Muscles and Muscle Tissue Flashcards
1
Q
Types of Muscle Tissue
A
- Skeletal Muscle
- Cardiac Muscle
- Smooth Muscle
2
Q
Special Characteristics of Muscle Tissue
A
- Excitability: responds to electrical stimulation
- Contractility: contraction-shortening- increase in tension
- Extensibility: ability to stretch
- Elasticity: can return to uncontracted length
3
Q
Muscle Functions
A
- Movement of body and its parts
- Posture maintenance
- Joint stabilization
- Heat generation
4
Q
Nerve & bloody supply (GA of SKM)
A
-Each muscle cell is “served” by:
one neuron axon
an artery
veins
5
Q
Connective Tissue Sheaths
A
- Endomysium: surrounds a single cell
- areolar CT containing blood vessels - bundle of muscle cells called a fasicle
- Perimysium: surrounds fasicle
- dense irregular CT
- Epimysium: surrounds a bundle of fasicles and makes up a whole musce
- dense irregular CT
6
Q
Connections
A
endomysium-perimysium-epimysium-fascia-tendon-periosteum-bone matrix
cell-fasicle-bundle of fasicles-whole muscle-fascia-tendon-bone
7
Q
Attachments to bone
A
- epimysium connect with fascia-attachment to bone:
- direct: epimysium continuous with periosteum
- indirect: fascia continuous with tendon which then merges with periosteum
8
Q
MA of skeletal muscle
A
- Sarcolemma
- Sarcoplasm
- Sarcoplasmic Reticulum
- Transverse tubules (T tubules)
- Terminal cisternae
- Triad
9
Q
glycogen
A
stored in muscle cell for energy source
10
Q
myoglobin
A
a red pigment that binds O for muscle use
11
Q
function of T tubules
A
-to carry current from cell surfaces to interior-release of internal calcium stores
12
Q
Myofilaments
A
Thick filament: myosin
Thin filament: actin
-tropomyosin
-troponin
13
Q
Striations
A
light zone- thin filaments
dark zone-overlapping actin and myosin
sacromere- z disc to z disc
14
Q
Motoneurons
A
somatic: body
somatic motor neuron: axons-skeletal muscles
autonomic motor neuron: axons- smooth muscles
each axon- app. 200 branches
each branch-middle of single muscle cell
15
Q
Motor Unit
A
- all the muscle cells innervated by a single axon (all its branches)- single unified contraction
- members of “unit” are dispersed throughout larger muscle-weak contraction in wide area
16
Q
Neuromuscular Junction (NMJ)
A
- synapse: point of contact between neuron & muscle cell
- pre-synaptic: neuronal side
- post-synaptic: muscle side
17
Q
NMJ: pre-synaptic side
A
- synaptic “knob” (on axon)
- synaptic cleft (between axon terminal & muscle cell)
- synaptic vesicles (axon)
- acetylcholine (ACh) neurotransmitter released by neuron
18
Q
NMJ: post-synaptic side
A
motor end plate: muscle cell
junctional folds: muscle cell
ACh receptors: muscle cell
acetylcholinesterase: AChE
19
Q
Membrane Potentials
A
- excitable tissues : “electrically excitable” (voltage & current charge)
- electrical potential (voltage)
- excitable cells as mini batteries
- due to difference between inside and outside ion concentrations
- potential difference between inside and outside cell
20
Q
Resting Membrane Potential (RMP): ionic basis
A
- outside cell: high Na; low K
- inside cell: high K; low Na
- selective permeability of membrane
- K: yes (K channels open)
- Na: no (Na channels close)
- negative charges: no (negative ion channels closed)
21
Q
Scenario of RMP
A
-K diffuses out (down conc. gradient)
-inside becomes less positive (more negative)
-negative charges cannot leave cell interior
- K outward flow slows
-K flow stops when tendency to flow back in (charge attraction) equals K flow outward
Equilibrium is achieved at a RMP of appr. 70 mV (membrane is polarized)
22
Q
RMP maintenance
A
- stimulation of cell-rundown of RMP
- Na/K pump(an enzyme requiring ATP)
- pumps out Na and pumps in K
23
Q
Excitation of Skeletal Muscle
A
- neuron action potential (AP) invades axon terminal
- Ca diffuses into neuron
- synaptic vesicles of neuron release ACh
- ACh binds to receptors on muscle membrane
- ACh activated ion channels open, Na enters and K leaves-endplate potential (EPP), a depolarization to about +30mV
- EPP opens a voltage-activated channels-Na and K cause adjacent membrane to depolarize.
24
Q
Excitation of Muscle Fiber
A
- Action potentials arrive at synaptic knob.
- Calcium ions diffuse into synaptic knob.
- Synaptic vesicles release ACh.
- ACh binds to receptors on the sarcolemma.
- Ion channel in ACh receptor opens. Na enters and K leaves sarcoplasm through the same channel, creating the end-plate potential (EPP).
- EPP excites voltage-gated ion channels in adjacent regions of sarcolemma. Diffusion of Na and K through their separate channels depolarizes membrane and initiates action potential in muscle fiber.
25
Excitation-Contraction Coupling
-how muscle cell excitation (depolarization) brings about muscle cell contraction
26
How contraction begins...
- depolarization of s.r. travels down through T tubule system to terminal cisternae
- Ca channels there open, releasing Ca ions into sarcoplasm
- Ca ions bind to troponin C
- troponin-tropomyosin complex changes position along actin fiber (thin filament)
- heads of myosin can now bind to actin
27
The sliding filament theory
- to explain how contraction occurs
- thin filaments anchored to Z discs slide past thick filaments
- cell shortens
- myofilaments do not shorten
28
Excitation-Contraction Coupling
7. Actin potentials propagated down T tubules to interior of muscle fiber
8. Terminal cisternae of sarcoplasmic reticulum a flood of Ca into the sarcoplasm
9. Calcium ions bind to troponin C
10. Troponin-tropomyosin complexes shift position, exposing active sites where actin will subsequently bind to myosin
11. Activation. An ATP molecule bound to the myosin head is hydrolyzed to ADP and P, which remain bound to the myosin.
12. Cross-bridge formation. Activated myosin is now able to bind to the active site of an actin monomer
13. Power Stroke. Myosin releases ADP and P. The head flexes and pulls the thin filaments along the thick filament.
14. Myosin remains flexed and bound to the actin until another ATP molecule binds to it.
15. Binding of a new ATP molecule causes myosin to release actin and return to the "cocked" forward position, ready to repeat the cycle.
29
Relaxation
16. Signals stop arriving from motor neuron.
17. ACh release ceases.
18. ACh dissociates from receptors on sarcolemma.
19. Free ACh in broken down by AChE. ACh fragments are reabsorbed by synaptic knob. Muscle stimulation ceases.
20. Calcium ions are transported back into sarcoplasmic reticulum.
21. Calcium ions dissociate from troponin.
22. Tropomyosin blocks active sites of actin, preventing actin-myosin cross bridges from forming.
30
Relaxation Summary
- motorneuron AP's stop (ACh release stops)
- ACh remaining in cleft is destroyed by AChE
- Muscle AP's cease
- Ca ions get pumped back into terminal cisternae (requires ATP)
- troponin-tropomyosin resumes position blocking active sites on actin
- muscle cell returns to resting length
31
Threshold (behavior of muscle)
-the minimum voltage necessary to produce muscle contraction
32
Twitch(whole muscle)
- the response of a motor unit to a single action potential of its motor neuron
- quick contraction-relaxation cycle causes by stimulus at or above threshold
- total twitch time is appr. 10-100 msec
33
latent period
- time between stimulus and response (twitch)
- for muscle, this is the time for
- excitation
- excitation-contraction coupling
- connective tissue component tightening
34
Whole Muscle (mutiple stimuli)
- applied rapidly (too fast for complete relaxation to occur)
- (high frequency stimuli)
- Produces incomplete tetanus
35
Higher frequency stimulation
- leads to complete tetanus
- no time for any relaxation occur
- sustained contraction
36
All or none responses (single cell)
-stimulus at or above threshold elicits maximal response, regardless of stimulus strength
37
Graded response (whole muscle)
-strength of response depends on stimulus strength and frequency
-higher voltages applied to axon-"recruitment" of more axons
-higher frequency stimulation-stronger ctxn.
-contraction strength of whole muscle depends on how many motor units are contracting
-
38
more motor units
-get recruited with increasing stimulus intensity
39
Muscle tone
- constant, slightly contracted state of all muscles
- controlled by the nervous system
- keeps muscles form, healthy, and ready to respond
40
Isometric contraction
- muscle cells contract, but tension absorbed by connective tissue components
- endomysium, perimysium, epimysium, tendon, etc.
- no external movement
41
Isotonic contraction
- muscle cells contract
| - muscle shortens-movement of load
42
Concentric contraction
- muscle shortens
| - example: biceps brachii-elbow flexion
43
Eccentric contraction
- muscle lengthens
| - example: biceps brachii contracts and lengthens during shortening of triceps-controlled elbow extension
