Hippocampus, limbic and olfactory system

Question 1

Location of the hypothalamus

Answer 1

Most ventral part of the diencephalon, lying beneath the thalamus and ventromedial to the subthalamus,.

It forms the floor and lower part of the lateral wall of the third ventricle, below the hypothalamic sulcus

Question 2

Visualisation of the hypothalamus on the base of the brain

Answer 2

Parts of the hypothalamus can be seen occupying the small area circumscribed by the crura cerebri, optic chiasm and optic tracts.

Between the rostral limits of the two crura cerebri on either side of the midline lie two distinct, rounded eminences, the mamillary bodies which contain the hypothalamic mamillary nuclei

Question 3

Location of the pituitary

Answer 3

Arises from the thin infundibulum found at the apex of the tuber cinereum

Question 4

Arrangement of the pituitary

Answer 4

Two major cytologically distinct parts, the posterior pituitary or neurohypophysis and the anterior pituitary or adenohypophysis,

The two parts are closely linked by the hypophyseal vessels which derive from the ICA

Question 5

Answer 5

Question 6

Input to the hypothalamus

Answer 6

Both circulatory and neural in origin.

Circulating blood provides physical, chemical and hormonal signals.

Neural signals come from a number of sources

Question 7

Neural stimuli to the hypothalamus

Answer 7

Largest input originates from limbic structures, the hippocampus and the amygdala.
Fibres of hippocampal origin constitute the fornix, which terminates in the medial mamillary nucleus.

Fibres from the amygdala run in the stria terminalis.

The nucleus solitarius of the medulla projects to the hypothalamus conveying information derived from the ANS.

Monoaminergic projections ascend in the medial forebrain bundle and the reticular formation provides input both directly and indirectly via the thalamus.

Question 8

Answer 8

Question 9

Answer 9

Question 10

Output of te hypothalamus

Answer 10

Both circulatory and neural.

It projects to the pituitary.

Neural output:

Descending fibres pass to the brainstem and some reach the spinal cord, it thus influences the reticular formation and exerts control over the autonomic system

Ascending connections pass to the limbic system both directly and via the thalamus

Question 11

Lateral hypothalamus

Answer 11

Region lying medial and ventral to the structures of the subthalamus,.

It is traversed longitudinally by many fibres including the medial forebrain bundle.

It is involved in the control of food and water intake. Lesions can cause aphagia and adipsia

Question 12

Supraoptic nucelsu

Answer 12

Found in the medial reigion of the thalamus.

Produces ADH

Question 13

Parventricular nucleus

Answer 13

Synthesies oxytocin

Question 14

Passage of supraoptic and paraventricular axons

Answer 14

Pass to the neurohypophysis in the hypothalamohypophyseal tract where they are released into the capillary bed and thus reach the general ciruclation

Question 15

Dopamine synthesis in the hypothalamus

Answer 15

Synthesised by neurones of the hypothalamic arcuate nucleus. It acts to inhibit prolactin release

Question 16

Suprachiasmatic nucleus

Answer 16

Concerned with control of diurnal rhythmns and the sleep/waking cycle. Receives some afferent fibres directly from the retina

Question 17

Ventromedial nuclei

Answer 17

Lie deep to the lateral wall of the third ventricle.
Concerned with the control of food and fluid intake.

Equated with the satiety centre.

Question 18

Activation of posterior hypothalamus

Answer 18

SNS

Question 19

Activation of anterior hypothalamus

Answer 19

PNS

Question 20

Entry of information to the limbic system?

Answer 20

Either directly to the amygdala or indirectly to the hippocampal formation via the entorhinal area.

Question 21

Amygdala

Answer 21

Vital to motivational and emotional connotations of expereince

Question 22

Hippocampal formation

Answer 22

Essential for episodic memory

Question 23

Location of the amygdala

Answer 23

Lies near the temporal pole, between the inferior horn of the lateral ventricle and lentiform complex

Question 24

Afferents to amygdala

Answer 24

Receives afferents from the inferior temporal association cortex, the thalamus, septum and olfactory tract.

It also receives catecholamine and sertonin containing projections from the brainstem in the medial forebrain bundle

Question 25

Efferents of the amygdala

Answer 25

Principle efferent is in th stria terminalis, which runs in the wall of the lateral ventricle, following the curvature of the caudate nucleus to terminate in the hypothalalmus. Efferent projections to the nucleus accumbens permit motor behavioural responses

Question 26

Answer 26

Question 27

Septum

Answer 27

Lies beneath the rostral part of the corpus callosum. It interconnects with the amygdala and projects to the hypothalamus via the medial forebrain bundle. It also connects to the monoaminergic nuclei in the brainstem It does so via fibres that project to the habenular nuclei of the diencephalon and constitute the stria medullaris thalami. The habenular nuclei project via the fasciculus retroflexus to the interpeduncular nuclei.

Question 28

Orbital frontal cortex

Answer 28

Comproses the frontal covexity and the orbital frontal cortex. Receives afferent information about the world from the posterior association cortex.Projections from the posterior association cortex to the inferior temporal neocortex also permit entry of this information into the limbic system.

Question 29

Projections of the orbital frontal cortex

Answer 29

To inferior temporal neocortex via the uncinate fasciculus Also projects directly to the hypothalamus

Question 30

Three kinds of memory processes

Answer 30

Episodic Semantic Implicit

Question 31

Episodic memory

Answer 31

Learning and recollection of autobiographical events and dependent on the hippocampal formation and its connections

Question 32

Semantic memory

Answer 32

Acquired knowledge of the meaning of verbal and perceptual context Middle and inferior temporal gyri

Question 33

Implicit memory

Answer 33

Sensorimotor skills and is dependent on corticosubcortical motor systems

Question 34

Components of the hippocampal formation

Answer 34

Hippocampus Dentate gyrus Parahippocamnpal gyrus.

Question 35

Answer 35

Question 36

Answer 36

Question 37

Hippocampal afferents

Answer 37

Principally from the inferior temporal cortex vian the entirhinal area of the tempraol lobe Also receives fibres from the contralateral entorhinalm ara and the hippocampus via the fornix system and hippocampal comsisure

Question 38

Principle hypothalamic effernt

Answer 38

Fornix which is a prominent C-shaped fascicle of fibres that links the hippocampus with the mamillary body of the hypothalamus and with the septum.

Question 39

Passage of the fornix

Answer 39

Efferent fibres converge on the ventricular surface of the hippocampus as the fimbira. This passes posteriorly and superiorly to become continuous with the crus of the fornix which then curves forward beneath the splenium of the corpus callosum. The crura unite in the midline beneath the corpus callosum to form the body of the fornix. Some fibres cross to the opposite side through the small hippocampal commisure. As it passes forwards beneath the corpus callosum, the body of the fornix divides into two columns which form the anterior border of the foramen of Monro and enter the hypothalamus where the majority of fibres terminate in the mamillary body.

Question 40

Features of the cingulate gyrus

Answer 40

Continuous with the parahippocampal gyrus around the splemnium of the corpus allosum.

Question 41

Passage of olfactory efferents

Answer 41

Olfactory efferents are specialised ciliated nerve cells that lie in the olfactory epithelium of the nasal cavity. Their axons assemble into numerous small fascicles that enter the cranial cavity through the cribiform plate and then attach to the olfactory bulb on the inferior surface of the frontal lobe. Prelimianry processing of olfactory information occurs within the olfactory bulbe which contains interneuonres and large mitral cells. Axons leave the bulb in the olfactory tract.

Question 42

Answer 42

Question 43

Passage of the olfactory tract

Answer 43

Passes backwards on the basal surface of the frontal lobe. Just before reaching the level of the optic chiasm, most olfactory tract fibres are deflected laterally in the lateral olfactory stria, these fibres pass into the depths of the lateral fissure which they cross to reach the teporal lobe, terminating mainly in the priamry olfactory cortex of the uncus and in the subjacent amygdala.

Question 44

Olfactory association cortex

Answer 44

Adjacent to the uncus, part of the parahippocampals gyrus or entorhinal area constitutes the olfactory association cortex

Question 45

Pyriform cortex

Answer 45

The collective priamry and association olfactory cortex

Question 46

How is the olfactory projection unique among sensory afferents

Answer 46

2 neurones. Does not projevt via the thalamus