Study Guide: Cerebrum and Cortex PDF

Study Guide Week 5 The Cortex: 1. The cortex is made up the outermost 6 layers of gray (unmyelinated) matter: 2. The six layers are: molecular, external granular, external pyramidal, internal granular, internal pyramidal and multiform. Please know the function of each layer. 3. Fu...

Study Guide Week 5 The Cortex: 1. The cortex is made up the outermost 6 layers of gray (unmyelinated) matter: 2. The six layers are: molecular, external granular, external pyramidal, internal granular, internal pyramidal and multiform. Please know the function of each layer. 3. Functionally, the cortex can be divided into motor, sensory and association cortex. The motor cortex is generally associated with the movement of body parts and sensory cortex such as auditory cortex or visual cortex is associated with sensory organs. The association cortex is the region devoted to higher mental activities like information processing, learning and reasoning so that in humans it covers 95% of the total cerebral cortex surface. 4. The cerebrum= the cortex plus the large hemispheres (including the subcortical structures but not including the cerebellum and brainstem). 5. Please know the lobes of the brain (frontal, temporal, parietal and occipital), their different functions and the landmarks (the longitudinal fissure, lateral fissure (Sylvian), central sulcus (Rolando), parieto-occipital sulcus. 6. Please know the location and function of Wernicke's area and Broca's areas. 7. The homunculus-Memory tool to describe the distorted scale model of a human drawn to reflect the relative space human body parts occupy on the somatosensory cortex (the \"sensory homunculus\") and the motor cortex (the \"motor homunculus\"). Both the motor and sensory homonculi usually appear as small men superimposed over the top of precentral or postcentral gyri for motor and sensory cortices. This representation of body parts at a specific location of the cortex is called the homunculus. 8. Body parts that perform precise and delicate movements (hands,face) are disproportionately large compared to representations of body parts that perform gross or unrefined movements (legs, trunk) 9. The homunculus does not represent individual muscles- it represents the movements of body parts that require the coordinated activity of large groups of muscles. Important Motor and Sensory Areas: 1. The motor cortex comprises three different areas of the frontal lobe : a. The primary motor cortex (Brodmann's area 4) -- PMC- generates neural impulses that control the execution of movement b. The premotor cortex- PreMC (Brodmann's area 6) The premotor and supplemental motor cortex are thought to be higher level motor areas that encode complex patterns of motor output and select the appropriate motor plans to achieve desired end results c. The supplemental motor cortex (SMC)- generates the planning of movement, the sequencing of movement and the coordination of both sides of the body 2. The primary sensory cortex (PSC) is also involved in movement by transforming sensory information into motor commands and assisting in motor planning based on sensory feedback. The Upper Motor Neuron (UMN) and Lower Motor Neuron (LMN) systems: 1. The motor neurons at the cortical level are the beginning of the UMN system. They are located in the primary motor cortex (30%) and the premotor cortex (30%) and to a lesser degree the primary sensory cortex (40%). They are the beginning of the corticobulbar and corticospinal motor tracts that make up the pyramidal tracts of the umn system 2. THE UMN System= The Pyramidal (corticobubar and corticospinal) Tracts and the Extrapyramidal Tracts 3. THE LMN System= the Cranial Nerves (12 pairs), the Spinal Nerves (31 pairs) and the peripheral nerves. 4. Both Tracts are descending motor pathways 5. Pyramidal tract- the express bus; the direct pathway, travels through the pyramids of the medulla; no synapses; responsible for fine, discrete, precise motor movements a. The corticobulbar tract- cortex to brainstem (Cranial Nerves); innervates the muscles of the head and neck b. The corticospinal tract- cortex to spinal nerves; innervates the muscles of the spine and limbs; tract decussates at the level of the distal medulla. DECUSSATE means to cross over midline to the other side 6. Extrapyamidal tract- local bus; indirect pathway; many synapses along the way; responsible for gross motor movements. How movement happens: 1. The motor cortex also activates the pyramidal system to relay motor commands to the motor neurons of the brainstem (cranial nerves) and spinal cord (spinal nerves). These neurons eventually innervate the muscles and cause them to contract. Finally, the muscles execute the movement 2. The motor cortex and areas just below the motor cortex also activate the extrapyramidal system which activates other parts of the brain, such as the basal ganglia and the cerebellum, and eventually the spinal nerves. How does auditory comprehension happen? 1. To comprehend a spoken message, Heschel's gyrus (the primary auditory cortex) must detect and discriminate the stimuli and make some elementary analysis of the acoustic signal. 2. Information is then sent to Wernicke's area (the auditory association area) where we briefly retain the message, categorize and assign meaning (decode) Wernicke's area selects or assigns the appropriate words to our thoughts (neurally coded according to the learned rules of semantics, syntax and grammar of our language). How does expressive language happen? 1. The message that has been encoded in Wernickes area is then forwarded to Broca's area via the arcuate fasciculus where it is translated into a series of neural language commands: How does speech happen? 1. The neural language command is then relayed to the appropriate parts of the premotor cortex (Apraxia) for planning, and primary motor cortex (dysarthria) where nerve impulses are sent along the motor pathways to the anatomical structures needed for speech production.