Brain and Cranial Nerves PDF

Brain and Cranial Nerves (MTT, Chap. 16) I. Introduction A. information processing 1. reflex responses (visual, visceral, CV, respiratory) 2. subconscious activity 3. conscious activity, memory, abstract thought B. embryological origin...

Brain and Cranial Nerves (MTT, Chap. 16) I. Introduction A. information processing 1. reflex responses (visual, visceral, CV, respiratory) 2. subconscious activity 3. conscious activity, memory, abstract thought B. embryological origin 1. initially derived from three components a. prosencephalon - forebrain (1) telencephalon - cerebrum (2) diencephalon - thalamus + hypothalamus, pituitary b. mesencephalon - midbrain c. rhombencephalon - hindbrain (1) metencephalon (i) pons (ii) cerebellum (3) myelencephalon - medulla C. adult brain 1. 100 billion neurons (more than six) 2. principle components a. brainstem b. diencephalon c. cerebrum d. cerebellum II. Rhombencephalon - hindbrain A. medulla oblongata 1. all ascending & descending tracts 2. most nerve tracts decussate 3. control centers: cardiac, vasomotor, respiratory, vomiting, coughing, swallowing B. pons (bridge) 1. bulge on underside of brainstem 2. relay center a. nerve tracts to cerebellum b. form cerebellar peduncles 3. pontine control centers (apneustic, pneumotaxic centers) C. cerebellum 1. structure a. second largest structure w/i cranial cavity b. subdivided into two hemispheres c. vermis - narrow lobular structure separating lobes d. thin layer of grey matter (1) white matter tracks have branched pattern (2) arbor vitae e. connected to medulla by 3 nerve tracts/lobe f. cerebellar peduncles (1) superior - fibers from cerebellum to motor cortex via thalamus (2) middle - fibers from motor cortex to cerebellum (3) inferior - incoming vestibular and proprioceptive fibers 2. cerebellar function a. control & coordination of skeletal muscle activity b. compares intended to actual movements c. damage results in tremors, loss of equilibrium & inaccurate movements III. Mesencephalon – Midbrain A. brainstem between pons & diencephalon 1. corpora quadrigemina a. superior colliculi – visual reflexes b. inferior colliculi – auditory reflexes 2. basal nuclei a. dark internal areas within CNS b. contain high density of cell bodies c. red nucleus and substantia nigra. (1) between cerebral hemispheres and cerebellum (2) motor coordination, posture IV. Prosencephalon – Forebrain A. diencephalon (thalamus & hypothalmus) 1. structure a. surrounded by cerebrum b. principally gray matter c. thalamus a. paired nuclei on each side of 3rd ventricle b. intermediate mass (commissure) – bridge between pair d. hypothalamus (1) scattered nuclei inferior to thalamus 2. function a. thalamus (1) relay station for all sensory traffic (except olfactory) (2) relay traffic to specific cerebral area for further processing (3) some sensory interpretation b. hypothalamus (1) autonomic nervous regulatory center (2) maintenance of homeostasis (CV, fluid and electrolyte, temperature, satiety, sleep, endocrine function) c. pituitary gland (hypophysis) (1) oval gland attached to hypothalamus by infundibulum (2) consists of two lobes i. adenohypophysis (anterior pituitary) ii. neurohypophysis (posterior pituitary) (3) function – present in endocrine section (2nd semester) d. pineal gland (1) small globular mass at post. corpus callosum (2) function i. secretes melatonin ii. maintains diurnal cycle B. cerebrum 1. structure a. largest part of mature brain b. two large cerebral hemispheres c. surface marked by convolutions (gyri) and grooves (sulci) d. lobes identified by cranial bones they underlay i. frontal ii. parietal iii. occipital iv. temporal v. insula e. other significant landmarks i. longitudinal cerebral fissure ii. central sulcus iii. lateral sulcus f. cerebral cortex (1) thin (2 – 5 mm ) gray matter, outermost cerebrum (2) contains 75% of cell bodies of nervous system g. white matter (1) bulk of cerebrum (2) contains myelinated nerve fibers h. two hemispheres joined at corpus callosum (1) C shaped structure, composed of decussating tracks (2) two lateral ventricles separated by septum pellucidum (3) intermediate mass (commissure of thalamus) (4) fornix – arches over thalamus, connects hippocampus to hypothalamus 2. limbic system a. ring of structures on inner border of the cerebrum (hippocampus, cingulate gyrus, fornix, hypothalamus, etc.) b. function i. emotional response center ii. memory 3. reticular activating system a. complex network of grey matter islands b. extends from spinal cord to diencephalon & cerebrum c. function: i. filter ii. adjusts state of wakefulness C. cerebral function 1. introduction a. early studies – brain lesions i. causes (1) stroke – cerebral vascular attack (2) TIA (transient ischemic accidents) ii. relate loci to loss of functionality b. imaging studies i. functional architecture (1) neurons with similar responses organized in cortical columns (2) neuronal activity evokes hemodynamic & metabolic changes ii. matching function with: (1) changes in cerebral blood flow (2) changes in metabolism iii. imaging techniques (1) PET (positron emission tomography) (2) MRI (magnetic resonance imaging) (3) optical imaging spectroscopy 2. sensory areas a. primary - receive input from sensory receptors b. primary somatosensory area (1) postcentral gyrus primary motor primary somatosensory area area (2) somatotropic organization (significance) c. primary visual area d. primary auditory area e.primary olfactory area f.primary vestibular area g.primary gustatory area 3. motor areas a. primary motor cortex (1) located on anterior central gyrus (2) neurons supply corticospinal tracts (3) somatotropic organization primary motor cortex b. language areas (1) translation of thought into writing or speech (2) Broca’s area – anterior motor cortex (3) coordinates speech (4) Broca’s aphasia – nonfluent, vocabulary reduced to a few words, sometimes expletives, reduced understanding written or spoken language. 4. association areas a. located close to each primary sensory area b. fn to analyze & interpret sensory experience c. somatosensory association area (spatial association area) (1) posterior primary sensory cortex (2) integrates & interprets sensation d. visual association area (secondary visual cortex) (1) occipital lobe (2) relates past with present visual information e. auditory association area (Wernicke’s) (1) inferior to primary auditory area (2) translates words into thoughts (3) Wernicke’s aphasia (a) fluent speech, most meaningless ("word salad") (b) loss of understanding of written & spoken language An example of Wernicke's speech: "Well this is... mother is away here, working her work out o'here to get better, what when she's looking, the two boys looking in other part, one their small tile, into her time here, she's working another time because she's getting to....." f. gnostic area (general interpretative area) (1) posterior sensory cortex (2) integrates sensory associative areas (3) determines responses somatosensory association area visual association area general intrepretative area (gnostic) g. premotor area (1) anterior to primary motor cortex (2) coordinates complex, learned motor movements h. frontal eye field area (1) frontal cortex (2) controls voluntary eye scanning movements V. Cranial Nerves A. Introduction 1. 12 pair of nerves, orginating from brain 2. travel through cranial foramina to destination 3. motor, sensory or mixed (majority) 4. designated by roman numeral and name B. learn name, number, and function (mnemonic devices) I. On Olfactory sensory - Some II. Old Optic sensory - Say III. OlympusOculomotor motor - Marry IV. Towering Trochlear motor - Money V. Top Trigeminal both - But VI.A Abducens motor - My VII. Foolish Facial both - Brother VIII. Austrian Vestibulocochlear (acoustic) sensory - Says IX. Grew Glossopharyngeal both - Big X. Vines Vagus both - Brains XI. And Accessory (somatoaccessory) motor - 1. olfactory I (sensory) a. sense of smell b. olfactory nerve is actually a “forest of nerves” c. olfactory receptors→ olfactory bulb → olfactory tract → olfactory cortex d. only cranial nerve attached directly to cerebrum 2. optic II (sensory) a. vision b. optic nerve carries 1 X 106 sensory fibers c. retina → optic chiasma → optic tract → thalamus (lateral geniculate nucleus) → primary visual cortex d. fibers from medial retina decussate, lateral remain ipsilateral e. each hemisphere recieves ipsilateral lateral & contralateral medial input 3. oculomotor III (motor) a. autonomic motor – parasympathetic, pupil and lens accommodation b. somatic motor – eyelid and eye muscles (superior, inferior, medial rectus, inferior oblique) c. sensory – proprioception, eye position (minor) 4. trochlear IV (motor) a. somatic motor – eye muscles (superior oblique) b. sensory - proprioception, eye position (minor) 5. trigeminal V(mixed) a. largest cranial nerve b. sensory (1) opthalmic - eye surface, tear gland, scalp, forehead, upper eyelid (2) maxillary – upper teeth, gums, face, palate, lower eyelid (3) mandibular – lower teeth, gums, lips, tongue c. motor- (mandibular) muscles of mastication 6. abducens VI (motor) a. motor – eye muscle (lateral rectus) b.sensory – proprioception, eye position (minor) 7. facial VII (mixed) a. sensory – taste, palate b. motor – facial muscles, tear & salivation 8. vestibulocochlear VIII (sensory) a. hearing and equilibrium b. originates from cochlea and semicircular canals 9. glossopharyngeal IX (mixed) a. sensory – tongue, pharynx, tonsils, baroreceptors b. motor - swallowing 10. vagus X (mixed) a. motor (somatic) – swallowing, vocalization b. motor (autonomic) – cardiovascular, repiratory & digestive organs c. sensory – visceral sensation 11. accessory – XI (motor) a. motor – larynx, sternocleidomastoid, trapezius b. sensory – proprioception from shoulders and neck (minor) 12. hypoglossal XII (motor) a. motor – tongue b. sensory – proprioception from tongue (minor)