Chapter 14: The Brain and Cranial Nerves

1. Chapter 14: The Brain and Cranial Nerves

2. 6 Regions of the Brain Cerebrum Cerebellum Diencephalon Mesencephalon Pons Medulla oblongata

3. Cerebrum Largest part of brain Controls higher mental functions Divided into left and right cerebral hemispheres Surface layer of gray matter (neural cortex) Also called cerebral cortex Folded surface increases surface area Elevated ridges (gyri) Shallow depressions (sulci) Deep grooves (fissures)

4. Cerebellum Second largest part of brain Coordinates repetitive body movements 2 hemispheres Covered with cerebellar cortex

5. Diencephalon Located under cerebrum and cerebellum Links cerebrum with brain stem 3 divisions: Thalamus - relays and processes sensory information Hypothalamus - hormone production, emotion, & autonomic function Epithalamus (Pineal gland)

6. Pituitary Gland Major endocrine gland Connected to hypothalamus Via infundibulum (stalk) Interfaces nervous and endocrine systems

7. The Brain Stem Processes information between: spinal cord and cerebrum or cerebellum Includes: Mesencephalon (midbrain) Processes sight, sound, and associated reflexes, & maintains consciousness Pons Connects cerebellum to brain stem & is involved in somatic and visceral motor control Medulla oblongata Regulates autonomic functions: HR, BP, and digestion

8. Primary Brain Vesicles The anterior end of the neural tube expands and constricts to form the three primary brain vesicles Prosencephalon � the forebrain Mesencephalon � the midbrain Rhombencephalon � hindbrain

9. Secondary Brain Vesicles In week 6 of embryonic development, secondary brain vesicles form Telencephalon and diencephalon arise from the forebrain Mesencephalon remains undivided Metencephalon and myelencephalon arise from the hindbrain

10. Adult Brain Structures Fates of the secondary brain vesicles: Telencephalon � cerebrum: cortex, white matter, and basal nuclei Diencephalon � thalamus, hypothalamus, and epithalamus Mesencephalon � brain stem: midbrain Metencephalon � brain stem: pons Myelencephalon � brain stem: medulla oblongata

11. Ventricles Lateral ventricles Deep w/in cerebrum Third ventricle Connected by interventricular foramen (Monro) Fourth ventricle Connected by cerebral aqueduct (Sylvius) Connects to subarachnoid space to return to bloodstream

12. Brain Protection and Support Physical protection: bones of the cranium cranial meninges cerebrospinal fluid Biochemical isolation: blood�brain barrier

13. The Cranial Meninges Has 3 layers: dura mater arachnoid mater pia mater Is continuous with spinal meninges Protects the brain from cranial trauma

14. Characteristics of Cranial Meninges Dura mater: inner fibrous layer (meningeal layer) outer fibrous layer (endosteal layer) fused to periosteum venous sinuses between 2 layers Arachnoid mater: contacts epithelial layer of dura mater Subarachnoid space b/t arachnoid and pia mater Pia mater: attached to brain surface by astrocytes

15. Dural Folds Folded inner layer of dura mater Extend into cranial cavity to stabilize and support brain Contain collecting veins (dural sinuses) Falx cerebri, tentorium cerebelli, and falx cerebelli

16. Cerebrospinal Fluid (CSF) Surrounds all exposed surfaces of CNS Interchanges with interstitial fluid of brain Functions of CSF Cushions delicate neural structures Supports brain Transports nutrients, chemical messengers, and waste products

17. Forming CSF Choroid plexus: Specialized ependymal cells and capillaries: secrete CSF into ventricles remove waste products from CSF adjust composition of CSF Produces about 500 ml of CSF/day Room for ~ 150 ml

18. Circulating CSF CSF produced from choroid plexus (in all ventricles) Lateral Ventricle (thru interventricular foramen of Monro) Third Ventricle (thru cerebral aquaduct of Sylvius) Fourth Ventricle (thru median & lateral apertures) To central canal of spinal cord & subarachnoid space around the brain, spinal cord, and cauda equina Thru arachnoid villi/granulations (into dural venous sinuses) DVS�s merge into Internal Jugular Vein

19. Blood Supply to the Brain Supplies nutrients and oxygen to brain Delivered by internal carotid arteries and vertebral arteries Removed from dural sinuses by internal jugular veins

20. Cerebrovascular Disease Disorders interfere with blood circulation to brain Stroke or cerebrovascular accident (CVA): shuts off blood to portion of brain neurons die Transient ischemic attack (TIA): temporary reduction in blood flow

21. Blood�Brain Barrier (BBB) Isolates CNS neural tissue from general circulation Formed by network of tight junctions between endothelial cells of CNS capillaries Lipid�soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord Astrocytes control blood�brain barrier by releasing chemicals that control permeability of endothelium

22. 4 Breaks in the BBB Portions of hypothalamus: secrete hypothalamic hormones Posterior lobe of pituitary gland: secrete hormones ADH and oxytocin Pineal glands: pineal secretions Choroid plexus: where special ependymal cells maintain blood�CSF barrier

23. The Medulla Oblongata Allows brain and spinal cord to communicate Coordinates complex autonomic reflexes Controls visceral functions

24. Medulla Oblongata Vital reflex centers (life sustaining decisions) Cardiac center � rate/force of contractions Vasomotor center � smooth mm in b.v.�s (BP control) Respiratory center � rate/depth of breathing (up into pons) Non-vital reflex centers Vomiting, hiccough, swallowing, coughing, sneezing CN VIII through XII nuclei Vestibular nuclei complex � subconsciously maintain balance (equilibrium) Solitary nucleus - receives visceral sensory information Olivary nuclei (olives)�lateral to pyramids Receive sensory info from proprioceptors (position) in skeletal muscles & joints & act as a relay point to the cerebellum

25. The Pons Links cerebellum with mesencephalon, diencephalon, cerebrum, and spinal cord Nuclei of cranial nerves V, VI, VII, VIII Nuclei involved with respiration: apneustic center and pneumotaxic center modify respiratory rhythmicity center activity Cerebellar peduncles � connect cerebellum to brainstem (6 in all) Superior cerebellar peduncles � to midbrain Middle cerebellar peduncles � to pons (largest) Inferior cerebellar peduncles � to medulla

26. Functions of the Cerebellum Adjusts postural muscles Fine-tunes conscious and subconscious movements Ataxia: damage from trauma or stroke intoxication (temporary disturbance) disturbs muscle coordination

27. Structures of the Cerebellum Folia: surface of cerebellum highly folded neural cortex Anterior and posterior lobes: separated by primary fissure Cerebellar hemispheres: separated at midline by vermis Flocculonodular lobe: below fourth ventricle Arbor vitae: Highly branched, internal white matter of cerebellum

28. Structures of the Mesencephalon Tectum: (corpora quadrigemina): superior colliculus (visual) inferior colliculus (auditory) Tegmentum: red nucleus (many blood vessels) substantia nigra (pigmented gray matter) Cerebral peduncles: Contain descending fibers to cerebellum motor command fibers

29. The Diencephalon Integrates sensory information and motor commands Thalamus Epithalamus Secretes hormone melatonin Hypothalamus

30. The Thalamus Filters ascending sensory information for primary sensory cortex Relays center to funnel information between basal nuclei and cerebral cortex

31. 5 Groups of Thalamic Nuclei Anterior group: part of limbic system (emotions) Medial group: provides awareness of emotional states Ventral group: relays sensory information Posterior group: pulvinar nucleus (sensory) lateral geniculate nucleus (visual) medial geniculate nucleus (auditory) Lateral group: affects emotional states integrates sensory info

32. Structures of the Hypothalamus Mamillary bodies: process olfactory and other sensory information control reflex eating movements Infundibulum: a narrow stalk connects hypothalamus to pituitary gland

33. 8 Functions of the Hypothalamus Provides subconscious control of skeletal muscle Controls autonomic function Coordinates activities of nervous and endocrine systems Secretes hormones: antidiuretic hormone (ADH) & oxytocin (OT) Produces emotions and behavioral drives: the feeding center (hunger) & the thirst center Coordinates voluntary and autonomic functions Regulates body temperature: Controls circadian rhythms (day�night cycles)

34. The Limbic System Is a functional grouping that: establishes emotional states links conscious functions of cerebral cortex with autonomic functions of brain stem facilitates memory storage and retrieval

35. Components of the Limbic System Amygdala: deals with anger, danger, and fear responses interfaces limbic system, cerebrum, and sensory systems Limbic lobe of cerebral hemisphere: cingulate gyrus - plays a role in expressing emotions via gestures, and resolves mental conflict hippocampus - converts short-term memory to long-term memory�memories charged w/ emotion are often retained Fornix: tract of white matter connects hippocampus with hypothalamus Anterior nucleus of the thalamus: relays information from mamillary body to cingulate gyrus Reticular formation: stimulation or inhibition affects emotions (rage, fear, pain, sexual arousal, pleasure)

36. The Cerebrum Is the largest part of the brain Controls all conscious thoughts and intellectual functions Processes somatic sensory and motor information Gray matter: in cerebral cortex and basal nuclei White matter: deep to cortex around basal nuclei

37. Structures of the Cerebrum Gyri of neural cortex: increase surface area (number of cortical neurons) Longitudinal fissure: separates cerebral hemispheres Lobes: divisions of hemispheres Central sulcus divides: anterior frontal lobe from posterior parietal lobe Lateral sulcus divides: frontal lobe from temporal lobe Parieto-occipital sulcus divides: parietal lobe from occipital lobe

38. 3 Functional Principles of the Cerebrum Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of body The 2 hemispheres have different functions although their structures are alike Correspondence between a specific function and a specific region of cerebral cortex is not precise

39. 3 Types of Axons in the Cerebrum Association fibers Connections within 1 hemisphere Commissural fibers Bands of fibers connecting 2 hemispheres Projection fibers Link cerebral cortex with diencephalon, brain stem, cerebellum, and spinal cord

40. Basal Nuclei Are masses of gray matter embedded in white matter of cerebrum Direct subconscious activities Are involved with: the subconscious control of skeletal muscle tone the coordination of learned movement patterns (walking, lifting)

41. Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory areas Precentral gyrus (Primary motor cortex) of frontal lobe: directs voluntary movements Postcentral gyrus (Primary sensory cortex) of parietal lobe: receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)

42. Special Sensory Cortexes Visual cortex: occipital lobe information from sight receptors Auditory cortex: temporal lobe information from sound receptors Olfactory cortex: frontal & medial temporal lobe information from odor receptors Gustatory cortex: insula (deep to temporal lobe) information from taste receptors

43. Association Areas Premotor cortex: coordinates somatic motor responses (learned movements) Somatic sensory association area: interprets input to primary sensory cortex (e.g., recognizes and responds to touch) Visual association area: interprets activity in visual cortex Auditory association area: monitors auditory cortex

44. Integrative Areas Wernicke�s area (General Interpretive Area ) Present in only 1 hemisphere Receives information from all sensory association areas Coordinates access to complex visual and auditory memories Speech center: coordinates all vocalization functions is associated with general interpretive area Prefrontal cortex of frontal lobe: integrates information from sensory association areas performs abstract intellectual activities (e.g., predicting consequences of actions)

45. Brodmann�s Areas Patterns of cellular organization in cerebral cortex

46. Hemispheric Lateralization Functional differences between left and right hemispheres In most people (90%), left brain (dominant hemisphere) controls: reading, writing, and math decision-making speech and language Right cerebral hemisphere relates to: senses (touch, smell, sight, taste, feel) recognition (faces, voice inflections) Unclear dominance may lead to dyslexia

47. Monitoring Brain Activity Brain activity is assessed by an electroencephalogram (EEG): electrodes are placed on the skull patterns of electrical activity are printed out (brain waves)

48. 4 Categories of Brain Waves Alpha waves: found in healthy, awake adults at rest with eyes closed Beta waves: higher frequency found in adults concentrating or mentally stressed Theta waves: found in children found in intensely frustrated adults may indicate brain disorder in adults Delta waves: during sleep found in awake adults with brain damage

49. Cranial Nerves 12 pairs connected to brain Name Number Function

50. Olfactory � CN I Sensory Terminates in olfactory bulbs Discrimination of smell

51. Optic � CN II Sensory Vision Terminates at optic chiasm

52. Occulomotor � CN III Motor Inferior oblique, sup/inf/medial rectus Test planes of gaze PSNS Function: Test constrictor mm of iris (ciliary mm) Pupillary reflex

53. Trochlear � CN IV Motor Superior oblique (down & out) Test planes of gaze

54. Trigeminal � CN V Mixed 3 divisions: ophthalmic, maxillary, mandibular Test: Motor- mandibular division to mm of mastication Corneal reflex to elicit blinking

55. Abducens � CN VI Motor Lateral rectus Test planes of gaze

56. Facial � CN VII Mixed Taste on anterior 2/3 of tongue Motor to mm of facial expression (not chewing) 5 motor branches Temporal, zygomatic, buccal, mandibular, cervical PSNS to lacrimal gland Test making faces

57. Vestibulocochlear � CN VIII Sensory Equilibrium & hearing Test hearing

58. Glossopharyngeal � CN IX Mixed Motor fibers to pharynx PSNS to parotid salivary gland Sensory conduct taste from posterior 1/3 of tongue; carotid sinus pressure & chemoreceptors (Oxygen), general sensation of pharynx Test swallowing (gag reflex w/ CN X)

59. Vagus � CN X Mixed Only nerve to descend beyond neck (into thorax & abdomen) PSNS serving heart, lung, abd viscera to regulate heart rate, breathing, & digestive activity Test gag reflex (w/ CN IX)

60. Spinal accessory � CN XI Motor Trapezius & SCM Test shrugging shoulders

61. Hypoglossal CN XII Motor Extrinsic & intrinsic muscles of the tongue Test by sticking out tongue