Understanding Lateralization of Cortical Functions

1. 12 The Central Nervous System: Part B

2. Lateralization of Cortical Function • Lateralization • Division of labor between hemispheres • Cerebral dominance • Designates the hemisphere dominant for language (left hemisphere in 90% of people)

3. Lateralization of Cortical Function • Left hemisphere • Controls language, math, and logic • Right hemisphere • Insight, visual-spatial skills, intuition, and artistic skills • Left and right hemispheres communicate via fiber tracts in the cerebral white matter

4. Cerebral White Matter • Myelinated fibers and their tracts • Responsible for communication • Commissures (in corpus callosum)—connect gray matter of the two hemispheres • Association fibers—connect different parts of the same hemisphere • Projection fibers—(corona radiata) connect the hemispheres with lower brain or spinal cord

5. Commissural fibers (corpus callosum) Longitudinal fissure Superior Lateral ventricle Association fibers Basal nuclei • Caudate Corona radiata • Putamen • Globuspallidus Fornix Internal capsule Thalamus Gray matter Third ventricle White matter Projection fibers Pons Decussation of pyramids Medulla oblongata (a) Figure 12.10a

6. Basal Nuclei (Ganglia) • Subcortical nuclei • Consists of the corpus striatum • Caudate nucleus • Lentiform nucleus (putamen + globus pallidus) • Functionally associated with the subthalamic nuclei (diencephalon) and the substantia nigra (midbrain)

7. Fibers of corona radiata Caudate nucleus Thalamus Lentiform nucleus • Putamen • Globus pallidus (deep to putamen) Tail of caudate nucleus Corpus striatum Projection fibers run deep to lentiform nucleus (a) Figure 12.11a

8. Anterior Cerebral cortex Cerebral white matter Corpus callosum Anterior horn of lateral ventricle Caudate nucleus Putamen Lentiform nucleus Globus pallidus Thalamus Tail of caudate nucleus Third ventricle Inferior horn of lateral ventricle (b) Posterior Figure 12.11b (1 of 2)

9. Cerebral cortex Cerebral white matter Corpus callosum Anterior horn of lateral ventricle Caudate nucleus Lentiform nucleus Thalamus Third ventricle Inferior horn of lateral ventricle (b) Figure 12.11b (2 of 2)

10. Functions of Basal Nuclei • Though somewhat elusive, the following are thought to be functions of basal nuclei • Influence muscular control • Help regulate attention and cognition • Regulate intensity of slow or stereotyped movements • Inhibit antagonistic and unnecessary movements

11. Diencephalon • Three paired structures • Thalamus • Hypothalamus • Epithalamus • Encloses the third ventricle PLAY Animation: Rotatable brain (sectioned)

12. 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

13. Thalamus • 80% of diencephalon • Superolateral walls of the third ventricle • Connected by the interthalamic adhesion (intermediate mass) • Contains several nuclei, named for their location • Nuclei project and receive fibers from the cerebral cortex

14. Dorsal nuclei Medial Lateral dorsal Lateral posterior Pulvinar Anterior nuclear group Medial geniculate body Reticular nucleus Lateral geniculate body Ventral postero- lateral Ventral anterior Ventral lateral Ventral nuclei (a) The main thalamic nuclei. (The reticular nuclei that “cap” thethalamus laterally are depicted as curving translucent structures.) Figure 12.13a

15. Thalamic Function • Gateway to the cerebral cortex • Sorts, edits, and relays information • Afferent impulses from all senses and all parts of the body • Impulses from the hypothalamus for regulation of emotion and visceral function • Impulses from the cerebellum and basal nuclei to help direct the motor cortices • Mediates sensation, motor activities, cortical arousal, learning, and memory

16. Hypothalamus • Forms the inferolateral walls of the third ventricle • Contains many nuclei • Example: mammillary bodies • Paired anterior nuclei • Olfactory relay stations • Infundibulum—stalk that connects to the pituitary gland

17. Paraventricular nucleus Dorsomedial nucleus Anterior commissure Fornix Preoptic nucleus Posterior hypothalamic nucleus Anterior hypothalamic nucleus Lateral hypothalamic area Supraoptic nucleus Ventromedial nucleus Supra- chiasmatic nucleus Mammillary body Arcuate nucleus Optic chiasma Pituitary gland Infundibulum (stalk of the pituitary gland) (b) The main hypothalamic nuclei. Figure 12.13b

18. Hypothalamic Function • Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility) • Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives

19. 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

20. 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

21. 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

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

23. 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

24. 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

25. 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

26. 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

27. 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

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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

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

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

38. 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

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

40. 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

41. 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

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

43. 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

44. 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

45. 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