110 Lever Systems + Muscles of the Head, Anterior Neck and Throat

3 components of lever system

Lever: rigid bar (bone) that moves on a fixed point, fulcrum (joint)

• the fulcrum position is relative to load and effort

Effort: force (supplied by muscle contraction) applied to lever to move resistance (load)

Load: resistance (bone + tissues + any added weight) moved by the effort

Functional groups of skeletal muscles

• prime mover of one movement

• antagonist for different movement

• synergist for third movement

Example of a circular fascicle arrangement

orbicularis oris

• fascicles arranged in concentric rings

Example of a convergent fascicle arrangement

pectoralis major

• fascicles converge toward single tendon insertion

Example of a fusiform fascicle arrangement

biceps brachii

• spindle-shaped muscles with parallel fibers

Example of a parallel fascicle arrangement

sartorius

• fascicles parallel to long axis of strap-like muscle

Pennates

Advantages of levers

• allows given effort to move heavier load

• moves the load farther or faster

Mechanical advantage

• aka power lever

• load is close to fulcrum

• effort is far from fulcrum

• small effort will move large load

  • slower

  • more stable

  • used where strength is a priority

Mechanical disadvantage

• aka speed lever

• load is far from fulcrum

• effort is close to fulcrum

• load moves rapidly over large distance; offers wider range of motion

  • force is lost

  • speed and range of movement are gained

First-class lever system

• aka CLASSICAL system

• fulcrum is between load and effort

examples:

• chin lowering and lifting (head nodding up and down)

  • load = weight of facial skeleton

  • fulcrum = atlanto-occipital joint

  • effort = posterior neck muscles

• seesaw, scissors

Second-class lever system

• load is between fulcrum and effort

• aka power system

examples

• standing on tippy toe

  • fulcrum = joints of the ball of the foot

  • load = weight of the body

  • effort = calf muscles pulling upward on the heel

• wheelbarrow

Third-class lever system

• effort is applied between fulcrum and load

• aka speed system

examples

• flexing the forearm by the biceps brachii muscle

  • load = hand and distal end of forearm

  • effort = exerted on the proximal radius of the forearm (bicep muscle)

  • fulcrum = elbow joint

• tweezers, forceps

Most skeletal muscles work by the _____ class lever system

third

How are facial expression muscles different?

Unlike most muscles, they insert into skin, not bone

Facial expression muscles are important in:

nonverbal communication

All facial expression muscles are _________________ by ____________ nerve ______.

innervated; cranial; 7

Cranial nerve VII is also known as?

facial nerve

Facial expression muscles consist of two groups: muscles of the __________ and ___________.

scalp; face

Key muscle of the scalp

Epicranius

Epicranius has 2 major ________.

bellies

• Frontal belly/frontalis muscle ==> raised eyebrows/wrinkled forehead

• Occipital belly/occipitalis muscle

Frontalis and occipitalis muscles are connected by:

a specialized tendon, epicranial aponeurosis

Which muscle raises/lowers eyebrows? (ie. frowning)

Corrugator supercilii

Corrugator supercilii

• has a frontal belly attachment

• inserts into eyebrow

Which muscle closes/blinks eyes?

Orbicularis oculi

Which muscle raises lateral corners of mouth? (aka smiling muscle)

Zygomaticus major and minor

• starts around zygomatic bone

• inserts on the lateral edges of lips

Which muscle draws corner of lip laterally?

Risorius

• masseter muscle

• lateral edges of lips

Which muscle opens lips?

Levator labii superioris

• zygomatic bone, maxilla

• inserts onto lateral parts of upper lip

Which muscle draws lower lip inferiorly? (aka pout)

Depressor labii inferioris

• mandible

• inserts into the lower lip

Which muscle draws corners of mouth down and laterally?

Depressor anguli oris

• mandible

• inserts around the mouth

Which muscle closes lips? (pucker lips)

Orbicularis oris

• origins around the maxilla and mandible

• encircles the whole mouth

Which muscle wrinkles chin?

Mentalis

• origins in mandible

• inserts into the chin

Which muscle compresses cheek? (sucking in)

Buccinator

• inserts on the orbicularis oris muscle

Which muscle tenses skin of neck?

Platysma

Facial expression muscle diagram

Different facial expressions

Muscles of mastication

• 4 pairs [MTPB]

• All innervated by cranial nerve V

What are the prime movers of jaw closure?

Temporalis and masseter

Which muscles are responsible for the mouth’s grinding movements?

Pterygoids

What extrinsic muscles promote tongue movement (anchor + move tongue)?

Genioglossus

Hyoglossus

Styloglossus

Which muscle moves and closes jaw?

Masseter

General location of temporalis?

• O: temporal bone

• inserts in the mandible

Temporalis muscle plays a role in ______ closure.

Jaw

What muscle protracts (pull anteriorly) the jaw/mandible and promotes side-to-side (grinding) movements?

Medial and lateral pterygoids

Which muscle compresses the cheeks and plays a role in chewing?

Buccinator

Purpose of buccinator muscle

• keeps food in mouth

• allows for good chewing surface

Which muscle protracts (stick out) tongue?

Genioglossus

Which muscle depresses tongue?

Hyoglossus

The styloglossus _______ and _______ the tongue.

retracts; elevates

The styloglossus origins at the

temporal bone

The lateral pterygoid has a _________ head and an ___________ head

superior; inferior

Styloglossus is ___________ to the hyoglossus

superior

Genioglossus is _________ to the hyoglossus

anterior

What muscle divides the neck into two triangles (anterior and posterior)?

Sternocleidomastoid muscle

Anterior neck and throat muscles are divided based on __________ to the ________ bone: ______hyoid and ______hyoid

location; hyoid; supra; infra

What muscles push food back towards the pharynx during the swallowing process?

The tongue and buccinator muscles

Muscles in __________ mouth and __________ complete the swallowing process

posterior; pharynx

___________ closes over _________ while muscles in walls of _________ propel food forward to stomach

Epiglottis; larynx; pharynx

Functions of suprahyoid muscles

• form floor of oral cavity

• anchor tongue

• elevate hyoid bone

• move larynx during swallowing

Functions of infrahyoid muscles

• depress hyoid bone and larynx during swallowing and speaking

Good Samaritan does marathon

suprahyoid muscles:

• Geniohyoid

• Stylohyoid

• Digastric

• Mylohyoid

All 4 suprahyoid muscles insert into the

hyoid bone

Which of the suprahyoid muscles open mouth and depress mandible?

Digastric

Which of the suprahyoid muscles elevates and retracts hyoid?

Stylohyoid

Which of the suprahyoid muscles elevates hyoid bone and floor of mouth?

Mylohyoid

Which of the suprahyoid muscles pulls hyoid bone superiorly and anteriorly?

Geniohyoid

Stylohyoid muscle origins at the

temporal bone

Which of the suprahyoid muscles origin at the mandible?

Mylohyoid and geniohyoid

All but 1 of the 4 infrahyoid muscles inserts into the hyoid bone. What muscle is it and where does it insert into instead?

Sternothyroid; thyroid cartilage

If mandible is fixed, which muscle depresses larynx and hyoid bone?

Sternohyoid

Sternohyoid origins at

manubrium and clavicle

Which muscle depresses larynx and hyoid bone?

Sternothyroid

Which muscle depresses and retracts hyoid bone?

Omohyoid

If hyoid is fixed, which muscle depresses hyoid bone or elevates larynx?

Thyrohyoid

Which muscle plays a role in constricting pharynx during swallowing?

Pharyngeal constrictor muscles

How many pharyngeal constrictor muscles are there?

3: superior, middle, inferior

Where do pharyngeal constrictor muscles originate from and insert into?

O: mandible (superior), hyoid bone (middle), and laryngeal cartilages (inferior)

I: pharynx

TOSS

infrahyoid muscles:

• Thyrohyoid

• Omohyoid

• Sternohyoid

• Sternothyroid

Digastric muscle

• has anterior and posterior belly

• U-shaped

Omohyoid muscle

• has superior and inferior belly

Geniohyoid is ________ to mylohyoid muscle

posterior