#14105 - Forebrain - Neuroscience 1

Neuro-anatomy

Central nervous system

-Consists of part of the nervous system that are encased in bone: brain and spinal cord

Planes: Coronal, Sagittal Horizontal

Orientation of the CNS:

Dorsal/posterior- behind or nearer the back

Ventral/anterior : infront or near the front

Rostral: Towards the rostrum/nearer the head

Cadual- nearer the tail/further from the head

Median: In the midline

Medial: Nearer the midline

Lateral: Further from the midline

Brain

-Consists of three parts: Cerebrum, cerebellum, Brain stem

a) Cerebrum: rostral most and largest part of the brain when viewed from above. It is split down the middle into two cerebral hemispheres separated by deep sagittal fissure. The right cerebral hemisphere receives sensations from an controls movements of the left side of the body. Left cerebral hemisphere is concerned with sensations and movements on the right side of the body

b) Cerebellum: Lying behind the cerebrum is the cerebellum. It is primarily the movement control center. Left side of the cerebellum is concerned with movements of the left side of the body and right side of the cerebellum is concerned with movements of the right side

c) Brain stem: Best seen in midsagittal view of the brain. Brain stem forms the stalk from which the cerebra hemispheres and cerebellum sprout. Neurons relay information from the cerebrum to the spinal cord and cerebellum and vice versa. Brain stem is also the site where vital functions are regulated

A) FOREBRAIN:

• Telencephalon

  • Cerebral Cortex

  • Basal Ganglia

  • Limbic System (hippocampus and amygadala)

• Diencephalon

  • Thalamus

  • Hypothalamus

Cerebral Hemispheres of the cerebrum

-The cerebral hemispheres (cerebrum) make up a large proportion of the brain.

-They have an outer region of grey matter (the cerebral cortex) and an inner region of white matter. (Note that this is the opposite of the spinal cord, which has inner grey matter and outer white matter.)

-The superficial cerebral cortex is convoluted. The fo lds/bumps are called gyri and are separated by fissures/grooves called sulci. -This folded structure increases the surface of the cerebral cortex.

-The cortex has a series of functional subdivisions (eg. visual, auditory, somatosensory, motor, pre-motor etc) and each of these functional subdivisions forms part of a more complex processing network in which primary afferent information is fed into secondary areas including the parietal association areas, the inferotemporal cortex, the limbic regions and the frontal lobes.

-Lesions at different regions result in different functional losses: eg. Phineas Gage – orbital and medial prefrontal areas.

Core: lobes – frontal parietal, temporal: By convention the cerebrum is subdivided into lobes named after the bones of the skull that lie over them

Core: longitudinal (sagittal) sulcus

-The great longitudinal cerebral fissure/sulcus divides the cerebrum into its two hemispheres, which are joined by the corpus callosum.

Core: central sulcus

The central sulcus, which runs from the lateral sulcus to the great longitudinal fissure, separates the frontal lobe from the parietal lobe.

Core: pre-central gyrus: Immediately anterior to the central sulcus is the pre-central gyrus, which contains the primary motor cortex-controls voluntary movement. Its anterior border is formed by the pre-central sulcus.

Core: post-central gyrus : On the other side of the central sulcus is the post-central gyrus, which contains the primary somatosensory cortex- involved in somatic sensation. Its posterior border is formed by the post-central sulcus.

Core: lateral sulcus: The lateral sulcus, which runs posteriorly and superiorly from the base of the hemispheres, separates the frontal and temporal lobes.

Core: superior temporal gyrus, Wernicke’s area:Just below the lateral fissure is the superior temporal gyrus, which contains the primary auditory cortex and Wernicke’s area, a sensory speech area.

Core: insula Deep in the lateral fissure is a region of the cortex called the insula, which is thought to be important in planning and coordinating the movements needed for speech. Insula is revealed if the margins of the lateral fissure are gently pulled apart. The insula borders and seperates the frontal and temporal lobes

Extension: opercula :The parts of the frontal, parietal and temporal lobes overlying the insula are called the opercula.

Core: Broca’s area: This makes up part of Broca’s area, which is a region of the frontal lobe involved in the motor aspects of speech.

Core: parieto-occipital sulcus : The parieto-occipital sulcus can be identified on the medial aspect of a mid-saggital section, but not on a whole brain. It divides the parietal and occipital lobes. It is a particularly deep sulcus found roughly 1/5 of the distance from the occipital to the frontal pole.

Core: calcarine sulcus, calcarine gyrus :On the medial aspect of the occipital lobes the calcarine sulcus can be seen. It runs from the occipital pole to the parieto-occipital sulcus.

This is an important landmark because the primary visual cortex is located just on either side of it.

Core: cingulate sulcus The cingulate gyrus curves around the corpus callosum and is separated from the rest of the hemisphere by the cingulate sulcus. It is part of the limbic system.

Core: parahippocampal, hippocampal gyrus As it passes around the posterior portion of the corpus callosum, the cingulate gyrus is continuous with the parahippocampal gyrus (part of the temporal lobe).

• The hippocampus lies just deep to this gyrus, within the temporal lobe.

Core: uncus :The anterior part of the parahippocampal gyrus is curved into a hook shape and is known as the uncus.

Extension: collateral sulcus :The collateral sulcus runs along the inferior surface of the hemisphere, running anteriorly from below the calcarine sulcus.

Extension: thalamo-hypothalamic sulcus. :The thalamo-hypothalamic sulcus separates the thalamus from the hypothalamus within the diencephalon.

The functions of these various regions of the brain have been established mainly through studies of lesions or electrical stimulation.

These are limited, however, because it is very difficult to accurately perform a lesion so that it leaves all surrounding areas and connections intact.

Grey Matter of the Cerebral Hemisphere Core: cerebral cortex

The cerebral cortex forms the outer surface of the cerebral hemisphere (the grey matter) – it is a layer which is several millimetres thick consisting of nerve cell bodies, dendritic arborisations and synaptic interconnections.

Core: Hippocampus; allocortex – 3 layers The allocortex consists of 3 layers – it includes the hippocampus and the olfactory cortex.

Core: neocortex – 6 layers; cells and connections of layers: thalamic afferents end on layer 4/granular cells; output pyramidal cells in layers 3 and 5.

Most of the cortex evolved much later than the allocortex – it is called the neocortex. It consists of 6 layers:

1. Most superficial, few cell bodies, many dendritic and axonal processes in synaptic interaction.

2. Many small neurones (establish intracortical connections)

3. Medium-sized neurons giving rise to association and commissural fibres

4. Site of termination of afferent fibres from the specific thalamic nuclei

5. Origin of projection fibres to extracortical targets eg. basal ganglia, thalamus, brain stem and spinal cord. In the primary motor cortex of the frontal lobe, this layer contains the giant Betz cells which project fibres into the pyramidal tract.

6. Association and projection neurons.

Functional organisation

-Cerebral cortex is needed for conscious awareness, though, memory and intellect

-All sensory modalities ascend and are consciously perceived and interpreted in the light of previous experience

Core: columnar organisation

Basal ganglia:

-Deep to the cortex lies the basal ganglia-Collection of nuclear masses: caudate nucleus, putamen, globus pallidus

-Caudate nucleus- found next to the lateral wall of the lateral ventricle. It is separated from the putamen and globus pallidus by the internal capsule, a large fibre tract of afferent and efferent fibres passing to and from the cortex.

-Inovlved in the control of posture and movement- abnormalities result in basal ganglia disorders

-Straitum: Caudate nucleus and the putamen

-Putamen: lateral to the internal capsule and globus pallidus. Seperated from the globus pallidus by a thin lamina of nerve fibres- lateral medullary lamina. Lateral to the putamen is the claustrum which seperates the white matter into extreme and external capsule

-Caudate nucleus: Large head, tapering curved tail

White Matter of the Cerebral Hemisphere

-Beneath the cortical surface lies an enormous mass of nerve fibres all of which have their origin or termination (or sometimes both) within the cortex.

-There are three main types of fibre in the white matter: commissural, association and projection.

Core: classification of commissural fibres. origin, course and major terminations of fibres in: corpus callosum: origin, course and major terminations of fibres in the fornix

A) Commissural fibres: connect left and right structures, run between the two cerebral hemspheres, connecting functionally related structures.

E.g:

1) They run in the corpus callosum (largest commissural fibre): The corpus callosum is the largest bundle of commissural fibres. It spans the two cerebral hemispheres and connects corresponding regions of neocortex for all but the temporal lobes (these have their own connection, the anterior commissure).

Corpus callosum: Found on both sides of the cortex-Splenium,...