ctr week 6:synaptic functions

synapse

a junction that allows information to be transferred between cells

what neuron can communicate with

another neuron

effector cell

presynaptic neuron

the neuron sending the signal

postsynaptic neuron

the cell receiving the signal

synaptic cleft

the small space between the presynaptic and postsynaptic cells

electrical synapses

• a type of gap junction

• directly connect the cytoplasm of adjacent neurons

• allow ions and small molecules to move between cells

• very rapid

• helps synchronize activity

• difficult to modulate

chemical synapses

use a neurotransmitter to transfer information from one cell to another

step one of chemical synaptic transmission

action potential arrives at the axon terminal of the presynaptic neuron

step two of chemical synaptic transmission

the action potential causes voltage gated Ca channels to open

Ca enters the axon terminal down its electrochemical gradient

step three of chemical synaptic transmission

Ca causes synaptic vesicles to release neurotransmitter

Ca interacts with synaptotagmin, which interacts with SNARE proteins

step four of chemical synaptic transmission

neurotransmitter crosses / diffuses across the synaptic cleft, it then binds to specific receptors on the postsynaptic membrane

these receptors are often chemically gated ion channels

step five of chemical synaptic transmission

graded potential occurs

neurotransmitter binds to its receptor, this causes the receptor protein to change shape, which opens ion channels

step six of synaptic transmissions

the neurotransmitter must be removed so that the postsynaptic response doesn’t continue indefinitely

there are 3 mechanisms:

1. reuptake: neurotransmitter is taken back uo by the axon terminal or astrocytes

2. enzymatic degradation: enzymes breakdown the neurotransmitter

3. diffusion: neurotransmitter diffuses away from the synaptic cleft

exocytosis

a process where vesicles fuse with the cell membrane and release their contents into the extracellular fluid

used to release neurotransmitters

requires ATP

endocytosis

a process where the cell membrane indents and forms a vesicle to bring material into the cell

helps recycle the synaptic vesicle membrane

require ATP

what determines the size of a graded potential

higher impulse frequency—→more neurotransmitter released—→larger graded potential

amount of neurotransmitter

because graded potentials are proportional to the stimulus: more neurotransmitters—>larger graded potential

neurotransmitter +receptor

which neurotransmitter is released and which postsynaptic receptor it activates are important because different receptors can cause diffrent effects

excitatory postsynaptic potential-EPSP

makes the postsynaptic membrane potential move toward threshold

makes an action potential more likely

inhibitory postsynaptic potential- IPSP

makes the postsynaptic membrane potential move away from threshold

makes an action potential less likely

neural integration

the process of combining the many excitatory and inhibitory signals received by a neuron

temporal summation

occurs when multiple stimuli occur close together in time

spacial summation

occurs when stimulaneous stimuli occur at diffrent locations

neural circuits

a functional group of neurons that process a particular type of information

neurons link together to preform specific tasks

diverging circuits

one neuron sends signals many downstream neurons

converging circuits

several receptors send infromation that converges on one neuron to produce a stronger response

reverberating circuits

contain neurons whose axons synapse with neurons upstream in the circuit

involved in repetitive or rhythmic activities such as:

breathing

certain motor activities

wake-sleep cycle

neuromuscular junction

the synapse between a motor neuron and skeletal muscle

important neurotransmitter: acetylcholine(ACh)

acetylcholinesterase

breaks down acetylcholine

myasthenia gravis

involves a reduction in ACh receptors at the neuromuscular junction

it is an autoimmune disease in which antibodies can occupy or destroy ACh receptors

curare

prevents ACh from binding to postsynaptic receptors

less receptor activation

less muscle stimulation

paralysis

organophosphates

inactivate acetylcholinesterase

ACh cannot be broken down—> ACh accumulates in the synaptic cleft —>ACh receptors continue being stimulated—>excessive muscle/neuronal activity

botulism

caused by a bacterial toxin

—>prevents release of ACh

acetylcholine : peripheral nervous system

autonomic and somatic motor neurons

norepinephrine: peripheral nervous system

autonomic neurons

dopamine: central nervous system

brain, substantia nigra

norepinephrine + epinephrine: cenral nervous system

brain, locus

can also act as hormones

serotonin:central nervous system

brain,raphe nuclei

histamine: central system

parts of brain, tuberomammillary

excitatory neurotransmitters

• glutamate

• aspertate

inhibitory neurotransmitters

• glycine

• GABA