Transcript Bio 105

Muscle
Functional Characteristics
Excitability (Irritability)- respond to
stimulus
Contractility- shorten forcibly
Extensibility- stretched
Elasticity- recoil to resting length
Muscle Functions
Produces movement
Maintains posture
Stabilizes joints
Generates heat
Gross Anatomy Skeletal Muscle
One nerve
One artery
One or more veins
Connective Tissue Sheaths
Endomysium- surrounds each muscle
fiber
Perimysium- surrounds bundles of
muscle fibers called fascicles
Epimysium- dense irregular CT that
surrounds entire muscle
Quiz
Picture
Attachments
Direct- the epimysium is attached
directly to bone ex: glute
Indirect- the CT extends in a sheet
(aponeurosis) or cord (tendon) to
attach to bone ex: bicep
Histology of Muscle Fiber (Cell)
Sarcoplasm- (cytoplasm) myoglobin
and glycogen
Myofibrils- (microfilaments) rod like
structures containing the contractile
units
Sarcolemma – (cell membrane)
connected to T-tubules
Quiz Picture
Sarcomere
Functional unit of muscle fiber
Quiz Picture
Banding Pattern of Sarcomere
Striations- repeating A bands and I
bands
H Zone- lighter band in center of A
Band
Z Disc- darker band in center of I
band
M Line- dark line in middle of the H
Zone
Filaments of Myofibril
Thick Filaments- make up the A
Band; Myosin
Thin Filaments- make up I Band;
Actin
Filaments
Thick- Myosin
- tail and 2 globular heads, cross bridges
– the function part
Thin- Actin
- subunits are function globular
- 2 strands Tropomyosin, hold it together
- and multiple units of Troponin,locks
Sarcoplasmic Reticulum/T Tubules
ER of muscle; calcium release
Wraps around each myofibril
Terminal Cisternae- cross channels at A
Band I Band Junctions
T Tubules  connect sarcolemma to SR
Triads  Connect of 2 SR and 1 Ttubule
Quiz
Picture
How does all that anatomical
structure, function physiologically?
What is the importance of the
membranes?
Why is it important that T-tubules
connect to SR?
Why are there extra mitochondria?
Why are thick and thin filaments
build the way they are?
Muscle
Contraction
3 Parts
1. Neuromuscular Junction
2. Excitation-Contraction
Coupling
3. Cross Bridge Formation
Part 1: Neuromuscular Junction
Axon Terminal- release Ach
(acetylcholine)
Synaptic Cleft- space
Junctional folds of sacrolemma of
muscle cell- Ach receptors
Video
Go to APFlix
Events at Neuromuscular Junction
Action Potential
Depolarization- change in membrane
potential from more negative to more
positive
Repolarization- membrane returns to
original negative state
Refractory Period- during repolarization;
cell cannot be stimulated until
repolarization complete
Video
APFlix
Three (3) videos to review Action
Potentials. Resting, Generation and
Propagation of Action Potentials.
Part 2: Excitation-Contraction
Coupling (Role of Ca)
Upon change in membrane potential
during depolarization from T-tubule
calcium is released from SR
Attaches to Troponin and uncovers
active binding site for Myosin heads
Video
APFlix
Excitation-Contraction Coupling
Part 3: Cross Bridge
Formation
Video
APFlix
Cross Bridge Cycle
Muscle Contraction
Neuromuscular junction/Generation of Action potential
(1-9 Goes with Neuromuscular Junction Video 10-12 goes
with Excitation–Contraction Coupling Video)
1. Stimulus travels down nerve to terminal end
2. Nerve impulse cause Ca+2 to enter end of nerve
3. Ca+2 changes shape of vesicles holding Ach (Acetylcholine)
4. ACh is released into and travels across synaptic cleft
5. ACh attached to Ach receptors on Sacrolemma
6. Binding of Ach open ion channels
7. Na+ rushes into cell, K+ rush out of cell
8. Shift of ions create an electrical impulse- Action Potential (AP)
9. ACh is absorbed back into nerve end or destroyed by Ache
(Acetylcholinesterase) stopping deplorization
10. AP is propagated down Sacrolemma
11. AP enters T-Tubules and makes contact with Sarcoplasmic
Reticulum (SR)
12. Channel on SR open allowing Ca+2 to rush into sarcoplasm of
the cell
Muscle Contraction
Filaments of Myosin racket or move the filaments of
Actin closer together, Cross Bridge Cycle (Goes with
Cross Bridge Cycle Video)
13.Calcium released from Sarcoplasmic Reticulum
14.Ca binds to Troponin
15.Troponin changes shape and shifts Tropomyosin,
unlocking (opening) binding sites for Myosin heads
16.ATP has already charged or cocked the Myosin heads,
which attached to Actin
17. ADP leave Myosin head, Myosin heads rackets and
shift Actin strands closer to each other
18.New ATP attaches to Myosin head, recharging or
cocking head, cycle continues as long as ATP and Ca
is present
19.Ca leaves Troponin, Tropomyosin shift back closing
off Actin binding sites
20.Muscle relaxes back to original position
Muscle Contraction
Put all the steps together
Stimulation comes down the nerve to
neuromuscular junction
All the steps of ExcitationContraction Coupling
Motor Unit
A motor neuron and all the muscle
fibers it supplies
43
Muscle Twitch
Response of a motor unit to a single
action potential; one single
contraction
LAB
Threshold Stimulus
The stimulus at which the first
observable contraction occurs
Maximal Stimulus
The stimulus which produces the
strongest contraction
All motor units are recruited and
contracting
Treppe
Staircase Effect
The increase seen in muscle tension
achieved when it is stimulated over
and over
No change in force; not rapid
Increased availability of calcium and
better enzyme activity
Isotonic Contractions
Muscle tension is generated and
contraction occurs; work is done
Eccentric contraction- contraction
causes lengthening of muscle
(reverse processes, letting weight
down)
Isometric Contractions
Muscle tension is generated but
contraction does not occur
No work gets done
Metabolic Pathways
With or Without Oxygen (what are
the names for those processes?)
3 types
FAST VS. SLOW MUSCLE FIBERS
SLOW TWITCH MUSCLE
FIBERS
Smaller fibers innervated by
smaller nerve fibers
More extensive blood supply and
greater number of mitochondria
Fibers contain large amounts of
myoglobin
Myoglobin gives slow muscle a
reddish appearance (red muscle)
FAST TWITCH MUSCLE FIBERS
Larger fibers for greater
strength of contraction
Extensive sarcoplamic reticulum
for rapid release of Ca2+
Large amounts of enzymes for
glycolysis
Less blood supply and fewer
mitochondria because
oxidative metabolism is
secondary
Low blood supply and absence
Every muscle is composed of large quantities of myoglobin
appearance
of a mixture of fast and slow give not-reddish
(white muscle)
muscle fibers, along with
ones between fast and slow.p.
306 Table 9.2
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Fiber Contraction Speed: Fast Twitch
Figure 12-15: Fast-twitch glycolytic and slow-twitch
muscle fibers
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Muscle Fatigue
Physiologically unable to contract
even though the muscle is receiving
stimuli
Relative lack of ATP and decreased
oxygen
Oxygen Debit  extra oxygen
needed to recovery after exercise
Exercise Effect on Muscle
Aerobic- increase in blood vessels,
number of mitochondria present;
better endurance (slow twitch fibers)
Resistance- increase in size of fibers
more myofibrils not in number of
fibers, more sarcomeres (fast twitch
muscles)
Exercise Physiology – Training:
Muscle Damage/Repair Overview
damage occurs during lengthening (eccentric)
movements (Weight Training)
damage commonly occurs to sarcolemma, Z-disc Ttubules/SR, myofibrils, cytoskeleton
Inflammatory response
WBCs destroy healthy muscle cells as well as
damaged ones. This causes the pain nerve fibers to
be excited.
repair begins ~1-2 d post-exercise (DOMS)
Pain can be lessened by massage therapy 2h after
intense exercise.
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Muscle Fiber
Damage
67