The Brain PDF

4. The Brain Human Anatomy & Course Physiology Status Complete Materials 5. The Brain - Slides Date @September 17, 2024...

4. The Brain Human Anatomy & Course Physiology Status Complete Materials 5. The Brain - Slides Date @September 17, 2024 The Brain Formation of Neural Tube Brain Regions Decussation RAS: Reticular Activating System Medulla Oblongata Pons Cerebellum Midbrain Dopamine Pathways Basal Nuclei Basal Nuclei pathway Diencephalon Thalamus 4. The Brain 1  Hypothalamus Endocrine System Regulation The Pituitary Gland Epithalamus: Pineal gland The Limbic System The Cerebrum Cerebral Cortex Somatotopy Sensory areas receive input Primary Somatosensory Cortex Primary Motor areas Sensory and Motor Homunculus Association Areas Integration Areas Lateralization Ex. Language The Brain Formation of Neural Tube In development, the CNS is derived by in-folding of the ectoderm layer of the embryonic disc first appears as a simple dorsal tube structure Brain Regions Hind brain: medulla pons cerebellum Mid brain: mid brain 4. The Brain 2  Brain stem: medulla pons midbrain Forebrain (diencephalon) thalamus hypothalamus epithalamus Forebrain (telencephalon) cerebrum Decussation Decussation: Crossing over of nerve fibers from one side of the CNS to the other Unique to vertebrates: evolution of spinal cord called the somatic twist i.e. 180 degree turn of forebrain to rest of body Examples: Pyramids of the medulla, sensory decussation Chiasm: is a crossing over of nerves outside the brain i.e. optic nerve chiasm 4. The Brain 3  RAS: Reticular Activating System Function: Controls level of arousal of cortex including attention ranges from sharp focus to sleep-state Reticular: means “net-like” Locations include: eyes & ears muscle tone (midbrain) medulla pons & midbrain hypothalamus cerebral cortex Locus coeruleus (attention) 4. The Brain 4  Medulla Oblongata Function: is the brain of vital signs 1. Respiratory center 2. Cardiac center: rate & force 3. Vasometer: BP & vessel diameter 4. Reflexes: swallowing, coughing, sneezing, hiccupping, vomiting 5. RAS 6. Relay station 7. Decussation Pyramid: the sensory and motor tracts seen on ventral surface Pons Function: Along with the medulla regulates breathing Reflexes: salivation, chewing Major tracts: cerebral and cerebellar peduncles Cerebellum Function: Subconscious control of all movements including balance, posture etc. 4. The Brain 5  Receives intent from higher brain Receives sensory info about body position (proprioceptors) Corrects movement: important for timing and coordination Holds memories of patterned movements Midbrain Functions: Reflexes: auditory & eye Substantia nigra: site of neuron (cell bodies) that synthesize dopamine with connections to basal nuclei and hypothalamus Part of descending motor pathways: involved in balance and equilibrium, body movements like arm swing and gait (coordinates small movements) Part of RAS Dopamine Pathways Location: of cell bodies of neurons that synthesize dopamine: Mid brain i.e. VTA (ventral tegmental area) Substantia nigra regions 4. The Brain 6  Axons project to 3 main regions: 1. Reward pathway of the limbic system (motivation and pleasure) involves: a. hippocampus for memory b. nucleus accumbens for motivation & mood i. i.e. seeking or wanting behavior 2. Frontal cortex for executive functions: attention, planning, working memory 3. Striatum of the basal nuclei for initiation of motor movement Basal Nuclei Structure: Buried gray matter Function: Regulates movement (start, stop & intensity of) & procedural learning for cerebral cortex Linked to: cortex motor areas, thalamus and midbrain but no direct access to motor pathways Includes: Corpus striatum Caudate nucleus Lentiform nucleus Putamen Globus pallidus 4. The Brain 7  Basal Nuclei pathway Motor pathways are ready to go but are inhibited The BN release this inhibition or initiate movement Dopamine (DA) is neurotransmitter released in this pathway Parkinson's: too little DA Huntington's or Tourettes: too much DA Excessive inhibition, Movement is difficult to initiate, rigidity, Excessive excitatory, tremors Unwanted, exaggerated movements Diencephalon Function: is the brain of drives and emotions Epithalamus, thalamus, hypothalamus Thalamus Functions: 1. Processes sensory info to cerebrum (except smell) Gateway (edits) Relay center Focuses attention 2. Site of first crude sensory awareness. 3. Part of RAS 4. The Brain 8  4. Part of limbic system 5. Area of memory Hypothalamus Functions: 1. Control center for all visceral function 2. Regulates much of the ES via pituitary gland 3. Regulates body temperature 4. Regulates basic drives (hunger, thirst) 5. Produces hormones: ADH and oxytocin 6. Regulates sleep-wake cycles 7. Part of RAS 8. Part of the limbic system 9. Involved in sexual response Endocrine System Regulation 1. Regulatory factors (neurotransmitters) called regulatory hormones control the activity of the anterior pituitary. The anterior pituitary regulates many glands through secretion of hormones called tropic hormones 2. The posterior pituitary (which is neural) releases neurotransmitters 4. The Brain 9  into circulation (becoming hormones): ADH & Oxytocin 3. Neural Pathways from hypothalamus regulate secretion of epinephrine and norepinephrine from adrenal medulla (gland) in the Sympathetic Response. The adrenal medulla is thought of as a misplaced ganglion. The Pituitary Gland Function: is a link between the nervous & endocrine systems The Posterior Pituitary neural Composed of axons whose cell bodies reside in the hypothalamus Release ADH and oxytocin into circulation i.e. neurotransmitter becomes hormone The Anterior Pituitary glandular Hormones secreted by anterior pituitary regulate other glands (tropic hormones) regulated by neurons in the hypothalamus that release regulatory factors called hormones onto anterior pituitary 4. The Brain 10  Epithalamus: Pineal gland Function: Synthesizes melatonin induces sleepiness Antioxidant The Limbic System Modified or inhibited by: cerebral cortex alcohol and drugs Function: establishes emotions & drives Involved in learning and memory Linked to hypothalamus (body or visceral function) Structures include: Hippocampus: memory Amygdala: emotional significance (desire or fear) Cingulate gyrus: mood Fornix: path that connects Hypothalamus: regulates drives The Cerebrum 4. The Brain 11  Function: is the conscious brain Consists of 5 Lobes: frontal, parietal, temporal, occipital, insula White matter of cerebrum consists of 3 types of fibers: Commissure Fibers: connect right and left hemisphere i.e. corpus callosum Projection fibers: connect to rest of brain and periphery i.e. internal capsule, corna radiata Association fibers: connect within each hemisphere Cerebral Cortex Cerebral Cortex: is the Conscious Brain Structure: outer layer of gray matter in the cerebrum Exhibits: Topographic mapping Plasticity Lateralization Functions: can be mapped to specific brain regions (Brodmann’s Areas) of cerebral cortex Somatotopy 4. The Brain 12  Somatotopy: body mapping Specific functions are localized in discrete cortical areas i.e. can be mapped Organized into 3 kinds of functions: sensory motor association Each hemisphere is concerned Two hemispheres are not entirely with functions of the opposite side equal in function (lateralization) of the body (contralateral) No area functions on its own Sensory areas receive input Primary visual: occipital lobe Primary auditory: temporal lobe Primary gustatory: insula & frontal lobe Primary olfactory: frontal lobe Primary Somatosensory Cortex The mapping of the neurons forms Location: postcentral gyrus of a homunculus parietal lobe The ability to determine body Function: receives sensory info region stimulated or spatial about the body discrimination reflects the Skin Receptors: about touch, stimulation of a specific neuron pressure temperature, vibration 4. The Brain 13  & pain path going to a specific region in cerebral cortex Proprioceptors: for sense of body position (muscles, joints & tendons) Primary Motor areas Location: precentral gyrus, frontal lobe Function: sends out command for voluntary movement of skeletal muscles Includes: Broca’s: motor speech, (frontal lobe usually left side) Frontal Eye Field: eye movement, (frontal lobe) Sensory and Motor Homunculus Functions can be mapped, neighboring points correspond to adjacent parts of the body i.e. reflects body Distorted: area depends on sensitivity i.e. number of receptors Upside down representation Contralateral control Borders overlap Sensory Homunculus: primary Motor Homunculus: primary motor, sensory, post central gyrus precentral gyrus receptors from a specific Specific areas of the cerebral region of the body travel along cortex control specific muscles specific paths to specific regions of the cerebral cortex 4. The Brain 14  Association Areas Function: interpret using memories Somatic sensory association: size, texture, relation to other parts i.e. can recognize an object by feel Premotor cortex or motor association: memory area for learned skilled movements (playing an instrument, typing) Plan and control an action: move an arm through a maze (receives sensory input) Auditory association: memory & recognition Visual association: color, shape, recognition Integration Areas Function: receive info from other association areas Prefrontal Cortex: learning, judgement, planning, ideas, personality, empathy, conscience, mood (connected to limbic system) General Interpretive area: integrates sensory info into one meaning or thought Includes Wernicke’s area: interprets words into meaning Left side: language & math Right side: spatial visualization and analysis i.e. recognize faces, interpret emotional meaning of speech 4. The Brain 15  Function depends on the connections between functional areas Sensory: somatosensory, visual, auditory, gustatory Motor: primary, Broca's Association: frontal, premotor, somatic sensory, visual, auditory, GIA, Wernicke's 1. Sensory info arrives at primary somatosensory cortex from thalamus 2. Is interpreted in somatosensory association 3. Is sent to prefrontal cortex (establishes intent) 4. Premotor cortex along with basal nuclei (& midbrain) sets up motor action. Includes many other areas i.e. posterior parietal cortex: guides movements in space 5. Primary motor sends out command to skeletal muscles and spinal cord 6. Cerebellum corrects ongoing movement: receives info from proprioceptors and intent from cortex 7. Spinal cord directs motor movements not involving higher brain Lateralization Lateralization: refers to a division of labor between the two hemispheres 4. The Brain 16  Left: logical or sequential processing, language Right: spatial abilities, musical and artistic abilities, facial recognition Both receive same info, Some individual variation Corpus callosum: ensures instant communication between 2 hemispheres Not exact Ex. Language 90% of right-handed people process language on the left side Broca's: motor speech (muscle action to speak words) Wernicke's: sound out words and integrates Frontal cortex: speech comprehension (understand words) Right side: adds emotions to speech and comprehends emotional context of speech Visual cortex: sees words Auditory cortex: hears words 4. The Brain 17