Transcript File
Hypothalamic Function • Regulates body temperature, food intake, water balance, and thirst • Regulates sleep and the sleep cycle • Controls release of hormones by the anterior pituitary • Produces posterior pituitary hormones Epithalamus • Most dorsal portion of the diencephalon; forms roof of the third ventricle • Pineal gland—extends from the posterior border and secretes melatonin • Melatonin—helps regulate sleep-wake cycles Cerebral hemisphere Septum pellucidum Interthalamic adhesion (intermediate mass of thalamus) Interventricular foramen Anterior commissure Hypothalamus Optic chiasma Pituitary gland Mammillary body Pons Medulla oblongata Corpus callosum Fornix Choroid plexus Thalamus (encloses third ventricle) Posterior commissure Pineal gland (part of epithalamus) Corpora quadrigemina MidCerebral brain aqueduct Arbor vitae (of cerebellum) Fourth ventricle Choroid plexus Cerebellum Spinal cord Figure 12.12 Brain Stem • Three regions • Midbrain • Pons • Medulla oblongata Brain Stem • Similar structure to spinal cord but contains embedded nuclei • Controls automatic behaviors necessary for survival • Contains fiber tracts connecting higher and lower neural centers • Associated with 10 of the 12 pairs of cranial nerves Frontal lobe Olfactory bulb (synapse point of cranial nerve I) Optic chiasma Optic nerve (II) Optic tract Mammillary body Midbrain Pons Temporal lobe Medulla oblongata Cerebellum Spinal cord Figure 12.14 View (a) Optic chiasma Optic nerve (II) Crus cerebri of cerebral peduncles (midbrain) Diencephalon • Thalamus • Hypothalamus Mammillary body Thalamus Hypothalamus Diencephalon Midbrain Oculomotor nerve (III) Trochlear nerve (IV) Pons Brainstem Medulla oblongata Trigeminal nerve (V) Pons Facial nerve (VII) Middle cerebellar peduncle Abducens nerve (VI) Vestibulocochlear nerve (VIII) Pyramid Glossopharyngeal nerve (IX) Hypoglossal nerve (XII) Vagus nerve (X) Ventral root of first cervical nerve Decussation of pyramids Accessory nerve (XI) Spinal cord (a) Ventral view Figure 12.15a Crus cerebri of cerebral peduncles (midbrain) Thalamus View (b) Infundibulum Pituitary gland Superior colliculus Inferior colliculus Trochlear nerve (IV) Trigeminal nerve (V) Pons Superior cerebellar peduncle Middle cerebellar peduncle Facial nerve (VII) Abducens nerve (VI) Glossopharyngeal nerve (IX) Hypoglossal nerve (XII) Inferior cerebellar peduncle Vestibulocochlear nerve (VIII) Olive Thalamus Vagus nerve (X) Hypothalamus Diencephalon Midbrain Accessory nerve (XI) Pons Brainstem Medulla oblongata (b) Left lateral view Figure 12.15b Thalamus View (c) Diencephalon Pineal gland Anterior wall of fourth ventricle Choroid plexus (fourth ventricle) Dorsal median sulcus Dorsal root of first cervical nerve Midbrain • Superior Corpora colliculus quadrigemina • Inferior of tectum colliculus • Trochlear nerve (IV) • Superior cerebellar peduncle Pons • Middle cerebellar peduncle Medulla oblongata • Inferior cerebellar peduncle • Facial nerve (VII) • Vestibulocochlear nerve (VIII) • Glossopharyngeal nerve (IX) • Vagus nerve (X) • Accessory nerve (XI) Thalamus Hypothalamus Midbrain Pons (c) Dorsal view Diencephalon Brainstem Medulla oblongata Figure 12.15c Midbrain • Located between the diencephalon and the pons • Cerebral peduncles • Contain pyramidal motor tracts • Cerebral aqueduct • Channel between third and fourth ventricles Midbrain Nuclei • Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) • Corpora quadrigemina—domelike dorsal protrusions • Superior colliculi—visual reflex centers • Inferior colliculi—auditory relay centers • Substantia nigra—functionally linked to basal nuclei • Red nucleus—relay nuclei for some descending motor pathways and part of reticular formation Tectum Periaqueductal gray matter Oculomotor nucleus (III) Medial lemniscus Red nucleus Substantia nigra Fibers of pyramidal tract (a) Midbrain Dorsal Superior colliculus Cerebral aqueduct Reticular formation Ventral Crus cerebri of cerebral peduncle Figure 12.16a Pons • Forms part of the anterior wall of the fourth ventricle • Fibers of the pons • Connect higher brain centers and the spinal cord • Relay impulses between the motor cortex and the cerebellum • Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) • Some nuclei of the reticular formation • Nuclei that help maintain normal rhythm of breathing Fourth ventricle Superior cerebellar peduncle Trigeminal main sensory nucleus Trigeminal motor nucleus Middle cerebellar peduncle Trigeminal nerve (V) Medial lemniscus (b) Pons Reticular formation Pontine nuclei Fibers of pyramidal tract Figure 12.16b Medulla Oblongata • Joins spinal cord at foramen magnum • Forms part of the ventral wall of the fourth ventricle • Contains a choroid plexus of the fourth ventricle • Pyramids—two ventral longitudinal ridges formed by pyramidal tracts • Decussation of the pyramids—crossover of the corticospinal tracts Medulla Oblongata • Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum • Cranial nerves VIII, X, and XII are associated with the medulla • Vestibular nuclear complex—mediates responses that maintain equilibrium • Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information Medulla Oblongata • Autonomic reflex centers • Cardiovascular center • Cardiac center adjusts force and rate of heart contraction • Vasomotor center adjusts blood vessel diameter for blood pressure regulation Medulla Oblongata • Respiratory centers • Generate respiratory rhythm • Control rate and depth of breathing, with pontine centers Medulla Oblongata • Additional centers regulate • Vomiting • Hiccuping • Swallowing • Coughing • Sneezing Reticular formation Fourth ventricle Choroid Hypoglossal nucleus (XII) plexus Dorsal motor nucleus of vagus (X) Inferior cerebellar peduncle Lateral nuclear group Medial nuclear group Raphe nucleus Medial lemniscus (c) Medulla oblongata Solitary nucleus Vestibular nuclear complex (VIII) Cochlear nuclei (VIII) Nucleus ambiguus Inferior olivary nucleus Pyramid Figure 12.16c The Cerebellum • 11% of brain mass • Dorsal to the pons and medulla • Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction Anatomy of the Cerebellum • Two hemispheres connected by vermis • Each hemisphere has three lobes • Anterior, posterior, and flocculonodular • Folia—transversely oriented gyri • Arbor vitae—distinctive treelike pattern of the cerebellar white matter Anterior lobe Cerebellar cortex Arbor vitae Cerebellar peduncles • Superior • Middle • Inferior Medulla oblongata (b) Flocculonodular lobe Posterior lobe Choroid plexus of fourth ventricle Figure 12.17b Anterior lobe Posterior lobe (d) Vermis Figure 12.17d Cerebellar Peduncles • All fibers in the cerebellum are ipsilateral • Three paired fiber tracts connect the cerebellum to the brain stem • Superior peduncles connect the cerebellum to the midbrain • Middle peduncles connect the pons to the cerebellum • Inferior peduncles connect the medulla to the cerebellum Cerebellar Processing for Motor Activity • Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction • Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum • Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction • A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei Cognitive Function of the Cerebellum • Recognizes and predicts sequences of events during complex movements • Plays a role in nonmotor functions such as word association and puzzle solving Protection of the Brain • Bone (skull) • Membranes (meninges) • Watery cushion (cerebrospinal fluid) • Blood-brain barrier Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in the skull Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Dura Mater • Strongest meninx • Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses Dura Mater • Dural septa limit excessive movement of the brain • Falx cerebri—in the longitudinal fissure; attached to crista galli • Falx cerebelli—along the vermis of the cerebellum • Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure Superior sagittal sinus Straight sinus Crista galli of the ethmoid bone Pituitary gland Falx cerebri Tentorium cerebelli Falx cerebelli (a) Dural septa Figure 12.25a Arachnoid Mater • Middle layer with weblike extensions • Separated from the dura mater by the subdural space • Subarachnoid space contains CSF and blood vessels • Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Pia Mater • Layer of delicate vascularized connective tissue that clings tightly to the brain Cerebrospinal Fluid (CSF) • Composition • Watery solution • Less protein and different ion concentrations than plasma • Constant volume Cerebrospinal Fluid (CSF) • Functions • Gives buoyancy to the CNS organs • Protects the CNS from blows and other trauma • Nourishes the brain and carries chemical signals Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation 2 choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a Choroid Plexuses • Produce CSF at a constant rate • Hang from the roof of each ventricle • Clusters of capillaries enclosed by pia mater and a layer of ependymal cells • Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes Ependymal cells Capillary Section of choroid plexus Connective tissue of pia mater Wastes and unnecessary solutes absorbed CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) (b) CSF formation by choroid plexuses Cavity of ventricle Figure 12.26b Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances Blood-Brain Barrier • Composition • Continuous endothelium of capillary walls • Basal lamina • Feet of astrocytes • Provide signal to endothelium for the formation of tight junctions Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia. Figure 11.3a Blood-Brain Barrier: Functions • Selective barrier • Allows nutrients to move by facilitated diffusion • Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood Homeostatic Imbalances of the Brain • Traumatic brain injuries • Concussion—temporary alteration in function • Contusion—permanent damage • Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death • Cerebral edema—swelling of the brain associated with traumatic head injury Homeostatic Imbalances of the Brain • Cerebrovascular accidents (CVAs)(strokes) • Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot • Typically leads to hemiplegia, or sensory and speed deficits • Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia • Tissue plasminogen activator (TPA) is the only approved treatment for stroke Homeostatic Imbalances of the Brain • Degenerative brain disorders • Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia • Parkinson’s disease: degeneration of the dopaminereleasing neurons of the substantia nigra • Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex Spinal Cord • Location • Begins at the foramen magnum • Ends as conus medullaris at L1 vertebra • Functions • Provides two-way communication to and from the brain • Contains spinal reflex centers Spinal Cord: Protection • Bone, meninges, and CSF • Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater • CSF in subarachnoid space Spinal Cord: Protection • Denticulate ligaments: extensions of pia mater that secure cord to dura mater • Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx T12 Ligamentum flavum Lumbar puncture needle entering subarachnoid space L5 L4 Supraspinous ligament L5 Filum terminale S1 Intervertebral disc Arachnoid matter Dura mater Cauda equina in subarachnoid space Figure 12.30 Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a Spinal Cord • Spinal nerves • 31 pairs • Cervical and lumbar enlargements • The nerves serving the upper and lower limbs emerge here • Cauda equina • The collection of nerve roots at the inferior end of the vertebral canal Cross-Sectional Anatomy • Two lengthwise grooves divide cord into right and left halves • Ventral (anterior) median fissure • Dorsal (posterior) median sulcus • Gray commissure—connects masses of gray matter; encloses central canal Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Pia mater Arachnoid mater Dura mater Spinal meninges Bone of vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a Dorsal median sulcus Dorsal funiculus White Ventral funiculus columns Lateral funiculus Dorsal root ganglion Gray commissure Dorsal horn Gray Ventral horn matter Lateral horn Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b Gray Matter • Dorsal horns—interneurons that receive somatic and visceral sensory input • Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots • Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons • Dorsal root (spinal) gangia—contain cell bodies of sensory neurons Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32 White Matter • Consists mostly of ascending (sensory) and descending (motor) tracts • Transverse tracts (commissural fibers) cross from one side to the other • Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) • Each spinal tract is composed of axons with similar functions