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Hypothalamic Function

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.

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Hypothalamic Function

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  1. 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

  2. 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

  3. Cerebral hemisphere Septum pellucidum Corpus callosum Interthalamic adhesion (intermediate mass of thalamus) Fornix Choroid plexus Thalamus (encloses third ventricle) Interven- tricular foramen Posterior commissure Pineal gland (part of epithalamus) Anterior commissure Corpora quadrigemina Mid- brain Cerebral aqueduct Hypothalamus Optic chiasma Arbor vitae (of cerebellum) Pituitary gland Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata Spinal cord Figure 12.12

  4. Brain Stem • Three regions • Midbrain • Pons • Medulla oblongata

  5. 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

  6. 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

  7. View (a) Optic chiasma Optic nerve (II) Diencephalon Crus cerebri of cerebral peduncles (midbrain) • Thalamus • Hypothalamus Thalamus Diencephalon Mammillary body Hypothalamus Midbrain Oculomotor nerve (III) Pons Brainstem Trochlear nerve (IV) Medulla oblongata Trigeminal nerve (V) Pons Middle cerebellar peduncle Facial nerve (VII) Abducens nerve (VI) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Hypoglossal nerve (XII) Pyramid Vagus nerve (X) Ventral root of first cervical nerve Accessory nerve (XI) Decussation of pyramids Spinal cord (a) Ventral view Figure 12.15a

  8. Crus cerebri of cerebral peduncles (midbrain) Thalamus View (b) Infundibulum Superior colliculus Pituitary gland Inferior colliculus Trochlear nerve (IV) Superior cerebellar peduncle Trigeminal nerve (V) Pons Middle cerebellar peduncle Facial nerve (VII) Inferior cerebellar peduncle Abducens nerve (VI) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Olive Hypoglossal nerve (XII) Thalamus Vagus nerve (X) Diencephalon Hypothalamus Midbrain Accessory nerve (XI) Pons Brainstem Medulla oblongata (b) Left lateral view Figure 12.15b

  9. Thalamus View (c) Diencephalon Midbrain • Superiorcolliculus Corpora quadrigemina of tectum • Inferiorcolliculus • Trochlear nerve (IV) Pineal gland • Superior cerebellar peduncle Pons • Middle cerebellar peduncle Medulla oblongata Anterior wall of fourth ventricle • Inferior cerebellar peduncle • Facial nerve (VII) • Vestibulocochlear nerve (VIII) • Glossopharyngeal nerve (IX) Choroid plexus (fourth ventricle) • Vagus nerve (X) • Accessory nerve (XI) Dorsal median sulcus Thalamus Dorsal root of first cervical nerve Diencephalon Hypothalamus Midbrain Pons Brainstem (c) Dorsal view Medulla oblongata Figure 12.15c

  10. Midbrain • Located between the diencephalon and the pons • Cerebral peduncles • Contain pyramidal motor tracts • Cerebral aqueduct • Channel between third and fourth ventricles

  11. 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

  12. Superior colliculus Dorsal Tectum Periaqueductal gray matter Cerebral aqueduct Oculomotor nucleus (III) Reticular formation Medial lemniscus Red nucleus Substantia nigra Fibers of pyramidal tract Ventral Crus cerebri of cerebral peduncle (a) Midbrain Figure 12.16a

  13. 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

  14. Fourth ventricle Reticular formation Superior cerebellar peduncle Trigeminal main sensory nucleus Trigeminal motor nucleus Middle cerebellar peduncle Pontine nuclei Trigeminal nerve (V) Fibers of pyramidal tract Medial lemniscus (b) Pons Figure 12.16b

  15. 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

  16. 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

  17. 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

  18. Medulla Oblongata • Respiratory centers • Generate respiratory rhythm • Control rate and depth of breathing, with pontine centers

  19. Medulla Oblongata • Additional centers regulate • Vomiting • Hiccuping • Swallowing • Coughing • Sneezing

  20. Fourth ventricle Solitary nucleus Choroid plexus Hypoglossal nucleus (XII) Dorsal motor nucleus of vagus (X) Vestibular nuclear complex (VIII) Inferior cerebellar peduncle Cochlear nuclei (VIII) Lateral nuclear group Nucleus ambiguus Medial nuclear group Reticular formation Inferior olivary nucleus Raphe nucleus Pyramid Medial lemniscus (c) Medulla oblongata Figure 12.16c

  21. The Cerebellum • 11% of brain mass • Dorsal to the pons and medulla • Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction

  22. 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

  23. Anterior lobe Cerebellar cortex Arbor vitae Cerebellar peduncles Posterior lobe • Superior • Middle Choroid plexus of fourth ventricle • Inferior Medulla oblongata Flocculonodular lobe (b) Figure 12.17b

  24. Anterior lobe Posterior lobe Vermis (d) (d) Figure 12.17d

  25. 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

  26. 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

  27. 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

  28. Protection of the Brain • Bone (skull) • Membranes (meninges) • Watery cushion (cerebrospinal fluid) • Blood-brain barrier

  29. Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in the skull

  30. Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater

  31. Skin of scalp Periosteum Bone of skull Dura mater Periosteal Meningeal Superior sagittal sinus Arachnoid mater Pia mater Arachnoid villus Subdural space Blood vessel Falx cerebri (in longitudinal fissure only) Subarachnoid space Figure 12.24

  32. Dura Mater • Strongest meninx • Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses

  33. 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

  34. Superior sagittal sinus Falx cerebri Straight sinus Crista galli of the ethmoid bone Tentorium cerebelli Falx cerebelli Pituitary gland (a) Dural septa Figure 12.25a

  35. 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

  36. Skin of scalp Periosteum Bone of skull Dura mater Periosteal Meningeal Superior sagittal sinus Arachnoid mater Pia mater Arachnoid villus Subdural space Blood vessel Falx cerebri (in longitudinal fissure only) Subarachnoid space Figure 12.24

  37. Pia Mater • Layer of delicate vascularized connective tissue that clings tightly to the brain

  38. Cerebrospinal Fluid (CSF) • Composition • Watery solution • Less protein and different ion concentrations than plasma • Constant volume

  39. 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

  40. 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 choroid plexus of each ventricle. Cerebral aqueduct Lateral aperture 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. Fourth ventricle Median aperture 2 Central canal of spinal cord 3 CSF flows through the subarachnoid space. (a) CSF circulation 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a

  41. 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

  42. 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.) Cavity of ventricle (b) CSF formation by choroid plexuses Figure 12.26b

  43. Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances

  44. Blood-Brain Barrier • Composition • Continuous endothelium of capillary walls • Basal lamina • Feet of astrocytes • Provide signal to endothelium for the formation of tight junctions

  45. Capillary Neuron Astrocyte (a) Astrocytes are the most abundantCNS neuroglia. Figure 11.3a

  46. 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

  47. 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

  48. 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

  49. 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 dopamine-releasing 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

  50. 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

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