15,5 - Structure and function of synpases

Question 1

What is a synpase?

Answer 1

Poit where the one neurone communicates with another or with an effector

They are important in linking different neurones together and therefore coordinating activities

Question 2

What is definition of synpase?

Answer 2

It is a junction between neurones

Question 3

What is neurotransmitters?

Answer 3

Synpases transmit information , but not impulses from one neurone to another by means of chemcials - neurotransmitter

Question 4

What is synpatic cleft?

Answer 4

Neurones separated by a small gap - 20-30nm wide

Question 5

What is the presynpactic neurone?

Answer 5

Neurone that releases the neurotransmitter

Question 6

What is the synpactic knob?

Answer 6

• The axon of this neurone ends in swollen portion

Question 7

What does the synpactic knob possess?

Answer 7

Many mitochondria and large amounts of endoplasmic recticulum (SER)

These are required to manfacture of the neurotransmitter which takes place in axon

Question 8

What is the synpactic vesicle?

Answer 8

Where the neurotransmitter is stored

Question 9

What are the features of synpases?

Answer 9

• Undirectional
• Summation

Question 10

Why synpases are unidirectional?

Answer 10

Synpases can only pass information in one direction - from presynaptic neurone to the postsynaptic neurone

In way synpases act like valves

Question 11

What is the problem with low-frequency action potentials?

Answer 11

Often lead to the release of insufficient concentrations of neurotransmitters to trigger a new action potential in the postsynpatic neurone

Question 12

What is summation?

Answer 12

Entails a build-up of neurotransmitter in synpase by one of two methods

Question 13

What are the two methods of summation?

Answer 13

1. Spatial summation
2. Temporal summation

Question 14

What is spatial summation?

Answer 14

In which a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynpatic neurone

Together they trigger a new action potential

Question 15

Diagram of spatial summation and temporal summation:

Answer 15

Question 16

What is temporal summation?

Answer 16

In which a single presynaptic neurone releases neurotransmitter many timers over a very short period of time

If the concentration of neurotransmitter exceeds the threshold value of postsynaptic neurone

new action potential is triggered

Question 17

What is inhibitory synpases?

Answer 17

Some synpases make it less likely that a new action potential will be created on postsynpatic neurone

Question 18

Instructions of spatial summation

Answer 18

• Neuone A release neurotransmitter but concentration is below threshold to trigger an action potential in postsynaptic neurone
• Neurone B releases neurotransmitter but concentration is below threshold to trigger an action potential in postsynaptic neurone
• Neurone A and B release neurotransmitter , concentration above threshold so action potential is triggered in postsynpatic neurone

Question 19

What happens to low frequency action potential in temporal summation?

Answer 19

Lead to neurotransmitter being broken down rapidly

Concentration is below threshold to trigger an action potential

Question 20

inhibitory synpases

Answer 20

• Presynpatic neurone releases type of neurotransmitter that binds to Cl- ion portein channels on postsynaptic neurone
• Neurotransmitter causes chloride ion protein to open
• Cl - move in postsynpatic neurone by facilitated diffusion
• Binding of neurotransmitter causes opening of nearby K+ protein channels
• K+ move out of postsynaptic neurone into synapse
• Combined effect of Cl - moving in and K+ moving out makes inside postsynpatic membrane more negative and + outside

Question 21

What is the end effect of inhibitory synpases?

Answer 21

Membrane potential increases as much to -80mV compared to usual -65mV resting potential

Hyperpolarisation makes it less likely that the new action potential will be created because of larger influx of sodium ions is needed to produce one

Question 22

Why do synpases act like junctions to allow?

Answer 22

• A single impulse along one neurone to initate new impulses in a number of different neurones at a synapse. This allows a single stimulus to create a number of simultaneous responses
• A number of impulses to be combined at a synapse. This allows nerve impulses from receptor to different stimuli to contribute to single response

Question 23

Synpases are unidirectional

Explain why

Answer 23

• A chemical/neurotransmitter is made on presynaptic neurone and not post-synaptic neurone
• The neurotransmitter is stored in synaptic vesicles . When an action potential reaches synaptic knob, the membran of vesicles fuse with pre-synaptic membrane to release neurotransmitter
• When released, neurotransmitter diffuse across the synaptic cleft to bind to specific receptor proteins that are found only on postsynaptic neurone
• Neurotransmitter binds with the receptor proteins and this leads to a new action potential in post- synaptic neurone - excitory synpases