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Intro Nervous system

TermDefinition
Basic functions of the nervous system Sensory function, integrative function, motor function
Sensory function Detect internal and external stimuli, carry sensory information to the brain.
Integrative function Process, analyse, stores and then makes decision or response
Motor function Create appropriate motor response by activating effectors
Main division of nervous system Central nervous system and Peripheral nervous system
Subdivision of the central nervous system Brain, spinal cord
Subdivision of the peripheral nervous system Somatic nervous system, autonomic nervous system, enteric nervous system
Somatic nervous system Sensory neurons relay to CNS, motor neurons signal from CNS to skeletal muscle, voluntary action.
Autonomic nervous system Involuntary actions of glands, sympathetic division fight or flight, parasympathetic division rest and digest.
Enteric nervous system Plexuses of neurons monitor change in gastrointestinal tract, control smooth muscle contractions to move food, enzyme secretion and hormones
Functions of neurons Sensing, thinking, remembering, controlling, muscle activity, regulating glandular secretions
Structure of neuron Cell body, dendrites, axon, myelin sheath, node of Ranvier, synaptic end bulb
Dendrites are for Receiving inputs
Axons are for Propagate nerve impulses towards other neurons, muscle fibre, gland cells
Types of axons Axon hillock (joins cell body), axon collateral (right angle branch off), axon terminal (end of neuron)
Structural classification of neurons Multipolar, bipolar, unipolar
Multipolar neuron Has several dendrites, one axon (brain, spinal cord)
Bipolar neuron One main dendrite, one axon (ears, eyes, noes)
Unipolar neuron Dendrites and axon fused together to for continuous process (sensing stimulus)
Impulse direction classification of neurons Sensory or Afferent neurons, motor or efferent neurons, interneurons
Sensory or afferent neurons Action potential from PNS to CNS
Motor or efferent neurons Action potential from CNS to PNS
Interneurons Action potentials from sensory neurons to motor neurons, integrate/process incoming sensory information to create a motor response.
Neuroglia 5 to 50 times more abundant than neurons, fill space originally occupied by nerves when damaged.
Neuroglia of CNS Astrocytes, Oligodendrocytes, Microglial cells (microglia), Ependymal cells
Neuroglia of PNS Schwann cells, satellite cells
Astrocytes Largest and most numerous, make contact with blood capillaries and neurons, cling to and support neurons, provide nutrients, remove waste. Blood brain barrier
Oligodendrocytes Smaller form maintain myelin sheath
Microglial Cells (microglia) Small cells with slender processes spinelike projections, phagocytise microbes and damaged nervous tissue.
Ependymal cells Cuboidal columnar cells arranged in single layer. Microvilli and cilia. Line ventricles of brain and CNS. Make and circulate cerebrospinal fluid
Schwann cells Form myelin sheath around axons, participate in axon regeneration.
Satellite cells Flat cells surrounding cell bodies of neurons in PNS ganglia provide structural support.
Myelin sheath multilayered lipid and protein sheath that electrically insulates axons
Myelinated axons Axons with myelin sheath
Unmyelinated axons Do not have a myelin sheath
White matter Of brain and spine, consists mainly of myelinated axons
Grey matter Of brain and spine, contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia
Types of neuron electrical signals Graded potentials, action potentials
Types of ion channels Leak channels, ligand-gated channels, mechanically gated channels, voltage gated channels
Leak channels Randomly alternate between open and closed
Ligand-gated channel Opens and closes as response to specific ligand (molecule that binds to receptor)
Mechanically gated channel Opens and closes in response to mechanical stimulus eg sound/touch pressure. Force distorts gate
Voltage gated channel Opens in response to change in membrane potential
Resting membrane potential Build-up of negative ions in cytosol inside plasma membrane. Equal build-up of positive ions in extracellular fluid. Separation of + and – ion is potential energy greater difference in charge, larger membrane potential.
Graded potentials Short communication, small deviation from membrane potential that makes membrane either more polarized – or less polarized +
Hyperpolarizing graded potential When response makes membrane more polarised
Depolarizing graded potential When response makes membrane less polarized
Summation Makes graded potential stronger, last longer by combining with other graded potentials.
Action potential Sequence of rapidly occurring events that briefly revers the membrane potential and then restore it to the resting state
Threshold Level of change required to generate an action potential
Subthreshold stimulus Weak depolarization that cannot bring membrane potential to threshold
Threshold stimulus Stimulus that is just strong enough to depolarize membrane to threshold
Suprathreshold stimulus Strong enough to depolarize membrane above threshold
All or nothing principle An action potential either occurs completely or not at all
Phases of action potential Resting state, depolarizating phase, repolarizing phase
After hyperpolarizing phase Voltage gated K+ channels remain open, membrane potential becomes even more negative. Once voltage gate K+ closes, membrane potential returns to resting level
Refractory period Period of time after action potential which excitable cell cannot generate another action potential
Absolute refractory period Occur from time Na+ channel activation gates open to when Na+ channel inactivation gate closes. Even a strong stimulus cannot reactivate it
Relative refractory period Period of time during with a second action potential can be initiated but only with a larger than normal stimulus
Impulse propagation Action potential keeps its strength as it spreads along membrane
Continuous conduction Step by step depolarization and repolarization of each adjacent segment of plasma membrane
Saltatory conduction Mode of action potential propagation that occurs along myelinated axons due to uneven distribution of voltage gated channels
Factors that affect speed of propagation Amount of myelination, axon diameter (larger diameter faster), temperature (colder slows propagation).
Axodendritic From axon to dendrite
Axosomatic From axon to cell body
Axoaxonic From axon to axon hillock
Presynaptic neuron Neuron that carries an impulse toward synapse
Postsynaptic neuron Neuron that carries an impulse away from synapse
Chemical synapse Impulse in presynaptic neuron causes the release if neurotransmitter molecules produce an impulse in postsynaptic neuron
Chemical synapses Action potential arrives, Calcium channels opened, Exocytosis of neurotransmitter, Neurotransmitter diffusion, Neurotransmitter binding and opening ligand-gated channels, Graded potential and action potential
Electrical synapse Impulses conduct directly between plasma membrane of adjacent neurons through gap junctions.
Electrical synapses advantages Faster communication, synchronisation
Excitatory postsynaptic potential (EPSP) Depolarizing postsynaptic potential. Total excitability effects greater than total inhibitory effects but less than threshold does not reach threshold
Inhibitory postsynaptic potential (IPSP) Potential hyperpolarizing postsynaptic potential. Effects are greater than excitatory effects, membrane hyperpolarizes. Results inhibition of neuron.
Removal of neurotransmitter Essential for normal synaptic function. If neurotransmitter could linger in synaptic cleft it would influence postsynaptic neuron, muscle fibre or gland indefinably.
Neurotransmitters are removed in three ways Diffusion, enzymatic degradation, uptake by cells
Created by: fanpeople