2 - Forebrain and Limbic System Flashcards
(170 cards)
1
Q
Forebrain:
A
Diencephalon:
Internal capsule
Limbic system:
,
2
Q
Diencephalon:
A
thalamus, hypothalamus, epithalamus, subthalamus
3
Q
Limbic system:
A
hippocampus, hypothalamus, amygdala
4
Q
Epithalamus:
A
pineal gland, habenula, few other things
5
Q
A large number of pathways relay in
A
thalamus
All sensory (other than olfaction) pathways
6
Q
Cerebellum, basal ganglia, limbic system
A
These systems use different parts (with some overlap) so thalamus is comprised of distinct nuclei
7
Q
Subdivisons of thalamic nuclei: Anterior division:
A
Anterior nucleus (AN)
8
Q
Subdivisons of thalamic nuclei: Medial division:
A
Dorsomedial (DM) aka (medial dorsal (MD))
9
Q
Subdivisons of thalamic nuclei: Lateral division:
A
Dorsal tier: lateral dorsal (LD), lateral posterior (LP), pulvinar
Ventral tier: ventral anterior (VA), ventral lateral (VL), ventral posterior lateral (VPL) and medial (VPM) and medial & lateral geniculates (MGN, LGN)
10
Q
Subdivisons of thalamic nuclei
A
Intralaminar: Centromedian, parafascicular, others
Reticular nucleus
Midline nuclei
11
Q
Subdivisons of thalamic nuclei: Defined by
A
internal medullary lamina (IML)
12
Q
Subdivisons of thalamic nuclei: Lateral subdivision is the
A
largest
13
Q
Subdivisons of thalamic nuclei: Anterior subdivision sits in a
A
split in the IML
14
Q
All thalamic nuclei (except reticular) are based on the same general theme
All consist of:
A
projection neurons: provide output from thalamus (green)
Interneurons, small, inhibitory (red)
Proportions vary from nucleus-to-nucleus
15
Q
Two basic types of thalamic inputs
A
Specific inputs (blue): Regulatory inputs (purple):
16
Q
Specific inputs (blue):
A
convey info a thalamic nucleus passes on nearly directly to cortex (or other places)
Example: medial lemniscus to VPL or optic tract to LGN
17
Q
Regulatory inputs (purple):
A
thalamic nucleus contributes to the info it receives before it is passed on to cortex
18
Q
Three categories of thalamic nuclei
A
Based on patterns of outputs and specific inputs
Relay nuclei
Association nuclei
Intralaminar & midline nuclei
19
Q
Relay nuclei: receive
A
well defined specific input from a subcortical source (e.g. medial lemniscus) and project to a well-defined area of cortex (e.g. somatosensory cortex
20
Q
2) Association nuclei: Receive
A
specific inputs from association cortex (e.g. prefrontal cortex) and project back
21
Q
3) intralaminar and midline nuclei: receive
A
distinct set of specific inputs (basal ganglia, limbic structures)
Project to cortex, basal ganglia and limbic structures
22
Q
Reticular nucleus; Important source of
A
regulatory input to thalamus
23
Q
Reticular nucleus; No projections to
A
cortex
Unlike all other thalamic nuclei
24
Q
Reticular nucleus; Input:
A
cortex & thalamus
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Reticular nucleus; Output:
inhibitory axons to thalamus
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Reticular nucleus; Nucleus is a
sheet of neurons, covers thalamus, axons must traverse nucleus to enter/ leave thalamus and send collaterals to it
27
Sensory, motor and limbic systems have
relay nuclei
Sensory: VPL & VPM
Motor: VA & VL
Limbic: Anterior, LD
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Anterior
Input: Mammillothalamic tract, hippocampus
| Cortical output: Cingulate gyrus
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Lateral dorsal (LD)
Input: Hippocampus
| Cortical Output: Cingulate gyrus
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VA/ VL
Input: Basal ganglia (mostly VA),
cerebellum (mostly VL)
Cortical Output: Motor areas
31
VPL
Input: Medial lemniscus, spinothalamic tract (ALP)
Cortical Output: Somatosensory cortex
32
VPM
Input: Trigeminal system
Cortical Output: Somatosensory cortex
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MGN
Input: Brachium of inferior colliculus
Cortical Output: Auditory cortex
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LGN
Input: Optic tract
Cortical Output: Visual cortex
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DM and Pulvinar are
main association nuclei
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DM and Pulvinar are main association nuclei: Two huge areas of
association cortex
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DM and Pulvinar are main association nuclei: Prefrontal: DM
Foresight, affect
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DM and Pulvinar are main association nuclei: Parietal-occipital-temporal:
Pulvinar-LP complex
| Function largely unknown; may be involved in visual perception or attention
39
DM
specific inputs: Prefrontal cortex, olfactory and limbic structures (amygdala)
cortical outputs: Prefrontal cortex
40
LP
specific inputs: Parietal lobe
cortical outputs: Parietal cortex
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Pulvinar
specific inputs: Parietal, occipital and temporal lobes
cortical outputs: Parietal, occipital and temporal lobes
42
Internal capsule (IC): Thalamocortical and corticothalamic fibers
pass thru
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Internal capsule (IC) Almost all fibers going to and from the
cortex pass thru
44
Internal capsule (IC) Collects and forms
cerebral peduncle down which corticopontine, corticobulbar and corticospinal fibers descend
45
Internal capsule has five parts
Based on relationship to lenticular nucleus
1. Anterior limb: lenticular nucleus, caudate
2. Posterior limb: lenticular nucleus, thalamus
3. Genu: between A & P limbs
4. Retrolenticular: behind lenticular nucleus
5. Sublenticular part: beneath lenticular nucleus
Not seen in horizontal sections
46
Sublenticular-
Superior visual field
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Retrolenticular-
Inferior visual field
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Hypothalamus: Critical in
autonomic, endocrine, emotional and somatic functions; maintains physiological range or homeostasis
49
Hypothalamus: 3 main types of connections:
Interconnected with limbic system
Output to pituitary
Interconnects visceral/ somatic nuclei
50
Anterior border:
Lamina terminalis
51
Hypothalamus: Superior border:
Hypothalamic sulcus
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Hypothalamus: Posterior border:
border: 3rd ventricle
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Hypothalamus: Lateral border:
internal capsule
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Hypothalamus: Inferior border:
Optic chiasm, tuber cinereum (contains median eminence), mammillary bodies
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Lateral: rostral continuation of
reticular formation
| Nuclei and tracts (medial forebrain bundle)
56
Periventricular: rostral continuation of
periaqueductal gray
| Contains nuclei and tracts (dorsal longitudinal fasciculus
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Hypothalamus: Medial:
nuclei
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Hypothalamic control of pituitary: Hypophyseal branches of
internal carotid artery
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Hypothalamic control of pituitary: Superior- supply
capillary bed in infundibulum, capillaries drain into portal vessels in adenohypophysis (anterior lobe)
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Hypothalamic control of pituitary: Second capillary bed around
endocrine cells of adenohypophysis
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Hypothalamic control of pituitary: Inferior hypophyseal arteries supply
neurohyposphysis (posterior lobe)
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Hypothalamic control of pituitary: Capillaries drain into
cavernous sinus, which delivers anterior and posterior pituitary hormones to systemic circulation
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Neuroendocrine cells: Pituitary secretions controlled by
2 types of neuroendocrine cells
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Neuroendocrine cells: Release secretions into
capillaries so true endocrine cells
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Somas of neuroendocrine cells in
hypophysiotrophic area
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Hypophysiotrophic area Located in
lower half of preoptic and tuberal regions; nuclei in red
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Parvocellular:
end in median eminence
68
Magnocellular:
end in posterior lobe
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Hypothalamic control of anterior pituitary
Parvocellular neurons give rise to tuberoinfundibular tract to infundibular capillary bed
Carry releasing or inhibiting hormones; all peptides except prolactin IH
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Hypothalamic control of posterior pituitary: Two hormones released by
separate neurons in paraventricular and supraoptic nuclei
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Hypothalamic control of posterior pituitary: Antidiuretic hormone or vasopressin:
↑water uptake by kidney; ↓urine output
Loss of ADH: diabetes insipidus
Sense blood osmotic pressure also input from subfornical circumventricular organ
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Hypothalamic control of posterior pituitary: Oxytocin: contraction of
uterine (labor contractions) and other smooth muscles
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Hypothalamic control of posterior pituitary: Breast;
infant suckling; reflex in Mom from nipple to spinoreticular tract
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Hypothalamic functions: Autonomics: Anterior hypothalamus:
Stimulation produces parasympathetic effects- slow HR, constrict pupil, peristalsis, salivation
75
Hypothalamic functions: Autonomics: Posterior hypothalamus:
Stimulation produces sympathetic effects- ↑ HR & BP, dilate pupils, intestinal stasis
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Hypothalamic functions: Autonomics: Axons from these areas project down
brainstem and spinal cord in dorsal longitudinal fasciculus (arrow)
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Hypothalamic functions: Feeding: Eating:
Baseline caloric/ nutrient intake, sensitive to blood glucose
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Hypothalamic functions: Feeding: Interplay of lateral and ventromedial nuclei creates
appestat (appetite set point) can be altered by serotonin anorexics often have high levels, bulimics reduced levels
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Hypothalamic functions: Feeding: Lateral nucleus: Stimulate-
feeding; lesion- refuse food
80
Hypothalamic functions: Feeding: Ventromedial:
Stimulate- refuse food; bilateral lesion- feeding
81
Hypothalamic functions: Feeding: This area also key to
rage and fear
Cats overweight due to ventromedial lesions are mean and aggressive
Cats underweight due to ventromedial stimulation: extremely docile
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Hypothalamic functions: Fight or flight: Male response: fight of flight
Corticotropin RH released by paraventricular nucleus→ACTH release pituitary →↑ cortisol from adrenal
Males: Show activation of lateral prefrontal cortex
83
Hypothalamic functions: Fight or flight: Female response (BTW: not reported until 2000!):
tend and befriend- protect offspring; affiliate with social groups
Calming effect in females: oxytocin released in capillary bed of neurohypophysis and estrogen counteract sympathetic over activity due to stress
Females: show activation of cingulate gyrus (a cortical emotional control center)
84
Sleeping and waking: Suprachiasmatic nucleus gets direct input from
retina, sets normal sleep/wake cycle with pineal gland
85
Sleeping and waking: Lesions in posterior hypothalamus:
hypersomnolence or coma
86
Sleeping and waking: Tuberomammillary nucleus in this region contains
histaminergic neurons with wide projections, arousal functions likely
87
Sleeping and waking: Tuberomammillary nucleus activated by
orexin, liberated by lateral nucleus. Failure of orexin function leads to nacrolepsy
88
Sexual arousal: A subset of neurons in the medial aspect of
preoptic nucleus is over twice as large in males than females
Rich in androgen receptors sensitive to circulating testosterone
89
Sexual arousal: Females estrogen rich neurons in
ventromedial nucleus
90
Memory
Mammillary bodies, limbic structure part of Papez circuit from hippocampus
91
Hypothalamic Inputs:
Come from many different places, but 2 general areas are key:
Parts of the forebrain, especially limbic system
Brainstem & spinal cord
92
Parts of the forebrain, especially limbic system
| Convey info needed for
the hypothalamus to mediate autonomic/somatic aspects of emotional states
93
Brainstem & spinal cord
| Convey
visceral and sensory information
94
Many inputs use
medial forebrain bundle, dorsal longitudinal fasciculus (DLF)
95
Hypothalamic outputs
Outputs use many of the same pathways used by inputs
| Cortical outputs end diffusely
96
Limbic system: Generates feelings/ emotions from
sensory inputs, evolved to promote survival so activity varies depending on physiologic needs
97
Limbic system: Limbic system includes
parts of brain that are primarily concerned with these functions
98
Limbic system: Bridges autonomic/ voluntary responses to
environmental changes
| Hypothalamus and cerebral cortex also involved
99
Limbic system: Mostly consists of
cingulate and parahippocampal gyri
100
Limbic cortex: 2 parts:
3-layered allocortex of hippocampus & septal area and mesocortex in parahippocampal gyrus, cingulate and insula
101
Subcortical nuclei:
amygdala, also hypothalamus, nucleus accumbens and reticular formation
102
Cingulate gyrus is superior to the
corpus callosum and can be followed around its posterior edge, the splenium, where it turns inferiorly as the isthmus and continues as the parahippocampal gyrus.
103
Uncus,
medial protrusion of anterior aspect of parahippocampal gyrus. The amygdala is deep to the uncus.
104
Superior border of the parahippocampal gyrus is the
hippocampal sulcus (seen on cut section)
105
At the hippocampal sulcus you find the
hippocampus, a medial temporal structure.
106
The limbic lobe and many structures it is interconnected with such as the hippocampus, make up the
limbic system, which is important in emotional responses, drive-related behaviors and memory.
107
Limbic system is Closely associated with
orbitofrontal cortex and temporal lobe
108
Amygdala:
emotional responses
109
Hippocampus:
learning & memory
110
Afferents to hippocampus: Input from septal nuclei is
modulatory in nature: affects chances that information in hippocampus will be retained
111
Afferents to hippocampus: Entorhinal cortex is
the main source; it gets info from olfactory (minor) and many other areas (major)
112
Hippocampus: Three distinct zones:
Dentate gyrus
Hippocampus proper (cornu ammonis)
Subiculum, transition between hippocampus proper and adjacent parahippocampal cortex
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Hippocampal connections: Afferent 2. Entorhinal cortex projects to
dentate gyrus
| Perforant pathway
114
Hippocampal connections: Afferent: 1. . Afferent fibers from
sensory cortex
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Hippocampal connections: Afferent: 3. Dentate neuron projects to
CA3
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Hippocampal connections: Afferent: 4. 4. CA3 neuron projects into
fimbria & CA1
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Hippocampal connections: Afferent: 5. CA1 neuron projects to
subiculum
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Hippocampal connections: Afferent: 6. Subiculum projects to
fimbria
| Alvear pathway
119
Hippocampal connections: Afferent: 7. Subicular neuron projects to
entorhinal cortex
120
Hippocampal connections: Afferent: 8. Entorhinal neuron projects to
sensory cortex
121
Fibers of the alveus collect and form the
fimbria, which transitions into the crus of the fornix.
122
The crura converge in the midline forming the
body of the fornix, which is located at the inferior edge of the septum pellucidum.
123
The fornix turns posteriorly and inferiorly forming the
columns of the fornix, which traverse the hypothalamus toward the mammillary bodies.
124
Fornix is the direct continuation of the
fimbria
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Axons from
subiculum and hippocampus (CA3)
126
Crus: arches up beneath
corpus callosum
127
Fornix has a long course under the
corpus callosum
128
Joins crus on other side, forming
trunk
| Near hippocampal commissure
129
Trunk divides into
two pillars, which split near anterior commissure
Precommissural fibers: Septal area
Postcommisural fibers: hypothalamus, mammillary body
130
Efferents from Hippocampus
Outputs from subiculum and entorhinal cortex
131
Papez circuit
1. Neurons in cingulate gyrus project back
2. Projection into entorhinal cortex
3. Projection into hippocampus
4. Fornix
5. Mammillothalamic tract
6. Projections from anterior nucleus of thalamus to cingulate cortex
132
Papez circuit
Interactions among limbic structures, cortex & hypothalamus
Papez proposed that emotional experiences were processed
Memory
133
Short-term
: hold information briefly in mind while you need it. A telephone number
134
Long-term:
Stored information, can be retrieved
| Explicit and implicit
135
Explicit:
recall of facts/ events, aka declarative memory or episodic memory
136
Implicit memory:
Performing a learned motor function, riding a bike
137
Working memory:
needed for task at hand, driving along a known route
138
Consolidation:
process of storing new information in long-term memory
139
Novel facts are relayed from
sensory association areas to hippocampus for encoding, processed, encoded info sent back to association area it came from and (for the most part) does not depend on hippocampus for retrieval
140
Bilateral removal of hippocampi impaired
declarative memory, could not form new:
```
Episodic memories (past personal experiences) or,
Semantic memories (ideas & concepts not related to personal experience) e.g. state capitals.
Working memory was intact and HM could learn new skills
```
141
Hippocampal asymmetries: Left anterior hippocampus and dorsolateral prefrontal cortex:
encode novel material involving language
142
Hippocampal asymmetries: Right hippocampus and inferior parietal lobe engaged in
spatial tasks like driving a car
143
Hippocampal asymmetries: Left anterior more active when material is novel,
as repetition makes it become familiar hippocampal activity shifts posteriorly
144
Amgydala: In anterior, medial temporal lobe; merges with
periamygdaloid cortex, part of uncus
3 nuclear groups:
Medial: olfaction
Central: hypothalamus, PAG; emotional responses
Basolateral: cortex; central nuclei; emotional responses
145
Amgydala: 3 nuclear groups:
Medial: olfaction
Central: hypothalamus, PAG; emotional responses
Basolateral: cortex; central nuclei; emotional responses
146
Amygdala afferents: All sensory association areas have
direct input to the lateral nucleus
147
Amygdala afferents: All these areas are also linked to
prefrontal cortex via association fibers so sensations can be cognitively evaluated
148
Amygdala afferents: Visual areas:
phobias, anxiety states
149
Most nuclei receiving afferents are
laterally situated, so collectively termed lateral nucleus
150
Amygdala fiber pathways: 1. Stria terminalis: from
hypothalamus & septal nuclei
151
Amygdala fiber pathways: 2. Ventral amygdalofugal pathway: from
thalamus, hypothalamus, orbital and anterior cingulate cortex
152
Amygdala efferent: Stria terminalis: Emerges from
central nucleus, follows curve of caudate; fibers go to septal area & hypothalamus then medial forebrain bundle and central tegmental tract
153
Amygdala efferent: Stria terminalis: Bed nucleus is regarded as
“extended amygdala” may be more active then amygdala in anxiety
154
Amygdala efferent: Ventral amygdalofugal pathway
Also synapses with nucleus accumbens (not shown)
155
Amygdala efferent: Periaqueductal gray (to medulla/ raphespinal tract)
Function: Antinociception
156
Amygdala efferent: Periaqueductal gray (to medullary recticulopinal tract)
Function: Freezing
157
Amygdala efferent: Norepinephrine medullary neurons
| Project to lateral gray horn
Function: ↑heart rate, ↑ blood pressure
158
Amygdala efferent: Hypothalamus/ dorsal nucleus of vagus (heart)
Function: ↓ heart rate, fainting
159
Amygdala efferent: Hypothalamus (release corticotropin RH)
Function: Stress hormone secretion
160
Amygdala efferent: Parabrachial nucleus to medullary respiratory nuclei
Function: Hyperventilation (panic attacks)
161
Klüver-Bucy Syndrome: Bilateral temporal lobe injury, involves
amygdala, parahippocampal gyrus
162
Klüver-Bucy Syndrome: Fearless, placid, no
emotional reactions, don’t respond to threats from others, don’t flee from threats
Amygdala damage
163
Klüver-Bucy Syndrome:
| Males become
hypersexual, indiscriminate will… um, with….. inanimate objects, different species
Amygdala damage
164
Klüver-Bucy Syndrome:
| Inordinate attention to all
sensory stimuli, sniff and examine everything orally. If possible to eat they will eat it
165
Klüver-Bucy Syndrome: May pick up the same object repeatedly
as they seem to recognize nothing (visual agnosia)
| Visual association cortex damage
166
Nucleus accumbens, aka ventral striatium: Stimulation: sense of
well-being
167
Nucleus accumbens, aka ventral striatium: “high” feeling due to
dopamine release in NA (and medial prefrontal cortex) from ventral tegmental area
168
Limbic loop in basal ganglia: Pleasure↑
ventral striatial dopamine release from ventral tegmental area in midbrain
169
Limbic loop in basal ganglia: Drive-related information to influence
movement/ behavior
170
Limbic loop in basal ganglia: Associate stimuli with
rewards
