Unit 3
What are the three types of muscles and describe their function?
The three types of muscles include: skeletal, smooth and cardiac.
Skeletal muscle attach to the bones to control movement, smooth muscle control muscle contraction, cardiac muscle is responsible for pumping blood around the body
Which type of muscle has the highest rate of Ca2+ removal from the cytosol?
Fast-twitch muscle, allowing for quick recovery between contractions helping them perform short, powerful bursts of activity.
What are the three components of the cardiovascular system?
Heart, blood vessels, blood plasma
What are the 4 major components of blood?
Plasma, red blood cells, white blood cell, platelets
What are two components that make up the motor unit
A group of muscle fibres (# of fibres varies) and the somatic motor neuron that controls the fibres
When and how does skeletal muscle relaxation occur?
Skeletal muscle relaxation occurs when Ca2+ is pumped back into the sarcoplasmic reticulum by Ca2+ ATPase, this causes myosin heads to be unable to bind to actin allowing elastic elements to pull filaments back into a relaxed state
What is muscle atrophy?
Muscles degenerate due to prolonged inactivity
Blood supply decreases →
If it lasts longer than 1 year, could result in permanent changes to muscle
Direct electrical stimulation to muscle for therapy
Name and explain an abnormal condition associated with the heart valves
Valvular prolapse
Endocarditis
List the 2 main heart sounds and why they make that sound?
Lub - due to the close of AV valve
Dub - due to closing of semilunar valve
What is the difference between incomplete and complete tetanus
Incomplete tetanus has a slow stimulation rate allowing fibers to relax slightly between stimuli. Complete tetanus has a fast stimulation rate meaning fibre doesn’t have time to relax
What is the Sliding Filament Theory
At rest the ends of thick and thin actin filaments slightly overlap in each sarcomere allowing the filaments to slide past each other without changing their length of filament, towards the M line of the sarcomere. This brings the z disk closer together causing muscle contraction
A direct connection between nerve and individual muscle cells is not required for which muscle type(s)?
Smooth (hormones, stretching), coordination via gap junctions
and cardiac muscle, connected by intercalated discs containing gap junctions
Gap junctions allow electrical impulses to pass between cells for synchronized contraction
Describe erythropoiesis and the role of erythropoietin
Formation of RBC
Regulated by by erythropoietin (EPO) → it is a cytokine
EPO is a glycoprotien made primarily in the kidneys
EPO synthesis and release is regulated by hypoxi
How many steps are there in Haemostasis and what are they?
3 steps:
1. Vascular spasm to constrict damaged vessels
2. Platelet plug to temporarily block break
3. Blood clot to seal the break (result of the coagulation cascade)
How do cardiac muscles differ from skeletal muscle?
Cardiac muscle cells are smaller with single nuclei (⅓ of cell is the mitochondria)
T-tubules are larger and branched while the sarcoplasmic reticulum SR is smaller
Adjacent cells are joined by intercalated discs with desmosomes
Explain how the length of contraction varies between fibers
Fast-twitch fibers contract quickly and generate more tension but fatigue faster leading to shorter contraction lengths. Slow-twitch fibers have a more prolonged contraction and more resistance to fatigue with longer contraction lengths.
What is the role of MLCK in smooth muscle contraction?
Activated by calcium-bound calmodiulin
Activates myosin by phosphorylating the light chain of the myosin molecule in the head using energy and terminal P from ATP
When myosin is phosphorylated, ATPase activity is blocked
When myosin is phosphorylated, ATPase is active
Additional ATP required for contraction
Myosin can now interact with actin and go through crossbridge cycling
Explain how the two pumps of the heart work in series
When pump 1 contracts → decrease V → increase P
Pumps blood into the lungs to pick up oxygen
Blood is oxygenated and has very low pressure in the lungs
When pump 2 contracts → decrease V → increase
Blood flows to the rest of the body
Blood is deoxygneated and has very low pressure, returns back the heart
Distinguish between Haematopoiesis and Haemostasis
Haematopoiesis (blood formation):
All blood cells are produced in the bone marrow
Arise from a single precursor → pluripotent haematopoietic stem
Haemostasis (blood stoppage):
Prevents blood loss from damaged vessels
Vital to maintaining the integrity of the blood vessels
Since 1% of cardiac muscle cells aren’t involved in contraction, what do they do?
Involved in electrical excitation of the heart (electrical conducting system of the heart)
Initiate heartbeat & allow the electrical excitation to spread through the heart
Connected to other cardiac cells through gap junctions
Give a brief rundown of the muscle contraction process
Muscle contraction starts with a neural signal causing the release of acetylcholine, which deploarizes the muscle fiber and triggers calcium release. Calcium binds to troponin, exposing active sites on actin, allowing myosin heads to from crossbridges and pull the filaments inward. This continues until stimulation causes resulting in calcium reabsorption and muscle relaxation
List three differences between smooth muscle myosin and skeletal muscle myosin
Less myosin per unit actin in smooth than skeletal
Longer myosin filaments and overlap more in smooth than skeletal
Myosin ATPase activity is slower in smooth than skeletal
Mysoin heads are located along the entire length of the filament in smooth vs skeletal
How do norepinephrine and acetylcholine differ in how they modulate the rate of pacemaker potentials?
Norepinephrine increases heart rate
Bind to beta1-adrenergic receptors
Release cAMP → alters transport properties of ion channels
Opens If and Ca2+ channels → increased influx of ions
Depolarization rate increased → increases rate of AP
Acetylcholine decreases heart rate
Bind to muscarinic receptors
Increase K+ permeability → hyperpolarize cell
Pacemaker potential starts at more negative value, takes longer to reach threshold potential
Pick one of the following:
Describe the baroreceptor reflex when:
(1) there is an increase in blood pressure
(2) there is a decrease in blood pressure
(1):
Membrane of baroreceptor stretches
Increases firing rate of receptor
Action potential travel to cardiovascular control centre in CNS
Control centre integrates the sensory input
Efferent output carried by autonomic neurons
increase in sympathetic output
Vasodilation
Decrease in force of cardiac contraction and heart rate
Decrease in peripheral resistance and cardiac output
Decrease in blood pressure
(2):
Membrane of baroreceptor stretches
decrease firing rate of receptor
Fewer action potential travel to cardiovascular control centre
Control centre integrates the sensory input
Efferent output carried by autonomic neurons
Decrease in sympathetic output
vasoconstriction
increase in force of cardiac contraction and heart rate
increased peripheral resistance and cardiac output
increase in blood pressure
What are the two factors that influence cardiac muscle contraction force and explain its impact
Changes in Ca2+: regulated by epinephrine & norepinephrine, binds/activates beta 1 - adrenergic receptors which activates cAMP second messenger signaling pathway to phosphorylation of voltage gated Ca2+ channels and phospholamban
Sarcomere Length: Tension generated is proportional to muscle fibre length, overlap of actin and myosin
Stretching a myocardial muscle cell allows more Ca2+ to enter through cell membrane Ca2+ channels causing a forceful contraction