LAB 3 Exam Notes Comprehensive Notes on Skeletal Muscle Tissue, Contraction Mechanism, and Muscular Anatomy of the Head and Neck

Administrative and Study Guidelines

  • Exam Preparation: For the upcoming lab exam, students must use the provided lecture PowerPoints rather than companion materials. The companion material images are often unclear for identifying models and specific muscles.

  • Slide Identification: Specific slides from Chapters 17 and 18 are designated for the lab exam. Students should mark these slides to focus their study efforts effectively.

  • Course Management: Only three weeks remain in the term (this is the end of the second week). Students are encouraged to evaluate their grades and make necessary adjustments immediately.

  • Learning Strategy: The lecture and lab materials overlap significantly. There are no tricks or surprises on exams; they reflect class discussions.

Anatomy of Skeletal Muscle Membranes

  • Hierarchical Membranes: Skeletal muscle is organized by three distinct layers of connective tissue membranes:

    • Endomysium: The innermost membrane that surrounds an individual muscle fiber.

    • Perimysium: The middle membrane that wraps a bundle of muscle fibers together. This bundle of fibers is structurally known as a fascicle.

    • Epimysium: The outermost membrane that wraps around the entire muscle.

Microscopic Anatomy of the Muscle Fiber

  • Internal Hierarchies: Muscles are broken down into individual muscle fibers, which contain deeper structures called myofibrils. Within myofibrils are the specific contractile components known as myofilaments.

  • Myofilaments: There are two primary types of contractile proteins:

    • Thin Filament: Composed of the protein actin.

    • Thick Filament: Composed of the protein myosin.

  • Sarcolemma: This is the specialized muscle membrane surrounding an individual myofibril. It is the site where the neuron interacts with the muscle at the neuromuscular junction.

  • Triad Components: A critical anatomical feature of the muscle fiber is the triad, which consists of three parts:

    • Sarcoplasmic Reticulum: A network that houses $Ca^{2+}$ (calcium).

    • Terminal Cistern (x2): These are the end segments of the sarcoplasmic reticulum that store calcium. Each triad has two terminal cisterns.

    • T Tubule (x1): Also known as a transverse tubule, it is a yellow-colored structure in diagrams that carries the action potential (impulse) deep into the muscle fiber.

    • Formula: 1 T tubule+2 terminal cisterns=triad1\, \text{T tubule} + 2\, \text{terminal cisterns} = \text{triad}.

The Sarcomere: The Functional Unit of Contraction

  • Definition: The sarcomere is defined as the functional unit of muscle contraction. Muscles contain millions of these units.

  • Sarcomere Borders: A sarcomere spans the distance from one Z line to the next Z line.

  • Internal Bands and Regions:

    • I band: Contains actin filaments only.

    • H band: Contains myosin filaments only.

    • A band: contains both actin and myosin filaments.

  • Effects of Contraction on Bands:

    • The H band shortens.

    • The I band shortens.

    • The entire sarcomere shortens as the Z lines come closer together.

    • Critical Distinction: The A band remains the same size and does not change length during contraction.

Molecular Components of Myofilaments

  • Thin Filament (Actin) Anatomy:

    • Actin Molecule: Contains an active site where the myosin head binds during contraction.

    • Troponin: The specific molecule where $Ca^{2+}$ (calcium) binds to initiate the contraction process.

    • Tropomyosin: A regulatory protein that covers the active sites on actin when the muscle is at rest. During contraction, it moves to expose those active sites.

  • Thick Filament (Myosin) Anatomy:

    • Myosin Head: Undergoes a hinge-like movement.

    • Power Stroke: The movement of the myosin head that causes the actual contraction (pulling the actin).

    • Recovery Stroke: The process where the myosin head resets to its original position after a contraction is complete.

The 14-Step Progression of Muscle Contraction

  1. Action Potential 1: A nerve impulse (action potential) travels down the motor neuron to reach the axon terminal (the end of the nerve).

  2. Calcium Entry: The arrival of the action potential causes calcium to enter the axon terminal.

  3. Neurotransmitter Release: The entry of calcium triggers the release of the neurotransmitter acetylcholine (ACh) from synaptic vesicles into the synaptic cleft (the space between the nerve and the muscle).

  4. ACh Binding: Acetylcholine travels across the synaptic cleft and binds to specific acetylcholine receptors on the sarcolemma.

  5. Sodium Influx: Binding of ACh opens channels, allowing sodium ($Na^+$) to rush into the muscle cell.

  6. Depolarization: The influx of positive sodium ions (cations) into a negative environment makes the inside of the muscle cell less negative, a process known as depolarization.

  7. Threshold: If enough sodium enters to reach a specific electrical charge called the threshold, the muscle will fire its own impulse.

  8. Action Potential 2: This second action potential travels along the T tubules through the muscle fiber.

  9. Calcium Release: The action potential in the T tubule causes $Ca^{2+}$ to be released from the terminal cisterns of the sarcoplasmic reticulum.

  10. Calcium-Troponin Binding: Released calcium binds to troponin on the actin filament.

  11. Tropomyosin Shift: The binding of calcium to troponin causes tropomyosin to move, exposing the active sites on the actin molecules.

  12. The Power Stroke: The myosin heads bind to the active sites on actin and undergo a power stroke, causing the sarcomere to shorten and the muscle to contract.

  13. Myosin Detachment: ATP is consumed to detach the myosin head from the actin active site so it can undergo a recovery stroke (resetting).

  14. Cleanup and Reset: Calcium is sequestered (pumped back) into the terminal cisterns, and the enzyme acetylcholinesterase breaks down the remaining acetylcholine in the synaptic cleft to prevent continuous stimulation.

Muscles of the Head and Face

  • Standard Identification:

    • Frontalis: Muscle over the frontal bone (anterior head).

    • Occipitalis: Muscle over the occipital bone (posterior head).

    • Temporalis: Muscle over the temporal bone.

  • Muscles of Mastication (Chewing): These include the Temporalis, the Masseter, and the Pterygoids (Lateral and Medial pteryoids).

    • Masseter: A superficial muscle with fibers running in a North-to-South direction.

    • Buccinator: Located deep to the masseter; fibers run in an East-to-West direction. Its function is cheek compression (e.g., blowing up a balloon or playing wind instruments like the saxophone or clarinet).

  • Circular Muscles (Orbicularis):

    • Orbicularis Oculi: The circular muscle surrounding the eye.

    • Orbicularis Oris: The circular muscle surrounding the mouth.

  • Smiling Muscles:

    • Zygomatic Minor: The superior smiling muscle.

    • Zygomatic Major: The inferior smiling muscle.

    • Rhizorius: Termed the "first day of fifth grade muscle" because it pulls the mouth laterally (creating a forced, wide expression rather than a full smile).

Muscles of the Neck and Throat

  • Terminology of Attachment:

    • Origin: The proximal attachment site of a muscle.

    • Insertion: The distal attachment site of a muscle.

  • Sternocleidomastoid (SCM):

    • Origins: One head on the sternum and one head on the clavicle (cleido).

    • Insertion: The mastoid process of the temporal bone.

    • Primary Actions: Neck (cervical) flexion and contralateral rotation. (Example: Contracting the right SCM turns the head to the left).

    • Clinical Condition: Torticollis, a medical condition involving spasms of the SCM that causes the head/chin to stay turned in one direction (often seen in infants post-birth).

  • Scalenes: Deep muscles located underneath the SCM that also aid in neck flexion.

    • Clinical Condition: Thoracic Outlet Syndrome (TOS) occurs when the scalenes spasm and pinch the nerve bundle in the neck, causing numbness in the arm and hand (common in baseball pitchers).

  • Digastric Muscle: A muscle used for opening the mouth.

    • Antagonistic Relationship: The digastric muscle is antagonistic to the muscles of mastication (the muscles of mastication close the jaw; the digastric opens it).






🦴 AHS 131 LAB EXAM 3 MASTER STUDY GUIDE

(Everything you actually need to know)

Professor said focus on:

✅ Identification
✅ Action
✅ Origin & Insertion (only when emphasized)


PART 1 — MUSCLE CONTRACTION (HIGH YIELD)

Know this IN ORDER.

1. Action Potential arrives at motor neuron terminal

↓

2. Calcium enters axon terminal

Calcium causes neurotransmitter release.

↓

3. Acetylcholine (ACh) released

Released into the synaptic cleft.

↓

4. ACh binds receptors

Receptors are on the sarcolemma (muscle membrane).

↓

5. Sodium rushes into muscle cell

This causes

Depolarization

(the inside becomes less negative.)

↓

6. More voltage-gated sodium channels open

Even more sodium enters.

↓

7. Threshold reached

A muscle action potential is created.

↓

8. Action potential travels down T-tubules

This causes the sarcoplasmic reticulum to release calcium.

↓

9. Calcium binds Troponin

Troponin changes shape.

↓

10. Tropomyosin moves away

Active sites on actin become exposed.

↓

11. Myosin binds Actin

Cross bridges form.

Power Stroke occurs.

Muscle shortens.

Sarcomere shortens.

Z-discs move closer together.

↓

12. ATP binds Myosin

ATP releases the myosin head.

No ATP = Rigor Mortis

↓

13. Calcium pumped back into SR

Muscle relaxes.

↓

14. Acetylcholinesterase breaks down ACh

Signal stops.


KNOW THESE DEFINITIONS

Sarcolemma

Muscle cell membrane

Sarcoplasm

Cytoplasm of muscle

Sarcoplasmic Reticulum

Stores calcium

T Tubules

Carry action potential deep into muscle

Troponin

Binds calcium

Tropomyosin

Blocks actin binding sites

Actin

Thin filament

Myosin

Thick filament


ORIGIN vs INSERTION

Professor wrote this on your sheet.

Origin

✅ Usually proximal
✅ Less movable

Insertion

✅ Usually distal
✅ More movable

Example:

Biceps

Origin = Shoulder

Insertion = Radius

When muscle contracts

Insertion moves toward Origin.


HEAD MUSCLES


Frontalis

Identification:
Forehead

Action:
Raises eyebrows
Wrinkles forehead


Occipitalis

Back of skull

Action

Pulls scalp backward


Temporalis

Side of skull

Fan-shaped

Action

Elevates mandible

Closes jaw


Masseter

Cheek

Very thick

One of the strongest muscles in body

Action

Elevates mandible

Main chewing muscle


Medial Pterygoid

Action

Elevates jaw

Grinding food


Lateral Pterygoid

Action

Protracts jaw

Opens mouth slightly

Moves jaw side to side


Orbicularis Oculi

Circular muscle around eye

Action

Closes eyelids

Blinking

Squinting


Orbicularis Oris

Circular muscle around mouth

Action

Closes lips

Puckers lips

“Kissing muscle”


FACIAL MUSCLES


Buccinator

Deep cheek muscle

Action

Compresses cheeks

Keeps food between teeth

Whistling

Sucking


Risorius

Action

Pulls corner of mouth laterally

Produces grin


Zygomatic Major

Action

Raises corner of mouth

Smiling


Zygomatic Minor

Action

Raises upper lip

Smiling


NECK MUSCLES


Sternocleidomastoid (VERY IMPORTANT)

Origin

Sternum
Clavicle

Insertion

Mastoid process

Action

Bilateral

Flexes neck

Unilateral

Rotates head to opposite side

Clinical

Torticollis


Scalenes

Action

Flex neck

Elevate ribs during inspiration

Clinical

Thoracic outlet syndrome


Levator Scapulae

Action

Elevates scapula

Shrugging

Neck side bending


Digastric

Action

Depresses mandible

Opens mouth

Swallowing

Opposes Masseter


MUSCLES OF THE TRUNK


Trapezius

Diamond shaped

Action

Elevates scapula

Retracts scapula

Depresses scapula

Extends neck


Latissimus Dorsi

Largest back muscle

Action

Extension

Adduction

Medial rotation of arm

Think:

Pull-ups
Swimming


Deltoid

Shoulder cap

Action

Abduction

Anterior fibers

Flexion

Posterior fibers

Extension


Pectoralis Major

Chest muscle

Action

Adduction

Flexion

Medial rotation

“Hugging muscle”


Serratus Anterior

Looks like fingers

Action

Protracts scapula

Holds scapula against ribs

Clinical

Winged scapula


Rhomboids

Action

Retract scapula


Levator Scapulae

Raises shoulder


ROTATOR CUFF MUSCLES

Remember

SITS

S

Supraspinatus

Starts arm abduction


I

Infraspinatus

Lateral rotation


T

Teres Minor

Lateral rotation


S

Subscapularis

Medial rotation


ARM MUSCLES


Biceps Brachii

Action

Flex elbow

Supinates forearm

Origin

Scapula

Insertion

Radius


Brachialis

Primary elbow flexor

Deep to biceps


Triceps

Action

Extends elbow


Brachioradialis

Neutral grip flexor

Hammer curl muscle


FOREARM FLEXORS

Generally

Flex wrist

Flex fingers

Located anteriorly


FOREARM EXTENSORS

Generally

Extend wrist

Extend fingers

Located posteriorly


ABDOMINAL MUSCLES


Rectus Abdominis

“Six pack”

Action

Flex trunk


External Oblique

Action

Contralateral rotation

Lateral flexion


Internal Oblique

Action

Ipsilateral rotation

Lateral flexion


Transversus Abdominis

Deepest

Action

Compresses abdomen

Core stabilization


LOWER EXTREMITY


Gluteus Maximus

Largest muscle

Action

Hip extension

Standing up

Climbing stairs


Gluteus Medius

Action

Hip abduction

Keeps pelvis level


Tensor Fasciae Latae

Action

Abducts thigh

Stabilizes knee


QUADRICEPS

Remember

RF + VL + VM + VI

Rectus Femoris

Flexes hip

Extends knee


Vastus Lateralis

Extends knee


Vastus Medialis

Extends knee


Vastus Intermedius

Extends knee


HAMSTRINGS

Remember

B-ST-SM

Biceps Femoris

Semitendinosus

Semimembranosus

Action

Hip extension

Knee flexion


ADDUCTORS

Action

Bring thigh toward midline


SARTORIUS

Longest muscle

Action

Flex

Abduct

Laterally rotate hip

Flex knee

“Crossing your legs”


TIBIALIS ANTERIOR

Action

Dorsiflexion

Inversion

Heel walking


GASTROCNEMIUS

Calf muscle

Action

Plantar flexion

Flexes knee

Standing on toes


SOLEUS

Deep calf

Action

Plantar flexion


FIBULARIS (PERONEUS) LONGUS

Action

Eversion

Plantar flexion


MUSCLE IDENTIFICATION TIPS

Circular around eye

Orbicularis Oculi

Circular around mouth

Orbicularis Oris

Thick cheek

Masseter

Fan-shaped temple

Temporalis

Forehead

Frontalis

Smile muscles

Zygomaticus

Deep cheek

Buccinator

Large chest

Pectoralis Major

Shoulder cap

Deltoid

Diamond back

Trapezius

Large wing muscle

Latissimus Dorsi

Six pack

Rectus Abdominis

Butt

Gluteus Maximus

Front thigh

Quadriceps

Back thigh

Hamstrings

Front shin

Tibialis Anterior

Calf

Gastrocnemius


⭐ LAST-MINUTE MEMORY TRICKS

  • Masseter = Mastication (chewing)

  • Orbicularis = Orbits (circles)

  • Zygomaticus = Smile

  • Buccinator = Blow/Whistle

  • SCM = Sternum + Clavicle → Mastoid

  • SITS = Rotator cuff

  • Biceps = Bend + Supinate

  • Triceps = Throw (extend)

  • Quadriceps = Knee extension

  • Hamstrings = Knee flexion

  • Tibialis anterior = Toes up (dorsiflexion)

  • Gastrocnemius = Tiptoes (plantar flexion)