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Intro Nervous system
| Term | Definition |
|---|---|
| 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 |
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