Joint and muscle physiology

Question 1

What are the three main types of joint?

Answer 1

Synovial (diarthroses- e.g. knee)
Fibrous (synarthroses e.g. skull sutures)
Cartilaginous (amphiarthroses e.g. pubic symphisis)

Question 2

What type of cells produce synovial fluid?

Answer 2

Fibroblasts

Question 3

What are the functions of synovial fluid?

Answer 3

Lubricate, reduce friction and wear/tear

Replenish chondrocytes

Question 4

The viscosity of synovial fluid is a function of which of its constituents?

Answer 4

Hyaluronic acid

Question 5

How would inflamed synovial fluid appear?

Answer 5

Straw coloured/completely opaque, white cell count 2000-7500, >50 polymorphs per mm3

Question 6

What are the main functions of articular cartilage?

Answer 6

Load distribution to subchondral bone

Provide low friction articular surface

Question 7

What are the three components of articular cartilage?

Answer 7

Water (lubrication, nutrition, resiliency), Type 2 collagen (stiffness and strength), proteoglycan (compressive properties associated with load bearing)

Question 8

What type of cells synthesise articular cartilage?

Answer 8

Chondrocytes

Question 9

What are the three main types of muscle?

Answer 9

Smooth
Cardiac
Skeletal

Question 10

Define “motor unit”

Answer 10

A single motor neurone and all the muscle fibres (cells) it innervates

Question 11

What is the functional unit of skeletal muscle?

Answer 11

Sarcomere

Question 12

Describe the hierarchical structure of skeletal muscle.

Answer 12

Muscle —> (many) muscle fibres —> (many) myofibrils (actin and myosin filaments) —> sarcomere

Question 13

What neurotransmitter is involved in excitation/contraction coupling?

Answer 13

Acetylcholine

Question 14

Action potential travels across …. and down the …. of muscle fibre, inducing …. release from the ….. of the…..

Answer 14

Surface membrane
T-tubules
Calcium release
Lateral sacs
Sarcoplasmic reticulum

Question 15

How does calcium enable cross bridge formation?

Answer 15

Binds to troponin on actin filaments, displacing tropomysin and uncovering cross-bridge formation sites

Question 16

What is ATP required for in excitation-contraction coupling?

Answer 16

To power cross-bridge formation; to release cross bridges (during relaxation) and actively pump calcium back into the sarcoplasmic reticulum

Question 17

What does the gradation of skeletal muscle tension depend on?

Answer 17

Number of contracting muscle fibres

Tension developed by each contracting muscle fibre

Question 18

What are the two types of skeletal muscle contraction?

Answer 18

Isotonic- tension remains the same as muscle gets shorter (moving objects etc)
Isometric- muscle length stays the same as tension develops (posture)

Question 19

What is a reflex action?

Answer 19

Stereotyped response to a specific stimulus

Question 20

How are passive changes in muscle length resisted?

Answer 20

Stretch reflex

Question 21

What are the sensory nerve endings for the stretch reflex?

Answer 21

Annulospiral fibres

Question 22

Describe the patellar stretch reflex.

Answer 22

Increased firing in afferent fibres due to stretch; synapse in spinal cord (L3/L4), firing in alpha motor neurones, contraction of muscle and relaxation of antagonist muscle

Question 23

What are the main differences between subtypes of skeletal muscle fibres?

Answer 23

Pathways used for ATP synthesis
Resistance to fatigue
Activity of the myosin ATPase which determines speed of contraction

Question 24

Describe how
a) Type 1
b) Type 2a
c) Type 2x
skeletal muscle fibres are adapted for their purpose

Answer 24

a) slow twitch fibres- prolonged low-work aerobic exercise- many mitochondria, few enzymes for anaerobic glycolysis
b) intermediate- mixed
c) fast twitch- fast glycolytic- few mitochrondria. Explosive movements