What is the thalamic nuclei responsible for?
- Relay general & special sensory information
- Receive inputs from cerebellum & basal ganglia
- Relay to associative & limbic cortical areas
Why is the thalamus important?
it consists of numerous nuclei, most with extensive reciprocal connections with the cerebral cortex
What is the direction of fibers that project from the functional thalamic nuclei?
Majority project to ipsilateral cerebral cortex
- precise, point-to-point projections between thalamic nuclei & defined cortical regions
What are the five (5) thalamic nuclei that make up the lateral nuclear group?
- Ventral anterior
- Ventral lateral
- VPM/VPL [ventral posteromedial nucleus/v. posterolateral]
- LGN [Lateral geniculate nucleus]
- MGN [Medial geniculate nucleus]
What does the ventral anterior thalamic nuclei do?
basal ganglia & primary/supplementary motor areas
What does the ventral lateral thalamic nuclei do?
basal ganglia, cerebellum, & primary/supplementary motor areas
What does the VPM/VPL thalamic nuclei do?
spinothalamic tracts & medial lemniscus, trigeminothalamic tracts
What does the LGN thalamic nuclei do?
visual afferents
What does the MGN thalamic nuclei do?
auditory afferents
The reticular nuclei (brainstem) of the reticular activating system are ______. They are located where?
diffuse and ill-defined, and have little apparent internal organization
- located at midbrain, pons, & medullary levels
What does the reticular activating system (RAS) control? It is interconnected with _____ & _____ in the brainstem.
Controls states of consciousness, sleep, REM, heart rate & respiration
- basal nuclei
- motor centers
Descending reticulospinal tracts originate _____ & _____ and influence _____ & ______.
Originate from the medullary and pontine RAS.
Influence muscle tone and posture
Raphe nuclei are a series of _____ nuclei that extend throughout the ________.
MIDLINE nuclei
length of the brainstem
What neurotransmitter are Raphe nuclei responsive to?
Serotonin
Most are serotonergic
Where do the ascending projections of Raphe nuclei go to? (6)
- thalamus
- hypothalamus
- striatum
- amygdala
- hippocampus
- widespread regions of cerebral cortex
What are Raphe nuclei believed to be involved in?
mood & cognitive function & in the neural mechanisms of sleep
What is the hypothalamus and what surrounds it?
Rostral
Lateral
Medial
Caudal
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]
What is the hypothalamus involved in?
control of visceral functions & emotional behavior
What is the preoptic area of the hypothalamus?
transition region that extends rostrally, forms a continuation with basal forebrain
What is the preoptic area of the hypothalamus composed of?
medial and lateral preoptic nuclei
Medial preoptic nucleus contains neurons that make GnRH
What is the periventricular zone of the hypothalamus adjacent to and what does it do?
adjacent to 3rd ventricle
- synthesizes releasing hormones
- projects via hypophyseal portal system to anterior pituitary
What is the medial zone of the hypothalamus and what “regions” does it contain?
cell-rich region composed of many nuclei
- Supraoptic (chiasmatic) region
- Tuberal region
- Mammillary region
What does the Lateral zone of the hypothalamus contain and what does it interconnect?
contains medial forebrain bundle
- interconnects lateral zone w/ the septal nuclei & the brainstem RF (reticular formation)
What else does the Lateral zone of the hypothalamus contain other than the medial forebrain bundle? And what does it do?
Lateral hypothalamic nucleus - which is a large cell group that constitutes the “feeding center”
What are the three (3) regions of the nuclei of the medial zone of the hypothalamus?
- Supraoptic region
- Tuberal region
- Mammillary region
What three (3) nuclei does the supraoptic region of the medial zone of the hypothalamus?
- Supraoptic/Paraventricular nucleus
- Suprachiasmatic nucleus
- Anterior nucleus
What is the supraoptic/paraventricular nucleus of the supraoptic region of the medial zone of the hypothalamus?
contains oxytocin (SO) & ADH (PVN), and transmit these substances to the posterior pituitary
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?
- ‘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
What is the anterior nucleus of the supraoptic region of the medial zone of the hypothalamus?
participates in a range of visceral/somatic functions, many neurons involved in temperature regulation
What are the three (3) nuclei that make up the tuberal region of the medial zone of the hypothalamus?
- Ventromedial nucleus
- Dorsomedial nucleus
- Arcuate nucleus
What is the ventromedial nucleus of the tuberal region of the medial zone of the hypothalamus?
considered to be a “satiety center”
What is the dorsomedial nucleus of the tuberal region of the medial zone of the hypothalamus?
subserves functions relating to emotional behavior
What is the arcuate nucleus of the tuberal region of the medial zone of the hypothalamus?
primary location of neurons that contain releasing hormones
What is the medial mammillary nucleus of the mamillary region of the medial zone of the hypothalamus?
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
What are the intermediate & lateral mammillary nuclei of the mammillary region of the medial zone of the hypothalamus?
lateral to the medial mammillary nucleus; receives input from midbrain reticular formation via mammillary peduncle
Where are hypothalamic afferent fibers connected to?
Connected to hippocampus, amygdala, brainstem tegmentum, various thalamic nuclei, septal nuclei, & infralimbic and cingulate cortex
Where does the Fornix of the hypothalamic afferent fibers arise from?
arises from neurons in the subiculum & hippocampus & is the largest single input to
the hypothalamus
What is the Fornix of the hypothalamic afferent fibers divided into?
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
What is the medial forebrain bundle of the hypothalamic afferent fibers?
contains fibers that course rostrocaudally through the lateral hypothalamic zone
- ascending and descending fibers that interconnect the septal nuclei, hypothalamus, & midbrain tegmentum
Korsakoff’s Syndrome is the progressive degeneration of what?
mammillary bodies, hippocampal complex, & dorsomedial thalamic nucleus
What does the progressive degeneration of various brain spaces lead to as seen in Korsakoff’s Syndrome?
- impedes the retention of newly acquired memory
- short-term memory does not transition to long-term memory
What can cause Korsakoff’s Syndrome?
Thiamine deficiency, typically associated with chronic alcoholism
What do patients typically do with Korsakoff’s Syndrome?
- 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
What are two (2) disorders of olfaction?
- Anosmia
- Phantosmia (olfactory hallucination)
What is anosmia and what lesions are associated?
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
What is phantosmia?
(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
What are inputs into the limbic system?
- Directly to the amygdala
- Indirectly to the hippocampal formation, via entorhinal area
What is the amygdala vital to? Where is its location?
Vital to the motivational & emotional connotations of experience
- Near the temporal pole, between the inferior horn of the lateral ventricle & lentiform complex
Describe the afferent/efferent fibers of the amygdala and projections from the brainstem.
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]
What are the three (3) amygdaloid efferents?
- Stria terminalis
- Ventral amygdalofugal pathway
- Stria medullaris thalami
What is the stria terminalis?
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)
What is the ventral amygdalofugal pathway? What are its two (2) general trajectories?
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
What is the stria medullaris thalami?
part of the amygdaloid efferent pathway.
fibers from septal nuclei target the habenular nuclei
What is the septal region?
small area just rostral to the anterior commissure and in the medial wall of the hemisphere
- thought to function in control of rage behavior
What are the fibers for the medial forebrain bundle? Where does it convey ascending input?
diffuse group of fibers that courses rostrocaudally through the lateral hypothalamic area
- Conveys ascending inputs into the hypothalamus & into the septal region
What is the medial forebrain bundle related with?
- 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
Where is the nucleus accumbens located?
Located in the rostral and ventral forebrain, where the head of the caudate nucleus and the putamen are continuous
Where does the nucleus accumbens receive input from?
Receives input from the amygdaloid complex, hippocampal formation & amygdalofugal fibers traversing the stria terminalis also enter the nucleus accumbens
Where does the nucleus accumbens play an important role? What about efferent fibers?
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
What is the hippocampal formation composed of?
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
What is the subiculum of the hippocampal formation?
transitional area between the three-layered hippocampus & five-layered entorhinal cortex (parahippocampal gyrus)
What are the three layers (3) of the dentate gyrus and the hippocampus?
- Internal layer (polymorphic layer)
- Middle layer (granule cell layer [dentate gyrus] & pyramidal layer [hippocampus])
- External layer (molecular layer)
What does the molecular layer contain part of the dentate gyrus and hippocampus?
External layer.
Contains afferent axons and dendrites of cells intrinsic to each structure
What does the granule cell layer (dentate gyrus) & pyramidal layer (hippocampus) contain?
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]
What does the polymorphic layer of the dentate gyrus and hippocampus contain?
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
What does the innermost part of the hippocampus consist of and what will it become?
Innermost part of the hippocampus consists of myelinated axons from cell bodies in subiculum & hippocampus, alveus → continuous w/ fimbria → will become the fornix
What is the major input for hippocampal afferent fibers?
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
What is the order of hippocampal afferents starting at the granule cell in the dentate gyrus and ending in the subiculum?
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
Where do hippocampal efferents originate primarily?
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
What is the major output of the hippocampus?
The Fornix is the major output of the hippocampus - does extend some fibers across the midline in the hippocampal decussation
Fornix fibers originating in the subiculum mainly form what?
Postcommisural fornix
Postcommissural fornix fibers terminate where?
Terminate in the medial mammillary nucleus, ventromedial nucleus of the hypothalamus & anterior nucleus of the dorsal thalamus
What is the precommissural fornix is composed of what fibers?
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
What is mediated through the hypothalamus and is controlled & modulated by fibers from the fornix?
Emotion
Cortical control of emotional activity can be viewed as a pathway originating from the cingulate gyrus, called what?
Papez circuit
Describe the flow of the Papez circuit.
- Cingulate gyrus projects → hippocampal formation & entorhinal cortex
- Hippocampus projects → mammillary nuclei
[Mammillothalamic tract that connects the medial mammillary nucleus to the anterior nucleus of the thalamus]
- Medial mammillary nucleus projects → anterior nucleus of the thalamus
[Thalamocortical fibers from the anterior nucleus to cortex of the cingulate gyrus]
- Anterior nucleus projects → cingulate gyrus
[Projection from the cingulate cortex (via cingulum) to entorhinal cortex, subiculum & hippocampus]
- The subiculum (via fornix) returns information to the mammillary body
Describe the initial segment of the Papez circuit.
from the subiculum to the medial mammillary nucleus (postcommissural fornix)
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?
Hippocampal Amnesia
Bilateral lesions of the hipoocampi
What other part of the brain plays a role with the Papez circuit that wasn’t discussed previously?
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
What type of patient would present with the ability to parkour and jump around with no fear and recent weight gain?
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
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?
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
