2. Synaptic Transmission

Question 1

What is a synapse ?

Answer 1

Is the junction between a neurone and another neurone or between a neurone and an effector

Question 2

What is a synaptic cleft ?

Answer 2

Tiny gap between the cells at synapses

Question 3

What is the presynaptic neurone ?

Answer 3

The one before the synapses has a swelling called a synaptic knob

This obtains synaptic vesicles Fuller with chemicals called neurotransmitters

Question 4

The effect of an action potential

Answer 4

When action potential reaches end of neurone it causes neurotransmitters to be released into synaptic cleft.

Diffuse across to post synaptic membrane and bind to specific receptors.

When neurotransmitters bind to receptors they might trigger an action potential ( in neurone ) cause muscle contraction ( in muscle cell ) or cause hormone to be sectreyed ( from gland cell )

Neurotransmitters are removed from cleft so response doesn’t keep happening

Question 5

What 3 things can be triggered when neurotransmitters bind to receptors on post snymoatic membrane

Answer 5

Action potential in neuron

Muscle contraction in muscle cell

Hormone secretion from gland cell

Question 6

How is the impulse unidirectional ?

Answer 6

Receptors are only on post synaptic membrane

Question 7

Where will neurotransmitters be taken to after they’re removed from synaptic cleft ?

Answer 7

Taken back to presynapuc neurone or broken down by enzymes

Question 8

Example of neurotransmitters

Answer 8

Acetylcholine ACh ( and noradrenaline)

It binds to cholingeric receptors

Synapses that use acetylcholine are called cholingeric synapses

Question 9

Cholingeric synapses

1. Arrival of action potential

Answer 9

• action potential arrives at synaptic know of presynaptic neurone
• this stimulates opening of voltage gated calicium ion channels
• calcium ions diffuse into presynaptic neurone and later pumped out by active transport

Question 10

Cholingeric synapses

2. Fusion of vesicles

Answer 10

• the Influx of calcium ions into presynaptic neurone causes the vesicles to bind with presynaptic membrane
• the vesicles then released neurotransmitters ACh into synaptic cleft by exocytosis

Question 11

Cholingeric synapses

3. Diffuse or ACh

Answer 11

• ACh diffuses across synaptic cleft and binds to complementary cholingeric receptors on post synaptic membrane
• sodium ion channels open on membrane and there’s influx of sodium ions into neurone which causes depolarisation
• if action potential reaches threshold then ACh is removed from synaptic cleft by enzyme acetylcholinsterase and products are reabsorbed by presynaptic neurone and used to make more ACh

Question 12

What is the exocytosis process ?

Answer 12

Vesicles inside cell move to cell surface membrane

Fuses with the membrane and releases it’s xontents outside of cell

Question 13

What can neurotransmitters be ?

Answer 13

Excitatory

Inhibitatory

Both

Question 14

What are excitatory neurotransmitters?

Answer 14

They depolarise the post synaptic membrane making it fire an action potential if threshold is reached

Eg acetylcholine is excitirory it binds to cholingeric receptors to cause an action potential in post synaptic membrane

Question 15

What does depolarise mean ?

Answer 15

Making the potential difference across neurone membrane more positive

Question 16

What does hyperpolarisation mean ?

Answer 16

Making potential difference across membrane more negative

Question 17

What are inhibitory neurotransmitters?

Answer 17

Hyperpolarise the postsynaptic membrane ( make the potential difference more negative )

Preventing it from firing an action potential

GABA is an inhibitory neurotransmitter when it binds to receptors it causes potassium ion channels to open on the post synaptic membrane - hyperpolorisinf thr netrone

Question 18

When is acetylcholine an inhibitory neurotransmitters?

Answer 18

At cholingeric synapses in heart

When it binds to receptors here it can cause potassium ion channels to open on the postynaptic membrane , huperpilarimf it

Question 19

A synapse where inhibitory neutrotransmitters are released from the presynaptic mambernae is called what ?

Answer 19

Inhibitory synapse