the diencephalon is a small central region of the brain it serves as a relay Center for sensory and motor pathways traveling between the brain stem and the cerebrum the diencephalon is divided into four regions the thalamus consists of a pair of oval masses of gray matter that lie on each side of the third ventricle the thalamus is often described as a relay station because almost all sensory information except for smell passes through the thalamus before being sent on to its destination it is also involved with processing the information and directing signals to various regions of the brain due to its involvement in these complex networks the thalamus plays a role in several important functions ranging from arousal to consciousness the epithalamus is the posterior sub-region that forms part of the roof of the diencephalon the epithalamus controls the pineal gland and endocrine gland that secretes the hormone melatonin this hormone controls sleep wake Cycles the hypothalamus forms the anterior inferior sub-region of the diencephalon it plays a major role in maintaining homeostasis and regulating hormone release let's look at a few of its major functions the hypothalamus controls most of the endocrine system's functions the hypothalamus does this by secreting hormones that control the anterior pituitary gland in turn secretions from the anterior pituitary control metabolism growth stress responses and reproduction let's look at this illustration at the right side of the screen this illustration shows the HPA axis the hypothalamus pituitary adrenal gland axis when someone is stressed the hypothalamus releases corticotropin releasing hormone abbreviated crh horticult tropin releasing hormone stimulates the anterior pituitary gland to release adrenal corticotropic hormone or ACTH adrenocorticotropic hormone stimulates the adrenal cortex to release cortisol the stress hormone well then or learn more about hormones and the endocrine system in a later lecture the hypothalamus produces two hormones that are stored and released in the posterior pituitary antidiuretic hormone reduces water loss at the kidneys and oxytocin is involved in Social bonding and stimulates smooth muscle contractions during labor the hypothalamus controls the autonomic nervous system this system regulates heart rate blood pressure digestive activities and respiration we'll learn more about the autonomic nervous system in a later lecture the hypothalamus regulates body temperature nuclei in this subregion control the mechanism that heats or cools the body shivering and sweating the hypothalamus controls food and water intake the hypothalamus responsible for generating feelings of hunger and thirst the hypothalamus regulates sleep wake Cycles by controlling the epithalamus and therefore melatonin release from the pineal gland finally the hypothalamus links the limbic system the emotional side of the brain to the autonomic and links emotions and memories to physical changes in the body when you see someone who has wronged you you become upset your heart rate decreases your breathing deepens this is due to the hypothalamus the final sub-region of the diencephalon is called the sub Thalamus the sub Thalamus lies between the thalamus and the midbrain it is part of the basal nuclei a collection of deep gray matter structures that inhibit or facilitate movement the cerebrum is the superior region and forms about 83 percent of the brain's volume the cerebrum generates voluntary motor movements and serves as the center of your intelligence reasoning sensory perception thought memory and judgment cerebral cortex is the outer layer of gray matter it contains neuron cell bodies dendrites and unmyelinated axons an upward fold in the cerebral cortex is called a gyrus a Groove between adjacent folds is called a sulcus these folds increase the surface area of the cerebral cortex more surface area allows more neurons to be packed into the cortex so that it can process more information the cerebrum is composed of two halves called the left and right cerebral hemispheres the cerebral hemispheres primarily control the opposite side of the body the right cerebral hemisphere primarily controls the left side of the body and vice versa one thing to keep in mind is that the hemispheres do display some functional differences this is called lateralization for example the portions of the brain that are responsible for controlling speech are frequently located in the left hemisphere the cerebral hemispheres are separated by a deep Groove called the longitudinal fissure This Groove extends along the mid-sagittal plane in addition to the longitudinal fissure there are a few other surface grooves in the cerebral cortex that we need to mention the central sulcus is a Groove that runs down the middle of the lateral surface of the brain and separates the frontal lobe from the parietal lobe the lateral sulcus runs along the lateral surface of the brain and separates the frontal and parietal lobes from the temporal lobes each cerebral hemisphere is divided into five anatomically and functionally distinct lobes the first four lobes are superficially visible and are named for the overlying cranial bones the frontal lobe lies deep to the frontal bone and forms the anterior part of the cerebral hemisphere it's primarily concerned with voluntary motor functions concentration verbal communication decision making planning memory Consciousness and personality the parietal lobe lies internal to the parietal bone and forms the upper aspect of each cerebral hemisphere it's involved with General sensory functions such as evaluating the shape and texture of objects being touched the occipital lobe forms the posterior region of each hemisphere and immediately underlies the occipital bone this slope is responsible for processing incoming visual information and storing visual memories the temporal lobe lies inferior to the lateral sulcus and beneath the temporal bone this lobe is involved with hearing and smell the insula is a small lobe deep inside the lateral sulcus the insula's lack of accessibility has made it difficult to study this region is thought to play a role in several functions including self-awareness perception and cognition