1. Is it possible to consciously control a part of the body that is normally under autonomic control?

2. Somatic nervous system
Signals from CNS are sent to skeletal muscles. Final result is a muscle contraction.
Motor neuron starts in CNS and its axon ends at a muscle cell.
Alpha
motor
neuron

3. Alpha motor neurons branch into several terminals (can be over 1000), each contacting a separate muscle cell.

4. Nerve meets muscle Acetycholinesterase Motor end plate
Axon of motor neuron
Action potential
of motor neuron
Terminal button
Voltage-gated
calcium channels
Action potential
propagation
in muscle fiber
Voltage-gated
Na+ channel
acetylcholine
Acetycholinesterase
Motor end plate

5. Organization of cells

6. Sarcomere
Myofibril
Muscle cell

7. Sarcomere – the unit of contraction, made of
thin (actin) and thick (myosin) filaments
Myofibril
sarcomere
sarcomere
Z band
Z band
Z band
A band

8. Contraction of filaments
Before Contraction
After Contraction Z Z Z Z
Length of sarcomere shortens with contraction
but filament length is unchanged
Myosin
Actin

9. Myosin

10. Actin

11. Tropomyosin normally covers the myosin binding site on actin
When calcium binds with troponin, it pulls tropomyosin away from the binding sites
troponin
tropomyosin
myosin
actin
myosin
binding site
blocked
Calcium
myosin
actin
cross-sectional view

12. Figure 8.2 (3) Page 259
Sarcomere
Myosin
Actin
Actin
Myosin

13. Muscle Contraction
Signal from motor neuron causes action potential in muscle cell
Calcium ions released (from sarcoplasmic reticulum)
Actin and myosin filaments slide relative to each other

14. bridge bends, pulling thin filament.
BINDING Myosin cross
bridge binds to actin
Myosin cross bridge
POWER STROKE Cross
bridge bends, pulling thin
filament.
DETACHMENT Cross bridge
detaches and returns to original shape- *ATP required*
BINDING to next actin molecule;
repeat

15. Bending (power stroke)
Figure Page 267
Myosin needs ATP to
change shape
Energized
Resting
Detachment
Binding
Bending (power stroke)
Myosin has a binding site for ATPase
Rigor complex

16. Signal coming to muscle
Sarcoplasmic reticulum
(Ca+2 storage)
motor
neuron
T tubule

17. From action potential to contraction
Calcium is the link
Acetylcholine released at the neuromuscular junction - action potential on muscle fiber
Action potential down “T tubule” to sarcoplasmic reticulum at muscle fibers
Calcium released from the SR to muscle fibers

18. Pathway review Terminal button Action potential A calcium pump
T tubule
Action potential
Acetylcholine-
gated cation
channel (Na+
moves in)
Acetylcholine
A calcium pump
in SR allows
muscle to relax
Troponin
Tropomyosin
Actin
Cross-bridge binding
Myosin cross bridge

19. How does polio virus cause paralysis?
How do botox injections decrease wrinkles?
How is chronic nerve pain or pain from spinal injuries treated?

20. Muscles contain groups of motor units
Units are recruited during motor activity
Muscle force depends on # muscle fibers contracting
Motor unit = motor neuron +
muscle fibers it innervates

21. The number of muscle fibers varies among different motor units.
muscles can have many small units or a few large units
Asynchronous recruitment of motor units delays or prevents muscle fatigue.

22. Tension and frequency of stimulation
twitch - brief contraction
resulting from 1 action pot’l
tetanus - twitch summation
from sustained Ca+2

23. Muscle length and force

24. Fast and slow twitch muscle cells
Differences in time when maximum tension is reached
Type IIb
Type IIa
Type I
Slow twitch (Type I) - have myoglobin, many mitochondria, oxidative
Fast twitch (Type IIa) - myoglobin, mitochondria, oxidative & glycol.
“Very” Fast twitch (Type IIb) - use glycolysis, split ATP quickly

25. Fast and slow twitch muscle cells
Oxidative - resistant to fatigue, high rate of O2 transfer from blood, recruited 1st
Glycolytic - more prone to fatigue b/c less ATP produced, harder to recruit
Endurance vs. Bursts of power

26. People are born with certain ratio of slow vs. fast twitch fibers
usually an even mix in most skeletal muscles

27. Contracting and elastic parts of a muscle
Contractile
section
Contractile
section
Series-elastic
section
Series-elastic
section
Load
Load

28. Sensation at muscle
Spindle muscle fibers (deep within muscle) and Golgi tendon organs (in tendons) sense stretch and tension.
Intrafusal (spindle) muscle fibers

29. Knee reflex Muscle spindle Extensor muscle motor neuron
Patellar tendon

30. What happens when we stretch? How does it help muscles, exercise?
Muscles don’t actually become longer, but you can train your NS to tolerate lengthening
When golgi tendons activate, they cause a reflexive inhibition (relaxation) of muscle
Activate golgi t. with a pattern of isometric contraction/relaxation of lengthened muscle
Leg gets lifted, relax, press
against hand, relax w/more range

31. Primary types of contraction
Isometric contraction - muscle tension is not enough to move load. Muscle doesn’t shorten.
Isotonic contraction
Concentric – muscle shortens to lift a load.
Eccentric - shortened muscle has controlled lengthening.
slowly lowering the weight

32. Exercising your muscles
Endurance training
type IIb type IIa
more mitochondria, glycogen, vascularization

33. Exercising your muscles
Strength training hypertrophy of type II fibers

34. Hypertrophy: how muscles get bigger
Muscle cells have satellite cells nearby that respond to muscle injury and wear
Why are muscles sore after lifting?

35. Hypertrophy: how muscles get bigger
Satellite cells:
activated at microtears
add nucleus to muscle cell
more myofibrils made
cell wider

36. Muscle hypertrophy vs. hyperplasia

37. Functional vs non-functional hypertrophy (strength vs. size)
Some hypertrophy can be due to growth of sarcoplasmic reticulum, increased glycogen (attracts water), but this is small
You cannot ‘train for’ sarcoplasmic hypertrophy

38. But can you gain force without hypertrophy?
The CNS can become trained to provide more force (apparent in early training)
Better inhibition of antagonistic muscles
Improved recruitment of different muscles over a movement to gain power

39. ATP sources at muscles 2 3a 1 3b

40. What does creatine do?

42. What are muscle cramps..can I eat a banana to avoid them?
When muscle fibers contract without our control it is a muscle spasm or cramp
Due to motor neurons being hyperexcited, often b/c of a shift in body fluids or ion levels (dehydration, low Ca, Mg, K) or vigorous activity

43. Smooth muscle Smooth muscle cells are small and unstriated
No sarcomeres
Smooth muscle cells contract when Ca+2 enters
Myosin cross bridges are phosphorylated and bind to actin

44. What is the cause of a ‘pulled’ muscle?
How can muscle hypertrophy help failing joints, ligaments?
Muscles lifting with and w/out adrenaline
Physiology bw bulky muscles and lean muscle growth
Why is a day off good when working muscles?

45. Smooth muscle Multiunit - similar to skeletal motor units
Single unit - gap jxns b/w muscle cells. Many cells contract as a unit. (uterus, intestine, bladder)
Smooth muscle
Striated muscle

46. Cardiac muscle Pacemaker muscle cells - action potential gradually
depolarizes, then repolarizes
Contraction spreads from pacemaker through gap jxns
Spontaneous action potential
Pacemaker cell
Action potential spread
to other cells
Gap junctions