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The Brain: Structure, Function, and Protection

This chapter provides an overview of the different parts of the brain, their functions, and how the brain is protected. Topics covered include the major divisions of the brain, the role of cerebrospinal fluid, the meninges, the blood-brain barrier, and the brain stem.

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The Brain: Structure, Function, and Protection

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  1. Chapter 14 The Brain and Cranial Nerves

  2. The Brain • The Brain is part of Central Nervous System (CNS) • It is divided into 6 major parts: • The cerebrum • The diencephalon • The mesencephalon • The cerebellum • The pons • The medulla oblongata

  3. Major divisions of the Brain

  4. The real thing Fig.14.01b

  5. The Human Brain • Ranges from 750 cc to 2100 cc • Contains almost 98% of the body’s neural tissue • Average weight about 1.4 kg (3 lb)

  6. Protection of the Brain • The brain is protected by bone, meninges, and cerebrospinal fluid • Harmful substances are shielded from the brain by the blood-brain barrier

  7. Cerebrospinal fluid • Protects by absorbing shock (it “floats” the brain. • Maintains the electrochemical environment (opitmal pH & osmolality). • Circulates nutrients and wastes.

  8. The Ventricles

  9. Formation of CSF

  10. Choroid Plexuses Figure 12.25a

  11. Fig. 14.04c Cirulaation of CSF

  12. Meninges • Three connective tissue membranes lie external to the CNS – dura mater, arachnoid mater, and pia mater • Functions of the meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions within the skull

  13. The Meninges of the Brain

  14. Dura Mater • Three dural septa extend inward and limit excessive movement of the brain • Falx cerebri – fold that dips into the longitudinal fissure • Falx cerebelli – runs along the vermis of the cerebellum • Tentorium cerebelli – horizontal dural fold extends into the transverse fissure

  15. Dural Folds • Falx cerebri, tentorium cerebelli, and falx cerebelli Figure 14–3b

  16. Arachnoid Mater • The middle meninx, which forms a loose brain covering • It is separated from the dura mater by the subdural space • Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vessels • Arachnoid villi protrude superiorly and permit CSF to be absorbed into venous blood

  17. Blood flow, O2 and the BBB • Though only 2% of body mass the brain consumes 20% of the oxygen and glucoseof the resting body. • No O2 for a minute = dizziness • 4 minutes = brain damage • 6 minutes = death • The brain is protected by the blood-brain barrier.

  18. Blood-Brain Barrier: Functions • Selective barrier that allows nutrients to pass freely • Is ineffective against substances that can diffuse through plasma membranes • Absent in some areas (vomiting center and the hypothalamus), allowing these areas to monitor the chemical composition of the blood • Stress increases the ability of chemicals to pass through the blood-brain barrier

  19. The Blood-brain barrier

  20. The Brain Stem • The brain stem is comprised of 3 main subdivisions: • The Medulla Oblongata • The Pons • The Mesencephalon

  21. The diencephalon & brainstem

  22. Medulla Oblongata: 3 Groups of Nuclei • Autonomic nuclei: • control visceral activities • Sensory and motor nuclei: • of cranial nerves • Relay stations: • along sensory and motor pathways

  23. Nuclei of the medulla oblongata

  24. Summary: The Medulla Oblongata Table 14-2

  25. The Pons • Links cerebellum with mesencephalon, diencephalon, cerebrum, and spinal cord Figure 14–6c

  26. The Pons: 4 Groups • Sensory and motor nuclei of cranial nerves V, VI, VII, VIII • Nuclei involved with respiration: • apneustic center and pneumotaxic center • modify respiratory rhythmicity center activity

  27. The Pons: 4 Groups • Nuclei and tracts: • process and relay information to and from cerebellum • Ascending, descending, and transverse tracts: • transverse fibers (axons) • link nuclei of pons with opposite cerebellar hemisphere

  28. The Cerebellum • An autonomic & motor processing center Figure 14–7a

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

  30. Structures of the Cerebellum Figure 14–7b

  31. Structures of the Cerebellum (1 of 2) • Folia: • surface of cerebellum • highly folded neural cortex • Anterior and posterior lobes: • separated by primary fissure

  32. Structures of the Cerebellum (2 of 2) • Cerebellar hemispheres: • separated at midline by vermis • Vermis: • narrow band of cortex • Flocculonodular lobe: • below fourth ventricle

  33. Summary: The Cerebellum Table 14-3

  34. The Mesencephalon Figure 14–8a

  35. Midbrain nuclei • Substantia nigra: dopamine release, control of subconscious muscle movents. • Red nuclei: synapses between neurons of cerebellum and cerebrum. Also origin of oculomotor nerve (CN III) and trochlear nerve (CN IV).

  36. Some major functions mesencephalon • Cerebral peduncles: contain motor axons connecting cerebrum to brain stem and sensory axons that connect medulla to thalamus • Tectum: • Superior colliculi: visual reflexes, including pupillary reflexes. • Inferior colliculi: auditory path from ear to thalamus. • Startle reflex

  37. Summary: The Mesencephalon Table 14-4

  38. The Diencephalon • The Thalamus - switch board for the cerebrum. Includes the: • Geniculate nuclei (part of the ventral group): • Medial processes auditory information. • Lateral processes visual input. • Other ventral nuclei connect motor & sensory areas of cortex to cerebellum & spinal cord • Anterior & medial nuclei • Anterior connects to limbic system & hypothalamus • Medial connects with cortex & limbic system

  39. The Diencephalon

  40. The Thalamus:Filters ascending sensory information for primary sensory cortex.Relays information between basal nuclei and cerebral cortex Figure 14–9

  41. Those pesky thalamic nuclei Fig. 14.09a-d

  42. Fig. 14.09e Oblique section of brain showing the Thalamus and basal nuclei

  43. Summary: Thalamic Nuclei Table 14-5

  44. The Hypothalamus Functions of the hypothalamus • ANS control • , heart rate, respiration, sweating, digestion, urination, stress response • Hormones - ADH, oxytocin, GnRH et al. • Basic emotions - rage, sex drive, fear, pain pleasure. • Thirst & appetite • Temperature & sleep/wake (circadian) cycles

  45. The Hypothalamus • Lies below thalamus Figure 14–10a

  46. Summary: The Hypothalamus Table 14-6

  47. 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

  48. The Limbic System Figure 14–11a

  49. The Limbic System Figure 14–11b

  50. Limbic System • Structures located on the medial aspects of cerebral hemispheres and diencephalon • Includes the rhinencephalon, amygdala, hypothalamus, and anterior nucleus of the thalamus • Parts especially important in emotions: • Amygdala – deals with anger, danger, and fear responses • Cingulate gyrus – plays a role in expressing emotions via gestures, and resolves mental conflict • Puts emotional responses to odors – e.g., skunks smell bad

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