5.1.3 Neuronal Communication Flashcards
What are the steps that an electrical impulse in a nervous response follows?
stimulus -> receptor -> sensory neurone -> relay neurone -> motor neurone -> effector cell -> response
What is the role of sensory neurones?
Carry impulses from sensory receptors to a relay neurone/motor neurone/brain (CNS)
What does the CNS stand for?
Central nervous system - brain/ relay neurone/ motor neurone/ sensory neurone
What is the role of relay neurones?
carry impulses between neurones
(e.g. between sensory neurones and motor neurones)
What is the role of motor neurones?
carry impulses from the CNS (relay/sensory neurone) to an effector (such as muscles and glands)
Draw and label diagrams of a motor neurone, a relay neurone, and a sensory neurone
on paper flashcard
on paper flashcard
1- motor neurones - 1 long axon and many short dendrites
2- relay neurones - many short axons and dendrons
3 - sensory neurone - 1 long dendron, short dendrites, 1 axon
Define dendron
short extensions which come from cell body
Define dendrite
short branched extensions of dendrons
- recieve impulses from other cells/receptors
Define axon
transmits impulses away from the cell body
- extension of neurone
Define axon terminal
ends of axons which make synaptic connections to other cells
Define myelinated neurone
axon of neurone covered in myelin sheath
Define myelin sheath
many layers of plasma membrane surrounding axon of some neurones (sensory+motor)
What is the role of the myelin sheath?
- myelination acts as insulating layer (doesnt conduct)
- myelinated neurones conduct electrical impulses at faster speeds
Define Schwann cell
Cells growing around the axon many times to form myelin sheath
Node of Ranvier
a gap in the myelin sheath of a neurone between adjacent schwann cells
- electrical impulse jumps from one node to next - faster impulse transmission
Draw and label a cross section diagram to show the nature of the myelin sheath
on paper flashcard
on paper flashcard
Why are some neurones myelinated and others unmyelinated?
some neurones unmyelinatd as distance of transmission is very short
Draw a table to compare the structure and function of motor neurones, relay neurones and sensory neurones
- all have cell body, axon, axon terminals ,
Sensory neurone:
- 1 long dendron
- short dendrites
- 1 short axon
- cell body on stalk separate from conduction
- myelinated
- receive connections from receptor cells
- make connections to relay neurons
Relay neurone:
- many short dendron
- many short dendrites
- many short axons
- cell body in middle of cell
- no myelination (conduct over short distances)
- receive from sensory neurones
- connections to motor neurones
Motor neurone:
- no dendron
- many short dendrites
- 1 long axon
- cell body in CNS
- myelinated
- recieve from relay neurone
- connect to effectors
What are the 6 different types of receptor and what is the stimulus that they detect?
1) mechanoreceptor - pressure and movement
2) chemoreceptor - chemicals
3) thermoreceptor - heat
4) photoreceptors - light
5) osmoreceptor - water potential
6) nociceptors - pain
Define sensory receptor
specialised cells which dectect stimulus
Define transducer
convert a stimulus into a nerve impulse
Define stimulus
detectable changes in the external or internal environment of an organism
What are the 3 characteristics of sensory receptors?
1) Specific to single type of stimulus
2) transducers convert stimulus into a nerve impulse
3) sensitive
Draw and label a diagram showing the structure of a Pacinian corpuscle
on paper flashcard
on paper flashcard
How does the Pacinian corpuscle convert mechanical pressure into a nerve impulse?
- Pressure (stimulus) applied to Pacinian Corpuscle causes the corpuscle to change shape
- this causes the membrane surrounding the neurone to stretch
- this causes stretch mediated sodium channels to deform
- the sodium channels widen allowing Na+ to diffuse into the neurone
- the large amount of movement of positive Na+ ions change the potential of the membrane
- this depolarises the membrane resulting in a generator potential
- if generator potential reaches threshold it creates an action pitential which passes along the neurone to CNS
Where are Pacinian Corpuscles located?
-deep within skin
- most abundant in fingers and soles of feet
Define resting potential
the potential difference across the membrane of the axon at rest
Define potential difference
the difference in charge (between inside and outside of the axon)
A membrane is said to be polarised when…
there is a potential difference across it
what is the potential difference at resting potential?
-70mV
What are the steps that create a Resting Potential?
- Na+ ions are actively transported (using ATP) out⬅️ of the axon
- K+ ions are actively transported into➡️ the axon by sodium potassium oump
- but not equal movement
- for every 3 Na+ ions pumped out, 2 K+ ions pumped in
- So more Na+ ions outside the membrane than inside axon cytoplasm and more K+ ions inside axon cytoplasm than outside the axon
- So sodium ions diffuse back into the axon down electrochemical gradient
- But Potassium ions diffuse out of axon
- however most gated Na+ ions channels are closed which prevent movement of Na+ ions
- but most K+ ion channels are open allowing them to diffuse out of axon
- more positively charged ions outside axon than inside the cell
- this creates resting potential across the membrane of -70mV
(Inside negative relative to outside)
Why does a resting potential occur?
as a result of the movement of sodium and potassium ions across the axon membrane
Explain why a neurone is active when it is said to be resting
Pump is active transport of ions therefore active transport processes are taking place even if no impulse is being sent
Define voltage-gated channel
ion channels that are activated by changes in the electrical membrane potential near the channel
- regulating opening and closing by changing the shape of the protein
Define threshold potential
the critical level to which a membrane must be depolarised to initiate an action potential
Define action potential
the change in potential difference across the neurone membrane of the axon when stimulated
Define nerve impulse
an action potential that starts at one end of the neurone and is propagated alonf the axon to the other end of the neurone
Define polarised
a membrane is polarised if there is a potential difference across it
Define depolarisation
a change in the potential difference from negative to postitive across the membrane of a neurone
Define repolarisation
a change in the potential difference from postitive back to negative across the membrane of a neurone
Define hyperpolarisation
the inside of the axon becoming more negative (compared to the outside) than its normal resting state
How does the initial depolarisation of the membrane occur (action potential) ?
1 ) energy of the stimulus triggers some VG Na+ channels to open
2) allows Na+ to diffuse into the axon down Na+ ion electrochemical gradient
3) so inside less negative compared to outside now
4) if threshold reached (-55mV) positive feedback happens
5) positive feedback causes more voltage gated Na+ ion channels to open - membrane depolarises ((- to +))
6) this leads to an action potential
What is the role of positive feedback in the depolarisation stage of the action potential?
- change in charge which is caused by Na+ ions diffusing through channels
- creates positive feedback which causes more Na+ VG channels to open and more diffusion of Na+ ions
Draw, label and annotate a graph of an action potential occurring over time to show the different stages of an action potential and what happens at each stage.
on paper flashcard
1- resting potential
2- threshold level
3- depolarisation
4- repolarisation
5- hyperpolarisation
How does repolarisation of the membrane occur? (action potential)
(after depolarisation)
1) when potential difference reaches around +40mV
2) Na+ ion channels close (no longer can enter axon)
3) VG K+ Channels open and membrane more permeable to K+ ions
4) k+ ions diffuse out of the axon down their electrochemical gradient
5) charge insdie of axon is more negative than the outside
How does hyperpolarisation of the membrane occur? (action potential)
1) K+ ion channels slow to close so too many of K+ ions diffuse out of axon
2) so inside of axon is more negative than the outside compared to its resting state (-90mV)
3) Potential difference becomes more negative than the resting potential (-90mV)
Define refractory period
a period immediately following stimulation when a nerve/muscle is unresponsive to any further stimulation
Explain the importance of the refractory period for the conduction of the action potential.
- important bc: prevents propagation of action potential backwards and forwards along the axon
- makes sure action potentials are unidirectional
- and do not overap but exist as discrete impulse
What is the role of the sodium/potassium pump after an action potential has occured?
pump restores resting potential conditions after an action potential
Define local circuits
the depolarisation of a small region of plasma membrane which creates a circuit of Na+ concentration gradients with neighbouring regions - causing depolarisation
Define saltatory conduction
form of nerve impulse conduction
- whrere the action potential ‘jumps’ from one Node of Ranvier to the next rather than travelling the entire length of the nerve fibre
Describe how an action potential is transmitted along an unmyelinated axon.
(waves of depolarisation)
1- stimulus 2- local circuit 3- repolarisation 4- resting potential
1) Resting potential
conc of Na+ ions outside axon membrane is higher than the inside
conc of K+ ions inside the membrane is higher than the outside
overall outside of axon is more postive than the inside so axon membrane is polarised
2) Stimulus
stimulus causes sudden influx of Na+ ions triggering an action porential and depolarisation of the area
3) local circuit
this establishes local circuit which triggers VG Na+ channels to open further along axon - depolarising that section
4) repolarisation
behind new region of depolarisation (action potential) VG Na+ channels close and K+ channels open
K+ ions leave axon down electrochemical gradient
axon membrane returns to its original state (+ve outside -ve inside)
now repolarised and returns to resting potential
How is an action potential transmitted along a myelinated axon?
depolarisation can only occur at Nodes of Ranvier so longer localised circuits arise and the action potential ‘jumps’ from one node to another (saltatory conduction)
How is the transmission of an action potential along a myelinated axon different to the transmission of a non-myelinated axon?
myelinated axon:
- faster
- longer local circuits, fewer action potentials occur
non-myelinated axon:
- slower
- impulse travels as wave along whole length of axon
- in wave every time ion channels open + diffusion happens so takes time
Describe how a graph of an action potential over time (with time on the x-axis) looks different to a graph of an action potential travelling along an axon from left to right (with distance along the axon on the x-axis)
- 2 graphs are reverse of eachother
- the regions at the start of the axon have completed more of the action potential than further along so they are ‘ahead’ in terms of the ‘time; axis of the action potential graph
What does the ‘all-or-nothing’ response of neurones mean?
- once threshold reached action potential always fires with same change in voltage no matter how big the stimulus
- if threshold not reached action potential doesnt fire
What information does the frequency of impulse transmission transmit to other neurone?
- the larger the stimulus the higher the more frequently action potentials/impulses generated
- stronger stimulus triggers more action potentials per unit time
Why does the “all-or-nothing” response of neurones mean that information must be transmitted by the frequency of impulse transmission?
- bc the strength of an action potential cannot change
- so the only variable to convey differing strengths of stimulus is the frequency at which action potentials are sent
How does the nervous system encode the nature of the information being transmitted? (e.g. type of stimulus - light or sound)
- type of stimulus is shown by the location its coming from
- all action potentials are the same but e.g. those from thermoreceptors convey heat
What are the 3 factors which affect the speed at which an action potential moves?
1) myelination - action potential ‘jumps’
2) axon diameter - bigger diameter = faster impulse transmission bc less resistance to flow of ions in cytoplasm
3) temperature - higher temp = faster nerve impulse bc ions diffuse faster at higher temps (only up to 40degrees as after proteins e.g sodium protein pump denatures)
Define neurotransmitter
chemicals that are used to transmit impulses across the synapse
Define synapse
the junction between 2 neurones/neurone+effector
Define cholinergic synapse
a synapse that uses acetylcholine as its neurotransmitter
Define synaptic knob
- swollen end of presynaptic neurone
- contains lots of mitochondria and endoplasmic reticulum to manufacture neurotransmitters
Define presynaptic membrane
the cell surface membrane of an presynaptic neurone
(neurone along which the impulse has arrived)
Define synaptic cleft
the space between neurones which separates the axon of one neurone from the dendrite of the next neurone
Define postsynaptic membrane
the cell surface membrane of the postsynaptic neurone (neurone which receives the neurotransmitter)
Define acetylcholine
compound which is a neurotransmitter (chemical transfering impulses across synapse) in cholinergic synapses
Define acetylcholinestrase
an enzyme that causes rapid hydrolysis of acetylcholine into acetate and choline
Draw, label and annotate a diagram to show the structures present in a cholinergic synaptic - for each structure explain what it is for.
on paper flashcard
on paper flashcard
What is the structure of the sodium channels on the post synaptic membrane?
- protein
- made from 5 polypeptide chains
What is the function of the sodium channels on the post synaptic membrane?
- Have complentary binding sites for acetylcholine (neurotransmitter)
- channels can be open or closed (gated)
What are the sequences of events that occur at a synapse that results in an action potential being generated in the post-synaptic neurone
(cholinergic synapse)
1) action potential reaches end of presynaptic neurone
2) presynaptic membrane depolarises which causes Ca2+ to open
3) Ca2+ iona diffuse into presynaptic knob
4) Vesicles containing neurotransmitters (acetylcholine) move and fuse with presynaptic membrane
5) neurotransmitters released into synaptic cleft via exocytosis
6) Neurotransmitter diffuses across syanptic cleft and binds to specific receptor molecule on postsynaptic membrane
7) this causes Na+ ion channels to open
8) Na+ ions diffus into postsynaptic neurone
9) triggers an action potential if threshold met
What is the role of acetylcholinesterase?
acetylcholinestrase hydrolyses acetylcholine into choline and ethanoic acid
Explain how acetylcholine is recycled
(acetylchoilinestrase breaks down acetylcholine so there is no neurotransmitter left in the synaptic cleft.)
- the products ethanoic acid and choline diffuse back across the synaptic cleft into the presynaptic neurone where it is recylced into acetylcholine and packaged into vesicles (recycled)
Why is synaptic transmission very energy demanding?
ATP is needed to synthesis acetylcholine (from choline and ethanoic acid) for reabsorption (recycle) and exocytosis
Why are synapses unidirectional?
-the neurotransmiter receptors only present on the postsynaptic membrane
-impulses can only travel from presynaptic to postsynaptic neurone
Define summation
build up of neurotransmitter in a synapse to sufficient levels to reach threshold and trigger an action potential
Define Spatial summation
- when a number of presynaptic neurones connect to one postsynaptic neurone
- each releases neurottansmitter which builds up high enough level in synapse to trigger an action potential in single postsynaptic neurone
Define temporal summation
- when a single presynaptic neurone releases neurotransmitter as a result of action potenial several times over a short period (high frequency)
- builds up in synapse until sufficient quanitity to trigger action potential
What are the 2 types of neurotransmitter?
1- excitatory
2- inhibitory
What is an excitatory neurotransmitter?
excitatory:
- neurotransmitters that result in depolarisation of postsynaptic membrane
- if threshold reached in postsynaptic membrane an action potenital is triggered
- e.g. acetylcholine
- synapse where excitatory neurotransmitter released is a excitatory synapse
What is an inhibitory neurotransmitter?
inhibitory:
- neurotransmitters that result in hyperpolarisation of postsynaptic membrane
- prevents an action potential being triggered
-e.g. GABA
- synapse where inhibitory neurotransmitter released is a inhibitory synapse
How does the central nervous system recieve information about the type of stimulus and intensity of stimulus?
1- type - loction - which receptor is signal from?
2- intensity - frequency - more action potentials per unit time=more intense
What are the 3 roles of synapses and what is the importance of it to the nervous system?
1) ensure impulses are unidirectional (bc neurotransmitter receptors are only present on postsynaptic membrane)
2) allow information to be dispersed - divergence
1 neurone connects to many neurones information can be dispersed to different parts of body (synaptic divergence)
3) allow information to be amplified (convergence)
many neurones connect to 1 neurone information can be amplified (made stronger)
What is synaptic divergence and synaptic convergence
1) Synaptic divergence - 1 neurone connects to many neurones information can be dispersed to different parts of bo
2) Synaptic convergence - many neurones connect to 1 neurone information can be amplified (made stronger)
Why is a Cholinergic synapse called an excitatory synapse?
- bc an action potential in presynaptic neurone increases likelihood of one occuring in postsynaptic neurone
Describe how an inhibitory synapse might work and give one example of a neurotransmitter used in inhibitory synapses.
e.g. dopaine
- works by hyperpolarising postsynaptic membrane instead of depolarising it.
- hyper polarised by influx of -ve charged ions
Define agonist in relation to neurotransmitters and describe ways in which they might work
agonist - makes synapses more active
-e.g. stimulates release of neurotransmitters
Define antagonist in relation to neurotransmitters and describe ways in which they might work
antagonist - acts to inhibit synapse
-e.g. blocks Ca2+ channels
