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Chapter 6

Muscles

TermDefinition
1. Contractility the ability of skeletal muscle to shorten with force.
2. Excitability the capacity of skeletal muscle to respond to a stimulus.
3. Extensibility the ability to be stretched
4. Elasticity ability to recoil to their original resting length after they have been stretched.
Muscles help to produce... heat essential for maintenance of normal body temperature.
epimysium 1. Each skeletal muscle is surrounded by a connective tissue sheath
2. Fascia is another connective tissue located outside the epimysium. It surrounds and separates muscles.
perimysium. 3. A muscle is composed of numerous visible bundles called muscle fasciculi (fascicle), which are surrounded by loose connective tissue
fibers 4. The fasciculi are composed of single muscle cells
endomysium. 6. Each fiber is surrounded by a connective tissue sheath
myofibrils a threadlike structure that extends from one end of the fiber to the other.
a. actin myofilaments thin myofilaments. They resemble 2 minute strands of pearls twisted together.
b. myosin myofilaments thick myofilaments. They resemble bundles of minute golf clubs.
sarcomeres 9. Actin and myosin myofilaments form highly ordered units
I band 13. On each side of the Z line is a light area it consists of actin.
A band extends the length of the myosin. It is the darker central region in each sarcomere.
Z line is an attachment site for actin
resting membrane potential. The charge difference across the
action potential. The brief reversal back of the charge
1. Motor neurons are nerve cells that carry action potentials to skeletal muscle fibers
neuromusclular junction, or.... synapse
Each branch that connects to the muscle forms.... neuromusclular junction
near the center of the cell synapse
motor unit 3. A single motor neuron and all the skeletal muscle fibers it innervates
presynaptic terminal 5. The enlarged nerve
the space between the presynaptic terminal and the muscle cell is the... synaptic cleft
the muscle fiber is the postsynaptic terminal
6. Each presynaptic terminal contains synaptic vesicles
synaptic vesicles secrete a neurotransmitter called acetylcholine
The acetylcholine released into the synaptic cleft between the neuron and muscle cell is rapidly broken down by an enzymes acetylcholinesterase
sliding filament mechanism 2. The sliding of actin myofilaments past myosin myofilaments during contraction
The H and I bands shorten, but the A bands do not change in length.
3. Muscle twitch is a contraction of an entire muscle in response to a stimulus that causes the action potential in one or more muscle fibers.
4. A muscle fiber will not respond to stimulus until that stimulus reaches a level called threshold
the muscle fiber will contract maximally. This phenomenon is called the all-or-none response.
5. The time between application of a stimulus to a motor neuron and the beginning of a contraction is the lag phase
6. The time of contraction is contraction phase
7. The time during which the muscle relaxes is the relaxation phase
8. If successive stimuli are given you get successive twitches that occur so frequently the muscle doesn’t have time to fully relax.
9. Tetany where the muscle remains contracted without relaxing
10. The increase in number of motor units being activated is called recruitment.
is needed for energy for muscle contraction. 1. ATP (adenosine triphosphate)
is produced in the mitochondria ATP
is short-lived and unstable ATP
When at rest they can’t stockpile ATP but they can store another high-energy molecule, called creatine phosphate.
6. Anaerobic respiration without oxygen
7. Aerobic respiration with oxygen (more efficient).
3. ATP is short-lived and unstable. It degenerates to the more stable ADP (adenosine diphosphate) plus phosphate
4. It is necessary for muscle cells to constantly produce ATP
oxygen debt is the amount of oxygen needed in chemical reactions to convert lactic acid to glucose and to replenish the depleted stores of creatine phosphate stores in muscle cells.
9. Muscle fatigue results when ATP is used during muscle contraction faster than it can be produced in the muscle cells.
10. 2 types of muscle contractions: a. isometric,b. isotonic
a. isometric (equal distance) the length of the muscle does not change, but the amount of tension increases during the contraction process.
b. isotonic (equal tension) the amount of tension produced by the muscle is constant during contraction, but the length of the muscle changes.
11. Muscle tone Muscle tone refers to constant tension produced by muscles of the body for long periods of time
11. Muscle tone keeps Keeps head up and back straight.
12. Fast-twitch fibers contract quickly and fatigue quickly
Ex. white meat of a chicken’s breast. 12. Fast-twitch fibers
13. Slow-twitch fibers contract more slowly and are more resistant to fatigue
. Ex. dark meat of a duck’s breast or the legs of a chicken 13. Slow-twitch fibers
1. The points of attachment of each muscle are its origin and insertion
At these attachment points the muscle is connected to the bone by a tendon.
2. The origin (head) is the most stationary end of the muscle.
3. The insertion is the end of the muscle undergoing the greatest movement.
4. The portion of the muscle between the origin and the insertion is the belly.
6. Muscles that work together to accomplish specific movements are called synergists.
7. Muscles that work in opposition to one another are called antagonists.
8. Among a group of synergists, if one muscle plays the major role in accomplishing the desired movement, it is the prime mover.
Some are named according to their location, size, orientation of fibers, shape, origin, insertion, and function, etc.
Occipitofrontalis raises the eyebrows
Orbicularis oculi closes the eyelids and causes “crows feet” wrinkles in the skin at the lateral corners of the eye.
Orbicularis oris puckers the lips
Buccinator flattens the cheeks. Trumpeter’s muscle.
Zygomaticus smiling muscle.
Levator labii superioris sneering
Created by: tiffanykane
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