6 - Skeletal tissues - ITS - Boston College · 6 - Skeletal tissues SKELETAL TISSUE TYPES ... components of skeletal tissues? Q: What are skeletal tissue made of? ... various arm

6 - Skeletal tissues

SKELETAL TISSUE TYPES notochord cartilage bone dentine enamel

ENDOSKELETON vs DERMAL SKELETON

SKELETAL TISSUE

USE & FUNCTION

BONE SCALING

Excitatory vs Inhibitory Influences: Neural Integration

EPSP: excitatory postsynaptic potential

IPSP: inhibitory postsynaptic potential

But also Ach,serotonin and others

3

1.EPSP: excitatory postsynaptic potential

2. IPSP: inhibitory postsynaptic potential (GABA and glycine are the main neurotransmitters)

Key point: An action potential in a presynaptic neuron results in a graded potential in the postsynaptic neuron.

4

NOTE: 1. The role of voltage-gated calcium channels

2. Vesicles with neurotransmitter

3.Neurotransmitter binding to postsynaptic receptors (often ligand-gated ion channels)

4.Re-uptake and enzymatic breakdown of neurotransmitter

5. At an excitatory synapse non-selective ion channels open and ions, mostly Na+ move down the gradient

6. At an inhibitory synapse Cl- channels open

5

•Real neurons receive as many as 200,000 synapses each •Ion flows from all inputs summate or average at the initial segment •An action potential in the postsynaptic neuron occurs if the membrane potential at the initial segment reaches threshold

Neural integration

6

7

72 kg

Q: What are the strengths and weaknesses of the organic and inorganic components of skeletal tissues?

Q: What are skeletal tissue made of?

Hydroxyapatite: Ca10(PO4)6(OH)2Collagen

Notochord

(not mineralized)

Cartilage (“chondro-”)

“blast” vs “cyte” organic components vs inorganic components

Bone (“osteo-”)

“blast” vs “cyte” organic components vs inorganic components

Dermal or membranous Endochondral direct development cartilage precursor shallow location deep location protection function support function

Modeling endochondral ossification

Kronenberg 2003. Nature 423:343.

Bone undergoes deposition and resorption by the activity of osteoblasts and osteoclasts throughout life.

Dentine (“odonto-”)

“blast” vs “cyte” organic components vs inorganic components

Enamel (“amelo-”)

“blast” vs “cyte” organic components vs inorganic components

Q: why might a single animal have more than one skeletal tissue at different times of life? In different parts of the body?

QQ: why might some single skeletal structures be formed of more than one tissue?

cartilage: alcian blue

calcified cartilage: alizarin red

ENDOSKELETON vs DERMAL SKELETON

SKELETAL TISSUE USE AND FUNCTION

Stress vs strain

Strain is measured as change in length relative to the original length (dimensionless)

Stress is measured in units of force / area (Gpa)

Q: Which skeletal tissues will strain (deform) most? Least? Q: Which skeletal tissue will break most easily? Least?

Stress-strain curves differ depending on the material, whether inorganic or organic

Q: Which curve represents cartilage? bone? dentine? enamel?

E = Young’s modulus elasticity

ba

c

d

Q: How does bone used for different purposes vary in composition?

Q: what is the relationship between the inorganic content and the modulus of elasticity?

b

a

c

ba c

Q: How might you explain the differences in mineral content among the various arm bones of a bat? http://youtu.be/rMSIauO-MJc?list=PL011EB0DA5D2CC028

Swartz and Middleton 2007

Glossophaga soricina

5 X

Q: Why aren’t large animals just “bigger models” of small animals?

Support is dependent on bone x-sec, NOT bone volume.

Q: Will the x-sec of legs increase less fast than, equally as fast as, or faster than mass (≈ volume)?

Q: Which animal was larger in life?

5 X

Q: How might we predict the factor by which the diameter of the leg bones of the small horse ”should” increase to support the larger horse?

Q: If linear dimensions increase by 5 …..by how much does leg cross section and volume (mass) increase if proportions are maintained?