Develops from the embryonic neural tube The Brain The anterior end expands and constrictions appear forming the primary brain vesicles namely: Prosencephalon (fore brain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) The primary brain vesicles differentiate into secondary brain vesicles Procencephalon Telencephalon (cerebrum) Diencephalon (thalamus, hypothalamus and Epithalamus) Mesencephalon Brain stem: midbrain Rhombencephalon Metencephalon Brain stem: Pons and cerebellum Myelencephalon Regional Organization Cerebral Hemispheres Brain stem: medulla oblongata Has three basic regions; Outer gray matter, internal white matter and the basal nuclei Conscious thoughts, intellect, memory, sensations and complex movements originate from here regional organization Marked by elevated tissue folds called gyri (increase surface area of the cortex) Gyri are separated by shallow grooves called sulci Deeper grooves, called fissures separate larger brain regions
Longitudinal fissure Separates the two cerebral hemispheres Transverse fissure Separates the cerebral hemispheres from the cerebellum Some sulci divide each hemisphere into lobes, Frontal, parietal, temporal, occipital, and insula Central Sulcus Lies in the frontal plane Separates the frontal lobe from the parietal lobe It is bordered anteriorly by the precentral gyrus (primary motor area) and posteriorly by the postcentral gyrus (primary somatosensory area) The parieto-occipital sulcus Located on the medial surface of each hemisphere Separates the occipital lobe from the parietal lobe The lateral sulcus The Insula Outlines the temporal lobe and separates it from the parietal and frontal lobes Lies deep to the temporal lobe and forms part of its floor Covered by portions of the frontal, parietal and temporal lobes Generalizations about brain regions The cortex contains 3 kinds of functional areas: motor, sensory and association Each hemisphere is chiefly concerned with motor and sensory functions from the opposite side of the body
Two hemispheres are not entirely equal in function (Lateralization) specialization of cortical functions exist No functional area of the cortex acts alone Regional Organization Motor areas Sensory areas Primary (somatic) motor cortex Conscious control of precise or skilled voluntary movements of the skeletal muscles Premotor cortex Lies anterior to the precentral gyrus Controls learned motor skills of a repetitious or patterned nature such as typing or playing a musical instrument Broca s area Lies anterior of the premotor area on one hemisphere (usually left) only Controls muscles involved in speech production Frontal eye field Located partially in and anterior to the premotor cortex and superior to the broca s area Controls voluntary movement of the eyes Primary somatosensory area Receives information from general somatic receptors in the skin and proprioceptors in skeletal muscles Spatial discrimination, the ability to identify the regions being stimulated occurs here Somatosensory association cortex Lies posterior to the somatosensory cortex
Visual area Integrates temperature, pressure etc, relayed from the primary somatosensory cortex to produce an understanding of any object being felt Lies on the extreme posterior tip of the occipital lobe Receives visual information from the retina of the eye The visual association area communicates with the visual area to interpret visual stimuli (color, form, movement) Auditory areas Located in the temporal lobe Converts impulses from the ear and relate them to pitch, rhythm and loudness The auditory association area permits the perception of sound stimulus which we hear as music, scream, noise etc Olfactory cortex Medial aspect of temporal lobes Enables us to be aware of changes in odors Gustatory cortex Located in the insula Involved in the reception of taste Visceral Sensory Area Posterior to gustatory cortex Conscious perception of visceral sensations, e.g., upset stomach or full bladder Vestibular cortex Multimodal Association Areas Posterior part of the insula and adjacent parietal cortex Responsible for conscious awareness of balance (position of the head in space)
Receive inputs from multiple sensory areas Send outputs to multiple areas, including the premotor cortex Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take Three parts of multimodal association area Anterior association area (prefrontal cortex) Posterior association area Limbic association area Anterior association area (Prefrontal cortex) Most complicated cortical region Involved with intellect, cognition, recall, and personality Contains working memory needed for judgment, reasoning, persistence, and conscience Development depends on feedback from social environment Posterior Association Area Large region in temporal, parietal, and occipital lobes Plays a role in recognizing patterns and faces and localizing us in space Involved in understanding written and spoken language (Wernicke s area) Limbic Association Area Part of the limbic system Provides emotional impact that helps establish memories Cerebral white matter Lies deep to the cortical gray matter Responsible for communication between the cerebral areas, cortex and lower CNS centers Consists mostly of myelinated fibers bundled into large tracts Fibers are classified according to the direction in which they run
Commisures (Commisural fibers) Connect corresponding gray areas of the two hemispheres enabling them to function as a whole The largest commisure is the corpus callosum Anterior and posterior commisures are less important Association fibers Connect different parts of the same hemisphere Short fibers connect adjacent gyri Long fibers are bundled in tracts that connect different lobes Projection fibers Fibers that enter and leave the to lower brain or cord centers Basal Nuclei (ganglia) Subcortical nuclei Consists of the corpus striatum Caudate nucleus Lentiform nucleus (putamen + globus pallidus) Functionally associated with the subthalamic nuclei (diencephalon) and the substantia nigra (midbrain Functions of Basal Nuclei Though somewhat elusive, the following are thought to be functions of basal nuclei Influence muscular control Help regulate attention and cognition Regulate intensity of slow or stereotyped movements Inhibit antagonistic and unnecessary movements
Diencephalon Thalamus Forms the central core of the forebrain Egg-shaped and forms the superolateral walls of the third ventricle and contains several nuclei Its bilateral masses of gray matter are held together by the intermediate mass Principal relay station for directing sensory information from the spinal cord, medulla and cerebellum to the cortex Relays and processes taste, visual, auditory and somatosnsory information Hypothalamus Lies below the thalamus, caps the brain stem and forms the inferolateral wall of the third ventricle It contains many functionally important nuclei and is the main visceral control center of the body Processes and relays olfactory information, integrates the ANS, produce hormones (ADH and Oxytocin), control over heart rate, digestive tract activity, rage and aggression, body temperature regulation, water balance and thirst, hunger and satiety centers and sleep pattern Epithalamus Brain stem The most dorsal portion of the diencephalon Forms the roof of the third ventricle The pineal gland lies on the exterior of its posterior border The pineal gland secretes melatonin that plays a role in the regulation of the sleepwake cycle Made up of the midbrain, pons and medulla Has a deep gray matter surrounded by white matter with nuclei of gray matter embedded in the white matter Produce rigidly programmed automatic behavior necessary for survival
Midbrain Pons Provides a pathway for fibers running between higher and lower neural centers Is associated with 10 of the 12 cranial nerves Located between the diencephalon and the pons The ventral surface has cerebral peduncles that consists of fiber tracts descending toward the spinal cord The superior peduncles contain tracts that link the midbrain to the cerebellum The cerebral aqueduct runs through the midbrain connecting the third and forth ventricle On the dorsal surface are superior and inferior colliculi (corpora quadrigemina) that coordinate head and neck movements in response to visual and auditory stimuli respectively Brainstem swellings that lie between the mid brain and the medulla oblongata Dorsally it forms part of the anterior wall of the fourth ventricle Longitudinal fibers connects the medulla with higher brain center Transverse fibers connect the cerebral hemispheres within the midbrain Respiratory centers of the reticular formation that help to maintain the normal rhythm of breathing are located here Medulla oblongata Cone shaped and lies between the pons and the spinal cord The foramen magnum is the anatomical landmark used to differentiate brain structures from spinal cord structures The ventral aspect has two longitudinal ridges called pyramids formed by large pyramidal fibers descending from the motor cortex These fibers decussate (pyramidal decussation) before they enter the spinal cord
Cerebellum On the dorsal surface are the nucleus cuneatus and gracilis that serve as relay nuclei for tracts that carry sensory information from the spinal cord and relay them to the thalamus These fibers decussate in the medulla Has a cardiovascular center(cardiac and vasomotor center), respiratory center (rate and depth of breathing) and other centers that regulates vomiting, sneezing, hiccups, swallowing etc Located dorsal to the pons and medulla and lies under the occipital lobe of the cerebral hemisphere from which it is separated by the transverse fissure Consists of two hemispheres that are connected in the midline by the vermis It functions primarily by fine-tuning movement and adjusting body posture to maintain balance