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 caudaequina • Thru arachnoidvilli/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 Figure 14–5a

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: • cingulategyrus - 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 cingulategyrus • 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 sulcusdivides: anterior frontal lobe from posterior parietal lobe • Lateral sulcusdivides: frontal lobe from temporal lobe • Parieto-occipital sulcusdivides: 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) • Caudate nucleus: • Lentiform nucleus: • globuspallidus • putamen

41. Motor and Sensory Areas of the Cortex • Central sulcusseparates motor and sensory areas • Precentralgyrus(Primary motor cortex) of frontal lobe: • directs voluntary movements • Postcentralgyrus(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 Figure 14–15c

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