Brainstem: Midbrain (Nursing)

00:01 The next structure that is a part of the brainstem is going to be the midbrain.

00:07 The midbrain is located superior to the medulla oblongata and extends from the pons to the diencephalon area of the brain.

00:19 The posterior region of the midbrain contains elevations with nuclei known as the superior colliculi, the inferior colliculi and together, these colliculi are referred to as the tectum of the midbrain.

00:37 On the anterior portion of the midbrain, we have these tracts known as cerebral peduncles.

00:45 The corticospinal tracts are going to go from cerebrum to the spinal cord, and as well, we have corticobulbar tracts which go from the cerebrum to the medulla oblongata.

00:59 And then, we have corticopontine tracts which are going to connect the cerebrum to the pons.

01:06 All of these tracts can be found in the cerebral peduncles.

01:12 So, if you take a closer look at the cranial nerves that contain nuclei in the midbrain, we have the oculomotor nerve and the trochlear nerve.

01:24 Both of these cranial nerves are important for motor impulses that control eyeball movement.

01:31 In the structural regions of the midbrain, we've already discussed the cerebral peduncles, as well as, the tectum and associated colliculi.

01:42 But there are also two other structures that we should note.

01:45 First, we have the neurons of the substantia nigra.

01:49 These are important for controlling subconscious muscle activities.

01:55 Loss of these neurons has been associated with Parkinson's disease.

02:00 Another structure is the red nuclei.

02:04 They are called this because they have a rich blood supply, an iron containing pigment, which makes them actually appear red.

02:14 These are also important for controlling muscular movements.

02:19 So, when we look at the functional regions of the midbrain, these are gonna convey motor impulses from the cerebrum, to the cerebellum and the spinal cord.

02:30 This happens by way of the peduncles.

02:32 Also, it's going to send sensory impulses from the spinal cord to the thalamus and also regulate auditory and visual reflexes.

02:43 These occur at the different colliculi of the tectum.

02:48 So, another structure that is not necessarily or particularly associated with the midbrain but is still important for brain activity is the reticular formation.

03:03 Much of the brain consists of small clusters of neuronal cell bodies that are interspersed among small bundles of myelinated axons.

03:15 So, they're these broad regions where white matter and gray matter exhibit a netlike arrangement and this is what's known as a reticular formation.

03:26 The reticular formation is going to help us regulate muscle tone, as well as, alerts to cortex to incoming sensory signals.

03:37 It is also responsible for our maintenance of consciousness and awakening from sleep.

03:44 And this just depicts where the reticular formation is located in relation to the other parts of the brainstem.

03:56 So, in this figure, you see your tectum which and because we are looking down or this is a superior view, we can see the superior colliculus or the superior colliculi.

04:08 As well, we can also see the red nucleus and the substantia nigra.

04:13 And in this part of the brainstem between the colliculi and the substantia nigra, we find our reticular formation.

04:23 The reticular formation extends from the superior spinal cord through the brainstem and all the way to the diencephalon.

04:34 The ascending portion of the reticular formation is referred to as the reticular activating system or the RAS.

04:44 This is going to be activated by stimuli such as visual and auditory stimuli, mental activities, as well as stimuli from pain, touch, and pressure receptors.

04:58 It is also activated by proprioceptors found in the limbs and the head.

05:04 This part or this system, the RAS system is important for consciousness, attention, and alertness and it is also responsible for subconsciously filtering out insignificant information.

05:21 So, for example, when you're sitting in a room full of people, you can still read a book because you're able to filter out all the noise around you.

05:31 So, in this, activation of the RAS is going to stimulate arousal and awakeness.

05:39 This allows you to wake up. Inactivation of RAS causes you or allows you to fall asleep.

05:48 Damage of RAS can result in a coma where a person is unable to actually awake from their sleep.

05:58 The interesting thing about the RAS is that it does not receive input from receptors in the nose.

06:06 So, odors are not associated with arousal.

06:11 This becomes important because for example, if you're in a fire, even though there's smoke in the room, the smell of smoke does not actually cause you to awaken.

06:25 That is not what is going to arouse you because the system does not receive input from the nose.

06:31 And therefore, a lot of times, people will remain asleep even when their place is on fire, unless something else happens that alerts them to wake up such as the heat or other things.