ANP1111 Lecture 14 Neuroanatomy & Neurophysiology Part 1 PDF

ANP1111 – Lecture 14: Neuroanatomy & Neurophysiology – Part 1 CNS (Chapt.11: pp.390-392; Chapt.12:p.434-456) The nervous system is connected as a single unit, but anatomically divided into 2 parts: (i) Central Nervous System (CNS): brain + spinal cord; integrating & comman...

ANP1111 – Lecture 14: Neuroanatomy & Neurophysiology – Part 1 CNS (Chapt.11: pp.390-392; Chapt.12:p.434-456) The nervous system is connected as a single unit, but anatomically divided into 2 parts: (i) Central Nervous System (CNS): brain + spinal cord; integrating & command centre (ii) Peripheral Nervous System (PNS): cranial & spinal nerves; communication between CNS & all parts of body A. Sensory division: somatic & visceral fibers; from receptors to CNS B. Motor division: motor nerve fibers from CNS to effectors B1. Somatic ns: voluntary; from CNS to skeletal muscle B2. Autonomic ns: involuntary; (visceral motor); from CNS to cardiac muscle, smooth muscle, glands a) Sympathetic division: “fight or flight” b) Parasympathetic division: conserve energy at rest Fig. 11.1 & 11.3. Organization of the Nervous System The Brain (jump to chapter 12 here) complexity of wiring rather than size is what matters subdivisions: cerebral hemispheres diencephalon (thalamus, hypothalamus, epithalamus) brain stem (midbrain, pons, medulla) Fig. 12.2 cerebellum Gray matter: short, nonmyelinated neurons and neuron cell bodies – some gray matter is organized into nuclei and we will identify some of these; other is distributed as cortical areas White matter: primarily myelinated axons; some nonmyelinated axons can be there as well  Arrangement of Gray & White matter: Spinal cord has central cavity surrounded by gray matter (butterfly shape) with white matter around the outside Brain has a similar design, but with additional regions of gray matter; cerebral hemispheres & cerebellum have outer “bark” of gray matter Fig. 12.3 Fig. 12.3 Ventricles of Brain: continuous with one another and with central cavity of spinal cord; filled with CSF & lined by ependymal cells (i) Paired lateral ventricles separated by narrow septum pellucidum (ii) Each communicates with narrow 3rd ventricle in diencephalon via interventricular foramen (iii) 3rd ventricle to 4th ventricle (dorsal to pons) via cerebral aqueduct (iv) 4th ventricle continuous with central canal (v) 3 apertures (paired lateral apertures & median aperture) connect ventricles to subarachnoid space (surrounds brain) Fig. 12.4  A1. The Cerebral Hemispheres superior; ~83% of brain mass gyri separated by sulci; anatomical landmarks Fig. 12.5c longitudinal fissure; transverse cerebral fissure Lobes: frontal, parietal, occipital, temporal, insular central sulcus: precentral/postcentral gyrus parieto-occipital sulcus, lateral sulcus Fig. 14.11 (T&G) Cerebral cortex (gray matter): allows us to perceive, communicate, remember, understand, appreciate, initiate voluntary movements → conscious behaviour cell bodies, dendrites & unmyelinated axons; only 2-4 mm thick, but many convolutions triple surface area Brodmann areas (BA): numbered in early 1900s by Korbinian Brodmann according to differences in thickness & histology; will use these only as landmarks when describing location of some functional areas of brain (i) 3 functional areas: motor, sensory & association (ii) each hemisphere handles sensory & motor functions of opposite side of body (contralateral) (iii) largely symmetrical, but not 100% equal in function (lateralization) (iv) no functional area of cortex acts alone; all conscious behaviour involves the entire cortex in some way https://thebrain.mcgill.ca/flash/capsules/outil_jaune05.html Fig. 12.6. Functional neuroimaging of cerebral cortex. Red & orange areas show increased blood flow when cortex involved in various activities. (i)Motor Areas: posterior part of frontal lobes: primary motor cortex, premotor cortex, Broca’s area & frontal eye field 1) Primary motor cortex (BA 4): - precentral gyrus of frontal lobe of each hemisphere; pyramidal cells (large neurons) allow control of skeletal muscles; axons project to spinal cord body represented spatially in primary motor cortex of each hemisphere = somatotopy which areas require most precise motor control? motor innervation is contralateral no overlap between muscles involved in unrelated movements stroke: damage to area of right Fig. 12.8 hemisphere paralyzes body muscles on left – only voluntary movement lost; reflex contraction still possible 2. Premotor cortex (BA 6): https://thebrain.mcgill.ca/flas h/capsules/outil_jaune05.html anterior to primary motor cortex helps plan movements by selecting and sequencing basic motor movements into more complex tasks (e.g., playing a musical instrument, keyboarding) coordinates movement of several muscle groups simultaneously / sequentially by activating motor cortex sometimes referred to as muscle memory, but, of course, muscles don’t have memory! can control voluntary actions that depend on sensory feedback – e.g., feeling for light switch in a dark room What if there is damage to the area of premotor cortex regulating keyboarding? Can you still move your fingers?  https://thebrain.mcgill.ca/flas h/capsules/outil_jaune05.html 3. Broca’s area: in region of BA 44 present in one hemisphere only – usually the left originally thought to be only a motor speech area newer studies: Broca’s area is active when we prepare to speak – to organize making the sounds that will be heard as words 4. Frontal eye field: close to BA 8; controls voluntary movements of the eyes https://thebrain.mcgill.ca/flas h/capsules/outil_jaune05.html (ii) Sensory Areas 1. Primary somatosensory cortex (PSC): in postcentral gyrus of parietal lobe (BA 1-3) receives info from somatic sensory receptors (skin) & proprioceptors (joints & muscles) – includes spatial discrimination 2. Somatosensory association cortex: posterior to PSC (BA 5-7) - many connections with PSC integrate/analyze somatic inputs (temp, pressure,..) – interpret as to size, texture, relationship of parts based on prior experience – think of feeling in your pocket for a particular item This is an excellent, short 6-minute video that gives you some real insight how important somatosensory and proprioceptive information is in allowing us to do very simple actions associated with everyday living! It features Ian Waterman, telling his story of how he compensates every day for the loss of that sensory input at the age of 19. Link to Cengage Video: https://wowzahttp.cengage.com/nextbook/life_sciences/sherwood_428834/student/vide o/9_vision_replaces_touch/9_vision_replaces_touch_hi.mp4 3. Visual areas: primary visual cortex (PVC) → posterior tip of the occipital lobe contains map of visual space on retina (contralateral, like somatosenory) visual association area → surrounds PVC interprets visual image based on prior experience – eg: recognition of a face, of a letter or a word (also movement!) What is the result of damage to the primary visual cortex? To the visual association area? https://classconnection.s3.amazonaws.com/642/flashcards/911642/png/screen_shot_2012-06-17 _at_124912_pm1339951774810.png Visual Agnosia – the inability to recognize/understand things that you see 4. Auditory areas: primary auditory cortex: sound is evaluated for pitch, rhythm, loudness auditory association area: interpretation based on memory – speech, words, music, recognition of what a loud, sudden noise means, etc. 5. Vestibular (equilibrium) cortex: awareness of balance – posterior part of insula & adjacent parietal cortex – not visible at surface – deep in lateral sulcus https://classconnection.s3.amazonaws.com/642/flashcards/911642/png/screen_shot_2012-06-17 _at_124912_pm1339951774810.png 6. Olfactory cortex: medial aspects of temporal lobes = uncus small in humans; most of surrounding tissue now forms limbic system (emotions, memory) conscious awareness of different odors Fig. 12.7b – Parasagittal view 7. Gustatory cortex: insula aware of different tastes 8. Visceral sensory area: posterior to gustatory cortex what sort of information?  (iii) Multimodal Association Areas: receive inputs from multiple senses & send outputs to multiple area sensory receptors ↓ primary sensory cortex ↓ sensory association cortex ↓ multimodal association cortex http://mind.in/images/easyblog_images/637/prefrontal_cortex.jpg 1. Anterior Association Area (Prefrontal Cortex): most complicated cortical area – associated with intellect, complex learning (cognition), recall, & personality (working memory is here) abstract ideas, judgment, reasoning, persistence, planning, concern, conscience matures slowly; dependent on feedback from social environment closely linked to limbic system; involved in mood Phineas Gage 25-year-old railway worker injured in 1848 by a tamping bar during an explosion – bar went up through his left cheek, through his brain and skull and landed some distance away Sensory, motor OK – but dramatic personality changes – prior to this he had been a model employee and a crew foreman – after the injury, he lost his ability to stick with a task as well as inhibitions over normal behaviour and language in social situations Autopsy revealed damage to some parts of the anterior association area First clear evidence of an association between an area of the brain and key personality traits. 2. Posterior Association area: parts of temporal, parietal & occipital lobes input from all sensory association areas – storage of complex memories linked to sensory input – put info together to understand what see, feel, etc. localization of self & surroundings in space – e.g. someone with damage to this area may not dress or wash one side of the body - they don’t see that as part of them – referred to as contralateral neglect recognition of patterns, faces some parts for understanding written & spoken language (Wernicke’s area) 3.Limbic Association area: provides emotional impact – e.g., be aware of the danger associated with a particular situation based on prior experience or learning Fig. 12.7a: Lateral view – left cerebral hemisphere Lateralization of Cortical Functioning each cerebral hemisphere has some abilities not completely shared by other hemisphere cerebral dominance = hemisphere that is dominant for language 90% of people: left hemisphere dominant for language, math, logic – e.g. compose a sentence, add numbers, memorize a list other hemisphere dominates for visual-spatial skills, intuition, emotion, artistic and musical skills – our creative & insightful side most individuals with left cerebral dominance are right-handed most individuals with right cerebral dominance are left-handed or ambidextrous both sides still communicate with each other – see next slide!  A3. Cerebral White Matter communication between cerebral areas, between cortex & lower CNS centres Commissural fibers: connect corresponding areas between the 2 hemispheres – largest is corpus callosum Frontal section Association fibers: connections within a hemisphere (connect gyri, lobes) Projection fibers: to or from cortex and rest of nervous Fig. 12.9 system; these ones run vertically Midsagittal section Basal Nuclei caudate nucleus, putamen and globus pallidus inputs from entire cerebral cortex, other subcortical nuclei & one other project to premotor & prefrontal cortices to influence muscle movements directed by primary motor cortex – have no direct access to motor pathways precise roles elusive (difficult to access; some roles overlap with cerebellum) – roles in starting, stopping, monitoring intensity of movements executed by cortex, especially if sustained like arm swinging while walking; also inhibit antagonistic and/or unnecessary actions by filtering them out and sending only best response to cortex also associated with cognition and emotions - again a filtering role Anterior Fig. 12.10 Posterior Disorders associated with basal nuclei can result in too much movement (e.g. Huntington’s disease) or too little movement (Parkinson’s disease) Huntington’s Disease hereditary disorder in which mutant huntingtin protein accumulates in brain cells degeneration of the basal nuclei and eventually of the cortex as caudate deteriorates, connections to frontal lobe become lost so that the affected individual in unable to control feelings, thoughts or movements http://web.stanford.edu/group/hopes/cgi-bin/wordpress/2010/06/the-behavioral-symptoms-of-huntingtons-disease/ Parkinson’s Disease degeneration of dopamine-releasing neurons of substantia nigra (midbrain) causes basal nuclei usually targeted by substantia nigra to become overactive persistent tremor at rest; muscles become rigid leading to difficulty walking, loss of facial expression, difficulty writing, etc. http://parkinsons-tmj.com/the-shaking-palsy-a-r eview-on-parkinsons-disease/ The Diencephalon = thalamus + hypothalamus + epithalamus – enclose the 3rd Fig. 12.12a ventricle Thalamus: two masses of gray matter held together by midline commissure called the interthalamic adhesion (intermediate mass) many different nuclei, named for their position in thalamus – afferent impulses from all senses & all parts of body converge on thalamus = gateway to cerebral cortex sorting & editing of information; direct impulses to appropriate region of cortex only a crude awareness of sensation at level of thalamus (pleasant/unpleasant?) also input pertaining to emotions & viscera from hypothalamus key roles in mediating sensation, motor activities, cortical arousal, learning, memory  http://idealab.ucdavis.edu/IST/ISTF08/lectures/F08Lecture3vhtml_files/image007.gif https://biologydictionary.net/thalamus/ Hypothalamus: “below” thalamus (i) Autonomic control centre: centres for bp, heart, GI, respiration, etc (ii) Centre for emotional response & behaviour: heart of limbic system (iii) Body temperature regulation: (iv) Regulation of food intake: hunger, satiety (v) Regulation of water balance & thirst: release of ADH; thirst centre (vi) Regulation of sleep-awake cycles: suprachiasmatic nucleus (vii) Control of endocrine system: releasing factors plus 2 nuclei (supraoptic & paraventricular) produce ADH & oxytocin Hypothalamic disturbances: cause disorders in body homeostasis such as body wasting, obesity, sleep disturbances, dehydration, emotional imbalances Fig. 12.12b Epithalamus: most dorsal part of diencephalon & forms roof of 3rd ventricle; pineal gland (melatonin) extends from its dorsal border choroid plexus (CSF-forming structure) also part of epithalamus Optic chiasma Fig. 12.11a: Midsagittal section