Support and Movement (3) Flashcards
Muscle types
Smooth, skeletal, cardiac
Smooth muscle
- 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
Cardiac muscle
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)
Skeletal muscle
- 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)
Properties of skeletal muscles
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
Microstructure of muscle
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.
Sarcomeres - contractile filaments
- 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
Power stroke
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.
Connection between the nervous system and skeletal muscle: the motor unit
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.
Muscle force is influenced by…
- Muscle architecture:
- Structure
- Size (muscle volume)
- Physiological cross sectional area (muscle volume/fibre length) - Sarcomere length (the length tension relationship):
- Active force production
- Passive force - Single motor unit:
- Number
- Discharge rate
- Fibre type - Type of contraction
- Isometric
- Concentric
- Eccentric
Muscle shape
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
Muscle PSCA
Muscle volume/ Fiber length
Greatest predictor of force.
Sarcomere length (the length tension relationship)
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.
Single motor unit
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.
Henneman’s size principle
Smaller units are recruited first
Type of contraction
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.
Mechanical functions of the skeleton
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.
Metabolic functions of the skeleton
Nutrient store (minerals and lipids), blood cell formation
Types of bones (broad sense)
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
How many bones make up the human skeleton?
206
What is an endoskeleton?
Skeleton within soft tissues
What is an exoskeleton?
Hard covering on the outside of the body (shell)
What is a hydrostatic skeleton?
Fluid held under pressure (worms)
What are the four anatomical planes?
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)
Joint movement terminology (FUN)
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
Fibrous joints
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).
Cartilaginous joints
Contain cartilage, cushions forces.
Allow a little movement (more than fibrous but less than synovial).
e.g. vertebral discs and the pubic symphysis
Synovial joints
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.
Types of bones (narrow sense)
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.
Composition of bones
Collagen:
40% of dry weight
-toughness and flexibility
Calcium and salts:
60% of dry weight
-Hardness and rigidity
-Laid down between collagen fibers
Four bone cells
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
Two types of bone structure
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
Bone remodelling
A bone grows or remodels itself in response to the forces applied upon it.
Bones are thickest where they’re most likely to buckle.
Human skeleton through life
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
Action potentials in the muscle
- 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.
- The AP triggers the release of Ca2+ ions from the sarcoplasmic reticulum.
- The calcium ions bind to troponin on the actin (thin filament) and expose the myosin binding sites.
- Cycles of myosin cross-bridge formation and breakdown, coupled with ATP hydrolysis, slide thin filament towards centre of sarcomere. Power stroke.
- Cytosolic calcium ions are removed by active transport into the sarcoplasmic reticum after the AP ends.
- Tropomyosin blockage of myosin binding sites is restored; contraction ends, and muscle fibre relaxes.
