Chapter 4B Flashcards
(51 cards)
Na+ initiates muscle action potential in the skeletal muscle fiber
true/false
true, p. 34
A nerve impulse (action potential) elicits a muscle action potential. Steps:
1.Binding of two molecules of ACh to the receptor on
the motor end plate opens a fast ion-channel in the Ach receptor
- Arrival of the nerve impulse at the synaptic end bulbs
stimulates voltage-gated channels to open - The inflow of Na+ makes the inside of the
muscle fiber more positively charged. This change in the membrane potential
triggers a muscle action potential - small cations,
most importantly Na+, enters the muscle cell downhill - Each nerve impulse normally elicits one muscle
action potential. The muscle action potential then propagates along the
sarcolemma into the system of T tubules - The
entering Ca2+ stimulates the synaptic vesicles to undergo exocytosis liberating ACh
into the synaptic cleft. The ACh then diffuses across the synaptic cleft - This causes the sarcoplasmic reticulum
to release its stored Ca2+ into the sarcoplasm, and the muscle fiber subsequently
contracts - Ca2+ enters the nerve cell downhil
- Arrival of the nerve impulse at the synaptic end bulbs
stimulates voltage-gated channels to open - Ca2+ enters the nerve cell downhil
- The
entering Ca2+ stimulates the synaptic vesicles to undergo exocytosis liberating ACh
into the synaptic cleft. The ACh then diffuses across the synaptic cleft
1.Binding of two molecules of ACh to the receptor on
the motor end plate opens a fast ion-channel in the Ach receptor - Small cations,
most importantly Na+, enters the muscle cell downhill - The inflow of Na+ makes the inside of the
muscle fiber more positively charged. This change in the membrane potential
triggers a muscle action potential - Each nerve impulse normally elicits one muscle
action potential. The muscle action potential then propagates along the
sarcolemma into the system of T tubules - This causes the sarcoplasmic reticulum
to release its stored Ca2+ into the sarcoplasm, and the muscle fiber subsequently
contracts
Almost everything discussed in Chapter 3 regarding initiation and conduction of action
potentials in nerve fibers applies equally to skeletal muscle fibers
see p.36
Almost everything discussed in Chapter 3 regarding initiation and conduction of action
potentials in nerve fibers applies equally to skeletal muscle fibers, except for small
quantitative differences:
- Lower resting membrane potential: −80 to −90 mV in skeletal fibers and …
mv in neurons. - Longer duration of action potential
- Faster velocity of conduction: 3 to 5 m/sec (about 1/13 the velocity of
conduction in the large myelinated nerve fibers that excite skeletal muscle).
−70
Excitation–contraction coupling: the sequence of events that links excitation (a muscle
action potential) to contraction (sliding of the filaments).
Triad: 1 transverse T tubule and 2 opposing terminal cisterns of the sarcoplasmic reticulum.
ok
- The T tubule and terminal cisterns are mechanically linked together by two groups of
integral membrane proteins: voltage-gated Ca2+ channels and Ca2+ release channels
ok
When a skeletal muscle fiber is excited and an action potential travels along the
T tubule, the voltage-gated Ca2+ channels/Ca2+ release
channels detect the change in voltage and
undergo a conformational change that ultimately causes the Ca2+ channels/Ca2+ release
channels to open.
* Large amounts of Ca2+ flow out of the sarcoplasmic reticulum around the thick
and thin filaments.
Ca2+ channels
Ca2+ release channels
END OF MUSCLE ACTION POTENTIAL:
Termination of ACh activity. Effect of ACh binding lasts only briefly because it is
rapidly broken down by acetylcholinesterase (geef afkorting): enzyme located on the
extracellular side of the motor end plate membrane.
(AChE)
END OF MUSCLE ACTION POTENTIAL: true or false?
- If another nerve impulse releases more acetylcholine, the acetylcholine is broken down
- If action potentials cease, ACh is no longer released and acetylcholinesterase
rapidly breaks down the Ach already present in the synaptic cleft .
Dit gebeurt al direct na ACh is releaseden bindt aan receptors
false: If another nerve impulse releases more acetylcholine, steps 2 and 3 repeat.
De rest klopt
the removal of ACh ends the production of muscle
action potentials, the Ca2+ moves
from the sarcoplasm of the muscle
fiber back into the X, and the Ca2+ release
channels in the sarcoplasmic
reticulum membrane close.
sarcoplasmic
reticulum
Strength of skeletal muscle contraction is hardly affected by moderate changes in
extracellular fluid calcium concentration because it is caused almost entirely by
calcium ions released from the X inside the skeletal muscle fiber.
sarcoplasmic reticulum
Voor een volledige samenvatting van muscle contraction, zie p.43
ok
True/false?
- Like cardiac muscle tissue, smooth muscle tissue is usually activated involuntarily.
- It is composed of far larger fibers than skeletal muscle
- The attractive forces between myosin and actin filaments that cause contraction
are the same that skeletal muscle, but the internal physical arrangement of smooth
muscle fibers is different. - Contraction in a smooth muscle fiber starts quicker and lasts much longer
than skeletal muscle fiber contraction. - Another difference is that smooth muscle can both shorten and stretch to a
lesser extent than the other muscle types.
*True
*False
*True
*False: starts slower
*False: to a greater extent
SMOOTH MUSCLE FIBER
* Two types:
1. X-unit smooth muscle tissue
2. X-unit smooth muscle tissue (syncytial or visceral)
Multi
Single
SMOOTH MUSCLE FIBER: MULTI-UNIT
Discrete, separate smooth muscle fibers.
- Each fiber operates independently/dependently of the others and often is
innervated by a single nerve ending: stimulation of one multiunit fiber causes contraction of that fiber only. - Outer surfaces of fibers covered by a thin layer of basement
membrane–like substance: insulate/joins the separate fibers
independently
insulate
SMOOTH MUSCLE FIBER: SINGLE-UNIT
Mass of hundreds to thousands of smooth muscle fibers that contract together as a
single unit.
- Fibers arranged in sheets or bundles with cell membranes adhered to each other
(force generated in one muscle fiber can be transmitted to the next).
Cell membranes are joined by many X through which ions can flow freely
from one muscle cell to the next.
When a neurotransmitter, hormone, or autorhythmic signal stimulates one fiber, the
muscle action potential is transmitted to neighboring fibers, which then contract individually/in
unison
X gap junctions
in unison
The sarcoplasm contains thick filaments (myosin), thin filaments (actine) and also
intermediate filaments.
True/false
True
Filaments have no regular pattern of overlap: no striations (smooth appearance)
true/false
true
Smooth muscle fibers also have transverse tubules and have only a small amount of
sarcoplasmic reticulum for storage of Ca2+
true/false
false: they lack transverse tubules
Smoth muscle fiber:
There are small pouchlike invaginations of
the plasma membrane called caveolae that
contain extracellular X that can be used
for muscular contraction
Ca2+
smooth muscle fiber:
The thin filaments attach to structures called X bodies that are dispersed
throughout the sarcoplasm or attached to the sarcolemma.
- Bundles of intermediate filaments also attach to X bodies and stretch from one
X body to another.
dense
Smooth muscle fiber
During contraction, the sliding filament mechanism involving thick and thin filaments
generates tension that is transmitted to X filaments.
* These in turn pull on the dense bodies attached to the sarcolemma, causing a
lengthwise shortening of the muscle fiber.
intermediate
As a smooth muscle fiber
contracts, it rotates as a
corkscrew turns: fiber twists
in a helix as it contracts, and
rotates in the opposite
direction as it relaxes.
true/false
true
Different stimuli modify the
membrane potential of smooth
muscle cells:
* action potentials from the
autonomic nervous system
* local factors: changes in pH,
oxygen and carbon dioxide
levels, temperature, and ion
concentrations
* stretching
* X
hormones
