Muscle Physiology Flashcards
(48 cards)
1
Q
Skeletal muscles are voluntary or involuntary?
A
voluntary
2
Q
How do voluntary contractions occur
A
- decision made in the brain (CNS) and instruction is transferred to muscle via specific motor neurons
3
Q
Motor Unit
A
- one motor neuron connected to many muscle fibers
- provides precise & powerful movement
4
Q
Neuromuscular junction
A
- connection between synaptic end bulb & skeletal muscle fibre
- how nerve & muscle cells communicate
5
Q
Explain process of muscle contraction
A
- Action potential travels down membrane through opening/closing voltage gated ion channels, Ca2+ channels open
- Signal ends at synaptic bulb. Increased Ca2+ conc. triggers exocytosis of acetylcholine (ACh) filled vesicles, released at neuromuscular junction. cadepolarization occurs
- neurotransmitter ACh binds to ligand gated cation channels, Na+ rushes into muscle cell
- muscle action potential travels down transverse tubule to sarcoplasmic reticulum, releasing Ca2+ into sarcoplasm
- Ca2+ binds to troponin, moves tropomyosin off actin
- myosin can grab actin, uses ATP to start sliding process
6
Q
Acetylcholine
A
- released at many synapses in the brain & PNS
- released at neuromuscular junction
- effects terminated through action of acetylcholinesterase
7
Q
Muscle action potential (MAP)
A
- Contracts muscle cell evenly along sarcolemma
- electron currently affects
8
Q
Conditions when a muscle is at rest (noMAP)
A
- no electrical signals travel along sarcolemma & transverse tubules
- sarcoplasmic reticulum acts like a storage centre for Ca2+
- Ca+ release channels closed, calcium pumps always working
-actin covered by tropomyosin, blocks myosin binding sites
-tropin attached to tropomyosin
9
Q
Muscle resting conditions (noMAP)
A
- no action potential
- Ca release channels closed in sarcoplasmic reticulum
- Ca pumps active
- Troponin/tropomysoin block myosin binding sites
10
Q
What is the name of the entire structure where a motor neuron communicates with a muscle fiber
A
neuromuscular junction
11
Q
What neurotransmitter is released from the synaptic bulb to initiate muscle contraction?
A
Acetylcholine
12
Q
When calcium ions are released into the sarcoplasm, which protein do they bind to?
A
Troponin
12
Q
What structure carries the action potential deep into the muscle fiber?
A
Transverse tubules
13
Q
What happens to calcium after the muscle action potential is over?
A
Pumped back into sarcoplasmic reticulum
14
Q
What structure stores calcium ions and releases them when a muscle contracts?
A
Sarcoplasmic reticulum
14
Q
How does myosin bind to actin during muscle contraction
A
- Ca2+ binding to troponin causes tropomyosin to twist & expose actin binding sites to myosin heads
- actin activates myosin through ATP
15
Q
How does the contraction cycle continue
A
- as long as ATP is available and there is a high level of Ca2+ in sarcoplasm
16
Q
What causes shortening of sarcomere
A
- ATP released from myosin causing it to change shape and bend
17
Q
How is muscle contraction stopped
A
- removal of Ca2+
- breakdown of acetylcholinesterase
18
Q
Muscle relaxation
A
- ACh is broken down by AChE
- sarcoplasmic reticulum recaptures Ca2+
- Active sites covered
- contraction ends
- relaxation occurs, passive return to resting length
19
Q
Muscle tone
A
- sustained, partial contraction of skeletal muscle in response to activated of stretch receptor
20
Q
Types of muscle cells
A
- skeletal - voluntary (posture)
- cardiac - involuntary (heart)
- Smooth - involuntary (bladder, blood vessels, intestines)
21
Q
Cardiac muscle structure
A
- only one nucleus per cell
- striated, branched
22
Q
How do cardiac muscles contract synchronously
A
- through intercalated disc (gap junctions & desmosomes)
23
Why do cardiac muscles contract synchronously?
to ensure normal heart function
24
What is a gap junction
- gap that allows ions & impulses to pass directly from 1 cell to another (cardiac muscle)
- communication channels
- "POWER CABLES"
25
Desmosomes
- prevents separation via cadherins (linker proteins)
- contains keratin filaments (anchors structure)
- contains plaque (protein structure, other proteins attached to)
- "GLUE"
26
Where are gap junctions & desmosomes found
- located inside intercalated discs
27
What is a pacemaker cell
- specialized cell that initiates an action potential
- helps regulate heartbeat by producing regular depolarization
28
Self-excitatory cardiac muscle cell function
- ensures muscle contraction occurs synchronously
29
How does a pacemaker cell regulate heartbeat
- by producing regular depolarization that spread rapidly throughout cardiac muscle
30
Process of cardiac contraction
- Pacemaker cells create depolarization (Ca2+ channels open), Ca2+ enters sarcoplasm
- action potential reaches gap junction, travels down transverse tubules releasing Ca2+ into sarcoplasmic reticulum
- myosin binds to actin, uses ATP to begin muscle contraction
31
Smooth muscle structure
- no striations, actin & myosin are still present
- single nucleus
- no individual synapse
- e.g. blood vessels, intestines
32
Why is smooth muscle not striated
- doesn't have sarcomeres
33
What does actin & myosin do
- cause contraction by sliding filament mechanism
- myosin; uses ATP to "pull" on actin
- actin; binding sites for myosin
34
Smooth muscle differences from skeletal muscle
- actin & myosin aren't arranged neatly
- actin filaments are anchored to dense bodies in smooth muscle
35
What gives smooth muscle a "puffy appearance" during contraction
sarcolemma bulging out
36
Why does smooth muscle spiral slightly during contraction
- due to arrangement of intermediate filaments & myofilaments
37
Varicosities & diffuse junction
Varicositie - releases neurotransmitters via synaptic vesicles
Diffuse junction - wide area where neurotransmitters diffuse to affect smooth muscle
38
Why does smooth muscle not have synapses
- they use diffuse junctions & gap junctions for slower contractions
39
Smooth muscle contraction
1. Ca2+ from ECF enters cytosol via voltage-gated Ca2+ channels or SR
2. Ca2+ binds to calmodulin (instead of troponin), activating myosin kinase (enzyme)
3. myosin kinase phosphorylates the myosin head, activating it allowing myosin to bind to actin & contraction cycle beings
40
Cholecystokinin
- induces relaxation of smooth muscle in digestive system around hepatopancreatic sphincter causing it to open
40
How does smooth muscle relax?
Ca2+ is pumped back into sarcoplasmic reticulum & interstitial fluid
41
Gastrin
- hormone that stimulates contraction of smooth muscle in stomach to enchance churning activity
42
Oxytocin
- stimulates uterine smooth muscle contraction in reproductive system to facilitate childbirth
43
Peristalsis
- contraction & relaxation of smooth muscle
of multiple layers of smooth muscle that surrounds structures with lumens
44
What type of muscle makes up the stomach
- smooth muscles
45
where else does peristalsis occur aside from the stomach
- uterus, bladder, esophagus, intestines & ducts (ureters, uterine tubes)
