1. every human body has an uncountable number of this basic unit of a muscle known as the: (1 point)
muscle fibers
ligaments
tendons
muscle tissues
2. slow-twitch muscles are needed for: (1 point)
quick, short bursts of energy for high intensity
endurance activities
speed or power activities
low endurance and short duration exercises
3. a group of muscle fibers responsible for a specific movement is called: (1 point)
a motor unit
a striated group
a fast-twitch unit
a slow-twitch unit
4. when a muscle fiber contracts as much as it can it is called the (1 point)
maximum potential principal
contraction principal
muscular capacity principal
all or none principal
5. select the answer below that best fits the following description.
voluntary
come in pairs
attach to the bones through tendons
made up of long, cylindrical fibers (1 point)
striated muscles
cardiac muscles
smooth muscles
contracted muscles
6. select the answer below that best fits the following description.

involuntary
found in internal organs
can stretch or maintain tension for long periods of time

(1 point)
striated muscles
cardiac muscles
smooth muscles
skeletal muscles
7. select the answer below that best fits the following description.
involuntary
only found in the heart
(1 point)
striated muscles
cardiac muscles
smooth muscles
skeletal muscles

Q1. The answer is muscle fibers.
Muscle fibers are actually muscle cells and, thus, they are a basic unit of a muscle. Muscle fibers are sheathed by endomysium of collagen fiber. They are bundled into fascicles and sheathed by perimysium. Fascicles are bundled into muscle tissue and sheathed by epimysium. Muscles are connected to bones by tendons while ligaments join one bone to another.

Q2. The answer is Endurance activities.
Two general types of skeletal muscle fibers are fast-twitch and slow-twitch muscle fibers. Slow-twitch muscle fibers are important in aerobic exercises which involve low levels of exertion but for long periods of time. Those are endurance activities during which muscles are used below their maximum contraction capacity but for a long time. For example, in a marathon, slow-twitch muscles are used.

Q3. The answer is a motor unit.
A motor unit consists of a motor neuron and the skeletal muscle fibers that are innervated by that motor neuron.  When an action potential reaches the end of the motor neuron, it will induce a release of neurotransmitters from it. Neurotransmitters pass through the synaptic cleft and bind to the receptor on the muscle fibers and induce muscle contraction.

Q4. The answer is All or none principal.
All or none principal is the principal that explains that strength of a muscle fiber contraction does not depend on the strength of the stimulus. If the stimulus passes the threshold, the muscle fiber will contract. If the stimulus does not pass the threshold, the muscle fiber will not contract. Simply, it will be or it will be not contraction, but there cannot be a little or a great contraction depending on the strength of the stimulus.

Q5. The answer is striated muscles.
Striated muscles are called striated because of the series of sarcomeres, basic units of striated muscles. Contraction of these muscles is voluntary (except for the heart muscles). During these contractions, the muscle is extended by the action of an antagonist muscle. They are made up of long cylindrical fiber and attach to the bones.

Q6. The answer is Smooth muscles.
Smooth muscles are opposite to the striated muscles. They are not striated and their contractions are involuntary. They are found in internal organs and what is important, they can stretch or maintain tension for long period of time. This is especially important for organs, such as urinary bladder or intestines. Imagine a bladder that can be stretched for long period of time and that is thanks to smooth muscles.

Q7. The answer is Cardiac muscles.
As their name suggests, cardiac muscles or heart muscles can be found in the heart. They are involuntary and striated muscles. Cardiac muscles are highly specialized muscle cells and provide blood pumping through the body. Because heart must pump blood all the time, these muscles must have high contractile strength and endurance.  

The correct answer is  b)