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

Pineal gland—extends from the posterior border and secretes melatonin 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 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 Hypothalamus Cerebral aqueduct Optic chiasma Arbor vitae (of cerebellum) Pituitary gland Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata 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

Oculomotor nerve (III) Trochlear nerve (IV) View (a) Optic chiasma Optic nerve (II) Diencephalon Crus cerebri of cerebral peduncles (midbrain) • Thalamus • Hypothalamus Thalamus Mammillary body Diencephalon Hypothalamus Oculomotor nerve (III) Midbrain Pons Brainstem Trochlear nerve (IV) Medulla oblongata Trigeminal nerve (V) Middle cerebellar peduncle Pons 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

Superior cerebellar peduncle Pons Middle cerebellar peduncle Crus cerebri of cerebral peduncles (midbrain) Thalamus View (b) Infundibulum Superior colliculus Pituitary gland Inferior colliculus Trochlear nerve (IV) Trigeminal nerve (V) Superior cerebellar peduncle 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 Accessory nerve (XI) Midbrain Pons Brainstem Medulla oblongata (b) Left lateral view Figure 12.15b

• Superior cerebellar peduncle Pons • Middle cerebellar peduncle Thalamus View (c) Diencephalon Midbrain • Superior colliculus Corpora quadrigemina of tectum • Inferior colliculus • 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) Choroid plexus (fourth ventricle) • Glossopharyngeal nerve (IX) • 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

Located between the diencephalon and the pons 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

Superior Tectum Dorsal colliculus 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

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 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

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

Autonomic reflex centers Cardiovascular center 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

Additional centers regulate Medulla Oblongata Additional centers regulate Vomiting Hiccuping Swallowing Coughing Sneezing

Hypoglossal nucleus (XII) Dorsal motor nucleus of vagus (X) 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

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 Posterior lobe • Superior • Middle Choroid plexus of fourth ventricle • Inferior Medulla oblongata Flocculonodular lobe (b) Figure 12.17b

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

All fibers in the cerebellum are ipsilateral 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

Skin of scalp Periosteum Bone of skull Dura Periosteal mater Meningeal Superior sagittal sinus Arachnoid mater Pia mater Subdural space Arachnoid villus Blood vessel Subarachnoid space 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

Dural septa limit excessive movement of the brain 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 Falx cerebri Straight sinus Crista galli of the ethmoid bone Tentorium cerebelli Falx cerebelli Pituitary gland (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

Skin of scalp Periosteum Bone of skull Dura Periosteal mater Meningeal Superior sagittal sinus Arachnoid mater Pia mater Subdural space Arachnoid villus Blood vessel Subarachnoid space 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

Right lateral ventricle (deep to cut) 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 CSF is produced by the choroid plexus of each ventricle. 1 Cerebral aqueduct Lateral aperture Fourth ventricle 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. 2 Median aperture 2 Central canal of spinal cord CSF flows through the subarachnoid space. 3 (a) CSF circulation CSF is absorbed into the dural venous sinuses via the arachnoid villi. 4 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

containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) 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

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

(a) Astrocytes are the most abundant CNS neuroglia. 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 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

Spinal Cord Location Functions 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

Ligamentum flavum Lumbar puncture needle entering subarachnoid space Supra- spinous ligament L5 Filum terminale S1 Inter- vertebral disc Cauda equina in subarachnoid space Arachnoid matter Dura mater Figure 12.30

(a) The spinal cord and its nerve roots, with the bony vertebral Cervical spinal nerves Cervical enlargement Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Lumbar spinal nerves 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. Sacral spinal nerves Figure 12.29a

Cervical and lumbar enlargements 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

(a) Cross section of spinal cord and vertebra Epidural space (contains fat) Pia mater Arachnoid mater Spinal meninges Subdural space Dura mater Subarachnoid space (contains CSF) Bone of vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a

(b) The spinal cord and its meningeal coverings Dorsal median sulcus Gray commissure Dorsal funiculus Dorsal horn White columns Ventral funiculus Gray matter Ventral horn Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral median fissure Ventral root (derived from several ventral rootlets) 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 horn (interneurons) Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Spinal nerve Ventral horn (motor neurons) Ventral root (motor) Somatic motor neuron 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