Chapter 9 Muscular System

Types of Muscle Cardiac Involuntary Smooth Skeletal Voluntary

Types of Muscle Cardiac muscle: Found only in the heart, consists of short, branching fibers that fit together at intercalated disks. It appears striped, or striated. Involuntary muscle because it contracts automatically. Smooth muscle: Found in the digestive tract, blood vessels, bladder, airways, and uterus, smooth muscle is nonstriated. Involuntary muscle because it contracts automatically (such as when the digestive tract processes food). Skeletal muscle: Is attached to bone and causes movement of the body. It appears markedly striated. Voluntary muscle because it can be contracted at will.

Skeletal Muscle Structure A skeletal muscle cell is called a muscle fiber. Skeletal muscle consists of bundles of tiny fibers that run the length of the muscle. Muscle fiber Endomysium Fascicle Perimysium Epimysium Fascia

Skeletal Muscle Structure Endomysium covers each muscle fiber. Muscle fibers are grouped in bundles called fascicles. Perimysium encases the fascicles. Epimysium, surrounds the muscle as a whole and binds all the muscle fibers together. Fascia surrounds the muscle outside the epimysium. (Deep fascia lies between muscles, whereas superficial fascia resides just under the skin.)

Structure of Muscle Fibers Myofibril Sarcolemma Myofilaments Sarcoplasmic reticulum Transverse (T) tubule

Structure of Muscle Fibers The membrane surrounding each muscle fiber (or cell) is called a sarcolemma. The cytoplasm of the cell is called sarcoplasm. Long protein bundles called myofibrils fill the sarcoplasm. (Myofibrils store glycogen and oxygen.) Sarcoplasmic reticulum (SR) surrounds each myofibril. Transverse (T) tubules extend across the sarcoplasm. Myofibrils consist of even finer fibers, called myofilaments. Two types of myofilaments: thin and thick. Thick = myosin. Thin = actin. Arrangement gives skeletal muscle its striated appearance.

Question A single muscle cell is called a: myofilament. muscle fiber. myofibril. fascicle.

Sliding-Filament Model of Contraction View animation on “Sliding-filament model of contraction”

Sliding Filament Model The thin and thick myofilaments stack to form the myofibrils; they are arranged in a type of lattice-work to form sarcomeres. A Z disc, or Z line, serves as an anchor point for the thin myofilaments. The section between the Z disks is the sarcomere.

Sliding Filament Model When a muscle begins to contract, the myosin latches on to the actin, forming a cross bridge. The sliding-filament model of contraction – the sarcomere shortens because the filaments slide over the top of one another. Muscle contraction requires ATP.

View animation on “How muscle fibers contract and relax” Muscle Contraction View animation on “How muscle fibers contract and relax”

Muscle Contraction The connection between a motor neuron and a muscle fiber is a neuromuscular junction. The synaptic cleft is a narrow space between the end of the motor nerve and the muscle fiber.

Muscle Contraction Muscle contraction involves the following sequence of events: Impulse reaches the end of a motor neuron, causing vesicles to fuse with cell membrane and release a neurotransmitter called acetylcholine (ACh). Ach diffuses across synaptic cleft, stimulating receptors in the sarcolemma. This sends electrical impulse over sarcolemma and inward along the T tubules, which then causes sacs in sarcoplasmic reticulum to release calcium. Calcium binds with troponin on actin filament to expose attachment points. In response, myosin heads grab on to the thin filaments and muscle contraction occurs.

Muscle Tone Length-tension relationship – strength of contraction depends on length of fibers before contraction begins.

Question During muscle contraction, the sarcoplasmic reticulum releases which substance? Calcium Acetylcholine ATP Acetylcholinesterase

Contraction of a Muscle Motor unit: A neuron and all the fibers it stimulates Threshold: The minimum voltage needed to cause muscle fiber contraction Twitch: Single, brief contraction

Other Factors Affecting Muscle Contraction Frequency of stimuli Strength of stimulus Type of contraction

Question A condition of rapid contraction with only partial relaxation is called: incomplete tetanus. complete tetanus. twitch. treppe.

Energy Source for Contraction Fatty acids Creatine phosphate Glucose

Energy Source for Contraction All muscle contraction – requires energy in the form of adenosine triphosphate (ATP) At rest – plenty of oxygen so aerobic respiration breaks down fatty acids Beginning exercise – supply of oxygen drops so muscles break down high-energy creatine phosphate (CP) making fuel for about 20 seconds of high-energy activity or about 1 minute of moderate activity

Energy Source for Contraction Continued exercise – muscles switch to anaerobic respiration of glucose; generates energy quickly and is useful for intense bursts of activity but produces lactic acid, which leads to muscle fatigue. After about 10 minutes of moderate activity – supply of oxygen increases and muscles shift back to aerobic respiration making more ATP than anaerobic.

Muscle Function Origin Belly Insertion

Muscle Function Skeletal muscles work in groups to create movement: The main muscle triggering the movement is the prime mover; the muscles that assist are synergists; the muscles balancing these movements are antagonists. When the prime mover contracts, the antagonist must relax and give the prime mover control. Antagonists oppose the action of the prime mover. The prime mover for one movement is the antagonist for the opposite movement.

Question At rest, muscles obtain most of their energy by metabolizing: glucose. lactic acid. creatine phosphate. fatty acids.

Major Muscles of the Body Muscles are named according to Size Shape Location Number of origins Direction of muscle fibers Actions The body has more than 600 muscles. Note: A table in the textbook details how muscles are named.

Muscles of the Head and Neck Frontalis Temporalis Orbicularis oculi Zygomaticus Masseter Orbicularis oris Sternocleidomastoid Trapezius

Muscles of the Head and Neck The following are muscles of facial expression: Frontalis Orbicularis oculi Zygomaticus Orbicularis oris Buccinator The following are muscles of chewing: Temporalis Masseter The following are muscles that move the head: Sternocleidomastoid Trapezius

Muscles of the Trunk External intercostals Internal intercostals Diaphragm

Muscles of the Trunk Some muscles of the trunk participate in respiration and form the abdominal wall. Additional muscles support and allow movement in the vertebral column; other muscles lie on top of each other to form the pelvic floor. The following muscles are involved in breathing: External intercostals Internal intercostals Diaphragm

Muscles That Form the Abdominal Wall Rectus abdominis External oblique Linea alba Transversus abdominis Internal oblique

Muscles That Form the Abdominal Wall The muscles of the abdominal wall are as follows: Rectus abdominis Transversus abdominis Internal oblique External oblique The aponeuroses of the muscles that form the abdominal wall meet in the midline of the abdomen to form a tough band of connective tissue called the linea alba (white line).

Which muscle or muscle group elevates the ribs during inspiration? Question Which muscle or muscle group elevates the ribs during inspiration? Temporalis Internal intercostals External intercostals External oblique

Muscles of the Shoulder and Upper Arm Deltoid Pectoralis major Serratus anterior

Muscles of the Shoulder and Upper Arm Key muscles are: Deltoid Pectoralis major Serratus anterior

Muscles of the Neck, Shoulder, and Back Trapezius Supraspinatus Infraspinatus Rotator cuff Teres minor Latissimus dorsi

Muscles of the Neck, Shoulder, and Back Trapezius Latissimus dorsi Rotator cuff Nicknamed the “SITS” muscles: supraspinatus, infraspinatus, teres minor, and subscapularis

Muscles That Move the Forearm Brachialis Biceps brachii Triceps brachii Brachioradialis Pronator muscle

Muscles That Move the Forearm Key muscles are: Brachialis Biceps brachii Triceps brachii Brachioradialis Pronator muscle Supinator muscle Flexors Extensors Muscles in the hands work with the flexors and extensors to help the fingers make delicate movements.

Muscles of the Thigh (Anterior View) Adductor magnus Iliacus Iliopsoas Psoas major Adductor brevis Adductor longus Gracilis Sartorius Rectus femoris Vastus lateralis Vastus medialis

Muscles of the Thigh (Anterior View) Iliopsoas (acting in opposition to the gluteus maximus) consists of the iliacus and psoas major. Sartorius Adductor muscles (adductor magnus, adductor brevis, adductor longus, and gracilis). Quadriceps femoris consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

Muscles of the Hip and Thigh (Posterior View) Gluteus medius Gluteus maximus Biceps femoris Semitendinosus Semimembranosus

Muscles of the Hip and Thigh (Posterior View) The gluteal muscles consist of the following: Gluteus medius Gluteus maximus Gluteus minimus Hamstrings consist of the biceps femoris, semitendinosus, and semimembranosus.

Muscles That Act on the Foot Gastrocnemius Soleus Calcaneal (Achilles) tendon

Muscles That Act on the Foot Bulging calf muscle consists of the gastrocnemius and the soleus Common tendon of the gastrocnemius and soleus is the calcaneal (Achilles) tendon.

Muscles That Act on the Foot Tibialis anterior Soleus Extensor digitorum longus

Muscles That Act on the Foot Digitorum longus Tibialis anterior Extensor digitorum longus

Question Which muscle is the prime mover when flexing the forearm? Biceps brachii Triceps brachii Brachialis Brachioradialis