Muscular system
Muscle Functions
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Producing movement
Maintaining posture
Stabilizing joints
Generating Heat
Contraction of a skeletal muscle as a
whole
• Graded responses: different degrees of
shortening.
– 1. changing the frequency of muscle stimulation
– 2. changing the number of muscle cells being
stimulated
• Muscle twitches: single brief, jerky contractions.
Not normal operation
• Fused or complete tetanus: contracted smoothly
and sustained
• Incomplete tetanus or unfused: when the muscle
is trying to reach fused contraction.
Muscle fatigue and oxygen debt
• Muscle fatigue: when a muscle cannot contract
even when being stimulated.
– Happens when we exercise our muscles strenuously
for a long time.
• Oxygen debt: muscle fatigue happens because of
oxygen debt. A person cannot take in oxygen fast
enough to supply with oxygen in the muscle.
– Working muscles vigorously
– When there is a lack of oxygen in the muscles lactic
acid starts to build up
Muscle contractions
• Isotonic contractions: “same tone” when
muscle is in sliding movement. Smiling,
bending arm, bending leg, rotating arm
• Isometric contracitons: “same measurement”
When muscles cannot move anymore.
– When you are trying to lift or move a 400 lb
dresser, when you push against the wall.
Muscle tone
• The state of continuous partial contraction.
• Flaccid: Soft and flabby which leads to
atrophy(waste away).
5 Golden Rules of Skeletal Muscle
Activity
1. All muscles cross at least one joint.
2. Typically, the bulk of the muscle lies proximal
to the joint crossed.
3. All muscles have at least two attachment
points: origin and insertion.
4. Muscles can only pull; the never push.
5. During contraction, the muscle insertion
moves toward the origin.
Origin and insertion
• Origin: immovable bone
• Insertion: movable bone attachment.
• When contraction occurs the insertion moves
toward the origin.
Movements
• Flexion: decreases angle of the joint
• Extension: increases the angle of the joint
• Rotation: movement of a bone around its
longitudinal axis.
• Abduction: moving limb away from midline
• Adduction: moving limb toward midline
• Circumduction: proximal end of bone is
stationary and the distal end is moving in a circle.
Special movements
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Dorsiflexion : moving the foot at the ankle up
Plantar flexion: moving the foot at the ankle down.
Inversion: turn the foot toward the middle
Eversion: turn the foot toward the outside of the leg
Supination: turning the hand to face the anterior side
Pronation: turning the hand to face the posterior side
Opposition: touching the fingers to the thumb.
Types of muscles
• Prime movers: major responsibility of a
particular movement.
• Antagonist: oppose or reverse movement.
• Synergist: helps the prime mover by reducing
undesirable movement.
• Fixator: specialized synergist, stabilize the
origin
Naming skeletal muscles
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Direction of the muscle fiber
Relative size of the muscle
Location of the muscle
Number of origins
Location of the muscle’s origin and insertion
Shape of the muscle
Action of the muscle
Head and Neck muscles
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Frontalis
Orbicularis oculi
Buccinator
Zygomaticus
Masseter
Temporalis
Playtusma
Sternocleidomastoid
Trunk Muscles
• Anterior muscles:
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Pectoralis major
Intercostal muscles
Rectus abdominis
External oblique
Internal oblique
Transverse abdominis
• Posterior muscles:
– Trapezius
– Latissimus dorsi
– Erector spinae
• Iliocostalis
• Longissimus
• Spinalis
– deltoid
Muscles of the upper limb
• Upper arm
– Biceps brachii
– Brachialis
– Triceps brachii
• Lower arm
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Brachioradialis
Flexor carpi radialis
Flexor carpi ulnaris
Extensor carpi ulnaris
Extensor digitorum
Muscles of the lower limb
• Upper leg
– Sartorius
– Adductor
– Quadricep group
• Rectus femoris
• Vastus lateralis
• Vastus medialis
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Fibularis longus
Extensor digitorum
Tibialis anterior
Hamstring group:
• Biceps femoris
• Semitendinosus
• Semimembranosus
– Gluteus maximus
– Gluteus medius
• Lower leg
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Fibularis longus
Extensor digitorum longus
Tibialis anterior
Gastrocnemius
Soleus
Fibularis longus
Homeostatic imbalances
• Muscular dystrophy: inherited muscle
destroying disease. Muscle degenerates and
atrophies
• Myasthenia gravis: happens during adulthood.
Shortage of acetylcholine receptors at the
neuro-muscular junction. Auto immune
disease. Will result in death because the
respiratory muscles fail.