The fore brain
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The Fore Brain. Diencephalon. Diencephalon. This represents the central core of the forebrain and is surrounded by the cerebral hemispheres. It is made up of three major paired structures:  The thalamus The hypothalamus The epithalamus. Diencephalon.

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The Fore Brain

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The fore brain

The Fore Brain

Diencephalon


Diencephalon

Diencephalon

This represents the central core of the forebrain and is surrounded by the cerebral hemispheres. It is made up of three major paired structures: 

  • The thalamus

  • The hypothalamus

  • The epithalamus


Diencephalon1

Diencephalon

Thalamus is a bilateral egg shaped nuclei that makes up 80% of the diencephalon.

It is the relay station for information coming into the cerebral cortex.


Thalamus

Thalamus

The thalamus is a collection of smaller nuclei, each having a functional specialty.

All afferent impulses converge on to the thalamus and synapse with at least one of its nuclei.

It serves as the gateway to the cerebral cortex.


Thalamus1

Thalamus

All the sensory fibers except olfaction go through one of the thalamic nuclei.

For example the lateral geniculate nuclei receive input from the retina.

The thalamus also plays an important role in sleep.


The fore brain

Dorsal nuclei

Medial

Lateral

dorsal

Lateral

posterior

Pulvinar

Anterior

nuclear

group

Medial

geniculate

body

Reticular

nucleus

Lateral

geniculate

body

Ventral

postero-

lateral

Ventral

anterior

Ventral

lateral

Ventral nuclei

(a) The main thalamic nuclei. (The reticular nuclei that “cap” thethalamus laterally are depicted as curving translucent structures.)


Thalamus2

Thalamus

Disorders of the Thalamus are usually due to stroke which can lead to the thalamic pain syndrome.


Hypothalamus

Hypothalamus

Hypothalamus lies just below the thalamus and forms the lower walls of the third ventricle.

It is the major visceral control center of the body and is the major center for regulating the body’s homeostatic mechanisms.


Hypothalamus1

Hypothalamus

These functions include:

  • Autonomic control

  • Emotional response

  • Temperature regulation

  • Food intake

  • Water balance

  • Sleep wake cycles

  • Endocrine function


The fore brain

Epithalamusforms the roof of the third ventricle. Its most visible landmark is the pineal gland which secretes melatonin and is involved in the sleep wake cycle.


Brains stem

Brains Stem

The brain stem is made up of the midbrain, pons and medulla oblongata. The brain stem produces programmed automatic behaviors necessary for survival.

It is similar in make up to the spinal cord and consists of projection fibers.


The fore brain

Pons

It is noticeable as a bulge on the anterior surface of the brain stem.

It is made up of conduction tracts.

Dorsally it forms part of the forth ventricle.


Medulla oblongata

Medulla Oblongata

It is the most inferior part of the brain stem. As it passes through the foramen magnum, it becomes the spinal column.


Medulla oblongata1

Medulla Oblongata

The medulla plays an important role in maintaining certain autonomic functions including: 

  • Heart rate

  • Respiration

  • Swallowing, sneezing & vomiting


Hanging

Hanging

The medulla oblongata is destroyed when a person is hung, leading to “instant” death.


Cerebellum

Cerebellum

It consists of two hemispheres connected by the vermis. It is highly convoluted and has gyri known as folia.

The cerebellum controls body movements. It is also involved in recognizing the sequence of events so adjustments in limb action can be made. Disorders are described as an ataxia.


Figure 12 17a cerebellum

Figure 12.17a Cerebellum.

Anterior lobe

Arbor vitae

Cerebellar

cortex

Pons

Fourth

ventricle

Posterior

lobe

Medulla

oblongata

Flocculonodular lobe

Choroid plexus

(a)


Functional brain systems

Functional Brain Systems

Functional brain systems are networks of neurons that incorporate various areas of the brain. Two major systems are the:

  • Limbic system

  • Reticular formation


Limbic system

Limbic System

Limbic System is a groups of structures located on the medial aspect of each cerebral hemisphere and the diencephalon. Its cerebral structures encircle the brain stem.


Limbic system1

Limbic System

It is a complex system with multiple functions. Included in it are the:

  • Septal nuclei

  • Cingulate gyrus

  • Parahippocampal gyrus

  • Dentate gyrus

  • Hippocampus

  • Amygdala

    These are all found in the cerebrum


Limbic system2

Limbic System

In the diencephalon:

  • Hypothalamus

  • Thalamic nuclei


Limbic system3

Limbic System

The limbic system is our emotional brain.

  • The Amygdala recognizes angry or fearful facial expressions and assesses danger.

  • The cingulate gyrus plays a role in expressing our emotions through gestures and helping us to “cope”.

  • The hippocampus is involved with long term memory


Limbic system4

Limbic System

The limbic system is our emotional brain.

  • Dentate gyrus is thought to regulate happiness 

  • Parahippocampal gyrus is thought to regulate spatial memory


The fore brain

Cingulate

gyrus

Primary

motor cortex

Premotor cortex

Central sulcus

Corpus

callosum

Primary somatosensory

cortex

Frontal eye field

Parietal lobe

Somatosensory

association cortex

Prefrontal

cortex

Parieto-occipital

sulcus

Occipital

lobe

Processes emotions

related to personal

and social interactions

Visual

association

area

Orbitofrontal

cortex

Olfactory bulb

Primary

visual cortex

Olfactory tract

Fornix

Uncus

Calcarine sulcus

Temporal lobe

Primary

olfactory cortex

Parahippocampal

gyrus

(b) Parasagittal view, right hemisphere

Motor association cortex

Primary sensory cortex

Primary motor cortex

Sensory association cortex

Multimodal association cortex


It looks like a sea horse

It looks like a sea horse?


The fore brain

Fiber tracts

connecting limbic

system structures

Septum pellucidum

Diencephalic structures

of the limbic system

Corpus callosum

•Fornix

•Anterior thalamic

nuclei (flanking

3rd ventricle)

•Anterior commissure

Cerebral struc-

tures of the

limbic system

•Hypothalamus

•Mammillary

body

•Cingulate gyrus

•Septal nuclei

•Amygdala

•Hippocampus

•Dentate gyrus

•Parahippocampal

gyrus

Olfactory bulb


Reticular formation

Reticular Formation

This system extends from the medulla oblongata, pons and midbrain.

The reticular formation is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli.


Reticular formation1

Reticular Formation

Lesions affecting the reticular formation cause severe alterations in level of consciousness and coma.


Figure 12 19 the reticular formation

Figure 12.19 The reticular formation.

Radiations

to cerebral

cortex

Visual

impulses

Auditory

impulses

Reticular formation

Descending

motor projections

to spinal cord

Ascending general

sensory tracts

(touch, pain, temperature)


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