Ch.14.1-14.8 notes BIOL 3455.001
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Ch.14 - The Brain and Cranial Nerves ▯ 14-1: Structures of the Brain (Martini, Nath, & Bartholomew 462) - brain weighs 1.3 kg (3 lb) and has volume of 1200 mL - male brains 10% larger than female brains - 6 major brain regions: cerebrum, cerebellum, diencephalon, midbrain, pons, medulla oblongata - cerebrum is largest portion - cortex - superficial layer of gray matter covering most of its surface - cerebral cortex forms series of elevated ridges (gyri) - gyri inc. its surface area - sulci - shallow depressions - fissure - deeper grooves - cerebrum is site of most higher mental functions - thoughts/sensations/intellect/memory/ complex movements - cerebellum 2nd largest portion - adjusts ongoing movements by comparing arriving sensations w/previously experienced sensations - diencephalon composed of right and left thalamus - hypothalamus involved with emotions, autonomic function, hormone production - infundibulum - narrow stalk - connects hypothalamus to pituitary gland - brainstem includes midbrain, pons, & medulla oblongata • Embryology of brain - CNS begins as hollow cylinder aka neural tube - neurocoel - fluid-filled internal cavity - primary brain vesicles - 3 prominent divisions created by enlargement by expansion of neurocoel • prosencephalon (forebrain) • mesencephalon (midbrain) • rhombencephalon (hindbrain) - secondary brain vesicles: prosencephalon and rhombencephalon - prosencephalon forms telencephalon & diencephalon - telencephalon forms cerebrum - metencephalon formed from rhombencephalon - dorsal part of metencephalon becomes cerebellum & ventral portion develops into pons - portion of rhombencephalon closer to spinal cord forms myelencephalon - myelencephalon becomes medulla oblongata • Brain Ventricles - neurocoel forms ventricles (Martini, Nath, & Bartholomew 464) - cells of ependyma line ventricles - each cerebral hemisphere contains lateral ventricle - septum pellucidum - thin medial partition - separates 2 lateral ventricles - third ventricle - ventricle in diencephalon - interventricular foramen - aka foramen of Monro - thru which each lateral ventricle - cerebral aqueduct - slender canal in midbrain - connects 3rd ventricle w/the 4th ventricle - ventricles filled w/CSF ▯ ▯ ▯ ▯Martini, Nath, & Bartholomew 463) ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯▯ (Martini, Nath, & ▯artholomew 464) ▯ ▯ ▯ ▯ ▯ Bartholomewath, & 465) ▯ ▯ ▯ ▯ 14Cranial meningesnges, CSF, BB-barrier protect Brain - cranial dura mater, arachnoid mater, & pia mater make up cranial meninges dura mater - outer periosteal layer & inner meningeal layer • arachnoid mater - covers brain • pia mater - sticks to surface of brain, anchored by processes of astrocytes ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ - Dural folds - provide additional stabilization & support to brain •3 largest dural folds are falx cerebri, tentorium cerebelli, falx cerebelli - cranial trauma - head injury resulting from impact w/another object - CSF functions: • cushion delicate neural structures • support brain • transport nutrients, chemical messengers, waste products - free exchange occurs btw interstitial fluid & CSF - CSF produced in choroid plexus - spinal tap provide useful clinical info about CNS injury, infection, disease • Clinical note: • epidural hemorrhage - if blood is forced btw dura mater & skull by arterial break - elevated fluid pressure distort underlying tissue of brain - lose consciousness & lead to death if untreated - rare, less than 1% of head injuries • subdural hemorrhage - bleeding btw dura mater & arachnoid mater - twice as common as epidural hemorrhages - venous BPin sub. hemorrhage lower than arterial epidural hemorrhage - distortion is gradual - ependymal cells secrete CSF into ventricles & remove waste products from CSF & adjust its composition over time - hydrocephalus - “water on the brain” - caused by problem w/resorption of CSF in infancy • result in expanded skulls due to large volume of CSF (Martini, Nath, & Bartholomew 468) ▯ ▯ ▯ Blood Supply to the Brain - arterial blood reaches brain through the internal carotid arteries & vertebral arteries - venous blood from brain leaves cranium in the internal jugular veins - cerebrovascular disease - cardiovascular disorder that interferes w/normal blood supply to the brain - cerebrovascular accident (CVA) - aka stroke - occurs when blood supply to a portion of the brain is shut off - blood-brain barrier (BBB) isolates neural tissue from the general circulation of blood - BBB formed by capillary endothelial cells that are interconnected by tight junctions - only lipid-soluble compounds can diffuse across membranes of endothelial cells into interstitial fluid of brain & spinal cord - permeability of endothelial lining of brain capillaries dependent on astrocytes - astrocytes release chemicals that control the permeabilities of the endothelium to various substances - if astrocytes are damaged or stop stimulating the endothelial cells, the BBB disappears - blood-CSF barrier - interconnected by tight junctions, surround capillaries of choroid plexus - BBB remains intact throughout the CNS except in small areas knowns as circumventricular organs (CVOs) which have fenestrated capillaries - bc they are outside the BBB, they provide direct link btw CNS & the peripheral blood - exceptions include: • portions of hypothalamus (Martini, Nath, & Bartholomew 469) • capillaries in posterior lobe of pituitary gland • capillaries in the pineal gland • capillaries at a choroid plexus ▯ 14-3: Medulla oblongata contains vital centers (Martini, Nath, & Bartholomew 470) - medulla oblongata (MO) most inferior of the brain region - All communication between the brain and spinal cord involve tracts that ascend or descend through the medulla oblongata - Medulla oblongata is a center for the coordination of complex autonomic reflexes and the control of the visceral functions - Medulla oblongata includes three groups of nuclei: 1. autonomic nuclei controlling visceral activities • reticular formation - loosely organized mass of gray matter that contains embedded nuclei - extends from MO to midbrain • processing centers that regulate vital autonomic functions • reflex centers receive inputs from cranial nerves, cerebral cortex, & brain stem • output controls or adjust the activities of one or more peripheral systems • Two major groups of reflex centers in MO: cardiovascular centers and respiratory rhythmicity centers - cardiovascular centers - adjust heart rate, strength of cardiac contractions and the flow of blood through peripheral tissues • subdivided into cardiac & vasomotor centers - respiratory rhythmicity centers - set basic pace for respiratory movements activity regulated by inputs from the apneustic & pneumotaxic respiratory centers • of the pons 2. sensory and motor nuclei of cranial nerves - provide motor commands to muscles of pharynx, neck, back, visceral organs of thoracic & peritoneal cavities - associated with 5 of the cranial nerves (VIII, IX, X, XI, XII) - cranial nerve VIII carries sensory info from receptors in internal ear to vestibular & cochlear nuclei 3. relay stations along sensory & motor pathways - nucleus gracilis & nucleus cuneatus pass somatic sensory info to the thalamus - decussation - tracts leaving these brain stem nuclei cross to the opposite side of the brain before reaching their destinations; crossing over at site decussation of pyramids - solitary nucleus receives visceral sensory info that reaches the CNS from the spinal & cranial nerves - olivary nuclei relay info to the cerebellar cortex about somatic motor commands as they are issued by motor centers at higher levels • bulk of the olivary nuclei creates the olives - prominent olive-shaped bulges along the ventrolateral surface of the MO (Martini, Nath, & Bartholomew 471) ▯ (Martini, Nath, & Bartholomew 471) ▯ ▯ ▯ (Martini, Nath, & Bartholomew 472) (Martini, Nath, & Bartholomew 472) ▯ ▯ ▯ ▯ 14-4: The pons contains nuclei & tracts that relay sensory/motor info - the pons contains 4 groups of components • sensory & motor nuclei of cranial nerves - cranial nerves (V, VI, VII, VIII) innervate jaw muscles, anterior surface of face, one extrinsic eye muscle (lateral rectus), & sense organs of internal ear • nuclei involved w/the control of respiration - 2 respiratory centers: apneustic center & pneumotaxic center - these centers modify activity of respiratory rhythmicity centers in the MO • nuclei & tracts that process & relay info sent to or from the cerebellum - pons links the cerebellum w/the brain stem, cerebrum, & spinal cord • ascending, descending, & transverse tracts - middle cerebellar peduncles are connected to the transverse fibers, which cross the anterior surface of the pons 14-5: Cerebellum coordinates patterns of muscular activity at the subconscious level (Martini, Nath, & Bartholomew 473) - cerebellum is an automatic processing center that has 2 primary functions: • adjusting the postural muscles of the body - coordinates rapid, automatic adjustments that maintain balance/equilibrium • programming & fine-tuning movements controlled at the conscious & subconscious levels - refines learned movement such as playing a piano or riding a bike - performs this function indirectly by regulating activity along motor pathways at cerebral cortex, basal nuclei, & motor centers in brain stem - compares motor commands w/proprioceptive info & makes adjustment to make movement smooth - folia - folds of cerebellum surface - vermis - narrow band of cortex that separates the cerebellar hemispheres - cerebellar cortex contains huge, branched Purkinje cells • dendrites of each Purkinje cell receive input from up to 200,000 synapses - arbor vitae - “tree of life” - internal white matter that connects cerebellar cortes & nuclei w/the cerebellar peduncles - cerebellum receives proprioceptive info from spinal cord & monitors all proprioceptive/visual/ tactile/balance/auditory sensations received by the brain - info about motor commands issued at the conscious/subconscious levels reaches the Purkinje cells indirectly, after being relayed by nuclei in the pons or by the cerebellar nuclei - tracts that link cerebellum w/the brain stem, cerebrum, & spinal cord leave the cerebellar hemispheres as the superior, middle, & inferior cerebellar peduncles: • superior cerebellar peduncles - link cerebellum w/nuclei in the midbrain, diencephalon, & cerebrum • middle cerebellar peduncles - are connected to broad band of fibers that cross the ventral surface of the pons at right angles to axis of the brain stem - also connects the cerebellar hemispheres w/sensory & motor nuclei in pons • inferior cerebellar peduncles - communicate btw the cerebellum & nuclei in the MO and carry ascending/descending cerebellar tracts from the spinal cord - cerebellum can be permanently damaged by trauma - cerebellum also affected temporarily by drugs and alcohol - ataxia - disturbance in muscular coordination; result of alcohol, etc. • in severe ataxia, individual cannot sit or stand w/out assistance 14-6: Midbrain regulates auditory & visual reflexes & controls alertness (Martini, Nath, & Bartholomew 475) - tectum - roof of the midbrain • contains 2 pairs of sensory nuclei known collectively as corpora quadrigemina • these nuclei - superior & inferior colliculi - process visual & auditory sensations • each superior colliculus receives visual inputs from the lateral geniculate nucleus of the thalamus on that side • each inferior colliculus receives auditory input from nuclei in the MO & pons • superior colliculi control reflex movements of the eyes, head, & neck in response to visual stimuli • inferior colliculi control reflex movements of the head, neck, & trunk in response to auditory stimuli - anterior area to cerebral aqueduct is called the tegmentum • tegmentum contains a red nucleus & the substantia nigra on each side • red nucleus - red bc contains numerous blood vessels - receives info from the cerebrum & cerebellum & issues subconscious motor commands that affect upper limb position & background muscle tone • substantia nigra is the largest midbrain nucleus - lies lateral to the red nucleus - gray matter in this region contains darkly pigmented cells (melanin) that look black - pigment (melanin) is byproduct of dopamine synthesis - substantia nigra inhibits activity of the basal nuclei in the cerebrum - basal nuclei involved in subconscious control of muscle tone & learned movements - Parkinson’s Disease is characterized by loss of neuronal activity in substantia nigra - cerebral peduncles - nerve fiber bundles on the ventrolateral surfaces of the midbrain • contain descending fibers that go to the cerebellum by way of the pons & descending fibers that carry voluntary motor commands issued by the cerebral hemispheres - reticular activating system (RAS) - in midbrain - specialized component of the reticular formation • stimulation of the RAS makes you more alert & attentive • damage to RAS produces unconsciousness ▯ ▯ ▯ ▯ ▯ figures: (Martini, Nath, & Bartholomew 476) ▯ ▯ ▯ ▯ ▯ (Martini, Nath, & Bartholomew 477) ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯Martini, Nath, & Bartholomew 478) ▯ ▯ ▯ ▯ ▯ ▯ 14-7: Diencephalon integrates sensory info w/motor output at the subconscious level (Martini, Nath, & Bartholomew 477) - diencephalon consists of the: epithalamus, thalamus, & hypothalamus - epithalamus is the roof of the diencephalon superior to the 3rd ventricle • anterior portion contains area of choroid plexus that extends thru the interventricular foramina into the lateral ventricles • posterior portion contains pineal gland (which secretes melatonin) - melatonin regulate day-night cycle & reproductive functions - most of neural tissue in diencephalon concentrated in left & right thalamus which form the lateral walls - hypothalamus forms floor - ascending sensory info from spinal cord & cranial nerves synapses in a nucleus in the left or right thalamus before reaching the cerebral cortex & our conscious awareness - hypothalamus forms the link btw the nervous & endocrine systems The Thalamus - thalamus is the final relay point for sensory info ascending to the primary sensory cortex - acts as a filter - coordinates activities of the basal nuclei (in cerebrum) & cerebral cortex by relaying info btw them - 3rd ventricle separates left & right thalamus - each thalamus consists of rounded mass of thalamic nuclei - interthalamic adhesion - projection of gray matter that extends into the ventricle from the thalamus on either side - thalamic nuclei deal w/the relay of sensory info to the basal nuclei & cerebral cortex - 5 major groups of thalamic nuclei: anterior, medial, ventral, posterior, & lateral groups: • anterior group - involved w/emotion & motivation; includes anterior nuclei which is part of limbic system • medial group nuclei - awareness of emotional states by connecting emotional centers in hypothalamus w.the frontal lobes of the cerebral hemispheres - also receives/relays sensory info from other portions of the thalamus • ventral group nuclei - relay info from basal nuclei to somatic motor areas of the cerebral cortex - relay sensory info about touch, pressure, pain, temp, position • posterior group include pulvinar & geniculate nuclei - pulvinar nuclei - integrate sensory info for projection to cerebral cortex - lateral geniculate nucleus - receives visual info over optic tract • output goes to the occipital lobes & midbrain - medial - geniculate nucleus relay auditory info to cerebral cortex from specialized receptors of the internal ear • lateral group nuclei - form feedback loops w/the limbic system & parietal lobes - affects emotional states & the integration of sensory info ▯ ▯ The Hypothalamus - extends from area superior to the optic chiasm to posterior margins of the mammillary bodies - mammillary bodies - process sensory info & olfactory sensations; involved in memory • contain motor nuclei that control reflex movements associated w/eating - tuberal area - floor of the hypothalamus btw the infundibulum & mammillary bodies • contain nuclei that are involved w/control of pituitary gland function - hypothalamus contain control & integrative centers - hypothalamus centers stimulated by: • sensory info from cerebrum/brain stem/spinal cord • changes in compositions of CSF & interstitial fluid • chemical stimuli in the circulating blood that move across highly permeable capillaries to enter the hypothalamus (where there is no BBB) - Hypothalamus performs following functions: 1. subconscious control of skeletal muscle contractions 2. control of autonomic function 3. coordination of activities of nervous & endocrine systems • regulatory hormones - produced at tuberal area - inhibit/stimulate endocrine cells 4. secretion of 2 hormones:ADH & oxytocin • supraoptic nucleus - producesADh • paraventricular nucleus - produce oxytocin (smooth muscle contraction in uterus, mammary glands, prostate gland) 5. production of emotions & behavioral drives • feeding center stimulation - sensation of hunger • thirst center, satiety center, drives 6. coordination btw voluntary & autonomic functions 7. regulation of body temp. • preoptic area - thermoregulation • coordinates activities of other CNS centers & physiological systems • vasomotor center - autonomic area in MO that controls blood flow by regulating diameter of peripheral b.vessels 8. control of circadian rhythms • suprachiasmatic nucleus - coordinates daily cycles • receives input from retina • output adjusts activities of other hypothalamic nuclei, pineal gland, & reticular formation 14-8: Limbic system function in emotion, motivation, memory -AKAmotivational system - includes nuclei & tracts along border btw cerebrum & diencephalon - functions of limbic system include: 1. establish emotional states 2. link conscious, intellectual functions of cerebral cortex w/unconscious & autonomic functions of the brain stem 3. memory storage & retrieval - amygdala - role in regulating heart rate, fight or flight, link emotions w/memories • interface btw limbic system, cerebrum, & sensory organs - limbic lobe - consist of gyri (superficial folds) - 3 gyri in limbic lobe: • cingulate gyrus - sits superior to corpus callosum • dentate gyrus - posterior portion of limbic lobe • parahippocampal gyrus - inferior portion of limbic lobe - hippocampus important in learning, storage/retrieval of new long-term memories - fornix - tract of white matter that connects hippocampus w/hypothalamus - diencephalon, several other nuclei in thalamus/hypothalamus are components in limbic system (figure: Martini, Nath, & Bartholomew 481) ▯ ▯ Works cited Martini, Frederic, Nath, and Bartholomew. Fundamentals ofAnatomy & Physiology. Tenth ed. San Francisco: Pearson Education, 2015. Print.