Quiz #4 Flashcards
What is a muscle twitch?
a single contraction-relaxation cycle
Describe the phases of a muscle twitch.
latent period
- time before Ca2+ has bound to troponin
contraction phase
- muscle tension increases to a maximum value
- crossbridge interactions
relaxation phase
- tension decreases
What are series elastic elements?
connective tissue, tendons
What is an isometric muscle contraction?
length remains constant
contractile elements contract and create tension
load is greater than tension, stretches series elastic elements
only sarcomeres shorten, muscle does not shorten, load not lifted
What are the 2 types of forces in muscle contraction?
tension - force exerted by contracting muscle
load - force opposing contraction
What is an isotonic muscle contraction?
constant tension
when tension is greater than load
- concentric contraction
- muscle shortens, load is lifted
when load is greater than tension
- eccentric contraction
- muscle lengthens, weight is lowered
What is a motor unit?
a motor neuron and all the fibers it innervates
of muscle fibers in unit varies according to degree of fine control capability of muscle
What is the innervation ratio?
motor neurons:muscle fibers
ex. gastrocnemius has about 2000 fibers/MU
- gross movement
extraocular has about 3-5 fibers/MU
- fine movement
What are the muscle fiber types?
slow twitch (I)
- fatigue resistant
- lower force/power
fast twitch (IIA)
- more fatigue resistant than IIB but less than I
- intermediate force/power
fast fibers (IIB)
- powerful
- easily fatigued
What makes muscle contractions vary?
type of active motor units
of active motor units
What are the 2 types of twitch summation?
temporal
- frequency of MU activation
- more forceful contraction
spatial
- # of MU recruited
- sustained tension less than maximal, lets MU to rest in rotation
What happens if time between APs is too long?
complete recovery in between
What is unfused/incomplete tetanus?
stimuli far enough apart to allow slight relaxation
fiber not firing at max rate
wavy curve
What is complete tetanus?
muscle never beings to relax inbetween stimuli since there is no time
continuous contraction and steady tension at maximum force
at fatigue, tension decreases rapidly
How does resting fibre length affect muscle twitch?
twitch force depends on length of individual sarcomeres before contraction
optimal overlap of filaments = optimal force
What is the sliding filament theory?
tension that a muscle fiber generates is directly proportional to the number of crossbridges formed between filaments
Describe the principle of asynchronous recruitment.
MUs take turns firing/relaxing so they have time to rest and can consistently maintain uniform tension across a muscle
How can motor unit sizes vary?
size of unit
- small for delicate movements, large for strength movements
fiber diameter
- small for weaker movements, large for stronger movements
What is the size principle?
the order of motor unit recruitment is related to their size
small units recruited before large units
larger neurons are more difficult to depolarize, they require more excitatory input to reach threshold
What is the relationship between load and velocity of shortening?
inverse relationship
for a muscle to shorten, it must generate force greater than the load
when load is greater than maximum tension, velocity of shortening is zero because the load cannot be lifted
What differs in the contraction of fast and slow twitch muscle fibers?
fast fibers contract and relax 2-3x faster than slow fibers
What are muscle spindles? What are the fibers that compose it?
detect changes in length
intrafusal fibers
- contractile cells of spindle
- innervated by gamma (slow) MU
- adjust sensitivity of muscle to stretch
extrafusal fibers
- contractile cells of muscle
- responsible for contraction
- innervated by alpha (fast) MU
What are golgi tendon organs?
detect changes in tension
inhibits muscle to protect against overactivity
sensory neurons from GTOs synapse on interneurons that make inhibitory synapses on motor neurons to prevent excessive contraction
What would happen to muscle if gamma neurons did not fire?
alpha MU would fire, muscle contracts but intrafusal fibers dont, less stretch experienced on centres, decreases firing rate of afferent neurons
What is reciprocal inhibition?
in a monosynaptic reflex, neuron synapses with antagonist muscle to inhibit activity at the same time as it activates the agonist
allows for reflex to occur
Where are some of the locations smooth muscle exists in?
vessels gastrointestinal tract urinary tract respiratory tract reproductive organs ocular muscles
What are some differences smooth muscle contraction has compared to skeletal muscle?
can sustain contractions for longer periods of time filaments run oblique not parallel contractile fibers not in sarcomeres controlled by ANS Ca2+ comes from both ECF and SR Ca2+ does not bind to troponin
Describe smooth muscle contraction cycle.
voltage-gated Ca2+ channels in plasma membrane open Ca2+ triggers release of Ca2+ from SR Ca2+ binds to calmodulin Ca2+-calmodulin activates MLCK MLCK phosphorylates myosin crossbridge cycling occurs
relaxation:
phosphotase removes phosphate from myosin
Ca2+ removed from cytoplasm by Ca2+-ATPase and Ca2+-Na countertransport
Describe the neural regulation of smooth muscle.
innervated by ANS
- both SNS and PNS
may be excitatory or inhibitory
NT released from varicosities
What are the 3 main components of the cardiovascular system?
the heart
blood vessels
blood
What are the 2 circuits of blood flow through the heart?
right = pulmonary circuit = to lungs and back for gas exchange
left side = systemic circuit = to all of the tissues of the body and back for off-loading of oxygenated blood
What is the pericardium?
membranous sac surrounding the entire heart
lubricates the heart to decrease friction
What are the true definition of arteries and veins?
arteries = vessels that travel away from the heart veins = vessels that travel to the heart
What is the SA node?
natural pacemaker of the heart
What are the layers of tissue of the heart?
epicardium
- outer layer covering the heart for protection
myocardium
- middle muscular wall of the heart
- contractile, concentric layers of muscle tissue
endocardium
- inner layer protecting valves and heart chambers
Which ventricle is thicker and why?
left because it has to push a stronger force of contraction to push blood to the entire body not just the lungs
What drives the blood flow through the heart?
pressure in different chambers
What are atrioventricular valves?
separate atria and ventricles
right side: tricuspid
left side: bicuspid/mitral
What are chordae tendinae?
attach to papillary muscles on muscular wall of ventricles, keep a level of tension between AV valve and papillary muscles to ensure valves close when ventricles contract
prevents backflow
What are semilunar valves?
between left ventricle and aorta (aortic valve) and right ventricle and pulmonary veins (pulmonary valve)
open with ventricular contraction, remaining blood pushes valve shut during relaxation to prevent backflow
What are the 2 types of myocardial cells?
contractile
- 99% of cells
autorhythmic - can generate AP spontaneously - pacemaker cells initiates APs and establishes heart rate - conduction fibers transmits/spreads generated APs
What are some similarities of cardiac muscle to skeletal muscle?
striations
sarcomeres
What are some differences of cardiac muscle to skeletal muscle?
less SR, no terminal cisternae
under ANS control
intercalated discs to connect cells
single nucleus
What are the 2 components of intercalated discs that connect cells together?
gap junctions
- direct electrical connection of adjacent cells to make them a functional unit
desmosomes
- “glue” that holds cells together
- proteins binding adjacent cells to allow for chemical communicatoin
What are the pacemaker cells of the myocardium?
SA node
- where APs originate
AV node
- slower, but still capable of generating APs
What are the conduction fibers of the myocardium?
internodal pathways
bundle of His
Purkinje fibers
Describe the initiation and conduction pathway of an impulse through the heart.
AP initiated in SA node, travels through atria
AV node, conduction slows (delay)
bundle of His
splits into left and right bundle brances
Purkinje fibers
travels back upwards through ventricles
heart eventually returns to rest until SA node regenerates
What cells have the highest firing rates at rest?
SA node
fastest depolarizing cells set the rate for the rest of the heart (pacemaker)
What is an ECG?
composite of all APs generated by nodal and contractile cells
What are the components or a normal ECG wave?
P wave
- atrial depolarization, initiated by SA node
delay at AV node
QRS complex
- ventricular depolarization
- and atrial repolarization but this is covered up by QRS
T wave
- ventricular repolarization
What are T-type and L-type channels?
T = transient, slow depolarization
L = long-lasting, rapid depolarization
What are funny channels and their role?
open up right after repolarization (unlike other ionic channels), lead to Na+ flow in making it less negative
at -55mV, Ca2+ channels open and funny channels close
T-type channels open
at -50mV, L-type channels open and Ca2+ rushes in causing full depolarization and action potential
K+ channels start opening, exiting the ICF and making it more negative until it is at -70mV again (resting state) and funny channels reopen
never a resting phase
What are the 5 phases of ionic activity in the hearT?
phase 0
- membrane depolarizes
- Na+ channels open
phase 1 - depolarization
- open Na+ channels start to close
- drop in membrane potential
- but Ca2+ channels start to open and K+ channels start to close, results in only small drop
phase 2 - plateau
- most K+ channels closed, most Ca2+ channels open
- keeps membrane depolarized
phase 3 - repolarization
- opening K+ channels take effect, make cell more negative
- Ca2+ channels close
phase 4 - rest
What things are not possible in myocardial cell activation that are in skeletal cell activation?
twitch summation and tetanus
due to long absolute refractory period
