Bio217 F2014 Unit 4 Bio217: Pathophysiology Class Notes Professor Linda Falkow Unit IV: Nervous System Disorders Structure and Function of the Nervous System Chap. 12: Structure & Function of the Nervous System Chapter 12 Chap. 13: Pain, Temperature, Sleep, and Sensory Chap. 14: Alterations in Cognitive Systems, Cerebral Dynamics, and Motor Function Chap. 15: Disorders of the Central and Peripheral Nervous Systems Overview of the Nervous System Overview of the Nervous System • Peripheral nervous system (PNS) • Central nervous system (_____) – Somatic nervous system – ____________ • Motor (efferent) and sensory (afferent) • Peripheral nervous system (_____) pathways regulating voluntary motor control of skeletal muscle – Cranial nerves – Autonomic nervous system (ANS) – Spinal nerves • Motor and sensory pathways regulating – Pathways body’s internal environment through • Afferent (__________) involuntary control of organ systems • Efferent (__________) – Sympathetic (“_____________”) – Parasympathetic (“Rest and repose”) Cells of the Nervous System Neuron • Neuron (conducts nerve impulses) • Axons – Variable size and structure – Myelin • Three components • Insulating layer of lipid material – Cell body (soma) • Formed by the Schwann cell • Nuclei = cell bodies in CNS – Endoneurium • Ganglia = cell bodies in PNS are ganglia • Delicate layer of CT around each axon – Dendrites – Neurilemma • __________ impulses • Thin membrane between myelin sheath and endoneurium – Axons • Carry impulses ________ from cell body 1 Bio217 F2014 Unit 4 Neuron Structural Classification of Neurons • Axons –Nodes of Ranvier • Based on number of processes • Regular interruptions of the myelin extending from cell body sheath –Unipolar – –Saltatory conduction Bipolar • Flow of ions between segments of –Multipolar myelin rather than along entire length of axon Functional Classification of Neurons Neurons • Sensory (afferent) – Transmit impulses from sensory receptors to CNS • Associational (interneurons) – Transmit impulses from neuron to neuron • Motor (efferent) – Transmit impulses from CNS to an effector Neuroglia Neuroglia • “Nerve glue” • Support the neurons of the CNS – Astrocytes – Oligodendroglia (oligodendrocytes) – Microglia – Ependemal A – astrocyte B – oligodendrocyte C – microglia D - ependymal 2 Bio217 F2014 Unit 4 Nerve Impulse Synapses • Region between adjacent neurons (pre- and • Neurons generate action potentials by postsynaptic neurons) is called a synapse selectively changing the electrical portion • Impulses are transmitted across synapse by of their plasma membranes and chemical and electrical conduction influencing other nearby neurons by release of neurotransmitters (chemicals) • Neurotransmitters – More than 30 substances • (ACh, serotonin, NE, dopamine) – Excitatory or Inhibitory Forebrain: Cerebrum Central Nervous System Gyri, sulci, and fissures Gray matter and white matter BRAIN: Cerebral nuclei (basal ganglia) • Forebrain – Cerebral hemispheres • Midbrain – Corpora quadrigemina, substantia nigra, and cerebral peduncles • Hindbrain – Cerebellum, pons, and medulla Forebrain Central Nervous System - functional areas • Diencephalon – Thalamus – Hypothalamus • Midbrain – Corpora quadrigemina • Superior and inferior colliculi – Tegmentum • Red nucleus and substantia nigra ( dopamine NE) • Cerebral peduncles 3 Bio217 F2014 Unit 4 Central Nervous System Spinal Cord • ____________ • Located in vertebral canal, protected – Cerebellum by vertebral column – Connects the brain and the body – Pons – Conducts somatic and autonomic reflexes – Medulla oblongata – Modulates sensory and motor function Spinal Cord Spinal Cord Reflex Arc Neuromuscular Junction • Receptor • Afferent (sensory) neuron • Efferent neuron • Effector 4 Bio217 F2014 Unit 4 Protective Structures Meninges • Cranium – Eight bones • Frontal, Occipital, Temporal (2), Parietal (2), Sphenoid, Ethmoid – Galea aponeurotica • Meninges – Protective membranes surrounding brain & SC • Dura mater • Arachnoid • Pia mater Protective Structures Protective Structures • Cerebrospinal fluid (CSF) • Vertebral column – Clear, colorless fluid similar to blood plasma and interstitial fluid – 33 vertebrae • 7 cervical, 12 thoracic, 5 lumbar, – 125 to 150 mL 5 fused sacral, 4 fused coccygeal – Produced by _____________ in lateral, third, and – Intervertebral disks fourth ventricles • Annulus fibrosus – Reabsorbed through _______________ • Nucleus pulposus Vertebral Column Blood Supply to the Brain • 800 to 1000 mL per minute • CO2 is the primary regulator for CNS blood flow • Internal carotid and vertebral arteries • Arterial circle (circle of Willis) 5 Bio217 F2014 Unit 4 Blood Supply to the Brain Blood Supply to the Brain Peripheral Nervous System Cranial Nerves • 31 pairs of spinal nerves – Named for vertebral level from which they exit – Mixed nerves – Arise from gray matter of the spinal cord • 12 pairs of cranial nerves – Sensory, motor, and mixed Spinal Nerves Autonomic Nervous System • Located in both the CNS and PNS • Maintains a homeostasis in visceral (internal) organs • Neurons – Preganglionic (myelinated) – Postganglionic (unmyelinated) 6 Bio217 F2014 Unit 4 Autonomic Nervous System Sympathetic Nervous System • Two divisions – Sympathetic • “Fight or flight” response • Thoracolumbar • Sympathetic (paravertebral) ganglia – Parasympathetic • “Rest or repose” response • Craniosacral • Preganglionic neurons travel to ganglia close to organs they innervate Neurotransmitters and Parasympathetic Nervous System Neuroreceptors of the ANS • SNS preganglionic fibers – ACh (_____________) • SNS postganglionic fibers – NE (_______________) • PSN preganglionic & postganglionic fibers – ACh Neurotransmitters and Aging and the Nervous System Neuroreceptors of the ANS • Decrease in the number of neurons – Decreased brain weight and size • Senile plaques • Neurofibrillary tangles • Slowing of neurologic responses 7 Bio217 F2014 Unit 4 Concept Check: • 1. One function of somatic NS that is not performed • 3. Which of the following best describes the SC? by the ANS is conduction of impulses: – A. Descends inferior to the lumbar vertebrae – A. To involuntary muscles and glands – B. Conducts motor impulses from the brain – B. To the CNS – C. To skeletal muscles – C. Descends to L4 – D. Between the brain and SC – D. Conducts sensory impulses to the brain • 2. Neurons are specialized for the conduction of impulses, while neuroglia: • 4. Which is not a protective covering of the CNS? – A. Support nerve tissue – A. Cauda equina – B. Serve as motor end plates – B. Dura mater – C. Synthesize ACh and AChE – C. Arachnoid – D. All of the above – D. Cranial bone • 5. The SNS: – A. Mobilizes E in times of need – B. Is innervated by cell bodies from T1 L2 – C. Is innervated by cell bodies located in the Pain, Temperature, Sleep, and cranial nerve nuclei – D. Both A and B are correct Sensory Function • 6. The PSN : Chapter 13 – A. Conserves and stores E – B. Has relatively short postganglionic neurons – C. Both A and B are correct – D. Has paravertebral ganglia Pain Neuroanatomy of Pain • “Pain is whatever the experiencing • Nociception person says it is, existing whenever he – Perception of pain says it does” —McCaffrey • Nociceptors – Free nerve endings in skin, muscle, joints, arteries, and the viscera that respond to chemical, mechanical, and thermal stimuli 8 Bio217 F2014 Unit 4 Pathways of Nociception Neuromodulation of Pain - Spinothalamic tracts • Neuromodulators – Located in pathways of NS – Triggered by tissue injury and or inflammation – Excitatory neuromodulation • Substance P, glutamate, somatostatin – Inhibitory neuromodulation • GABA, glycine, serotonin, NE, endorphins Neuromodulation of Pain Endorphin Response • Endorphins (endogenous morphines) – Neuropeptides – inhibit pain transmission in CNS – Bind opioid receptors • Beta-endorphins (rel. from hypothalamus & pit. gland) • Enkephalin (weaker than other endorphins) • Dynorphins (can stimulate pain) • Endomorphins (cause VD due to NO2 released from endothelial cells) Acute Pain Acute Pain • Referred pain – Pain present in an area removed or distant • Manifestations from point of origin – Fear and anxiety – Area of referred pain is supplied by same • Tachycardia, hypertension, fever, spinal segment as the actual site diaphoresis, dilated pupils, outward • Myocardial pain behaviors, elevated BG, infarction pain decreased gastric acid secretion and intestinal motility, and a general decrease in blood flow 9 Bio217 F2014 Unit 4 Chronic Pain Neuropathic Pain • May be sudden or develop insidiously • Result of trauma or disease of nerves • Usually defined as lasting at least 3 to 6 months • Peripheral • Produces significant behavior and psychologic changes – Painful diabetic neuropathy • Types: • Central – Low back pain – Phantom limb – Myofascial pain syndromes – Chronic postoperative pain – Cancer pain Temperature Regulation Heat Loss • Peripheral & central thermoreceptors • Hypothalamic control (range ~37o + 0.7o) • Radiation, Conduction, Convection • Vasodilation • Heat production • Decreased muscle tone – Metabolism • Evaporation – Skeletal muscle contraction • Increased respirations – Chemical thermogenesis • Voluntary measures • Heat conservation • Adaptation to warmer climates – Vasoconstriction – Voluntary mechanisms Temperature Regulation Fever • Resetting of the hypothalamic thermostat • Aging – Slow blood circulation, vasoconstrictive response, and metabolic rate • Activate heat production and conservation – Decreased sweating and perception