Topic 5_Anatomy of the Muscular System

Muscle System Overview

• Chapter 9: p. 281-282

• Chapter 10: p. 323-384 (Sections 10.1 – 10.5, omit p. 325-327)

• Content focus: only the muscles included in the PowerPoint presentation.

Usage Rights

• Educational Only: This PowerPoint presentation is for educational purposes only.

• Do not post or distribute without permission from the author.

• Affiliation: Université d’Ottawa | University of Ottawa

Skeletal Muscles Overview

Learning Objectives

• Describe the functions of skeletal muscles.

• Describe characteristics of muscle tissue.

• Understand the gross structure of skeletal muscles, including membranes and tendons/aponeuroses.

Functions of Skeletal Muscles

• Produce movement

• Maintain posture and body position

• Stabilize joints

• generate heat- shivering

Additionally:

• protects organs forms valves controls pupil size

• support soft tissue

• guard entracnes and exit

• store nutritional reserves.

Characteristics of muscle tissue

• excitability (responsiveness)

• Contractility (the ability to shorten and generate force) is another key characteristic, allowing muscles to perform work and produce movement.

• Extensibility: ability to be stretched

• Elasticity: ability to recoil or resume resting length after being stretched

Fascicle Arrangements

• Identify different types of fascicle arrangements in skeletal muscles.

• Define:

  • Agonist: muscle that provides major force for a movement.

  • Antagonist: opposes/reverses a particular movement.

  • Synergist: helps the prime mover and reduces undesirable movement.

  • Fixator: a type of synergist that immoblizes bone.

  • Origin: attachment of muscle that remains fixed.

  • Insertion: attachment that moves during contraction.

Muscle Nomenclature

• Explain the general nomenclature of skeletal muscles.

• Discuss origin, insertion, and action of:

  • Muscles of facial expression.

  • Muscles that move the eyeballs, mandible, and tongue.

  • Muscles of the neck.

  • Muscles moving the vertebral column.

  • Respiratory muscles.

  • Muscles of the pelvic floor and perineum.

  • Muscles that move the pectoral girdle.

  • Muscles of the arm, forearm, thigh, leg, hand, and foot.

Connective Tissue Sheaths

Types of Connective Tissue Wrappings

• Endomysium: fine areolar CT surrounding each muscle fiber.

• Perimysium: dense irregular CT around fascicles (groups of muscle fibers).

• Epimysium: dense, irregular CT surrounding the entire muscle.

• Deep Fascia: coarser layer binding muscles into functional groups.

Muscle Attachments

• Direct Attachment: epimysium fused to the periosteum of bone or perichondrium of cartilage.

• Indirect Attachment: most muscles attach via tendons or aponeuroses, spanning joints and attaching to bones at two points.

Muscle Actions and Interactions

• muscles can only pull;never push

• muscles can work together or in opposition

• 3 functional groups: prime movers, antagonists, synergists

  • muscles can change their role depending on the movement

Functional Groups

• Prime Mover (Agonist): major force for a specific movement.

  • e.g. brachialis in elbow flexion

• Antagonist: opposes the action of prime movers.

  • e.g. triceps in elbow flexion

• Synergist: assists the prime mover to create the same movement.

  • add force

  • reduce unecessary movements

  • holding a bone steady: fixators

• All muscles can change roles depending on the activity (ex: triceps brachii).

Fascicle Arrangement

Types of Fascicle Arrangements

• Circular: concentric rings around openings (e.g., orbicularis oculi).

• Parallel: fascicles parallel to long axis (e.g., sartorius, biceps brachii).

• Pennate: short fascicles attaching obliquely to a central tendon (unipennate, bipennate, multipennate).

• Convergent: fascicles converge towards a single tendon (e.g., pectoralis major).

Naming Skeletal Muscles

Criteria for Naming

• Location: associated with a bone or body region (e.g., intercostals).

• Shape: named based on shape (e.g., deltoid = triangle).

• Size: descriptors (e.g., maximus for largest).

• Direction: fiber orientation (e.g., rectus = straight).

• Number of Origins: e.g., biceps (two heads).

• Attachments: named for points of origin and insertion.

extensor carpi radialis longus

• muscle that extends the wrist and is located along the radial side of the forearm.

• when it gets this specific, usually means there is a carpi ulnaris, otherwise it would just be extensor carpi longus.

Muscles of Facial Expression

Key Muscles

• Epicranius (Frontal and Occipital Bellies): raises eyebrows and fixes the aponeurosis.

• Platysma: tenses neck, depresses the mandible.

• Orbicularis Oculi: protects eyes, enables blinking.

• Zygomaticus: raises corners of the mouth.

• Buccinator: involved in whistling and chewing.

Muscles of Mastication

Key Muscles

• Masseter: primary jaw closure muscle.

• Temporalis: elevates and retracts mandible.

  • Innervated by mandibular division of cranial nerve V.

Eye Movement Muscles

Key Muscles and Functions

• Lateral Rectus: moves the eye laterally (innervated by CN VI).

• Medial Rectus: moves the eye medially (innervated by CN III).

• Superior Rectus: elevates the eye (innervated by CN III).

• Inferior Rectus: depresses the eye (innervated by CN III).

• Superior Oblique: depresses and turns the eye laterally (innervated by CN IV).

• Inferior Oblique: elevates and turns the eye laterally (innervated by CN III).

Muscles of the Neck

Key Muscles

• Sternocleidomastoid: prime mover for head flexion.

• Scalenes: elevates first two ribs and aids in neck rotation.

Back and Vertebral Muscles

Key Muscles

• Erector Spinae: prime mover of back extension.

• Quadratus Lumborum: helps lateral flexion of the vertebral column.

Respiratory Muscles

Key Muscles

• External Intercostals: elevate the rib cage during inspiration.

• Internal Intercostals: depress the rib cage during expiration.

• Diaphragm: prime mover of inspiration, flattening during inhalation.

Abdominal Wall Muscles

Key Muscles

• Rectus Abdominis: flexes and stabilizes the pelvis.

• External Obliques: aid in trunk rotation.

• Transversus Abdominis: compresses abdominal contents.

Muscles of the Pelvic Floor

Key Functions

• Levator Ani and Coccygeus: support pelvic organs, resist intra-abdominal pressure.

Muscles of the Upper Limb

Shoulder Joint Muscles

• Pectoralis Major: prime mover of arm flexion, adduction, and medial rotation.

• Latissimus Dorsi: prime mover of arm extension and adducts the arm.

• Deltoid: prime mover of arm abduction.

Elbow Joint Muscles

• Biceps Brachii: flexes elbow and supinates forearm.

• Triceps Brachii: powerful forearm extensor.

Muscles of the Lower Limb

Key Groups

• Iliopsoas: major hip flexor.

• Quadriceps Femoris: prime mover of knee extension.

• Hamstrings: prime movers of thigh extension and knee flexion.

Leg and Ankle Muscles

• Gastrocnemius: plantar flexes the foot.

• Soleus: assists in plantar flexion.

• Tibialis Anterior: prime mover of dorsiflexion.

Intrinsic Muscles of the Hand and Foot

• Control precise movements of fingers and toes; not required to memorize specific muscles.