Anatomy of Forebrain
Forebrain
The forebrain is the largest part of the brain that has two main parts i.e. cerebrum and diencephalon. The limbic system is also a part of the forebrain.
The cerebrum has two parts;
- Cerebral cortex
- Olfactory lobe
Cerebral cortex
The outer thin surface of the cerebrum is called the cerebral cortex which is composed of grey matter. It contains cell bodies of neurons along with non-myelinated fibers and dendrons. The outer surface of the cerebral cortex has depressions called sulci and elevations called gyri. The sulci and gyri increase the surface area of the cerebral cortex which allows more neurons to be packed into the cortex, hence they determine intelligence. The inner medulla is composed of white matter which has axons of nerve cells.
Cerebral hemispheres
The cerebrum consists of two hemispheres called the left cerebral hemisphere and the right cerebral hemisphere. These hemispheres are separated by a long deep fissure known as corpus callosum. Each hemisphere has three layers i.e. super-lateral layer, medial layer and inferior layer. Both hemispheres are internally connected by a thick band of nerve fibers called corpus callosum. The interior fold of the corpus callosum I called genu while the posterior fold is called a splenium.
Lobes of the cerebral hemisphere
Each cerebral hemisphere is further divided into four lobes which are divided by deep fissures sulci. These lobes are;
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
The frontal and parietal lobes are separated by the central sulcus.
The parietal and occipital lobes are separated by parieto-occipital sulcus.
The temporal lobe is separated from the parietal and occipital lobe by the lateral sulcus.
Olfactory lobe or Rhinencephalon
The olfactory lobe is a pair of lobes located at the anterior side of the cerebrum. Each lobe has an olfactory peduncle and an olfactory bulb that's concerned with the sense of smell.
Diencephalon
The diencephalon is the middle structure largely embedded in the center of the brain. Its cavity forms the greater part of the 3rd ventricle. The hypothalamic sulcus divides the diencephalon into dorsal and ventral parts. The dorsal part of the diencephalon consists of the thalamus, hypothalamus and meta thalamus and the ventral part of the diencephalon consists of the hypothalamus and sub-thalamus.
Thalamus
The thalamus is situated in the form of a pair on the lateral wall of the 3rd ventricle and the floor of the central part of the diencephalon. It is composed of interconnected masses of grey and white matter having an ovoid shape and located on either side of the 3rd ventricle. Both sides of the thalamus are joined together by inter-thalamic adhesion. The thalamus contains multiple nuclei which perform specific functions.
Hypothalamus- The master of the master gland
The hypothalamus is located in the anterior portion of the 3rd ventricle and under the thalamus. It is much smaller in size but it has incredible functions in the body. It contains several distinct nuclei that perform specific functions. It acts as an engine for the endocrine system and controls the secretions of the pituitary gland.
The pituitary gland is connected to the hypothalamus situated in the bony cavity. It releases various hormones that influence the body's organs and glands.
Epithalamus
The epithalamus is located on the posterior side of the thalamus. It is a very small area that consists of the pineal gland that releases melatonin. Melatonin controls the sleep-wake cycle.
Subthalamus
The subthalamus is located below the thalamus which is a part of the basal ganglia. It consists of some important nuclei such as red nuclei and substantia nigra.
Limbic system
The limbic system is a group of structures found deep beneath the cerebral cortex and just above the brainstem that controls emotions, memory and some motor functions. The limbic system has the following major parts;
Amygdala
The amygdala is a small almond-shaped structure located under the thalamus, deep immediately within the temporal lobe and adjacent to the hippocampus. It is often known as the emotional center of the brain.
The amygdala is a collection of nuclei such as the lateral nucleus, basal nucleus, accessory basal nucleus, central nucleus, medial nucleus and cortical nucleus which are further divided into sub-nuclei.
Hippocampus
The hippocampus is a seahorse-like structure located deep in the temporal lobe of each cerebral hemisphere. Several associated structures with the hippocampus are dendate gyrus, hippocampal proper, subiculum and fornix which is the main output fiber from the hippocampus.
Basal ganglia
Basal ganglia lie under the anterior portion of lateral ventricles that is made up of grey matter. It is a collection of subcortical nuclei that include caudate, putamen, globus pallidas, substantia nigra, subthalamic nuclei, nucleus accumbens and olfactory cubicle.
Cingulate Gyrus
The cingulate gyrus is an arc-shaped structure located in the medial aspect of the cerebral hemisphere just superior to the corpus callosum and separated by the corpus sulcus.
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