Unit 4: The Brain PDF

Unit 4 The Brain Likitha S (Department of Psychology) Myelencephalon: The myelencephalon (or medulla), the most posterior division of the brain, is composed largely of tracts carrying signals between the rest of the brain and the body. It is a complex network of about 100 tiny nuclei th...

Unit 4 The Brain Likitha S (Department of Psychology) Myelencephalon: The myelencephalon (or medulla), the most posterior division of the brain, is composed largely of tracts carrying signals between the rest of the brain and the body. It is a complex network of about 100 tiny nuclei that occupies the central core of the brain stem from the posterior boundary of the myelencephalon to the anterior boundary of the midbrain. It is so named because of its netlike appearance (reticulum means “little net”). Sometimes, the reticular formation is referred to as the reticular activating system because parts of it seem to play a role in arousal. Likitha S (Department of Psychology) Metencephalon: The metencephalon, like the myelencephalon, houses many ascending and descending tracts and part of the reticular formation. These structures create a bulge, called the pons, on the brain stem’s ventral surface. The pons is one major division of the metencephalon; the other is the cerebellum (little brain) The cerebellum is the large, convoluted structure on the brain stem’s dorsal surface Likitha S (Department of Psychology) Mesencephalon: The mesencephalon, like the metencephalon, has two divisions. The two divisions of the mesencephalon are the tectum and the tegmentum. The tectum (roof) is the dorsal surface of the midbrain. In mammals, the tectum is composed of two pairs of bumps, the colliculi (little hills). The posterior pair, called the inferior colliculi, have an auditory function. The anterior pair, called the superior colliculi, have a visual-motor function, specifically to direct the body’s orientation toward or away from particular visual stimuli The tegmentum is the division of the mesencephalon ventral to the tectum. In addition to the reticular formation and tracts of passage, the tegmentum contains three colorful structures Likitha S (Department of Psychology)  The periaqueductal gray, the substantia nigra, and the red nucleus. The periaqueductal gray is the gray matter situated around the cerebral aqueduct, the duct connecting the third and fourth ventricles; it is of special interest because of its role in mediating the analgesic (pain-reducing) effects of opioid drugs. The substantia nigra (black substance) and the red nucleus are both important components of the sensorimotor system Likitha S (Department of Psychology) Likitha S (Department of Psychology) Diencephalon: The diencephalon is composed of two structures: the thalamus and the hypothalamus. The hypothalamus is located just below the anterior thalamus (hypo means “below”) It plays an important role in the regulation of several motivated behaviors (e.g., eating, sleep, and sexual behavior). It exerts its effects in part by regulating the release of hormones from the pituitary gland Likitha S (Department of Psychology) Telencephalon The telencephalon, the largest division of the human brain, mediates the brain’s most complex functions. It initiates voluntary movement, interprets sensory input, and mediates complex cognitive processes such as learning, speaking, and problem-solving. Cerebral cortex: The cerebral hemispheres are covered by a layer of tissue called the cerebral cortex (cerebral bark). the layer beneath the cortex is mainly composed of large myelinated axons, which are white and often referred to as the white matter. Because the cerebral cortex is mainly composed of small, unmyelinated neurons, it is gray and is often referred to as the gray matter Likitha S (Department of Psychology)  In humans, the cerebral cortex is deeply convoluted (furrowed). The cerebral hemispheres are almost completely separated by the largest of the fissures: the longitudinal fissure. The cerebral hemispheres are directly connected by a few tracts spanning the longitudinal fissure; these hemisphere-connecting tracts are called cerebral commissures. The largest cerebral commissure, the corpus callosum. The convolutions have the effect of increasing the amount of cerebral cortex without increasing the overall volume of the brain The two major landmarks on the lateral surface of each hemisphere are the central fissure and the lateral fissure. These fissures partially divide each hemisphere into four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe. Likitha S (Department of Psychology) Likitha S (Department of Psychology) Likitha S (Department of Psychology) Likitha S (Department of Psychology) Thank you Likitha S (Department of Psychology)