Support and Movement (3)

Question 1

Muscle types

Answer 1

Smooth, skeletal, cardiac

Question 2

Smooth muscle

Answer 2

• Found within walls of the gastrointestinal tract, blood vessels, lymphatic vessels, the urinary bladder, uterus, male and female reproductive tracts, respiratory tract, skin and the iris (eye)
• Non-striated

Question 3

Cardiac muscle

Answer 3

Found only in the contractile walls of the heart

From SA node, cardiac muscle cells are interconnected by intercalated discs, allow electrical signal to pass from one cell to another. Helps synchronise heart muscle contraction

Uni-nucleate (one nucleus per cell)

Question 4

Skeletal muscle

Answer 4

• Striated
• Made up of sarcomeres
• Muscle attaches to bone via connective tissue (tendon) and produces movement around joints
• Muscle cells are long, so also called muscle fibres
• Multinucleated (fuse multiple muscle cells into muscle fibres)
  - Multiple nuclei direct protein synthesis and repair of the cell faster
• Controlled by somatic nervous system (consciously influenced)

Question 5

Properties of skeletal muscles

Answer 5

Contractility: Ability to shorten and thicken, and develop tension

Extensibility: Ability to be stretched without damage

Excitability: Ability to respond to appropriate stimuli

Elasticity: Ability to store some energy, and recoil to the resting length

Question 6

Microstructure of muscle

Answer 6

Muscle (surrounded by Epimysium connective tissue), fascicles (surrounded by Perimysium connective tissue), muscle fibres (surrounded by Endomysium connective tissue, myofibrils, sarcomeres (basic contractile unit of skeletal muscle). Connective tissue dispersed throughout the muscle.

Question 7

Sarcomeres - contractile filaments

Answer 7

• Myosin thick filaments (anchor at M line in the centre of the sarcomere)
• Actin thin filaments (attach at Z line)
• Elastic filament: Titin - anchors myosin to the Z-line, contributes to passive force in the muscle

Question 8

Power stroke

Answer 8

Actin binding sites on Myosin heads form cross bridges with actin thin filaments.

Myosin pulls the actin across, shortening the muscle fibre and producing force.

Question 9

Connection between the nervous system and skeletal muscle: the motor unit

Answer 9

Motor unit = 1 motor neuron, its motor axon and all of the muscle fibres it innervates.
+ Motor units range in:
-Size (number of muscle fibres)
-Contractile properties (speed, fatigability)

This allows graded, sustained and controlled force.

• Excitatory and inhibitory input from descending pathways, spinal interneurons and afferent fibres.
• Many dendrites allow input from multiple sources.
• When sufficient excitatory input to reach firing threshold, an action potential is generated
• Every AP generated in motor neuron generates an AP in the motor units muscle fibres.
• Every AP in the muscles generates a little bit of force.

Question 10

Muscle force is influenced by…

Answer 10

1. Muscle architecture:
   - Structure
   - Size (muscle volume)
   - Physiological cross sectional area (muscle volume/fibre length)
2. Sarcomere length (the length tension relationship):
   - Active force production
   - Passive force
3. Single motor unit:
   - Number
   - Discharge rate
   - Fibre type
4. Type of contraction
   - Isometric
   - Concentric
   - Eccentric

Question 11

Muscle shape

Answer 11

The shape of a muscle affects the action of a muscle.

• Circular muscle can close an opening
• Long muscles are better at controlling movement over joints that have a large range of motion.
• Shorter-wider muscles are better at generating larger forces over a smaller joint range of motion

Question 12

Muscle PSCA

Answer 12

Muscle volume/ Fiber length

Greatest predictor of force.

Question 13

Sarcomere length (the length tension relationship)

Answer 13

Hill’s mechanical model of the muscle-tendon unit:

+ Contractile component (CC) - muscle fibers, actin and myosin cross bridges

+ Series elastic component (SEC) - intracellular titin, tendon. Gives the muscle elasticity, the tendency of a material to revert to its previous shape after deformation.

+ Parallel elastic component (PEC) - connective tissue - epimysium and perimysium, endomysium and passive cross bridge connections

Sarcomere length (myofilament overlap)
+ Optimal sarcomere operating length (80% - 120% of resting strength)
+ Most muscle force can be produced at this length
+Highest point of tension

Both active (CC) and passive (SEC and PEC) structures contribute to total force.

Question 14

Single motor unit

Answer 14

1 motor neuron, its motor axon and all of the muscle fibers it innervates.

Force is altered by number and discharge rate of motor units.

-Number of motor units discharging affects the amount of force produced by the muscle.
Amount of excitatory input determines how many motor units discharge.

-Discharge RATE of motor units: Force is influenced by the tyoe of muscle fiber being innervated.

Type I: Slow oxidative motor units. Slow twitch, low force, fatigue resistant. Aerobic resp. Lots mito (uses oxygen to produce ATP). High myoglobin cont.

Type IIa: Fast oxidative motor units. Quicker twitch duration, higher force, less fatigue resistant than TI. Aerobic resp. Lots mito. High myoglobin cont.

Type IIb: Fast glycotic. Fast twitch. High force. Fatigues quickly. Glycolysis - ATP source. Low myoglobin content. Less need for O2.

Question 15

Henneman’s size principle

Answer 15

Smaller units are recruited first

Question 16

Type of contraction

Answer 16

Static - isometric (same length)

Dynamic - Concentric (shortening)
- Eccentric (lengthening)

Max force that can be produced by each type is in the order: Ecc > Isometric > Conc

An eccentrically contracting muscle can produce more force at the same muscle length than a concentrically contracting muscle.

Can hold more load than you can lift, and lower more load than you can hold steady.

Question 17

Mechanical functions of the skeleton

Answer 17

Support, protect and move.

Support:
For muscles that contract to maintain posture, body shape and body functions. (ribs to hold lungs, pelvis as floor for pelvic organs)

Protection:
Of body organs from potential harm (skull and brain, verterbral column and spinal chord, rib cage and spine and sternum protect tthe lungs heart and major blood vessels)

Movement:
Converting muscle contraction into movement of ourselves or something in the environment requires a rigid structure on which the muscles can attach.

Question 18

Metabolic functions of the skeleton

Answer 18

Nutrient store (minerals and lipids), blood cell formation

Question 19

Types of bones (broad sense)

Answer 19

Axial bones:
Relating to or situated in the head and trunk region of the body.
(Axial - relating to or forming an axis)

Appendicular bones:
Relating to limbs
(Append - to add something to the end)

ADD EXAMPLES

Question 20

How many bones make up the human skeleton?

Answer 20

206

Question 21

What is an endoskeleton?

Answer 21

Skeleton within soft tissues

Question 22

What is an exoskeleton?

Answer 22

Hard covering on the outside of the body (shell)

Question 23

What is a hydrostatic skeleton?

Answer 23

Fluid held under pressure (worms)

Question 24

What are the four anatomical planes?

Answer 24

Sagital (red) (or median): divides the body into left and right

Parasagittal: is parallel with sagittal

Coronal (or frontal) (big blue corona bottle): divides the body into back and front (dorsal and ventral, posterior and anterior)

Transverse (horizontal): Divides the body into head and tail (cranial and caudal, superior and inferior)

Question 25

Joint movement terminology (FUN)

Answer 25

``` Sagital plane: Extension Flexion Foot- Dorsiflexion (up) Plantarflexion (down - plant fut into ground) ``` Coronal plane: Abduction - away from midline Adduction - towards midline Wrist - Pronation Supination Head - Right and left rotation ``` Forearm - Lateral rotation (up tall palms forward) Medial rotation (up tall palms back) ``` On both sides = bilateral

Question 26

Fibrous joints

Answer 26

Contain fibrous connective tissue. Some cannot move at all (skull sutures hold the skull bones tightly in place) and some allow for little movement (ligs between tibia and fibula in the ankle).

Question 27

Cartilaginous joints

Answer 27

Contain cartilage, cushions forces. Allow a little movement (more than fibrous but less than synovial). e.g. vertebral discs and the pubic symphysis

Question 28

Synovial joints

Answer 28

Joints that have space (a synovial cavity filled with fluid) between the adjoining bones. This allows the greatest range of movement. Cartilage and ligaments are important to keep the bones together. e.g. Hinge joint - Humerus and ulna Ball-and-socket joint - head of humerus and scapula Pivot joint - ulna and radius Skeletal muscle provides the active force applied to the bone. The joints allow movement of the skeleton. Antagonist muscle pairs allow the skeleton to move back into its original place.

Question 29

Types of bones (narrow sense)

Answer 29

Long: - Shaft with ends - Important for leverage/movement Short: - Square shaped - Important for fine movements Flat: - Important for protection - Hematopoiesis (to make blood) Irregular: -Important for protection, support, movement and hematopoiesis.

Question 30

Composition of bones

Answer 30

Collagen: 40% of dry weight -toughness and flexibility Calcium and salts: 60% of dry weight -Hardness and rigidity -Laid down between collagen fibers

Question 31

Four bone cells

Answer 31

Osteoclasts: V large cell, many nuclei which is thought to improve reabsorption efficiency. Breakdown bone matrix, destrow and resorb bone, respond to mechanical stress 'Dig tunnels' to be lined with collagen by the osteoblasts. sum: resorbs bone Osteoblasts: Line the tunnels with collagen. Create bone matrix, build bone (construction). Surface of the bone. Differentiate to osteocytes when trapped in bone. sum: forms bone matrix Osteocytes: Maintain bone matrix, hold bone together. Mineralise the bone matrix (calcium and salts). Long cytoplasmic extensions, can supply nutrients into the bone matrix. sum: maintains bone tissue Osteogenic cells: Stem cells, develop into an osteoblast (to form bone) and then an osteocyte (to maintain bone) sum: stem cell

Question 32

Two types of bone structure

Answer 32

Trabecular bone (spongy bone): Greater surface area compared to a compact bone. Promotes bone marrow to develop (produces RBCs and lymphocytes, support the immune system). Trabeculae form along lines of stress. Compact bone: Hard, dense bone Support the body, stores calcium Organised structure

Question 33

Bone remodelling

Answer 33

A bone grows or remodels itself in response to the forces applied upon it. Bones are thickest where they're most likely to buckle.

Question 34

Human skeleton through life

Answer 34

11 weeks before birth: 800 ossification centres (where bone is forming) Neonate: 2/3 of the skeleton is cartilaginous 450 ossification centres Subadult Adult: 10% of the skeleton is cartilaginous Peak bone mass is reached at around 35 years old

Question 35

Action potentials in the muscle

Answer 35

1. Acetyl choline (ACh) released at synaptic terminal diffuses across neuromuscular junction and binds to receptor proteins that propagate an action potential along the muscle fibre's plasma membrane and down T-tubules. 2. The AP triggers the release of Ca2+ ions from the sarcoplasmic reticulum. 3. The calcium ions bind to troponin on the actin (thin filament) and expose the myosin binding sites. 4. Cycles of myosin cross-bridge formation and breakdown, coupled with ATP hydrolysis, slide thin filament towards centre of sarcomere. Power stroke. 5. Cytosolic calcium ions are removed by active transport into the sarcoplasmic reticum after the AP ends. 6. Tropomyosin blockage of myosin binding sites is restored; contraction ends, and muscle fibre relaxes.