Chapter 14: Brain and Cranial Nerves PDF

Chapter 14: Brain and Cranial Nerves - Neurulation During the 3rd week of gestation, the ectoderm thickens forming the neural plate. The neural plate folds inward forming the longitudinal groove and eventually the folds meet to form the neural plate. -...

Chapter 14: Brain and Cranial Nerves - Neurulation During the 3rd week of gestation, the ectoderm thickens forming the neural plate. The neural plate folds inward forming the longitudinal groove and eventually the folds meet to form the neural plate. - The Nervous System: The development of the nervous system begins with a thickening of the ectoderm called the neural tube. *The spinal cord and brain begin as a a neural tube* - Primary vesicles: Neural tube’s anterior end expands and constrictions form Prosencephalon or forebrain Mesencephalon or midbrain Rhombencephalon or hindbrain - Brain protective layers 1. Cranial bones 2. Cranial meninges - Pia mater (composed of two layers) - Arachnoid mater - Cura mater 3. Cerebral spinal fluid. - Dura mater: is the strong meaning that extends inward in several areas to form flat partitions that divide cranial activity. Limits excessive brain movement and its made up of two layers 1. Periosteal layer: attaches to inner surface of skull and found only in brain 2. Meningeal layer: true external covering of brain and extends into cerebral cna as spinal dura mater - Dural venous sinuses: Two layers are most fused but separate in certain areas to form this. They collect venous blood from the brain, empty into jugular veins. - Arachnoid: middle layer separated from dura mater by subdural space. Permits reabsorption of CSF. Subarachnoid space: contains CSF and largest blood vessels of the brain. - Pia mater: delicate connective tissue that clings tightly to the brain, and contains many tiny blood vessels that feed the brain. - Blood: flows to the brain via the vertebral and carotid arteries and flows back to the heart via the jugular veins. - Brain: utilizes about 20% of the body oxygen, but any damage to it can causes weakening, permanent damage, or death of brain cells - Glucose deficiency: may produce mental confusions, dizziness, convulsions, and unconsciousness. - Blood Brain Barrier (BBB): protects brain cells from harmful substances and pathogens by serving as a selective protective barrier to prevent passage of many substances from the blood to the brain *Can prevent the entry of therapeutic drugs* - 4 regions of the Adult Brain 1. Cerebral hemispheres 2. Diencephalon  3. Brainstem - Midbrain - Pons - Medulla 4. Cerebellum - Cerebral cortex: composed of ray matter which contains billions of neurons Gray matter: short, nonmyelinated neurons and cell bodies. White matter: myelinated and nonmyelinated axons. It is also tracts that connect parts of the brain to each other and the spinal cord. - Corpus callosum: A bundle of white matter tracts that connects the left and right hemispheres of the cerebrum - Cerebral white matter: consists primarily of myelinated axons and there are three types of tracts 1. Association tracts: conducts nerve impulses between cerebral gyri in the same hemisphere. 2. Commissural tracts: conducts nerve impulse from cerebral gyri in one cerebral hemisphere to corresponding, cerebral gyri in the other cerebral hemisphere. *Groups that provide communication between two hemispheres* - Corpus callosum - Anterior commissure - Posterior commissure 3. Projection tracts: conducts nerve impulse from the cerebrum to lower parts of the CNS s or from lower parts of the CNS to the cerebrum. - Basal nuclei: are paired masses of gray matter in each cerebral hemisphere. Also known as the corpus striatum. - Function of the basal nuclei Influences muscle movements Plays role in cognition and emotion Regulate intensity of slow or stereotypes movements Filter our incorrect/ inappropriate responses Inhibit antagonistic/unnecessary movements - Disease of basal nuclei Parkinson's disease: is the degeneration of the midbrain. Huntigton’s disease - Limbic system: Found in the cerebral hemispheres and diencephalon. Part of the forebrain and referred to as the emotional brain. It is also involved in olfaction and memory. - Components of the limbic system: Limbic lobe, dentate gyrus, amygdala, septal nuclei, mammillary bodies, anterior thalamic bodies, olfactory bulbs, and bundles of myelinated axons. - CSF: Production is from the choroid plexus. Iti circulates in the central canal of the spinal cord. - Ventricles: are fluid-filled chambers that are continuous to one another and to the central canal of the spinal cord. It is filled with CSF and lined by ependymal cells. Lateral ventricle: is connected to the third ventricle vi interventricular. Third ventricle: is connected to the fourth ventricle via cerebral aqueduct and lies in diencephalon  Fourth ventricle: lies in the hindbrain and continuous with the central canal of spinal cord. - Cerebrum Frontal lobe Parietal lobe Temporal lobe Occipital lobe Insula lobe: buried under portions of temporal, parietal, and frontal lobes. - Three types of functional areas Motor areas: Located in the frontal lobe, motor areas act to control voluntary movement. Sensory areas: conscious awareness of sensation. Association: integrate diverse information - Primary (somatic) Motor cortex: Located in the precentral gyrus at the frontal lobe. Pyramidal cells: large neurons that allows conscious control of precises, skilled, skeletal muscle movements, - Premotor cortex: helps plan movements and its voluntary (controls learned, repetitious or patterned motor skills) - Broca’s areas: present in left hemispheres, directs muscles of speech production, and voluntary motor activities. - Frontal eye field: control voluntary eye movements. - Brain waves: indicated electrical activity of the cerebral cortex and recorded via electrocardiogram. Alpha waves: occurs when people are aware and resting with their eyes closed. They disappear during sleep. Beta waves: appear when the nervous system is active. During periods of sensory and mental activity. Theta waves: occurs when children and adults experience emotional stress. Delta waves: occurs during sleep in adults and in awake infants. - Diencephalon: forms the thalamus, hypothalamus, and epithalamus,, and third ventricle. - Thalamus: makes up 80% of diencephalon, Relay station for all sensory impulses to the cerebral cortex. Sort, edit, and relay,ascending input and act to mediate sensation, motor activities, cortical arousal, learning and memory. - Hypothalamus: control many body activities, inferior to the thalamus, and is one of the major regulators of homeostasis. Sensory impulses related to both somatic and visceral senses arrive here. Functions of hypothalamus - Control of the Autonomic Nervous System (ANS) - Production of hormones - Regulation of emotional and behavioral protein. - Regulation of eating and drinking - Control of body temperature - Regulation of circumduction - Epithalamus: lies superior and posterior to the thalamus. Consists of the pineal gland a and habenular nuclei - Pineal gland: secretes melatonin, which regulates circadian rhythms. - Circumventricular organs (CVOs): Can monitor chemical changes in blood because they lack a blood-brain barrier. Site of entry into the brain of HIV, regulates blood pressure, fluid balance, hunger, and thirst. - Cerebellum: consists of 2 hemispheres and central vermis, 11% of brain mass: Process input from cortex, brainstem, and sensory receptors to provide precise, coordinated movements of skeletal muscles. Also play a major role in balance. Folia: transversely oriented gyri Purkinje fibers: originate in coretex, synapse with cerebellum. - Cerebellum fine tune motor activity Receives impulses from cerebral cortex of intent to initiate voluntary impulse muscle control Receives signals from proprioceptors throughout the body, as well as visual and equilibrium pathways. Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction Send “Blueprint” of coordinated movement to the cerebral motor cortex and brainstem nuclei. - Brainstem: control automatic behavior necessary for survival and has three regions. It contains nuclei embedded in white matter, and fibers tracts containing higher and lower neural centers. - Medulla: Relay sensory pathway information from skin and proprioceptors. Control heart rate, blood vessel diameters, and respiratory rate vomiting, and coughing. - Structures of the medulla Pyramids: two ventral longitudinal ridges, formed by pyramids tracts from the motor cortex. Discussion of the pyramids: point where pyramids tracts cross over to opposite side of body Olives: swellings caused by underlying inferior olivary nuclei that relay stretch information from muscles and joints to cerebellum. - Functional groups of medulla. Cardiovascular center - Cardiac center: adjusts force and rate of contractions - Vasomotor center: adjusts blood vessel diameter for blood pressure regulation. - Pons: relays information from the cerebrum to the cerebellum, it links parts of the brain with one by way of tracts - Cranial nerves for Pons: trigeminal, abducens, facial, and vestibulocochlear. - Midbrain: relaxes that govern movement of the head, eye, and trunk, in response to visual stimuli.Relays system for information obtained in vision and hearing, coordinates start reflex - Structural regions of midbrain Cerebral peduncle: two ventral bulges that contain pyramidal motor tracts Corpora quadrigemina: paired dorsal protrusions. Superior colliculus: auditory relay centers Inferior colliculi: auditory relay centers. Substantia nigra: functionally, linked to basal nuclei. Red nuclei  Medial lemniscus - Functional regions of Midbrain Conveys motor impulses from the cerebrum to the cerebellum and spinal cord Sends sensory impulses from the spinal cord to the thalamus Regulated auditory and visual reflexes. - Cranial nerves of midbrain: oculomotor and Trochlear. - Reticular formation: is responsible for maintaining consciousness and awakening from sleep. Helps regulate muscle tones, and visceral muscle activity. - Cranial nerves: arise from the brain and pons through the foramina in the bones of the cranium and there are 12 pairs. 1, 2,8: carry of sensory neurons and thus are called special sensory nerves. 3, 4, 6, 1, 12: motor nerves. 5, 7, 9, 10: mixed nerves. It contains axons of both sensory neurons entering the brainstem and motor neurons leaving the brainstem. - Olfactory (I): conscious awareness of dors - Optic (II): vision - Oculomotor (III): Movement of eyelid and eyeball, accommodation of lens, and pupillary constriction. - Trochlear (IV): Movement of eyeball and smallest. - Trigeminal (V): cutaneous sensation from ophthalmic, maxillary, and mandibular areas. - Abducens (VI): Lateral rotation of the eyeball - Facial (VII): Tastes, facial expression, secretion of tears, and salivation. - Vestibulocochlear (VIII): Equilibrium and hearing - Glossopharyngeal (IX): Tastes, swallowing, and speech, and secretion, of saliva. - Vagus (X): Tastes, somatic sensation from epiglottis and pharynx, swallowing, voice production, slows heart rate. - Accessory (XI): Swallowing, movement of head and shoulders. - Hypoglossal (XII): Speech and swallowing.