Hindbrain (Parts and Function)
The hindbrain has three parts: medulla oblongata; cerebellum; and pons. The medulla oblongata, also called medulla or myelencephalon, is an enlargement where the spinal cord enters the brain. It contains centres that control several visceral (autonomic homeostatic) functions, such as breathing, heart and blood vessel activity, swallowing, vomiting, and digestion (gastric secretions). It serves as a screen for information that leaves or enters the brain. The medulla oblongata is well developed in all the vertebrates.
The cerebellum is a dorsal outgrowth of the medulla. In cartilaginous fishes it has anterior and posterior lobes. In bony fishes it is large in actively swimming forms; and in passive swimmers, as well as in amphibia it is rudimentary. In other tetrapods, the cerebellum is laterally expanded into lobes which provide locomotory control of
Cerebellum is large in birds and mammals reflecting their complex locomotor pattern i.e. agility of limb movement and balance. The cerebellum coordinates
movements, receives sensory information about the position of the joints and length of the muscles, as well as from the auditory and visual systems. The pone is a bridge of transverse nerve tracts from the cerebrum of the forebrain to both sides of the cerebellum.
Midbrain (Parts and Function)
The midbrain or mesencephalon, originally a centre for coordinating reflex responses to visual output, has taken an added function related to touch (tactile) and auditory (hearing) input. The roof of the midbrain is called optic tectum, which is a thickened region of gray matter that integrates visual and auditory signals. The lateral outgrowths from it form the optic lobes. Fig. 2.13, 2.14
Forebrain (Structure and Function)
The forebrain has two main parts: the diencephalon and telencephalon. During evolution both the diencephalon and telencephalon progressively increased in size and complexity to handle more and more sensory and motor functions, which are most sophisticated.
The diencephalon lies just in front of the midbrain and contains the pineal gland (epiphysis), pituitary gland (hypophysis), hypothalamus, and thalamus. The hypothalamus lies below the thalamus and regulates functions, such as body temperature, sexual drive, carbohydrate metabolism, hunger, and thirst. (Hypothalamus is the source of two sets of hormones, posterior pituitary hormones and releasing hormones of the anterior pituitary). Part of hypothalamus called suprachiasmatic nucleus, functions as our biological clock. The thalamus relays all sensory information to higher brain centers i.e.
1-The thalamus contains many different nuclei, each one dedicated to sensory information of a particular type. Incoming information from all the senses is sorted out in the thalamus and sent on to the appropriate higher brain centres for further interpretation and indignation The thalamus also receives input from the cerebrum and from parts of the brain that regulate emotion and arousal, making it an important station for controlling access to the cerebrum
The telencephalon is divisible into: cerebrum, divided into left and right cerebral hemispher; olfactory bulbs (not developed in many mammals including man); limbic system; and corpus striatum.
Each cerebral hemisphere consists of: an outer covering of gray matter, the cerebral cortex; and internal white matter with cluster of nuclei, the basal ganglia. The cerebral cortex is the largest and more complex part and has changed the most (increased in size and complexity) during vertebrate evolution. It is highly folded. The two hemispheres are connected by a thick band of fibres known as corpus callosum. The surface of each cerebral hemisphere has four discrete lobes; frontal lobe, parietal lobe, occipital lobe and temporal lobe. Two functional cortical areas, motor cortex and somatosensory cortex, form the boundary between frontal lobe and parietal lobe.
The motor cortex functions mainly in sending commands to skeletal muscles while somatosensory cortex receives and partially integrates signals from touch, pain, pressure, and temperature receptors throughout the body. Other areas of cortex are involved in the perception of visual or auditory signals from the environment. In humans, this includes the ability to use language both written and spoken.
The limbic system, though still only loosely defined includes parts of the thalamus, hypothalamus, and inner portions of the cerebral cortex, including two nuclei called the amygdala and hippocampus, are said to be concerned with emotions and memory-learning, reasoning, and personality. Fig. 2.15.
Olfactory bulbs; well developed in fishes and early terrestrial vertebrates but located deep in frontal lobe of cortex in mammals especially in primates, are–basically concerned with sense of smell (olfaction).