KIN 1Y03 Lecture 33: Skeletal Muscle Gross Anatomy Pt1

origin/head vs insertion vs belly

Origin/Head: muscle end attached to more stationary of 2 bones – ū more proximal 

Insertion: muscle end attached to bone with greatest movement – ū distal 

Belly: largest portion of hte muscles between origin and insertion – able ot have multiple bellies (eg. bellies)

tendons vs ligaments

ligaments = connect bone to bone

tendons = connect muscle to bone

aponeurosis

very broad tendon (u sheet-like)

agonist vs antagonist

[Agonist: muscle that, when contracted, will cause an action 

[Antagonist: a muscle working in opposition to agonist 

⇒ both will vary based on movement: 

•  Bicep contracting ⇒ cause flexion @ elbow ⇒ agonist 

  • ⤷ triceps = antagonist 

• Elbow going from flexion ⇒ extension 

  • ⤷ bicep = antagonist 

  • ⤷ tricep = agonist

synergists

muscles that work together to cause a movement 

Prime mover: plays a major role in accomplishing movement 

Fixators: stabilize joints crossed by the primer mover; prevents movement of the origin of the prime mover 

• ⤷ eg.scapula ⇒ ū just “floating” but fixed in place that allows other joints to move 

examples of muscles named according to… location

• Location: pectoralis (chest), gluteus (butt), brachial (arm) 

examples of muscles named according to… size

• Size – ū group of muscles: maximus (largest in group), minimus (smallest), longus (longest), brevis (shortest), vastus (huge), major (larger-causing more action), minor (smaller) 

examples of muscles named according to… shape

• Shape: deltoid (triangle), quadratus (shape), teres (rounded from cross-section), trapezius (trapezoid) 

examples of muscles named according to… action/function

• Action/function: abductor, adductor, masseter (mastication/chewing), extensors 

examples of muscles named according to… orientation or direction of fibers

• Orientation or direction of fibers: rectus (fibers in erect fashion, parallel to midline), transverse (perpendicular to midline), oblique (@ angle) 

examples of muscles named according to… origins/insertions

• Origin and insertion: sternocleidomastoid (attaches to sternum, clavicle, and mastoid process on temporal bone), brachioradialis (attach on radius + brachial region) 

examples of muscles named according to… number of heads

• Number of heads: biceps (2), triceps (3) 

examples of muscles named according to… number of muscles

• Number of muscles: quadriceps (4 diff muscles) 

What muscle groups allow for flexion, extension and rotation + lateral flexion for neck ?? (idk relationship between question)

Flexion: are ū muscles deep within the neck along and originate from anterior margins of the vertebral bodies ⇒ then extend up to occipital bone

• ⤷ anterior muscles that allow for flexion 

Extension: posterior neck muscles attached to occipital bone and mastoid process 

Rotation and lateral flexion (tile of neck to shoulder): lateral and posterior groups 

sternocleidomastoid

 prime movers that originate on manubrium of sternum and clavicle 

⤷ will extend up and insert on mastoid process 

⤷ lateral muscle ⇒ will cause forward flexion of head if all muscles are contracting OR tilting ear to sternum (working both muscle heads) 

⤷ has 2 heads – the sternal head – originates from the manubrium of the sternum & clavicular head – originates from the medial third of the clavicle 

Trapezius

prime mover posterior muscle that is trapezoid shaped

• ⤷ has fibers in many diff DIR (which dictate the way muscles contract) 

• ⤷ movement for neck → extension + lateral flexion 

muscles that move the vertebral column is divided into deep and superficial groups

Deep group: short muscles that go from vertebra to vertebra 

Superficial group: extends from vertebrae to ribs 

⤷ eg. erector spinae: prime mover of the back extension with 3 subgroups 

Subgroups – spinalis thoracis (ū medial), longissimus muscle (ū intermediate), iliocostalis muscle (ū lateral)  [DONT NEED TO KNOW, JUST KNOW IT HAS 3 SUBGROUPS]

erector spinae

prime mover of the back extension with 3 subgroups 

scalene

thoracic muscles associated w rib cage

scalene: u elevates the first 2 ribs during inspiration (bc it doesn’t have anything above them)

external intercostal

thoracic muscles associated w rib cage

• External intercostal: elevate the ribs 

  • ⤷ muscles are found in between the ribs → goes superficial to deep as they go from inferior margin of 1 rib to superior border of the rib below 

  • ⤷ during contraction, ribs will expand up and down

    • Muscle DIR = “hands in pocket” oblique angle, pointing towards the midline 

internal intercostal

thoracic muscles associated w rib cage

• Internal intercostal: depress ribs during expiration 

• ⤷ job: pull inferior ribs back into place 

• ⤷ deeper muscles than external intercostals

• ⤷ DIR of muscles = perpendicular to “hands in pocket”

transversus thoracis

thoracic muscles associated w rib cage

• Transversus thoracis: depresses ribs during expiration 

  • ⤷ work w internal intercostals to depress ribs during expiration 

  • ⤷ run from sternum to costal cartilages 

diaphragm

dome-shaped muscle that runs upward-medially/inferior-superior DIR

• ⤷ separation between thoracic and abdominal cavity

inspiration vs expiration + what happens to the ribs and diaphragm

Inspiration: “breathing in” 

• Ribs – will move upward and outward as the external intercostal muscles contract 

• Diaphragm – contracts and moves downward, increasing the volume of the chest cavity 

• ⤷ will create a vacuum & cause the lungs to expand and draw air in from the outside (↑ volume of the thoracic cavity)  

Expiration: “breathing out” 

• Ribs – move downwards and inwards 

• Diaphragm – relaxes and moves upwards 

• ⤷ will decreases the volume of the thoracic cavity – increasing the pressure inside the lungs and forces air out.

abdominal wall

• Will flex and rotate vertebral column, decrease volume of abdominal and thoracic cavities ⇒ “compression” 

• Compression movement will help in forced expiration, vomiting, defecation, urination, childbirth 

• Muscle fibers has a criss-cross pattern of muscles, adding to the strength of the abdominal wall to support organs – enforced with muscles bc no bone

rectus abdominis

 most medial (only medial muscles) 

⤷ fibers run up/down in rectus formation

⤷ gives the “six-pack” appearance 

⤷ muscles separated in intervals by CT, involved in flexion of vertebral column + some compression

external abdominal oblique

superficial muscles, where fibers run @ oblique DIR (“hands in pocket”) 

⤷ flexion and rotation of vertebral column + compression

Internal abdominal oblique

deep muscles, where fibers run perpendicular to “hands in pocket”

⤷ flexion, rotation, and compression

transversus abdominis

fibers that run in transverse (horizontal) DIR, responsible for compression of the abdominal cavity

linea alba

CT @ center line, where all the muscles will attach to the linea alba 

scapular movement

muscles that attach the upper limbs to the body and move/stabilize the scapula and clavicle 

⤷ will originate on the axial skeleton – limbs are connected to the scapula 

• incl. trapezius, levator scapulae, rhomboideus/rhomboid (minor and major), serratus anterior, pectoralis minor

trapezius

trapezoid looking muscle on the posterior side, responsible for elevation and depression of the scapula + rotation

levator scapulae

 deep to trapezius, responsible for elevation/rotation of scapula 

• ⤷ goes up to the cervical vertebrae and inserts @ top point of scapula 

rhomboideus/rhomboid + 2 components

runs from vertebrae to medial border of scapula, will pull scapula towards vertebrae that “square” shoulders  

Composed of 2 muscles: 

Rhomboid minor: lower, smaller

Rhomboid major: higher, bigger

serratus anterior

holds scapula in place on the thoracic cage 

• ⤷ anterior to teh scapula 

• ⤷ runs from teh lateral edge of series of ribs and runs underneath scapula to medial border of scapula @ midline 

• ⤷ responsible for movements of arms held anterior (“boxers muscles”) 

• ⤷ looks like serrated knife

pectoralis minor

Pectoralis minor: goes from the 3rd-5th ribs, extending up and inserts onto the coracoid process of scapula ⇒ wrapping around shoulder joints 

• ⤷ job: depresses scapula and pulls on top of scapula