Lecture 11 Muscular System Lecture Review
Muscular System Notes
Structure and Functions of Muscle
Skeletal muscles produce movement by exerting force on tendons.
Tendons attach to bones and pull on them, leading to movement.
Muscle Attachments: Origin, Insertion, and Actions
Most muscles cross at least one joint and are attached to the articulating bones.
When a muscle contracts, it draws one articulating bone toward the other.
Origin: The attachment to the stationary bone.
Insertion: The attachment to the moveable bone.
Action(s): The main movements that occur during contraction (e.g., flexion/extension).
Muscle Group Coordination
Most muscle movements are coordinated by several skeletal muscles acting in groups, rather than individually.
Most skeletal muscles are arranged in opposing pairs at joints.
Agonist/Prime Mover: The principal muscle involved with a specific movement.
Antagonist: A muscle that opposes the action of the agonist; it relaxes when the agonist contracts (e.g., biceps/triceps).
Synergist: Muscles that contract at the same time as the agonist to cause movement in the same direction, assisting the prime mover.
Muscle Naming Criteria
Muscles may be named based on:
Location/region
Size
Number of origins
Appearance
Direction of fibers
Origin and Insertion
Muscle action
Skeletal Muscle Structure Recall
Epimysium: Surrounds the entire muscle.
Muscle contains muscle fascicles.
Perimysium: Surrounds each muscle fascicle.
Muscle fascicles contain muscle fibers (muscle cells).
Endomysium: Surrounds each muscle fiber.
Muscle fibers contain myofibrils.
Sarcoplasmic Reticulum: Surrounds myofibrils.
Myofibrils consist of sarcomeres (from Z line to Z line).
Sarcomeres: Contain myofilaments (thick and thin).
Myofilaments: Composed of actin (thin) and myosin (thick).
Regions of a sarcomere include: I band, A band, Z line, M line, H band, and Titin.
Fascicle Arrangement in Muscle Movement
Muscle fibers are arranged in parallel bundles within fascicles, but the arrangement of fascicles varies in relation to the tendon.
Fascicular arrangement is correlated with:
The amount of power a muscle can produce.
The range of motion a muscle can produce.
Organization of Skeletal Muscle Fibers
Muscle fibers within a fascicle are all parallel to each other.
However, fascicles within a muscle can have different arrangements.
Muscle fiber arrangements are classified based on shape or arrangement:
Parallel: Muscle fascicles are parallel to the longitudinal axis (e.g., biceps brachii, rectus abdominis).
Can be fusiform (spindle-shaped, with a belly) or non-fusiform.
Pennate: Fascicles attach obliquely to a central tendon.
Unipennate: Fibers on one side of a tendon (e.g., extensor digitorum).
Bipennate: Fibers on both sides of a central tendon (e.g., rectus femoris).
Multipennate: Tendon branches within the muscle (e.g., deltoid).
Circular: Fascicles are arranged in a concentric ring (e.g., orbicularis oris).
Convergent: Fascicles spread over a broad area and converge at a common attachment point (e.g., pectoralis major).
Muscle Terminology for Actions
2 methods to describe muscle actions:
Reference to the bone region the muscle is associated with (e.g., biceps brachii causes "flexion of the forearm").
Reference to a specific joint the muscle is associated with (e.g., biceps brachii causes "flexion at the elbow").
Major Superficial Anterior and Posterior Skeletal Muscles and Their Functions
Muscles are broadly divided into two categories for identification:
Axial: Muscles of the trunk and head.
Appendicular: Muscles of the limbs and everything else.
Muscles Involved in Facial Expression
Muscles of facial expression lie within the subcutaneous layer.
They originate on the fascia or bones of the skull and insert into the skin.
When these muscles contract, they move the skin rather than a joint.
Examples: Occipitofrontalis (frontal and occipital bellies), Corrugator supercilii, Orbicularis oculi, Orbicularis oris, Buccinator, Epicranial aponeurosis.
Muscles Involved in Eye Movement
The muscles that move the eyeballs are called extrinsic eye muscles because they originate in the orbit and insert on the sclera.
There are 3 pairs (total 6) of extrinsic eye muscles:
Superior and inferior recti of the eyes.
Lateral and medial recti of the eyes.
Superior and inferior obliques of the eyes.
The Levator palpebrae superioris moves the upper eyelid.
Muscles Involved in Mastication and Speech (Mandible Movement)
These muscles are responsible for moving the mandible for chewing.
Examples: Temporalis, Masseter, Lateral pterygoid, Medial pterygoid.
Muscles of the Anterior Neck (Deglutition and Speech)
These muscles assist in swallowing (deglutition) and speech.
Suprahyoid muscles (superior to the hyoid bone): Geniohyoid, Digastric, Mylohyoid, Stylohyoid.
Infrahyoid muscles (inferior to the hyoid bone): Thyrohyoid, Omohyoid, Sternohyoid, Sternothyroid.
The Styloglossus muscle is also associated with the tongue and speech.
Muscles of the Neck (Head Movement)
The head articulates with the vertebral column at joints formed by the atlas and occipital bone.
Balance and movement of the head involve several neck muscles.
The sternocleidomastoid muscle is an important landmark that divides the sides of the neck into two major triangles:
Anterior triangle: Important anatomically and surgically due to the structures within its boundaries.
Posterior triangle: Also anatomically and surgically important for the structures it contains.
Examples: Sternocleidomastoid, Trapezius, Splenius capitis, Levator scapulae, Scalenes (anterior, medial, posterior), Splenius cervicis.
Deep Neck Muscles: Suboccipital muscles, Multifidus, Longissimus capitis, Semispinalis capitis/cervicis.
Muscles of the Abdomen (Protection, Vertebral Column Movement)
The anterolateral abdominal wall is composed of skin, fascia, and 6 layers of muscles.
These muscles protect abdominal viscera and contribute to vertebral column movement.
Examples: Rectus abdominis, Abdominal external oblique.
Muscles of the Thorax (Respiration)
Respiratory muscles alter the size of the thoracic cavity, which affects pressure in the lungs and determines air movement (inhalation/exhalation).
Primary Respiratory Muscles:
Diaphragm: The most important respiratory muscle.
External and Internal Intercostal muscles.
Accessory muscles: Muscles useful in forced breathing.
Diaphragm Features: Contains a central tendon and openings for major vessels and tubes:
Caval opening: For the vena cava.
Esophageal hiatus: For the esophagus.
Aortic hiatus: For the aorta.
Muscles of the Thorax (Pectoral Girdle Movement)
Muscles that move the pectoral girdle also stabilize the scapula.
Scapular movements increase the range of motion of the humerus, which would not be possible otherwise (e.g., raising your arm above the head).
Examples: Subclavius, Pectoralis minor, Serratus anterior, Trapezius, Rhomboid minor, Rhomboid major.
Muscles of the Thorax and Shoulder (Humerus Movement)
7 out of 9 muscles that cross the shoulder joint originate on the scapula (exceptions: pectoralis major and latissimus dorsi).
Rotator Cuff: A nearly complete circle of tendons attached to muscles around the shoulder joint (like a shirt cuff).
Composed of four deep shoulder muscles.
Strengthen and stabilize the shallow shoulder joint.
Join the scapula to the humerus.
Rotator Cuff Muscles: Subscapularis, Teres minor, Supraspinatus, Infraspinatus.
Other Muscles Moving Humerus: Pectoralis major, Deltoid, Latissimus dorsi, Teres major.
Muscles of the Upper Limb (Radius and Ulna Movement)
Most muscles that move the forearm cause flexion and extension at the elbow.
Flexors: Biceps brachii, Brachialis, Brachioradialis.
Extensors: Triceps brachii, Anconeus.
Some muscles that move the forearm are involved in pronation and supination.
Pronators: Pronator teres, Pronator quadratus.
Supinator: The only supinator muscle (functions like a corkscrew or screwdriver).
Muscles of the Forearm (Wrist, Hand, Thumb, and Fingers)
Extrinsic muscles of the hand: Originate outside the hand and insert within it.
These muscles are divided into anterior and posterior compartment groups based on location and function:
Anterior (Flexor) Extrinsic Muscles: Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris, Flexor digitorum superficialis, Flexor digitorum profundus, Flexor pollicis longus.
Posterior (Extensor) Extrinsic Muscles: Extensor digitorum, Extensor digiti minimi, Abductor pollicis longus, Extensor pollicis longus, Extensor pollicis brevis, Extensor indicis.
Retinacula: Strong fascial bands that hold the tendons of these muscles close to the bones as they cross the wrist.
Intrinsic Hand Muscles (associated with eminences):
Thenar Eminence (thumb side): Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.
Hypothenar Eminence (pinky side): Abductor digiti minimi, Flexor digiti minimi brevis, Opponens digiti minimi.
Other intrinsic hand muscles include Adductor pollicis and Lumbricalis muscles.
Muscles of the Neck and Back (Vertebral Column Movement)
Splenius muscles: Extend, laterally flex, and rotate the head (includes Splenius capitis, Splenius cervicis).
Erector spinae muscles: Primarily responsible for extension of the vertebral column; also affect flexion, lateral flexion, and rotation.
Include three groups: Iliocostalis (lateral), Longissimus (intermediate), and Spinalis (medial).
Many other small, deep muscles also contribute.
Muscles of the Gluteal Region (Femur Movement)
Gluteus maximus: The chief extensor of the femur.
Gluteus medius: Primarily an abductor of the femur.
Also Gluteus minimus.
Muscles of the Thigh (Femur, Tibia, and Fibula Movement)
Deep fascia separates thigh muscles into medial, anterior, and posterior compartments.
Most originate on the pelvic girdle and insert on the femur.
Medial (Adductor) Compartment of the Thigh: Adduct the femur at the hip joint.
Muscles: Adductor longus, Adductor brevis, Adductor magnus, Gracilis, Obturator externus, Pectineus.
Gracilis: A long, straplike muscle on the medial aspect of the thigh and knee that adducts and medially rotates the thigh, and flexes the leg at the knee joint.
Anterior (Extensor) Compartment of the Thigh: Extend the leg (and flex the thigh).
Quadriceps Group (common tendon: quadriceps tendon, inserts into patella):
Rectus femoris: Anterior thigh.
Vastus lateralis: Lateral thigh.
Vastus medialis: Medial thigh.
Vastus intermedius: Deep to the rectus femoris, between the vastus lateralis and vastus medialis.
Sartorius: A long, narrow muscle forming a band across the thigh from the ilium to the medial side of the tibia.
Other muscles include Iliopsoas, Pectineus, Articularis genu.
Posterior (Flexor) Compartment of the Thigh: Flex the leg (and extend the thigh).
Hamstrings:
Biceps femoris.
Semitendinosus.
Semimembranosus.
Femoral Triangle
A space at the junction between the trunk and lower limb.
Base: Formed superiorly by the inguinal ligament.
Medial border: Formed by the lateral border of the adductor longus muscle.
Lateral border: Formed by the medial border of the sartorius muscle.
Contents (from lateral to medial): Femoral nerve and its branches, femoral artery and its branches, femoral vein and its proximal tributaries, and the deep inguinal lymph nodes.
Muscles of the Leg (Foot and Toes Movement)
Note: The term "leg" scientifically refers only to the region from the knee down (does not include the thigh).
Leg muscles are divided by deep fascia into three compartments: anterior, lateral, and posterior.
Anterior compartment muscles: Primarily dorsiflex the foot (e.g., Tibialis anterior, Extensor digitorum longus, Extensor hallucis longus, Fibularis tertius).
Lateral compartment muscles: Primarily plantar flex and evert the foot (e.g., Fibularis longus, Fibularis brevis).
Posterior compartment muscles: Divided into superficial and deep groups.
Superficial group: Share a common tendon of insertion, the calcaneal (Achilles) tendon (e.g., Gastrocnemius, Soleus, Plantaris).
Deep group: (e.g., Popliteus, Tibialis posterior, Flexor digitorum longus, Flexor hallucis longus).
Motor Units and Muscle Control
Muscle Hypertrophy:
Enlargement of the muscle.
Exercise causes an increase in:
Number of mitochondria.
Activity of muscle spindles.
Concentration of glycolytic enzymes.
Glycogen reserves.
Number of myofibrils.
The net effect is enlargement of the muscle.
Muscle Atrophy:
Discontinued use of a muscle.
Disuse causes:
Decrease in muscle size.
Decrease in muscle tone.
Physical therapy helps to reduce the effects of atrophy.
Aging and Skeletal Muscle (SKM)
SKM fibers become smaller in diameter as we age.
The number of myofibrils decreases.
Muscles contain less glycogen reserves.
Muscles contain less myoglobin.
There is a decrease in myosatellite cells (stem cells for muscle repair).
There is an increase in fibrous connective tissue.
These changes result in:
A decreased ability to recover from muscular injuries.
A decrease in strength and endurance.
Muscles fatigue rapidly.
Structure and Functions of Muscle
Skeletal muscles produce movement by exerting force on tendons.
Tendons attach to bones and pull on them, leading to movement.
Muscle Attachments: Origin, Insertion, and Actions
Most muscles cross at least one joint and are attached to the articulating bones.
When a muscle contracts, it draws one articulating bone toward the other.
Origin: The attachment to the stationary bone.
Insertion: The attachment to the moveable bone.
Action(s): The main movements that occur during contraction (e.g., flexion/extension).
Muscle Group Coordination
Most muscle movements are coordinated by several skeletal muscles acting in groups, rather than individually.
Most skeletal muscles are arranged in opposing pairs at joints.
Agonist/Prime Mover: The principal muscle involved with a specific movement.
Antagonist: A muscle that opposes the action of the agonist; it relaxes when the agonist contracts (e.g., biceps/triceps).
Synergist: Muscles that contract at the same time as the agonist to cause movement in the same direction, assisting the prime mover.
Muscle Naming Criteria
Muscles may be named based on:
Location/region
Size
Number of origins
Appearance
Direction of fibers
Origin and Insertion
Muscle action
Fascicle Arrangement in Muscle Movement
Muscle fibers are arranged in parallel bundles within fascicles, but the arrangement of fascicles varies in relation to the tendon.
Fascicular arrangement is correlated with:
The amount of power a muscle can produce.
The range of motion a muscle can produce.
Organization of Skeletal Muscle Fibers
Muscle fibers within a fascicle are all parallel to each other. However, fascicles within a muscle can have different arrangements.
Muscle fiber arrangements are classified based on shape or arrangement:
Parallel: Muscle fascicles are parallel to the longitudinal axis (e.g., biceps brachii, rectus abdominis).
Can be fusiform (spindle-shaped, with a belly) or non-fusiform.
Pennate: Fascicles attach obliquely to a central tendon.
Unipennate: Fibers on one side of a tendon (e.g., extensor digitorum).
Bipennate: Fibers on both sides of a central tendon (e.g., rectus femoris).
Multipennate: Tendon branches within the muscle (e.g., deltoid).
Circular: Fascicles are arranged in a concentric ring (e.g., orbicularis oris).
Convergent: Fascicles spread over a broad area and converge at a common attachment point (e.g., pectoralis major).
Major Superficial Anterior and Posterior Skeletal Muscles and Their Functions
Muscles are broadly divided into two categories for identification:
Axial: Muscles of the trunk and head.
Appendicular: Muscles of the limbs and everything else.
Muscles Involved in Facial Expression
Lie within the subcutaneous layer, originate on fascia or skull bones, and insert into the skin.
Cause movement of the skin rather than a joint.
Examples: Occipitofrontalis (frontal and occipital bellies), Orbicularis oculi, Orbicularis oris, Buccinator.
Muscles Involved in Eye Movement
Called extrinsic eye muscles; originate in the orbit and insert on the sclera.
There are 3 pairs (total 6) of extrinsic eye muscles: Superior/inferior recti, lateral/medial recti, superior/inferior obliques.
Levator palpebrae superioris moves the upper eyelid.
Muscles Involved in Mastication and Speech (Mandible Movement)
Responsible for moving the mandible for chewing and speech.
Examples: Temporalis, Masseter, Lateral pterygoid, Medial pterygoid.
Muscles of the Anterior Neck (Deglutition and Speech)
Assist in swallowing (deglutition) and speech.
Suprahyoid muscles (e.g., Geniohyoid, Digastric) and Infrahyoid muscles (e.g., Thyrohyoid, Omohyoid).
Styloglossus is also associated with the tongue and speech.
Muscles of the Neck (Head Movement)
Balance and movement of the head involve several neck muscles.
Sternocleidomastoid muscle divides the neck into anterior and posterior triangles.
Examples: Sternocleidomastoid, Trapezius, Splenius capitis, Levator scapulae, Scalenes.
Muscles of the Abdomen (Protection, Vertebral Column Movement)
Anterolateral abdominal wall muscles protect abdominal viscera and contribute to vertebral column movement.
Examples: Rectus abdominis, Abdominal external oblique.
Muscles of the Thorax (Respiration)
Alter the size of the thoracic cavity to facilitate inhalation/exhalation.
Primary Respiratory Muscles: Diaphragm (most important, with caval opening, esophageal hiatus, aortic hiatus), External and Internal Intercostal muscles.
Accessory muscles: Useful in forced breathing.
Muscles of the Thorax (Pectoral Girdle Movement)
Stabilize the scapula and increase humerus range of motion.
Examples: Subclavius, Pectoralis minor, Serratus anterior, Trapezius, Rhomboid minor, Rhomboid major.
Muscles of the Thorax and Shoulder (Humerus Movement)
These muscles cross the shoulder joint to move the humerus.
Rotator Cuff: Four deep shoulder muscles (Subscapularis, Teres minor, Supraspinatus, Infraspinatus) strengthen and stabilize the shoulder joint.
Other Muscles Moving Humerus: Pectoralis major, Deltoid, Latissimus dorsi, Teres major.
Muscles of the Upper Limb (Radius and Ulna Movement)
Cause flexion and extension at the elbow, and pronation/supination.
Flexors: Biceps brachii, Brachialis, Brachioradialis.
Extensors: Triceps brachii, Anconeus.
Pronators: Pronator teres, Pronator quadratus.
Supinator: The only supinator muscle.
Muscles of the Forearm (Wrist, Hand, Thumb, and Fingers)
Extrinsic muscles of the hand: Originate outside the hand and insert within it, divided into anterior (flexor) and posterior (extensor) compartments.
Anterior (Flexor) Extrinsic Examples: Flexor carpi radialis, Palmaris longus, Flexor digitorum superficialis, Flexor pollicis longus.
Posterior (Extensor) Extrinsic Examples: Extensor digitorum, Extensor digiti minimi, Abductor pollicis longus, Extensor pollicis longus.
Retinacula: Strong fascial bands holding tendons at the wrist.
Intrinsic Hand Muscles: Associated with Thenar Eminence (thumb side, e.g., Opponens pollicis) and Hypothenar Eminence (pinky side, e.g., Abductor digiti minimi).
Muscles of the Neck and Back (Vertebral Column Movement)
Splenius muscles: Extend, laterally flex, and rotate the head.
Erector spinae muscles: Primarily for extension of the vertebral column, also affect flexion, lateral flexion, and rotation (Iliocostalis, Longissimus, Spinalis).
Muscles of the Gluteal Region (Femur Movement)
Gluteus maximus: Chief extensor of the femur.
Gluteus medius: Primarily an abductor of the femur.
Also Gluteus minimus.
Muscles of the Thigh (Femur, Tibia, and Fibula Movement)
Deep fascia separates thigh muscles into medial, anterior, and posterior compartments.
Medial (Adductor) Compartment: Adduct the femur (e.g., Adductor longus, Gracilis).
Anterior (Extensor) Compartment: Extend the leg and flex the thigh.
Quadriceps Group: Extends the leg (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius).
Sartorius: Flexes the leg and thigh.
Posterior (Flexor) Compartment: Flex the leg and extend the thigh.
Hamstrings: Biceps femoris, Semitendinosus, Semimembranosus.
Muscles of the Leg (Foot and Toes Movement)
Divided into three compartments: anterior, lateral, and posterior.
Anterior compartment: Primarily dorsiflex the foot (e.g., Tibialis anterior, Extensor digitorum longus).
Lateral compartment: Primarily plantar flex and evert the foot (e.g., Fibularis longus).
Posterior compartment: Divided into superficial and deep groups.
Superficial group: Share the calcaneal (Achilles) tendon (e.g., Gastrocnemius, Soleus