Download Transcripts/01_15 11

Neuro: 11:00 - 12:00
Scribe: Laura Adams
Thursday, January 15, 2009
Proof: Brittney Wise
Dr. Banos
Diencephalon (Thalamus/Hypothalamus)
Page 1 of 4
I. Introduction [S1]:
a. Thalamus plays a role in a lot of systems.
II. Overview [S2]
a. Parts of the diencephalon: the thalamus, the hypothalamus, and then a couple other parts wewill discuss.
III. The diencephalon (Diagram) [S3]
a. He pointed to the positions of the medulla, pons, midbrain, thalamus and hypothalamus
IV. The diencephalon [S4], [S5], [S6]
a. Four major parts: Epithalamus, Dorsal thalamus, Subthalamus, and hypothalamus
b. When we say dorsal thalamus that is the thalamus
c. Epithalamus or the pineal gland is located on the back of the thalamus (sticks out the back) and it is an unpaired
midline structure which is unusual in the nervous system, most things are bilateral. It is just rostral to superior
colliculi. Supposedly it looks like a pine cone (“pineal” = pine cone), but it really looks like more like a mushy
blob. It is an endocrine gland related to seasonal light cycles, and secretes melatonin
V. Descartes [S7] JUST TRIVIA NOT ON TEST
a. What did Descartes think?
b. He thought it was a joystick, basically that your soul controls your physical body.
VI. Clinical Correlation [S8]
a. Melatonin affects the sleep wake cycle that the pineal gland would usually be involved in. So there are
melatonin pills you can take and use as a sleep aid, for jetlag, so on.
b. [S9] Pineal tumors: they would cause hydrocephalus and eye movement abnormalities. Why? Where is the
pineal gland located? Right by the cerebral aqueduct, so if you have a big space occupying lesion, you have a
high probably of pinching off the cerebral aqueduct and causing hydrocephalus. You also have the superior
colliculi nearby, so you could cause problems with reflexive eye movements that would be mediated by the
superior colliculus.
VII. The diencephalon [S10], [S11] (lost audio for slides 10, 11), [S12], [S13], [S14]
a. Dorsal thalamus has two thalamic hemispheres.
i. The dorsal thalamus is 80% of the diencephalon.
b. The subthalamus is the little area right below the thalamus. It includes the zona incerta, which is the rough area
below thalamus, and the subthalamic nucleus which is below the zona incerta but above the midbrain and
substantia nigra.
c. A quick clinical application: Deep Brain stimulation is when they stick a tiny electrode in brain, usually in
subthalamus, to dampen the effects of Parkinson’s disease.
d. Hypothalamus: (“hypo” is sort of used here to describe “below”) it is anterior and below the dorsal thalamus, but
it is a completely separate structure that does a lot of different things.
i. If you look at the ventral surface of the hypothalamus you can see the optic chiasm, the optic nerve (or
tract), mammilary bodies which are part of hypothalamus (hear mammilary and remember two little round
structures), and the infundibulum or the stalk of the pituitary
1. The infundibulum is very short or ripped off on the gross specimens; however you can see the
hypothalamus grossly on the brain, around the interpeduncular cistern. Cranial nerve III will be on
either side.
ii. Look at a mid-saggital of the brain to find the infundibulum and optic chiasm. These are easy to confuse
and very close together. If the structure has a big optic nerve attached then obviously it is the optic chiasm.
e. The pituitary gland is close to the optic chiasm, so if you have a pituitary tumor you can develop tunnel vision,
because the chiasm has fibers that tend to be associated with peripheral vision.
VIII.
Dorsal Thalamus [S15]
a. Don’t panic with all the little nuclei. Know the big picture, general organization, and general functional
information.
IX. Functional Roles [S16]
a. Thalamus has four basic functional roles:
i. Sensory: People often say the thalamus “gates” the incoming sensory information. All sensory information
(except olfaction) is relayed to the cortex via the thalamus. The recurring theme is that almost everything
on its way to the cortex goes through the thalamus, not just sensory but other things as well.
ii. Motor: The descending motor pathways and the corticospinal tract don’t go through the thalamus, but
when you get to the basal ganglia and cerebellar systems, which are adjunct motor systems, these have
feedback loops that go back to the cortex and these go through the thalamus. So you can argue that the
thalamus has a motor function in this respect.
iii. Emotion/memory: The thalamus is part of the Papez circuit which helps control some emotional and
memory information going to limbic cortex (cingulate gyrus).
Neuro: 11:00 - 12:00
Scribe: Laura Adams
Thursday, January 15, 2009
Proof: Brittney Wise
Dr. Banos
Diencephalon (Thalamus/Hypothalamus)
Page 2 of 4
iv. Vegetative: The thalamus has some intrinsic nuclei associated with alertness and arousal. Can be
associated with disorders of consciousness. The thalamus is part of the ascending reticular activating
system as information is relayed to the cortex.
X. Thalamus trivia! [S17]
a. What is the single largest source of input to the thalamus? The cortex! The thalamus is way more than just a
sensory gate of info coming from below.
XI. Functional Roles [S18]
a. Thalamus doesn’t just send information to the cortex. It receives cortical feedback. It wouldn’t serve much good
to just send info up and get no feedback about what is going on. This signal helps regulate what is coming to
the cortex. Cortical input is a feedback inhibition loop, letting the thalamus know that information has been
received and inhibiting further relaying of the information.
b. You have sensory things that you are aware of, like holding your pen. There is a lot of repetitive info coming in
that your cortex says ok I got it, and you stop consciously processing that info anymore. The cortex can use that
as a way of controlling the amount of info it has to deal with. So to redundant sensory info the cortex says “that
is enough”, the things that change the thalamus puts importance on.
XII. Anatomic Divisions [S19]
a. Internal medullary lamina (lamina means sheet). This is a thin sheet of myelinated fibers that divides the
thalamus into four major divisions, each containing specific nuclei: Anterior, medial, lateral, plus the others that
don’t fit into those three.
1. The intralaminar nuclei and The Reticular nucleus do not belong to one of the first three groups.
XIII. Picture of slices of the thalamus (see page 395 in the book) [S20]
a. Anterior, Medial, lateral
XIV.
Anatomical Divisions [S21] (know that these are in the thalamus, not necessarily what they do)
a. Within each of these divisions you have one or more nuclei. You should know that they are in the thalamus, but
you don’t have to know what each of them do. Note that the abbreviations are commonly used.
b. Anterior Division: Anterior nucleus
c. Medial Division: Dorsomedial Nucleus (DM)
d. Lateral Division: you have two tiers: Dorsal Tier and Ventral Tier.
i. Dorsal Tier: Lateral dorsal (LD), Lateral Posterior (LP), and Pulvinar
ii. Ventral Tier: Ventral Anterior (VA), Ventral Lateral (VL), Ventral Posterior (VP). The ventral posterior has
two divisions the Ventral posteriolateral (VPL) and Ventral posteriomedial (VPM).
e. The laminas are not clean divisions of anterior, medial, and lateral. The nuclei names are not even as intuitive
as they seem, so do not get caught up in these maybe just know the divisions and the way they are organized.
XV. Anatomical Divisions (continued from previous) [S22]
a. Aside from these divisions you have the Medial Geniculate Nucleus (MGN), Lateral Geniculate Nucleus (LGN),
Intralaminar Nuclei [which has two parts Centromedian (CM) and Parafascicular (PF)] and the Reticular
Nucleus.
b. Do know the functions of the lateral geniculate nucleus which is part of the visual pathway and medial geniculate
nucleus which plays a role in the auditory pathway.
c. Intralaminar nuclei are located in the medullary lamina.
XVI.
No Title (see page 395 in book) [S23]
a. Rough divisions, then they break up into the nuclei, but the names don’t always make sense. So just
understand how they are divided up at least.
XVII. Functional Divisions [S24], [S25], [S26], [S27], [S28]
a. Another way to think of this is to group by the nuclei functions.
i. So you have relay nuclei (i.e., relay to the cortex), Association nuclei, and “Other” nuclei including the
Interlaminar and Reticular.
b. Relay Nuclei:
i. Note that there is a table in the book that may break these relay nuclei down and be helpful to you.
ii. When we say the thalamus is a sensory gate, this means it has relay function.
iii. Relay specific information from a particular tract or modality
iv. This is not just sensory information (anything going through the cortex will be relayed by the thalamus). So
you will have specific relay nuclei that relay specific information from a particular tract or modality, so you
will specific nuclei that take the information from the basal ganglia send it back to the cortex and you will
have specific nuclei that take information from the cerebellum output and send it back to the cortex. So
these relay nuclei are part of several important modulatory loops in the CNS. This is not simple passive
“passing on” of the signal, the thalamus is sophisticated. The relay nuclei engage in some complex
condensing and processing of the incoming raw information.
v. The Relay Nuclei are as follows:
Neuro: 11:00 - 12:00
Scribe: Laura Adams
Thursday, January 15, 2009
Proof: Brittney Wise
Dr. Banos
Diencephalon (Thalamus/Hypothalamus)
Page 3 of 4
1. Anterior & Lateral Dorsal (LD): Hippocampus to Cingulate Gyrus
2. Ventral Anterior (VA)/Ventral Lateral (VL): Basal Ganglia/cerebellum to motor areas
3. Ventral Posterolateral (VPL): Medial Lemniscus & Spinothalamic Tract to somatosensory cortex
(body)
4. Ventral Posteromedial (VPM):Medial Lemniscus & Spinothalamic Tract to somatosensory cortex
(face)
5. Medial Geniculate (MGN): Inferior colliculus to auditory cortex
6. Lateral Geniculate (LGN): Optic Tract to visual cortex
c. Association nuclei (these are a little harder)
i. Support areas of association cortex specifically the Prefrontal cortex and Parietal-occipital-temporal cortex.
ii. Association cortex is where a lot of your real thinking is going on. It is involved in higher cognitive function.
So these loops between the thalamus, the cortex, and the association nuclei help us think in a higher level,
the thalamus processes a little and bounces it back to the cortex; the cortex does the same and so on.
XVIII. Other Nuclei [S29], [S30]
a. Intralaminar nuclei
i. Inputs are diverse: from the Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic
tract
ii. Project to widespread areas of cortex (gets info from everyway and sends it everywhere) and the Basal
ganglia.
iii. They produce general changes in cortical function including arousal, alertness, and cortical tone. This is
brain stem reticular formation input.
b. Reticular nucleus
i. Reticular means net-like, so this is a sheet-like layer of neurons partially covering the thalamus. It receives
some of the feedback from the cortex and it will send inhibitory projections to specific thalamic nuclei. So
the cortex can shut of the signal by saying, “enough” and reticular formation can selective inhibit thalamic
nuclei to stop that info from constantly being sent to the cortex. It is the only thalamic nucleus with no
projections to the cortex. So in summary they regulate the activity of the thalamus in the form of cortical
feedback.
XIX.
Clinical Correlation [S31], [S32]
a. Thalamic Stroke – What’s the number one symptom you might predict? A lot of things.
i. Loss of consciousness/coma (Other strokes, like a cortical stroke, the patient can tell you what happened
during the stroke, these patients cannot.)
ii. Attention/Arousal problems
iii. Widespread disruption of cortical function.
iv. Severe cognitive deficits
XX. Clinical Correlation [S33]
a. Anterior nucleus
i. Part of the Papez Circuit in the limbic system (another one that might be good to know)
ii. Involved in memory. Unilateral damage would cause an encoding deficit in memory. You can have a
encoding or retrieval deficits. If you hit anything in the Papez circuit you cause an encoding deficit and you
cannot store memory into the system. Bilateral Damage would cause severe encoding deficit, almost
completely wiped out. This patient you could meet and then 5 minutes later they would not know who you
are because they do not remember.
XXI.
Hypothalamus [S34], [S35], [S36], [S37], [S38]
a. Hypothalamus coordinates Drive-related behaviors: Behaviors follow the principal of homeostasis and “drive”
refers to drive to correct homeostatic imbalance.
i. This would include Hunger/satiety, Thirst, Sexual behavior, Temperature regulation, and Sleep. A lot of
these vegetative type things that are drive related you want to think hypothalamus.
b. Hypothalamus is also the integrative link between the external (the world) and internal (what is going on in your
body) environment
i. Interaction with external environment occurs through integration with the cortex. So your cortex gets all the
sensory information, and it is thinking all your thoughts about what is going on around you, so indirectly the
hypothalamus gets that information and knows what is going on.
ii. Interaction with the internal environment occurs through: “Sampling” of blood or CSF and Release of
hormones (via the pituitary). The position of the hypothalamus is not a coincidence, borders the third
ventricle so a good bit of the hypothalamus in direct contact with CSF so it can figure out what is going on.
It is also connected to the pituitary by the infundibulum so it can exert response to the body.
XXII. Anatomic Considerations [S39]
a. Can be divided into three regions: Posterior, Anterior, and Tuberal
Neuro: 11:00 - 12:00
Scribe: Laura Adams
Thursday, January 15, 2009
Proof: Brittney Wise
Dr. Banos
Diencephalon (Thalamus/Hypothalamus)
Page 4 of 4
i. Each region includes medial and lateral zones. Medial and lateral also include Periventricular Zone.
ii. Don’t get caught up in this, it will be more important for you to learn the thalamic nuclei than the
hypothalamic nuclei so we are not listing them today. They just want us to be aware that the hypothalamus
is not just unitary structure.
b. [S40] and [S41] Inputs: are very Widespread
1. From the Cortex, Limbic system (Helps integrate autonomic responses with emotional state), as well
as the Brain Stem and Spinal cord, (Visceral somatic information).
2. Also have intrinsic sensory neurons that are directly responsive to physical stimuli such as
Temperature, Blood osmolality, and Glucose. Remember it gets this information by “Sampling” the
blood and CSF.
c. [S42] Outputs (reciprocal outputs)
i. Neural: Reciprocate inputs that go to Hippocampus, Amygdala, Thalamus, Brain Stem, and Spinal Cord
ii. Hormonal: Pituitary gland (this is unique to the hypothalamus)
XXIII. Anatomic Considerations – Pituitary Gland [S43]
i. Two parts of the pituitary gland: Neurohypophysis and Adenohypophysis
1. The neurohypophysis has direct neural control of hormone release into blood via neurosecretory
cells, neuronal signal means release of hormones into the blood
2. Adenohypophysis is not a direct neural link but it has a vascular connection with hypothalamus that
have hormones released into them, which can then go to parts of the endocrine system and cause
other hormones to be released.
XXIV. Anatomic Considerations [S44] picture where he added the pituitary so you can see its position
a. Find the Adenohypophysis and the neurohypophysis. The gross brains will not have the pituitary on it.
XXV. Clinical Correlation [S45]
a. Suprachiasmatic Nucleus is the center for circadian rhythm regulation and has a natural 25 hour set cycle.
Daylight cues and melatonin from the pineal gland “train” it to a 24-hour cycle. This is important in sleep/wake
cycle. So the melatonin pills are working on the suprachiasmatic nucleus. This nucleus is located above the
chiasm.
XXVI. Clinical Correlation [S46]
a. Mammillary Bodies are part of the limbic Papez Circuit and are crucial for memory function
i. If the Mammillary bodies are damaged you can get the same memory deficit that you get when you
damage the anterior thalamus. A specific way you can damage the mammillary bodies is by chronic
alcohol abuse. With years of alcoholism, they start to erode and hemorrhage, you end up with alcohol
induced dementia which causes a temporally graded severe memory loss; as they degrade the memories
get weaker and weaker. So if you drink a lot for four decades your memories of the first decade will be the
best and it will decrease every decade.
ii. TV test: Show patients list of real and fake TV shows; ask them to identify which are real. Patients could
identify shows from the 50s and 60s, but could not in the 70s and 80s. You could identify the temporal
gradient.
XXVII. Conclusion [S48], [S49]
a. Dr. Lester is going to lecture about Motivation, reward, and addiction which will clear up how these things fit in
with the hypothalamus
b. For questions you can email Dr. Banos at [email protected]
[end 31 min]