Component 3 Human Musculoskeletal anatomy

Option B

What type of tissue is cartilage?

Connective tissue

Cartilage features

Hard, but flexible

Compressible

Elastic

How is cartilage built?

All cartilage built by Chondrocytes - these build a matrix around them

Chondrocytes

Cells responsible for cartilage formation

Found in lacunae

Lacunae

Pockets that they (Chondrocytes) live in within the matrix

Matrix

Made of Chondrin (forms the matrix of cartilage)

Made of proteins (collagen) and glycoproteins

Collagen

A fibrous protein that provides structural support and strength to tissues.

Collagen molecules assemble into fibrils (small strands), which then organise into larger fibres.

True or False

The relative abundance of collagen and glycoproteins varies depending on the type of cartilage.

True

What are the 3 types of cartilage?

Hyaline cartilage

Yellow elastic cartilage

White fibrous cartilage

Hyaline cartilage

It has a high proportion of collagen fibres for added strength

Weakest type of cartilage

Location of Hyaline cartilage

Found in the most different places

Location - as support rings in the trachea and bronchi and as articular cartilage on the bone ends.

Articular cartilage is made of Hyaline cartilage

Hyaline cartilage extra information

Blood vessels do not penetrate cartilage, nutrients and oxygen slowly diffuse through it, leading to slow healing.

Long bones are laid down and grow as cartilage and gradually turn to bone (ossify).

Yellow elastic cartilage

Contains yellow elastic fibres containing elastin - matrix is flexible but retains it’s shape

Can see fibres in matrix

Location of Yellow elastic cartilage

Located in the external ear and end of nose

White fibrous cartilage

The cartilage that has the greatest tensile strength

With added parallel bundles of collagen fibres within Chondrin matrix

Located in discs between the vertebrae

Ossification

Involves the conversion of other types of connective tissue turning into bone

Why does cartilage take a long time to heal?

Because it doesn’t have blood vessels running through it so the oxygen and nutrients have to slowly diffuse through.

Cartilage to bones

Most bone is first deposited as hyaline cartilage

It turns bone (ossifies) during growth

A small plate of cartilage is left near the tips of bone shafts until after puberty

Cartilage is maintained at the bone ends as articular cartilage

Compact bone

Compact bone is in a tube at the edge of the bone shaft. Bars of spongy bone support the heads

Compact bone matrix components

30% organic - mainly collagen, which resists tensile forces and fracture

70% inorganic - Hydroxyapatite, which resists compressive forces

Organic

Has carbon to hydrogen covalent bonds

Hydroxyapatite

Collective name for calcium salts, most abundant in bones is calcium phosphate

Collagen structure

Amino acid → Collagen molecule → Collagen fibre

How are bones so strong?

The combination of the two (high tensile strength and resistance to compressive forces) make bones so strong

Tension is resisted by…

Collagen

Compression is resisted by…

Hydroxyapatite

The properties of tension and compression combine to resist other forces like…

Bending and torsion

Cytoplasmic threads linking osteocytes

Canaliculi

What is bone formation called?

Ossification

Bone cells

Osteocytes - cells that build and destroy bones

Osteoblasts

Secrete layers of bone matrix around the cartilage

Osteoclasts

Break down the cartilage/matrix and bone

Why do osteoclasts break down cartilage?

So it can be replaced by bone

Osteoporosis

A condition that weakens bones, making them more susceptible to fractures

Causes of Osteoporosis

Osteoclasts working more than osteoblasts as we age

Abnormal loss of bone density - as calcium salts dissolve out

More fragile bones

Change in bone mass with age

Bone mass increases up until the age of 30 for both men and woman and then stays the same till 40, where it starts to decrease.

In women, their bone mass is lower than men and decreases more rapidly after 40 due to the menopause.

Symptoms of Osteoporosis

Decline in bone density (seen in x-rays and scans)

Fractures

Collapsed spine

Chronic debilitating pain

Risk factors of Osteoporosis

Age

Family history

Inflammatory conditions

Smoking

Medical conditions or long-term use of drugs that affect hormone levels e.g. steroids

Treatment and Prevention of Osteoporosis

Regular weight bearing exercise

Foods rich in calcium and Vitamin D

Drugs

Stop smoking and reduce alcohol consumption

HRT - Hormone Replacement Therapy

Learning to prevent falls

Osteogenesis imperfecta

Brittle Bone disease

What is Brittle Bone disease?

When collagen is not made properly

Inherited condition

Mutation (various) impacting the gene responsible for collagen

True of False

With Brittle Bone disease, in some forms, glycine is replaced with the bulkier amino acids so the molecule cannot coil as tightly and the hydrogen bonds holding the triple helix together are weaker.

True

Symptoms of Brittle Bone disease

Bone pain

Blue sclera

Hearing loss

Brittle bones that break easily

Weak, brittle misaligned teeth

Loose joints - regularly pop out joints

Difficulty breathing

Why is a symptom of Brittle Bone disease having a blue sclera?

Because collagen has a different structure

What does the treatments for Brittle Bone disease aim to do?

Aims to increase bone strength, prevent fractures and maintain mobility

Treatment for Brittle Bone disease

Drugs

Surgery - insert metal rod in bones

Physiotherapy - increase muscle strength around bones

Rickets

Rickets is a childhood bone disorder in which bones soften and become prone to fractures and deformity

Who does rickets affect?

Affects mainly children, may also affect adults

Name for adults who get rickets

Osteomalacia

Why is the main cause of rickets a lack of Vitamin D?

For proper absorption of calcium and phosphorus from the gut, we need Vitamin D. If Vitamin D levels are low in a child, they may have inadequate calcium and phosphorus bone levels.

Vitamin D sources

Fat soluble vitamin found in butter, eggs, oily fish and liver or liver extracts such as cod liver oil.

Vitamin D may be manufactured by the action of sunlight on the skin.

Symptoms of rickets

Enlarged wrists

Bones break easily

Low calcium blood levels (hypocalcaemia)

Bowed legs or knock knees

Child’s physical growth (height, weight) may be affected

There may be spinal, pelvic or cranial deformities

Causes of rickets

Not having enough calcium in one’s diet

Some childhood kidney and liver diseases

Digestive disorder complication that affects calcium and phosphorus absorption

Lack of Vitamin D

Why do our bodies need Vitamin D?

Our bodies need Vitamin D in order to absorb calcium from the intestines. Ultraviolet light (from sunlight) helps our skin convert Vitamin D from an inactive into an active state.

If we don’t have enough Vitamin D, calcium that we eat is not absorbed properly, causing hypocalcaemia to develop.

Risk factors for rickets

Sunlight - children who don’t get enough sunlight are dependant on excellent nutrition to make sure they are getting enough Vitamin D.

Malnutrition - rickets is more common in areas of the world where severe droughts and starvation occur.

Skeletal/striated muscles

Muscles which are attached to bones by tendons

Individual cells combine to form fibres which have lots of nuclei

Why is a muscle a tissue?

Because it is composed of many similar fibres working together to achieve the same function

Muscle contraction is under…

conscious control by the somatic (voluntary) nervous system

Why do myofibrils have mitochondria lying between them?

To provide ATP for energy for muscle contraction

Myofibril structure

Each myofibril consists of long thin structures called filaments

What are thick filaments made of?

Protein myosin

What are thin filaments made of?

Protein actin, with Tropomyosin and Troponin

Thick myosin filaments make…

dark bands - A bands

Thin actin filaments align to make…

pale bands - I bands

Sliding filament theory

The filaments do not change length - they slide past each other

I band structure

Actin

A band structure

Actin and myosin

H zone structure

Myosin

Sarcomere

From Z line to Z line

Made up of myosin

I band changes during contractions

Shortens

A band changes during contraction

No change

Why is there no change in A band during contraction?

Because it contains the entire length of the thick filaments (myosin), which don’t change length

H zone changes during contraction

Shortens

Sarcomere changes during contraction

Shortens

What happens at the secretory vesicle when an action potential arrives at a neuromuscular junction?

Voltage-gated calcium ion channels open

Calcium ions diffuse rapidly into pre-synaptic knob causing vesicles containing Acetylcholine to move to the pre-synaptic membrane for exocytosis into the cleft

What happens at the motor end plate when an action potential arrives at a neuromuscular junction?

Acetylcholine binds to receptors on the motor end plate, causing ligand gated sodium ion channels to open

Sodium ions diffuse rapidly into the sarcoplasm

Motor end plate is depolarised

What is the motor end plate also known as?

Post-synaptic membrane

What happens at the sarcolemma when an action potential arrives at a neuromuscular junction?

Depolarisation spreads to the sarcolemma

Sarcolemma carries depolarisation to the myofibrils

What is the sarcolemma?

Outer membrane

What happens at the T tubule when an action potential arrives at a neuromuscular junction?

T tubule carries wave of depolarisation into the myofibrils

What happens at the Sarcoplasmic reticulum when an action potential arrives at a neuromuscular junction?

The sarcoplasmic reticulum releases calcium via diffusion, causing the muscles to contract

Function of the sarcoplasmic reticulum

Stores calcium

Stage 1 of the Ratchet mechanism

Role of calcium ions

Role of calcium ions in the Ratchet mechanism

When an action potential arrives, calcium ions are released from the sarcoplasmic reticulum

Calcium ions bind to troponin and change its shape

This causes tropomyosin to change position exposing the myosin binding sites on actin

The myosin heads can now form crossbridges with the myosin binding sites on the actin filaments

Stage 2 of the Ratchet mechanism

Power stroke

Role of Power stroke in the Ratchet mechanism

ADP and Pi attached to the head are released. This changes the angle of the head back to its relaxed shape. The myosin head rotates pulling the actin past the myosin, the power stroke.

Stage 3 of the Ratchet mechanism

Role of ATP

Role of ATP in the Ratchet mechanism

An ATP molecule binds to the myosin head and this breaks the crossbridge with actin.

Hydrolysis of the ATP makes energy available and extends the myosin head again, ready to reattach to actin.

Stage 4 in the Ratchet mechanism

End of contraction

End of contraction in the Ratchet mechanism

The sequence repeats until the calcium ions are pumped back into the sarcoplasmic reticulum and the muscle relaxes

Types of muscle fibres

Slow twitch and fast twitch

Slow twitch and fast twitch muscle fibres occur together in varying combinations depending on…

Genetics of the person

Training

Type of muscle

What type of respiration is used in slow twitch muscle fibres?

Aerobic respiration - more efficient at using oxygen in oxidative phosphorylation to generate more ATP without lactate build up.

What type of respiration is used in fast twitch muscle fibres?

Depend on anaerobic respiration and glycolysis to synthesis ATP

Slow twitch muscle fibre characteristics

Used for slow, continuous muscle contractions over a long time

Contains large numbers of mitochondria

Contains lots of myoglobin

Small diameter of fibres

Has many blood capillaries

Low tolerance of lactate

Colour of slow twitch fibres

Red

Sporting events for slow twitch muscle fibres

Marathon running

Aerobics

Distance cycling/walking/swimming

Fast twitch muscle fibres characteristics

Generate short bursts of strength or speed

Contain few mitochondria

Contain little myoglobin

Has a larger diameter of fibres than slow twitch

Has few blood capillaries

Can tolerate reasonable levels of lactate

Colour of fast twitch fibres

White

Sporting events for fast twitch muscle fibres

100m sprint

Javelin throw

High jump