Chapter 18 - Brain & CNS PDF

Chapter 18 – Brain & CNS I. Development & General Structure a. 3 Germ Layers (Table 4.1, p. 104) i. Endoderm: epithelial linings of many organs & Gametes ii. Mesoderm: all skeletal & cardiac ms, most smooth ms., blood, lymph, marrow, vessels, dermis, kidneys/ureters/adrenal glands, dura mater iii. E...

Chapter 18 – Brain & CNS I. Development & General Structure a. 3 Germ Layers (Table 4.1, p. 104) i. Endoderm: epithelial linings of many organs & Gametes ii. Mesoderm: all skeletal & cardiac ms, most smooth ms., blood, lymph, marrow, vessels, dermis, kidneys/ureters/adrenal glands, dura mater iii. Ectoderm: all nervous tissue, arachnoid mater and pia mater, almost all skeletal & connective tissue, epidermis, hair/nails, skin glands, lens/cornea/internal eye ms., epithelium of pineal gland, pituitary gland and adrenal medulla b. Neurulation = process of forming neural plate, neural folds & neural groove, starting 17 days after fertilization Primary Brain Vesicles Secondary Brain Vesicles Prosencephalon Telencephalon Diencephalon Mesencephalon Mesencephalon Rhombencephalon Metencephalon Myelencephalon Walls Cerebrum Thalamus, hypothalamus, epithalamus Midbrain Pons & Cerebellum Medulla Oblongata c. Brainstem = Midbrain + Pons + Medulla Oblongata II. Protection & Blood Supply a. Cranium – bones surrounding brain b. Cranial meninges – continuous with those of SC i. Dura mater: “tough mother” 1. Dense irregular CT 2. 2 layers – periosteal & meningeal layers > dural venous sinuses in between 3. Extensions of the dura a. Falx cerebri – separate the cerebral hemispheres b. Falx cerebelli – separates hemispheres of CBM c. Tentorium cerebelli – separates cerebrum from CBM 4. Subdural space b/n dura mater & arachnoid mater: contains ISF ii. Arachnoid mater: “spider-like” 1. Thin avascular layer of loose collagen 2. Subarachnoid space contains cerebrospinal fluid (CSF) – in next section iii. Pia mater 1. Thin vascularized layer of squamous to cuboidal cells adhering to brain & SC like saranwrap c. Cerebrospinal Fluid (CSF) i. Protects brain & SC from chemical & physical injury ii. Carries small amounts of O2, glucose, proteins, lactic acid, urea, electrolytes and some WBC’s in subarachnoid space iii. 80-150 ml circulating iv. Formation in Ventricles 1. 4 ventricles – all interconnected a. 2 lateral ventricles (separated anteriorly by septum pellucidum) Interventricular foramina b. 3rd ventricle – between R & L thalamus, above hypothalamus cerebral aqueduct c. 4th ventricle – between CMB & brainstem 2. Choroid plexuses (modified capillary networks) in walls of ventricles 3. Ependymal cells (tight junctions) + pia matter line capillary networks v. Functions 1. Mechanical protection: shock absorbing medium, buoys brain (reducing weight from 3 lbs to 0.1 lb) 2. Chemical protection: change in ionic concentration alters neuronal functioning 3. Circulation: minor exchange of nutrients and metabolic waste b/n blood and nervous tissue. Continuous with perivascular space of blood vessels entering the brain > becomes like a lymphatic function. vi. Circulation of CSF 1. Formed in choroid plexus of lateral ventricles & 3rd ventricle 2. Flows through cerebral aqueduct to 4th ventricle 3. Some continues through SC via central canal but majority exits roof 4th ventricle to subarachnoid space surrounding SC. 4. Is reabsorbed into dural venous sinuses via arachnoid villi and directly into the blood/lymph vessels of the pia mater d. Blood Flow & Blood Brain Barrier i. Tight junctions b/n endothelial cells of brain blood capillaries ii. Thick basement membrane iii. Astrocytes – secrete chemicals to maintain strength of tight junctions 1. Lipid soluble molecules can cross: O2, CO2, steroid hormones, alcohol, barbiturates, nicotine, caffeine 2. Water 3. Glucose & ions (ions transported slowly) 4. Prevents proteins, most antibiotic drugs III. Cerebrum (“seat of intelligence”) a. Conscious analytical thought, intelligence, personality traits, motivation, decision making b. Outer cortex: thing (2-4mm) and grey c. Internal white matter: axons d. Deep cerebral nuclei: grey e. Highly convoluted: gyri/sulci (fissure if deep) i. Cranium is getting smaller with evolution, but brain is getting bigger in size: folding into itself > ↑ SA f. Hemispheres i. Anatomically essentially identical ii. Corpus callosum (hard body): tracts of white matter connecting hemispheres (corpus callosotomy for epilepsy in 1970’s) 1. Fxnl differences: hemisphere lateralization a. L side: language centers b. R side: creative, artistic centers c. Now we’re starting to see there may not be as much lateralization as we once thought iii. Longitudinal fissure separates hemispheres, separated by falx cerebri iv. Motor and sensory to/from opposite sides of body (decussation of pyramids) v. Lobes 1. Frontal lobe a. Deep to frontal bone b. Ends posteriorly at central sulcus c. Houses pre-central gyrus i. Location of primary motor area 1. Almost all voluntary mvmts occur here ii. Motor homunculus – huge amt of tissue dedicated to head/face & hands d. Broca’s speech area i. L hemisphere ii. Control motor aspect of speech > ms of larynx, pharynx & mouth/tongue e. Concentration, verbal communication, decision making, planning, personality, Broca’s speech 2. Parietal a. Underlies parietal bones b. Ends ant at central sulcus c. Houses post-central gyrus i. Location of primary (somato)sensory cortex ii. Sensory homunculus – similar to motor humunculus iii. Involved with general sensory processing of general somatic senses (“body” senses: pressure, pain, mvmt position). 3. Temporal a. Inferior to lateral sulcus b. Hearing & smell 4. Occipital a. Posterior region of hemispheres b. Processes incoming visual info and stores visual memories i. Image from cornea > retina is upside down and inverted: brain corrects this (experiment with reversing glasses) 5. Insula a. Deep to lateral sulcus b. Memory and interpretation of taste (gustation) vi. Cerebral White Matter 1. 3 types of myelinated tracts a. Association tracts – axons conduct impulses b/n gyri in same hemisphere b. Commissural tracts – axons conduct impulses b/n gyri in one hemisphere to corresponding gyri in opposite hemisphere i. via corpus callosum (largest commissural tract) ii. ant & post commissure c. Projection tracts – axons project to lower parts of CNS (brainstem & SC) vii. Basal nuclei 1. 3 nuclei collectively called basal nuclei (globus pallidus, putamen, & caudate nucleus) 2. Receive input from motor cortex – initiate & terminate mvmt, ms tone & unconscious mvmt of skel ms viii. Limbic system 1. Composed of multiple cerebral & diencephalic structures that collectively process & experience emotion 2. Cingulate gyrus, parahippocampus, hippocampus, dentate gyrus, amygdala, septal nuclei, mammillary bodies 3. Hippocampus – storage of STM and coverts to LTM in frontal lobe. Cells can divide by mitosis. 4. Fornix, Olfactory bulbs, tracts, olfactory cortex associated – tied into most of evoking memories/emotion 5. 4 F’s a. Fighting b. Fleeing c. Feeding d. Fornicating (sexual behavior) g. Functional Areas of the Cerebrum i. Sensory Areas 1. Primary somatosensory area a. Parietal, post central gyrus (structural name) b. General somatic sensory (touch, pressure, temp, pain) c. Sensory homunculus 2. Primary visual area a. Posterior tip of occipital lobe b. Receives & processes visual information/perception 3. Primary auditory area a. Temporal lobe, superior aspect near lateral cerebral sulcus b. Auditory info & memory (hippocampus) 4. Primary gustatory area a. Base of postcentral gyrus, superior to lateral cerebral sulcus in parietal lobe (some include insular lobe) b. Taste / gustatory perception 5. Primary olfactory area a. Medial aspect of temporal lobe b. Conscious awareness of smell / olfa0looooolctory perception ii. Motor Areas 1. Primary motor area (cortex) = precentral gyrus a. Frontal lobe b. Voluntary skeletal ms activity c. Motor homunculus 2. Broca’s area (motor speech area) a. Just anterior to primary motor cortex, superior lateral cerebral sulcus b. L hemisphere c. Coordinates with several sensory, motor & association areas d. Brocas > premotor cortex (ms. larynx, pharynx & mouth) & Primary motor cortex (coordinates with breathing) iii. Association Areas – originate in 1 lobe, communicates with other lobes 1. Premotor Cortex (somatic motor association) a. Frontal lobe b. Processes motor info & learned/skilled motor activities (memories of mvmt) c. Thinking part, chooses mvmts d. Ie. playing musical instrument 2. Frontal eye field a. Frontal corex i. Voluntary scanning of eyes – reading this sentence 3. Prefrontal cortex (frontal association area) a. Most anterior portion of frontal lobe b. Connects to cerebral cortex, thalamus, hypothalamus, limbic sys & CBM c. Personality, intellect, complex learning abilities, recall of info (LTM), initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, and development of abstract ideas 4. Somatosensory a. Parietal lobe, posterior to postcentral gyrus b. Integrates & interprets sensory info (recognize objects w/o vision), sensory memory 5. Auditory association area a. Temporal lobe, posterior to primary auditory area b. Integrates sound characteristics, recognition of particular sounds of speech, music or noise 6. Visual association area a. Occipital – receives impulses from primary occipital area & thalamus b. Processes visual info (memories of objects) – facial recognition 7. Wernicke’s area a. Left temporal/parietal lobes b. Interprets meaning of speech/spoken words, damage > “Word salad” IV. Diencephalon (from Prosencephalon) a. Thalamus i. Paired oval masses, either side of 3rd ventricle ii. Interthalamic adhesion – band of grey matter (unmyelinated axons, connecting two bodies, no fxnl importance) iii. Sensory from all senses EXCEPT olfactory (smell) [olfactory routed through limbic system] 1. Final relay for sensory projected to somatosensory cortex 2. Sensory filter: filters out conversations when studying, nonessential info iv. 7 major groups of nuclei on each side for sensory info b. Hypothalamus i. Master control center of entire endocrine & ANS ii. Anteroinferior diencephalon iii. Hypothalamic nuclei: regulates thirst, sodium sex drive 1. Axons extend to parasympathetic and sympathetic nuclei in BS & SC > regulate visceral activities, HR, peristalsis, urinary bladder 2. Produce hormones – to ant/post pituitary gland a. Controls release of hormones in ant pituitary gland 3. Mammillary bodies – relay station for reflexes related to smell iv. Fxn’s 1. Master control of ANS 2. Master control of endocrine sys – produces many hormones 3. Regulation of body temp 4. Control emotional behavior 5. Control of food & water intake 6. Regulation of sleep-wake (circadian rhythms) > effecting Pineal gland c. Epithalamus i. Posterior roof of diencephalon ii. Pineal gland (pine cone shaped) – secretes melatonin to regulate sleep cycle/circadian rhythm iii. Habenular nucleus – involved in olfaction (mom’s chocolate chip cookies, perfume/cologne) V. The Brainstem & Reticular Formation a. = midbrain + pons + medulla oblongata (reticular formation extends throughout BS) b. Midbrain (mesencephalon) i. From diencephalon to pons ii. Contains cerebral aqueduct iii. Anterior: cerebral peduncles tracts of axons 1. Motor: corticospinal, corticobulbar, corticopontine 2. Sensory: tracts from medulla > thalamus iv. Posterior: Tectum: 1. 2 superior colliculi – visual reflexes: tracking, scanning stationary images, accommodation (lens of eye), neck mvmts 2. 2 inferior colliculi – auditory reflexes (startle reflex) v. Nuclei 1. Substantia nigra: release dopamine to control subconscious motor activity (Parkinson’s due to impairment) 2. Red nuclei: coordinates motor activity with CBM 3. Mesencephalic nuclei: cell bodies of unipolar sensory neurons, proprioception from head vi. CN’s 1. Oculomotor (CN III): extraocular ms & smooth ms (regulates pupil constriction and lens) 2. Trochlear (CN IV): motor to superior oblique ms (abducts, depresses & internally rotates, cross-eyed) c. Pons = “bridge” i. From midbrain to superior to medulla, anterior to cerebellum (CBM) ii. Bridge (“peduncles”) connecting R & L CBM and CBM to ↑’ing & ↓’ing tracts iii. Nuclei – pontine respiratory group (work with Respiratory Control Center of Medulla) iv. CN’s 1. Trigeminal (V): sensory from head/face, motor for chewing 2. Abducens (VI): extraocular eye mvmt (lateral rectus) 3. Facial (VII): sensory for taste (ant 2/3 of tongue); motor for secretion of saliva & tears, facial expression muscles 4. Vestibulocochlear (VIII): sensory from vestibular apparatus related to balance/equilibrium; (motor to same side stereocilia – still classified as sensory n.) d. Medulla Oblongata i. From pons to foramen magnum ii. Anterior 1. Pyramids – largest motor tracts, 90% of tracts cross (decussation) 2. Olives (lateral to pyramids) – proprioceptive nuclei/tracts (spinocerebellar) to CBM, iii. Autonomic Nuclei 1. Cardiac control center: regulates HR & contractility 2. Respiratory control center: basic rhythm for breathing (apneustic and pneumotaxic) 3. Vasomotor control center: controls BP through contraction/relaxation of smooth blood vessels iv. Posterior medulla: tracts for touch, conscious proprioception, pressure & vibration 1. Medial lemniscus sends info to thalamus on opposite side v. CN’s 1. Vestibulocochlear (VIII): sensory – hearing (motor to cochlea stereocilia, still classified as sensory) 2. Glossopharyngeal (IX): sensory (post 1/3 tongue for taste), & motor related to swallowing and salivary glands, regulates BP, blood gasses (O2, CO2) 3. Vagus (X): sensory & motor to pharynx, larynx, thoracic/abdominal viscera (“the wanderer”), taste 4. Accessory (XI) – cranial portion: assist Vagus with swallowing 5. Hypoglossal (XII): motor for tongue mvmt (speech) & swallowing e. Reticular Formation i. Mixed grey & white matter. ii. Ascending: Reticular Activating System – axons to cortex; involved with consciousness, arousal (wakening), attention, filtering 1. Receives sensory info except smell (people die in fires during sleep) iii. Descending: to CBM & SC regulating muscle tone, HR, BP, RR VI. Cerebellum (hind brain) a. Inferior & posterior cranial cavity b. 2nd largest part of brain c. 1/10 total mass, but ½ of neurons d. Cortex grey matter, inner white e. Transverse fissure separates CBM from cerebrum with tentorium cerebelli (tent-like fold of dura mater) f. Shape resembles butterfly i. Vermis = center, body ii. Hemispheres = wings g. White matter = arbor vitae h. 3 Cerebellar peduncles connect CBM to BS i. Superior cerebellar peduncle: from red nucleus (motor) & to thalamus (sensory) ii. Middle cerebellar peduncle: between pons & cerebellum iii. Inferior cerebellar peduncle: from vestibular nuclei & spinal cord(sensory), and to spinal cord (motor) i. Fxn i. Coordinates & fine tunes motor output with how motor plan is being carried out ii. Stores memories of mvmt patterns (plasticity develops in CBM, remember how to ride a bike) iii. Equilibrium & posture (proprioceptive input) iv. Monitors body & joint position v. Non-motor fxns: cognition, language processing, sensory info processing VII. Aging & the Nervous System a. Rapid growth first years of life i. ↑ size of neurons, amt neuroglia, development of dendritic branches and synapses, continued myelination b. Mass starts to decline in early adulthood (by 80 yrs old, brain weighs 7% less than young adulthood VIII. Summary of Cranial nn a. Table 18.4 – see last slide of powerpoint & video b. Oh Oh Oh To Touch And Feel Very Green Vegetables And Herbs c. On On On They Traveled And Found Voldemort Guarding Very Ancient Horcruxes