5.3 Neuronal communication Flashcards
describe the reflex arc
sensory receptor ->sensory neurone ->relay neurone ->motor neurone -> effector
what is the central nervous system
brain and spinal cord
what does the sensory neurone consist of
dendrites
dendron
myelin sheath
node of ranvier
cell body with a nucleus
axon
axon terminals
what is the node of ranvier
the gaps between layers of myelin sheath wrapped around the dendron/axon
what does the relay neurone consist of
dendrites
cell body with a nucleus
axon
axon terminals
what does the motor neurone consist of
dendrites
cell body with a nucleus
axon
myelin sheath
node of ranvier
axon terminals
how is myelin sheath found on neurones
wrapped around each segment of the dendron/axon
describe the structure of the sensory neurone
-long dendron
-has myelin sheath
-short axon
describe the function of the sensory neurone
transmits action potential from the sensory receptor to the cell body (CNS)
describe the structure of the relay neurone
-many short dendrites
-many divisions of the axon
-no myelin sheath
-no dendron
describe the function of the relay neurone
transmits action potential within the central nervous system. Connects sensory and motor neurones
describe the structure of the motor neurone
-long axon
-has myelin sheath
-no dendron
describe the function of the motor neurone
transmits action potential from the CNS to axon terminals
What do Shwann cells do to neurones
they wrap themselves around the axon/ dendron to create the myelin sheath
the myelin sheath is the cell plasma membrane of the shwann cell
why are many neurones very long
because they can transmit the action potential over a long distance
describe myelinated neurones
-myelin sheath is wrapped tightly around neurones
-consists of several layers of the cell plasma membrane of the shwann cell
describe non-myelinated neurones
-several neurones are enshrouded in one loosely wrapped shwann cell
what are the advantages of myelination
-can transmit action potentials faster
-carry action potentials over long distances
what does the plasma membrane of the axon/dendron contain
sodium potassium ion pumps
describe the sodium potassium ion pumps
work through active transport (use of ATP) 3 sodium ions are pumped out the cell and 2 potassium ions are pumped into the cell
sodium ion channels are closed so sodium ions cannot reenter
potassium ion channels are open so some potassium ions may leave through facilitated diffusion
what does the cell cytoplasm contain and what does this mean
negative anions so the interior of the cell is maintained at a negative potential compared to the outside
define the resting potential
the potential difference across the membrane while the neurone is at rest
usually -60mv but can differ
what is depolarisation
when the sodium ion channels in the plasma membrane open and the ions diffuse into the neurone
when it reaches -50mv it is at the threshold value
positive feedback causes the sodium ion voltage gated channels to open and allows more sodium ions to diffuse into the neurone
define positive feedback
a mechanism that increases a change taking the system further away from the optimum
what happens after depolarisation
a value of +40 is achieved and this is an action potential
the sodium ion voltage gated channels close.
what is repolarisation
when potassium ions diffuse out of the neurone and then hyper polarisation occurs
what is hyper polarisation and what happens after it
where the potential difference overshoots slightly
the potassium ion voltage gated channels close and the sodium potassium ion pumps restore the resting potential
describe the formation of an action potential
threshold value
depolarisation
action potential is achieved
repolarisation
hyperpolarisation
return to resting potential
define action potential
a brief reversal of the potential across the membrane of a neurone causing a peak of +40mv compared to the resting potential of -60mv
what are sensory receptors
specialised cells that can detect changes in our surroundings- most are energy transducers (cells that convert one form of energy to another)
describe the receptor and energy involved in change in light sensitivity
light sensitive cells in retina
light to electrical
describe the receptor and energy involved in change in temp
temp receptors in skin
heat to electrical
describe the receptor and energy involved in pressure on the skin
pacinian corpuscles in skin
mechanical to electrical
describe the receptor and energy involved in change in sound
vibration receptors in the ear
sound to electrical
describe the receptor and energy involved in chemicals in air
olfactory cells in epithelium lining in the nose
chemical to electrical
describe the receptor and energy involved in chemicals in food
receptors in taste buds in the tongue
chemical to electrical
describe what happens when pressure is applied to the pacinian corpuscle
the rings of connective tissue are deformed which causes the sodium ion channels to open and sodium ions to enter the neurone which creates the generator potential. If the pressure applied is high enough to reach the threshold potential, the sodium ion voltage gated channels open and more sodium ions enter (positive feedback/depolarisation) When the value of +40 is reached, that is an action potential. The sodium ion voltage gated channels close and the potassium ion voltage gated channels open so potassium ions leave the neurone (depolarisation) The value will dip below -60mv (hyper polarisation) then the sodium potassium ion pumps start pumping and regulate the neurone to return to resting potential
What would happen if only a little bit of pressure was applied to the pacinian corpuscle
the rings of connective tissue will deform which will cause the sodium ion channels to open but the pressure won’t be high enough to reach the threshold value so the sodium ion voltage gated channels will not open
how are action potentials transmitted along an unmyelinated neurone
When there is a stimulus, it causes the sodium ion channels to open at one region of the neurone. Sodium ions that diffuse in make it positive. These ions diffuse down the neurone creating a local current and make the next region less negative which causes the sodium ion channels to open as a slight depolarisation has occurred and the potential difference has changed and another action potential is created. At the previous region, the sodium ion voltage gated channels close and the potassium ion voltage gated channels open.
why can you not have a action potential straight after another one
sodium potassium ions are in the wrong places and the concentration of the ions inside and outside the cell must be restored by the action of the sodium potassium ion pumps. Refractory period allows cell to recover and ensures action potentials are transmitted in one direction
what is saltatory conduction
transmission of action potentials in a myelinated neurone
describe saltatory conduction
myelin sheath is impermeable to sodium potassium ions as it insulates the neurone so action potentials can only occur at the nodes of ranvier. action potentials jump from one node of ranvier to the next and the current is an elongated local current which means speed of action potential transmission increases.
describe the all or nothing law
all action potentials are the same size/magnitude and create a depolarisation of +40.. you either have an action potential or you don’t
what does the frequency of action potentials suggest
High frequency of action potentials = more intense stimulus. When a stimulus has a higher intensity, more sodium ion channels open and the sensory receptor which produces more generator potentials
why is the maximum frequency of action potentials limited
an action potential cannot form in the refractory period
define synapse
the junction between two or more neurones when one neurone can communicate with or signal to another neurone. The gap between neurones is called a synaptic cleft
describe what a synapse consists of
PRESYNAPTIC BULB(axon terminals)
membrane of presynaptic neurone
smooth endoplasmic reticulum
synaptic vesicle containing acetylcholine
mitochondria
calcium ion voltage gated channels
SYNAPTIC CLEFT
POSTSYNAPTIC NEURONE
sodium ion channels
post synaptic membrane
describe the postsynaptic membrane
-contains specialised sodium ion channels that respond to the neurotransmitter
-the channels consist of 5 polypeptide molecule-2 have receptors that are specific to acetylcholine (complementary)
-when acetylcholine is present in the synaptic cleft, it binds to the two receptor sites and causes the sodium ion channels to open
describe how action potentials are transmitted across a synapse
- action potential arrives at synaptic bulb
2.calcium ion voltage gated channels open and the ions diffuse into the synaptic bulb
3.calcium ions cause the synaptic vesicles to move and fuse with the presynaptic membrane
4.acetylcholine released by exocytosis and diffuses across the cleft
5.the acetylcholine molecules bind to the receptor sites on the sodium ion channels in the postsynaptic membrane
6.generator potential is created
7.if there’s sufficient generator potentials, postsynaptic membrane reaches threshold value - New action potential is created in the postsynaptic membrane and continues to be passed down it
why does the presynaptic bulb contain lots of mitochondria
ATP is needed to move vesicles, fuse them with the membrane, exocytosis and the recombining of ethnic acid and choline to recreate acetylcholine
why does the presynaptic bulb contain lots of smooth endoplasmic reticulum
it packages the neurotransmitters into vesicles
why are calcium ion channels voltage gated
when action potential passes through the membrane, there is a change in the membrane potential
why does the synaptic cleft need to contain acetylcholinesterase
if acetylcholine is left in the cleft, it will continue to open sodium ion channels in the post synaptic membrane and will continue to cause action potentials. Acetylcholinesterase is in the cleft and hydrolyses acetylcholine into ethanoic acid and choline. It stops the transmission of signals so the synapse doesn’t continue to produce action potentials. Ethanoic acid and choline are recycled as they reenter the presynaptic bulb by diffusion and recombine with the use of ATP so it can be stored for future use
define summation
occurs when the effect of several epsp’s are added together
define spacial summation
several pre synaptic neurones each contribute to producing an action potential in the post-synaptic neurone
define temporal summation
small epsp’s in post synaptic neurone act together to create an action potential
how could several epsp’s be prevented from producing an action potential
by one IPSP (inhibitory post synaptic potentials). EPSP’s and IPSP’s compete with eachother and determine whether the post synaptic membrane will create an action potential. GABA and glycine are common neurotransmitters involved in IPSP’s- achieved by opening chloride ion channels into post synaptic neurones or by opening potassium ion channels so potassium ions leave the cell. Temporary polarisation is caused.
why may one presynaptic neurone diverge to several post synaptic neurones
to allow one action potential to be transmitted to several parts of the nervous system. It is useful in a reflex arc as one post synaptic neurone elicits the response another informs the brain
what do synapses ensure
that action potentials are transmitted in the correct direction- only presynaptic bulb contains vesicles of acetylcholine so if an action potential starts half way along a neurone and ends at the post synaptic membrane, it will not cause a response in the next cell as receptors are only found on the postsynaptic membrane
how do synapses filter out unwanted low level signals
low level stimuli that creates an action potential is unlikely to pass across the synapse to the next neurone as several vesicles must be released to create action potentials in the post synaptic membrane
how can low level action potentials be amplified
summation- if low level stimulus is persistent, it will generate several successive action potentials in the pre synaptic neurone which releases many vesicles over a short time which will enable post synaptic epsp’s to combine and produce an action potential
what may happen to a synapse after repeated stimulation
synapse may run out of vesicles containing the neurotransmitter (synapse is fatigued) nervous system no longer reacts to stimulus as it becomes habituated. This helps avoid overstimulation which could cause damage
