anat and phys lecture 12

prime mover/agonist

the muscle that generates most of the force

antagonist

the opposing muscle groups that lengthens/controls the action

mechanical advantage

exists when the distance between the effort and fulcrum is greater than the distance between load and fulcrum

• generates greater force

mechanical disadvantage

when the distance between load and fulcrum is greater than the distance between effort and fulcrum

class I lever

1) load 2) fulcrum 3) effort

example:

• load: the mass of the skull is in front of the foramen magnum

• fulcrum: the occipital condyles onto the vertebral column (C1)

• effort: the splenius muscle that extends your neck

may have mechanical advantage

class II lever

1) effort 2) load 3) fulcrum

• always has a mechanical advantage

example:

• effort: calf muscle pulling leg up

• load: body weight traveling down onto heel of foot

• fulcrum: toes/metatarsal

class III lever

1) load 2) effort 3) fulcrum

no mechanical advantage because distance between load and fulcrum is greater than distance between effort and fulcrum but most muscles are class III lever because the load is traveling a longer distance than insertion but will take the same amount of time to move the load

example:

• load: weight on the hand

• effort: the bicep pulling the weight up

• fulcrum: the elbow joint

facial muscles

occipital frontalis

orbicurcilaris oculi

orbicurcularis oris

zygomaticus

buccinator

risourius

levatator labii

depressor labii

corrugator supercili

platysma

occipital frontalis

also called the epicranius

• frontal portion/epicranius frontalis:

  • origin: galea aponeurotica (a fascia sheet/connective tissue on top of the skull)

  • insertion: fascia of the eyebrows

  • when activated: lifts up the eyebrows and causes the forehead to furrow

• occipital portion/epicranius occipitalis

  • origin: occipital bone

  • insertion: galea aponeurotica

  • when activated: holds the galea aponeuritca in place by pulling it posteriorly

orbicularis oculi

• origin: maxilla/frontal bone

• insertion: tissues around the eye

• when activated: closes eyes/squinting

orbicularis oris

• origin: maxilla/mandible

• insertion: tissues around the mouth

• when activated: lips are closed/portrude

zygomaticus

• origin: zygomatic bone

• insertion: angle of the mouth

• when activated: pulls the mouth laterally and superiorly (smile)

buccinator

deep under the fascia and masseter

• origin: maxilla

• insertion: orbicurcularis oris at angle of the mouth

• when activated: pulls the mouth laterally

risorius

superficial to the masseter

• origin: superficial fascia over the masseter

• insertion: orbicularis oris at angle/corner of the mouth

• when activated: pulls the mouth laterally

levatator labii

• origin: maxilla

• insertion: tissue on the lips

• when activated: pulls the lips up

depressor labii

• origin: mandible

• insertion: tissue on the lips

• when activated: pull the lips down

corrugator supercilli

• origin: frontal bone

• insertion: tissue on the eyebrow

• when activated: pulls the eyebrows towards each other

platysma

• origin: fascia of the chest

• insertion: inferior edge of the mandible

• when activated: depresses the mandible

muscles of mastification

masseter

temporalis

medial pterygoid

lateral pterygoid

masseter

• origin: zygomatic arch

• insertion: mandibular ramus

• when activated: elevates the jaw/mandible (occurs when chewing)

temporalis

• origin: temporal bone

• insertion: coronoid process of mandible

• when activated: pulls the mandible back to keep the jaw closed when you aren’t talking/chewing, can elevate the jaw

medial pterygoid

• origin: medal side of the lateral pterygoid

• insertion: medial side of the mandible

• when activated: elevates the jaw

lateral pterygoid

• origin: lateral side of the pterygoid plate

• insertion: condylar process of mandible

• when both are activated: pushes the mandible forward

• when only one is activated: can push mandible side to side

extrinsic muscles of the tongue

muscles outside of the tongue that move the tongue, we have more voluntary control

• genioglossus

• hyoglossus

• styloglossus

genioglossus

• origin: inside of the mandible

• insertion: tongue

• when activated: tongue is extended forward

hyoglossus

• origin: hyoid bone

• insertion: tongue

• when activated: depresses the tongue

styloglossus

• origin: styloid process

• insertion: tongue

• when activated: pulls tongue back

muscles that move the head and neck

extension:

• splenius capitis

• trapezius

flexion:

• sternocleomastoid

• scalene muscles

splenius capitis

• origin: vertebral column

• insertion: superior nuchal line and mastoid process

• when activated simultaneously: extends the neck

• when activated individually: laterally tilts the head

trapezius

• origin: occipital bone

• insertion: clavicle

• when activated simultaneously: extends neck

• when activated individually: laterally flexes the neck

sternocleomastoid

• origin: manubrium/clavicle

• insertion: mastoid process/superior nuchal line

• when activated simultaneusly: flexes the head

• when activated individually: laterally flexes

scalene muscles

• origin: vertebral column

• insertion: first two ribs

• when activated: can contribute to flexing and laterally flexing the head

intrinsic muscles of the back

erector spinae: illiocostalis, longissimus, spinalis

• all have their origins inferior to its insertion

• function: holds upper part of vertebral column/pulls it back to keep it erect

• illiocosalis and lonigssimus have their insertions lateral to the origins allowing for lateral flexion

illiocostalis

• region: most lateral

• costal=ribs: tendons attach to ribs

longissimus

• region: in between (intermediate) illiocostalis and spinalis

spinalis

• region: closest to the vertebral column