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Nervous System: Nervous Tissue and Brain 1 Divisions of the Nervous System • Central nervous system (CNS) – Brain – Spinal Cord • Peripheral nervous system – Everything outside the CNS Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 2 Types of Nervous Tissue • Neurons – Do the communicating for the nervous system – Long shape makes them delicate – Do NOT replicate or self-repair • Neuroglia or glia – Most abundant type – Support, protect, insulate, nourish, and generally care for neurons 3 Neuroglia (Glia) • Astrocytes – Star shaped – Transfer nutrients from blood • Ependymal cells – Produce fluid • Microglia – Phagocytic • Schwann cells (PNS) – Produce myelin sheath • Oligodendrocytes (CNS) – Produce myelin sheath 4 Types of Neurons • Unipolar: one process off of cell body • Bipolar: one axon, one dendrite (2 things) • Multipolar: one axon, several dendrites Parts of a Neuron • Cell body • Dendrites (receives info) • Axon – Schwann cell/Olig. • Myelin sheath • Nodes of Ranvier • Neurilemma – Axon terminal 7 8 Nerves and Tracts Nerves: bundles of peripheral nerve fibers held together Endoneurium: delicate layer nerve fiber (innermost) Perineurium: tissue holding together fascicles (middle) Epineurium: surrounding numerous fascicles and blood vessels to form a complete nerve (outermost) 9 10 Nerves and Tracts Tracts: bundles of nerve fibers within the CNS DO NOT have connective tissue coverings White matter CNS—myelinated tracts PNS—myelinated nerves Gray matter Made up of cell bodies and unmyelinated fibers CNS—referred to as nuclei PNS—referred to as ganglia 11 Functions of the Nervous System 12 Types of Neurons • Sensory (afferent) neurons – Carry information from periphery toward the CNS • Interneurons – Found only in CNS; connect sensory and motor nerves • Motor (efferent) neurons – Carry information from CNS toward periphery 13 14 Nerve Impulses or Signals • Electrical signals convey information along a neuron • Also called action potential • Move along sensory or motor neurons 15 The Action Potential • Polarization: Resting state • Depolarization: Stimulated state • Repolarization: Return to resting Ionic Basis of the Action Potential • Polarization – K+ leaks from neuron. – Determines resting membrane potential • Depolarization – Na+ rushes in. • Repolarization – K+ rushes out. 17 Why Action Potential “Moves” • Action potential – Forms at axon’s beginning – Regenerates along axon’s length – Enters axon terminal – Releases ACh from vesicles 18 Increasing Action Potential’s Speed • Myelin insulates axon. • Action potentials jump quickly from node to node – like a kangaroo. 19 Communication across the Synapse • ACh is – Secreted from neuron A – Diffused across synaptic cleft – Bound to receptors on neuron B • Neuron B is activated. 20 Random thing about biology • Suffix of –ase – Tells reader it is an enzyme – Inactivate/Inhibits the enzyme it’s named after. • Acetylcholine= neurotransmitter • Acetylochoinesterase = Inactivator 21 Application • In Multiple Scleroses the myelin sheath is destroyed. • The myelin sheath hardens to a tissue called the scleroses. • This is considered an autoimmune disease. • Why does MS appear to affect the muscles? Four Major Areas of the Brain • • • • Brain stem Cerebellum Diencephalon Cerebrum Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 23 Cerebellum • Mediates reflexes • Coordinates motor activity • Evaluates sensory input • Rhythmic movements 24 Brain Stem • Midbrain • Reflex for eye and ear • Pons • Breathing rate and rhythm • REM and Sleep Paralysis?? • Medulla oblongata • Vital center • Emetic center • Reflex center 25 Diencephalon • Thalamus: intergrates sensory from lower brain • Links to a number of Disorders – – – – Bipolar ADHD Autism Depression • Hypothalamus: body thermostat, endocrine(hormones) 26 Cerebrum: Four Lobes • • • • Frontal lobe Parietal lobe Temporal lobe Occipital lobe 27 Cerebrum: Markings • Gyrus (convolution) • Fissures (sulci) – Central – Lateral – Longitudinal Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 28 Frontal Lobe • • • • “ The executive” Behavior Personality Motor control Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 29 Frontal Lobe: Motor Activity • Primary motor area – Precentral gyrus • Frontal eye field • Motor speech area – Broca’s area Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 30 Frontal Lobe: Motor Homunculus • Shows percentages of frontal lobe devoted to body’s motor activities Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 31 Other Cerebral Lobes • Parietal – Somatosensory area – Gustatory area • Temporal – Auditory cortex – Gustatory area – Olfactory area • Occipital – Visual cortex Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 32 Functions Spanning Cerebral Lobes • Speech areas – Span temporal, parietal and occipital lobes – Usually in left hemisphere – Wernicke’s area (helps translate thought into speech) • Association areas – Helps to interpret sensory information – Examples: Visual, auditory, somatosensory Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 33 Structures Spanning Brain Divisions • Limbic system – Emotional brain • Reticular formation: Reticular activating system; sleep-wake cycle, consciousness, gaze center • Memory areas – Immediate memory – Short-term memory – Long-term memory Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 34 Protecting the CNS: Four Layers • • • • Bone Meninges Cerebrospinal fluid Blood-brain barrier Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 35 Protecting the CNS: Meninges • Dura mater • Arachnoid mater – Subarachnoid space • Pia mater Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 36 Protecting the CNS: Cerebrospinal Fluid (CSF) • Formed in ventricles by choroid plexus • Circulates through subarachnoid space – From central canal of spinal cord – From foramina 37 Drainage of CSF • Drainage of CSF must equal its production. • Arachnoid villi project into dural sinuses filled with blood. • CSF drains into blood and leaves the brain. Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 38 Protecting the CNS: The Blood-Brain Barrier • Made of special cells (astrocytes) within cerebral capillaries. • Prevents some toxins from entering CNS from blood Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 39