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
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