Lecture 3 - Muscles Flashcards
Muscles can only generate force by shortening. True or False?
True
What is the difference between CIlia and Flagella?
Cilia are 0.2-0.5 um and are found in all animals except nematodes (and limited in some arthropods). Cilia beat asymmetrically. Fluid propelled parallel to surface.
Flagella are longer and beat symmetrically. Fluid propelled perpendicular to surface.
Functions of muscles
Posture, movement, peristalsis, generation of heat and electricity, sound, internal organ function
What are the four functional characteristics of muscle?
Contractility, excitability, extensibility, elasticity
Contractility
Muscles can forcefully shorten
Excitability
Muscles respond to a stimulus
Extensibility
Muscles can be stretched
Elasticity
Muscles recoil or bounce
What are the types of invertebrate muscle?
Smooth (bivalve adductor muscle - slow), striated (e.g. bivalve closure muscle - fast), fibrillar (e.g. insect flight, very fast)
Direct flight of insects
Muscles directly attach to wings
Indirect flight in insects
Muscles attach to the thorax, rather than to wings, and cause flight by movement of the thorax.
Types of vertebrate muscle
Smooth (gut and blood vessels)
Striated (skeletal and cardiac)
Skeletal muscle
Attached to skeleton
Responsible for movement and posture
Striated, many nuclei, transverse tubules
Voluntary control
Fast contraction, relaxes and tires quickly
Cardiac muscle
Located in walls of the heart
Role in the pumping of the heart
Striated, uninuclear, transverse tubules, intercalated discs
Involuntary control
Contracts as a unit, self-exciting, rhythmic
Smooth muscle
Located in walls of hollow viscera in gut
Role in movement and peristalsis
Not striated, uninuclear, no transverse tubules
Involuntary control
Contracts and relaxes slowly, self exciting, rhythmic contractions
True or false. Muscle can be attached to other muscle
True. e.g. Flehmen response
Power is affected by
Type of fiber
Muscle cross-sectional area
Type of leverage
Power formula
Force x speed
Components of a lever
Resistance, Fulcrum, Effort
Mechanical Advantage
High MA = high force but low speed
Low MA = low force but high speed
In a muscle/joint attachment, the muscle provides
The effort
1st class lever
Fulcrum in the middle. E.g. neck atlantooccipital joint.
2nd class lever
Resistance in the middle. Example; jaw joint.
3rd class lever
Effort in the middle. Most joints in body.
Antagonistic muscle pairs
Act against each other and balance each other out. When one is stimulated, the other is not.
Spongy bone
Open interlacing framework of bony tissue, trebeculi, lots of blood vessels, red blood cells
Compact bone
On the outside of shafts, stronger than spongy bone, dense, supports more weight.
Levers are usually attached to the spongy bone.
Tendons
Attach muscle to bone
Contraction of skeletal muscle
See slides. Actin and myosin filaments in a sarcomere (unit of a myofibril) slide towards each other due to the movement of the myosin head mediated by ATP.
Contraction vs relaxation
Contraction requires energy. Relaxation is passive
Muscle contraction requires
ATP, calcium, a stimulus
Muscle contraction produces
Lactic acid
Energy for muscle use is provided by
Cellular respiration, or anaerobic respiration with sustained use
Motor unit
A neuron and all the muscle fibres it activates (a few to 2000).
Higher force is achieved with more motor units.
Neural control of muscle
Neuron releases ACH
Fibre depolarises and relases Ca2+
Fibre contracts
Vertebrate vs invertebrate muscle force
Vertebrate is an all-or-nothing response, where a threshold is met and then the muscle fibers contract.
Invertebrate muscles can contract gradually.
Vertebrate vs invertebrate muscle force
Vertebrate is an all-or-nothing response, where a threshold is met and then the muscle fibers contract.
Invertebrate muscles can contract gradually.
Variables in muscle performance
The trade-off between force and velocity
The proportion of fast and slow-twitch fibres
Physiological cross-sectional area
Energy storage by tendons.
Vmax
Occurs when there is no weight. The fastest rate of contraction.
Type 1
Slow fibres which fatigue slowly, are well vascularised and have large oxygen stores
Type IIa
Fast fibres - little force, slow fatigue, aerobic function
Type IIb
Fast fibres - large force, fatigue quickly, can function unaerobically
Fast-twitch vs slow twitch
Fast-twitch has higher Vmax, generates more force, but requires more energy.
Compared with contraction at Vmax, biceps contracting at half Vmax generate
More force
What occurs during a muscle contraction?
Generation of heat
Shortening of sarcomeres
Thickening of muscle due to contraction
