Chapter 3: Synapses Flashcards
describe Sherrington’s inferences concerning the speed of a reflex .
Sherrington=communication along an axon and between 2 separate axons is different
SPEED- reflexes (muscles reflex arc) is slower than conduction along axon (delay at synapse)
-one set of muscles is excited another different set become relaxed
temporal summation (Sherrington’s inference)
TEMPORAL SUMMATION- repeated weak stimuli over short period of time have cumulative effect, several weak stimuli presented at slightly different times produce strong reflex than single stimulus
spatial summation (Sherrington’s inference)
SPATIAL SUMMATION- inputs from separate locations combine effects on a neuron (pinch 2 points at the same time) *critical to brain functioning
mechanisms underlying the excitatory postsynaptic potentials
EPSP- excitatory postsynaptic potential
- depolarization
- Na+ into neuron
- if EPSP does not reach threshold it decays quickly
mechanisms underlying inhibitory postsynaptic potentials
IPSP- inhibitory post synaptic potential
- hyperpolarization (more -ve)
- decrease probability of action potential
- open K+ gates (K+ leaves or Cl- enters)
how synaptic potentials contribute to the firing rates of neurons and the integration of information.
- synapses vary in duration and effects
- most neurons have a spontaneous firing rate that EPSP or IPSP can change
- cells have different thresholds meaning same stimulus will not reach threshold of each cell
describe the contributions of T.R. Elliott and O. Loewi to the question of whether most synaptic transmission is electrically or chemically mediated.
T.R Elliot- applying adrenaline directly to the surface of heart, stomach, and pupils produces same effect as sympathetic nervous system therefore sympathetic nerves stimulate muscles by releasing adrenaline or something similar
describe the contributions of O. Loewi to the question of whether most synaptic transmission is electrically or chemically mediated.
O. Loewi- frog hearts experiment- transferred chemicals not electricity from 1 frog to another
conclusion: nerves send messages by releasing chemicals
- discovery led to development of drugs for psychiatric use
list the six major types of neurotransmitters
1) Amino Acids
2) Monoamines
3) Acetylcholine
4) Neuropeptides
5) Purines
6) Gases
role of diet in the synthesis of neurotransmitters
Almost all NTs are synthesized from amino acids in the diet
ex) Phenylalanine-> dopamine, norepinephrine, epinephrine (catecholamines)
ex) tryptophan -> serotonin
processes of transport of neurotransmitters.
Transport: NTs are transported in vesicles until released
processes of release of neurotransmitters.
Release: depolarization opens voltage dependent Ca2+ gates in presynaptic terminal, 1-2ms later NTs released in bursts from presynaptic neuron into synaptic cleft
processes of diffusion of neurotransmitters.
Diffusion: NTs diffuse across cleft to postsynaptic membrane and attach to receptors
-neurons release combinations of NTs
ionotropic effects of neurotransmitters
- begin quickly (less than 1ms post NT attaches)
- NT attaches and channel twists open
- convey visual info, auditory info, and anything that needs ASAP updates
- excitatory or inhibitory
- localized to point on membrane
metabotropic effects of neurotransmitters
- sequence of metabolic reactions
- slower (30ms or more after release of NT)
- last for a few seconds or longer
- NT attaches, bends protein, released G-protein, triggers 2nd messenger system
- influences activity in almost all of cell
- taste, smell, pain, arousal, attention, pleasure, emotion
describe the similarities and differences between neurotransmitters and hormones
NTs- message from sender to receiver
Hormones- chemical secreted by cell in one part of body and conveyed in blood to influence other cells
-long lasting changes in multiple parts of the body
-modify brain activity
-convey message to anyone that can receive it
difference in control mechanisms of the anterior and posterior pituitary and be able to list some of the hormones released from each.
Anterior Pituitary -glandular tissue -synthesizes 6 hormones -hypothalamus controls release by secreting releasing hormones -ACTH, TSH, Prolactin, GH, FSH, LH -works via -ve feedback loop Posterior Pituitary -neural tissue -considered extension of hypothalamus -oxytocin, vasopressin
why inactivation of neurotransmitters is important and the two major ways in which this is achieved
- if was not inactivated it would continue exciting or inhibiting receptor and amplifying response
- Acetylcholine- broken down by acetylcholinesterase in to acetate and choline, choline diffuses back to pre-synaptic neuron
- Serotonin or catecholamines- detach from receptor then reuptake via transporter membrane proteins, enzyme breaks it down and washes away broken down products (excrete in blood and urine)
- Neuropeptides- diffuse away
two mechanisms for producing negative feedback.
Autoreceptors- respond to release of NTs by inhibiting further synthesis and release
Stimulation by special chemicals- chemicals travel back to presynaptic terminal where they inhibit further release of NT
why our brains have receptors for plant chemicals
-all NTs and hormones that are the same as humans in other species so if a plant evolves a chemical to attract bees or repel caterpillars the chemical is likely to affect humans
difference between agonists, antagonists, and mixed agonist-antagonists
Agonist- drug that increases or minimizes effect of NT
Antagonist- blocks a NT
Mixed Agonist/Antagonist- agonist for some effects of NT and antagonist for others, can depend on dose of drug
difference between a drug’s affinity for a receptor and its efficacy at that receptor.
Affinity- if the drug binds to the receptor
Efficacy- drug activates the receptor
-drug can have high affinity but low efficacy if it binds to the receptor but doesn’t activate it
common mechanism of action of nearly all abused drugs
- share effects on dopamine and norepinephrine synapse
- activates nucleus accumbens (central to reinforcing experiences of all types)
- almost all abused drugs and addictive activities increase dopamine release in nucleus accumbens
relation of dopamine in the nucleus accumbens to motivation (“wanting”) and why dopamine does not seem to be related directly to pleasure (“liking”)
- wanting is not always the same as liking
- addiction (wanting) is triggered by dopamine release in nucleus accumbens
- you can want something and have an all-consuming drive to get it even though it doesn’t bring pleasure ex) drug addiction after a bit
