Hello and welcome back. In this section, we begin the discussion of the hind
brain and all of the structures that are within it. As we see in slide one,
the hind brain is also called the reptilian brain and surrounds the 4th
ventricle. As we saw in the previous section, the hind brain has two major
divisions with three major structures. The divisions are the
Rhombencephalon which consists of the pons and the cerebellum, and the
myencephalon which consists of the medulla oblongata or what we commonly
call the medulla.
Let’s talk about the medulla first on slide two. The
medulla is the structure that’s going to regulate things that keeps us
alive. It’s going to regulate breathing, heart rate, digestion,
temperature, and lots and lots of other things. You can damage other major
structures in the brain. For example, I can take a gun and shoot through
the upper part of the brain and you probably would still survive, provided
that the bullet went through very quickly and cauterized all the major
tissue and blood vessels. On the other hand, if I shot you in the medulla,
you would die. The medulla, in addition to doing all the things of
regulation of major systems, also contains part of another brain system
called the reticular formation. We’ll talk about the reticular formation a
little bit later, but it is a series of pathways that begins in the medulla
and ultimately ends in the thalamus.
Well, now that we’ve talked about the medulla for a
minute, let’s talk about the next major structure called the pons. The pons
is superior to the medulla, that means it is located above the medulla and
it is ventral to the cerebellum, that is, it’s more toward the stomach. The
pons also contains a portion of the reticular activating system like the
medulla. Primarily the pons is responsible for the wakefulness or the sleep
cycle. So when you can’t sleep well or when you don’t feel sleepy when you
should, that’s the pons influencing that. The one thing about the sleep
cycle is that it can be trained. Sometimes individuals can live on less
sleep than what they normally have for a long period of time.
Let’s talk about the next major structure and this is
shown in slide four and is called the cerebellum, or what is called the
little brain. The cerebellum looks very, very similar to a lot of cortical
structures and that’s why it was given the name that it has. It is located
behind the medulla and pons and is connected to the pons by three basic
bundles of peduncles called the cerebellar peduncles, which include the
superior, middle and inferior which we’ll talk about in a minute.
The cerebellum, as we continue in slide five, has two
major hemispheres and is covered by a cortex called the cerebellar cortex.
Like other structures that we have within our cortex, it also has deeper
structures, so we have are deep cerebellar nuclei. Ultimately the
cerebellar nuclei send information to the cerebellum and other brain
structures, and it receives information from the cerebellar cortex.
Ultimately the cerebellum gets information from a wide variety of different
structures, including the visual system, sensory, motor, and vestibular
systems and others as well. Ultimately all of these systems are involved
with movement. As we see in slide six, the major function of the cerebellum
is to help control muscle tone and body balance. What it does is smooth out
the muscle movement so they’re not jerky, and helps to coordinate voluntary
muscle movement.
The thing about movements is that there’s a wide variety
of different movements. The thing the cerebellum does is help control rapid
movement such as startle responses. It also has a memory system to help
with particular motor control. So, think of when you hit a tennis ball or
throw or hit a baseball. When you do things such as hit the tennis ball
with a racket, it has a smooth movement. However, when you damage the
cerebellum, as we can see in slide seven, the results are that you get
jerky, exaggerated movements and the movements are very poorly coordinated.
Another major way to think about the cerebellum and all
the structures and functions that it does is to think of a gymnast on the
balance beam or another gymnast on the mat. Each of these individuals is
doing flips. Basically doing the flip and landing back on the balance beam
in perfect location or a gymnast on the mat doing seven or eight flips in a
row. Each of these requires a wide variety of different structures to be
coordinating and working together. The cerebellum helps control these motor
movements.
So that’s a general overview of the hind brain structures
and what they do. In the next section we’ll talk about midbrain structures,
so until then, we hope you have a good day.
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