Chapter 5: How Neurons Communicate and Adapt Flashcards
What does Acetylcholine (ACh) do?
activates skeletal muscles in the SNS; may either excite or inhibit internal organs in the NAS; also the first neurotransmitter discovered
What does Epinephrine do?
it is a chemical messenger that acts as a neurotransmitter in the CNS and as a hormone to mobilize the body for fight or flight during times of stress
What does Norepinephrine do and where is it found?
it accelerates heart rate in mammals; found in the brain and sympathetic division of the ANS
What is a Neurotransmitter?
it is a chemical with an excitatory or inhibitory effect when it is released by a neuron on a target
What does Dopamine do and what class of NT is it?
it is involved in coordinating movement, attention, learning and reinforcing behaviors; it is an Amine NT
What happens in the brain if you have Parkinsons?
there is a substantia nigra dysfunction involved with dopamine loss in the substantia nigra
What is a Synaptic Vesicle?
a membranous compartment that encloses neurotransmitters
What is a Synaptic Cleft?
a gap between the presynaptic and post-synaptic membranes
What is a Chemical synapse?
the junction at which messenger molecules are released when stimulated by an action potential
What are Storage Granules?
compartments in the neuron that hold several vesicles containing a specific neurotransmitter
What is a gap junction and what process are they relevant in?
it is an area of contact between adjacent cells in which ion channels form a pore that allows ions to pass directly from one cell to the next; it is relevant in electrical synapses because that is when the neurons come in to contact
What are the 4 steps of neurotransmission?
1) Neurotransmitter synthesis and storage
2) Neurotransmitter release
3) Receptor-site activation
4) Neurotransmitter deactivation
What are the 2 ways neurotransmitters are derived?
1) Synthesized in cell body from instructions in DNA and transported to axon terminal
2) Synthesized in axon terminal from building blocks derived from food
What is a transporter molecule and what role does it play in the 2nd way NTs are derived?
it is a protein molecule that pumps substances across the membrane; it absorbs precursor chemicals from the blood used in this NT synthesis process
What happens during neurotransmitter release?
an action potential changes the voltage of the presynaptic cell and causes an influx of Ca2+; these Ca2+ ions cause the vesicles to fuse with the membrane and get released by exocytosis
What are transmitter-activated receptors and what 3 things can happen to them when something binds to them?
protein that has specific neurotransmitter binding site and is embedded in the membrane of the cell; 1) Depolarized 2) Hyperpolarized 3) other chemical reactions that modulate excitatory/inhibitory happenings
What are autoreceptors and what do they affect?
they respond to the same transmitter released by the neuron and may affect that presynaptic neuron
What is a quantum?
a vesicle worth of NTs that is the minimum required for any change
What are the 4 ways the neurotransmitters can become deactivated?
1) Diffusion: some of the NT simply diffuse away
2) Degradation: enzymes in the cleft break down NT
3) Reuptake: transporters bring them back in as well as broken NT
4) Astrocyte uptake: can be taken up by neighbouring astrocytes
What are some different varieties of synapses?
Axomuscular, axodendritic, axosomatic, axoaxonic, axosynaptic (another synapse), axoextracellular (outside cell), axosecretory (into blood vessel), dendrodenritic (dendrite to dendrite)
What are some qualities of excitatory vs inhibitory synapses?
Excitatory: round vesicles, wider cleft, active areas are larger
What parts of the cell are typically excitatory and what are inhibitory?
cell body inhibitory and dendritic tree excitatory; cell body kind of stops it if it isn’t enough to overcome it
What are the 4 criteria for identifying NTs?
1) must be synthesized in neuron or present in it
2) when neuron is active, chemical must be released and produce a response in target
3) same response when chemical is experimentally placed on target
4) mechanism must exist to remove chemical once it is done
What NT do all motor neurons leaving the SC use?
ACh (acetylcholine)
What is a Renshaw loop?
axon goes to muscle and to interneuron which can be inhibitory to prevent the overexcitation of the neuron
What is a small molecule transmitter and what are examples of them?
quick acting NT that is synthesized in the axon terminal from products derived from diet; Histamine (sleep and wake, can cause constriction of smooth muscles), Acetylcholine
What is acetylcholine synthesized from?
choline and acetate
What are the 3 main Amine’s and how are they synthesized?
dopamine, norepinephrine, epinephrine; go from tyrosine to L-Dopa to Dopamine to Norepinephrine to Epinephrine; they all can be only produced in limited quantities
What affects does Serotonin have on the brain/body?
mood, aggression, appetite, pain and arousal
What are the 2 main amino acids, how do they differ and what do they do?
Glutamate: excites neurons
Gaba: inhibits neurons, same as glutamate but without carboxyl
What is a neuropeptide? What does it do? Where is it made? What are examples?
a short amino acid chain; acts as a NT but a slow acting oneand as a hormone and may contribute to learning, does not affect post synaptic voltage, affects indirectly the structure and function; it is made in the ribosomes; opium and morphine
What is the most common lipid transmitter and what does it do?
endocannabinoid; synthesized in postsynaptic to act on presynaptic; affects appetite, pain, sleep, mood, and stress respone; almost like post synaptic controls presynaptic
What are 3 examples of Gaseous Transmitters and what do they do?
1) Nitric oxide: dilate blood vessels, aids digestion and cellular metabolism (in viagra)
2) Carbon monoxide: activates cellular metabolism
3) Hydrogen Sulfide: slows cellular metabolism
They diffuse across the cell membrane and immediately become active
What is an Ionotropic receptor and how does it function?
an embedded membrane protein; acts as a 1) binding site of NT 2) pore that regulates ion flow; basically allows ions to move across membrane
What is a metabotropic receptor and how does it function
an embedded membrane protein; has a binding site for a NT linked to a G protein; it can affect other receptors or act with 2nd messengers to affect other cellular processes including opening a pore (doesn’t do it directly though); can activate an “amplification cascade”
What is a G protein and what are its subunits?
a Guanyl nucleotide binding protein, when activated it binds to other proteins; Alpha, Beta and Gamma
What are 2 things the alpha sub unit of the G protein does?
1) Binds to channels to allow ion flow
2) bind to enzyme which activates the second messenger
What is a second messenger and what does it do?
it initiates a biochemical process when activated by a NT; it can cause a channel to change structure, form new channels or bind to DNA to initiate or cease production of proteins
What is a Cholinergic neuron and what is it’s main receptor?
a neuron that us ACh as its main NT (motor neurons); its main receptor is nAChr (nicotinic acetylcholine receptor) which is ionotropic
What NT do the sympathetic and parasympathetic systems use the most of?
Sympa: norepinephrine
Parasympa: acetylcholine
What is an activating system?
a neural pathway that coordinates brain activity through a single NT, cell bodies are in the brainstem nucleus and it goes throughout a wide CNS region
What is a habituation response in neurons and what is the neural basis of one?
a learned behavior in which response to a stimulus weakens with repeated presentations; reduced sensitivity of Ca2+ channels underlies habituation, there is less of an influx of Ca2+
What is a sensitization response in neurons and what is the neural basis of one?
it is a response that strengthens with repeated presentations; less responsive potassium channels underlie sensitization, repolarization does not happen as quickly
What neurotransmitter is crucial to learning?
cAMP, but it must be in the right amounts
