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Chapter 14 – Part 1, Brain! Chapter 14, Part 1! The Brain and Cranial Nerves! pp. 461–481 ! SECTION 14-1! The brain has several principal structures, each with specific functions! Herculano-Houzel and her colleagues used a technique to analyze the brains of four deceased men and published their results in 2009: they consistently found a whole human brain glia to neuron ratio of almost exactly 1:1. Specifically, they found that the human brain contains about 170.68 billion cells, 86.1 billion of which are neurons and 84.6 billion of which are glial cells. ( http://blogs.scientificamerican.com/ brainwaves/2012/06/13/know-your-neurons-what-is-theratio-of-glia-to-neurons-in-the-brain/ )! ! 2 Principal Parts – 1! 1. Brain stem! • Medulla! • Pons! • Midbrain (mesencephalon)! 2. Cerebellum (2 hemispheres)! 3. Diencephalon! • Thalamus! • Hypothalamus (Infundibulum connects to pituitary)! • Epithalamus ! Pineal gland, choroid plexus! ! 3 1! Chapter 14 – Part 1, Brain! Principal Parts – 2! 4. Cerebrum (cerebral cortex)! • Two cerebral hemispheres, each contains a:! Frontal lobe! Parietal lobe! Temporal lobe! Occipital lobe! ! 4 Embryology of the Brain! Neural tube with neurocoel = a hollow tube! Develops primary brain vesicles! 1. Prosencephalon (“forebrain”)! 2. Mesencephalon (“midbrain”)! 3. Rhombencephalon (“hindbrain”)! ! Primary vesicles develop into secondary vesicles! ! 5 Secondary Brain Vesicles! 1. Prosencephalon becomes:! A. Telencephalon → cerebrum! B. Diencephalon! 2. Mesencephalon → midbrain! 3. Rhombencephalon becomes:! A. Metencephalon → cerebellum and pons! B. Myelencephalon → medulla (oblongata)! ! See Table 14-1! ! 6 2! Chapter 14 – Part 1, Brain! Development of the Brain Table 14-1! ! 7 Ventricles of the Brain Figure 14-2! See brain ventricle model in lab.! ! 8 Ventricles! • Fluid-filled chambers within the brain! Neurocoel develops into the ventricles ! • Lined with ependymal cells! • Filled with cerebrospinal fluid (CSF)! Produced by choroid plexuses in all ventricles! ! 9 3! Chapter 14 – Part 1, Brain! SECTION 14-2 ! The brain is protected and supported by the cranial meninges, cerebrospinal fluid, and the blood-brain barrier! • • • • Cranial bones! Cranial meninges! Cerebrospinal fluid! Blood-brain barrier! ! 10 Cranial Meninges! 1. Dura mater! • Endosteal layer! Thicker part, fused with periosteum! • Meningeal layer! Thinner part, next to arachnoid membrane! ! Forms dural folds which:! • Stabilize and support brain! • Contain dural (venous) sinuses! Between endosteal and meningeal layers! Contain venous blood (and CSF)! ! 11 The Cranial Meninges Figure 14-3a! ! 12 4! Chapter 14 – Part 1, Brain! Dural Folds! A. Falx cerebri (falx = “sickle”)! • Between cerebral hemispheres! • Superior and inferior sagittal sinuses! A.! B.! B. Tentorium cerebelli! • Between cerebrum and cerebellum! • Transverse sinus! C. Falx cerebelli! • Between cerebellar hemispheres! C.! ! 13 Arachnoid Membrane and Pia Mater! 2. Arachnoid! • Subarachnoid space contains CSF! Arachnoid ! • Membrane does not follow into sulci! Pia mater! 3. Pia mater! • Closely adheres to brain surface! • Follows sulci! ! 14 Cerebrospinal Fluid (CSF) Functions! Formed by choroid plexuses! • Cushions brain! • Supports brain (brain floats in CSF)! Actual mass about 1400 grams! Effective weight in CSF about 25 grams! • Transports nutrients, wastes, chemicals! • Turnover rate: about 4x - 5x per day! Note that, except in the choroid plexuses, there is a free exchange of fluids and solutes between CSF and the extracellular fluid of the brain. Why is this important? ! 15 5! Chapter 14 – Part 1, Brain! CSF Formation by Choroid Plexuses! 1. “Leaky” (permeable) capillaries covered by ependymal cells! 2. Ependymal cells joined by tight junctions • Secrete CSF from fluid filtered by leaky capillaries! • Remove wastes from CSF! Composition of CSF is different from blood! • No blood cells! • Much less protein! • Lower pH! ! 16 Circulation of Cerebrospinal Fluid Figure 14-4! Arachnoid granulation! (cluster of villi)! ! 17 CSF Circulation (Also good for “blood tracing” next term.)! • Lateral ventricles → ! • Interventricular foramen (of Monro) → ! • Third ventricle → ! • Cerebral aqueduct → ! • Fourth ventricle → ! • Central canal of spinal cord or lateral and median apertures → ! • Subarachnoid space → ! • Arachnoid villi/granulations → ! • Superior sagittal sinus → Venous return to heart! ! 18 6! Chapter 14 – Part 1, Brain! Blood Supply to the Brain! Arterial supply:! • Internal carotid and vertebral arteries! Venous return:! • Dural sinuses → internal jugular (most)! Vasomotion:! Neurons rely on glucose - blood supply must be continuous (no energy or oxygen reserves)! ↑ Metabolism → ↑ CO2 → ↑ [H+] → ↑ vasodilation → ↑ blood flow! (remember: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-)! ! 19 Blood-Brain Barrier – 1! 1. Brain capillary endothelial cells have tight junctions! • Restricts diffusion of non-lipid materials! • Water and ions move through cells via channels! • Large, water-soluble materials may be transported actively! • Glucose constantly transported into brain ECF! 2. Astrocytes (chapter 12)! • Pseudopods cover capillaries! Regulate capillary permeability, blood flow! Note that choroid plexus has blood-CSF barrier produced by ependymal cells! ! 20 Blood-Brain Barrier – 2! No blood-brain barrier:! 1. Part of hypothalamus! • Endocrine function! 2. Posterior pituitary! • Endocrine function! 3. Pineal gland! • Endocrine function! 4. Choroid plexuses! • Have choroid-blood barrier! See a pattern here?! ! 21 7! Chapter 14 – Part 1, Brain! SECTION 14-3 ! The medulla oblongata, which is continuous with the spinal cord, contains vital centers! See Figure 14-6 for summary of functions! ! 22 Medulla (Oblongata) ! Medulla ! 23 Medulla – 1! 1. Ascending and descending tracts! 2. Autonomic nuclei - visceral control (part of reticular formation)! • Receive inputs from cranial nerves, cortex, brain stem! A. Cardiovascular centers! • Cardiac center! • Vasomotor center! B. Respiratory rhythmicity center! • Sets basic breathing rhythm! ! 24 8! Chapter 14 – Part 1, Brain! Medulla – 2! 3. Sensory and motor nuclei! • Cranial nerves VIII (with pons), IX - XII! 4. Relay centers! A. Nucleus gracilis and nucleus cuneatus! • Somatic sensory relays to thalamus! B. Olivary nuclei! • Relay proprioceptive info to cerebellum! 5. Pyramids! • Decussation of the pyramids! • Voluntary motor fibers cross over here! Medulla Oblongata ! 25 Figure 14-6! ! 26 SECTION 14-4 ! The pons contains nuclei and tracts that carry or relay sensory and motor information! ! Pons = “bridge”! ! See Figure 14-7 for summary of functions! ! 27 9! Chapter 14 – Part 1, Brain! Pons (“Bridge”)! Pons ! 28 Pons! 1. Ascending, descending, transverse fiber tracts! 2. Sensory and motor nuclei! • Cranial nerves V, VI, VII, and VIII (with medulla)! 3. Respiration nuclei! • Apneustic and pneumotaxic centers! Modify basic rhythm set by medulla! 4. Nuclei and tracts associated with cerebellum! • Process and relay info to/from cerebellum! ! 29 Pons Figure 14-7! ! 30 10! Chapter 14 – Part 1, Brain! SECTION 14-5 ! The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level! See Figure14-8 for summary of functions! ! 31 Cerebellum! Cerebellum ! 32 Cerebellum – 1! Cerebellum = “little brain”! • Communicates with brain stem, cerebrum, spinal cord via cerebellar peduncles! • Modifies motor outputs of brain stem centers and motor pathways! Compares intended with actual movements and makes necessary adjustments! • Subconscious (automatic)! • Facilitates coordinated movements! • Adjusts posture, muscle tone, balance! ! 33 11! Chapter 14 – Part 1, Brain! Cerebellum – 2! Receives input from:! • Proprioceptors! • Equilibrium sensors! • Visual receptors! • Touch receptors! • Auditory receptors! Purkinje fibers important:! • Receive up to 200,000 inputs per cell!!! ! 34 SECTION 14-6! The mesencephalon regulates auditory and visual reflexes and controls alertness! See Figure14-9 for summary of functions! ! 35 Midbrain (Mesencephalon)! Tectum! Cerebral! peduncles! Midbrain! (mesencephalon)! Cerebral! aqueduct! ! 36 12! Chapter 14 – Part 1, Brain! Midbrain (Mesencephalon)! Contains:! 1. Cerebral peduncles! 2. Cerebral aqueduct! 3. Tectum (“roof” of cerebral aqueduct)! • Superior colliculus! • Inferior colliculus! 4. Substantia nigra + red nucleus = tegmentum! 5. Part of reticular activating system! 6. Cranial nerve nuclei (III and IV)! ! 37 Cerebral Peduncles and Tectum! 1. Cerebral peduncles (“little feet”)! • Motor and sensory fiber tracts! ! 2. Tectum (“roof” of aqueduct)! • Corpora quadrigemina (part of tectum)! A. Superior colliculus! • Visual reflexes: eye tracking, reflexive head and neck movements! B. Inferior colliculus! • Auditory reflexes: reflexive head, neck, trunk movements! ! 38 Tegmentum! Tegmentum - anterior to aqueduct! 1. Substantia nigra (“black substance”)! • Regulates activity of basal nuclei! • Involved in muscle tone (discussed later with basal nuclei)! 2. Red nucleus! • Muscle tone, subconscious movements of arms! 3. Reticular formation of RAS! • General level of arousal, muscle tone! ! 39 13! Chapter 14 – Part 1, Brain! Midbrain Cranial Nerve Nuclei! A. Oculomotor nerve C.N. III! • Eye movement, proprioception! All extrinsic eye muscles except superior oblique and lateral rectus! • Lens shape (ciliary muscles)! • Pupil diameter (iris)! B. Trochlear nerve (“pulley”) C.N. IV! • Eye movement, proprioception! Superior oblique (extrinsic eye) muscle! ! 40 The Mesencephalon Figure 14-9! ! 41 SECTION 14-7 ! The diencephalon integrates sensory information with motor output at the subconscious level! • Thalamus! • Hypothalamus! • Epithalamus! ! 42 14! Chapter 14 – Part 1, Brain! Diencephalon! Thalamus Hypothalamus ! 43 Thalamus – “Inner Chamber”! Major sensory relay area! Except for smell, relays all sensory signals to specific area of cortex for conscious perception! Crosses third ventricle as:! • Intermediate mass = massa intermedia = interthalamic adhesion = middle commissure!! Allows a crude appreciation of:! • Pain, temperature, pressure! • Sensation not localized to a particular area! Part of limbic system! • Influences emotional states! ! 44 Posterior Thalamic Nuclei to Know! A. Lateral geniculate - visual relay center! • Optic tract → thalamus → occipital lobe! B. Medial geniculate - auditory relay center! • Auditory receptors → thalamus → temporal lobe! ! Table 14-2 summarizes functions of thalamic nuclei: know that they are all sensory relays/ integrators. ! Know lateral and medial geniculate functions specifically.! ! 45 15! Chapter 14 – Part 1, Brain! The Hypothalamus! Corpu s call Pineal! o su m x rni Fo Thalamus Hypothalamus! Optic chiasm! Infundibulum! (cut)! Mamillary body! ! 46 Hypothalamus Functions – 1! 1. Subconscious control of skeletal muscles associated with emotions! • E.g. facial expressions of rage, pleasure, pain! • E.g. body position associated with sexual arousal! 2. Control of the autonomic nervous system! • Influences centers in pons and medulla! • E.g. heart rate, BP, respiration! 3. Secretion of hormones! • Oxytocin! • Antidiuretic hormone! • Both stored in posterior pituitary! ! 47 Hypothalamus Functions – 2! 4. Coordinates nervous and endocrine systems! • Releases regulatory hormones that control release of anterior pituitary hormones! 5. Influences emotions, behavioral drives! • Feeding, fighting, pleasure, thirst! 6. Coordinates voluntary and autonomic functions! • Think about stressful situation → ↑ HR and ↑ BP before stress begins! • I.e., prepares body for stress! ! 48 16! Chapter 14 – Part 1, Brain! Hypothalamus Functions – 3! 7. Body temperature regulation! • Cold → vasoconstrict, shiver, etc.! • Hot → vasodilate, sweat, etc.! 8. Circadian rhythms! • Light → retina → hypothalamus → pineal (↓ melatonin) → ↑ reticular activating system activity! ! Figure 14-11 summarizes hypothalamic functions – know what’s listed here in the notes.! ! 49 SECTION 14-8 ! The limbic system is a group of tracts and nuclei with various functions! ! 50 Limbic System Figure 14-12! ! 51 17! Chapter 14 – Part 1, Brain! Limbic System – 1! “The emotional brain” or “motivational system”! • A network of structures! • Deals with primitive emotions! Functions:! 1. Establishes emotional states! 2. Links conscious, intellectual functions with unconscious, autonomic functions! 3. Memory storage and retrieval! ! 52 Limbic System – 2! Some functions of some elements of the system:! • Hippocampus → memory! • Amygdala → e.g. , fight-or-flight, sexual behavior! • Septal nuclei → rage, fear! • Mamillary bodies → responses to smell! • Olfactory lobes → duh! • Fornix → connects hippocampus to hypothalamus to mamillary bodies! • Thalamus, hypothalamus, reticular formation! ! 53 18!
