Chapter 15 - Nervous System

• #tags column:4
• Neuronal communication is rapid, direct, and specific.Hormonal communication is slower, longer lasting, and affects many cells/tissues in many ways Hormones are spread throughout the body, whereas neurons have specific destinations DATBooster_Biology::15.Nervous_System
• The neuron consists of dendrites, axon, and cell body "" """Blausen 0657 MultipolarNeuron"", link, by BruceBlaus, CC BY 3.0" DATBooster_Biology::15.Nervous_System
• Dendrites receive information and transfer it to the cell body DATBooster_Biology::15.Nervous_System
• The axon transfers impulses away from the cell body DATBooster_Biology::15.Nervous_System
• Glial cells offer support to nervous tissue and are capable of cellular division DATBooster_Biology::15.Nervous_System
• Oligodendrocytes produce myelin in the CNS. "" "Image link, Public Domain" DATBooster_Biology::15.Nervous_System
• Schwann cells produce myelin in the PNS. "<img alt=""Illustration A shows various types of glial cells surrounding a multipolar nerve of the central nervous system. Oligodendrocytes have an oval body and protrusions that wrap around the axon. Astrocytes are round and slightly larger than neurons, with many extensions projecting outward to neurons and other cells. Microglia are small and rectangular, with many fine projections. Ependymal cells have small, round bodies lined up in a row. Long extensions connect from the ependymal cells to an astrocyte. Il...
• Myelin sheaths act as insulators and are separated by gaps called nodes of Ranvier "" "Image from OpenStax, CC BY 4.0" DATBooster_Biology::15.Nervous_System
• An action potential jumps from node to node, called saltatory conduction, speeding up impulse This occurs only in myelinated axons. Otherwise, the impulse would travel continuously down the axon. DATBooster_Biology::15.Nervous_System
• Only vertebrates have myelinated axons.Myelinated axons appear white; neuronal cell bodies appear gray White matter and gray matter refer to these DATBooster_Biology::15.Nervous_System
• Other glial cells include microglia, ependymal cells, satellite cells, and astrocytes "Ganglia are groups of cell bodies in the PNS" "Image from ...
• Microglia are phagocytes of the CNS DATBooster_Biology::15.Nervous_System
• Ependymal cells produce and circulate CSF DATBooster_Biology::15.Nervous_System
• Satellite cells envelop ganglia (PNS neurons' cell bodies) "Note the satellite cells on the right side:<img alt=""Illustration A shows various types of glial cells surrounding a multipolar nerve of the central nervous system. Oligodendrocytes have an oval body and protrusions that wrap around the axon. Astrocytes are round and slightly larger than neurons, with many extensions projecting outward to neurons and other cells. Microglia are small and rectangular, with many fine projections. Ependymal cells have small, round bodies lined up in a row. Long extensions...
• Astrocytes give physical support to CNS neurons, maintain mineral and nutrient balance DATBooster_Biology::15.Nervous_System
• "There are three types of neurons:
• 1. Sensory neuron: afferent neurons that receive initial stimuli (ex: neurons in the retina)
• 2. Motor neuron: efferent neurons that stimulate effectors, or target cells that produce a response (ex: neurons can stimulate muscles and sweat glands)
• 3. Association neuron/interneuron: located in the brain and spinal cord; receive impulses from sensory neurons and send then to motor neurons. These make up ~99% of nerves." DATBooster_Biology::15.Nervous_System
• The inside of an unstimulated neuron is negatively charged due to the negatively charged proteins and nucleic acids residing in the cell. The membrane of an unstimulated neuron is polarized, although there's a high [Na+] outside and a high [K+] inside DATBooster_Biology::15.Nervous_System
• "Nerve impulse stages:
• Resting potentialAction potentialRepolarizationHyperpolarizationRefractory period
• " DATBooster_Biology::15.Nervous_System
• "Nerve impulse stages:
• Resting potential: the normal polarized state of neuron, -70 mV.Action potential: after stimulus, gated ion channels let Na+ into the cell, which depolarize the cell. If the cell reaches the threshold of -50 mV, it will create an action potential that causes voltage-gated Na+ channels down the entire axon to openRepolarization: in response to Na+ flowing in, more gated ion channels let K+ out of the cell, restoring polarization, but n...
• " "Note that refractory period is what prevents an AP from moving backwards, even though ions are theoretically rushing in and diffusing in both directions.The absolute refractory period is absolute because Na+ channels are inactivated." "Image from OpenStax, CC BY 4.0" DATBooster_Biology::15.Nervous_System
• Graded potentials are transient potentials that cannot spread. The size of a graded potential is proportional to the size of the input. Only action potentials can open neighboring voltage-gated channels and spread the impulse. DATBooster_Biology::15.Nervous_System
• Action potentials are all-or-nothing, meaning there either is an action potential or there is none. The size of an action potential is unrelated to the size of the input. DATBooster_Biology::15.Nervous_System
• Action potentials have the same amplitude and intensity, so the strength of a neural signal is determined by action potential frequency or the number of action potentials generated DATBooster_Biology::15.Nervous_System
• There are two types of neural synapses: electrical and chemical DATBooster_Biology::15.Nervous_System
• Electrical synapses involve gap junctions Gap junctions allow ions to flow from one neuron to the next.Ex: cardiac tissue and visceral smooth muscle tissue use electrical synapses to enable fast, coordinated contractions. DATBooster_Biology::15.Nervous_System
• Chemical synapses mainly involve neurotransmitters and flow in one direction DATBooster_Biology::15.Nervous_System
• "Chemical synapse mechanism (after action potential arrives at new neuron):Voltage-gated Ca2+ gates open: depolarization allows Ca2+ to enter the cellSynaptic vesicles release neurotransmitters: influx causes release into synaptic cleftNeurotransmitters bind to postsynaptic receptorsThe postsynaptic membrane is excited or inhibited. Two possible outcomes: 1. Na+ gates open, membrane is {{c6::depola...
• " "In case of an EPSP, if the threshold potential is reached, a new action potential is generatedIn the case of an IPSP, it becomes more difficult to generate an action potential<img alt=""This illustration shows closely juxtaposed bulbous protrusions of presynaptic and postsynaptic cells. The presynaptic cell stores neurotransmitter in synaptic vesicles. When signaling occurs, the vesicles fuse with the cell membrane, thereby releasing the neutrotransmitter, which then binds to receptors on the postsynaptic cell. An enzyme on the surface of the postsynaptic cell destroys the neurotras...
• Acetylcholine is secreted at neuromuscular junctions and causes muscle contraction/relaxation. Everywhere else, it is inhibitory. DATBooster_Biology::15.Nervous_System
• Epinephrine, norepinephrine, dopamine, and serotonin (aka 5HT) are amino acid derived and are secreted between neurons of the CNS DATBooster_Biology::15.Nervous_System
• Gamma aminobutyric acid (GABA) is an inhibitory neurotransmitter among neurons in the brain DATBooster_Biology::15.Nervous_System
• Axons with larger diameters and more myelin will propagate faster impulses "A larger diameter helps because it has less resistance to the ""flow” of ions – think of water flowing through a large pipe vs. a small pipe.Myelination helps because of more efficient saltatory conduction; it can’t leak out of myelin wrapped sections, so the impulse goes straight to the next node" DATBooster_Biology::15.Nervous_System
• Synaptic vesicles fuse with the presynaptic membrane, then release neurotransmitter, neurotransmitter binds to receptors on the postsynaptic membrane "" """Synapse diag1"", link, CC BY-SA 3.0" DATBooster_Biology::15.Nervous_System