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Altered Neuronal Transmission.docx

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Dalhousie University
NURS 2090
Heather Helpard

Altered Neuronal Transmission Neuron Components: 1. Cell body/ Soma: filled with cytoplasm + nucleus 2. Dendrites: branched ends that transmit impulses to the cell body 3. Axon: carry impulses away from cell body Functional Types: 1. Sensory/Afferent: carry impulses from receptors in periphery of brain + SC → CNS 2. Motor/Efferent: carry impulses away from brain + SC → target in body that regulates activity 3. Interneuron: most abundant, are connections btw neurons, transmitting signals btw afferent/efferent Supporting cells: 1. Glia: provides support + nutrition, maintain homeostasis and form myelin that covers neurons in the brain. 2. Oligodendrocytes: myelin segments around multilayered axons in the brain (CNS) 3. Schwann Cells: myelin on single axon in PNS Membrane Potential: Difference in electrical charge between the inside and outside of the cell Action Potential: * polarized at rest! (inside = more negative, difference = -70mV) 1. Resting membrane potential: state of tension inside CM 2. Depolarization phase: rapid movement of Na into cell through Na channels in CM 3. Repolarization phase: efflux of K+ Neural Communication: Flow of information across a synapse 1. Electrical: through gap junctions, fast and direct, multidirectional 2. Chemical: neurotransmitters between nerve cells/excitable cells, unidirectional Synapse structures 1. Presynaptic terminal 2. Synaptic cleft 3. Postsynaptic membrane Action Potential Hypopolarization: towards threshold (more positive, less negative) Hyperpolarization: away from threshold (more negative) ** promotes inhibition Interruption of NT: 1. Reuptake 2. Diffusion 3. Enzymatic Breakdown Types of NT: 1. Amino acids: glutamic acid, GABA 2. Peptides: endorphins, Substance P 3. Monoamines: Serotonin, dopamine, NE Neuromodulators:  Can alter effects of NT  Are released from axon terminals Nervous System Organization Central Nervous System  Lobes: are divided by sulci (fissures), and gyri (convolutions)  Hemispheres: R/L Frontal: reasoning, planning, speech and movement Parietal: perception of touch, pressure, temperature and pain Temporal: perception, memory, and recognition of auditory stimuli Occiptal: vision Spinal cord: central to control reflex response 1. Ventral horns: (Anterior extensions)  Efferent motor neurons leaving cord (via ventral roots) 2. Dorsal horns: (Posterior extensions)  Sensory neurons receiving afferent impulses (via dorsal roots) Spinal Cord Structures Dorsal root: of each spinal nerve is specialized to carry incoming sensory info. Dorsal root ganglia: are swellings in the dorsal root just before they enter the cord which contains cell bodies of sensory neurons Ventral root: carries info from CNS to muscles/glands. Ascending tracts: take sensory info to the brain (dorsal/external lateral part) Descending tracts: carry mostly efferent (motor) signals from the brain to the cord (ventral/interior lateral portion of white matter) Upper Motor Neurons:  cell bodies in motor cortex and axons extending to brain stem and SC  cross over in the medulla and descend on the contralateral side  synapse onto LMN’s leaving the SC via the ventral root  **the UMN’s that don’t cross over in the medulla travel down the ipsilateral SC, crossing over and synapsing on the LMN at the level of the SC exit. Lower Motor Neurons: located in the ventral horns of the SC  Synapse onto motor fibers in the PNS, providing innervations and motor function to the legs.  Injury to axons before they cross over, leads to paralysis on the opposite side  Injury to axons after they cross over exerts its effect on the same side of the body. Interneurons connect UMN’s and LMN’s in the SC Tissue composition 1. White matter: myelinated axons and dendrites (tip: pale color comes from myelin)  Contains ascending sensory/ descending motor tracts with axons that communicate within the CNS  Increases as cord reaches brain due to the increase in ascending fibers 2. Gray matter: Cell bodies (which have color)  Contains synapses btw sensory, motor and interneurons Pyramidal Motor System  Extends from the sensorimotor areas of the brain to the motor neurons of the ventral horn of the spinal cord  Controls voluntary movement Extrapyramidal System  Basal ganglia  Fine-tunes and stabilizes movement (erratic motions, stability of trunk, motor fx) Coronal View of the Brain Central Nervous System Protection 1. Cerebrovascular circulation: Circle of willis is a cerebral arterial structure that connects vertebral/carotid circulations. It is important as a collateral circulation in case perfusion is impaired in another arterial system. It allows removal of excess fluid in the CNS btw pia mater and blood vessels b/c lymphatics are absent 2. Blood-brain barrier: tight junctions decrease permeability. Only small lipid soluble/uncharged particles can pass, which protects the body from substances, NT/hormones and the environment. 3. Cerebrospinal fluid (CSF): Baths the surface of CNS, is produced by the choroid plexus, flows through interventricular foramen. It cushions, reduces pressure, removes substances and transports hormones. Peripheral Nervous System ** not protected by BBB or boney support of CNS 1. Somatic Peripheral Nervous Systems (coordination of body movement, reception of stimuli, conscious control)  Motor and sensory impulses between the central nervous system and the periphery  Cranial nerves (12, originate in brain)  Spinal nerves (31, all have sensory/afferent, motor/efferent neurons) o Dermatomes: spinal nerves carry info to/from body regions called dermatomes Manifestations of pain/pressure can be associated with the regions. o Plexus formation: spinal nerves make a interconnection of fibers. 1. Cervical Plexus, 2. Brachial, 3. Lumbar, 4. Sacral *body position, pain, temp, touch Dermatomes 2. Autonomic Peripheral Nervous System (involuntary functions) 1. Preganglionic neurons: cell bodies originate in the brain/SC 2. Autonomic ganglion: group of nerve cell bodies 3. Postganglionic neurons: Fibers projecting from the autonomic ganglion to a target organ Sympathetic (Autonomic) Parasympathetic (Autonomic) Fiber lengths: Fiber lengths: Short preganglionic Long preganglionic Long postganglionic fibers Short postganglionic fibers Spinal nerves exit between T1 and L2 Spinal nerves between S2 and S4 Neuron exit sites Cranial nerves between midbrain and medulla Sympathetic Actions Parasympathetic Actions 1. Increased heart rate, contractility, blood 1. Decreased heart rate, contractility, blood pressure, respiratory rate pressure, respiratory rate 2. Bronchial smooth muscle relaxation 2. Bronchial smooth muscle constriction 3. Vascular smooth muscle constriction 3. Vascular smooth muscle relaxation 4. Decreased constriction of bladder and peristalsi4. Increased constriction of bladder and of gastrointestinal smooth muscle peristalsis of gastrointestinal smooth muscle 5. Constriction of anal and bladder sphincter 5. Relaxation of anal and bladder sphincter Distribution of Parasympathetic Fibers Distribution of Sympathetic Nerve Fibers Nervous System Integration Reflex Arc Neuronal Injury Injury types 1. Chromatolysis: the swelling of a neuron b/c of injury 2. Atrophy: ↓ in side of a cell (neuron) 3. Neuronophagia: phagocytosis + inflammation responses caused by dead neuron damaging neighboring cells 4. Intraneuronal inclusions: distinctive structures formed in nucleus/cytoplasm Injury responses 1. Astrogliosis: astrocytes respond to local tissue injury through proliferation, forming a glial scar. (i.e. during wounds/ tumors/abscess/ hemorrhage) 2. Microglial nodules: when astrocytes join with microglia 3. Axonal degeneration: caused by necrosis in response to injury to the cell body or axon of the neuron. Creates an inflammatory response, leading to phagocytosis of cellular debris by macrophages. **when done by a crushing injury, its called Wallerian degeneration. 4. Axonal regeneration: regeneration is possible if the cell body and proximal axons are not damanged. 5. Neuropathy: a p
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