Chapter 13 Book Notes
Chapter 13 Book Notes CBIO 2200
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This 12 page Class Notes was uploaded by Rholonda Pruitt on Sunday March 27, 2016. The Class Notes belongs to CBIO 2200 at University of Georgia taught by Leslie Pryor in Fall 2016. Since its upload, it has received 186 views. For similar materials see Anatomy & Physiology I in Anatomy at University of Georgia.
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Date Created: 03/27/16
Chapter 13 Notes 03/23/2016 ▯ 13.1 The Embryologic Perspective The Neural Tube o Ectoderm neuroectoderm = precursor for nervous system tissue o Neural plate – formed by neuroepithelium o Neural groove – visible as a line along the dorsal surface of the embryo o Neural fold – ridge-like edge on either side of the neural groove o Neural tube – when neural folds converge, underlying structure forms into tube beneath ectoderm o Neural crest – cluster of cells formed from cells from neural fold that separate from the ectoderm o Early nervous system is hollow tube o Anterior end of brain becomes brain and posterior end becomes spinal cord Primary Vesicles o Three primary vesicles Prosencephalon – forward-most vesicle; forebrain Mesencephalon – also referred to as the midbrain Rhombencephalon – also referred to as the hindbrain Secondary Vesicles o 3 primary vesicles 5 secondary vesicles Prosencephalon telencephalon cerbrum Prosencephalon diencephalon thalamus and hypothalamus as well as retina Mesencephalon doesn’t differentiate further Rhombencephalon metencephalon pons and cerebellum Rhombencephalon myelencephalon medulla oblongata o Brain stem – midbrain, pons and medulla Spinal Cord Development o As spinal cord develops, cells of neural tube proliferate and differentiate into neurons and glia of the spinal cord o Dorsal tissues sensory functions o Ventral tissues motor functions Relating Embryonic Development to the Adult Brain o Neuroaxis – anterior-posterior dimension of the nervous system o Cephalic flexure – major curve between the brain stem and forebrain o Primary vesicles help establish basic regions in the nervous system o Secondary vesicles establish major regions of the nervous system o No direct connection between the cerebrum and cerebellum in adult brain o Ventricles are remnant of the hollow center of the neural tube ▯ 13.2 The Central Nervous System The Cerebrum o Cerebrum – iconic gray mantle of the brain that appears to make up most of the mass of the brain o Cerebral cortex – wrinkled portion of the cerebrum; outer covering o Longitudinal fissure – large separation between the two sides of the cerebrum; separates the cerebrum into the left and right cerebral hemisphere o Corpus callosum – provides major pathway for communication between the two hemispheres of cerebral cortex o Basal nuclei – responsible for cognitive processing; most important function associated with planning movements o Limbic cortex – part of limbic system; collection of structures involved in emotion, memory, and behavior o Cerebral Cortex Gyrus – ridge of the wrinkles on the cerebral cortex Sulcus – the groove between two gyri Head limited by the size of the birth canal Folding of cerebral cortex allows more of brain to fit into a smaller area Lateral sulcus – separates the temporal lobe from other regions Parietal lobe and frontal lobe separated by central sulcus Occipital lobe – in the posterior region of the brain Parietooccipital sulcus – separates parietal and occipital lobes Brodmann’s areas – describes the anatomical distinctions within the cortex Areas 17 and 18 in occipital lobe associated with primary visual perception Areas 41 and 42 in the temporal lobe associated with primary auditory sensation Temporal lobe associated with long term memory Somatosensation (general sensations associated with the body) associated with parietal lobe Postcentral gyrus – posterior to central sulcus; also known as the primary somatosensory cortex; Brodmann’s areas 1, 2 and 3 Tactile senses processed in this area Proprioception (sense of body position) and kinesthesia (sense of body movement) also processed here Precentral gyrus – also known as the primary motor cortex Premotor area – responsible for thinking of a movement to be made Frontal eye fields – elicit eye movements and attend visual stimuli Broca’s area – responsible for the production of language; control movements responsible for speech Prefrontal lobe – serves cognitive functions that can be the basis of personality, short-term memory, and consciousness o Subcortical Structures Subcortical nuclei – located beneath the cerebral cortex; augments cortical processes; responsible for comparing cortical processing with the general state of activity in the nervous system Striatum Caudate Putamen Globus pallidus Streams of information processing Direct pathway – projection of axons from the striatum to the globus pallidus internal segment and the substantia nigra pars reticulate o GPi/SNr thalamus cortex o Causes disinhibition (inhibition of one cell on a target cell that then inhibits the first cell) Indirect pathway – projection of axons from the striatum to the globus pallidus external segment o GPe subthalamic nucleus GPi/SNr thalamus o Reinforces normal inhibition of the thalamus Substantia nigra pars compacta – projects to striatum and releases dopamine Direct pathway activated by dopamine Indirect pathway inhibited by dopamine Hippocampus – involved in long-term memory formation Amygdala – involved in emotional responses The Diencephalon o Information is sent to the cerebrum through the diencephalon o Olflaction (sense of smell) does not pass through the diencephalon but rather goes directly to/from the cerebrum o Makes up walls of third ventricle o Two major regions: thalamus and hypothalamus Epithalamus contains the pineal glans Subthalamus is part of basal nuclei o Thalamus Thalamus – collection of nuclei that relay information between the cerebral cortex and periphery, spinal cord, or brain stem all sensory information passes through and is processed in thalamus before going to the cortex o Hypothalamus Inferior and slightly anterior to the thalamus Hypothalamus – collection of nuclei that are largely involved in regulating homeostasis Brain Stem o Midbrain Located between the thalamus and the pons Separated into two sections Tectum has 4 colliculi Inferior colliculi – inferior pair of enlargements; part of auditory brain stem pathway Superior colliculi – superior pair of enlargements that combines sensory information about visual, auditory and somatosensory space Tegmentum contains nuclei that send and receive info through cranial nerves o Pons Main connection between the cerebellum and the brain stem o Medulla Reticular formation – diffuse region of gray matter throughout the brain stem that is related to sleep and wakefulness, such as general brain activity and attention The Cerebellum o Is attached to the brain stem but considered a different part of the o Cerebellum – little brain; largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord o Inferior olive - a nucleus in the medulla that sensory information from the spinal and cranial nerves is copied to o Output of cerebellum is into midbrain which then goes to the spinal cord The Spinal Cord o Anterior median fissure – marks the anterior midline of the spinal cord o Posterior median sulcus – marks the posterior midline of the spinal cord o Dorsal (posterior) nerve root – where axons enter the posterior side of the spinal cord; marks the posterolateral sulcus on each side o Ventral (anterior) nerve root – where axons emerge from the anterior side of the spinal cord o Dorsal sensory functions o Ventral motor functions o Basal plate - becomes the anterior face of the spinal cord and gives rise to motor neurons o Alar plate – gives rise to neurons will receive sensory input from the periphery o Regions of the spinal cord from superior to inferior: Cervical thoracic lumbar sacral o Cauda equina – bundle of nerves at caudal end of spinal cord o Gray Horns Posterior horn – responsible for sensory processing Anterior horn – sends out motor signals to the skeletal muscles Lateral horn – only found in thoracic, upper lumbar, and sacral regions; central component of the sympathetic division of the autonomic nervous system o White Columns Ascending tracts – carry sensory information up to the brain Descending tracts – carry motor commands from the brain Posterior columns – white matter between the two dorsal horns; composed of axons of ascending tracts Anterior columns – white matter between the two ventral horns Lateral columns – white matter between the posterior horn and the anterior horn ▯ 13.3 Circulation and the Central Nervous System Blood Supply to the Brain o Arterial Supply Aorta is major artery that carries oxygenated blood away from the heart Arteries that branch off the aorta Common carotid artieries Internal carotid arteries Enters cranium through carotid canal Orthostatic reflex – reaction to change in body position so that blood pressure is maintained against the increasing effect of gravity Vertebral arteries enter the cranium via the foramen magnum Anterior spinal artery – Consists of left and right branches of the vertebral arteries; supplies anterior aspect of the spinal cord Basilar artery – branch off of vertebral artery; gives rise to branches to the brain stem and cerebellum Circle of willis – confluence of arteries that maintain perfusion of the brain o Venous Return Dural sinuses Superior sagittal sinus – absorbs CSF from meninges Drains to confluence of sinuses along with occipital and straight sinuses transverse sinuses Transverse sinuses connect to sigmoid sinuses connect to the jugular vein heart Protective Coverings of the Brain and Spinal Cord o Meninges – series of membranes composed of connective tissue which protects the brain o Dura Mater thick fibrous layer that is a strong protective sheath over the entire brain and spinal cord directly attached to the inner surface of the bones of the cranium and vertebral cavity o Arachnoid Mater Middle layer; membrane of thin fibrous tissues that forms loose sack around CNS Subarachnoid space – where trabeculae are located; filled with circulating CSF Arachnoid trabeculae – think filamentous mesh beneath the arachnoid mater Arachnoid granulations – wehre arachnoid emerges into dural sinuses; where CSF is filtered back into the blood for drainage from the nervous system o Pia Mater Thin fibrous membrane that directly adheres to the brain and spinal cord *needle can be inserted through the dura and arachnoid layers to withdraw CSF at the bottom of the vertebral column since the spinal cord does not extend through its entirety (lumbar puncture) The Ventricular System o Ventricles – open spaces within the brain where CSF circulates o The Ventricles Four ventricles that developed from the central canal Lateral ventricles (2) Third ventricle - connects to the lateral ventricles via the interventricular foramina; space between left and right sides of diencephalon; opens to cerebral aqueduct Cerebral aqueduct opens to the fourth ventricle (space between cerebellum and pons and upper medulla) Ventricular system opens up to the subarachnoid space from the fourth ventricle via the median and lateral aperatures Choroid plexus – specialized membrane within the ventricles that produce the CSF via filtering blood o Cerebrospinal Fluid Circulation Lateral ventricles 3 ventricle cerebral aqueduct 4 ventricle central canal of spinal cord or subarachnoid space (via median and lateral aperatures) Functions of the CSF Picks up metabolic wastes from nervous tissue and removes it from CNS Acts as cushion for brain and spinal cord ▯ 13.4 The Peripheral Nervous System enteric nervous system – special subset of the PNS dealing with the digestive system Ganglia o Sensory ganglia Dorsal (posterior) root ganglion – cell bodies of sensory nerves in periphery; unipolar cells Cranial nerve ganglion – analogous to dorsal root ganglion but cranial nerves instead of spinal nerves o Autonomic system ganglion Sympathetic chain ganglia – receive central input from the lateral horn of the thoracic and upper lumbar spinal cord Paravertebral ganglia – located in the cervical region Prevertebral ganglia – located anterior to vertebral column Terminal ganglia – receive input from cranial nerves or sacral spinal nerves and are responsible for regulating the parasympathetic aspect of homeostatic mechanisms o Plexus – terminal ganglia below the head and neck that are incorporated into the wall of the target organ Enteric plexus – extensive network of axons and neurons in wall of small and large intestines Gastric plexus Esophageal plexus Nerves o Epineurium – outer surface of a nerve o Fascicles – bundles of axons o Perineurium - fibrous connective tissue that covers the fascicles o Endoneurium – loose connective tissue that covers each individual axon o Cranial Nerves 12 nerves that are attached to the brain I. olfactory – sense of smell sensory II. optic – sense of vision sensory III. oculomotor – eye movements; controls four extraocular muscles motor IV. trochlear – eye movement; controls some extraocular muscles motor V. trigeminal – cutaneous sensations of face and controls muscles of mastification both VI. abducens – eye movement; controls some extraocular muscles motor VII. facial – facial expressions, sense of taste, production of saliva both VIII. vestibulocochlear (auditory) – senses of hearing and balance sensory IX. glossopharyngeal – controls muscles of the oral cavity and upper throat; involved in sense of taste and saliva production both X. vagus – contributes to homeostatic control of organs of thoracic and upper abdominal cavities both XI. spinal accessory – controls muscles of neck and cervical spinal nerves motor XII. hypoglossal – control muscles of lower throat and tongue motor o Spinal Nerves Nerves connected to spinal cord All 31 pairs spinal nerves contain sensory (dorsal) and motor (ventral) fibers 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal systemic nerve – where axons from different spinal nerves converge into nerve plexuses cervical plexus – contains axons from C1-C5 and branches into nerves of neck and head as well as phrenic nerve (connects diaphragm to thoracic cavity) brachial plexus – contains axons from C4-T1; give rise to nerves of upper limbs radial nerve branches into axillary nerve which goes to armpit region; paralleled by ulnar nerve and median nerve lumbar plexus – contains axons from L1-L5; give rise to nerves of pelvic region and anterior leg femoral nerve gives rise to saphenous nerve sacral plexus – contains axons from L4-L5 and S1-S4 sciatic nerve consists of tibial and fibular nerves o associated with sciatica (result of compression or irritation of nerves giving rise to it) thoracic spinal nerves from T2-T11 give rise to intercostal nerves ▯ ▯
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