188 ❯ STEP 4. Review the Knowledge You Need to Score High
hunger-meter of the body, regulating temperature, hunger, and thirst. The amygdalais the
portion of our brain that controls impulsive emotions and anger. The cerebrumis split into
two “hemispheres” that connect to each other in the middle via the corpus callosum.Each
half is divided into four different lobes, each specializing in various functions:Lobes of the Brain and Their Functions
Frontal lobe Speech, motor cortex.
Parietal lobe Speech, taste, reading, somatosensory.
Occipital lobe Vision.
Temporal lobe Hearing and smell.Muscular System
Our tour of the muscle types of the body will include a look at the types of muscles and a
quick demonstration of muscle contraction. There are three main types of muscle: skele-
tal, smooth,andcardiac:- Skeletal muscle. Muscle type that works when you do pushups, lift a book, and do other
voluntary activities. Skeletal muscle cells contain multiple nuclei. This muscle type has
astriatedappearance. - Smooth muscle. Involuntary muscle that contracts slowly and is controlled by the ANS.
Smooth muscle cells contain a single nucleus. Found in the walls of arteries, digestive
tract, bladder, and elsewhere. Smooth muscle is not striated in appearance. - Cardiac muscle. Involuntary muscle of the heart. Cardiac muscle cells contain a single
nucleus. Cardiac muscle cells are striated in appearance.
Muscle cells are activated by the mechanism described earlier involving the action
potentials and ion channels. When an action potential reaches a muscle cell, acetylcholine
is released at the neuromuscular junction—the space between the motor neuron and the
muscle cell. This neurotransmitter depolarizes the muscle cell and, through a series of intra-
cellular reactions, causes the release of large amounts of stored calcium inside the cell, lead-
ing to muscle contraction. Muscle contraction stops when the calcium is taken back up by
the sarcoplasmic reticulum of the cell.
Folks, we are going to be treated to a demonstration of skeletal muscle contraction.
Skeletal muscle consists of fiber bundles, which are composed of myofibrils. What are
myofibrils? Good question. They are structures that are made up of a combination of
myofilamentscalledthin filaments(actin) and thick filaments(myosin).
The Actin-Myosin “Tango”
It takes two to tango, and myosin and actin are up to the task. Myosin is the lead partner of
this dynamic duo and powers muscle contraction. Myosin, the heart of the thick fibers, has
a “head” and a “tail.” The tails of the numerous myosin molecules unite to form the “thick
filament” seen in Figure 15.6. The heads of the myosin molecules stick out from the thick
filament and serve as the contact point with the actin. The head can exist in two forms: low
and high energy. A relaxed muscle begins with the myosin heads in the low-energy form,
attached to ATP. If the ATP is converted into ADP and phosphate, the myosin changes to
the higher-energy form and is ready to dance. Myosin smoothly approaches its beloved
partner, actin. When ready, the myosin and actin attach to each other, forming the
“cross-bridge.” As they get ready to slide, myosin loses its ADP and phosphate, releasing itsCT teacher:
“Know the func-
tional units of the
various systems
discussed in this
chapter. How the
structure of these
functional units
relates to their
function could be
a nice essay.”