topic 5.1.3: neuronal communication

Question 1

what is a transducer?

Answer 1

converts one form of energy into another ie in receptors they convert stimulus energy into nervous impulse

Question 2

outline the 4 types of receptors

Answer 2

photoreceptors (light)
chemoreceptors (chemicals)
mechanoreceptors (pressure and movement)
thermoreceptors (temperature)

Question 3

outline how receptor cells function

Answer 3

1. differing ion concs cause voltage (resting potential)
2. stimulus makes membrane more permeable
3. ions cause voltage to change (generator potential)
4. if GP reaches threshold level, action potential is triggered (signal sent down neuron)

Question 4

describe the structure of a Pascinian corpuscle

Answer 4

end of sensory neuron wrapped in lamellae which detect pressure changes

Question 5

outline what happens when a Pascinian corpuscle is stimulated

Answer 5

lamellae deform, pressure on neurone ending, neurone memb deforms, more ions let in, voltage changes and action potential triggered

Question 6

describe the structure and function of a sensory neurone

Answer 6

one dendron with dendrites, one axon
receptors –> CNS

Question 7

describe the structure and function of a relay neurone

Answer 7

lots of short dendrons and axons
impulses around CNS

Question 8

describe the structure and function of a motor neurone

Answer 8

lots of dendrites, one long axon
CNS –> effectors

Question 9

describe the structure and function of a Schwann cell

Answer 9

wraps around axon, memb forms myelin sheath
insulator that prevents the passage of ions in or out of the axon

Question 10

how do impulses travel through myelinated axons?

Answer 10

impulse jumps between gaps (nodes of Ranvier) in sheath to increase the speed

Question 11

describe the structure of a non-myelinated axon

Answer 11

Schwann cells loosely contains a few neurones- action potential moves in a wave

Question 12

what are the 3 types of receptors?

Answer 12

photo, thermo, mechano

Question 13

what does transducer mean?

Answer 13

receptors convert energy to electrical impulses

Question 14

describe the function and structure of a pacinian corpuscle

Answer 14

-formed by rings of lamellae around the end of a sensory neurone
-pressure changes on skin deform lamellae and membrane which widens Na+ channels

Question 15

what is resting potential?

Answer 15

more Na+ and K+ outside neurone than inside so inside is comparatively negative (-70mV)
maintained by Na+/K+ pump which actively transports 3 Na+ out for every 2K+ in

Question 16

what is action potential?

Answer 16

neurone’s voltage increases past set point and generates impulse

Question 17

describe the graph produced by a nervous impulse

Answer 17

stimulus triggers Na+ channels to open, charge reaches threshold (-50mV) so voltage gated channels open, action potential (+40mV) reached so voltage gated channels close, K+ channels permanently open so no Na+ entering while K+ leaves, enters refractory period during hyperpolarisation while pump restores K+

Question 18

why is the refractory period important?

Answer 18

stop backflow, keep impulses separate, prevent overstimulation

Question 19

describe the process of synaptic transmission

Answer 19

depolarisation opens ca2+ channels, causes synaptic vesicles to fuse with membrane, releasing neurotransmitters which diffuse across cleft to receptors. na+ channels are conformationally changed by binding, neurone becomes depolarised, neurotransmitter recycled in presynaptic neurone

Question 20

what is a cholinergic synapse?

Answer 20

neurotransmitter is acetylcholine, enzyme acetylcholinesterase hydrolyses it to acetate and choline

Question 21

define the term saltatory conduction

Answer 21

the way in which nerve impulses move more quickly down myelinated neurones

Question 22

define the term spatial summation

Answer 22

multiple neurones meet and collectively trigger an ap in next neurone by releasing neurotransmitters into shared cleft

Question 23

define the term temporal summation

Answer 23

one neuron releasing neurotransmitters repeatedly into a synapse to collectively trigger ap

Question 24

what is an excitatory neurotransmitter?

Answer 24

results in the depolarisation of post synaptic neurone

Question 25

what is an inhibitory neurotransmitter?

Answer 25

results in the hyperpolarisation of post synaptic neurone