MUSCULAR SYSTEM

Muscle Facts!

The human body has 640 voluntary/skeletal muscles. This means muscles which we can control, as opposed to muscles of the heart and intestines which we can not voluntarily control.

Muscles are made of microscopic filaments which contract and slide over each other causing the the muscles to shorten and therefore contract.

No matter how much you exercise you can not increase the number of muscle cells you have. By getting bigger, via strength training, you are simply increasing the size of each muscle cell. The quantity of muscle cells remain the same.

The strongest muscles are: The Soleus, part of the calf muscle, below the calf muscles, as it can

apply the most force. The Masseter, also known as the jaw muscles. The tongue. Yes, the tongue is a muscle! And for its size it's very

strong.

Major Muscles

The functions of muscles

Producing movement – facial expressions, movement of food stuffs through digestions and blood through the heart.

Maintaining posture (skeletal only), very fatigue resistant muscles, ex. erector spinae; and stabilizing joints (holding the skeleton together)

Generating heat to maintain body temperature. Muscles make up 40% of body weight and ¾ of energy given off by ATP is heat.

Three types of Muscle: Skeletal, smooth and cardiac

Skeletal muscle fibers contain numerous nuclei and mitochondria --> Energy

The muscle fiber membrane is called the SARCOLEMMA and the cytoplasm is called the SARCOPLASM. Within the sarcoplasm are many parallel fibers known as MYOFIBRILS

Each myofibril is made of many protein filaments called MYOFILAMENTS. There are two types MYOSIN - thick filamentsACTIN - thin filaments

Muscles are made of muscle fibers (cells) Muscle fibers (cells) are made of

myofibrils which contain the functioning units of contraction called sarcomeres

Muscle Structure

Relaxed vs. Contracted Sarcomere

How the muscle fiber contracts – The Sliding Filament Theory

Basic structure of sarcomere.

1. Sarcomere is the functional contracting unit of the muscle fiber.

Steps in the Sliding Filament Theory

1. Nerve impulse reaches the synaptic cleft between the nerve and the muscle fiber (each fiber must be individually stimulated). This is called the neuromuscular junction.

Steps in the Sliding Filament Theory

2. Signal causes Calcium (Ca) to be released from the sarcoplasmic reticulum. (as soon as nerve impulse is over Ca is reabsorbed)

Steps in the Sliding Filament Theory

3. Calcium causes the protein complex on actin to move away from the binding site.

Steps in the Sliding Filament Theory

4. ATP activates the myosin head to form the cross bridge (myosin head )attached to actin and pivots toward the H-zone. Causing a shortening of the sarcomere.

5. This action occurs simultaneously through out the entire muscle fiber and through out the entire muscle causing the muscle itself to contract/shorten. In order to maintain a contraction (ex. hold your arm out in front of you for several seconds) the nerve must constantly restimulate the muscle fiber.

Steps in the Sliding Filament Theory

Energy for muscle contractions

Muscle fibers typically keep 4 to 6 seconds worth of ATP stored. Therefore the cell must very quickly begin generating more ATP

First, use of creatine phosphate to make more ATP. (about 20 seconds)

Aerobic respiration. Used during light exercise and rest. 95% of all muscle energy is generated this way. Requires oxygen.

Anaerobic respiration. During more intense exercise (30 to 60 seconds) but results in the build up of lactic acid (byproduct) in the muscles which promotes muscle fatigue and soreness.

Sliding Filament Theory Videos http://bcs.whfreeman.com/thelifewire/co

ntent/chp47/4702001.html Good simple animation

http://www.youtube.com/watch?v=GC_CUfLP6Pc song

http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP2904

http://www.youtube.com/watch?v=sJZm2YsBwMY Cartoon version

Types of Muscle Contractions Isotonic – the muscle shortens and

movement occurslifting weightsrunning

Isometric – muscle contracts or shortens but no movement occurs (pushing against a brick wall)

Types of Body Movements

A. Flexion- bending movement that brings two articulating bones closer together.

B. Extension- reverse of flexion, moves the bones further apart.

C. Abduction- movement of limb away from the mid-line

D. adduction- movement of limb toward the mid-line.

Body Movements continued

E. Circumduction- moving a limb so it describes a cone in space

F. Rotation- turning of a bone on its long axis, this also includes lateral and medial rotation of hip and shoulder

G. Supination- palm up H. Pronation palm down

Special Body Movements

Inversion: sole of foot is turned medially

Eversion- sole of foot is turned laterally

plantar flexion- point toes

dorsiflexion- pull toes towards shin

Muscle Movements

Muscle Movements

Types of Muscles

A. Prime mover- provide the major force for producing a specific movement.

Ex. Biceps Brachii for forearm flexion B. Antagonist- oppose or reverses a particular

movementEx. Triceps brachii for forearm

extension (oppose biceps) C. synergist- aid prime movers by promoting

the same movement or reducing undesireable or unnecessary movements that might occur as the prime mover contracts.

Ex. Semimembranosis helps the biceps femoris with thigh extension and knee flexion

Types of Muscles

D. Fixators- a synergist that immobilizes or stabilizes a bone or a muscle’s origin

Ex. Rotator cuff muscles (terest minor, infraspinatus, supraspinatus, subscapularis)

E. Example of movement of all four involved in a movement

a. prime mover= pectoralis major (shoulder flexion)

b. antagonist= lattisimus dorsic. synergist= biceps brachiid. fixator= rotator cuff

Skeletal muscles are named according to certain criteria

1. Location- may indicate bone or body region that muscle is associated with

Ex. Zygomaticus- associated with the zygomatic arch in the skull

2. Shape- Muscles often have a definitive shape, after which they are nameEx. Deltoid means triangle (and the deltoid muscle is triangular)

3. Relative Size Maximus= largest Minimus= smallest Longus= long Brevis= short Ex. Gluteus maximus (larger) and

minimus (smaller)

4. Direction of Muscle Fibers- may reflect the direction of the fibers in relation to midline or other axis

Rectus= straight (runs parallel)Transversus/oblique ( right

angles)/ obliquelyEx. Rectus femoris- muscle that

runs parallel with the femur 5. Number of OriginsBiceps= two originsTriceps= three origins Quadriceps= four origins Ex. Biceps Brachii

6. Location of origin and insertions may be named according to the attachment points

Origin is always named first Ex. Sternocleidomastoid (dual origin on sternum and clavicle;

insertion on mastoid process 7. ActionUses words such as flexor, extensor, or adductorEx. Adductor longus on thigh adducts the thighSometimes several criteria are combined in a name.Ex. Extensor carpi radialis longus muscle’s action (extensor) joint it acts on (carpi= wrist) Where it is (radialis = radius of forearm) size (long relative to other wrist muscles