5.1.3 - Neuronal Communication Flashcards
Main functions of nervous system
Send, recieve and interpret info
Two parts of the nervous system
CNS
PNS
What is a neuron
Conductive, excitable cells of the nervous system that are specialized to transmit electrical nerve impulses
Nerves vs neurons
Neurons are the cells and nerves are the elongated congregation of tissues
Rods and cones
Receptors in eyes
Detect changes in light
Taste buds
Receptors on tongue
Detect change in chemical potential
Pacinian corpuscles
Receptors on skin
Detect changes in movement and pressure
Meissners corpuscles do the same
Ruffinis endings
Receptors on skin
Detect changes in heat
Proprioreceptors
Receptors on muscles
Detect mechanical displacement
Involved in placement of limbs/ body awareness
What do the hair cells in semi-circular canals do
Detect movement
Involved in balance
What do the hair cells in the cochlea do
Detect sound
Transducers
Detect a spp type of energy and convert it into another e.g electrical energy
Where is action potential summed
At axon hillock which is then propagated down the axon
Resting membrane potential
Potential diff across the membrane of a neuron
Na^+/K^+ pump
Pump binds 3 Na^+ and 1 ATP
Hydrolysis of ATP provides energy to undergo a conformational change
Na is released to outside of the membrane and the shape changes to allow 2 K^+ to bind
Release of the phosphate allows the channel to revert to its original form, releasing the K^+ on the inside of the membrane
How do sensory receptors change the resting potential of the axon membrane
By taking the energy its detecting and using it to change the membrane permeability to Na^+ ions to start an action potential
Need for refractory period
Prevents overlap of action potential
Prevents action potential from moving backward (unidirectional)
Receptor potentials
Localised changes in membrane potential
Graded and arent self-propagated
Mechanoreceptor
Pressure/ stretch opens a VG ion channel
Thermoreceptors
Temp affects enzymes controlling an ion channel
Chemoreceptors
Chemical binds to a receptor, initiating a signal cascade to control an ion channel
Photoreceptors
Light alters a membrane protein initiating a signal that controls an ion channel
Motor neurons
Transmit impulses from a sensory/relay neuron to an effector. Have a long axon and short dendrites
Found in CNS
Myelin sheaths
Made of many layers of a plasma membrane produced by Schwann cells. Acts as insulating layer and allows impulses to be conducted much faster
Nodes of Ranvier
Impulses ‘jump’ from one node to another as it travels along the neuron which speeds up the transmission
Axon
Singular elongated nerve fibres that transmit impulses away from the cell body. Cytoplasm surrounded by plasma membrane
Relay neurons
Transmit impulses between sensory and motor neurones
Many short axons and dendrons
Cell body
Contains nucleus surrounded by cytoplasm. Contains ER and mitochondria (involved in making neurotransmitters)
Dendrons
Short extensions that come from the cell body, divide into smaller branches (dendrites). Responsible for transmitting electrical impulses towards the cell body
Sensory neuron
Transmit impulses from a sensory receptor cell to a relay/ motor neurone or the brain
Dendron carries the impulse to the cell body and the axon carries impulse away from the cell body
Found in PNS
Why do motor neurons have long axons
In order to transmit the action potential to the effectors all over the body
Myelination
Prevents ion movement and forces the current to ‘jump’ along the axon
Reduces energy expenditure
Stops leakage of charge across mebrane and local current is attenuated and insufficient to polarise next node
Why are myelinated neurons found in the PNS
Neurons in the PNS frequently have to transmit over long distances so speed of impulse is crticital to efficient function
Action potential
Self regenerating depolarisation that allows excitable cells to carry a signal over a distance -60 to +40
Why does the pre-synaptic knob end in a bulb
To increase SA for release for acetylcholine by exocytosis
Why are Ca^+ channels on the pre-synaptic neuron VG
To prevent acetylcholine being released if theres no action potential
Touch stimulus
Distortion of Pacinian Corpuscles
Causes stretch-mediated Na^+ channels to open
Causes Na^+ to move in and depolarises
Depolarisation
The condition of the membrane that is less highly polarized than the usual resting state so the inside of the cell becomes less -ve with respect to the outside
VG Na - open
VG K - closed
Repolarisation
The condition of the membrane when mechanisms are trying to bring the potental diff. across the cell back being to more - ve on the inside of the cell w/ respect to the outside
VG Na - closed
VG K - open
Hyperpolarisation
The condition of the membrane that is more highly polarized than the usual resting state so the inside of the cell becomes more - ve than usual w/ respect to the outside
Threshold potential
The critical level to which a membrane potential must be depolarised to initiate an action potential
-50 mV
Describe and explain how a resting potential is maintained
Na/K ion pump - 3 Na ions out and 2 K into axon
VG Na+ channels are closed to stop Na diffusing in
Some K ion channels are leaky. Effect of conc. gradient is greater than the electrochemical gradient so diffuse out into extracellular fluid
Cell cytoplasm contain large organic anions (proteins)
Results in polarised cell membrane (+ve out/ -ve in)
Describe what is happening at the cell membrane during an action potential
Resting membrane potential
Detection of stimuli - causes VG Na^+ to open. Begins to get depolarised
+ve feedback - More VG Na^+ channels open and moves in
When potential reaches +40mV VG Na^+ close and VG K^+ open - eflux of K+ causes repolarisation
K+ diffuse back out of the cell
Too -ve, hyperpolarisation
Resting membrane restored by Na/K pump
Saltory conduction
Propagation of action potential along myelinated axons from one node to another
Done by creating longer local currents
Uninsulated nodes are the only place ions are exchanged across axon membrane
More intense the stimulus …
The more frequently the neurons fire
Synaptic cleft
Gap between pre-synaptic and post-synaptic Neuron
Adaptations of post synaptic neuron
Contains specialised proteins in its membrane that act as acetylcholine receptor sites
They form Na^+ channels, which open in response to acetylcholine (generates action potential)
Transmission across the synapse
Action potential arrives at presynaptic neuron and calcium ions open, so Ca^+ diffuse into knob
Vesicles move towards membrane and fuse to release acetylcholine into the cleft (exocytosis)
Diffuse across cleft and bind to receptors
Na^+ channels on post open and diffuses into post neurone
Membrane is depolarised
Acetylcholinesterase breaks down acetylcholine
Na^+ channels close and the choline is recycled back into the presynaptic knob
Role of synapses in the nervous system
Ensures that action potentials travel in one direction; only receptor on post
Filters out low intensity stimulus; many vesicles must be released to cause a post synaptic action potential
Continuous, unimportant stimulus can be ignored; vesicles run out (fatigue) —> acclimatisation
Summation - amplify many low level stimulus
Are relay neurons myelinated
No
Which neuron has dendrons
Sensory - one long one
Do motor neurons end at synaptic knobs as well
No, motor end plate
Why are mitochondria needed for transmission of impulses across the cleft
Mitochondria in the pre-synaptic bulb is needed for:
Energy to move vesicles
Exocytosis
Na+/K+ pump to maintain resting potential
Vesicle formation
Active transport of Ca2+
Propagation of action potentials
Once membrane is depolarised Na+ inside membrane attracted to -ve charge ahead and conc gradient causes it to diffuse further into axon, triggering depolarisaton
Why is saltatory conduction more efficient
Repolarisation requires ATP and less repolarisation is necessary
Factors affecting speed of conduction
Axon diameter
Temperature
How does axon diameter affect speed of conduction
Bigger the axon diameter faster the transmission
Less resistance to flow in cytoplasm
How does temperature affect speed of conduction
Higher the temp, faster the transmission
Ions diffuse faster at higher temp but only up to 40 degrees as proteins get denatured
Inhibitory synapses
Release transmitters that lead to hyperpolarisation of the postsynaptic membrane so there’s no ap
What is acetylcholine hydrolysed into
Choline and ethanoic acid
Spatial summation
Several presynaptic neurones connectto postsynaptic neurones
Each releases a transmitter so the conc increases in the synapse
Temporal summation
Single presynaptic neurone releases transmitter due to several ap in a short time
