Understanding the Central Nervous System: Structure and Function

The central nervous system - Two subsystems of the nervous system ● Central nervous system (CNS) ● Peripheral nervous system (PNS) ➔ Nerve: bundle of axons running together ➔ Tracts: bundle of axons in CNS ➔ Nucleus: group of cell bodies in CNS ➔ Ganglion: group of cell bodies in PNS Peripheral Central Bundle of axons Nerve Tract Group of cell bodies Ganglion Nucleus The forebrain: Cerebral Hemisphere - Cerebral hemispheres: large, wrinkled structures dominating brain’s appearance ● Humans have disproportionately large cerebral hemispheres - Longitudinal fissure: division running length of the brain separating cerebral hemispheres ● Two hemispheres= ~ mirror images; often same area in each hemisphere serves identical functions ● Each hemisphere receives sensory input from and primarily controls the opposite side of the body ● Convoluted - Gyrus: each ridge in surface of the brain - Sulcus: groove or space between two gyri - Fissure: large groove or space between two gyri - Cortex: outer surface of brain (bark) - Cortex ● Made up mostly of the cell bodies of neurons ● Cell bodies not myelinated; results in a gray appearance ● Gray matter - Cortex is a central part of cognition - Cortex is 1.4 to 4.0 mm thick, but the convolutions of the cortex triple its total surface area ● Convolutions also provide axons with better access to more cell bodies than a thickened cortex would - Axons come together in large bands in the central core of the gyrus; myelination of axons gives the area a whitish appearance (white matter) - The human cortex typically has 6 layers, though some layers may be absent in some areas ● Layer I is inhibitory ● Layers II and III are associational ● Layer IV is sensory ● Layers V and VI have motor functions - Cells of the cortex are also grouped into columns of interconnected neurons, which run perpendicular to the cortical surface and unify the cortex’s horizontal layers ● Primary information processing unit in cortex, with each cell in the column serving an interrelated function and surrounding columns performing similar functions - Brain size and intelligence ● There is a small and highly variable relationship between the size of the brain and intelligence; people with large brains may tend to be more intelligent, but other factors are much more important ● Brain size is more related to body size than intelligence, and complexity determines intellectual power TERMS TO KNOW - Dorsal: directional term meaning toward the back (sharks have a dorsal fin on their back) - Ventral: directional term meaning toward the stomach - Anterior: directional term meaning toward the front - Posterior: directional term meaning toward the rear - Superior: directional term meaning above another structure - Inferior: directional term meaning below another structure - Lateral: directional term meaning toward the side - Medial: directional term meaning toward the middle Certain lobes and functional areas - Frontal lobe: located to the central sulcus and superior to the lateral fissure; complex and control some of the highest human capabilities and movement - Precentral gyrus: extends the length of the central sulcus - Motor cortex: located in the precentral gyrus, this structure controls voluntary (non reflexive) movement - Central sulcus: a sulcus which separates the frontal lobe from the parietal lobe - Lateral fissure: a prominent fissure which separates the frontal and temporal lobe Prefrontal cortex - Prefrontal cortex: region involved in planning and organization of behavior, decision making, adjusting behavior in response to its consequences, and planning how to achieve goals ● Largest region in the human brain and accounts for 29% of all cortical area ● Malfunction in the prefrontal cortex tends to strike at our “most human” capabilities; both schizophrenia and depression are associated with dysfunction in the prefrontal cortex The central nervous system - In the 1940s and 1950s, surgeons performed many lobotomies to detach the prefrontal area from the rest of the brain ● Started with severe schizophrenia, but then was used on patients with much milder conditions ● ~40,000 done in US total - Results: agitated patients were calmed, but became emotionally blunted, distractible, and childlike behavior ● Often unable to live independently ● Up to half of them remained hospitalized long after the procedure - Psychosurgery: use of surgical intervention to treat cognitive and emotional disorders; held in disfavor now THINGS TO REALLY KNOW; POTENTIAL LABEL QUESTION ON TEST: - Precentral gyrus - Central sulcus - Lateral fissure - Parietal lobe - Central sulcus - Frontal lobe