neurones Flashcards
(22 cards)
define temporal summation
where multiple nerve impulses / action potentials from a single presynaptic neurone occur in succession
define spatial summation
when multiple presynaptic neurone form a junction with a single neurone
~one lone wont form action potential in postsynaptic
describe the components and events involved in a reflex arc
~action potential in sensory neurone
~passes along synapse between 2 or more neurones
~passes through relay neurone
~passes through motor neurone to effector/ muscle
what happens during repolarisation
NA+ channels close
K+ channels open
~membrane potential decreasing
explain why fewer action potentials occur along a myelinated axon
saltatory conduction is created as myelinated sheath acts as electrical insulator
~only nodes of Ranvier depolarise and repolarise
explain how depolarisation occurs
-NA+ ion channels open
-changes membrane potential makes inside more positive
-more channels open positive feedback
explain repolarisation
- NA+ ion channels shut
-K+ ion channels open
-changes membrane potential to more negative inside
-more channels open ~ positive feedback
escribe conditions inside and outside of neurone during resting potential
membrane polarised outside
- higher conc NA+ ions and higher conc K+ ions inside
what is the electrical charge difference across their plasma membrane
electrochemical gradient
explain how resting potential is re-established
-active transport moves ions against conc gradient
- sodium ions out
- potassium ions in
suggest how the immune system causes damage to the nervous system
-antigens on nerve cells activate immune system - immune system fails to identify myelin sheath as self
-antibodies against nerve cells / Schwann cells / myelin sheath are produced
-phagocytes break down nerve cells
explain how a pain receptor is an example of a transducer
converts chemical stimulus to action potential
-serotonin diffuses across the synaptic gap and binds to receptors
-describe how this causes depolarisation of post-synaptic membrane
-causes sodium ion channels to open
- as sodium ions enter causes depolarisation
it is important that a neurotransmitter such as serotonin is transported back out of synapses explain why
-if not removed keeps binding to receptors
-keeps causing action potentials which prevents info being transported across synapse
describe the sequence of events leading to the release of acetylcholine and its binding to the post synaptic membrane
-action potential arrives
-depolarisation occurs
-calcium ions enter synaptic knob
-vesicles fuse with membrane
-acetylcholine diffuses and binds to receptors
Gaba receptors cause negatively charged chloride ions to enter post synaptic neurones
-explain how this will inhibit transmission of nerve impulses by postsynaptic neurones
-inside becomes more negatively charged - hyperpolarisation
-therefore stimulus doesn’t reach threshold level - action potential doesn’t occur
-therefore depolarisation doesn’t occur
in humans when stomach is full, receptors on stomach wall stimulated, this leads to negative feedback on the desire to eat
- why is this important
-stops desire to eat
-limits amount eaten
-reduces risk of obesity
lobsters, sea cucumbers + squids have statocysts
-students concluded have recent conmen ancestor classified in same phylum
~evaluate conclusion
support/statement is weak
-classification based on phylogeny
-statocysts could have evolved on more than one occasion
what features are common to all sensory receptors
-act as energy transducers which establish a generator potential
-respond to specific stimuli
describe the basic structure of the Pacinian corpuscle
- single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
-stretch-mediated NA+ channels on plasma membrane
-capillary runs along base layer of tissue
what stimulus does a Pacinian corpuscle respond to ? how?
1 pressure deforms membrane, causing stretch-mediated NA+ ion channels to open
2 if influx of NA+ raises membrane to threshold potential, a generator potential is produced
3 action potential moves along sensory neuron
describe the features of all neurons
cell body- contains organelles & high proportion of RER
dendrons - branch into dendrites which carry impulses towards the cell body
axon- long, unbranched fibre carries nerve impulses away from cell body
