1. The Muscular System (rev 3-10)
Muscular tissue enables the body and its parts to move
Movement is caused by ability of muscle cells (called fibers) to shorten or contract
Function of muscle tissue is to contract (or shorten)
Muscle cells use energy to produce movement
We have 3 types of muscle tissue in our bodies
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2. Muscle Lecture-BIO 006 Handout
Skeletal muscle —also called striated or voluntary muscle
This type muscle has stripes or striations
Contractions can be voluntarily controlled
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3. Muscle Lecture-BIO 006 Handout
Cardiac muscle —composes bulk of heart
Striated muscle; involuntary (contractions not under voluntary control)
Characterized by unique dark bands called intercalated disks
Cells branch frequently
Interconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit
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4. Muscle Lecture-BIO 006 Handout
Smooth or visceral muscle
Nonstriated, involuntary muscle
Lacks cross stripes or striations when seen under a microscope; appears smooth
Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters
Contractions not under voluntary control; movement caused by contractions is involuntary
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5. Structure of Skeletal Muscle
Each skeletal muscle is an organ composed of skeletal muscle cells and connective tissue
Most skeletal muscles extend from one bone across a joint to another bone
Parts of a skeletal muscle
Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs
Insertion—point of attachment to the bone that moves when a muscle contracts
Body or Belly—main part of the muscle
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6. Muscle Lecture-BIO 006 Handout
Muscles attach to the bone by tendons which are made of strong fibrous connective tissue
Some tendons are enclosed in synovial-lined tubes, called tendon sheaths, and are lubricated by synovial fluid
--Bursae—small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones
Both tendon sheaths and bursae make it easier for a tendon to slide over bone
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7. Muscle Lecture-BIO 006 Handout
Microscopic structure
Specialized contractile cells called fibers are grouped into bundles
Each skeletal muscle fiber contains thick myofilaments (formed from the protein myosin) and thin myofilaments (formed from the protein actin)
These myofilaments make the striations or stripes we can see in skeletal muscle fibers
The basic functional (contractile) unit of the muscle cell is called a sarcomere. Sarcomeres are separated from each other by dark bands called Z lines
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Sliding filament model explains mechanism of contraction
Thick and thin myofilaments slide toward each other as a muscle contracts and shorten the muscle. This is called the sliding filament model.
Contraction requires calcium and ATP
Functions of Skeletal Muscle:
Movement
Posture or muscle tone
Heat production
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9. Muscle Lecture-BIO 006 Handout
Movement
Muscles produce movement; as a muscle contracts, it pulls the insertion bone closer to the origin bone
Movement occurs at the joint between the origin and the insertion
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10. Muscle Lecture-BIO 006 Handout
Groups of muscles usually contract to produce a single movement
Prime mover —muscle whose contraction is mainly responsible for producing a movement
Synergist —muscle whose contractions help the prime mover produce a movement
Antagonist —muscle whose actions oppose the action of a prime mover in a movement
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11. Types of Movements Produced by Skeletal Muscle Contractions
Flexion—movement that decreases the angle between two bones at their joint: bending
Extension—movement that increases the angle between two bones at their joint: straightening
Abduction--movement of a part away from the midline of the body
Adduction--movement of a part toward the midline of the body
Rotation—movement around a longitudinal axis
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12. Muscle Lecture-BIO 006 Handout
Supination--hand position with the palm turned to the anterior position
Pronation—hand position with the palm turned to the posterior position
Dorsiflexion--elevation of the dorsum or top of the foot and
Plantar flexion--the bottom of the foot is directed downward
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13. Muscle Lecture-BIO 006 Handout
Posture
A specialized type of muscle contraction, called tonic contraction, enables us to maintain body position
In a tonic contraction, only a few of a muscle’s fibers shorten at one time
Tonic contractions produce no movement of body parts but DO hold muscles in position
Tonic contractions maintain muscle tone called posture
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14. Muscle Lecture-BIO 006 Handout
Heat production
Survival depends on the body’s ability to maintain a constant body temperature
Fever—an elevated body temperature; often a sign of illness
Hypothermia—a reduced body temperature
Contraction of muscle fibers produces most of the heat required to maintain normal body temperature
Energy for muscle contraction is obtained from ATP. Some of the energy is lost as heat and this is what maintains our body temperature
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15. Muscle Lecture-BIO 006 Handout
Fatigue
Causes reduced strength of muscle contraction due to lack of sufficient rest
Caused by repeated muscle stimulation
Repeated muscular contraction uses up the cellular ATP store and exceeds the ability of the blood supply to replenish oxygen and nutrients
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Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness
Oxygen debt —term used to describe the metabolic effort to remove the excess lactic acid that may accumulate during prolonged periods of exercise; the body is attempting to return the cells’ energy and oxygen reserves to pre-exercise levels
Heavy breathing after exercises helps to return level of oxygen in blood to normal levels
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17. Muscle Lecture-BIO 006 Handout
Motor Unit
Stimulation of a muscle by a nerve impulse is required before a muscle can produce movement
A motor neuron is the nerve that transmits an impulse to a muscle, causing contraction
A neuromuscular junction is the specialized point of contact between a nerve ending and the muscle fiber it innervates
A motor unit is the combination of a motor neuron with the muscle cell or cells it innervates
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18. Muscle Lecture-BIO 006 Handout
Muscle Stimulus
A muscle will contract only if the stimulus reaches a certain level of intensity
A threshold stimulus is the minimal level of stimulation required to cause a muscle fiber to contract
Once stimulated by a threshold stimulus, a muscle fiber will contract completely; this is called an all or none response
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Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levels
Although individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does not
Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force
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20. Types of Skeletal Muscle Contraction
Isotonic contractions
Contraction of a muscle that produces movement at a joint
During isotonic contractions, the muscle changes length, causing the insertion end of the muscle to move relative to the point of origin
Most types of body movements such as walking and running are caused by isotonic contractions
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21. Muscle Lecture-BIO 006 Handout
Types of Skeletal Muscle Contraction
Isometric contractions
Isometric contractions are muscle contractions that do not produce movement
Although no movement occurs, tension within the muscle increases
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22. Selected Skeletal Muscle Groups
Muscles of the head and neck
Facial muscles
Orbicularis oculi—closes your eye
Orbicularis oris—puckers your lips (kissing muscle)
Zygomaticus—raises the corners of the mouth (smiling muscle)
Temporalis—chewing muscle; closes jaw
Masseter—chewing muscle; closes jaw
Neck and Shoulder muscles
Sternocleidomastoid—flexes head
Trapezius—elevates shoulders and extends head
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Muscles that move the upper extremities
Pectoralis major—flexes upper arm; hugging muscle
Latissimus dorsi—extends upper arm
Deltoid—abducts upper arm
Biceps brachii—flexes forearm
Triceps brachii—extends forearm
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Muscles of the trunk
Abdominal muscles
Rectus abdominis—flexes trunk
Respiratory muscles
Intercostal muscles
Diaphragm
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Muscles that move the lower extremities
Iliopsoas—flexes thigh
Gluteus maximus—extends thigh
Hamstring muscles—flex lower leg
Semimembranosus
Semitendinosus
Biceps femoris
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Muscles that move the lower extremities
Quadriceps femoris group—extend lower leg
Rectus femoris
3 Vastus muscles
Tibialis anterior—dorsiflexes foot
Gastrocnemius—plantar flexes foot
Muscle Lecture-BIO 006 Handout