The Fore Brain

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

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

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.

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.

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Dorsal nuclei

Medial

Anteriornucleargroup

Reticularnucleus

Ventralanterior

Ventrallateral

Ventralpostero-lateral

Lateralgeniculatebody

Medialgeniculatebody

Pulvinar

Lateraldorsal

Lateralposterior

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

Ventral nuclei

Thalamus

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

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.

Hypothalamus

These functions include:– Autonomic control – Emotional response– Temperature regulation– Food intake– Water balance– Sleep wake cycles– Endocrine function

Epithalamus forms 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

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.

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

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

Medulla Oblongata

The medulla plays an important role in maintaining certain autonomic functions including: – Heart rate– Respiration– Swallowing, sneezing & vomiting

Hanging

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

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.

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Figure 12.17a Cerebellum.

(a)

Medullaoblongata

Flocculonodular lobe

Fourth ventricle Posterior

lobe

Arbor vitae

Cerebellarcortex

Anterior lobe

Choroid plexus

Pons

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 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 System

It is a complex system with multiple functions. Included in it are the:– Septal nuclei– Cingulate gyrus– Parahippocampal gyrus– Dentate gyrus – Hippocampus– AmygdalaThese are all found in the cerebrum

Limbic System

In the diencephalon:

– Hypothalamus– Thalamic nuclei

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 System

The limbic system is our emotional brain.– Dentate gyrus is thought to regulate

happiness – Parahippocampal gyrus is thought to regulate

spatial memory

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Frontal eye field

Prefrontalcortex

Processes emotionsrelated to personaland social interactions

(b) Parasagittal view, right hemisphere

Olfactory bulbOrbitofrontalcortex

Olfactory tractFornix

Temporal lobe

Corpuscallosum

Premotor cortexPrimarymotor cortex

Cingulategyrus Central sulcus

Primary somatosensorycortex

Parietal lobe

Parieto-occipitalsulcus

Somatosensoryassociation cortex

OccipitallobeVisualassociationarea

Calcarine sulcusParahippocampalgyrus

UncusPrimaryolfactory cortex

Primaryvisual cortex

Primary motor cortex Motor association cortex Primary sensory cortexSensory association cortex Multimodal association cortex

It looks like a sea horse?

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Corpus callosum

Septum pellucidum

Olfactory bulb

Diencephalic structuresof the limbic system

•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body

Fiber tractsconnecting limbic system structures

•Fornix•Anterior commissure

Cerebral struc-tures of the limbic system•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus

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 Formation

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

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Figure 12.19 The reticular formation.

Visualimpulses

Reticular formationAscending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex