1. 9.3 Muscular Responses & Actions
Sponge: Set up Cornell Notes on p. 75 Topic: 9.3 Muscular Responses & Actions Essential Question: Text:
9.3 Muscular Responses & Actions
2.1 Atoms, Ions, and Molecules
Describe how connective tissue is associated with a skeletal muscle. *

2. Threshold Stimulus
A muscle fiber will remain unresponsive until a certain strength of simulation is reached
Threshold stimulus: the strength of stimulation needed for contraction
Action potential will be generated
Muscle impulse generated
Fiber contracts

3. Recording of a muscle contraction
The contractile response of a single muscle fiber is called a twitch
Period of contraction during which the fiber pulls at its attachments
Followed by a period of relaxation, during which pulling declines
A series of twitches

4. Recording of a muscle contraction
All-or-none response: When a muscle fiber is brought to threshold under a given set of conditions, it tends to contract completely, such that each twitch generates the same force
This is misleading, however, because in normal muscles, the force generated by muscle fibers must vary otherwise we would only have one amount of strength

5. Recording of a muscle contraction
A single muscle fiber contraction by itself is of little significance to day-to-day activities
In order to perform everyday activities we require a few things:
The contribution of multiple muscle fibers simultaneously
A sustained contraction of a whole muscle
Control of contraction force

6. Recording of a muscle contraction
Ex: Holding a Styrofoam cup of coffee firmly enough that it doesn't slip through your fingers, but not so forcefully that we crush it
This requires precise control of contractile forces

7. Summation
A muscle fiber exposed to a series of stimuli of increasing frequency reaches a point when it is unable to completely relax before the next stimulus in the series arrives
When this happens, the individual twitches begin to combine by the process of summation

8. Summation
A tetanic contraction is when the resulting forceful, sustained contraction lacks even partial relaxation

9. Recruitment of motor units
The number of muscle fibers in a motor unit varies considerably:
A whole muscle is composed of many motor units controlled by different motor neurons

10. Recruitment of motor units
The fewer muscle fibers in the motor units, the more precise the movements that can be produced in a particular muscle
Ex: The muscles that move the eyes may include fewer than 10 muscle fibers per motor unit and can produce very slight movements

11. Recruitment of motor units
Ex: The motor unites of the large muscles of the back may include 100 or more muscle fibers. When these motor units are stimulated, the movements that result are less gradual compared to the eye

12. Recruitment of motor units
Since the muscle fibers within a muscle are organized into motor units and each motor units is controlled by a single motor neuron, all the muscle fibers in a motor unit are stimulated at the same time
If only the more easily stimulated motor neurons are involved, few motor units contract

13. Recruitment of motor units
Recruitment: At higher intensities of stimulation, other motor neurons respond, and more motor units are activated

14. Sustained Contractions
During sustained contractions:
Smaller motor units are recruited earlier
Large motor units respond later and with more force
The result is a sustained contraction of increasing strength

15. Sustained Contractions
Ex: When a person lifts a weight or walks, sustained contractions are maintained in the upper limb or lower limb muscle for varying lengths of time

16. Sustained Contractions
Even when a muscle appears to be at rest, a certain degree of sustained contraction occurs in its fibers.
Muscle tone is an example of an involuntary partial sustained contraction
Important for maintain posture
Tautness in the muscles of the neck, trunk, and lower limbs enables a person to hold the head upright, stand, or sit
If tone is suddenly lost, such as when a person loses consciousness, the body collapses
Muscle tone is maintained in health but is lost if motor nerve axons are cut of it diseases interfere with conduction of nerve impulses

17. Fast- and Slow-Twitch Muscle Fibers
Muscle fibers vary in contraction speed

18. Fast- and Slow-Twitch Muscle Fibers
Slow-twitch fibers (type I)
Resistant to fatigue
Often called red fibers because they contain the red, oxygen-storing pigment myoglobin
Well supplied with O2-carrying blood
Contain many mitochondria
Can generate ATP fast enough to keep up with ATP breakdown
Can contract for long periods of time without fatigue
Activities such as swimming and running are most likely to stimulate the development of slow-twitch fibers
Ex: those found in the long muscles of the back

19. Fast- and Slow-Twitch Muscle Fibers
Fast-twitch fibers (type II) maybe fatigable or fatigue resistance
Type II a
Called white fibers because they have less myoglobin
Poor blood supply
Ex: certain hand muscles and muscles that move the eyes
Few mitochondria
Can form ATP faster than red fibers, but because of their ability to contract rapidly, they fatigue as lactic acid accumulates
Type II b
Have fast twitch-speed but have substantial O2 capacity, more characteristic of red fibers

20. Fast- and Slow-Twitch Muscle Fibers
All muscles include a combination of both fiber types (fast/slow-twitch)
The speed of contraction and aerobic capacities of the fibers reflect the specialized functions of the muscle
Ex: Muscles that move the eye contract about 10x faster than those that maintain posture
Ex: The muscles that move the limbs contract at intermediate rates

21. Fast v. Slow Twitch Muscle Fibers 2m5s

22. Crash Course: Muscles Part 2

23. 9.4 Skeletal Muscle Actions
Sponge: Set up Cornell Notes on p. 77 Topic: 9.4 Skeletal Muscle Actions Essential Question: Text:
9.4 Skeletal Muscle Actions
2.1 Atoms, Ions, and Molecules
Describe how connective tissue is associated with a skeletal muscle. *

24. Levers and Movement *

25. Skeletal Muscle Actions
Skeletal muscles generate a great variety of body movements.
The action of each muscle mostly depends upon:
the kind of joint it is associated with and the way the muscle is attached on either side of that joint
The context of a particular movement

26. Body Movement
Whenever limbs or other body parts move, bones and muscles interact as simple mechanical devices called levers

27. Body Movement Ex: A pair of scissors is a lever
The handle/blade form a rigid bar that rocks on a fulcrum near the center (screw)
The material to be cut by the blades represents the resistance
While the person on the handle end supplies the force needed for cutting the material

28. Body Movement
The actions of bending and straightening the upper limb at the elbow illustrate bones and muscles function as levers When the upper limb bends, the forearm bones represent the rigid bar The elbow joint is the fulcrum The hand is moved against the resistance provided by the weight The force is supplied by muscles on the anterior side of the arm

29. Origin an Insertion
One end of a skeletal muscle is usually fastened to a relatively immovable or fixed part, and the other end is connected to a movable part of on the other side of a joint Origin: The immovable end of muscle Insertion: The moveable end of a muscle When a muscle contracts, its insertion is pulled towards its origin The head of a muscle is the part nearest its origin

30. Origin an Insertion
Some muscles have more than one origin or insertion Ex: Biceps brachii has two origins (bi=two) When the biceps brachii contracts, its insertion is pulled toward its origin, and the elbow bends

31. Interaction of Skeletal Muscles
Skeletal muscles almost always function in groups As a result, when a particular body part moves, a person must do more than contract a single muscle Instead, after learning to make a particular movement, the person wills the movement to occur, and the nervous system stimulates the appropriate group of muscles

32. Interaction of Skeletal Muscles
By carefully observing body movements, it is possible to determine the roles of particular muscles Ex: