1

Graded potential

Could be

depolarisation or

hyperpolarisation

Magnitude various;

can be added;

reduces while

propagated

2

Action potential

Changes in membrane potential reach a

threshold; becomes a brief reversal of

membrane potential

e.g. -70mV +30mV

Depolarisation only

Magnitude is the same; does not reduce

while propagated (all-or-none)

Mem

bra

ne

po

ten

tial

(m

V)

-55

+30

-70

Phase 1 Phase 2

Phase 3

Threshold

Resting potential

Ion permeability

PNa

PK

Action potential

Mem

bra

ne

po

ten

tial

(m

V)

-55

+30

-70

Phase 1 Phase 2

Phase 3

Threshold

Resting potential

Phases of action potential

Membrane potential

reaches the threshold

Phase 1: depolarisation

Phase 2: repolarisation

Phase 3:

hyperpolarisation

5

Depolarisation

Opening of VDSC in membrane

Increased membrane Na+ permeability

Decreased MP (depolarisation)

Increased flow of Na+ into cell

— a typical positive feedback mechanism

Voltage-gated sodium channels (VDSC)

6

Repolarisation

After Na+ channels open, they become

deactivated & Na+ flux stops

Voltage-gated K+ channels slowly open

K+ ions rush outwards

Membrane potential returns to the resting one (-70mV)

7

Hyperpolarisation

Voltage-gated K channels close slowly

K ions continue to flow outwards

Membrane becomes more polarised (-80mV)

8

Refractory period

Period of reduced excitability

Absolute refractory period

Relative refractory period

Significance: single direction of propagation

9

Refractory period

Stanfield & Germann Fig 7.17

10

Propagation of action potential

myelinated

not myelinated

11

Propagation of action potential - myelinated axon

Myelin sheath acting as insulator to prevent

leakage of charges from the axon

Current can only pass through the membrane at

the Node of Ranvier

Propagation is much faster than unmyelinated

axon

Dr. Fang Lou

12

Overview of the musculoskeletal system

including bone and soft tissue

Learning Outcomes:

Describe the types of connective tissue found in the body and indicate their characteristic functions

Describe the functional properties of the three types of cartilage tissue

Name the major regions of the skeleton and describe their relative functions

List and describe five important functions of bones

13

Following this session and appropriate independent study, you should be able to:

Connective tissue proper (inc. fat and fibrous tissue of ligament)

Cartilage

Bone tissue

Blood

Connective Tissues

Four main classes

Functions of connective tissue

Binding and support

Protection

Insulation

Transportation

Major classes of connective tissue

Mesenchyme

Connective tissue proper

Cartilage Osseous Blood

1. Loose connective tissue- Areolar- Adipose- Reticular2. Dense connective tissue- Regular- Irregular

Subclasses1. Hyaline cartilage2.Fibrocartilage3. Elastic cartilage

1. Compact bone2. Spongy (cancellous) bone

Class of connective tissue

Common embryonic form

Has qualities between dense connective

tissue and bone

Tough but flexible

Stands up to both tension & compression

Lack of nerve fibres and is avascular

Up to 80% water

Calcify/ossify in later life

Cartilage

Varieties of cartilageHyaline Elastic

Fibrocartilage

www.kumc.edu/instruction/medicine/anatomy/histoweb/cart/cart.htm

Location: embryonic skeleton

covers end of long bones in joint cavity

costal cartilage of the ribs

respiratory tract (nose, larynx, trachea, etc.)

Provide firm support with some flexiability

Hyaline Cartilage

20

The bones and cartilage of the human skeleton

Fig. 6.1 Marieb

Bones of axial skeleton

Bones of appendicular skeleton

Hyaline cartilage

Elastic cartilage

Fibrocartilage

Location: External ear

epiglottis

More elastic fibres

Provide strength and exceptional stretchability

Elastic Cartilage

Location: intervertebral disc

disc of knee joint

Between hyaline cartilage and dense regular connective tissue

Absorb shock

Fibrocartilage

206 named bones, two groups:

Axial skeleton

Protecting

Supporting

Appendicular skeleon

Locomotion

Manipulation

Classification of Bones

The axial skeleton The skull

The vertebral column

The bony thorax

The appendicular skeleton The pectoral (shoulder) girdle

The upper limb

The pelvic (hip) girdle

The lower limb

Major regions of the skeleton

25

skull

vertebraethoracic

Axial SkeletonSupport & protect

Modified from Fig. 7.1 Marieb 7th ed.

26

pectoral (shoulder) girdle

the lower limb

the upper limb

Appendicular SkeletonSupportMovementMineralBlood cells

Modified from Fig. 7.21 Marieb 7th ed.

pelvic (hip) girdle

Support (framework)

Protection (skull, vertebrae & ribs)

Movement (lever for muscles)

Store minerals (calcium & phosphate)

Blood cell formation (marrow)

Functions of Bones