Nervous system: Synapses Flashcards
synapse
anatomically specialised junction between two neurones
can converge or diverge
0.2ms
excitatory synapse
generate excitatory post synaptic potential: membrane potential of post-synaptic neuron is brought closer to threshold (i.e., depolarised). graded potential generated
inhibitory synapse
generate an inhibitory postsynaptic potential: membrane potential of post-synaptic is either driven further from threshold (i.e., hyperpolarised) or stabilised at resting potential
made more negative
electrical synapse
electrical activity of the presynaptic neurone affects that of the postsynaptic neuron
pre and post synaptic cells connected by gap junctions
chemical synapse
neurotransmitters transmit the signal
active zones
release regions in which vesicles are docked on the presynaptic membrane
types of receptors in post synaptic neurone
ionotropic (ion channels)
metabotropic (G protein/second messenger signalling)
removal of neurotransmitter
diffusion of transmitter from cleft
degradation of neurotransmitter by enzymes
reuptake into presynaptic cells for re use
why are multiple excitatory postsynaptic potentials needed
one=0.5mV
need a change of 15mV
not enough to reach threshold
temporal summation
repeated stimulation of one neurone
spatial summation
multiple neurones activated simultaneously to produce graded potentials
inhibitory synapses can also do this
muscle spindle
stretch receptors consist of peripheral endings of afferent nerve fibers wrapped around modified muscle fibers (intrafusal) enclosed within a connective tissue capsule
intrafusal fibres
specialised muscle fibres to detect changes in stretch
extrafusal fibres
generate force, bulk of muscle
what does tension depend on
muscle length
load
fatigue
golgi tendon organs
endings of afferent nerve fibers that wrap around collagen
bundles in the tendons near their junction with the muscle
action potentials triggered when muscle stretches/contracts
electroencephalogram (EEG)
recording of brain electrical activity
patterns largely due to graded potentials
alpha rhythm
associated with decreased levels of attention
beta rhythm
attentive to external stimulus
5 major divisions of sensory receptors
Mechanoreceptors – pressure / stretch
Thermoreceptors– cold / warmth
Photoreceptors – different ranges of light
Chemoreceptors – binding of chemicals to the receptor (smell, taste, pH, O2)
Nociceptors– painful stimuli, such as heat, tissue damage
sensory receptors
specialised cells that generate graded potentials called
receptor potentials in response to a stimulus
ends of afferent neurons
and can convert stimuli into graded potentials
Stimuli opens ion channels directly or indirectly
ion flux
results in a change in membrane potential which results in a local graded
potential (receptor potential)
A larger stimulus results in a
larger graded potential which
results in more frequent action
potentials
receptive field
The area of the body that when stimulated, leads to activity in a particular afferent neuron
coding
the conversion of a stimulus into a signal
that conveys the relevant information
modality
type of stimulus
adequate stimulus
A given receptor is particularly sensitive to one stimulus modality
acuity
The precision for locating the
stimulus depends on convergence where greater convergence causes less acuity
A neuron responds vigorously
when stimulus is in the
middle of the receptive field-more receptors activated, more ATs
lateral inhibition
neurones stimulated at centre of stimulus inhibit adjacent neurones at periphery
enhances contrast
brain can localise exact point of stimulation
