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Cells of the nervous system
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Central dogma
DNA in nucleus undergo transcription to be converted into mRNA which is then translated into protein
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Neurons
specialized for electrical signaling, communication with other cells
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Neuroglia or glia
supporting cells
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Components of a neuron
- Dendrites
- Synapses
- Myelinated axon
- Cell body
- Node of ranvier
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Dendrites
- Arborized
- Info received via synapses on dendrites
- Primary location of post-synaptic specialization (many neurotransmitter receptors)
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Composition of synaptic contacts
- Presynaptic terminal
- Synaptic cleft
- Post-synaptic specialization
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Presynaptic terminal
- (aka synaptic ending)
- Versicles with neurotransmitter molecules or neurotransmitters
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Synaptic cleft
space between presynaptic terminal and post-synaptic specialization
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Post-synaptic specialization
- (aka post-synaptic cell)
- On dendrite or cell body
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Receptors
receive chemical signal and convert to an electrical
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Axon
- specialized for electrical conduction
- Short = interneuron (local circuit)
- Long = projection neurons
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Myelin
- insulator
- increases speed of AP along axon
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Axon hillock
AP is initiated
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Cell body
- occasionally the site of synapses
- location of nucleus
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Node of ranvier
- filled with ion channels
- AP propagation
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Roles of glia
- Maintain signal ability of neurons (maintain ionic environ)
- Modulate rate of nerve cell propagation (myelination)
- Modulate synaptic action (control uptake of neurotransmitters at synaptic cleft)
- Scaffolding for development
- Aid neurons in recovery
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Three types of glia
- Astrocyte
- Oligodendrocyte
- Microglia
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Astrocyte
- Maintain chem environ for neural signaling
- Stem cells
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Oligodendrocyte
- Myelinate CNS neurons
- (equivalent in PNS is Schwann cell)
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Microglia
- Scavenge cellular debris after injury
- Moduilate inflammation and cell death
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Neural circuits
- composed of many neurons
- Afferent neurons
- Interneurons
- Efferent neurons
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Afferent neurons
Carry info toward brain/spinal cord
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Interneurons
Local aspects of circuit
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Efferent neurons
Carry info away from brain or spinal cord
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Example of simple circuit
Myotatic spinal reflex
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Myotatic spinal reflex
- 1) Tap stretches tendon, stretching sensory receptors in leg extensor muscle
- 2A) Sensory neuron excites motor neuron
- 2B) Sensory neuron excites spinal interneuron
- 2C) Interneuron inhibits motor neuron to flexor muscle
- 3A) Motor neuron conducts AP to synapses on extensor muscle fibers, causing contraction
- 3B) Flexor muscle relaxes, no activity
- 4) Leg extends
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Functions of neural systems
- Sensory interactions (organism and environ)
- Motor-organize and generate actions
- Link sensory and motor, produce higher order functions (cognition, emotion)
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Depolarization
More likely to fire AP
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Hyperpolarization
Less likely to fire AP
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Components of PNS
- Cranial nerves
- Spinal nerves
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Subdivisions of PNS
- Sensory pathways
- Motor pathways
- -Somatic nervous system
- -Autonomic nervous system (symphatic vs parasymphatic)
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PNS
- cell bodies in ganglia
- axon are nerves
- myelinated by schwann cells
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CNS
- Cell bodies are in gray matter
- Axons are in tracts (white matter)
- Myelinated by oligodendrocytes
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Commissure
Tracts containing axon crosses midline
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