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Chapter 14 – Part 1, Brain!
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Chapter 14, Part 1!The Brain and Cranial Nerves! pp. 461–481 !
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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-the-ratio-of-glia-to-neurons-in-the-brain/ )!
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Chapter 14 – Part 1, Brain!
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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!
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Principal Parts – 2!
4. Cerebrum (cerebral cortex)!• Two cerebral hemispheres, each contains a:!
Frontal lobe!Parietal lobe!Temporal lobe!Occipital lobe!
Chapter 14 – Part 1, Brain!
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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!
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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!
Chapter 14 – Part 1, Brain!
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Development of the Brain Table 14-1!
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Ventricles of the Brain Figure 14-2!
See brain ventricle model in lab.!
Chapter 14 – Part 1, Brain!
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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!
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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!
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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)!
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The Cranial Meninges Figure 14-3a!
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Dural Folds!
A.!B.!
C.!
A. Falx cerebri (falx = “sickle”)!• Between cerebral
hemispheres!• Superior and inferior sagittal
sinuses!B. Tentorium cerebelli!
• Between cerebrum and cerebellum!
• Transverse sinus!C. Falx cerebelli!
• Between cerebellar hemispheres!
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Arachnoid Membrane and Pia Mater!
Arachnoid !
Pia mater!
2. Arachnoid!• Subarachnoid space
contains CSF!• Membrane does not
follow into sulci!3. Pia mater!• Closely adheres to brain
surface!• Follows sulci!
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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?
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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!
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Circulation of Cerebrospinal Fluid Figure 14-4!
Arachnoid granulation!(cluster of villi)!
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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!
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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-)!
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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!
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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?!
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SECTION 14-3 !The medulla oblongata, which is continuous with the spinal cord, contains vital centers!
See Figure 14-6 for summary of functions!
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Medulla (Oblongata) !
Medulla
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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!
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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!
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Medulla Oblongata Figure 14-6!
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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!
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Pons (“Bridge”)!
Pons
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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!
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Pons Figure 14-7!
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SECTION 14-5 !The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level!
See Figure14-8 for summary of functions!
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Cerebellum!
Cerebellum
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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!
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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!!!
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SECTION 14-6!The mesencephalon regulates auditory and visual reflexes and controls alertness!
See Figure14-9 for summary of functions!
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Midbrain (Mesencephalon)!
Midbrain!(mesencephalon)!
Tectum!
Cerebral!aqueduct!
Cerebral!peduncles!
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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)!
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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!
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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!
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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!
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The Mesencephalon Figure 14-9!
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• Thalamus!• Hypothalamus!• Epithalamus!
SECTION 14-7 !The diencephalon integrates sensory information with motor output at the subconscious level!
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Diencephalon!
Thalamus
Hypothalamus
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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!
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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.!
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The Hypothalamus!
Hypothalamus!
Optic chiasm!Infundibulum!
(cut)!Mamillary body!
Thalamus
Corpus callosum
Fornix
Pineal!
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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!
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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!
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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.!
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SECTION 14-8 !The limbic system is a group of tracts and nuclei with various functions!
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Limbic System Figure 14-12!
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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!
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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!
