The Brain

1. The Brain Muse Fall 2430 Lecture #10 11/30/11

2. An Introduction to the Brain and Cranial Nerves • The Adult Human Brain • Ranges from 750 cc to 2100 cc • Contains almost 97% of the body’s neural tissue • Average weight about 1.4 kg (3 lb)

3. The Brain • Six Regions of the Brain • Cerebrum • Cerebellum • Diencephalon • Mesencephalon • Pons • Medulla oblongata

4. The Brain Figure 14–1 An Introduction to Brain Structures and Functions.

5. Anterior Longitudinal fissure Frontal lobe Cerebral veins and arteries covered by arachnoid mater Parietal lobe Right cerebral hemisphere Left cerebral hemisphere Occipital lobe Posterior (c) Figure 12.6c

6. The Brain Figure 14–2 Ventricles of the Brain.

7. Brain Protection and Support • 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

8. Brain Protection and Support Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid.

9. 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

10. Brain Protection and Support • Blood Supply to the Brain • Supplies nutrients and oxygen to brain • Delivered by internal carotidarteries and vertebral arteries • Removed from dural sinuses by internal jugular veins

11. Brain Protection and Support Figure 21–23 Arteries of the Brain.

12. Brain Protection and Support • Blood–Brain Barrier • 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

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

14. Brain Protection and Support • Four Breaks in the BBB • Portions of hypothalamus • Secrete hypothalamic hormones • Posterior lobe of pituitary gland • Secretes hormones ADH and oxytocin • Pineal glands • Pineal secretions • Choroid plexus • Where special ependymal cells maintain blood–CSF barrier

15. The Medulla Oblongata • The Medulla Oblongata • Allows brain and spinal cord to communicate • Coordinates complex autonomic reflexes • Controls visceral functions • Nuclei in the Medulla • Autonomic nuclei: control visceral activities • Sensory and motor nuclei: of cranial nerves • Relay stations: along sensory and motor pathways

16. The Medulla Oblongata Figure 14–5a The Diencephalon and Brain Stem.

17. 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

18. The Cerebellum • Functions of the Cerebellum • Adjusts postural muscles • Fine-tunes conscious and subconscious movements

19. The Cerebellum • Structures of the Cerebellum • Purkinje cells • Large, branched cells • Found in cerebellar cortex • Receive input from up to 200,000 synapses • Arbor vitae • Highly branched, internal white matter of cerebellum • Cerebellar nuclei: embedded in arbor vitae: • relay information to Purkinje cells

20. The Cerebellum Figure 14–7b The Cerebellum.

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

22. The Cerebellum • Disorders of the Cerebellum • Ataxia • Damage from trauma or stroke • Intoxication (temporary impairment) • Disturbs muscle coordination

23. The Diencephalon • Integrates sensory information and motor commands • Thalamus, epithalamus, and hypothalamus • The pineal gland • Found in posterior epithalamus • Secretes hormone melatonin

24. The Diencephalon • The Hypothalamus • Mamillary bodies • Process olfactory and other sensory information • Control reflex eating movements • Infundibulum • A narrow stalk • Connects hypothalamus to pituitary gland • Tuberal area • Located between the infundibulum and mamillary bodies • Helps control pituitary gland function

25. The Diencephalon Figure 14–10a The Hypothalamus in Sagittal Section.

26. The Diencephalon • Eight 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) by supraoptic nucleus • Oxytocin (OT; OXT) by paraventricular nucleus

27. The Diencephalon • Eight Functions of the Hypothalamus • Produces emotions and behavioral drives • The feeding center (hunger) • The thirst center (thirst) • Coordinates voluntary and autonomic functions • Regulates body temperature • Preoptic area of hypothalamus • Controls circadian rhythms (day–night cycles) • Suprachiasmatic nucleus

28. The Limbic System • 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

29. The Limbic System Figure 14–11a The Limbic System.

30. The Limbic System • Components of the Limbic System • Amygdaloid body • Acts as interface between the limbic system, the cerebrum, and various sensory systems • Limbic lobe of cerebral hemisphere • Cingulate gyrus • Dentate gyrus • Parahippocampal gyrus • Hippocampus

31. The Limbic System • Components of the Limbic System • 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)

32. The Limbic System Figure 14–11b The Limbic System.

33. Fiber tracts connecting limbic system structures Septum pellucidum Diencephalic structures of the limbic system Corpus callosum •Fornix •Anterior thalamic nuclei (flanking 3rd ventricle) •Anterior commissure Cerebral struc- tures of the limbic system •Hypothalamus •Mammillary body •Cingulate gyrus •Septal nuclei •Amygdala •Hippocampus •Dentate gyrus •Parahippocampal gyrus Olfactory bulb Figure 12.18

34. Limbic System • Emotional or affective brain • Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response • Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict • Puts emotional responses to odors • Example: skunks smell bad

35. Limbic System: Emotion and Cognition • The limbic system interacts with the prefrontal lobes, therefore: • We can react emotionally to things we consciously understand to be happening • We are consciously aware of emotional richness in our lives • Hippocampus and amygdala—play a role in memory

36. The Cerebrum • The Cerebrum • Is the largest part of the brain • Controls all conscious thoughts and intellectual functions • Processes somatic sensory and motor information

37. The Cerebrum • Gray matter • In cerebral cortex and basal nuclei • White matter • Deep to basal cortex • Around basal nuclei

38. The Cerebrum Figure 14–12c The Brain in Lateral View.

39. The Cerebrum • Special Sensory Cortexes • Visual cortex • Information from sight receptors • Auditory cortex • Information from sound receptors • Olfactory cortex • Information from odor receptors • Gustatory cortex • Information from taste receptors

40. The Cerebrum Figure 14–15a Motor and Sensory Regions of the Cerebral Cortex.

41. The Cerebrum Figure 14–16 Hemispheric Lateralization.

42. The Cerebrum • Monitoring Brain Activity • Brain activity is assessed by an electroencephalogram (EEG) • Electrodes are placed on the skull • Patterns of electrical activity (brain waves) are printed out

43. The Cerebrum • Four Categories of Brain Waves • Alpha waves • Found in healthy, awake adults at rest with eyes closed • Beta waves 12-30 Hz • 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 1-4 Hz • During sleep • Found in awake adults with brain damage

44. The Cerebrum Figure 14–17a-d Brain Waves.

45. Cerebral Cortex • Thin (2–4 mm) superficial layer of gray matter • 40% of the mass of the brain • Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding • Each hemisphere connects to contralateral side of the body • There is lateralization of cortical function in the hemispheres

46. Functional Areas of the Cerebral Cortex • The three types of functional areas are: • Motor areas—control voluntary movement • Sensory areas—conscious awareness of sensation • Association areas—integrate diverse information • Conscious behavior involves the entire cortex

47. Motor Areas • Primary (somatic) motor cortex • Premotor cortex • Broca’s area • Frontal eye field

48. Primary Motor Cortex • Large pyramidal cells of the precentral gyri • Long axons  pyramidal (corticospinal) tracts • Allows conscious control of precise, skilled, voluntary movements • Motor homunculi: upside-down caricatures representing the motor innervation of body regions

49. Posterior Motor Anterior Motor map in precentral gyrus Toes Jaw Primary motor cortex (precentral gyrus) Tongue Swallowing Figure 12.9

50. Premotor Cortex • Anterior to the precentral gyrus • Controls learned, repetitious, or patterned motor skills • Coordinates simultaneous or sequential actions • Involved in the planning of movements that depend on sensory feedback