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Chapter 12 The Central Nervous System - 10/21/2015 Press Images © Annie Leibovitz/Contact MDufilho 1 Cerebrospinal Fluid (CSF) • Composition – Watery solution formed from blood plasma • Less protein and different ion concentrations than plasma – Constant volume 10/21/2015 MDufilho 2 Cerebrospinal Fluid (CSF) • Functions – Gives buoyancy to CNS structures • Reduces weight by 97% – Protects CNS from blows and other trauma – Nourishes brain and carries chemical signals 10/21/2015 MDufilho 3 Choroid Plexuses • Hang from roof of each ventricle; produce CSF at constant rate; keep in motion – Clusters of capillaries enclosed by pia mater and layer of ependymal cells • Ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes • Normal volume ~ 150 ml; replaced every 8 hours 10/21/2015 MDufilho 4 Figure 12.24b Formation, location, and circulation of CSF. Ependymal cells Capillary Connective tissue of pia mater Wastes and unnecessary solutes absorbed Section of choroid plexus Cavity of ventricle CSF formation by choroid plexuses 10/21/2015 MDufilho CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) 5 Figure 12.24a Formation, location, and circulation of CSF. Slide 1 4 Superior sagittal sinus Arachnoid villus Choroid plexus Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Interventricular foramen Third ventricle 3 Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation 10/21/2015 Right lateral ventricle (deep to cut) MDufilho Choroid plexus of fourth ventricle 2 1 The choroid plexus of each Ventricle produces CSF. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. 6 Figure 12.25 Hydrocephalus in a newborn. 10/21/2015 MDufilho 7 Blood Brain Barrier • Helps maintain stable environment for brain • Separates neurons from some bloodborne substances • Composition – Continuous endothelium of capillary walls – Thick basal lamina around capillaries – Feet of astrocytes • Provide signal to endothelium for formation of tight junctions 10/21/2015 MDufilho 8 Figure 11.3a Neuroglia. Capillary Neuron Astrocyte Astrocytes are the most abundant CNS neuroglia. 10/21/2015 MDufilho 9 Blood Brain Barrier: Functions • Selective barrier – Allows nutrients to move by facilitated diffusion – Metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids, K+ denied – Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center and hypothalamus, where necessary to monitor chemical composition of blood 10/21/2015 MDufilho 10 Homeostatic Imbalances of the Brain • Traumatic brain injuries – Concussion—temporary alteration in function – Contusion—permanent damage – Subdural or subarachnoid hemorrhage— may force brain stem through foramen magnum, resulting in death – Cerebral edema—swelling of brain associated with traumatic head injury 10/21/2015 MDufilho 11 Blood Flow to the Brain • Brain requires more blood flow and oxygen • Receives 15 – 20% of body’s blood flow • Uses 15 – 20% of body’s oxygen 10/21/2015 12 MDufilho Figure 19.22b Arteries of the head, neck, and brain. Ophthalmic artery Branches of the external carotid artery Basilar artery Vertebral artery • Superficial temporal artery • Maxillary artery • Occipital artery • Facial artery • Lingual artery • Superior thyroid artery Larynx Internal carotid artery External carotid artery Common carotid artery Thyrocervical trunk Costocervical trunk Subclavian artery Axillary artery Thyroid gland (overlying trachea) Clavicle (cut) Brachiocephalic trunk Internal thoracic artery (b) Arteries of the head and neck, right aspect 10/21/2015 MDufilho 13 Figure 19.22d Arteries of the head, neck, Anterior Cerebral arterial and Frontalbrain. lobe circle (circle of Willis) Optic chiasma • Anterior communicating artery • Anterior cerebral artery • Posterior communicating artery • Posterior cerebral artery Basilar artery Middle cerebral artery Internal carotid artery Mammillary body Temporal lobe Pons Occipital lobe Vertebral artery Cerebellum Posterior (d) Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed) 10/21/2015 MDufilho 14 Figure 19.22c Arteries of the head, neck, and brain. 10/21/2015 MDufilho 15 Homeostatic Imbalances of the Brain • Cerebrovascular accidents (CVAs or strokes) – Ischemia • Tissue deprived of blood supply; brain tissue dies, e.g., blockage of cerebral artery by blood clot – Hypoxia • condition in which inadequate oxygen is available to tissues – Hemiplegia (paralysis on one side), or sensory and speech deficits – Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia – Tissue plasminogen activator (TPA) is only approved treatment for stroke 10/21/2015 MDufilho 16 Degenerative Brain Disorders • Alzheimer’s disease (AD) – Progressive degenerative disease of brain that results in dementia • Key proteins appear to be misfolded and malfunction – Memory loss, short attention span, disorientation, eventual language loss, irritability, moodiness, confusion, hallucinations – Plaques of beta-amyloid peptides form in brain – Neurofibrillary tangles inside neurons interfere with transport mechanisms, eventually killing neuron – As brain cells die, brain shrinks 10/21/2015 MDufilho 17 Figure 12.26 Brain activity is decreased by Alzheimer’s disease. Normal Alzheimer Anterior 10/21/2015 MDufilho 18 Homeostatic Imbalances of the Brain • Parkinson's disease – Degeneration of dopamine-releasing neurons of substantia nigra – Basal nuclei deprived of dopamine become overactive tremors at rest – Cause unknown • Mitochondrial abnormalities or protein degradation pathways? – Treatment with L-dopa; deep brain stimulation; gene therapy; research into stem cell transplants promising 10/21/2015 MDufilho 19 Homeostatic Imbalances of the Brain • Huntington's disease – Fatal hereditary disorder – Caused by accumulation of protein huntingtin • Leads to degeneration of basal nuclei and cerebral cortex • Initial symptoms wild, jerky "flapping" movements • Later marked mental deterioration • Treated with drugs that block dopamine effects • Stem cell implant research promising 10/21/2015 MDufilho 20 Physiology of Addiction • Definition • Psychological or Physiological? • Kinds of addictions? 10/21/2015 MDufilho 21 Day in the Life of Nicotine Junkie • 1 st Cigarette/chew of the day – Nicotine = ACh – Stimulates release of hormones Epi and NE – Lasts 30 min • 2nd, 3rd, 4th cig/chew – Stimulates release of hormone cortisol – Then NT dopamine and glutamate – Lasts 30 min 10/21/2015 MDufilho 22 Why is Nicotine Addictive? • ↓ ACh • ↑ # Nicotinic of Receptors • So what? 10/21/2015 MDufilho 23 Physiology of Depression • Definition • Psychological or Physiological? • Causes? – Environmental and neurotransmitters 10/21/2015 MDufilho 24 Physiology of Depression • ↓ in NE and/or Serotonin • Due to????? • Treatment – dual approaches – MAO Inhibitors (monoamine oxidase) – Tricyclic antidepressants – SSRI (serotonin specific reuptake inhibitors) 10/21/2015 MDufilho 25 What about anxiety? • What system creates anxiety? • Treatment – Valium (diazepam), Ativan (lorazepan), Xanax • Rohypnol – date rape drug is in the same family of drugs as Valium, Ativan • Barbiturates (penobarbital) bind to GABA receptor – opens chloride channels which cause hyperpolarization 10/21/2015 MDufilho 26