PSIO 201 LAB block 3

🧠 Muscles of the Face, Head, and Neck

What is the action of the Frontalis?

Raises eyebrows and wrinkles forehead.

Which muscle works with the frontalis to move the scalp?

Occipitalis (via epicranial aponeurosis).

What is the antagonist of the frontalis?

Orbicularis oculi (closes the eyes).

What does the Occipitalis do?

Draws the scalp posteriorly.

What is the action of Orbicularis oculi?

Closes eyes (blinking or squinting).

What is the action of Orbicularis oris?

Closes and puckers lips (kissing or whistling).

Which muscle helps you smile by raising mouth corners?

Zygomaticus major.

What does the Masseter do?

Elevates and protracts the mandible (closes jaw).

What is the main antagonist of the Masseter?

depresses mandible

What is the action of the Platysma?

Depresses lower lip and mandible; tenses neck skin.

What is the main action of the Sternocleidomastoid?

One side rotates head to opposite side; both flex neck.

Which muscles are antagonists to the sternocleidomastoid?

Splenius capitis and trapezius (neck extension).

💪 Muscles of the Abdomen and Vertebral Column

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What is the antagonist of the Rectus abdominis?

Erector spinae group.

What is the action of the External oblique?

Compresses abdomen, flexes and rotates trunk to opposite side.

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Frontalis

Raises eyebrows and wrinkles forehead; draws scalp anteriorly.

Occipitalis

Draws scalp posteriorly; connected to frontalis by the epicranial aponeurosis.

Orbicularis oculi

Closes each eye as in blinking or squinting.

Orbicularis oris

Closes and puckers lips, as in kissing or whistling.

Zygomaticus major

Raises lateral corners of mouth upward (smiling).

Zygomaticus minor

Elevates upper lip, exposing upper teeth.

Masseter

Elevates and protracts mandible; helps with chewing.

Platysma

Depresses lower lip and mandible; tenses skin of neck.

Sternocleidomastoid

One side rotates head to opposite side; both sides flex the neck.

💪 Muscles of the Abdomen and Vertebral Column

Rectus abdominis

Flexes vertebral column and compresses the abdomen.

External oblique

Compresses abdomen; flexes and rotates trunk to opposite side.

Internal oblique

Compresses abdomen; flexes and rotates trunk to same side.

Transverse abdominis

Compresses abdomen (deepest abdominal layer).

Erector spinae (Iliocostalis, Longissimus, Spinalis)

Extends vertebral column and maintains erect posture.

Mnemonic for abdominal muscle order (deep → superficial)

TIRE — Transverse abdominis, Internal oblique, Rectus abdominis, External oblique.

Mnemonic for erector spinae order (lateral → medial)

I Like Standing — Iliocostalis, Longissimus, Spinalis.

🦴 Muscles that Move the Pectoral Girdle

Trapezius (superior fibers)

Elevates and superiorly rotates scapula.

Trapezius (middle fibers)

Retracts (adducts) scapula.

Trapezius (inferior fibers)

Depresses and helps superiorly rotate scapula.

Levator scapulae

Elevates and inferiorly rotates scapula.

Pectoralis minor

Depresses, protracts (abducts), and inferiorly rotates scapula.

Serratus anterior

Protracts (abducts) and superiorly rotates scapula.

💪 Muscles that Move the Arm

Pectoralis major

Flexes, adducts, and medially rotates the arm.

Deltoid (anterior fibers)

Flex and medially rotate the arm.

Deltoid (middle fibers)

Abduct the arm.

Deltoid (posterior fibers)

Extend and laterally rotate the arm.

Supraspinatus

Abducts the arm (initiates abduction).

Infraspinatus

Adducts and laterally rotates the arm.

Teres major

Extends, adducts, and medially rotates the arm.

Teres minor

Extends and laterally rotates the arm.

Subscapularis

Medially rotates the arm.

Latissimus dorsi

Adducts, extends, and medially rotates the arm.

💪 Muscles that Move the Forearm

Brachioradialis

Flexes forearm, especially when hand is midway between pronation and supination.

Pronator teres

Pronates and flexes forearm.

✋ Muscles that Move the Hand and Digits (Flexors)

Mnemonic for flexors (lateral → medial, anterior side)

Pass, Fail, Pass, Fail — Pronator teres, Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris.

Flexor carpi radialis

Flexes and abducts wrist.

Palmaris longus

Flexes wrist.

Flexor carpi ulnaris

Flexes and adducts wrist.

Flexor digitorum superficialis

Flexes middle phalanges (PIP joints) of digits 2–5.

Flexor digitorum profundus

Flexes distal phalanges (DIP joints) of digits 2–5.

✋ Muscles that Move the Hand and Digits (Extensors)

Mnemonic for extensors (lateral → medial, posterior side)

Longus, Brevis, Longus, Brevis — Brachioradialis, Extensor carpi radialis longus, Extensor carpi radialis brevis, Abductor pollicis longus, Extensor pollicis brevis.

Extensor digitorum

Extends fingers 2–5.

Extensor carpi ulnaris

Extends and adducts wrist.

Extensor carpi radialis longus

Extends and abducts wrist.

Extensor carpi radialis brevis

Extends and abducts wrist.

Extensor digiti minimi

Extends little finger (digit 5).

Abductor pollicis longus

Abducts and extends thumb.

Extensor pollicis brevis

Extends thumb at metacarpophalangeal joint.

🫁 Primary Muscles of Respiration

External intercostals

Elevate ribs during inspiration (quiet and labored).

Internal intercostals

Depress ribs during forced expiration.

Diaphragm

Contracts downward during inspiration to expand thoracic cavity.

Is quiet expiration active or passive?

Passive — it occurs when diaphragm and external intercostals relax.

Muscle fiber

A single muscle cell composed of myofibrils, enclosed by a plasma membrane called the sarcolemma.

Sarcolemma

Specialized plasma membrane of a muscle fiber that conducts action potentials and is continuous with T-tubules.

Endomysium

Connective tissue layer surrounding each individual muscle fiber.

Fascicle

A bundle of individual muscle fibers.

Perimysium

Dense irregular connective tissue that surrounds fascicles.

Skeletal muscle (whole muscle)

Formed by groups of fascicles.

Epimysium

Dense irregular connective tissue that surrounds the entire muscle.

Tendon

Formed from the combined endomysium, perimysium, and epimysium; attaches muscle to bone.

Are the sarcolemma and endomysium the same?

No — sarcolemma is the muscle cell membrane; endomysium is connective tissue surrounding the cell.

⚡ EXCITATION SUMMARY (Neuromuscular Junction)

Step 1 of excitation

Nerve signal (action potential) arrives at the axon terminal.

Step 2 of excitation

Acetylcholine (ACh) is released from synaptic vesicles into the synaptic cleft.

Step 3 of excitation

ACh binds to receptors on the motor end plate of the sarcolemma.

Step 4 of excitation

ACh binding opens receptor-channels → sodium enters → End Plate Potential (EPP) is generated.

Step 5 of excitation

The EPP triggers a muscle action potential (AP) on the sarcolemma.

⚙️ EXCITATION–CONTRACTION (E–C) COUPLING SUMMARY

Step 6 of E–C coupling

Muscle AP travels down T-tubules.

Step 7 of E–C coupling

DHP receptor activates the RYR channel, releasing Ca²⁺ from the sarcoplasmic reticulum into the sarcoplasm.

Step 8 of E–C coupling

Calcium binds to troponin.

Step 9 of E–C coupling

Troponin moves tropomyosin, exposing actin’s myosin-binding sites.

🔁 CROSS-BRIDGE CYCLE SUMMARY

Step 10

ATP hydrolysis “cocks” the myosin head into a high-energy position.

Step 11

Cross-bridge forms as myosin head binds to exposed actin site.

Step 12

ADP + Pi released → Power stroke → Myosin head pulls thin filament toward center (sarcomere shortens).

Step 13

New ATP binds to myosin → cross-bridge breaks → cycle can repeat.

💤 RELAXATION SUMMARY

Step 14

Nerve signals stop arriving at the neuromuscular junction.

Step 15

ACh release stops; remaining ACh is broken down by acetylcholinesterase (AChE).

Step 16

No ACh → no EPP → no muscle AP → Ca²⁺ release from SR stops → Ca²⁺ reabsorbed into SR.

Step 17

Ca²⁺ concentration in sarcoplasm drops; troponin no longer bound to Ca²⁺.

Step 18

Tropomyosin covers binding sites on actin → cross-bridges cannot form → muscle relaxes.

🔬 MICROANATOMY OF A SKELETAL MUSCLE FIBER

Transverse (T) tubules

Extensions of the sarcolemma that transmit APs deep into the cell.

Sarcoplasmic reticulum (SR)

Network that stores and releases calcium ions into the sarcoplasm.

Terminal cisternae

Enlarged areas of the SR that store calcium; located on either side of T-tubules.