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.

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” the thalamus laterally are depicted as curving translucent structures.)

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.

These functions include: 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 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.

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 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 Amygdala These are all found in the cerebrum

Limbic System In the diencephalon: Hypothalamus Thalamic nuclei

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

The limbic system is our emotional brain. Dentate gyrus is thought to regulate happiness  Parahippocampal gyrus is thought to regulate spatial memory

Primary somatosensory cortex 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 Olfactory tract Primary visual cortex Fornix Temporal lobe Uncus Calcarine sulcus Primary olfactory cortex Parahippocampal gyrus (b) Parasagittal view, right hemisphere Primary motor cortex Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex

It looks like a sea horse?

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 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.

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)