Neuroanat 4 Ex1

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the BRAIN STEM provides the continuity of connections from

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the spinal cord to the higher CNS. It is located in the posterior cranial fossa along with the cerebellum.

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CRANIAL NERVES connected to the medulla are #6 through #12. Therefore, much of the muscle control of, and sensations received from the head relate to the

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medulla, and in this way, the brain stem is similar to the spinal cord.

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Brain stem differs from spinal cord in that

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connections to the cerebellum
vital centers', in its core, e.g. cardiovascular and respiratory centers.
'open' ventricular system.
special sensory afferents (e.g. hearing) and special motor efferents (e.g. muscles of facial expression).
basilar myelinated tracts;
cerebral peduncle of midbrain
basilar pons
pyramids of medulla.

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and we found a number of bumps and humps and certainly a lot of cranial nerve associated with it. There is a ridge with fibers next to the medulla called a pyramid, it turns out to be a bunch of fibers. And this is a

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control pathway. It makes a ridge on the ventralmedial surface of the medulla.

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Nerves that come out laterally on the medulla or on the rest of the brain stem are more involved with

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brachial arch derivatives

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Most of the information going through here is coming out of the cerebral cortex to connect to basilar pontine nuclei whose axons cross making

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cross making this bridge or pons that form the middle part of the brain stem.

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Vascular accidents or tumors in or on the brain stem give wide spread clinical deficits, because of

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the long tracts found here, therefore, cranial nerve signs will usually be the best localizing indicators

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The Pons has nuclei for cranial nerves

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#5 to #8

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The vital centers for respiratory and cardiovascular control are at junction with

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medulla

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The Pons is connected to the cerebellum from

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the basilar nuclei through the middle cerebellar peduncle.

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The one nerve you found particular associated with the pons is

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trigeminal. it gives sensory information from the face and inside the mouth and nose, as well as the motor innervations to muscles of mastication

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You didn’t see much of the midbrain because this is at the mesencephalic flexure, the brainstem comes up through the posterior cranial fossa and at the midbrain you get a

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the mesocephalic flexure

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The trigeminal nerve enters through

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middle cerebellar peduncle to reach its nuclei found throughout the brain stem.

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at the junction of pons and medulla

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The fourth ventricle is widest

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Spinal cord junction at the caudal end. The medulla is going to be in front of the spinal cord. The medulla is at this point

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closed. and in front of that is open into the fourth ventricle, so the upper part, the dorsal part of the medulla is toward the back of the head is open, as we’re into the fourth ventricle

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dotted line that came out of the central canal refers to the

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sulcus limitans, from embryo lecture, that is the separation from the dorsal and ventral horn nuclei

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the sensory nuclei are out lateral to

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that sulcus limitans, and medial nuclei is medial to it

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hypoglssa is next to he midline, in the floor of

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the fourth ventricle

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Pons has fibers continuing up here, and that’s going to form the

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middle cerebellar pinnacule

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. Some of you found choroid plexus near the 7 and 8 nerves, that is at the

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the widest part of the fourth ventricle

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One of the bumps that is evident at the floor of the fourth ventricle in the pons is

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the facial colliculus it is a motor nucleus. it is a motor nucleus. It is the nucleus for the sixth cranial nerve that abducts the eye, the abducens. It includes some fiber from the facial motor nucleus that loop over it, thus the name facial colliculus

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The dorsal surface of the midbrain, has four hills and they are superior and inferior colliculi. These are processing two different kinds of sensory info

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Auditory for inferior colliculus and visual for the superior colliculus.

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The cerebellum cortex continues across the midline unlike the cerebral hemisphere which are interrupted and just connected by

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axonal bundles.

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The cerebellum just continues right across the midline and that medial part, looks like a worm so it was called

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the vermis of the cerebellum

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. Another name for the superior and inferior colliculi is the

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tectum, as in the roof over the ventricular system. The only place we find tectum is in the midbrain

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On the base of the midbrain we can see a structure that came, its axons that came out of the cerebral cortex, called

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the cerebral peduncle, made up of myleninated axons and comes down to innervate motor nuclei in the brain stem. Many of them will synpase in neurons within the basal pon

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The vast majority of cerebral peduncle is made up of

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choridal pontine fibers, they are going from cortex to basilar pons. But a few of them pass on through, and they form a basilar part of the medulla that we found next to the midline, called the pyramid. So these basilar structures are all related to cortical outputs, cerebral cortical outputs

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Tegmentum of the brainstem will have

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have cranial nerve nuclei, ascending sensory tract coming up from the spinal cord, and the reticular formation. So we’ll have tegmentum throughout the brainstem and tectum only in the midbrain.

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Midbrain inferior colliculi relay auditory sensations to

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thalamus

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Tectum refers to the

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superior and inferior colliculi collectively.

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Tegmentum is found throughout the brain stem, below the

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ventricular system

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Basilar structures on the ventral side of brain stem are mostly

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myelinated fiber tracts

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Cerebellum is between the

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external occipital protuberance and the foramen magnum, you have muscles back there so you cannot feel the skull to push in where the beginning of the foramen magnum is.

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. So the dorsal column continue up into the medulla and they will end in these lightly stained area, they are lightly stained because

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there isn’t much myelinated fibers, and has lots of neural cell bodies

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. In the spinal cord we have a very lightly stained nucleus at the dorsal extent of the dorsal horn which is

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the substantia gelatinosa. When we get into the medulla we have the spinal nucleus of the trigeminal nerve, it looks very similar, looks like unstained jelly and it is processing the same info for the face as the substantia gelatinosa does for the rest of the body and that is pain and temperature.

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We have the fourth ventricle and in the floor of the fourth ventricle another minor bump on each side and that is the

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the abducens nucleus innervates muscles that abducts the eye from the middline. And there are fibers that go over it , and that is why it is called the facial calliculi.

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basilar pons and it is made of fibers from the cerebral cortex. It also has a lot of nuclei and neurons, so the basilarpontine nuclei, who’s axons are going

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to cross the midline, and ascend up to form the middle cerebellar peduncle

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another peduncle forms the root of the fourth ventricle that is the

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the superior cerebellar penduncle on both sides

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Tegmentum is the floor of the fourth ventricle down to

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basilar pons. Also in this area that doesn’t look like a condense nucleus or fiber tract is the reticular formation.

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Most of the cerebral peduncle is made up of

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corticopontine fibers, but the middle part are the fibers that are going to go into the pyramid down in the medulla, those are corticospinal fibers

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So if we have two cerebral peduncle, then there will be an

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interpeduncular cistern. Cistern give better definition in cat scans of the brain and separating it from adjoining tissue

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Out of the cistern is the

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third cranial nerve, oculomotor nerve. the substantia nigra with dopananergic cells

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You can see the substantia nigra has few myelintaed fibers so it is very lightly

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stained

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The locus ceruleus is an

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aggregate of neurons, and most of it is will be in the corner of the fourth ventricle

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these cells accumulate some pigments so even on gross inspection you can see it as a bluish color. It will stand out from the rest of the tissue. It is important because that is where we have cells that make

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norepinephrine and project to wide areas of the brain. Wide diffuse connections for the locus ceruleus.

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Some of the structures included in brain stem

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midbrain tectum
Pontine tectum
12th cranial nerve nucleus
pyramidal tract

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In the core of the medulla, in the core of the pons, and in the core of the midbrain we have this integrated center we call

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the reticular formation, it receives afferent input from a lot of sensory pathways that are ascending up here. It received input from the cerebral cortex, that tells the reticular formation what it is planning to do

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With that integrated information the reticular formation is going to control

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respiration, cardiovascular function, micturition, walking, many basic functions you expect to do without having to think about it.

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The reticular formation is found in which of the following parts of the brain stem

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tegmentum

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neurons of the reticular formation have their dendrites in

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one place

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Neurons of the reticular formation affect

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affect the dorsal column nuclei and sensory info coming up, it can influence ventral horn neurons in the spinal cord, on the other side it has connections into the tectum or the thalamus or the hypothalamus to affect hunger or other visceral functions that are controlled through the hypothalamus. So we that an intergrated neuron isn’t just doing one thing, or sampling one sensory information, it is integrating lots of information in order to help control how the body functions.

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The nuclei for the most part looks diffuse from midbrain to the medulla, we can see that the back dots are mostly diffused. There is a midline nucleus that can be picked out. Its on the seam so it is called a

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raphe nucleus, most of the large neurons are on the medial part, and mostly it is smaller neurons on the lateral part throughout the reticular formation. Some of these nuclei can be stained for the transmitters they use or for the enzymes that create those transmitters

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raphe nuclei that we said were on the midline are seratoninergic and use it to connect to

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wide parts of the cerebral hemisphere or down to the spinal cord, those in the locus ceruleus that make norepinephrine can be stained very clearly, and then it looks like quite a condensed nucleus. In the lateral parts of the medulla there are neurons synthesizing epinephrine as a neutrotranmitter

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pontine reticulus spinal tract

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those are going to affect muscles of the medial part of the ventral horn. Those motor neurons mostly innervate muscles close to the vertebral column. This is a connection that is mostly about posture and this working for most of us at an unconscious level.

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The reticular formation of the medulla gives rise to a second tract, a second or medullar reticular spinal tract that is going to

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affect more lateral groups of neuron in the ventral horn and those tend to be more involved with the more peripheral muscle innervations

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Locus ceruleus tells your brain to remember your exciting moments. The activation is telling the brain

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get ready this is important

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These tiny nuclei within the brainstem reticular formation have widespread connections, the seratoninergic ones are very important in

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behavior phenomenon

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cholingergic neurons from the brain stem and well as more rostrallyin the basil nucleus that have wide spread connection and are going to participate in

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ascending reticular activating system, this system is important in gating the information that goes through the diencephalon and the cerebral cortex, its important for keeping you awake and helping you go to sleep

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Individual neurons receive input from several, but not

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all tracts

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Some neuronal groups may be identified by specific transmitters

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NE, E, DA, 5HT, ACh

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Axons are long and carry the integrated messages to widely dispersed effectors, including

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vital centers

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Reticular formation is a

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suprasegmental integrative area