ANATOMY & PHYSIOLOGY OF CEREBRUM
The cerebrum is the largest part of the brain and occupies the anterior and middle parts of the cranial cavity. It is divided by a deep cleft into right and left cerebral hemispheres. Deep within the brain, the hemispheres are connected by a mass of nerve fibres called the corpus callosum. The superficial part of the cerebrum is composed of nerve cell bodies forming the cerebral cortex.
The cerebral cortex shows many enfoldings of varying depth. The exposed areas of the folds are called gyri or convolutions, separated by sulci or fissures. These convolutions help increase the surface area of the cerebrum.
Lobes of the Cerebrum
Each hemisphere of the cerebrum is divided into the following lobes:
- Frontal Lobe
- Parietal Lobe
- Temporal Lobe
- Occipital Lobe
The boundaries of these lobes are marked by deep sulci: central, lateral, and parieto-occipital sulci.
White Matter and Nerve Fibres
Within the cerebrum, the lobes are connected by masses of nerve fibres (white matter). These fibres include:
- Arcuate (association) fibres: Connect different parts of a cerebral hemisphere from one gyrus to another.
- Commissural fibres: Connect corresponding areas of the two hemispheres. The largest commissural fibre is the corpus callosum.
- Projection fibres: Connect the cerebral cortex with the grey matter of the lower brain and spinal cord. The internal capsule is a key projection fibre carrying all nerve impulses to and from the cortex.
FUNCTIONS OF THE CEREBRUM
- Mental activities such as memory, intelligence, reasoning, moral sense, and learning.
- Sensory perception, including pain, temperature, touch, sight, hearing, taste, and smell.
- Initiation and control of voluntary muscle contractions.
FUNCTIONAL AREAS OF THE CEREBRUM
The functional areas of the cerebrum are divided into motor and sensory areas, though both functions are anatomically mixed.
Motor Areas
The precentral area in the frontal lobe initiates voluntary muscle contractions. Fibres from these cells pass through the internal capsule, cross at the medulla oblongata, and descend to the opposite side of the body. Thus, the right motor cortex controls the left side of the body and vice versa.
The premotor area lies anterior to the motor area and coordinates orderly movements. The motor speech area controls muscles for speech and is dominant in the left hemisphere in right-handed people.
The frontal area (remaining frontal lobe) is responsible for behaviour, character, and emotional states.
Sensory Areas
The postcentral (sensory) area behind the central sulcus perceives sensations like pain, touch, and temperature. The right sensory cortex receives signals from the left body side and vice versa.
The parietal area helps in recognizing and understanding objects. The sensory speech area interprets spoken words and extends into the temporal lobe.
The auditory area in the temporal lobe interprets impulses from the inner ear via the vestibulocochlear nerves.
The olfactory area lies deep within the temporal lobe and interprets smell impulses, while the taste area perceives taste sensations from the tongue and palate. The visual area in the occipital lobe processes visual information from the optic nerves.
OTHER AREAS OF THE CEREBRUM
Deep within the hemispheres are groups of nerve cell bodies called nuclei, acting as relay stations between neurons. The main grey matter structures include:
1. Basal Nuclei
Located deep in the hemispheres, they influence skeletal muscle tone. When control is poor, movements become jerky or uncoordinated.
2. Thalamus
Two masses of nerve cells below the corpus callosum act as relay centers for sensory input before it reaches the cerebral cortex.
3. Hypothalamus
Situated below the thalamus and above the pituitary gland, it connects to the pituitary via nerves and blood vessels. It regulates hormone secretion and controls:
- Autonomic nervous system
- Hunger and thirst
- Body temperature
- Emotional responses (pleasure, fear, etc.)
- Sexual behaviour
- Biological rhythms (sleep–wake cycles)
Detailed Notes
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