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Questions and Answers
Which arrangement of fascicles is characterized by concentric rings?
Which arrangement of fascicles is characterized by concentric rings?
What is the primary purpose of knowing a muscle's origin and insertion points?
What is the primary purpose of knowing a muscle's origin and insertion points?
Which type of muscle fascicle arrangement features fibers that run parallel to the long axis?
Which type of muscle fascicle arrangement features fibers that run parallel to the long axis?
Which of the following muscle actions is associated with the contraction of the biceps brachii?
Which of the following muscle actions is associated with the contraction of the biceps brachii?
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What can be inferred about the name 'extensor carpi radialis longus'?
What can be inferred about the name 'extensor carpi radialis longus'?
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Which of the following describes the role of agonists in muscle movement?
Which of the following describes the role of agonists in muscle movement?
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What term describes muscles that work together with agonists to enhance a movement?
What term describes muscles that work together with agonists to enhance a movement?
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Which classification would a muscle that immobilizes a bone or muscle origin fall under?
Which classification would a muscle that immobilizes a bone or muscle origin fall under?
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What naming convention would be applied to a muscle with fibers running perpendicular to an imaginary axis?
What naming convention would be applied to a muscle with fibers running perpendicular to an imaginary axis?
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Which muscle condition is identified by its size as being the smallest among its group?
Which muscle condition is identified by its size as being the smallest among its group?
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What action do muscles primarily serve to achieve?
What action do muscles primarily serve to achieve?
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Which of the following naming conventions would apply to a muscle that has two origins?
Which of the following naming conventions would apply to a muscle that has two origins?
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Which group of muscles opposes the actions of agonists?
Which group of muscles opposes the actions of agonists?
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Which muscle is primarily responsible for closing the eye?
Which muscle is primarily responsible for closing the eye?
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What action does the Masseter muscle perform?
What action does the Masseter muscle perform?
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Which muscle helps elevate the first two ribs during inspiration?
Which muscle helps elevate the first two ribs during inspiration?
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Which muscle is part of the forearm flexors?
Which muscle is part of the forearm flexors?
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What is the main function of the Rectus abdominis muscle?
What is the main function of the Rectus abdominis muscle?
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Which muscle acts to abduct the shoulder?
Which muscle acts to abduct the shoulder?
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What is the primary action of the Gastrocnemius muscle?
What is the primary action of the Gastrocnemius muscle?
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Which muscle is considered a part of the erector spinae group?
Which muscle is considered a part of the erector spinae group?
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What best describes the action of the Biceps brachii?
What best describes the action of the Biceps brachii?
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Which of the following muscles is responsible for internally rotating the hip?
Which of the following muscles is responsible for internally rotating the hip?
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What is the muscular action of the Orbicularis oris?
What is the muscular action of the Orbicularis oris?
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Which of the following muscles is most closely associated with the function of chewing?
Which of the following muscles is most closely associated with the function of chewing?
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Which muscle is known as the 'boxer's muscle' due to its role in protracting the scapula?
Which muscle is known as the 'boxer's muscle' due to its role in protracting the scapula?
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Which of the following describes the Iliotibial (IT) band?
Which of the following describes the Iliotibial (IT) band?
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Study Notes
Identifying Skeletal Muscles
- Skeletal muscles are categorized into three functional groups: agonists, antagonists, and synergists.
- Agonists are the "prime movers" that produce a specific movement, while antagonists oppose the agonist's movement.
- Synergists are accessory muscles that work with agonists to add extra force to the same movement.
- Fixators are a type of synergist that immobilize a bone or muscle origin to help with stability.
- Muscles can act as agonists, antagonists, or synergists depending on the movement being performed.
How to Name Muscles
- Muscles are named based on various criteria:
- Location: Refers to the bone or body region the muscle is associated with.
- Shape: Describes the distinct shape of the muscle, e.g., deltoid muscle is triangular.
- Size: Uses terms like "maximus" for the biggest, "minimus" for the smallest, "longus" for longer, and "brevis" for shorter.
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Fiber or Fascicle Direction: Indicates how muscle fibers run:
- Rectus: Fibers run straight.
- Transversus: Fibers run at right angles.
- Oblique: Fibers run at angles to an imaginary axis.
- Number of Origins: Refers to the number of points where a muscle originates, e.g., biceps have two origins.
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Location of Attachments: Indicates where the muscle originates and inserts:
- Origin: Attachment to the less movable bone.
- Insertion: Attachment to the movable bone.
- Muscle Action: Describes the specific movement caused by the muscle's contraction, e.g., flexors, extensors, abductors.
Classing by Fascicle Directions
- The arrangement of muscle fascicles influences striations, shape, and function.
- Common fascicle patterns include:
- Circular: Concentric rings, such as the orbicularis oris.
- Convergent: Broad muscle converging to a single tendon, such as the pectoralis major.
- Parallel: Fibers run parallel to the long axis, such as the sartorius.
- Pennate: Spindle-shaped with parallel fibers, such as the rectus femoris.
- Fusiform: Large muscle belly with tapered ends near the tendon, such as the biceps brachii.
Learning Skeletal Muscles
- The human body has over 600 muscles, each with its own description, origin, insertion, action, and innervation.
- Focus on muscle description and actions, as detailed innervation is complex for introductory anatomy courses.
- Use lab sessions to tie muscle location to its description, location to its action, and attachments to its actions.
- Reverse engineer muscle names to understand their function.
- Find muscles on your own body to learn through tactile and kinesthetic experiences.
Facial Expression Muscles
- These muscles differ from others by inserting into skin instead of bone.
- They are crucial for non-verbal communication and body language.
- Bell's Palsy is a condition that causes hemiparalysis of facial expression muscles.
- Some facial expression muscles include:
- Zygomaticus major: Raises the corners of the mouth for smiling.
- Orbicularis oris: Closes and protrudes lips for puckering, kissing, and whistling.
- Orbicularis oculi: Closes the eye for blinking and squinting, pulls eyebrows inferiorly for a furrowed brow.
- Mentalis: Wrinkles the chin and protrudes the lower lip for a pout.
- Corrugator supercili: Pulls eyebrows medially and inferiorly for a vertical wrinkle, creating a "frowning" expression.
- Epicranius (Occipitofrontalis): The frontal belly raises eyebrows and wrinkles the forehead horizontally for surprise.
- Platysma: Tenses the skin of the neck.
Mastication & Neck Muscles
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Mastication (Chewing):
- Masseter & Temporalis: Muscles responsible for jaw closure.
- Medial & Lateral Pterygoids: Deep muscles involved in grinding movements.
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Anterior Neck:
- Sternocleidomastoid (SCM): Flexes the neck forward, laterally flexes the neck on the same side (ipsilaterally), and rotates the neck to the opposite side (contralaterally).
- Scalenes: Laterally flex and rotate the neck, elevate the first two ribs during inspiration.
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Posterior Neck:
- Trapezius: Originates on the occipital bone, stabilizes, elevates, retracts, and rotates the scapula.
- Levator scapulae: Originates on C1-C4 vertebrae, elevates and retracts the scapula.
Spinal Muscles
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Erector Spinae group:
- Composed of three muscles - iliocostalis, longissimus, and spinalis - that collectively keep the back erect and extend the spinal column.
- These muscles can laterally flex the spinal column ipsilaterally if activated unilaterally.
- Each muscle can be further divided into subsections at different spinal segments (capitis, cervicis, thoracis, lumborum).
- Quadratus lumborum (QL): Shares similar actions to the erector spinae group.
Thoracic Muscles
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Respiratory Muscles:
- Diaphragm: The primary muscle of inspiration, its contraction depresses to expand the thoracic cavity, while relaxation elevates the diaphragm.
- External Intercostals: Elevate the rib cage during inspiration, expanding the thoracic cavity.
- Internal Intercostals: Depress the rib cage during expiration, compressing the thoracic cavity.
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Abdominals:
- Rectus Abdominis: Flexes and rotates the lumbar vertebrae, stabilizes the pelvis during walking, and is responsible for the "six-pack" appearance.
- External Oblique: Flexes the lumbar vertebrae, aids back muscles in laterally flexing the trunk ipsilaterally and rotating the trunk contralaterally.
- Internal Oblique: Shares similar actions with the external oblique.
- Transversus Abdominis: The deepest abdominal muscle, compresses abdominal contents and stabilizes the spine.
Shoulder Girdle & Upper Arm (Anterior)
- Pectoralis major: Adducts and internally rotates the shoulder.
- Anterior deltoid: Flexes and internally rotates the shoulder.
- Medial deltoid: Abducts the shoulder.
- Biceps brachii: Flexes the elbow and supinates the forearm.
- Brachialis: Flexes the elbow.
- Brachioradialis: Assists in elbow flexion and stabilizes the elbow.
- Serratus anterior: "Boxer's muscle," protracts the scapula.
Shoulder Girdle & Upper Arm (Posterior)
- Latissimus dorsi: Extends, adducts, and internally rotates the shoulder.
- Triceps brachii: Extends the elbow.
- Supraspinatus: Abducts the shoulder.
- Infraspinatus: Externally rotates the shoulder.
- Teres minor: Externally rotates the shoulder.
- Subscapularis: Internally rotates the shoulder.
- Rhomboids: Attach to the medial border of the scapula, stabilize and retract the scapula.
- Rotator Cuff Muscles (Supraspinatus, Infraspinatus, Teres minor, Subscapularis): Synergists and fixator muscles for the shoulder, preventing dislocation. These muscles are commonly injured in activities involving a lot of arm movements.
Forearm Muscles
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Forearm Flexors:
- Pronator teres: Pronates the forearm and assists with elbow flexion.
- Flexor carpi radialis: Flexes and abducts the wrist.
- Palmaris longus: Flexes the wrist and tenses the skin and fascia of the hand during movements.
- Flexor carpi ulnaris: Flexes and adducts the wrist.
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Forearm Extensors:
- Extensor carpi radialis longus: Extends and abducts the wrist.
- Extensor carpi radialis brevis: Extends and abducts the wrist.
- Extensor digitorum: Prime mover for finger extension and abduction.
- Extensor carpi ulnaris: Extends and adducts the wrist.
Thigh Muscles (Anterior/Medial)
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Iliopsoas:
- Iliacus: Flexes the hip and flexes the trunk at the hip.
- Psoas major: Shares actions with Iliacus, also laterally flexes the trunk ipsilaterally.
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Quadriceps Group:
- Rectus femoris: Flexes the hip and extends the knee.
- Vastus lateralis (VL): Extends and stabilizes the knee.
- Vastus medialis (VM): Extends the knee.
- Vastus intermedius (VI): Extends the knee.
- Sartorius: Flexes, abducts, and externally rotates the hip.
- Tensor fasciae latae (TFL): Flexes, abducts, and internally rotates the hip.
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Adductor Group:
- Adductor magnus: Flexes, adducts, and internally rotates the hip; posterior fibers assist with hip extension.
- Adductor longus: Flexes, adducts, and internally rotates the hip.
- Adductor brevis: Flexes, adducts, and internally rotates the hip.
- Pectineus: Flexes, adducts, and internally rotates the hip.
- Gracilis: Flexes, adducts, and internally rotates the hip.
Hip Muscles (Posterior)
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Glutes:
- Gluteus maximus: Extends, abducts, and externally rotates the hip; is a powerful hip extensor.
- Gluteus medius: Abducts and internally rotates the hip.
- Gluteus minimus: Shares the same action as the gluteus medius.
- Piriformis: Externally rotates the hip when the hip is extended, abducts the hip when it's flexed. This muscle is commonly implicated in cases of sciatica.
Thigh Muscles (Posterior)
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Hamstrings:
- Biceps femoris: Extends the hip, flexes the knee, and externally rotates the knee when it's flexed.
- Semitendinosus: Extends the hip, flexes and internally rotates the knee.
- Semimembranosus: Shares actions with the semitendinosus.
- Iliotibial (IT) Band: Thick fascial band on the lateral aspect of the thigh stemming off the gluteus maximus and TFL, aids in pelvic stability. When abductors are weak, it can become injured and create a "snapping" noise when moving over the greater trochanter, known as Dancer's Hip.
Shank Muscles (Anterior Compartment)
- Tibialis anterior: Dorsiflexes and inverts the ankle.
- Extensor digitorum longus: Dorsiflexes the ankle and extends the toes.
- Extensor hallucis longus: Dorsiflexes the ankle and extends the big toe.
- Shin Splints: Excess tightness or hypertrophy of the anterior compartment muscles puts pressure on the tibia, causing pain.
- These muscles are crucial for preventing toe dragging while walking, although not powerful.
Shank Muscles (Lateral Compartment)
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Peroneals:
- Fibularis longus: Plantar flexes and everts the ankle, may help apply pressure to the lateral arch of the foot to keep it flat on the ground.
- Fibularis brevis: Plantar flexes and everts the ankle.
- Important for ankle and foot arch stabilization.
Shank Muscles (Posterior Compartment)
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Triceps Surae:
- Gastrocnemius: Plantar flexes the ankle when the knee is extended, assists with knee flexion when the ankle is dorsiflexed. Attaches to the calcaneus via the calcaneal (Achilles) tendon, commonly injured with ankle sprains and can rupture in "stop and go" movements involving rapid plantar flexion with knee extension.
- Soleus: Plantar flexes the ankle.
- Plantaris: Aids in knee flexion and ankle plantar flexion.
- Popliteus: Flexes and internally rotates the knee, "unlocks" an extended knee to initiate flexion.
Skeletal Muscular System Summary
- Muscles are named based on location, shape, size, fiber/fascicle direction, number of origins, locations of attachments, and action(s).
- To study muscles, group them by location or action, use their names, and incorporate clinical pathologies for differentiation.
- Use tactile and kinesthetic learning by finding these muscles on your own body.
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Description
Test your knowledge on skeletal muscle classification and naming conventions. This quiz covers functional groups, such as agonists and antagonists, and explores criteria used in muscle naming based on location, shape, and size. Strengthen your understanding of muscle roles in movement!
