movement Flashcards
function of muscles
- movement
- thermoregulation
- energy metabolism + storage
- appetite regulation
- drug storage
- endocrine functions
skeletal muscles
Attached to skeleton
Contract - pull on bones and cause them to move
Most common type
We control consciously
Cardiac muscles (Myocardium)
- Forms the heart
- Responsible for pumping blood
- Involuntary movement
Smooth muscle
- Located in tissues
- Responsible for controlling the diameter of certain structures and peristalsis
- Involuntary movement
muscles in general are…
- Electrically excitable
- Contracts actively - requires energy
- Relaxes passively
- Elastic
- Extensible
Characteristics of muscles
75% water
20% protein - contract
5% carbohydrate and fat - energy stores, active process of muscle contraction
Men have more skeletal muscle than women?
true
Gender differences are greater in the upper body than in the lower body
muscle loss due to age
Skeletal muscle starts to decrease in the third decade but a noticeable change does not occur until the end of thefifth decade
Most loss is in the lower body
Contractions (general)
Chemical energy is transformed into mechanical energy
ATP is converted
muscle fibres contain…
myosin (thick) - has heads that project towards actin, cause it to move
actin (thin) - binding sites for myosin heads
filament arrangement in skeletal and cardiac muscle
regular, parallel pattern
filament arrangement in smooth muscle
random
sacromeres
myosin and actin are organsied into sacromeres
muscle contraction
- myosin heads link to actin to form cross-bridges
- The myosin heads cycle (rotate) towards the centre of the sarcomere (connection to actin is broken)
- Muscle contracts
muscle relaxation in skeletal muscle
- Tropomyosin blocks the binding sites on actin and prevents cross-bridge formation
- Electrical excitation of the muscle cell releases calcium from calcium stores in SR
- Calcium binds to troponin and moves the tropomyosin out of the way to allow cross-bridge formation
- When electrical excitation finishes, calcium pumped back into the SR and tropomyosin once again blocking the binding sites
T-tubules
brings action potentials into interior of muscle fibre
process of contraction is the same in skeletal and cardiac muscle?
true
Cross-striations in cardiac muscles
- less distinct because there are many mitochondria and many lipid and glycogen droplets around the cells
- muscles cells often branch at acute angles and are electrically connected to each other
skeletal muscle cells
individual cells are electrically isolated, therefore we have more control as to which cells contract and which don’t
ATP in cycle
used twice
1. when the cross bridge rotates
2. when the myosin head returns to its resting point (i.e. breaking the cross bridge)
ATP can be produced in…
cytoplasm - anaerobic met (fast/inefficient)
mitochondria - aerobic met (slower/more efficient)
smooth muscles are found in…
The walls of hollow organs
The walls of blood vessel
In airways
The eye
Skin
smooth muscles can be controlled by…
- Hormones
- Neural stimulation from the ANS
- Change in pH in muscle - change in diameter
- Lack of oxygen - diameter or blood vessel
- Stretching the muscles
Ca2+ role in smooth muscles
Uses calcium from both inside and outside the cell
Calcium binds to calmodulin (protein) that initiates contraction
speed of ATP use and replacement determines…
how quickly muscle cells contract
Type 1/slow twitch/red
- Contract slowly but fatigue slowly
- Can’t generate that much power
- Supplied by nerves that activate them first during muscle contraction
- Use aerobic metabolism
- Lots of capacity to deliver oxygen to cells
- Contain myoglobin that transport oxygen to mitochondria
Type 2/fast twitch/white
- Much quicker but fatigue quickly
- Generate lots of power
- Use anaerobic metabolism
- No myoglobin
We increase the force of a muscle by…
activating more motor units simultaneously
power of contraction
Change power of contraction by changing the number of motor unit used - control tension
Small motor units
Few fibres innervated by a single nerve
* Generate little tension
* Enable fine control
* Are fatigue resistant
Large motor units
- Generate much more tension but figure quickly
- Less fine control
Twitch
One action potential in a motor neuron produce one contraction
Summation
- Latent period - action potential is being propagated along the membrane and Ca2+ ions released from SR
- Contraction phase - period of cross bridge formation
- Relaxation phase - Ca is pumped back into the SR, and cross bridge cycling stops
If a muscle cell is stimulated while a previous twitch is occurring…
the second twitch will be stronger
The tension produced in skeletal muscle is a function of
- The frequency of neural stimulation and
- The number of motor neurons (i.e. number of motor units) involved
Fast twitch fibres
possess smaller neuromuscular junctions (NMJs), which may facilitate efficiency and speed of neurotransmission.
Slow twitch fibres
possess NMJs with larger surface area which may facilitate sustained stimulation
