Neuronal Communication Flashcards
dendrons branch off into?
dendrites
dendrites ?
:Connect to the synaptic knob of the previous neuron, allowing an impulse to be received.
all neurones have?
a cell body - which contains a nucleus and other organelles
axon?
Carries neurones away from the cell body to the synapses
synapses?
lie at the end of the axon and pass the AP onto the next cell
the central nervous system is composed of?
the brain and the spinal cord
describe a sensory neurone?
- An axon on one side of the cell body and a dendron on the other side of the cell body
- cell body is in the MIDDLE
- kind of looks like a spider
how do signals travel in a sensory neurone?
from the dendron (to cell body) then to the axon and onto the next neurone
relay/ intermediate neurones?
carry nerve impulses between neurones
- often have highly branched dendrites and axons
effectors?
cells that carry out the response, are muscles or glands
Neurons?
- Responsible for the detection of stimulus, relay of impulse and stimulation of response.
- Allow for rapid changes in an organisms internal and external environment.
Dendron:
Long nerve fibre extension leading to the cell body.
Cell Body:
Contains nucleus, mitochondria, endoplasmic reticulum and neurotransmitters
Axon:
Long nerve fibre extension from the cell body through which impulses are transferred. Surrounded by a plasma membrane.
Myelin Sheath:
Myelinated tissue which insulates the nerve fibre helping the impulse travel more quickly.
Nodes of Ranvier:
Gaps in the myelin sheath which only allow depolarisation to occur at distanced intervals, speeding up transmission.
Synaptic Knob:
Neurotransmitters are released from here into the synaptic cleft when action potential stimulates an influx of calcium ions.
what do sensory neurones do?
transmit impulses from a sensory receptor cell to a relay or motor neuron.
Motor Neurons:
Transmit impulses from a relay neuron or sensory neuron to an effector cell such as a muscle or gland.
sensory receptors?
specialised cells in the NS that detect physical stimuli
transducers?
cells that convert one form of energy into another
sensory receptors role?
convert a type of energy e.g. light into electrical signals.
- These electrical signals are called the generator potential
a generator potential?
is the depolarisation of the membrane of a receptor cell
dendrites?
- dendrons branch into these
dendrites receive signals
how was the resting potential and action potential discovered?
Hodgkin, Huxley and the giant axons of squid. 1952.
RP value?
-70mV
what does the nervous system allow?
us to react to our surroundings and co-ordinate our behaviour
the parts that comprise our NS?
- Brain
- spinal cord which runs through the spine (CNS)
- peripheral NS - the NS outside the CNS
We have sense organs which?
relate stimuli e.g. heat, pain, noise receptors
Sensory receptors?
tend to be found in sense organs, convert diff forms of energy into APs. They act as transducers.
chemical energy ?
- the energy input causes a change in the membrane potential of the sensory receptor cell
- this potential is causes by the difference in the conc of ions across the membrane
- it can be described as ‘chemical potential energy’ bc the ions are charged
- can be measured as a tiny voltage
e.g.s of sensory receptors?
- hair cells in the cochlea - convert sound energy into APs
- Stretch receptors (cells in muscles and joints) - convert KE into APs
what is the difference between nerve and neuron?
neuron = single
nerve = bundle of neurons (packaged) surrounded by a protective layer called the perineum
neurons = nerve cells
3 types of neurons are?
- motor
- sensory
- intermediate (relay)
what do motor neurons do?
- carry APs away from the CNS (they say “mmm see ya to the CNS” to muscles/ glands
- effectors can the response
- efferent - away from CNS (eff off)
What do sensory neurons do?
carry nerve impulses to CNS (can only hear a snake when its coming towards you)
what do intermediate neurons do?
carry APs within the CNS
MNs: facts
- the dendron can / into multiple terminal branches which synapse with the effector
- each synaptic bulb touches a muscle/ gland
- one output along a long axon, but multiple inputs from multiple RN in CNS
dendrons?
carry to the CB
Dendrites?
Come off dendrons
cell body?
Contains nucleus and all other organelles
axon?
Carries away from the CB. Can be μm -m long.
terminal branches lead to?
synaptic bulbs
generator potential?
a depolarisation in a SN caused by a stimulus e.g. pressure. If the generator potential reaches threshold potential then APs are generated.
Pacinian corpuscle?
a pressure sensitive receptor
SN in relation to CNS
- the cell body of a SN is found in the dorsal root ganglion of the spinal cord
- a stimulus causes APs to be generated at the dendrites of a SN
- CARRY AFFERENT APs FROM sensory receptors in the PNS ➡ CNS
- spidery looking
Intermediate Neuron info?
- the majority of CNS is formed from them
- each neuron can be connected to up to 10k others
- multiple inputs from multiple dendrites from SN/ other IN
- 1 output via dendron which can / into multiple terminal branches
interconnected INs carry out …
the processing and co-ordination of the afferent and efferent APs - the input and output
SRCER
some riders can eat rats
stimuli ➡ receptor ➡ (via SN) CNS (RN)➡ (via motor neuron) effector) ➡ response
response is usually?
a skeletal muscle contracting
which type of neuron are never myelinated?
IN
Myelination?
- about 1/3 of all of our MN & SN are myelinated
- Myelin sheath is made up of Schwann cells (20 layers of membranes)
- insulate the axon and ⬆ the speed of the impulse by up to x100
how does myelination keep the membrane in place?
They increase the proportion of cholesterol in the membrane
myelinated dendrons?
- myelinated dendrons and axons are wrapped in Schwann cells which form the myelin sheath
- in between Schwann cells are gaps called nodes of Ranvier where the plasma membrane of the neuron is exposed
the reflex arc?
- the simplest way 3 neurons can be connected
- w/o conscious thought (bypasses the brain)
- other neurons will be simulated to the brain after the response
why does some matter appear white and some grey in the reflex arc?
grey = almost all INs no myelination
white matter = lot of myelin sheath, high level of fat
ganglion means?
swelling
resting potential?
- the inside is always slightly negatively charged compared to the outside
the diff is called the potential difference which is at around -70mV at rest
what causes the RP?
The RP is maintained. caused by the sodium/ potassium pump in the membrane of axons
the Na+/K+ pump?
- 3 Na+ picked up via carrier proteins and placed outside
- at the same time, 2K+ are brought in (both move against conc gradient so ATP required
- causes outside the axon to be more +ve than inside
- called an electrochemical gradient
- some ions leak back (mainly K+) leaving outside more negative compared to inside (less + than outside NOT - charged)
Rp value?
-70mV
voltage gated channels?
- channels in the membrane which change the permeability to Na+/K+
- they open and close in response to voltage changes across the membrane
sequence of events after a stimulus is detected?
- RP
- depolarisation
- threshold reached
- repolarisation
- hyperpolarisation
- RP
Hyperpolarisation?
time taken for K+ VGC to close
what is a localised circuit/ local circuit?
the AP is occurring at just one point on the axon
how is depolarisation an e.g. of positive feedback?
- the opening of Na+ VGC causes the membrane to become more depolarised
- which causes more Na+VGC to open
- which causes the membrane to become more depolarised
depolarisation?
change within a cell during which the cell undergoes a shift in electric charge distribution resulting in a less - charge inside the cell.
Transmission of an AP?
- At a localised circuit, there is an increased conc of Na+ inside the axon
- these Na+ will diffuse quickly down a conc gradient (electrochemical gradient) to the neighbouring regions of the axon
- this depolarises the section next to it causing Na+VGC o open
- this causes a further influx
- this causes a start of an AP (and so on)
(transmission of an AP) reality
In reality, this only happens ahead of the last AP because the section behind is recovering from the last AP (overshoot) & will not be back to normal yet. This recovery period is called the refractory period.
Speed of conduction of a myelinated vs unmyelinated neuron?
- Myelinated up to 100 m^s-1
- Unmyelinated around 1ms^-1 (some as slow as 0.5ms^-1)
Myelinated neurons and the node of Ranvier?
- Myelinated neurons are insulated - Na+ K+ can’t go thru these regions
- AP can only occur at the Node of Ranvier (node to node 1-3mm)
- This is called saltatory conduction
saltatory conduction?
where the AP jumps from node to node. This speeds up tranimssion and saves ATP (so there are less Na/k+ pumps), less leakage of K+
What impact does diameter have on speed of conduction?
- bigger the diameter ➡ faster transmission (less resistance to flow & less leakage)
= larger = smaller SA:V ratio of membrane - cell body contains organelles. if larger, Na+ more likely to bump into organelles
how do we ensure that the AP only goes one way?
- when Na+ come in through NaVGC, it diffuses along the axon
- once depolarisation happens, NaVGC have a refractory period - cannot open
- this ensures AP only goes one way
how does temp affect speed of conduction?
increases it due to increased KE (but over 40 degrees denatures the channels)
what is all or nothing?
- either the stimulus causes an AP or it doesn’t
- If the stimulus is strong enough., it causes Na+VGC to open for long enough to cause depolarisation (allows a potential difference of around -55mV)
- The min change needed to start an AP is called a threshold value
How does our brain know if it was a strong or light touch?
- the freq of an AP
- increased freq for strong stimuli
- strong stimuli will stimulate more receptors (neurons, brain interprets the frequency and no. of neurons)
how does the brain tell between APs?
- All APs are the same whether they’re to light, smell, touch
- It’s the area of the brain that the APs arrive at that determines the nature of the stimulus
- e.g. light (stimuli): Rods and cones so brain interprets from the eye
what is a synapse?
where 2 neurons meet, it’s a gap
Presynaptic neuron ➡
Presynaptic neuron ➡ synapse ➡ post synaptic
What is the difference between the synapse and synaptic cleft?
Synapse = ends of neurons and gap
Synaptic cleft - just gap
how is the message transmitted at a synapse?
NT molecules
no ? at the synapse?
No nucleus. It’s only in the cell body.
What is the key player in synaptic transmission ?
Ca2+
what else is there at the synapse?
- Na+/K+ VGC
- Na+/K+ pumps
what do receptors on the post synaptic neuron do?
open channels
neurotransmitters?
- many different (40)
- most common: Acetylcholine (Ach), glutamic acid
if Ach is the NT, then the synapse is?
cholinergic
e.g. of a cholinergic synapse?
the neuromuscular junction
if noradrenaline is the NT?
the synapse is adrenergic synapse
Role of the synapse?
- communication
- ensuring unidirectional transmission of an AP
- synaptic convergence & divergence
- summation and decision making
how does the synapse ensure the unidirectional transmission of AP?
- no receptors for NT on he presynaptic neuron, no Ach can bind, no AP generated
- No Ach vesicles in the post synaptic neuron, can’t be released into synapse
- local circuits in presynaptic neuron in refractory period
2 types of NT?
- excitatory
- inhibitory
Excitatory NT?
Open Na+ channels, causing more Na+ to enter - more likely that post synaptic neuron will depolarise
Inhibitory NT?
less Na+, less chance of depolarisation
E.g. of NT: Ach?
- used by spinal cord neurons to control muscles and by many neurons in the brain to regulate memory
- excitatory in most cases
E.g. of NT: Dopamine?
- produces feelings of pleasure when released by the brain reward system
- multiple functions depending on where in the brain it acts
- usually inhibitory
E.g. of NT: Norepinephrine?
- acts as NT & hormone
- in the peripheral NS, it’s part of the fight/ flight response
- in brain, acts as NT, regulating normal brain processes
- usually excitatory but inhibitory in some areas
E.g. of NT: GABA
the major NT in the brain
how many other neurons can 1 neuron communicate with and receive signals?
1000s
Synaptic convergence?
- Come together
- multiple sensory inputs
- 1 output causing
synaptic divergence?
- 1 input
- multiple outputs
so divergence and convergence are?
opposites
Summation?
- whether synapses are inhibitory or excitatory depends on the NT involved or the type of post synaptic protein
- sometimes an AP doesn’t automatically cause another AP, but does cause a post synaptic potential (PSP)
- These ‘blips’ of voltage can be ESPS - a depolarisation towards threshold
- or ISPS - a hyperpolarisation away from threshold
These PSPs…
- summate (Add together) at a synapse
- If threshold is reached, then an AP is generated in the post SN.
how can summation occur?
- in space: spatial summation
- in time: temporal summation
spatial summation?
- summation can occur in space
- APs arriving from diff areas of the body
temporal summation?
- summation can occur in time
- APs arriving at different frequencies from the same place
whether a post synaptic cell generates an AP is controlled
- by spatial and temporal summation of ESPS & ISPS
- This concept also explains how synapses filter out low levels of sensory stimulation
stimulant drugs?
- if a drug amplifies the effect of the NT at a synapse= stimulant
- drugs that stimulate the NS create more APs in the post SN resulting in an enhanced response
inhibitory drugs?
- if a drug inhibits the effect of the NT at a synapse = inhibitor
the effect of other chemicals at the synapse?
- many drugs cause their effects by acting at synapses
- this will result in the NS being stimulated/ inhibited
stimulant drugs may work by?
- mimicking the shape of NT (e.g. nicotine is the same shape as Ach so can bind instead)
- stimulating the release of more NT
- inhibiting the enzyme responsible for breaking down the NT in the synapse
drugs that inhibit the NS….
create fewer APs in the post SN, resulting in a ⬇ response
inhibitory drugs may work by?
- blocking receptors - NT can no longer bind & activate receptor
- Binding to spec receptors on the post membrane and changing the shape of the receptor
- preventing the release of NT from pre SN cell
synaptic transmission: what happens to excess ACh?
- to prevent over stimulation, Ach is broken down by Ach esterase
- which changes its shape so it can’t bind to the receptor
- Ach re-enters cell and reused - requires ATP
Temporal summation alt wording
might need repeated signals to release enough Ach to open enough Na+ channels to allow enough Na+ in so threshold can be reached
order of events in the generation of an AP?
- sodium potassium pump
- depolarisation (Na+ VGC)
- repolarisation (K+ VGC)
- PR
Continuous conduction?
opp of saltatory conduction, happens in unmyelinated neurons
the effect of other chemicals at the synapse?
Atropine: blocks Ach receptors on post SN membrane
Curare: competes w Ach preventing the opening of post synaptic Na+ ion channels
organs and cells that detect sight?
organ: eye
cell: rods and cones
organs and cells that detect smell?
organ: nose
cell: olfactory cells
organs and cells that detect taste?
organ: tongue
cell: taste receptor cells
organs and cells that detect touch?
organ: skin
cell: mechanoreceptors
organs and cells that detect sound?
organ: ears
cell: hair cells in the ear
The spinal reflex arc?
receptor ➡ enter CNS through dorsal root ➡ motor neurons leave through ventral root ➡ effector
dorsal route?
sensory neurons enter
grey matter?
contains almost all intermediate neurons - mostly cell bodies
CNS?
sends APs down a motor neuron to effector
white matter?~
a lot of myelin sheath - high level of fat
ventral route?
motor neurons leave via ventral route
SN
- Stimuli causes APs to be generated at the dendrites of a SN
- the cell body of a SN is found in the dorsal root ganglion of the SC
- terminal ranches synapse w RN in the CNS
what do neurons do generally/
carry electrical signals in the NS. The NS is just a collection of neurons
sensory receptors?
specialised cells in the NS that detect physical stimuli
Pacinian corpuscle?
- pressure receptors in the skin that detect pressure changes
- when pressure is detected, it deforms
- this results in electrical signals in the sensory neuron
- signals are sent during deformation, but after a while the signals stop
