Unit 4 Muscular System

Muscular System

• The body’s “flesh”

• The typical body contains approximately 640 muscles

• Span a joint and taper at each end into a fibrous tendon anchored to a bone

Muscle Functions (all muscle types)

• Producing Movement

  • Result of muscle contractions

Muscle Functions (skeletal muscle only)

• Maintains posture

  • Maintain an erect or seated posture despite the downward pull of gravity

• Stabilizes joints

  • Muscle tendons reinforce and stabilize joints

• Generates heat

  • By-product of muscle activity

  • Vital in maintaining normal body temperature

What are the three types of muscle tissue?

• Cardiac muscle

• Skeletal muscle

• Smooth muscle

What are skeletal muscles?

• Attached to bones or, for some facial muscles, to skin

• Largest of the muscle fibre types

• Multinucleated cells

• Striated (ridges)

• Voluntary muscles (can consciously control)

What is smooth muscle?

• No striations (ridges)

• Involuntary (cannot consciously control it)

• Found in the walls of the visceral organs (stomach, urinary bladder and respiratory passages)

What is cardiac muscle?

• Only found in the heart

• Striated 

• involuntary

What are tendons?

Tough, fibrous cords that link skeletal muscle to bones

What are myofibres?

• Densely packed groups of elongated muscle fibres

• In skeletal muscle

• Grouped into bundles called fascicules

What are myofibrils?

• Narrower structures that make muscle fibres

• Contain thick and thin contractile ligaments made up of the proteins myosin and actin

How do muscles contract?

• In relaxed muscles, myofilaments only partly overlap

• When contracted, the myosin filaments slide between the actin filaments shortening myofibril and muscle fibre

• Contraction amount depend on how many muscle fibres shorten overall

How do we move?

• Skeletal muscles, attached to bone by tendons, produce movement by bending the skeleton at moveable joints

• The connecting tendon closest to the body of head is called the proximal attachment

  • This is termed by the origin of the muscle

• The distal attachment is called the insertion

• During contraction the origin remains stationary and the insertion moves

What is origin?

• More stable attachment site

• Usually the centre of the body

• Doesn’t move during contraction

What is insertion?

• Other attachment site

• Towards the body’s periphery (outer area)

• Moves more during contraction

What are agonists?

• Prime movers

• When two muscles work together by producing the same movements or by reducing undesirable movement

• Example:

  • Biceps

  • Rotator cuff

What are antagonists?

• Specialized synergists that hold bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone

• Example:

  • Triceps

  • Biceps Brachii and brachioradialis

What is muscle tone?

• The state of continuous partial contractions 

• Even when muscle is voluntarily relaxed, some of its fibres are contracting

• Keeps muscles firm, healthy and constantly ready for action

What effect does exercise have on the muscle?

• Regular exercise increases muscle strength, size and endurance

• Aerobic (endurance) exercise result in stronger more flexible muscles with greater resistance to fatigue

• Resistance (isometric) exercises results in an increase in muscle size and strength

What are contractures?

• The lack of joint mobility caused by an abnormal shortening of a muscle

• The contracted muscle is fixed into position, is deformed and cannot stretch

• May be a result of immobilization from injury or disease; nerve injury, such as spinal cord damage and stroke; or muscle, tendon, or ligament disease

• Permanent deformity and disability

Where are common sites of contractures?

• Fingers

• Wrists

• Elbows

• Toes

• Ankles

• Knees

• Hips

What is muscular atrophy?

• Muscle inactivity leads to muscle weakness and wasting

• If nerve supply to a muscle is destroyed (as in an accident), the muscle is no longer stimulated, and it loses its tone and becomes paralyzed.  Soon after it becomes flaccid, or soft and begins to atrophy (waste away)

What is atrophy?

The decrease in size or the wasting of tissue

What is hypertrophy?

An increase and growth of muscle cells

What is muscular dystrophy?

• A group of disorders characterized by progressive degeneration and loss of muscle tissue

• These disorders are distinguished from each other by the type of gene mutation (sex-linked, dominant gene, recessive gene), the age when the symptoms appear, and the types of symptoms that develop

• It is an inherited disorder, so family history is a factor

What is ALS (amyotrophic lateral sclerosis) aka Lou Gehrig’s Disease?

• A fatal type of motor neuron disease

• Affects voluntary control of arms and legs, and leads to trouble breathing