The Skeletal and Muscular Systems

ByDr Shamshad Begum Loni

LECTURE NOTES

Axial skeletonskull (cranium and facial bones) hyoid bone (anchors tongue and muscles

associated with swallowing) vertebral column (vertebrae and disks) thoracic cage (ribs and sternum)

Appendicular skeletonpectoral girdle (clavicles and scapulae)upper limbs (arms)pelvic girdle (coxal bones, sacrum, coccyx)lower limbs (legs)

The Human Skeleton 1. Carpals

2. Cranium

3. Femur

4. Innominate

5. Mandible

6. Metacarpals

7. Metatarsals

8. Phalanges

9. Rib

10. Scapula

11. Sacrum

12. Vertebra

1. Clavicle

2. Fibula

3. Humerus

4. Patella

5. Radius

6. Sternum

7. Tarsals

8. Tibia

9. Ulna

1. Protect the vital organs we talked about last week

2. Give us shape

3. Allow us to move because our muscles are attached to our bones

4. Storage of nutrients such as calcium and silicon

5. Formation of blood cells

What are the Five main functions of the human skeleton

Classification of Bones on the Basis of Shape

Types of Bone Cells· Osteocytes Mature bone

Osteoblasts(remove calcium from blood and buildnew matrix. They become trappedosteoclasts)

Bone-forming cells

•Osteoclasts remove damaged cells and releasecalcium into blood (Bone-destroying cells)

· Break down bone matrix for remodeling and release of calcium

· Bone remodeling is a process by both osteoblasts and osteoclasts

• Do we have more bones when we are a baby or when we are all grown up?Baby has 305 bones and an adult has 206 bones. This is because as we grown some of our bones join together to form one bone.

• The longest bone in our bodies is the femur (thigh bone).

• The smallest bone is the stirrup bone inside the ear.

• Each hand has 26 bones in it.

• our nose and ears are not made of bone; they are made of cartilage, a flexible substance that is not as hard as bone.

Interesting Facts about the Skeletal System

Compact boneosteocytes within lacunaearranged in concentric circles called lamellae

This surround a central canal; complex is calledHaversian system

Canaliculi connect osteocytes to central canal andto each other

Structures Associated with the Synovial Joint· Bursae – flattened fibrous sacs

· Lined with synovial membranes

· Filled with synovial fluid

· Not actually part of the joint

· Tendon sheath

· Elongated bursa that wraps around a tendon

Types of JointsHinge- A hinge joint allows extension and

retraction of an appendage. (Elbow, Knee)

Types of Synovial Joints Based on Shape

Types of Synovial Joints Based on Shape

Types of freely movable joints

Saddle: carpal and metacarpal bones of thumb

Ball and socket: shoulder and hip joints

Pivot- rotation only: proximal end of radius and ulna

Hinge- up and own movement in one plane:knee and elbow

Gliding- sliding and twisting: wrist and ankle

Condyloid- movement in different planes but notrotations: btw metacarpals and phalanges

Ball and Socket- A ball and socket joint allows for radial movement in almost any direction. They are found in the hips and shoulders. (Hip, Shoulder)

Gliding- In a gliding or plane joint bones slide past each other. Mid-carpal and mid-tarsal joints are gliding joints. (Hands, Feet)

Saddle- This type of joint occurs when the touching surfaces of two bones have both concave and convex regions with the shapes of the two bones complementing one other and allowing a wide range of movement. (Thumb)

Types of movement and examples (with muscles)flexion- move lower leg toward upperextension- straightening the leg

abduction- moving leg away from bodyadduction- movong leg toward the body

rotation- around its axissupination- rotation of arm to palm-up positionpronation- palm down

circumduction- swinging arms in circles

inversion- turning foot so sole is inwardeversion- sole is out

Elevation and depression- raising body part upor down

Aging and bonesboth bone and cartilage tend to deterioratecartilage: chondrocytes die, cartilage becomes calcified

osteoporosis bone is broken down faster

than it can be builtbones get weak and brittle; tend to fractureeasilyRisk factors for osteoporosis

Inadequate calcium

Little weight-bearing exerciseDrinking alcohol, smokingBeing female: decreased estrogen secretion

after menopause

Types of bone breaks

Simple- skin is not piercedCompound- skin is piercedComplete- bone is broken in halfPartial- broken lengthwise but not into two

partsGreenstick- incomplete break on outer arcComminuted- broken into several piecesSpiral- twisted

Arthritis

Osteoporosis• Osteoporosis is a term that means

"porous bones.”. • Osteoporosis is a condition in which

bones have lost minerals especially calcium, making them weaker, more brittle, and susceptible to fractures (broken bones).,

• the most common places where fractures occur are the back (spine), hips, and wrists.

Scurvy• We depends on exogenous dietary

sources to meet vitamin C needs.• Consumption of fruits and vegetables or

diets fortified with vitamin C are essential to avoid ascorbic acid deficiency.

• Even though scurvy is uncommon, it still occurs and can affect adults and children who have chronic dietary vitamin C deficiency.

Bursitis• Inflammation of the Bursa (fluid

filled sac surrounding the joint).• A bursa can become inflamed from

injury, infection (rare in the shoulder), or due to an underlying rheumatic condition.

• Bursitis is typically identified by localized pain or swelling, tenderness, and pain with motion of the tissues in the affected area.

Skeleton and other systems

Skin makes vitamin D which enhances calciumabsorption

Skeleton stores calcium for muscle contraction,nervous stimulation, blood clot formation

Red marrow- site of blood cell formation

Calcium levels regulated byparathyroid hormone and calcitoninkidneys (can help provide vitamin D)digestive system (can release calciuminto blood

Muscular System Functions

• Body movement (Locomotion)• Maintenance of posture• Respiration

– Diaphragm and intercostal contractions• Communication (Verbal and Facial)• Constriction of organs and vessels

– Peristalsis of intestinal tract– Vasoconstriction of b.v. and other structures (pupils)

• Heart beat • Production of body heat (Thermogenesis)

Properties of Muscle

• Excitability: capacity of muscle to respond to a stimulus

• Contractility: ability of a muscle to shorten and generate pulling force

• Extensibility: muscle can be stretched back to its original length

• Elasticity: ability of muscle to recoil to original resting length after stretched

Interesting facts about the Muscular System

• Muscle: A tissue composed of fibers capable of contracting to effect bodily movement

• There are about 650 muscles in the human body.

Some Muscles

2. Sartorius3. Deltoid4. Sternocleidomastoid5. Tibialis 6. Hamstring group7. Rectus Abdominus8. Triceps 9. Biceps 10. Extensor Group

1. Gastrocnemius

Types of muscles

Muscle

Tendons

Connective tissue

Blood vessel

Muscle fibre

Skeletal muscles: Attached to bones. (what happens when you extend your arm?)

Smooth muscle: Surround organs, tubes, eg. stomach, urinary bladder, blood vessels. Contract propels content through organs (eg. expel urine).

Cardiac muscles: Heart muscle makes your heart pump blood.

Muscle Classification

Functionally1. Voluntarily2. Involuntarily

Structurally1. Striated2. Smooth

Combined1. Visceral2. Cardiac3. Skeletal

Nerve and Blood Vessel Supply

• Motor neurons– stimulate muscle fibers to contract– Neuron axons branch so that each muscle fiber (muscle cell) is

innervated– Form a neuromuscular junction (= myoneural junction)

• Capillary beds surround muscle fibers– Muscles require large amts of energy– Extensive vascular network delivers necessary oxygen and

nutrients and carries away metabolic waste produced by muscle fibers

Basic Features of a Skeletal Muscle• Muscle attachments

– Most skeletal muscles run from one bone to another

– One bone will move – other bone remains fixed

• Origin – less movable attach- ment

• Insertion – more movable attach- ment

Basic Features of a Skeletal Muscle

• Muscle attachments (continued)– Muscles attach to origins and insertions by

connective tissue• Fleshy attachments – connective tissue fibers are short• Indirect attachments – connective tissue forms a

tendon or aponeurosis – Bone markings present where tendons meet

bones• Tubercles, trochanters, and crests

Skeletal Muscle Structure• Composed of muscle cells (fibers),

connective tissue, blood vessels, nerves• Fibers are long, cylindrical, and

multinucleated• Tend to be smaller diameter in small

muscles and larger in large muscles. 1 mm- 4 cm in length

• Develop from myoblasts; numbers remain constant

• Striated appearance• Nuclei are peripherally located

Muscle Fiber Anatomy

• Sarcolemma - cell membrane– Surrounds the sarcoplasm (cytoplasm of fiber)

• Contains many of the same organelles seen in other cells• An abundance of the oxygen-binding protein myoglobin

– Punctuated by openings called the transverse tubules (T-tubules)• Narrow tubes that extend into the sarcoplasm at right angles to the

surface• Filled with extracellular fluid

• Myofibrils -cylindrical structures within muscle fiber– Are bundles of protein filaments (=myofilaments)

• Two types of myofilaments1. Actin filaments (thin filaments)2. Myosin filaments (thick filaments)

– At each end of the fiber, myofibrils are anchored to the inner surface of the sarcolemma

– When myofibril shortens, muscle shortens (contracts)

Sarcoplasmic Reticulum (SR)• SR is an elaborate, smooth endoplasmic reticulum

– runs longitudinally and surrounds each myofibril– Form chambers called terminal cisternae on either side

of the T-tubules• A single T-tubule and the 2 terminal cisternae form

a triad• SR stores Ca++ when muscle not contracting

– When stimulated, calcium released into sarcoplasm– SR membrane has Ca++ pumps that function to pump

Ca++ out of the sarcoplasm back into the SR after contraction

Sarcoplasmic Reticulum (SR)

Parts of a Muscle

Sarcomeres: Z Disk to Z Disk

• Sarcomere - repeating functional units of a myofibril

– About 10,000 sarcomeres per myofibril, end to end

– Each is about 2 µm long• Differences in size, density, and distribution

of thick and thin filaments gives the muscle fiber a banded or striated appearance.

– A bands: a dark band; full length of thick (myosin) filament

– M line - protein to which myosins attach– H zone - thick but NO thin filaments– I bands: a light band; from Z disks to ends of

thick filaments• Thin but NO thick filaments• Extends from A band of one sarcomere to A

band of the next sarcomere– Z disk: filamentous network of protein. Serves

as attachment for actin myofilaments– Titin filaments: elastic chains of amino acids;

keep thick and thin filaments in proper alignment

Structure of Actin and Myosin

Sarcomere

Z ZZ

Z ZZ

I

AA

A (I)

Myofilaments

1. Myosin: 110Å thick; confined to the A-band. (Mole. wt. 500,000 deltons; 200 molecules/myofilament)A. Tail- 800Å long, composed of a double helixB. Head (cross bridges)-600Å terminating in a

globular double structure. Contains binding sites for actin & ATP

Myofilaments

2. Actin: 60A thick; runs from Z-line (disc) to just inside A-band. Mole wt. 60,000 deltons.G-actin (globular units): contracted formF-actin (fibrous polymers): relaxed form

Actin associated proteinsA. TropomyosinB. Troponin

Neuromuscular Junction• Region where the motor neuron stimulates the muscle

fiber• The neuromuscular junction is formed by :

1. End of motor neuron axon (axon terminal)• Terminals have small membranous sacs (synaptic vesicles) that

contain the neurotransmitter acetylcholine (ACh)2. The motor end plate of a muscle

• A specific part of the sarcolemma that contains ACh receptors• Though exceedingly close, axonal ends and muscle fibers

are always separated by a space called the synaptic cleft

Neuromuscular Junction

Motor Unit: The Nerve-Muscle Functional Unit

• A motor unit is a motor neuron and all the muscle fibers it supplies

• The number of muscle fibers per motor unit can vary from a few (4-6) to hundreds (1200-1500)

• Muscles that control fine movements (fingers, eyes) have small motor units

• Large weight-bearing muscles (thighs, hips) have large motor units

Motor Unit: The Nerve-Muscle Functional Unit

Mechanics of Muscle Contraction

1. An action potential is generated by a motor nerve.

2. This causes the release of acetylcholine from the axon terminals at the neuromuscular junctions.

3. This Ach causes an increase in membrane permeability at the motor-end plate, causing the production of an end-plate potential (EPP).

Mechanics of Muscle Contraction

4. The EPP depolarizes the fiber membrane (sarcolemma) causing a muscle action potential which spreads over the entire surface of the fiber membrane.

5. This depolarizes the T-tubules, causing ionic conduction through their extracellular fluid, and the release of inositol triphosphate as a second messenger.

Mechanics of Muscle Contraction

6. Ca++ is then released from the endoplasmic reticular fluid of the cisterns (lateral sacs) into the surrounding myofibril.

7. Ca++ binds to the actin associated protein troponin, allowing the attachment of actin to the myosin-ATP complex to form a strong ATPase.

8. The ATPase splits ATP, releasing the energy needed for the movement of the myosin cross bridges.

Mechanics of Muscle Contraction

9. Energy from creatine phosphate replaces ADP on the myosin cross bridges, thereby breaking the A-M bond and allowing the cross bridges to relax.

10. The Ca++ are forced back into the walls of the longitudinal tubules by active transport.

11. This restores the inhibitory action of the troponin-tropomyosin complex.

A I

ZH

Muscle Energy

• Hold two books above your head for as long as you can…..

• How is the muscle able to do this? Where does it get its energy from?

• When your exercising how does this process change?

•Muscle needs energy to move just as we do. •Its energy can run out and needs to be replenished•Muscle gets its energy from the oxygen we breathe and the food we eat.•Muscle stores its food in the muscle fibres themselves. This food is called glycogen and is a type of sugar. •When we exercise, these stores are used to make energy and can run out.•We need to replenish our muscle food stores by eating carbohydrates

Selective Terms

1. Motor Unit: consists of all the muscle fibers innervated by terminals from a single axon. (Range from 23 - 2,000 fibers)

2. All or None Law: at or above threshold levels; the degree of contractile response of a single muscle fiber (or motor unit) is independent of stimulus strength

3. Tension: force exerted by a contracting muscle4. Load: force exerted on a muscle by the weight of an object5. Isotonic contraction (same tension): the tension developed

by the contracting is greater than the load. Therefore, the muscle shortens.

Selective Terms

6. Isometric contraction (same length): the strength of the load is greater than the tension of the muscle. Therefore, the muscle remains at the same length.

7. Muscle spindle apparatus: a series of small spindle shaped fibers within the muscle for detecting changes in the length (stretch) of the muscle.

8. Golgi tendon organ: tension receptors located in tendons, and activated by the pull of a contracting muscle