ANA 303 Limbic system

Question 1

The limbic system comprises of

Answer 1

The hippocampal formation
Septal area
Amygdala
Prefrontal cortex
Cingulate gyrus

Question 2

What is the hippocampal formation and what does it consist of?

Answer 2

The hippocampal formation is a prominent C-shaped structure bulging in the floor of the temporal horn of the lateral ventricle

Hippocampus (sea horse)
Dentate gyrus (tooth-like bump)
Subicular cortex: pre and parasubiculum

Question 3

Layers of the hippocampus

Answer 3

(1) External Plexiform Layer
Situated adjacent to the inferior horn of the lateral ventricle
Contains axons of pyramidal cells and hippocampal afferent fibers from the entorhinal cortex (i.e., the alvear pathway);
(2) Stratum Oriens
Contains basal dendrites and basket cells
(3) Pyramidal Cell Layer
Contains the pyramidal cells of the hippocampus
(4) Stratum Radiatum and
(5) Stratum Lacunosum-moleculare
The last two layers contain the apical dendrites of the pyramidal cells and hippocampal afferents from the entorhinal cortex

Question 4

The pyramidal cells of the hippocampus and locations

Answer 4

The pyramidal cells of the hippocampus are arranged in a C-shaped fashion, which is interlocked with another C-shaped arrangement of the dentate gyrus.

The hippocampus is divided into a number of distinct fields: CA1, CA2, CA3, and CA4.

The pyramidal cells situated closest to the subiculum are referred to as the CA1 field, whereas the CA4 field is located within the hilus of the dentate gyrus.

Question 5

Layers of the dentate gyrus is also multilayered

Answer 5

(1) Granular Cell Layer
Granule cells are the principal cells
Their axons (Mossy fibres) synapse with CA3 pyramidal cells

(2) Polymorphic Cell Layer
Composed of modified pyramidal cells
Lies deep to the granule cell layer.

(3) Molecular cell layer
Is apposed to the molecular layer of the hip…
Contains mainly axons of hippocampal afferent fibers.

Question 5

Describe the subiculum

Answer 5

A transitional region between the entorhinal cortex and hippocampus.
The primary histological distinction between the hippocampus and subicular cortex is a thicker pyramidal cell layer.

Question 6

Afferent Connections of the Hippocampal Formation

Answer 6

The entorhinal cortex is a major source of inputs

Different groups of fibres arise from the entorhinal cortex laterally and medially

Lateral perforant pathway
Into the ML of the hippocampus

Medial perforant pathway
Into the alveus through the white matter adjoining the subiculum and ending as the fornix

Prefrontal cortex, anterior cingulate gyrus, premammillary region, brainstem

Question 7

Efferent Connections of the Hippocampal Formation

Answer 7

Efferent fibres arise from pyramidal cells from hippocampus and the subiculum

Axons of these cells contribute to the fornix massiveness

Thus, 3 components of the fornix system exist in the hippocampal formation

The Pre-commissural Fornix
Passes rostral to the ant.commissure and supplies the septal area

The Post-commissural Fornix
Innervates the diencephalon

Commissural component
Connects the hippocampi
Has clinical significance

Question 8

Pyramidal Cells

Answer 8

Pyramid-shaped
Conical-shape cell body of over 30um with an apex directed towards the surface
Cylindrical axons arise from the bases of the cells & pass down into the underlying white matter.
They are output cells
Betz cells – largest, giant pyramidal cells

Question 8

Functions and Dysfunctions of the H.F

Answer 8

Modulation of different functions:
Learning and memory
Aggressive behaviour
Autonomic and endocrine functions

Question 9

Diseases associated with the limbic system

Answer 9

Alzheimer’s
Schizophrenia
forms of epilepsy

Question 10

Describe the The septal area

Answer 10

The histological appearance of the septal area differs between humans and other animals.
In animals, there exists a dorsal septal area:
Carries the lateral and medial septal nuclei.
In humans, a dorsal septal area is not present, only a ventral septal area.
Two cell groups are sometimes associated with the septal area:
(1) the bed nucleus, and
(2) the nucleus accumbens, close to the Band of Broca

Question 11

Afferent connections to the s.a.

Answer 11

The septal area receives sensory afferent fibres from the:
Medial olfactory stria
Monoaminergic systems of the brainstem
Hippocampal formation
Amygdala, and
Feedback signals from the lateral hypothalamus.
The septal area serves principally as a relay of the hippocampal
formation to the hypothalamus.

Question 12

Efferent connections from the S.A.

Answer 12

The primary efferent projections of the septal area are directed on the hypothalamus and hippocampal formation
Fibres to the hypothalamus arise primarily from the lateral septal nucleus

The hippocampal formation uses the septal area as a relay nucleus to modulate functions of the hypothalamus

Question 13

The nuclei of the diagonal band of Broca have widespread connections with other parts of the limbic system:

Answer 13

Olfactory,
Prefrontal
Anterior cingulate cortices
Amygdala
Mammillary bodies
Habenular complex, and
Mediodorsal thalamic nucleus

Question 14

Function of the septal area

Answer 14

It serves not only as a relay for the transmission of hippocampal impulses to the hypothalamus, but also as a feedback system to the hippocampal formation.

Functions of the septal area are highly similar to those of the hippocampal formation.

Like the hippocampal formation, the septal area has been implicated in the control of functions normally attributable to the hypothalamus, such as aggression, rage, autonomic functions, self-stimulation, and drinking behaviour.
Septal rage.

Question 15

amygdala

Answer 15

In humans, the amygdala is located deep to the uncus

It comprises various nuclei, which differ in their anatomical connections and neurochemical and physiological properties.

The amygdala contains a cortical mantle called the pyriform lobe that provides significant input to the amygdala

Question 15

The major groups of nuclei include the

Answer 15

Lateral
Basal
Medial
Anterior
Central and
Cortical nuclei.

Question 16

Functionally, the amygdaloid complex is divided into two components:

Answer 16

(1) A Corticomedial Group
Comprises the cortical, medial, and medial aspect of the basal nuclei
(2) A Basolateral Group,
Comprises the lateral, central, and lateral aspects of the basal nuclei

Question 17

How is the amygdala is intimately related to the pyriform lobe?

Answer 17

The cortex immediately adjacent to the amygdala at rostral levels of this structure is referred to as the prepyriform area, and more posterior regions of the pyriform lobe are referred to as the periamygdaloid cortex.

Question 18

Basic function of the limbic system

Answer 18

Is the brain’s emotional powerhouse
Maintains body homeostasis
Controls fight/flight/fright response
Forms and retrieves memories

Question 19

What is the executive center of the brain

Answer 19

prefrontal lobes

Question 20

What is the emotional center of the brain

Answer 20

limbic system

Question 21

What is the survival center of the brain

Answer 21

brain stem

Question 21

Function of the cingulate gyrus

Answer 21

A pathway that transmits messages between the inner between the inner and outer portion of the limbic system and helps regulate emotions and pain

Question 22

Function of Hypothalamus

Answer 22

Responsible for the production of essential hormones that control temperature regulation, thirst, hunger, sleep, mood, sex drive and the release of other hormones in the body.

Question 23

Hippocampus

Answer 23

Involved in forming memory, organizing, storing and retrieving it. It helps in determining how you respond (including emotional responses) to the world around you

Question 24

Amygdala

Answer 24

It gets direct sensory information, which it learns, stores and uses to control emotional responses, including enabling your body to react quickly to the sight or sound of a threat

Question 25

The limbic system and the PAG

Answer 25

These limbic structures directly or indirectly communicate with the hypothalamus and midbrain PAG

A critical function of the limbic system is to regulate functions associated with the hypothalamus and/or PAG