of pull on a muscle. directly related to muscle's length at time of contraction, as the length dictates the amount of overlap between thick and thin filaments of sarcomeres

when a muscle has already been shortened

the amount of active tension it can produce is reduced, as sarcomeres have already shorted & can't shorten any more

-Too much overlap = less interaction between filaments = less tension produced

when a muscle is already stretched out

the amount of active tension it can produce is reduced, as sarcomeres are already stretched and can't stretch any more

-Too little overlap between thick/thin filaments = less interaction between them = less tension produced

Resting Length

length at which a muscle can produce the maximum amount of tension. there is maximum (but not too much) overlap between thick/thin filaments, so sarcomeres are in the best position to generate the most amount of force possible

muscle action

movement/s that occur when a muscle contracts concentrically

-refers to either the body segment being moved or the joint at which the movement occurs

Muscle Function

what you actually use a muscle for. can either be action (concentric contraction), to resist motion (isometric contraction), or to slow down motion (eccentric contraction)

Principles of Muscle Action

1. Not all parts of a muscle need to be active at the same time; different parts of the same muscle may have different, or even opposing, actions

2. Action of a muscle may differ depending on the starting position of the joint it crosses

3. Most muscles have multiple actions that occur simultaneously when they contract, & opposing muscles can be used to balance out unwanted actions

to Deduce Muscle Action, look at

1. Motions that occur at the joint it crosses

2. Direction of its pull

3. Location of its attachments

joint

location at which adjacent bones meet

Types of joints

fibrous, cartilaginous, synovial

fibrous joints

joints held together by fibrous connective tissue. largely immobile.

cartilaginous joints

joints held together by cartilage. largely immobile.

synovial joints

joints held together by an articular capsule. freely mobile.

articular cartilage

cartilage that covers the surfaces of bones where they come together to in synovial joints to prevent friction

joint cavity

the space between two connecting bones in synovial joints filled with synovial fluid

articular capsule

connective tissue structure that encloses the joint cavity of a synovial joint. composed of a fibrous joint capsule & a synovial membrane.

fibrous joint capsule

outer fibrous layer of an articular capsule that keeps bones in juxtaposition

synovial membrane

inner surface of an articular capsule that secretes synovial fluid into the joint cavity

types of synovial joints

1. Hinge

2. Pivot

3. Ellipsoidal

4. Saddle

5. Ball & Socket

6. Planar

hinge and pivot joints

synovial joints that allow motion in 1 plane. rotational movements of pronation & supination

ellipsoidal and saddle joints

synovial joints that allow motion in 2 planes. flexion & extension, abduction & adduction.

ball and socket joints

synovial joints that allow motion in 3 planes. flexion & extension, abduction & adduction, medial rotation & lateral rotation.

planar joints

synovial joints that allow limited sliding motions

scapular spine

bony ridge on posterior aspect of scapula

acromion

the lateral end of the spine of the scapula that articulates with the clavicle

coracoid process

superior & anterior projection of the scapula

glenoid fossa

part of the scapula that articulates with the head of the humerus

humeral head

top of the humerus that articulates with the glenoid fossa

anatomical neck

junction between humeral head & rest of humerus

surgical neck

region where the wider proximal end of the humerus meets the narrower shaft of the humerus. Neurovasculature runs around it.

shoulder joints

sternoclavicular, acromioclavicular, glenohumeral, scapulothoracic

Acromioclavicular Joint

planar shoulder joint between acromion process and clavicle

Sternoclavicular Joint

saddle shoulder joint between manubrium and clavicle

Glenohymeral Joint

ball & socket shoulder joint between humeral head and glenoid fossa

Scapulothoracic Joint

articulation between muscle of the scapula with muscle of the posterior thoracic wall. Not a true joint, but range of upper limb motion is augmented by movement of the shoulder girdle

around the thorax

extension of the arm

posterior movement of humerus relative to scapula

flexion of the arm

anterior movement of humerus relative to scapula

abduction of the arm

Movement of the arm away from the midline of the body

adduction of the arm

Movement of the arm towards the midline of the body

lateral rotation of the arm

anterior surface of arm turns to face more laterally

medial rotation of the arm

anterior surface of arm turns to face more medially

Flexors of the arm

- Anterior part of deltoid

- Sternocostal head of pectoralis major

*located anteriorly

Extensors of the arm

- Posterior part of deltoid

- Teres Major

- Latissimus Dorsi

- Long head of triceps brachii

*located posteriorly

Abductors of the arm

- Middle part of Deltoid

- Supraspinatus

*Pass superiorly to glenohumeral joint

Adductors of the arm

- Teres Major

- Latissimus Dorsi

*Inferior to glenohumeral joint

medial rotators of the arm

- Pectoralis Major - both parts

- Latissimus Dorsi

- Subscapularis

- Teres Major

*wrap around humerus from the front

lateral rotators of the arm

- Infraspinatus

- Teres Minor

*wrap around humerus from the back

pectoralis major

muscle of the chest/upper arm with a clavicular head (originates at clavicle) & a sternocostal head (originates at sternum) that both insert on the lateral lip of the intertubercular sulcus of the humerus.

-Clavicular head functions in flexion, adduction, & medial rotation, & is innervated by the lateral pectoral nerve

-Sternocostal head functions in extension (when arm is already flexed), adduction, & medial rotation, & is innervated by the medial pectoral nerve

Deltoid

three-part muscle of the upper arm

-Anterior part originates at the clavicle & functions to flex the arm

-Middle part originates at the acromion & functions to abduct the arm

-Posterior part originates at the scapular spine & functions to extend the arm

-All insert at the deltoid tuberosity of the humerus and are innervated by the axillary nerve

latissimus dorsi

muscle of the back that runs from the thoracolumbar aponeurosis to the intertubercular surface of the humerus & functions to extend, adduct, & medially rotate the arm

-Innervated by the thoracodorsal nerve/middle subscapular nerve

-Shares its actions with teres major

teres major

muscle of the shoulder that runs from the inferior angle of the scapula to the medial lip of the intertubercular surface of the humerus & functions to extend, adduct, & medially rotate the arm

-Innervated by the lower subscapular nerve

-Shares its actions with latissimus dorsi

posterior rotator cuff muscles

supraspinatus, infraspinatus, teres minor

supraspinatus muscle

posterior rotator cuff muscle that runs from the supraspinous fossa of the scapula to the greater tubercle of the humerus. Functions to abduct the arm.

-Innervated by the suprascapular nerve

Infraspinatus

posterior rotator cuff muscle that runs from the infraspinous fossa of the scapula to the greater tubercle of the humerus. Functions to laterally rotate the arm.

-Innervated by the suprascapular nerve

teres minor

posterior rotator cuff muscle that runs from the lateral border of the scapula to the greater tubercle of the humerus. Functions to laterally rotate the arm.

-Innervated by the axillary nerve

Anterior rotator cuff muscles

subscapularis

Subscapularis

anterior rotator cuff muscle that runs from the subscapular fossa of the scapula to the lesser tubercle of the humerus. Functions to medially rotate the arm.

-Innervated by upper & lower subscapular nerves

function of all rotator cuff muscles

reinforce fibrous capsule of glenohumeral joint to help stabilize and protect joint

Motions of Scapula occur at

primarily sternoclavicular and scapulothoracic joints, but also involve acromioclavicular joint

elevation of scapula

pulling scapula upwards

depression of scapula

pulling scapula downwards

protraction of scapula

pulling scapula forwards/laterally around thoracic wall

retraction of scapula

pulling scapula backwards/medially around thoracic wall

upward rotation of scapula

rotating scapula so glenoid fossa faces more superiorly

downward rotation of scapula

rotating scapula so glenoid fossa faces more inferiorly

scapula elevators

- Upper fibers of Trapezius

- Levator Scapulae

- Rhomboid minor

- Rhomboid Major

*extend superior from attachment on scapula

scapula depressors

- Lower fibers of trapezius

- Pectoralis Minor

*extend inferior from attachment on scapula

scapula protractors

- Pectoralis Minor

- Serratus Anterior

*extend anterior from attachment on Scapula

scapula retractors

- Middle fibers of trapezius

- Rhomboid minor

- Rhomboid major

*extend medially from attachment on medial border of scapula

scapula upward rotators

- Trapezius (upper & lower fibers)

- Serratus Anterior (lower part laterally)

*pull upper part of scapula medially and/or lower

part laterally

scapula downward rotators

- Rhomboid Minor

- Rhomboid Major

*pull lower part of scapula medially

trapezius

muscle of the back that runs from the superior nuchal line/nuchal ligament to the clavicle, acromion, & scapular spine. Innervated by CN XI & C3-C4 ventral rami

-Upper fibers elevate the scapula

-Middle fibers retract the scapula

-Lower fibers depress the scapula

-Upper & lower fibers together do glenoid up rotation of scapula, allowing for full range of reaching motion

levator scapulae

muscle of the upper back that runs from transverse processes of upper C vertebrae to the superior angle of the scapula, & functions to elevate the scapula

-Innervated by the dorsal scapular nerve

rhomboid major & minor

upper back muscles that run from the nuchal ligament/upper thoracic transverse processes to the medial border of the scapula, & function to retract, elevated, & glenoid down rotate the scapula.

-Innervated by the dorsal scapular nerve

serratus anterior

muscle that runs from the upper 9 ribs to the medial border of the scapula, & functions to protract & glenoid up rotate the scapula.

-Innervated by the long thoracic nerve

pectoralis minor

muscle of the chest that runs from ribs 3-5 to the coracoid process of the scapula, & functions to protract & depress the scapula

-Innervated by the medial pectoral nerve

long head of triceps brachii runs

posterior to teres major & anterior to teres minor

quadrangular space

passage connecting axilla and posterior shoulder region that allows neurovasculature to get to posterior shoulder region. Contains posterior circumflex humeral artery & axillary nerve.

-Superior border = teres minor

-Lateral border = Surgical neck of humerus

-Inferior border = teres major

-Medial border = long head of triceps brachii

posterior circumflex humeral artery

supplies deltoid & teres muscles. Loops around surgical neck of humerus in quadrangular space.

axillary nerve

innervates deltoid and teres minor muscles. Loops around surgical neck of humerus in quadrangular space.