The brain and spinal cord are collectively known as the central neural system. The brain is the ’command and control system’ and controls voluntary and involuntary movement of organs. It helps to maintain the balance of our body, thermoregulation, circadian rhythms, hunger, thirst, the activities of the endocrine glands, human behavior, vision, hearing, speech, memory, intelligence, emotions and thought.
The brain lies inside the skull, and is protected by three meninges. The brain can be divided into three main parts – forebrain, midbrain and hindbrain. The forebrain is the largest part and consists of cerebrum, thalamus and hypothalamus. A deep cleft divides the cerebrum into two halves – the left and right cerebral hemispheres. Corpus callosum connects the two hemispheres and facilitates communication between them.
The cerebral cortex has prominent folds with ridges and depressions called gyri and sulci respectively. The neuron cell bodies concentrated in the cerebral hemispheres give grey colour to the region so grey matter. Due to the presence of myelinated axons, the inner part of the cerebral hemisphere appears white and is thus called white matter. It contains motor areas, sensory areas and association areas. Association areas are responsible for complex functions.
The thalamus acts as a major coordinating centre for sensory and motor signaling. The hypothalamus is contains the centres that control temperature, the circadian rhythms and the urge to eat and drink. It secrete hormones that control the pituitary, which in turn controls the secretions of other endocrine glands. Forebrain, includes the amygdala and hippocampus known as the limbic system. It controls the sexual behaviour, long-term memory, olfaction, and the expression of emotional reactions .
The cerebral aqueduct connects the third ventricle to the fourth ventricle of the brain. The dorsal portion of the midbrain consists corpora quadrigemina with reflex centers. The midbrain and hindbrain form the brain stem which acts as a relay station for auditory and visual information and every impulse conducted between brain and spinal cord passes through the brainstem. The hindbrain is formed of the pons, cerebellum and medulla oblongata. Cerebellum is responsible for coordinated body movement. The medulla oblongata acts as a link between the brain and spinal cord and control involuntary activities and saves us from harmful stimuli with reflex action. The path through which the reflex action is conducted is called the reflex arc. The reflex arc consists of a receptor, a sensory neuron, an association neuron, motor neuron and an effector organ.