neuronal communications

what do all sensory receptors act as?

• transducers to convert a stimulus into a nerve impulse

what are receptor cells specific to?

• single type of stimulus

• e.g light, chemical, pressure/movement, heat

how do ears acts as receptors?

• ear drum detects vibrations

• in cochlea the vibrations cause fluid to ripple and tiny hairs pick this up

• auditory nerves carry an electrical signal to the brain

what does chemoreceptors detect?

• chemicals

what are examples of chemoreceptors?

• olfactory receptors

what are a sense organ example of a chemoreceptor?

• nose

what do photoreceptors detect?

• light

what are receptor examples of photoreceptors?

• rod and cone cells on retina

what is a sense organ example of photoreceptor?

• eye

what do thermoreceptors detect?

• heat

what is receptor example of thermoreceptor?

• end-bulbs of Krause

what is a sense organ example of a thermoreceptor?

• tongue

what do mechanoreceptor detect?

• pressure and movement

what is a receptor example of a mechanoreceptor?

• Pacinian corpuscle

what is a sense organ example of a mechanoreceptor?

• skin

what is the structure of a pacinian corpuscle?

how does the pacinian corpuscle work?

what happens to the Na⁺ channels at rest?

• no pressure so not stretched

what happens to Na⁺ channels when pressure is exerted?

• membrane stretched at excited section

what is adaptation?

how can adaptation be explained with pacinian corpusle?

what does a dendrite do as part of a neurone?

• transmits electrical impulses towards the cell body

what does the cell body do as part of a neurone?

• contains the nucleus and produces neurotransmitters

what does the axon do as part of a neurone?

• transmits impulses away from the cell body

what does the sheath do as part of a neurone?

• made of myelin, insulates the electrical signal for rapid signalling

what does the axon terminal do as part of a neurone?

• synapse to transmit message to next neurone/cell

how is the motor neurone specialised for rapid signalling?

• long as carry signals across long distances

• branched as can connect to lots of other nerve cells

• sheath which insulates the electrical signal for rapid signalling

what are features of the sensory neurone?

• transmit impulses from sensory receptor cell to a relay or motor neurone

• one dendron which carries impulses to the cell body

• one axon which carries the impulse away from the cell body

how does a sensory neurone look like?

what are features of a relay neurone?

• transmit impulses between neurones

• many short dendrites coming into the cell body from lots of other neurones

• axon tend to be short and non-myelinated, short-distance messages

how does a relay neurone look?

what are features of a motor neurone?

• transmit impulses from a relay neurone or sensory neurone to an effector such as muscle of a gland

• one long axon and many short dendrites

how does a motor neurone look like?

what is the myelin sheath made up of?

• Schwann cells with Nodes of Ranvier between

what is the point of node of ranvier between Schwann cells?

• allows impulse to be transmitted a lot quicker as it jumps from one node to another

what is the speed of transmission affected by?

• myelin sheath

• axon diameter

• temperature

explain about the myelin sheath affecting speed of transmission?

why are unmyelinated neurons slower that myelinated neurons?

• no nodes of ranvier

• shorter and more local circuits

• whole axon needs to be depolarised

how does axon diameter affect speed of transmission?

how does temperature affect speed of transmission?

• the higher the temperature, the faster the nerve impulse

• ions diffuse at higher temperatures

• however only occurs up to 40 degrees as higher temperature cause proteins to denature

what is multiple sclerosis?

what is the resting potential?

• when a neurone is not being stimulated so at rest

• the outside membrane is positively charged compared to the inside

• the resting potential is created and maintained by sodium-potassium pumps and potassium ion channels

explain the steps for resting potential?

1. sodium-potassium pumps use active transport to move 3 Na+ ions out of the neurone for every 2 K+ that moves in

2. potassium ion channels use facilitated diffusion out of the neurone down their concentration gradient

3. membrane is less permeable to Na+, voltage-gated Na+ channels close so fewer Na+ can diffuse back

4. the membrane is ‘polarised’ and the voltage across it is -70mV when it is at rest called the resting potential

how would you create an action potential?

• when a neurone is stimulated, Na+ channels in cell membrane opens

• if signal is big enough (reaches the threshold) the membrane will become depolarised

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what is refractory period?

what and where is absolute refractory period and relative refractory period?

what is significance of refractory period?

what is all or nothing law?

how do neurons work together?

1. pressure detected by Pacinian corpuscle

2. electrical impulses sent along sensory neuron

3. chemical messages diffuse across synapse

4. electrical messages sent along relay neuron

5. chemical message diffuses across the synapse

6. electrical message sent along motor neurone

7. chemical message diffuses across the neuromuscular junction

where are synapses found?

• synapse is junction between 2 neurons or a neuron and an effector (muscle/gland)

how does a synapse pass on a message?

1. action potential arrives at axon terminal

2. depolarisation causes voltage-gated Ca2+ channels to open and Ca 2+ enters cell

3. Ca2+ signals to vesicles to move and fuse with presynaptic membrane

4. vesicles release ACh into the synaptic cleft by exocytosis

5. ACh diffuses across the synaptic cleft and bind to specific cholinergic receptors

6. Na+ channels open and Na+ diffuse in

7. Action potential continues

8. After an impulse, enzymes (acetylcholinesterase) digest neurotransmitters and products are transported back to presynaptic knob to recycle the neurotransmitter and rpevent the response happening again

what is the importance of a synapse?

• ensure the impulses travel in one direction and neurotransmitter receptors are only on the post synaptic membrane

what is convergence?

• allows impulses from more than one neuron to be passed to a single neuron

what is divergence?

• allow impulses from a single neuron to be passed to more than one neuron

what is summation?

• when enough neurotransmitter builds up and action potential is able to continue

what is 2 types of summation?

• spatial summation

• temporal summation

what is spatial summation?

• when 2 or more presynaptic neurons converge to one post synaptic neuron

• each release a small amount of neurotransmitter but together is enough to stimulate an action potential

what is temperal summation?

• where 2 or more impulses arrive in quick succession from same presynaptic neuron

• the quantity of neurotransmitter in a short period of time is enough to trigger and action potential

what are features of excitatory synapses?

• have receptors that are Na+ channels

• when open, Na+ ions diffuse in

• causes a local depolarisation and makes an action potential more likely

• neurotransmitters such as acetylcholine, glutamate, aspartate

what are features of inhibitory synapses?

• have receptors that make membrane potential more negative

• causes hyper polarisation and makes action potential less likely

• impulse in one neurone can inhibit an impulse in next

• neurotransmitters like GABA and glycine

what are some effects of drugs on synapses as they use chemical communication?

• mimicking

• inhibiting neurotransmitters

• inhibiting enzymes

• blocking

what is mimicking?

• mimicking the shape of the neurotransmitter

• e.g nicotine is similar shape to acetylcholine and binds to cholinergic receptors

what is inhibiting neurotransmitters?

• some chemicals inhibit the release of neurotransmitters from presynaptic neurone

• fewer receptors are activated

• e.g opioids block Ca2_ channels so fewer vesicles fuse with membrane and less neurotransmitters is released

what is inhibiting enzymes?

• some chemicals inhibit the enzyme that digests neurotransmitter so they are left in the synaptic cleft for longer

• e.g nerve gases (Sarin) inhibits enzymes and reduce muscle control

what is blocking?

• some chemicals block receptors so they can’t be activated by neurotransmitters

• e.g Curare blocks the effects of acetylcholine by blocking cholinergic receptors at neuromuscular junctions so muscle cells not stimulated, muscle is paralysed