14 Hypothalamic, RF, and Limbic Systems - A

Question 1

What is the thalamic nuclei responsible for?

Answer 1

1. Relay general & special sensory information
2. Receive inputs from cerebellum & basal ganglia
3. Relay to associative & limbic cortical areas

Question 2

Why is the thalamus important?

Answer 2

it consists of numerous nuclei, most with extensive reciprocal connections with the cerebral cortex

Question 3

What is the direction of fibers that project from the functional thalamic nuclei?

Answer 3

Majority project to ipsilateral cerebral cortex

• precise, point-to-point projections between thalamic nuclei & defined cortical regions

Question 4

What are the five (5) thalamic nuclei that make up the lateral nuclear group?

Answer 4

1. Ventral anterior
2. Ventral lateral
3. VPM/VPL [ventral posteromedial nucleus/v. posterolateral]
4. LGN [Lateral geniculate nucleus]
5. MGN [Medial geniculate nucleus]

Question 5

What does the ventral anterior thalamic nuclei do?

Answer 5

basal ganglia & primary/supplementary motor areas

Question 6

What does the ventral lateral thalamic nuclei do?

Answer 6

basal ganglia, cerebellum, & primary/supplementary motor areas

Question 7

What does the VPM/VPL thalamic nuclei do?

Answer 7

spinothalamic tracts & medial lemniscus, trigeminothalamic tracts

Question 8

What does the LGN thalamic nuclei do?

Answer 8

visual afferents

Question 9

What does the MGN thalamic nuclei do?

Answer 9

auditory afferents

Question 10

The reticular nuclei (brainstem) of the reticular activating system are ______. They are located where?

Answer 10

diffuse and ill-defined, and have little apparent internal organization

• located at midbrain, pons, & medullary levels

Question 11

What does the reticular activating system (RAS) control? It is interconnected with _____ & _____ in the brainstem.

Answer 11

Controls states of consciousness, sleep, REM, heart rate & respiration

1. basal nuclei
2. motor centers

Question 12

Descending reticulospinal tracts originate _____ & _____ and influence _____ & ______.

Answer 12

Originate from the medullary and pontine RAS.

Influence muscle tone and posture

Question 13

Raphe nuclei are a series of _____ nuclei that extend throughout the ________.

Answer 13

MIDLINE nuclei

length of the brainstem

Question 14

What neurotransmitter are Raphe nuclei responsive to?

Answer 14

Serotonin

Most are serotonergic

Question 15

Where do the ascending projections of Raphe nuclei go to? (6)

Answer 15

1. thalamus
2. hypothalamus
3. striatum
4. amygdala
5. hippocampus
6. widespread regions of cerebral cortex

Question 16

What are Raphe nuclei believed to be involved in?

Answer 16

mood & cognitive function & in the neural mechanisms of sleep

Question 17

What is the hypothalamus and what surrounds it?

Rostral

Lateral

Medial

Caudal

Answer 17

small anatomical region of the diencephalon that is separated superiorly from the dorsal thalamus by the hypothalamic sulcus

Rostral = lamina terminalis

Lateral = substantia innominate (rostral) & medial edge of the posterior limb of the internal capsule (caudal)

Medial = inferior portion of 3rd ventricle

Caudal = merges into the midbrain tegmentum & PAG [periaqueductal gray]

[according to Dennis, location is pretty low-yield but still included]

Question 18

What is the hypothalamus involved in?

Answer 18

control of visceral functions & emotional behavior

Question 19

What is the preoptic area of the hypothalamus?

Answer 19

transition region that extends rostrally, forms a continuation with basal forebrain

Question 20

What is the preoptic area of the hypothalamus composed of?

Answer 20

medial and lateral preoptic nuclei

Medial preoptic nucleus contains neurons that make GnRH

Question 21

What is the periventricular zone of the hypothalamus adjacent to and what does it do?

Answer 21

adjacent to 3rd ventricle

• synthesizes releasing hormones
• projects via hypophyseal portal system to anterior pituitary

Question 22

What is the medial zone of the hypothalamus and what “regions” does it contain?

Answer 22

cell-rich region composed of many nuclei

• Supraoptic (chiasmatic) region
• Tuberal region
• Mammillary region

Question 23

What does the Lateral zone of the hypothalamus contain and what does it interconnect?

Answer 23

contains medial forebrain bundle

• interconnects lateral zone w/ the septal nuclei & the brainstem RF (reticular formation)

Question 24

What else does the Lateral zone of the hypothalamus contain other than the medial forebrain bundle? And what does it do?

Answer 24

Lateral hypothalamic nucleus - which is a large cell group that constitutes the “feeding center”

Question 25

What are the three (3) regions of the nuclei of the medial zone of the hypothalamus?

Answer 25

1. Supraoptic region 2. Tuberal region 3. Mammillary region

Question 26

What three (3) nuclei does the supraoptic region of the medial zone of the hypothalamus?

Answer 26

1. Supraoptic/Paraventricular nucleus 2. Suprachiasmatic nucleus 3. Anterior nucleus

Question 27

What is the supraoptic/paraventricular nucleus of the supraoptic region of the medial zone of the hypothalamus?

Answer 27

contains oxytocin (SO) & ADH (PVN), and transmit these substances to the posterior pituitary

Question 28

Describe what the anterior & medial nuclear groups & intralaminar groups of the functional thalamic nuclei do and why are they different than the five (5) that make up the lateral nuclear group?

Answer 28

- 'non-specific' nuclei - largely project to broad limbic & hypothalamic areas - among these, the lateral dorsal nucleus is part of the limbic system - instinctive drives, mood, emotional behavior

Question 29

What is the anterior nucleus of the supraoptic region of the medial zone of the hypothalamus?

Answer 29

participates in a range of visceral/somatic functions, many neurons involved in temperature regulation

Question 30

What are the three (3) nuclei that make up the tuberal region of the medial zone of the hypothalamus?

Answer 30

1. Ventromedial nucleus 2. Dorsomedial nucleus 3. Arcuate nucleus

Question 31

What is the ventromedial nucleus of the tuberal region of the medial zone of the hypothalamus?

Answer 31

considered to be a "satiety center"

Question 32

What is the dorsomedial nucleus of the tuberal region of the medial zone of the hypothalamus?

Answer 32

subserves functions relating to emotional behavior

Question 33

What is the arcuate nucleus of the tuberal region of the medial zone of the hypothalamus?

Answer 33

primary location of neurons that contain releasing hormones

Question 34

What is the medial mammillary nucleus of the mamillary region of the medial zone of the hypothalamus?

Answer 34

primary termination point for the axons of the postcommissural fornix, which originate primarily from the subiculum of the hippocampus - source of axons directed to the anterior nucleus of the dorsal thalamus as the mammillothalamic tract

Question 35

What are the intermediate & lateral mammillary nuclei of the mammillary region of the medial zone of the hypothalamus?

Answer 35

lateral to the medial mammillary nucleus; receives input from midbrain reticular formation via mammillary peduncle

Question 36

Where are hypothalamic afferent fibers connected to?

Answer 36

Connected to hippocampus, amygdala, brainstem tegmentum, various thalamic nuclei, septal nuclei, & infralimbic and cingulate cortex

Question 37

Where does the **Fornix** of the hypothalamic afferent fibers arise from?

Answer 37

arises from neurons in the **subiculum** & **hippocampus** & is the largest single input to the hypothalamus

Question 38

What is the **Fornix** of the hypothalamic afferent fibers divided into?

Answer 38

divided into a 1: small **precommissural bundle** (hippocampus): passes to septal and preoptic nuclei and to the anterior hypothalamic region 2: Large **postcommissural bundle** (subiculum): projects to medial mammillary nucleus, with lesser inputs to the anterior thalamic nucleus and lateral hypothalamus

Question 39

What is the **medial forebrain bundle** of the hypothalamic afferent fibers?

Answer 39

contains fibers that course rostrocaudally through the lateral hypothalamic zone - ascending and descending fibers that interconnect the septal nuclei, hypothalamus, & midbrain tegmentum

Question 40

**Korsakoff's Syndrome** is the progressive degeneration of what?

Answer 40

mammillary bodies, hippocampal complex, & dorsomedial thalamic nucleus

Question 41

What does the progressive degeneration of various brain spaces lead to as seen in **Korsakoff's Syndrome**?

Answer 41

- impedes the retention of newly acquired memory - short-term memory does not transition to long-term memory

Question 42

What can cause **Korsakoff's Syndrome**?

Answer 42

Thiamine deficiency, typically associated with chronic alcoholism

Question 43

What do patients typically do with **Korsakoff's Syndrome**?

Answer 43

- Affected patients typically have severe difficulties learning new tasks & transforming into longterm memory - Difficulty in understanding written material & conducting meaningful conversations - Patient will **confabulate**, combine fragmented memories into a synthesized memory of an “event” that never occurred

Question 44

What are two (2) disorders of olfaction?

Answer 44

1. Anosmia 2. Phantosmia (olfactory hallucination)

Question 45

What is anosmia and what lesions are associated?

Answer 45

loss of smell due to a viral infection of the olfactory mucosa, obstruction of the nasal passages, or may be congenital - Lesions due to shearing of CN1 or tumors in the floor of the anterior cranial fossa - Patients typically do not recover the sense of smell

Question 46

What is phantosmia?

Answer 46

**(olfactory hallucination)** distortion in a smell experience or the perception of a smell when no odor is present - Abnormal sequence of neuronal activity - Lesion of anterior/medial termporal lobe - Hippocampus, amygdala, or medial dorsal thalamic nuclei

Question 47

What are inputs into the limbic system?

Answer 47

- Directly to the amygdala - Indirectly to the hippocampal formation, via entorhinal area

Question 48

What is the amygdala vital to? Where is its location?

Answer 48

Vital to the motivational & emotional connotations of experience - Near the temporal pole, between the inferior horn of the lateral ventricle & lentiform complex

Question 49

Describe the afferent/efferent fibers of the **amygdala** and projections from the brainstem.

Answer 49

Afferents from inferior temporal association cortex, the thalamus, septum & olfactory tract - Projections from the brainstem in the medial forebrain bundle Efferent projections include the **ventral** **amygdalofugal** **pathway**, the stria terminalis, & stria medullaris thalami [these discussed in other notecards]

Question 50

What are the three (3) amygdaloid efferents?

Answer 50

1. Stria terminalis 2. Ventral amygdalofugal pathway 3. Stria medullaris thalami

Question 51

What is the stria terminalis?

Answer 51

Part of amygdaloid efferent pathway. - Runs in wall of the lateral ventricle - Follows curvature of the caudate nucleus→ hypothalamus. - Outputs to the hypothalamus & basal ganglia (permit motor behavioral responses)

Question 52

What is the ventral amygdalofugal pathway? What are its two (2) general trajectories?

Answer 52

part of the amygdaloid efferent pathway. major efferent fiber bundle with two general trajectories: - Axons primarily from the basolateral cells synapse in the hypothalamus & septal nuclei, as well as the frontal & prefrontal, cingulate, insular, and inferior temporal cortices - Fibers from central nucleus descend in brainstem to terminate in visceral (dorsal motor vagal) nuclei, raphe nuclei & others

Question 53

What is the stria medullaris thalami?

Answer 53

part of the amygdaloid efferent pathway. fibers from septal nuclei target the habenular nuclei

Question 54

What is the **septal region**?

Answer 54

small area just rostral to the anterior commissure and in the medial wall of the hemisphere - thought to function in control of rage behavior

Question 55

What are the fibers for the **medial forebrain bundle**? Where does it convey ascending input?

Answer 55

diffuse group of fibers that courses rostrocaudally through the lateral hypothalamic area - Conveys ascending inputs into the hypothalamus & into the septal region

Question 56

What is the **medial forebrain bundle** related with?

Answer 56

- Major conduit for septal nuclei & hypothalamus communicate with the brainstem - Dopamine-containing fibers in this area are thought to be related to perceptions of pleasure or drive reduction

Question 57

Where is the **nucleus accumbens** located?

Answer 57

Located in the rostral and ventral forebrain, where the head of the caudate nucleus and the putamen are continuous

Question 58

Where does the **nucleus accumbens** receive input from?

Answer 58

Receives input from the amygdaloid complex, hippocampal formation & amygdalofugal fibers traversing the stria terminalis also enter the nucleus accumbens

Question 59

Where does the **nucleus accumbens** play an important role? What about efferent fibers?

Answer 59

Play an important role in behaviors related to addiction and chronic pain - Efferents include fibers to the hypothalamus, nuclei of the brainstem, and the globus pallidus

Question 60

What is the hippocampal formation composed of?

Answer 60

Composed of the subiculum, hippocampus (hippocampus proper), & dentate gyrus - Medial edge of the hippocampal formation is formed by the dentate gyrus & fimbria of the hippocampus

Question 61

What is the **subiculum** of the hippocampal formation?

Answer 61

transitional area between the three-layered hippocampus & five-layered entorhinal cortex (parahippocampal gyrus)

Question 62

What are the three layers (3) of the dentate gyrus and the hippocampus?

Answer 62

1. Internal layer (**polymorphic** **layer**) 2. Middle layer (**granule cell layer** [dentate gyrus] & **pyramidal layer** [hippocampus]) 3. External layer (**molecular layer**)

Question 63

What does the **molecular** **layer** contain part of the dentate gyrus and hippocampus?

Answer 63

External layer. Contains afferent axons and dendrites of cells intrinsic to each structure

Question 64

What does the **granule cell layer** (dentate gyrus) & **pyramidal layer** (hippocampus) contain?

Answer 64

Middle layer. - Contains the efferent neurons of each structure - Named according to the shape of the cell body of the principal type of neuron found therein - Dendrites of both cell types radiate into the molecular layer [*external layer*]

Question 65

What does the **polymorphic layer** of the dentate gyrus and hippocampus contain?

Answer 65

Inner layer. - Contains the axons of pyramidal and granule cells, a few intrinsic neurons, and many glia - Contains the elaborate dendrites of neurons in the pyramidal layer, **double pyramidal cells**

Question 66

What does the *innermost* part of the hippocampus consist of and what will it become?

Answer 66

Innermost part of the hippocampus consists of myelinated axons from cell bodies in subiculum & hippocampus, alveus → continuous w/ fimbria → **will become the fornix**

Question 67

What is the major input for hippocampal afferent fibers?

Answer 67

Major input is from cells of the entorhinal cortex via the **perforant pathway** - Most terminate in the molecular layer [external layer] of the dentate gyrus - few in the subiculum & hippocampus

Question 68

What is the order of hippocampal afferents starting at the granule cell in the dentate gyrus and ending in the subiculum?

Answer 68

Granule cells in the dentate gyrus project --\> molecular layer of the CA3 region of the hippocampus --\> CA3 projects --\> CA1 of the hippocampus --\> subiculum Subiculum receives projections from amygdaloid complex **Fornix** will convey projections to hippocampal formation & entorhinal cortex

Question 69

Where do hippocampal efferents originate primarily?

Answer 69

They originate primarily from cells of the subiculum & pyramidal cells of the hippocampus - axons of these neurons enter the alveus, coalesce to form the fimbria, & then continue as the fornix

Question 70

What is the major output of the hippocampus?

Answer 70

The **Fornix** is the major output of the hippocampus - does extend some fibers across the midline in the **hippocampal decussation**

Question 71

**Fornix** fibers originating in the subiculum mainly form what?

Answer 71

**Postcommisural fornix**

Question 72

**Postcommissural fornix** fibers terminate where?

Answer 72

Terminate in the **medial mammillary nucleus**, ventromedial nucleus of the hypothalamus & anterior nucleus of the dorsal thalamus

Question 73

What is the **precommissural fornix** is composed of what fibers?

Answer 73

fibers arising primarily in the hippocampus - distribute to the septal nuclei, medial areas of the frontal cortex, the preoptic & anterior nuclei of the hypothalamus, & nucleus accumbens

Question 74

What is mediated through the hypothalamus and is controlled & modulated by fibers from the fornix?

Answer 74

Emotion

Question 75

Cortical control of emotional activity can be viewed as a pathway originating from the cingulate gyrus, called what?

Answer 75

**Papez circuit**

Question 76

Describe the flow of the **Papez circuit**.

Answer 76

1. Cingulate gyrus projects → hippocampal formation & entorhinal cortex 2. Hippocampus projects → mammillary nuclei [**Mammillothalamic** **tract** that connects the **medial mammillary nucleus** to the **anterior nucleus** of the thalamus] 3. Medial mammillary nucleus projects → anterior nucleus of the thalamus [​**Thalamocortical fibers** from the anterior nucleus to cortex of the **cingulate gyrus**] 4. Anterior nucleus projects → cingulate gyrus [Projection from the cingulate cortex (via cingulum) to entorhinal cortex, subiculum & hippocampus] 5. The subiculum (via fornix) returns information to the mammillary body

Question 77

Describe the initial segment of the **Papez circuit**.

Answer 77

from the subiculum to the medial mammillary nucleus (postcommissural fornix)

Question 78

What type of patient would present with profound deficit in anterograde episodic memory (cannot learn new material), combined with spared procedural & working memory. The Patient's I.Q. and formal reasoning were fairly normal. If other surrounding areas are also impaired, other deficits would be apparent. What is the DDx?

Answer 78

**Hippocampal Amnesia** Bilateral lesions of the hipoocampi

Question 79

What other part of the brain plays a role with the **Papez circuit** that wasn't discussed previously?

Answer 79

*Cingulate gyrus* & **parahippocampal gyrus** are continuous around splenium of corpus callosum Projects to the parahippocampal gyrus via the fibres of the cingulum The principal structures of the limbic system are thus linked by a series of connections, which constitute the **Papez circuit**

Question 80

What type of patient would present with the ability to parkour and jump around with no fear and recent weight gain?

Answer 80

**_Kluver-Bucy Syndrome_** - Bilateral temporal lobe lesions that abolish amygdaloid complex (fear) Results in behavioral changes - **Visual agnosia**, inability to recognize an object by sight - **Hyperorality**, tendency to examine objects by mouth - **Hypermetamorphosis**, compulsion to intensively explore the immediate environment or overreact to visual stimuli - **Placidity**, may not show fear or anger even when such a reaction is appropriate) - **Hyperphagia**, eating excessive amounts even when not hungry or when objects are not actually food - **Hypersexuality** (suggestive behavior and talk with vague or ill-conceived attempts at sexual contact

Question 81

What type of patient's imaging would see movement of the **uncus** (rostromedial edge of the temporal lobe), and possibly **parahippocampal gyrus**, downward over the edge of the tentorium cerebelli resulting in hemorrhagic lesion or tumor in the hemisphere?

Answer 81

**Uncal** **Herniation** It initially compresses the midbrain, but if unchecked, the damage may extend into lower brainstem levels Signs include: - Dilated pupil and abnormal eye movements (CN III involvement) with double vision ipsilateral to the herniation - Weakness of the extremities (CST involvement) opposite to the dilated pupil - As it progresses, respiration is affected, abnormal reflexes appear, & there is a potentially rapid decline