5.1.3 Neuronal communication Flashcards
What is a stimulus?
Change in the internal or external environment of an organism
What are the structures within a neurone?
- Cell body
- Dendrons
- Dendrites
- Axons
- Myelin sheath
- Schwann cells
- Node of Ranvier
What is the cell body?
Contains the nucleus and organelles to produce neurotransmitters
What is the dendron?
Short extensions from cell body
What are dendrites?
Branches of dendrons
What is the axon?
Singular extension from cell body
What is the myelin sheath?
Fatty layers of insulation produced by Schwann cells that surround axon multiple times
Why is the myelin sheath needed?
Provides insulation for the electrical impulse to allow for a faster transmission of impulse
What are Schwann cells?
Cells that produce layers of membrane making up myelin sheath
What are the Nodes of Ranvier?
Unmyleinted gap between myelin sheath
Electrical impulse can _______ from one node to the next in a myelinated neurone
Jump
What does sensory neurone do?
Transmit impulse from sensory receptor cells to CNS
Is sensory neurone afferent or efferent neurone?
Afferent neurone
Where is the cell body located on a sensory neurone?
In the middle of the neurone
What does relay neurone do?
Transmit impulse between neurones e.g. between sensory and motor neurones
Which neurones are myelinated and which are unmyelinated?
Myelinated - sensory & motor
Unmyelinated - relay
What type of neurone makes up the brain and spinal cord?
Relay neurone
What does motor neurone do?
Transmit impulses from CNS to effector cells
Is motor neurone afferent or efferent neurone?
Efferent neurone
Where is the cell body found on motor neurone?
At the start of the neurone
What is the direction of impulse?
Dendrites to axon
What is the electrical impulse pathway?
Sensory receptor -> sensory neurone -> relay neurone -> motor neuorne -> effector
What are the features of sensory receptor?
- Specific to a single type of stimulus
- Act as a transducer
What does a transducer do?
Coverts stimulus (light, heat, sound or pressure) into nerve impulse called the generator potential
What is a generator potential?
Nerve impulse created when detected by sensory receptor
Describe mechanoreceptor with example?
- Stimulus: pressure and movement
- Example: Pacinian corpuscle
- Example of sense organ: skin
Describe chemoreceptor with example?
- Stimulus: chemicals
- Example: olfactory receptor
- Example of sense organ: nose
Describe thermoreceptor with example?
- Stimulus: heat
- Example: end-bulbs of Krause
- Example of sense organ: tongue
Describe photoreceptor with example?
- Stimulus: light
- Example: cone cell
- Example of sense organ: eye
What is the structure of the Pacinian corpuscle?
Nerve ending in centre surrounded by layers of connective tissue with gel in between layers
What does the membrane of the neurone ending in a Pacinian corpuscle contain?
Stretch mediated sodium ion channels
What is the function of the stretch mediated sodium ion channels?
Change in shape due to pressure and changes permeability to Na+
Describe steps in Pacinian corpuscle to covert mechanical pressure to nerve impulse
- Resting potential - stretch mediated Na+ channel too narrow
- Pressure applied - corpuscle membrane stretches and changes shape
- Sodium ion channels widen - Na+ diffuses in
- Depolarised - influx of Na+ results in generator potential
- Generator potential creates action potential
- Action potential to CNS
Describe the movement of Na+ and K+ ions during the RESTING POTENTIAL
3Na+ OUT
2K+ IN
Via Na+ and K+ ion pump (active transport)
What is the potential difference at resting potential?
-70mV
Which channel is closed at resting potential?
Voltage gated Na+ ion channel
Which channel is open at resting potential?
Non voltage gated K+ ion channel
The outside of the membrane is ______ positive than the inside at RESTING POTENTIAL
More
Why do the K+ ions leave the polarised membrane at RESTING POTENTIAL?
High concentration inside axon so leave via facilitated diffusion
Describe the INITIAL movement of Na+ at DEPOLARISATION?
Synapse sends impulse which causes a few voltage gated Na+ to open and some Na+ ions enter via facilitated diffusion
Describe the positive feedback involved in DEPOLARISATION?
Na+ concentration increases until the threshold potential is reached (-55mV) this causes MORE voltage gated Na+ ion channels to open and INLFUX of Na+ ions enter
What is the threshold potential?
-55mV
What is the potential difference at DEPOLARISATION?
+40mV
What happens to the Na+ and K+ ion pump at REPOLARISATION?
Re opens and 3Na+ OUT 2K+ IN
What happens to the voltage gated Na+ channel when potential difference is +40mV?
Closes
What opens at +40mV during REPOLARISATION?
Voltage gated K+ channels open so MORE K+ can leave
What happens to the potential difference inside the axon during REPOLARISATION?
Becomes less positive
Why does HYPERPOLARISATION occur?
When voltage gated K+ channel opens, initially many K+ ions leave so the potential difference becomes slightly more negative than resting potential
What is the refactory period?
Short period of time after action potential where axon cannot be excited again
What occurs during the refactory period?
Voltage gated Na+ channels remain closed
Why is the refactory period important?
Ensures action potential only travels in one direction
What is saltatory conduction?
Action potential jumping from one node to another
Where does depolarisation occur and why?
Nodes of Ranvier as there is no myelin sheath so Na+ ions can pass through protein channels in membrane
Why is saltatory conduction beneficial?
- Faster nerve transmission
- Reduces amount of repolarisation needed (which uses energy)
What affects the speed of an action potential?
- Axon diameter: bigger = faster impulse as less resistance to flow of ions
- Temperature: higher (to an extent as proteins can get denatured)= faster impulse as ions diffuse faster
What is the all or nothing principle?
Only the threshold value will tigger an action potential
What happens to the action potential when a larger stimulus is present?
Action potential same size, but occurs more frequently
What is an excitatory neurotransmitter?
- Result in depolarisation of post synaptic membrane
- Action potential is triggered (if threshold reached)
- E.g. Acetylcholine
What is an inhibitory neurotransmitter?
- Result in hyperpolarisation of post synaptic membrane
- Prevents action potential being triggered
- E.g. GABA
What is the cholinergic synapse?
Synapses that use the neurotransmitter acetylcholine
Where are cholinergic synapses commonly found?
CNS and neuromuscular junctions
Which enzyme breaks down (hydrolyses) acetylcholine and where is it found?
Acetylcholinesterase on the post synaptic membrane
What products is acetylcholine hydrolysed into?
- Acetyl (ethanoic acid)
- Choline
How do synapses ensure impulses are unidirectional?
Neurotransmitter receptors only found on the post synaptic membrane
What is spatial summation?
Multiple presynaptic neurones connect to one post synaptic neurone
What is temporal summation?
Single presynaptic neurone releases neurotransmitter several times over a short period
What is summation?
Amount of neurotransmitter builds up enough to reach threshold and trigger action potential
