Chapter 7: Neurons Flashcards
Neurons
conduct impulses, but generally do NOT divide (can repair)
Neuroglia
support neurons and cannot conduct impulses, divide
Sensory neurons
conduct impulses from sensory receptors to the CNS, afferent
Motor neurons
conduct impulses from the CNS to target organs, efferent
Interneurons
located completely within the CNS + integrate functions of the nervous system
Somatic motor neurons
reflexes and voluntary control of skeletal muscles
Autonomic motor neurons
innervate involuntary targets (smooth muscle, cardiac muscle, and glands)
Pseudounipolar
single short process, branches like a T to form 2 longer processes
- sensory neurons
Bipolar
2 processes, one on either end
- retina of eye
Multipolar
several dendrites and one axon
- most common, motor neurons
Schwann Cells
form myelin sheaths around peripheral axons
- in PNS
Satellite Cells
support cell bodies within the ganglia of the PNS
Oligodendrocytes
form myelin sheaths around CNS neuron axons
Microglia
migrate around CNS tissue and phagocytize foreign and degenerative material
Astrocytes
regulate the external environment of the neurons
Ependymal cells
line the ventricles central canal of spinal cord, secrete cerebrospinal fluid
Nodes of Ranvier
Gaps between Schwann cells on axons of neurons in PNS
White matter
myelinated neurons
Grey matter
unmyelinated neurons
Blood-Brain Barrier
capillaries in the brain don’t have pores between adjacent cells, joined by tight joint junctions
- substances can only be moves by very selective processes of diffusion through endothelial cells, ion channels, transport proteins and active transport
Polarized
Neurons at rest, inside is negative
Depolarized
Membrane potential inside the cell increases due to Na+ moving into cell
Repolarization
Return to resting potential (K+ exits the cell)
Hyperpolarization
membrane potential inside the cell decrease (become VERY negative), due to K+ leaving the cells
- inhibits immediate depolarization
K+ Channels
not gated (always open)
- voltage gated = open when a membrane potential (+30 mV) is reached, closing at resting potential
Na+ Channels
Voltage-gated only
- closed at rest, open if potential depolarizes to -55 mV, Na+ enters
- deactivated at +30 mV
All-or-None Law
once threshold is reached, action potential will happen
- size of stimulus does not equal size/duration of action potential
- stronger stimulus = more frequent action potentials, recruitment of neurons
Refractory Periods
after an action potential, neuron cannot become excited again
Absolute Refractory Period
during the action potential, Na+ channels are inactive
Relative Refractory Period
K+ channels are still open, only a very strong stimulus can overcome
- during hyperpolarization
Conduction rate
Only occurs in Nodes of Ranvier (in myelinated neurons)
- increased by diameter of neuron and myelination
Synapse
functional connection between a neuron and the cell it is signaling
- chemical vs electical
Electrical Synapse
Passage of ions across gap junctions
- faster, can occur in both directions
- no independent action, forced to do a coordinated action
- ie. smooth muscle. cardiac muscle, brain neurons, neuroglial cells
Chemical Synapse
Release a chemical (neurotransmitter) from a terminal bouton, most common
- specific interaction depending on NT
Graded Potential
- ligand-regulated gates open = membrane potential changes (depending on which ion channel opens)
EPSP
Excitatory Postsynaptic Potential
- graded depolarization
- opening Na+/Ca+ channels
IPSP
Inhibitory Postsynaptic Potential
- graded hyperpolarization
- Opening K+/Cl-
ACh
Acetylcholine
- NT, directly opens ion channels when bound to its receptor
- excitatory or inhibitory depending on organ (Excitatory in ALL somatic motor neurons)
Nicotinic ACh receptor
Can be stimulated by nicotine
- found in: end plate of skeletal muscle cells, autonomic ganglia, some parts of the brain
- Ligand-Gated channel
Muscarinic ACh receptor
Can be stimulated by muscarine
- found in: autonomic nervous system, smooth muscle, cardiac muscle, glands
- G-protein Coupled Channels
AChE
Acetylcholinesterase
- enzyme that deactivates ACh shortly after binds to the receptor, hydrolyzes ACh into acetate and choline (which are reused in presynaptic cells)
Monoamines
regulatory molecules from amino acids
ie. Catecholamines, Serotonin, Histamine
Serotonin
Used by neurons in the raphe nuclei
Made by L-tryptophan
Implications in mood, behavior, appetite
SSRI
Serotonin Specific Reuptake Inhibitors
- treat depression
- ie prozac, paxil, zoloft, lexa pro, Luvox
Dopamine
Dopaminergic Neurons: motor and emotional control
Involved in emotional reward systems and associated with addictions such as nicotine, alcohol, and other drugs
Parkinson’s Disease
Caused by degeneration in dopaminergic neurons
- treated by L-dopa and MAOIs (monoamine oxidase inhibitors)
Schizophrenia
Too much dopamine
- drugs to treat inhibit dopamine
Glutamate
the major excitatory NT in the brain
- glutamate receptors = ion channels
Glycine
NT to produce IPSPs
- opens Cl- channels, makes it harder to reach threshold
- important for antagonistic skeletal muscle contraction
GABA
Gamma-aminobutyric Acid
- most common NT in the brain
- inhibitory, opening Cl-
- motor control
Huntington’s Disease
Degeneration of GABA-secreting neurons in the cerebellum
Neuropeptide Y
Most abundant neuropeptide in the brain
- stress response, circadian rhythm, cardiovascular control
- stimulates hunger (leptin inhibits when full)
- inhibits release of glutamate
Endocannabinoids
NT that binds to the same receptors as THC
- affects GABA, Glutamate, ACh G-protein-coupled receptors in the brain
Nitric Oxide
Gas made from L-arginine
- Diffuses across the presynaptic axon plasma membrane into the target cell to activate the production of cGMP (second messenger)
- blood vessel dilation, kills bacteria
Divergence
one presynaptic neuron forms synapses with several postsynaptic neurons
Convergence
many presynaptic neurons form synapses with one postsynaptic neuron
Spatial summation
occurs due to convergence of signals into one postsynaptic neuron
- all EPSP and IPSP are added together at one axon hillock
Temporal summation
due to successive waves of neurotransmitter release that add up together at the initial segment of the axon hillock
Synaptic plasticity
repeated use of a neural pathway = strengthen OR reduce synaptic transmission in that pathway
- ability of synapses to change
Long-term potentiation
repeated stimulation = enhanced excitability
- in the hippocampus (where memories are stored)
Long-term depression
suppressed transmission due to non-use
- learning is impaired
