Forebrain Notes

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.

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