chapter 11 skeletal muscle
Chapter 11 – The Muscular System
Describe how skeletal muscles produce movement
Skeletal muscles attach to bones to produce movement. When a muscle contracts, it pulls on a tendon, which then pulls on a bone.
Describe the relationship between bones and skeletal muscles in producing body movements
To understand movement you need to know where the muscle attaches to:
Origin: the end of the muscle attached to the bone that stays still (fixed in place)
Insertion: the end of the muscle attached to the bone that moves
Muscles work by pulling insertion towards origin
For example, when you bend your elbow:
Biceps brachii contracts → pulls on tendon → forearm bones move toward upper arm bone (humerus) → elbow bends
Origin: scapula (shoulder blade) → stays fixed
Insertion: radius (forearm bone) → moves
When the muscle contracts:
scapula (origin stays still) → biceps shortens → radius is pulled upward → elbow flexes (bends)
Define lever and fulcrum and compare the three types of levers based on location of the fulcrum, effort, and load.
Lever- Bones
Fulcrum- Joints used as a pivot for the lever
Load- Resistance, mass/object that the lever will move
Effort- The muscular force that's being applied to the lever system
First Class lever- the FULCRUM is in the between the load and the effort
EX. The Head & Neck
Effort (The back neck muscles)- The force that pulls your head up, keeping it from dropping
Fulcrum (The neck joint)- The “hinge” that allows the head to rotate
Load (The front of head/face)- The weight that is trying to stay up
Second Class lever- the LOAD is in between the fulcrum and the effort
EX. The foot in plantar flexion
Fulcrum (The toes/ball of the foot)- The “hinge” or pivot point that stays on the ground and lets your body rock forward
Load (The body weight above your foot)- The weight of your body that is being lifted upward when you stand on tiptoes
Effort (The calf muscles/Achilles tendon) – The force that pulls your heel up, lifting your body onto your toes
Third Class lever- the EFFORT is between the fulcrum and the load
Fulcrum (The elbow joint) – The “hinge” where your forearm rotates
Effort (The biceps brachii muscle) – The force that pulls your forearm upward when you lift something
Effort (The biceps brachii muscle) – The force that pulls your forearm upward when you lift something
Identify the types of fascicle arrangements in a skeletal muscle and relate the arrangements to strength of contraction and range of motion
Skeletal muscles are classified by how their fascicles (bundles of muscle fibers) are arranged. This arrangement affects both strength of contraction and range of motion.
Parallel Muscles (most common type)
Fibers run along the axis of the muscle (biceps branchii, sartorius)
Offers a lot of movement (shortens 30% of its length)
Fusiform is a type of parallel muscle
Lower strength
Convergent Muscles
Muscle starts wide (comes from different directions) and tapers into one tendon
Allows wide range of movement because muscle fibers come from different directions (pectoralis major)
Are separated into sections (ex. gluteus medius, maximus, and minimus)
Pennate Muscles (unipennate, bipennate, multipennate)
Fibers attached at an angle to a central tendon
Less movement but more strength, the arrangement allows for more muscle fibers (myofibril) in one area
Allows for more tension, allowing for more force
Unipennate all muscle fibers are one side of the tendon, ex flexor pollicis longus (forearm) looks like half of a feather with tendon on one side with muscle fibers attached
Bipennate muscle fibers are on both sides of the tendon ex rectus femoris (middle thigh) resembles a feather
Multipennate the tendons branch into the muscle fibers ex deltoid (shoulder)
Circular/Sphincters Muscle
Muscle open and close to guard entrances ex orbicularis oris (mouth)
Fibers form circles around an opening
Very limited motion (only opens and closes)
Explain how the prime mover, antagonist, synergist, and fixator in a muscle group work together to produce movement.
When your body creates movement your muscles coordinate together as a team and each muscle has a specific role.
Agonist/Prime Mover
The main muscle doing the movement
The masseter muscle is the main muscle in opening and closing your mandible
Antagonist Muscle
Muscles that oppose the prime mover
Flexing your elbow biceps is a prime mover and the triceps would be the antagonist
Extend your elbow your triceps would be the prime mover and the biceps becomes the antagonist
Relaxes/stretches muscle when prime mover contracts
controls/slows down movement
Synergist
Muscles that help the prime mover
They add extra force to assist in a movement reduce unnecessary force to make movement smoother
Fixator
Muscles that stabilize of the prime mover by holding a bone/joint steady
This allows for another muscle to do their job more efficiently
Ex. abdominal muscle stabilizing the spine
How they work together:
Prime mover → creates the movement
Antagonist → relaxes and controls the movement
Synergists → assist and add strength
Fixators → stabilize parts so movement is smooth and efficient
How Skeletal Muscles Are Named
Explain features used in naming skeletal muscles.
Skeletal muscles are named using Latin and Greek roots that describe important features of the muscle:
Location, where they are in the body
Example: temporalis → located on the temporal bone (side of the head)
Example: frontalis → located on the frontal bone (forehead)
Shape, named for how they are shaped
Example: deltoid → triangle-shaped (delta=triangle in greek)
Example: orbicularis → circular shape Example: orbicularis → circular shape (orbis=circle in latin)
Size, how big/small the muscle is
maximus = largest
medius = medium
minimus = smallest
longus = long
brevis = short
Direction of fibers, how muscle fibers are arranged.
rectus = straight fibers
oblique = angled fibers
5. Number of origins (heads)
How many origins/starting points they have
biceps = 2 heads
triceps = 3 heads
quadriceps = 4 heads
6. Location of attachments
Origin+Insertion
Example: sternocleidomastoid
sterno = sternum
cleido = clavicle
mastoid = mastoid process
Action, what they can do
flexor = bends a joint
extensor = straightens a joint
adductor = moves toward the body
8. Function or group name
Some names describe a group of muscles or their function.
quadriceps = group of four muscles
buccinator = muscle used for blowing (like a trumpet)
Big idea
Muscles of the Head That Produce Facial Expressions
Describe the origin, insertion, and action of the muscles of facial expression
The muscles of facial expressions usually insert into skin surrounding the eyelids, nose, and mouth. Their origins are usually on a bone of the skull. You make expressions by moving actual skin instead of bone.
Orbicularis oris
circular/sphincter muscle that moves the lips
Makes close and pucker movements also known as the “kissing muscle”
Orbicularis Oculi
circular/sphincter muscle around the eye
Closes and squeezes the eyelids also known and the blinking muscle
Muscles That Move the Mandible and Assist in Mastication and Speech
Describe the origin, insertion, and action of the muscles that move the mandible and assist in mastication and speech.
The main origin and insertion of the mandible are found within the cheek and originate from the process of the skull. The main muscles that move the mandible
Masseter
Origin: zygomatic arch
Insertion: angle and ramus of the mandible
Temporalis
Origin: temporal bone
Insertion: coronoid process of the mandible
The action for the masseter and temporalis is to close the jaw (elevates mandible)
The muscles that move the tongue play an important role for mastication (chewing) and speech.
Tongue muscles are divided into extrinsic (move whole tongue located outside the muscle) and intrinsic (four paired muscles on the tongue that has the ability to make the tongue change its shape)
Four Extrinsic Tongue Muscles:
Genioglossus
Origin: mandible (chin area)
Insertion: tongue
Action: moves tongue downward and forward
Helps with: pushing food forward for chewing and forming speech sounds
Styloglossus
Origin: styloid process (temporal bone region)
Insertion: tongue
Action: moves tongue upward and backward
Helps with: pulling food back for swallowing and controlling speech articulation
Palatoglossus
Origin: soft palate
Insertion: tongue
Action: elevates back of the tongue
Helps with: swallowing (mastication process) and speech sound control
Hyoglossus
Origin: hyoid bone
Insertion: tongue
Action: depresses and flattens the tongue
Helps with: flattening tongue during chewing and shaping speech sounds
How this helps mastication and speech
During chewing, tongue muscles move food between teeth and toward the throat for swallowing
During speech, they help position and shape the tongue to form clear sounds
Muscles of the Neck That Move the Head
Describe the origin, insertion, and action of the muscles that move the head.
The primary muscles that move the head are located in the neck attached to the vertebral column.
Sternocleidomastoid (SCM) — separate muscle (NOT part of erector spinae)
Origin: sternum (manubrium) and clavicle
Insertion: mastoid process of the temporal bone
Action:
One side: rotates head to the opposite side and laterally flexes to the same side
Both sides: flexes the head forward
Important: This is a standalone superficial neck muscle, not part of the erector spinae group
Scalene muscles (part of deeper neck musculature, work with spinal extensors)
Origin: cervical vertebrae
Insertion: first and second ribs
Action: flex and stabilize the neck; assist in lateral flexion of the head
Splenius muscles — part of the erector spinae group—>
Splenius capitis
Origin: midline of the upper back/neck (spinous processes and ligaments)
Insertion: skull (head region)
Action: extends the head, laterally flexes it, and rotates it
Splenius cervicis
Origin: spinous processes of upper thoracic vertebrae
Insertion: cervical vertebrae (neck region)
Action: extends the neck, laterally flexes it, and rotates it
Important: Both splenius muscles are part of the erector spinae muscle group, which helps maintain posture and move the spine and head
SCM = separate neck muscle for flexion and rotation
Splenius muscles = part of erector spinae group that extends and stabilizes the head/neck
Scalenes = assist in neck flexion and stability
Muscles of the Abdomen That Protect Abdominal Viscera and Move the Vertebral Column
Describe the origin, insertion, and action of the muscles that protect the abdominal viscera and move the vertebral column.
The muscles of the vertebral column, thorax, and abdominal wall extend, flex, and stabilize the vertebral column. The deep muscles of the core of the body help maintain posture as well as carry out other functions. Four pairs of abdominal muscles cover the front and sides of the abdomen, meet in the middle, and help hold the organs in place. These muscles are the external obliques, internal obliques, transversus abdominis, and rectus abdominis.
Rectus abdominis
Origin: pubic crest and pubic symphysis
Insertion: xiphoid process and costal cartilages of ribs 5–7
Action: flexes the vertebral column (trunk flexion); compresses abdominal viscera; stabilizes posture
External oblique
Origin: ribs 5–12
Insertion: iliac crest, linea alba, and pubis
Action: flexes and rotates vertebral column; compresses abdominal organs; supports abdominal wall
Internal oblique
Origin: iliac crest, thoracolumbar fascia, and inguinal ligament
Insertion: lower ribs and linea alba
Action: flexes and rotates vertebral column (opposite direction of external oblique); compresses and supports abdominal viscera
Transversus abdominis
Origin: lower ribs, iliac crest, thoracolumbar fascia
Insertion: linea alba (via aponeurosis)
Action: compresses abdominal contents (strong “corset” muscle); stabilizes trunk and supports posture
Muscles of the Thorax That Assist in Breathing
Describe the origin, insertion, and action of the muscles of the thorax that assist in breathing.
The muscles of the chest facilitate breathing by changing the size of the thoracic cavity. When you inhale, the thoracic cavity expands allowing air into the lungs. Alternately, when you exhale your chest decreases and shrinks because air is being forced out of the lungs. The most important muscle associated in breathing is the diaphragm.
Diaphragm (main breathing muscle)
Origin: lower ribs, sternum, and lumbar vertebrae (inner lower thorax)
Insertion: central tendon
Action:
Contracts (inhale): flattens and increases thoracic cavity size → draws air into lungs
Relaxes (exhale): returns to dome shape → helps push air out
Muscles of the Thorax That Move the Pectoral Girdle
Describe the origin, insertion, and action of the muscles of the thorax that move the pectoral girdle.
The muscles of the thorax that move the pectoral girdle help move and support your shoulders. When they contract, they pull your shoulder blades and collarbone in different directions so you can lift your arms, reach, and rotate your shoulders. They also keep your shoulders stable so your arm movements are controlled and don’t feel loose or weak. The two main muscles that move your scapula (shoulder blade) are:
serratus anterior
Origin: Lateral region of 1st to 9th ribs
Insertion: Vertebral border of the anterior surface of scapula
Action: Protracts and rotates scapula upwards
Trapezius
Origin: Occipital bone, ligamentum nuchae, and spinous processes of thoracic vertebrae
Insertion: Clavicle and scapula
Action: Elevates, depresses, rotates, and retracts scapula
Muscles of the Thorax and Shoulder That Move the Humerus
Muscles of the thorax that move the humerus (origin, insertion, action)
The muscles that move the humerus work depending on where they are located on the body. Muscles in the front move the arm forward, muscles on top lift the arm upward, muscles in the back and lower back pull it down and backward, and muscles on the back of the shoulder help move it backward. Overall, their position determines the direction the arm moves.
Pectoralis major
Origin: sternum and clavicle (front of chest)
Insertion: humerus
Action: flexes, adducts, and medially rotates the arm (brings arm forward and across body)
Latissimus dorsi
Origin: lower back and spine
Insertion: humerus
Action: extends, adducts, and medially rotates the arm (pulls arm down and back)
Deltoid
Origin: clavicle and scapula
Insertion: humerus
Action: abducts the arm (lifts arm away from body)
Subscapularis
Origin: anterior surface of scapula
Insertion: humerus
Action: medially rotates the arm and stabilizes the shoulder
Supraspinatus
Origin: superior scapula
Insertion: humerus
Action: initiates arm abduction (first part of lifting arm)
Infraspinatus
Origin: posterior scapula
Insertion: humerus
Action: laterally rotates the arm
Teres minor
Origin: scapula
Insertion: humerus
Action: laterally rotates and stabilizes the arm
Teres major
Origin: scapula
Insertion: humerus
Action: extends, adducts, and medially rotates the arm
Chest/back muscles (pectoralis + latissimus) → power movements like pushing and pulling
Deltoid → main arm lifter
Rotator cuff muscles (subscapularis, supraspinatus, infraspinatus, teres minor) → stabilize and fine-tune shoulder movement
Muscles of the Arm That Move the Radius and Ulna
Describe the origin, insertion, and action of the muscles of the arm that move the radius and ulna.
Our muscles that move the forearm produce flexion, extension, pronation, and supination at the elbow (a hinge joint). Primary muscles that move the forearm are biceps brachii, brachialis, brachioradialis, triceps brachii.
Biceps brachii (long head)
Origin: Supraglenoid tubercle of scapula
Insertion: Tuberosity of radius
Action: Flexes forearm and flexes arm
Biceps brachii (short head)
Origin: Coracoid process of the scapula
Insertion:Tuberosity of radius
Action:Flexes forearm and flexes arm
Brachialis
Origin: humerus
Insertion: ulna (forearm bone)
Action: main muscle that flexes the elbow
Brachioradialis
Origin: Distal-lateral humerus
Insertion: Styloid process of radius
Action: Flexes forearm
Triceps brachii (long head)
Origin: Distal-Infraglenoid tubercle of scapula
Insertion: Olecranon process of ulna
Action: Extends forearm and extends arm
Triceps brachii (lateral head)
Origin: Proximal posterior surface of humerus
Insertion: Olecranon process of ulna
Action: Extends forearm
Triceps brachii (medial head)
Origin: Distal posterior surface of humerus
Insertion: Olecranon process of ulna
Action: Extends forearm
Muscles of the Forearm That Move the Wrist, Hand, Thumb, and Digits
Describe the origin, insertion, and action of the muscles of the forearm that move the wrist, hand, and digit
The wrist, hand, and fingers move by two groups of muscles. Extrinsic muscles are located in the forearm and provide flexion and extension with tendons spanning the wrist to fingers. Extrinsic muscles are further grouped into anterior and posterior compartments of the forearm. The anterior are mostly flexors and the posterior are mostly extensors.Intrinsic muscles are located within the hand to provide fine motor control and dexterity. Hand muscles include:
Select wrist flexors: Flexor carpi radialis Flexor digitorum superficialis Flexor carpi ulnaris
Origin: Medial epicondyle and humerus
Insertion: Wrist and hand
Action: Flexes wrist and hand
Select wrist extensors: Extensor digitorum Extensor carpi radialis (longus) Extensor carpi ulnaris
Origin: lateral epicondyle and humerus
Insertion: Wrist and hand
Action: extends wrist and hand
Muscles of the Neck and Back That Move the Vertebral Column
Describe the origin, insertion, and action of the muscles that move the vertebral column.
The erector spinae group makes up most of the back muscles and is the main muscle group that straightens the spine. It also helps control bending, side bending, and twisting of the vertebral column, while keeping good posture and helping you stand upright. It is made up of three parts: iliocostalis on the outside, longissimus in the middle, and spinalis closest to the spine.
Erector spinae group: Spinalis group Longissimus group Iliocostalis group
Origin: Sacrum, iliac crest, transverse process of lumbar, thoracciac, and cervical vertebrae.
Insertion: Insertion: ribs and transverse processes of vertebrae about six levels above where the muscle starts.
Action: Extends and laterally flexes vertebral column, head, and neck
Muscles of the Gluteal Region That Move the Femur
Describe the origin, insertion, and action of the muscles of the gluteal region that move the femur.
The muscles in the gluteal region move the femur and usually have their origin on the pelvic girdle and insertion on the femur. They mainly extend, abduct, and rotate the thigh, and they also help keep the hip stable during standing and walking.
Gluteus maximus
Origin:Ilium, sacrum, coccyx
Insertion: Upper posterior surface of femur and IT Band (tract)
Action: Extends and laterally rotates hip
Gluteus medius
Origin:Outer surface of ilium
Insertion: Greater Trochanter of the femur
Action: Abducts and medially rotates hip
Gluteus minimus
Origin:Outer surface of ilium
Insertion: Greater Trochanter of the femur
Action: Abducts and medially rotates hip
Pisiformis
Origin:Sacrum
Insertion: Greater Trochanter of the femur
Action: Laterally rotates hip
Iliopsoas
Origin: lumbar vertebrae and ilium
Insertion: femur (lesser trochanter)
Action: flexes the thigh (brings leg forward)
Tensor fascia latae
Origin: ilium
Insertion: iliotibial tract → tibia
Action: abducts and stabilizes the thigh
Adductor longus
Origin: pubis
Insertion: femur
Action: adducts the thigh (brings leg inward)
Muscles of the Thigh That Move the Femur and Tibia and Fibula
Describe the origin, insertion, and action of the muscles that move the femur, tibia, and fibula
The deep fascia (connective tissue) separates the thigh into anterior, posterior, and medial compartments. Muscles within these compartments typically share a common action and innervation.
Gracilis
Origin:Pubic symphysis
Insertion: Pes anserinus (conjoined tendon of three muscles) of tibia
Action:Adducts hip and flexes knee
Rectus Femoris
Origin: Anterior inferior iliac spine
Insertion: Tibial tuberosity via the patella
Action:Flexes hip. Extends knee and laterally rotates hip
Vastus lateralis
Origin: Greater Trochanter and linea aspera of femur
Insertion: Tibial tuberosity via the patella
Action:Extends knee
Vastus Medialis
Origin: Linea aspera of femur
Insertion: Tibial tuberosity via the patella
Action:Extends knee
Semimembranosus
Origin: Ischial tuberosity
Insertion: Pes anserinus (conjoined tendon of three muscles) of tibia
Action:Extends hip and flexes knee
Semitendinosus
Origin: Ischial tuberosity
Insertion: Pes anserinus (conjoined tendon of three muscles) of tibia
Action:Extends hip and flexes knee
Biceps Femoris
Origin: Ischial tuberosity
Insertion: Head of the fibula and lateral Condyle of tibia
Action:Extends hip and flexes knee
Muscles of the Leg That Move the Foot and Toes
Describe the origin, insertion, and action of the muscles of the leg that move the foot and toes.
The muscles of the leg are divided by deep fascia into anterior, lateral, and posterior compartments. The anterior compartment muscles of the lower leg are responsible for dorsiflexing the ankle and extending the toes. The lateral compartment of the leg produces plantarflexion and evert the ankle. The posterior compartment of the lower leg are very powerful plantar flexors and help to keep us upright.
Gastrocnemius
Origin: Medial and lateral condyles of the femur
Insertion: Calcaneus
Action:Flexes knee and plantar flexes foot
Tibialis anterior
Origin: Anterior tibia and interosseous membrane
Insertion: Medial surface of 1st cuneiform and 1st metatarsal
Action:Dorsiflexes and inverts foot
Fibularis longus
Origin: Head and body of fibula
Insertion: Metatarsal I and first cuneiform
Action:Plantar flexes and everts foot
Extensor digitorum longus
Origin: Lateral condyle of tibia, fibula, and interosseous membrane
Insertion: Dorsal surface of phalanges 2-5
Action:Dorsiflexes, everts foot and extends toe 2-5
Flexor digitorum longus.
Origin: Posterior surface of tibia
Insertion: Plantar surface of phalanges of toes 2-5
Action:Flexes toes 2-5, plantar flexes, and inverts foot
Focus on Homeostasis: The Muscular System
Describe how the muscular system contributes to homeostasis.
The muscular system helps maintain homeostasis by producing movement, keeping posture, and generating heat. Skeletal muscles work with bones and joints to allow body movement, while also making constant small adjustments to keep the body balanced when sitting or standing. Muscle contractions also help regulate body temperature by producing heat during activity, which helps keep the body at a stable internal temperature.
Disorders: Homeostatic Imbalances that Affect the Muscular System
Describe the disorders that affect the muscular system.
Carpal Tunnel Syndrome – caused by inflammation and compression of the median nerve in the wrist from overuse of the flexor tendons, leading to pain, numbness, and weakness in the hand.
Golfer’s elbow – caused by repetitive strain of the forearm flexor muscles (like flexor carpi radialis), leading to pain around the inner elbow.