ELM 8.2 Flashcards
what is special about skeletal muscle? (lets __ be maintained)
force
____ is increased in cytoplasm
calcium
what classes of skeletal muscle are there?
slow twitch
fast twitch
what metabolism do slow twitch muscles use?
oxidative
what are the fast twitch muscles subdivided into?
glycolytic and oxidative
describe slow fibres (type I)
used to posture maintenance
have myoglobin (red) as oxygen store
many mitochondria
richly supplied by capillaries
resistant to fatigue
describe fast fibres (type IIA, IIB)
both have fast myosin isoform
fast CA transient (high SERCA in cytoplasmic reticulum)
allows rapid shortening but at high energy cost as ATP is hydrolyzed quickly
describe IIA oxidative fibres
lots of mitochondria
pretty good blood supply
good glycogen stores
resist fatigue
develops intermediate force
medium diameter
describe IIB glycolytic fibres
lactate accumulation and acidosis can limit contraction
white in colour
describe duchenne muscular dystrophy
x-linked disorder
caused by mutation in dystrophin gene
cause skeletal muscle fibres to not be linked properly to the extracellular matrix
excess calcium enters the cell and muscle fibres die - then are replaced by fat or connective tissue
skeletal muscle is a series of fused cells called a ____
syncytium
what is the difference between cardiac and skeletal muscle?
- branched syncytium
- cells are incompletely fused
- joined by intercalated discs
- control mechanisms different
- action potentials different
- excitation-contraction coupling different
- only found in heart (cardiac)
what is calcium induced calcium release?
when calcium activates the ryanodine receptors to release calcium
80-90% of calcium comes from what
the sarcoplasmic reticulum
10-20% of calcium comes from what
Ca current from outside
what channel carries the pacemaker curent?
nonspecific cation channel called HCN channel
frank-starling law of the heart
force of contraction is determined by the degree of stretch of cardiac muscle
describe smooth muscle (3)
- no striations
- no t-tubules
- small, spindle shaped cells
unitary
acts as syncytium
smooth muscle is often found where?
around hollow organs:
- blood vessels
- gut
- bladder
- uterus
- bronchi
how does smooth muscle contract?
actin-myosin cross bridges (same as skeletal and cardiac)
contrast smooth muscle with skeletal and cardiac muscle
- contracts slowly
- more energy efficient than skeletal and cardiac muscle
- different mech of E.C. coupling
- contracts well over greater range (i.e. bladder)
calcium is still important in smooth muscle, however, _____ is not involved, and not all smooth muscle requires _____ to contract. its source of calcium is _____
troponin
action potential
extracellular and SR
IP3 is what
inositol triphosphate - an intracellular second messenger
ligand gated calcium channel
IP3 is produced by what
the action of phospholipase C on membrane lipids
phospholipase C has to be activated by the actions of ____
a g coupled receptor
what muscles have t tubules
cardiac and skeletal
what muscles are regulated by ANS
smooth and cardiac
what muscle has intercalated discs?
cardiac
what muscles have calcium binding to troponin C
cardiac and skeletal
what muslce has calcium bidning to calmodulin?
smooth
what muslces have myogenic contraction?
smooth and cardiac
what muslces have gap junctions
smooth and cardiac
what muscle has regulation only via MLCK?
smooth
what muslces have regulation via troponin and tropomyosin?
cardiac and skeleatl
Which of the following is a characteristic of a slow oxidative fibre?
a. high fatigability b. low density of capillaries c. low myosin ATPase activity d. low mitochondrial density
c
Slow oxidative fibres have a 2-3 times lower rate of ATP hydrolysis than fast twitch fibres. This low rate of energy use makes them suitable for activities that require endurance or maintenance of posture. The difference in ATPase activity is because the myosins in the different muscle fibre types contain different heavy chain isoforms.
The plateau phase of the cardiac muscle action potential is largely mediated by:
a. calcium channels b. chloride channels c. potassium channels d. sodium channels
a
In the heart the initial spike of the action potential involves sodium currents, but the plateau phase is largely due to calcium channel activity.
Which of the following is a characteristic of a fast oxidative fibre?
a. high density of capillaries b. high fatiguability c. low mitochondrial density d. low myosin ATPase activity
a
Oxidative fibres in general have a high capillary density because they rely on the oxygen-consuming citric acid cycle for most of their energy needs. Low myosin ATPase activity is a characteristic of slow oxidative fibres.
Which type of muscle fibre has the lowest level of myoglobin?
a. Fast glycolytic b. Fast oxidative c. Slow glycolytic d. Slow oxidative
a
Fast glycolytic fibres have the lowest levels of myoglobin. Myoglobin is the oxygen “store” in skeletal muscle. It is found in oxidative fibres primarily. Is there such a thing as “slow glycolytic fibres”…….?
Intercalated discs are found in:
a. fast oxidative skeletal muscle fibres b. heart (cardiac) muscle c. slow oxidative skeletal muscle fibres d. smooth muscle
b
Intercalated disks are the junctions between individual cardiac muscle cells. They contain gap junctions that connect individual cardiac cells together electrically. This connection is key to allowing the heart to function as a syncytium (set of fused cells), rather than a collection of individual cells.
Calcium-induced calcium release from the sarcoplasmic reticulum can play a major role in excitation-contraction coupling in:
a. skeletal and cardiac muscle b. smooth muscle and cardiac muscle c. smooth muscle and skeletal muscle d. cardiac muscle, smooth muscle and skeletal muscle
b
The answer is smooth and cardiac muscle. In skeletal muscle SR calcium release occurs primarily because of a physical linkage between L-type calcium channels and the ryanodine receptor. In cardiac and smooth muscle there is no physical linkage but rather, calcium entering through the L type channels activates the ryanodine receptor (which is a calcium channel on the SR).
Myosin light chain kinase is converted from an inactive to an active form by the action of:
a. cAMP b. Calcium-calmodulin c. Calponin d. IP3
b
MLCK phosphorylates myosin in smooth muscle, thus allowing myosin-actin cross-bridges to form. MLCK is converted to an active form by the calcium-binding protein calmodulin (when it has bound calcium). This is the mechanism by which calcium regulates smooth muscle contraction.
Deficiency of which protein causes changes in muscle mass in Belgian Blue cattle?
a. Actin b. Dystrophin c. Myosin d. Myostatin
d
Myostatin regulates muscle growth. Belgian Blues have null mutations in myostatin and this results in increased muscle mass.
Who established the principle that in skeletal muscle smaller motor units are recruited first?
a. Frank and Starling b. Henneman c. Huxley d. Loewi
b
This is Henneman’s size principle. Small motor units are controlled by neurons with smaller cell bodies. These are more easily excited by upper motor neurons and so are recruited first.
Which types of muscle always require an action potential in order to contract?
a. cardiac and smooth b. cardiac and skeletal c. skeletal and smooth d. skeletal, smooth and cardiac
b
