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Central Nervous System Chapter 12 Embryonic Nervous System Development • Ectoderm thickens to form the neural plate • Invaginates to form neural groove • Neural folds fuse to neural tube (3rd week) – Anterior end expands out = brain – Posterior = spinal cord • Neural crest become PNS ganglia and glia – Pigment cells too Embryonic Brain Development Primary vesicle system Secondary vesicle system Adult brain structures Ventricle system Lateral ventricles prosencephalon 3rd ventricle Cerebral aqueduct mesencephalon 4th ventricle rhombencephalon ANATOMICAL BRAIN REGIONS Ventricles • • • • Interconnected tubular system Filled with CSF (ependymal cells) Apertures in 4th ventricle connect to subarachnoid space Need to know (CSF pathway): – – – – – – – – Lateral ventricles Septum pellucidum Interventricular foramen 3rd ventricle Cerebral aqueduct 4th ventricle Central canal Aperatures Cerebral Hemispheres • Gyri - ridges of tissue – Pre- & postcentral • Sulci – shallow grooves – Central, pareito-occipital, & lateral • Fissures – deeper grooves – Longitudinal & transverse • Lobes – Frontal, parietal (2), temporal (2), occipital, & insula* • Basic regions – Cotex, white matter, & basal nuclei Cerebral Cortex • Gray matter composed of interneurons • 3 Functional areas – Motor areas – Sensory areas • Olfactory cortex – Association areas • Demonstrates lateralization – Left: math, speech, concrete processing, logic – Right: creativity, facial and pattern recognition • Contralateral control Homunculus • Entire body mapped within the brain = somatotopy – Most neurons to areas w/ most precise control or sensitivity • Somatosensory version receives message from sensors – Spatial discrimination • Motor version sends message to muscles • Areas are adjacently mapped • Contralateral control http://www.pc.rhul.ac.uk/staff/J.Zanker/P S1061/L6/homuncul.gif http://www.fizyka.umk.pl/~duch/ref/01/01-plastic/motorsomato.gif Cerebral Cortex Damage • Primary motor cortex – Paralyzes voluntary muscles; reflexes intact – Contralateral effects • Premotor cortex – Loss of motor skills; strength and ability unaffected – Practice rewires • Visual cortex – Primary: functional blindness – Association: can see, but not comprehend • Language areas – Broca’s: speech production – Wernike’s: speech comprehension Cerebral White Matter • Communication between cerebral areas and lower CNS • Directional myelinated fibers – Commissural fibers • Connect hemispheres • E.g. corpus callosum – Association • Connect parts of same hemisphere • Adjacent gyri or different lobes – Projection • Enter or leave cerebral cortex • Connect cortex to rest of NS, receptors, & effectors • E.g internal capsule & corona radiata Basal Nuclei • Input from all of cerebral cortex – Project to premotor & prefrontal areas via the thalamus • Limit excessive mov’ts; multitasking – PD and HD connection • Corpus striatum – Caudate nucleus – Lentiform nucleus • Putamen • Globus pallidus • Associated with subthalamic nuclei and substantia nigra Diencephalon • Thalamus – Gray matter masses joined by the intermediate mass – Regionally named specialty nuclei http://academic.kellogg.cc.mi.us/ herbrandsonc/bio201_McKinley/f 15-15_diencephalon_c.jpg • All afferents ‘relay’ through sorts and edits • Mediates sensation, motor activities, arousal, learning and memory • Hypothalamus – Walls form infundibulum which attaches to pituitary gland – Homeostatic control • Basic survival needs • 4 F’s: feeding, fighting, fleeing, and sex • Epithalamus – Pineal gland produces melatonin to help regulate sleep-wake cycle Brain Stem • Brain stem organized like spinal cord • Survival responses and cranial nerves (10 of 12) • Midbrain – Cerebral peduncles: pyramidal motor tracts (descending) – Corpora quadrigemina: superior (eyes) and inferior (ears) – Substantia nigra: melanin (DA); voluntary initiation of mov’t (PD) – Red nucleus: hemoglobin; coordinates limb motor mov’ts • Pons – Bridges cerebrum and cerebellum – Respiratory centers assist breathing • Medulla oblongata – Decussation of pyramids – Olives: sensory info about muscle and joint stretch to cerebellum – Cardiovascular and respiratory centers; emesis, hiccupping, sneezing, and coughing Cerebellum • Anterior & posterior lobes – Vermis connects 2 hemispheres of posterior • Instructions for coordination, balance, & proprioception – Ipsilateral input/output • Cerebellar processing – Interprets intent of mov’t from cortex & proprioception from sensors – Plans best means of mov’t execution – Sends plans to motor cortex to coordinate • Constant monitoring to adjust as needed • Damage results in clumsy, misguided mov’ts FUNCTIONAL BRAIN REGIONS Limbic System • Emotional center • Interactions with prefrontal lobes – Coordinates sensory input with emotions • Hippocampus – Learning and memory • Amygdala – Emotional center of self (laughter, fear, aggression, etc.) – Assess situation and elicit response to emotional stimuli – Perception of emotion in others • Cingulate gyrus – Associating memories to smells and pain – Expression of emotions through gestures – Focusing attention on emotionally significant events Reticular Formation • Arousal and alertness due to constant stimulation – Studying w/ background noise – Filters repetitive, familiar, and weak stimuli – 99% sensory stimuli ignored – LSD interrupts = overload stimuli • Inhibited by sleep centers • Depressed by alcohol & tranquilizers • Coarse skeletal mov’t http://www.daviddarling.info/images/reticular_formation.jpg PROTECTING OUR BRAIN Meninges • Covers and protects CNS • 3 layers (superficial to deep) – Dura mater • Periosteal layer attaches to skull (periosteum) • Meningeal layer invaginates into fissures to form septa which anchor brain in place – Falx cerebri: longitudinal fissure – Falx cerebelli: vermis – Tentorium cerebelli: transverse fissure • Sinuses (superior sagittal and transverse) where layers separate to collect blood – Arachnoid mater • Doesn’t follow convolutions • Serous fluid in subdural space above • CSF in subarachnoid space below (arachnoid villi) into superior sagittal sinus – Pia mater • Connected to brain, follows all convolutions Cerebrospinal Fluid • Surrounds the brain & spinal cord – Buoyancy – Supply for nutrients & chemical signals • Secreted by choroid plexus – In all ventricles – Lined with ependymal cells – Selective barrier to ions and removes wastes • CSF pathway – Basic ventricle pathway (earlier) Blood Brain Barrier • Maintains stable environment for brain • Allows selective permeability – Nutrients in – Wastes and toxins/dugs out – Ineffective against fats, O2, and CO2 • Absent at 3rd and 4th ventricle – Alcohol and other poisonings – Metabolic activity monitoring SPINAL CORD Vertebral Protection • Within the vertebral foramen – End L1/L2 – Lumbar puncture L3/L4 or L4/L5 • Epidural space – Padding of veins and fat • Dura mater – Meningeal layer only • Subdural space – histology only • Arachnoid • Subarachnoid space – Extends beyond spinal cord (S2) • Pia mater – Denticulate ligaments connect to dura External Anatomy • Cervical and lumbar enlargements – Increased gray matter • Conus medularis, cauda equina, & filum terminale • 31 spinal nerve pairs – Dorsal roots: sensory w/ganglia – Ventral roots: motor • Shingles attacks dorsal root ganglia and cranial nerves Internal Anatomy • Anterior median fissure • Posterior median sulcus • Gray commissure – Central canal • Gray and white matter – Anterior, posterior, and lateral horns • Ascending (sensory) and descending (motor) tracts