Chapter 14 The Brain and Cranial Nerves Largest organ in the body? Brain functions in sensations, memory, emotions, decision making, behavior 19-1 19-2 Embryonic Brain Development Principal Parts of the Brain (a) 4 weeks (c) Fully developed Telencephalon Prosencephalon Optic vesicle Mesencephalon Metencephalon Rhombencephalon Myelencephalon (b) 5 weeks Telencephalon Forebrain Mesencephalon Midbrain Metencephalon Hindbrain Myelencephalon (medulla oblongata) Figure 14.4 14-3 Cerebrum thalamus hypothalamus Epithalamus Pineal gland Brainstem: Medulla oblongata pons midbrain 19-4 Protective Coverings of the Brain Bone, meninges & CSF Meninges same as around the spinal cord dura mater arachnoid mater pia mater Skull Dura mater: Periosteal layer Meningeal layer Arachnoid villus Arachnoid mater Blood vessel Pia mater Brain: Gray matter White matter Meninges of the Brain Subdural space Subarachnoid space Superior sagittal sinus Falx cerebri (in longitudinal fissure only) 19-5 Figure 14.5 14-6 1
Blood Supply to Brain 2% of weight - uses 20% of our oxygen Internal carotid & vertebral arteries to circle of Willis Vessels on surface of brain----penetrate tissue Blood-brain barrier (BBB) protects cells from some toxins and pathogens a couple of areas without BBB (glucose, ph, osmolarity) Blood-CSF barrier at ependymal cells of choroid plexus Cerebrospinal Fluid 80-150 ml (3 5 oz) Clear liquid water, oxygen, glucose, proteins, & ions Continuously circulates around brain (ventricles, central canal, subarachnoid space) Functions: Buoyancy Mechanical protection Chemical protection (homeostasis) ionic concentrations for AP s removes some metabolic products from nervous tissue 19-7 19-8 Ventricles Flow of Cerebrospinal Fluid 8 Arachnoid villus Superior sagittal sinus Arachnoid mater 1 CSF is secreted by choroid plexus in each lateral ventricle. 2 CSF flows through Interventricular foramina into third ventricle. 2 1 Subarachnoid space Dura mater Choroid plexus 3 Choroid plexus in third ventricle adds more CSF. 3 Third ventricle 4 CSF flows down cerebral aqueduct to fourth ventricle. 4 7 Cerebral aqueduct Lateralaper ture 5 Choroid plexus in fourth ventricle adds more CSF. Fourth ventricle 2 lateral ventricles, one within each cerebral hemisphere, 3rd ventricle, fourth ventricle CSF produced by choroid plexus (ependymal cells Circulation 6 CSF flows out two lateral apertures and one median aperture. 7 CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord. 8 At arachnoid villi, CSF is reabsorbed into venous blood of dural venous sinuses. 6 5 7 Median aperture Centralcanal of spinal cord 19-9 Subarachnoid space of spinal cord Brain stem Medulla oblongata - Relays motor & sensory - brain and spinal cord - all fibers going to/from brain/spinal cord - consciousness/alert - cardiovascular center - respiratory center - bv diameter - motor control - sensory info. Principal Parts of the Brain CSF is reabsorbed through arachnoid villi 19-11 19-12 2
: Infundibulum Mammillary body Midbrain: Cerebral peduncle Medulla and Optic tract Cranial nerves: Optic nerve (II) Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Facial nerve (VII) Vestibulocochlear nerve (VIII) Brain Stem: Medulla Oblongata Nuclei of 5 cranial nerves: 1. Vestibulochochlear (VIII): 2. Glossopharyngeal (IX): (taste, saliva, swallow) 3. Vagus (X): pharynx larynx, thoracic and abdom orgs 4. Accessory (XI): swallowing 5. Hypoglossal (XII): tongue & swallowing Glossopharyngeal nerve (IX) Vagus nerve (X) Medulla oblongata: Pyramid (Decussation) Anterior median fissure Pyramidal decussation (a) Anterior view Figure 14.8a Accessory nerve (XI) Hypoglossal nerve (XII) Spinal nerves Regions of the brainstem Midbrain Medulla oblongata 14-13 19-14 Brain Stem: One inch long Tracts (a & d) Respiratory nuclei Sensory info to cerebellum Trigeminal (V) (head & face) Abducens (VI) eye movement Facial Nerves (VII) head and face, chew, taste Vestibulocochlear (VIII) equilibrium 19-15 Brain Stem: Midbrain (Mesencephalon) One inch in length Extends from pons to diencephalon Cerebral aqueduct connects 3rd to 4th ventricle Cerebral peduncles: - anchor cerebrum to brainstem - impusles to/from cerebellum - inhibitory signals to thalamus - Relays sensory & motor impulses Tectum: -superior and inferior colliculi (reflexes) Oculomotor (III) eye movement & sight Trochlear (IV) eye 19-16 movements Midbrain -- Cross Section : Posterior Infundibulum Mammillary body Midbrain: Cerebral peduncle -Anchor cerebrum to brainstem Optic tract Cranial nerves: Optic nerve (II) Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Tectum Reticular formation Cerebral peduncle: Tegmentum Substantia nigra Superior colliculus leaves Cerebral aqueduct Medial geniculate nucleus Central gray matter Oculomotor nucleus Medial lemniscus Red nucleus (a) Midbrain Medulla oblongata: Pyramid Anterior median fissure Pyramidal decussation (a) Anterior view Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Regions of the brainstem Hypoglossal nerve (XII) Midbrain Spinal nerves Medulla oblongata 14-17 Cerebral crus Anterior (a) Midbrain Oculomotor nerve (III) (b) (c) Medulla 1. Tegmentum - with cerebellum for fine motor control 2. Substantia nigra motor center relays inhibitory signals to thalamus & basal nuclei preventing unwanted body movement 3. Cerebral crus: fibers that connects cerebrum to the pons carries corticospinal tracts 3
Visual input Reticular formation Ascending general sensory fibers Descending motor fibers to spinal cord Reticular Formation Radiations to cerebral cortex Auditory input reticular formation loosely organized web of gray matter that run vertically through all levels of the brainstem has connections with many areas of cerebrum and cerebral cortex 14-19 Functions of Reticular Formation Somatic motor control adjust muscle tension (maintain tone, balance, and posture) relays signals from eyes and ears to the cerebellum integrates visual, auditory, and balance and motion stimuli into motor coordination cardiovascular control: cardiac and vasomotor centers of M.O. pain modulation One route pain signals may take to reach cerebral cortex sleep and consciousness central role in states of consciousness!!!!!!!! Habituation (filter) 14-20 relay Superior colliculus Inferior colliculus Pineal gland Posterior commissure Cerebral aqueduct White matter (arbor vitae) Gray matter Mammillary body Midbrain Oculomotor nerve Fourth ventricle Medulla oblongata 2 cerebellar hemispheres and vermis (central area) Function Sensory input from muscles Receives fibers from cerebral cortex associated with vision, hearing, coordination i.e., correct voluntary muscle contraction and posture & balance skilled fine tuned movements indirectly by sending information to midbrain knowledge/language/emotional component?? 19-21 (a) Median section cerebellar peduncles three pairs of stalks that connect the cerebellum to the brainstem inferior peduncles connected to medulla oblongata middle peduncles connected to the pons superior peduncles connected to the midbrain 14-22 The Forebrain 1. diencephalon encloses the third ventricle 3 major areas thalamus hypothalamus epithalamus 2. Telencephalon cerebrum (c) Fully developed Telencephalon Forebrain Mesencephalon Midbrain Metencephalon Myelencephalon (medulla oblongata) Hindbrain 14-23 19-24 4
: Gateway to the Cerebral Cortex 1 inch long mass of gray mater Relay station for sensory information on way up to cerebral cortex Motor control: relay information from cerebellum to cerebrum Crude perception of some sensations 19-25 relays auditory and visual impulses, taste and somatic sensations, touch, pain, temperature receives sensory impulses from cerebellum re. motor control autonomic activities & consciousness (RAS) 19-26 Hypothalamus Functions of Hypothalamus Controls & integrates activities of ANS Synthesizes hormones that controls the anterior pituitary Regulates rage, aggression, pain, fear, pleasure, contentment even arousal & orgasm Feeding, thirst & satiety centers Controls body temperature Sleep and circadian rhythms Memory Many nuclei (masses of grey matter) Major regulator of homeostasis!!!!!!!!!! 19-27 19-28 Cerebrum Composed of 2 cerebral hemispheres Cerebral cortex is gray matter 2-4 mm thick contains billions of cells Folds (gyri) & grooves (sulci or fissures) Cerebral hemispheres Longitudinal fissure: separates L & R Cerebral Hemispheres Corpus callosum band of white matter connects L & R cerebral hemis. Each hemisphere is subdivided into 4 lobes 19-29 19-30 5
Lobes and Fissures Longitudinal fissure (green) Frontal lobe Central sulcus (yellow) Parietal lobe Parieto-occipital sulcus (red) Occipital lobe Lateral sulcus (blue) Temporal lobe Insula Cerebral Cortex 2 principal types of neurons: 1. stellate cells receive sensory input & process information on a local level 2. pyramidal cells tall, conical. output neurons of the cerebrum only neurons that leave the cortex and connect to other parts of CNS neocortex six layered tissue that constitutes about 90% of the human cerebral cortex I II III IV V Cortical surface Small pyramidal cells Stellate cells Large pyramidal cells VI 19-31 White matter 14-32 Cerebral White Matter The Basal Nuclei Cerebrum Corpus callosum Lateral ventricle Internal capsule Caudate nucleus 1. Association fibers - between gyri in same hemi. 2. Commissural fibers - from one hemi. to other 3. Projection fibers - form descending & ascending tracts (info to and from whole body) 19-33 Insula Third ventricle Hypothalamus Pituitary gland Subthalamic nucleus Optic tract masses of gray matter buried deep in white matter, lateral to the thalamus receive & send info to midbrain & motor areas of cerebral cortex involved in motor control At least three areas form basal nuclei caudate nucleus putamen globus pallidus 14-34 Putamen Globus pallidus Lentiform nucleus Corpus striatum Figure 14.16 Limbic System Amygdala, cingulate gyri, & hippocampus Emotional brain--intense pleasure & intense pain Strong emotions increase efficiency of memory 19-35 Important center of emotion and learning most anatomically prominent components are: cingulate gyrus arches over the top of the corpus callosum in the frontal and parietal lobes hippocampus in the medial temporal lobe - memory amygdala immediately rostral to the hippocampus - emotion limbic system components are connected through complex loop of fiber tracts. limbic system structures have centers for both gratification and aversion gratification sensations of pleasure or reward aversion sensations of fear or sorrow Medial prefrontal cortex Corpus callosum Cingulate gyrus Orbitofrontal cortex Basal nuclei Amygdala Temporal lobe Limbic System Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-36 Fornix Thalamic nuclei Mammillary body Hippocampus 6
Functional organization of the cerebral cortex Movements Sensations: Touch, Pain, Temp. Thought Understanding written & spoken language Forethought Judgment Feelings Speech Emotions Recognition Memory 19-37 7