Neuronal Communication Flashcards
Role of neurones
To transmit electrical impulses rapidly around the body to allow the organism to respond to changes in internal and external environment
Parts of a general neurone
Cell body, Dendron, axon,
Role of the cell body
To produce neurotransmitters
Structure of cell body
Nucleus, cytoplasm, lots of endoplasmic reticulum, mitochondria
Function of dendrons
To transmit electrical impulses towards the cell body
Function of axons
To transmit electrical impulses away from the cell body
Structure of axons
Cylindrical, narrow region of cytoplasm surrounded by plasma membrane
Types of neurone
Sensory, relay, motor
Structure of sensory neurones
One Dendron, one axon
Structure of relay neurones
Many short axons and dendrons
Structure of motor neurones
One axon, many short dendrites
Function of sensory neurones
To transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain
Function of relay neurones
To transmit impulses between neurones
Function of motor neurones
To transmit impulses from a relay or sensory neurone to an effector
Myelinated neurones
Neurones that have axons covered in myelin sheaths
What makes the myelin sheath in myelinated neurones?
Schwann cells grow around the axon multiple times, surrounding the axon with layers of membrane
Name for gap between Schwann cells
Node of Ranvier
Why nodes of Ranvier are useful?
Cause signal to jump which allows faster rate of transmission
Why is the rate of transmission slower in non-myelinated neurones?
No nodes of Ranvier so no jumping, continuous transmission is much slower
Types of sensory receptors
Mechano, chemo, thermo, photo
Stimulus mechanoreceptors respond to
Pressure, movment
Example of mechanoreceptor
Pacinian corpuscle
Example of sense organ with mechanoreceptors
Skin
Example of chemoreceptor
Olfactory receptor
Example of thermoreceptor
End bulbs of Krause
Where do you find end bulbs of Krause?
Tongue
Shared features of sensory receptors
Specific to a single type of stimulus, transducers
Role of sensory receptors as transducers
Sensory receptors convert stimulus into a nerve impulse (Generator potential)
Structure of Pacinian Corpuscle
End of neurone surrounded by layers of connective tissue separated by layers of gel, sodium ion channels in membranes, stretch-mediated sodium channels
How Pacinian Corpuscles do transducing
Sodium ion channels too narrow in a normal state, resting potential present, corpuscle changes shape when pressure applied to the corpuscle, membranes stretch, channels widen, sodium ions diffuse in, membrane depolarises, generates generator potential, generator potential creates action potential
Resting potential
The potential difference across a neurone’s membrane when it isn’t transmitting an impulse
When there is a resting potential, where is there a more positive charge?
Outside the membrane
How resting potential develops
Sodium ions actively transported out of the axon and potassium ions actively transported in by sodium potassium pump, more sodium ions outside the membrane and more potassium ions inside the cytoplasm, sodium ions try to diffuse in and potassium ions try to diffuse out, gated sodium ion channels closed so sodium ions can’t diffuse, potassium ions can move freely, more positive ions outside than inside
General value for resting potential
-70mV
Depolarisation
Change in potential difference across a membrane from negative to positive
How generator potential develops
Receptor cells respond to stimuli, gated sodium ion channels open, larger stimuli will open more channels, sodium ions diffuse into the axon, inside of neurone is less negative, change in potential difference across the membrane is a generator potential
How action potential develops
Generator potential reaches threshold, voltage gated Na+ channels open, lots of Na+ diffuse into the axon (Positive feedback), membrane depolarised, voltage gated Na+ channels close, voltage gated K+ channels open, K+ diffuse out of membrane and become depolarised, potential difference overshoots, membrane becomes hyper polarised, resting potential restored by sodium potassium pump, refractory period
Where is there positive feedback in action potentials?
The diffusion of sodium ions into the axon when doing a generator potential will open voltage-gated sodium ion channels so more sodium ions diffuse in
Threshold voltage value
-50mV
Potential difference across membrane when depolarised
+40mV
Name for phase after repolarisation
Refractory period
Role of refractory period
To allow cell to recover, to only allow action potentials to be transmitted in one direction
How an action potential is transmitted down a myelinated neurone
Depolarisation happens at the nodes of Ranvier, sodium ions pass through protein channels at the nodes, localised circuits between nodes, action potential jumps from one node to another
Technical name for transmitting an action potential down a myelinated neurone
Saltatory conduction
Benefits of saltatory conduction
Faster as fewer places where channels have to open, more energy efficient as less repolarisation so less ATP required
All-or-nothing principle
If a stimulus crosses a threshold value, a response will always be triggered. If it doesn’t, no action potential will be triggered. Size of action potential not affected by the size of the stimulus
How does size of the stimulus affect action potentials?
Larger stimuli cause more action potentials to be generated in a given time, increasing frequency, increasing degree of response.
Parts of a synapse
Synaptic cleft, presynaptic neurone, postsynaptic neurone, synaptic knob, synaptic vesicles, neurotransmitter receptors
Approximate size of the synaptic cleft
20-30 nm
Organelles the synaptic knob contains
Mitochondria, large amounts of endoplasmic reticulum
Types of neurotransmitter
Excitatory, inhibitory
Excitatory neurotransmitters
Neurotransmitters that result in the depolarisation of the postsynaptic membrane
Inhibitory neurotransmitters
Neurotransmitters that result in the hyperpolarisation of the postsynaptic membrane
Example of excitatory neurotransmitter
Acetylcholine
Example of inhibitory neurotransmitter
GABA
How impulses are transmitted across a synapse
Action potential reaches end of presynaptic neurone, depolarisation causes calcium ion channels to open, calcium ions diffuse to knob, vesicles containing neurotransmitters fuse with membrane, released by exocytosis, diffuse over, bind with receptor on the membrane, sodium ion channels open, sodium ions diffuse into neurone, triggers action potential, propagated along the neurone
Why neurotransmitter must be removed
Prevents response from happening again, neurotransmitter can be recycled
Specifics of the structure of cholinergic synapses
Acetylcholine is the neurotransmitter, hydrolysed by acetylcholinesterase, breaks down to choline and ethanoic acid, reformation requires ATP
Role of synapses
Ensuring impulses are unidirectional, allow impulse from one neurone to be transmitted to a number of neurones, allow an impulse from a number of neurones to feed into one
Summation
When the amount of neurotransmitter builds up to reach the threshold to trigger an action potential
Types of summation
Spatial, temporal
Spatial summation
When a number of presynaptic neurones are connected to one postsynaptic neurone
Temporal summation
When a single presynaptic neurone releases neurotransmitter several times over a short period as a result of several action potentials
