Muscular System lab Review pg 42

Region-by-Region Muscle Survey

(All muscles named in the transcript are reproduced exactly; bold indicates the instructor expects you to learn origin, insertion, and action.)

Region 1 – Head

• Temporalis
• Masseter (jaw clenching on side[s])
• Frontalis
• Buccinator (cheek)
• Orbicularis oculi (eye)
• Orbicularis oris (lips)
• Sternocleidomastoid (technically neck but listed on p. 1)

Region 2 – Neck & Back

• Trapezius
• Levator scapulae
• Rhomboid major
• Rhomboid minor
• Latissimus dorsi

Region 3 – Posterior Upper Limb (Shoulder/Arm)

• Deltoid
• Supraspinatus
• Infraspinatus
• Subscapularis
• Teres minor
• Teres major
• Triceps brachii (three heads: long, lateral, medial)

Region 4 – Anterior Upper Limb

• Pectoralis major
• Pectoralis minor
• Serratus anterior
• Coracobrachialis
• Biceps brachii (two heads)
• Brachialis

Region 5 – Forearm

• Brachioradialis
• Extensor carpi radialis longus
• Extensor carpi radialis brevis
• Extensor digitorum
• Extensor carpi ulnaris
• Flexor carpi ulnaris
• Palmaris longus
• Flexor carpi radialis

Region 6 – Thorax & Abdomen

• Diaphragm
• External intercostals
• Internal intercostals
• Rectus abdominis
• External obliques
• Internal obliques
• Transverse abdominis
• Inguinal ligament (tendinous landmark)
• Psoas major

Region 7 – Anterior & Medial Thigh

• Rectus femoris
• Vastus lateralis
• Vastus medialis
• Vastus intermedius (listed again in Region 8)
• Sartorius
• Gracilis
• Pectineus
• Adductor longus
• Adductor brevis
• Adductor magnus

Region 8 – Gluteal Region & Posterior Thigh

• Gluteus maximus
• Gluteus medius
• Biceps femoris (two heads)
• Semitendinosus
• Semimembranosus
• (Re-listed) Vastus intermedius

Region 9 – Leg

• Plantaris
• Popliteus
• Gastrocnemius (two heads)
• Soleus
• Tibialis anterior
• Peroneus (fibularis) longus

Detailed Origins, Insertions, & Actions

(The instructor uses bold in the packet; those entries are reproduced here with full detail. Remember the O → I rule: muscle action occurs as fibers shorten, pulling insertion toward origin.)

• Sternocleidomastoid
– Origin: Manubrium of sternum & sternal end of clavicle
– Insertion: Mastoid process of temporal bone
– Actions: Flex neck (bilateral); rotate head to opposite side (unilateral)
– Clinical note: A tight SCM gives the appearance of torticollis (“wry neck”).

• Deltoid
– Origin: Clavicle, acromion, spine of scapula
– Insertion: Deltoid tuberosity of humerus
– Action (middle fibers): Abduct \text{glenohumeral} joint; anterior & posterior fibers also flex/extend & rotate.
– Real-world: Site for intramuscular injections ≤ 2\,\text{mL}.

• Supraspinatus
– Origin: Supraspinous fossa
– Insertion: Superior part of greater tubercle
– Action: Initiates first 15^{\circ} of abduction; stabilizes rotator cuff.

• Infraspinatus
– Origin: Infraspinous fossa
– Insertion: Middle greater tubercle
– Action: Lateral rotation of shoulder; rotator-cuff stabilization.

• Subscapularis
– Origin: Subscapular fossa
– Insertion: Lesser tubercle
– Action: Medial rotation of shoulder.

• Teres minor
– Origin: Lateral scapular border
– Insertion: Inferior part of greater tubercle
– Action: Lateral rotation; weak adduction.

• Teres major
– Origin: Inferior angle of scapula
– Insertion: Crest just distal to lesser tubercle
– Actions: Extend, adduct, medially rotate shoulder (a “lat assistant”).

• Brachialis
– Origin: Anterior humeral diaphysis
– Insertions: Ulnar tuberosity & coronoid process
– Action: Primary elbow flexor (all forearm positions).

• Triceps brachii
– Origins: Long-head – infraglenoid tubercle; Lateral-head – posterior/lateral humerus; Medial-head – posterior humerus
– Insertion: Olecranon
– Action: Extend elbow (long head also extends & adducts shoulder).

• Coracobrachialis
– Origin: Coracoid process
– Insertion: Medial humeral diaphysis
– Actions: Flex & adduct shoulder (brings humerus “coracoid-ward”).

• Biceps brachii
– Origins: Long-head – supraglenoid tubercle; Short-head – coracoid process
– Insertion: Radial tuberosity (and via bicipital aponeurosis to fascia)
– Actions: Flex elbow, supinate forearm (powerful when elbow flexed ≈90^{\circ}).

• Rectus femoris
– Origin: Anterior inferior iliac spine (AIIS)
– Insertion: Tibial tuberosity (via patellar ligament)
– Actions: Flex hip; extend knee (the only bi-articular quadriceps head).

• Vastus lateralis / medialis / intermedius
– Origins: Lateral – greater trochanter & linea aspera; Medial – linea aspera; Intermedius – anterior/lateral femoral diaphysis
– Insertion: Tibial tuberosity
– Action: Extend knee (VM also stabilizes patella medially).

• Adductor longus / brevis / magnus
– Origins: Body of pubis (longus); Inferior pubic ramus (brevis); Inferior pubic & ischial rami + ischial tuberosity (magnus)
– Insertion: Linea aspera (magnus also adductor tubercle)
– Actions: Adduct hip; magnus also flexes (adductor part) or extends (hamstring part) hip.

• Biceps femoris
– Origins: Long-head – ischial tuberosity; Short-head – linea aspera
– Insertion: Head of fibula
– Actions: Extend hip (long); flex knee; laterally rotate leg when knee flexed.

• Semitendinosus / Semimembranosus
– Origin: Ischial tuberosity
– Insertions: Proximal medial tibia (pes anserinus, ST); medial tibial condyle (SM)
– Actions: Extend hip; flex & medially rotate knee.

• Gastrocnemius
– Origins: Posterior medial condyle (medial head) & posterior lateral condyle (lateral head) of femur
– Insertion: Calcaneus via calcaneal tendon
– Actions: Plantar-flex ankle; flex knee.

• Soleus
– Origin: Posterior fibula & soleal line of tibia
– Insertion: Calcaneus
– Action: Plantar-flex ankle (postural muscle for standing).

• Plantaris
– Origin: Femoral supracondylar line
– Insertion: Calcaneus (via long thin tendon)
– Action: Weak plantar-flexion; “freshman’s nerve”.

• Popliteus
– Origin: Lateral femoral condyle & lateral meniscus
– Insertion: Proximal posterior tibia
– Action: Medially rotates tibia to unlock knee (“key to the knee”).

• Tibialis anterior
– Origin: Lateral tibial condyle & shaft
– Insertion: Medial cuneiform & 1st metatarsal
– Actions: Dorsiflex & invert ankle; supports medial arch.

Action-Only Muscles (Name & Primary Function)

• Frontalis – elevate eyebrows (surprise wrinkle lines).
• Buccinator – compress cheeks; keeps bolus between teeth for mastication.
• Orbicularis oculi – close eyes (blink, squint).
• Orbicularis oris – close/protrude lips (kissing, whistle).
• Trapezius – elevate, adduct, stabilize scapula; extend neck.
• Levator scapulae – elevate scapula.
• Rhomboid major/minor – retract (adduct) scapula.
• Latissimus dorsi – extend, adduct, medially rotate shoulder (swimmer’s stroke).
• Pectoralis major – flex, adduct, medially rotate shoulder (push-up).
• Pectoralis minor – depress scapula.
• Serratus anterior – abduct/protract scapula (prevents winging).
• Brachioradialis – flex forearm; brings radius/ulna to neutral (beer-lifting muscle).
• Extensor carpi radialis longus/brevis – extend & abduct wrist.
• Extensor digitorum – extend fingers.
• Extensor carpi ulnaris – extend & adduct wrist.
• Flexor carpi ulnaris – flex & adduct wrist.
• Palmaris longus – weak wrist flexor; tendon used for grafting.
• Flexor carpi radialis – flex & abduct wrist.
• Diaphragm – prime mover of inhalation.
• External intercostals – elevate ribs (quiet inspiration).
• Internal intercostals – depress ribs (forced expiration).
• Rectus abdominis – flex trunk; compress abdomen (sit-ups).
• External & Internal obliques – flex, laterally flex, rotate trunk; compress abdomen.
• Transverse abdominis – compress abdomen; stabilizes spine.
• Inguinal ligament – forms inferior border of abdominal wall; landmark for hernias.
• Psoas major – flex trunk & hip.
• Sartorius – flex & laterally rotate hip; flex knee (“tailor sit”).
• Gracilis – flex & adduct hip; flex knee.
• Pectineus – flex & adduct hip.
• Gluteus maximus – extend & laterally rotate hip (climb stairs).
• Gluteus medius – abduct hip; stabilizes pelvis during gait.
• Peroneus (fibularis) longus – plantar-flex & evert ankle; supports lateral arch.

Comparative Chart – Three Types of Muscle Fibers

(Original page gives raw data; converted to concise bullet comparison.)

• Smooth Muscle
– AKA: involuntary, non-striated, plain
– Fiber length: 0.02 \text{ mm} to 0.5 \text{ mm}
– Diameter: up to 10\,\mu\text{m}
– Single central nucleus; no cross striations; no intercalated discs
– Contraction: slow, rhythmic, sustained
– Control: myogenic; CNS input modulates but isn’t required
– Location: walls of viscera, vessels, ducts, ciliary muscle, arrector pili.

• Skeletal Muscle
– AKA: voluntary, striated, red or white
– Fiber length: 1–40\,\text{mm}
– Diameter: 10–40\,\mu\text{m}
– Multinucleate syncytium (nuclei at periphery); conspicuous striations
– Rapid, powerful contractions but easily fatigued
– Neurogenic: contracts only when stimulated by somatic motor neuron
– Distribution: locomotor muscles, diaphragm, body wall.

• Cardiac Muscle
– Striated, branching fibers; intercalated discs present
– Fiber length: \le 0.08\,\text{mm}; diameter \approx 15\,\mu\text{m}
– Single central nucleus
– Contraction: moderately rapid, rhythmic with rest periods; not fatiguing
– Myogenic pacemaker; rate modulated by autonomic nerves
– Found only in heart.

Mnemonic tip: “SkiLL – Skeletal is Large & Long”; “Smooth is Small & Slow.”
Ethical/clinical note: Cardiac & smooth muscle regeneration is limited; skeletal muscle can hypertrophy but not readily replace lost fibers.

Connections & Significance

• Rotator cuff (SITS = Supraspinatus, Infraspinatus, Teres minor, Subscapularis) stabilizes glenohumeral joint; tears common in overhead athletes.
• Quadriceps femoris (RF + vasti) share insertion on patella → tibial tuberosity; imbalance → patellar tracking issues.
• Hamstring group (biceps femoris, semitendinosus, semimembranosus) crosses hip & knee; strains occur during sprinting.
• Diaphragm innervated by phrenic nerve (C3–C5) – “C3,4,5 keeps the diaphragm alive.”
• Abdominal wall muscles create intra-abdominal pressure (Valsalva) useful for defecation, childbirth, heavy lifting.
• Inguinal ligament landmark for femoral artery puncture & inguinal hernia assessment.
• Plantar flexors (gastrocnemius, soleus) form triceps surae; crucial for push-off in gait.
• Popliteus unlocking mechanism prevents damaging hyperextension when initiating knee flexion.

Helpful Study Strategies

• Create flash cards with O-I-A on one side, muscle name on the other.
• Trace actions on your own body to feel the muscle contract.
• Use color-coding: red for origin, blue for insertion, green for action.
• Compare muscle fiber charts to predict fatigue resistance (e.g., soleus = predominantly slow-twitch).
• Relate movements to daily activities (e.g., temporalis & masseter during chewing dinner).
• Group by innervation to deepen understanding (e.g., median nerve forearm flexors).