BP: Neurons and synaptic transmission

Question 1

Most of the brain is made up of cells called…

Answer 1

… glial cells and astrocytes.

Question 2

What are neurons?

Answer 2

Specialised cells whose function is to move electrical impulses to and from the central nervous system (carry neural information throughout the body).

Question 3

What gives the brain its impressive processing capabilities?

Answer 3

The highly complex neural networks within in.

Question 4

What must neurons transmit?

Answer 4

Must transmit information both within the neuron and from one neuron to the next.

Question 5

What do the dendrites of neurons receive?

Answer 5

Information from sensory receptors or other neurons.

Question 6

What happens once the dendrites of neurons have received information from sensory receptors?

Answer 6

The information is passed down to the cell body and on to the axon.

It then travels down the length of the axon in the form of electrical signal known as an action potential.

Question 7

What three types of neurons are there?

Answer 7

• Sensory neurons
• Relay neurons
• Motor neurons

Question 8

What things do neurons typically consist of?

Answer 8

• A cell body
• Dendrites
• An axon

Question 9

What are dendrites connected to?

Answer 9

The cell body, which is the control center of the neuron.

Question 10

In a neuron, where does the impulse terminate?

Answer 10

The axon terminal.

Question 11

In many nerves, what is there around the axon?

Answer 11

An insulating layer, known as a myelin sheath.

Question 12

What is a myelin sheath?

Answer 12

An insulating layer that forms around the axon of a neuron.

Question 13

Why is the myelin sheath important?

What happens when this is damaged?

Answer 13

It allows the nerve impulses to transmit more rapidly along the axon.

When damaged, the impulses slow down.

Question 14

What is the length of a neuron?

Answer 14

It can vary from a few millimetres up to one metre.

Question 15

What do sensory neurons do?

Answer 15

They carry nerve impulses from sensory receptors to the spinal cord and the brain.

Question 16

What are sensory receptors?

Answer 16

Receptors for vision, taste, and touch etc.

All the senses.

Question 17

Where are sensory receptors found?

Answer 17

They are found in various locations in the body.

For example in the eyes, ears tongue and skin.

Question 18

What do sensory neurons convert?

Answer 18

They convert information from the sensory receptors into neural impulses, which can then travel to the brain.

Question 19

What happens when impulses from the sensory neurons reach the brain?

Answer 19

They are translated into sensations of, for example, visual input, heat, pain etc. so that the organism can react appropriately.

Question 20

If sensory information does not go to the brain, where does it go?

Why is it more beneficial for it to go there instead?

Answer 20

Some sensory neurons terminate at the spinal cord, and this allows reflex actions to occur quickly without the delay of sending the impulses to the brain.

Question 21

What are relay neurons?

Answer 21

The most common type of neuron in the CNS.

They allow sensory and motor neurons to communicate with each other.

Question 22

Where are relay neurons found?

Answer 22

They are only found in the brain or the spinal cord.

Question 23

What does the term ‘motor neurons’ refer to?

Answer 23

To neurons located in the PNS that project their axons outside the PNS and directly or indirectly control muscles.

Question 24

What do most motor neurons form?

Answer 24

Synapses with muscles to control their contractions

Question 25

When stimulated, what happens to the **motor neuron?**

Answer 25

It releases neurotransmitters that bind to receptors on the muscle and triggers a response which leads to muscle movement.

Question 26

What happens when the **axon** of the **motor neuron fires?**

Answer 26

The muscle with which it has formed synapses with contracts.

Question 27

What is **muscle relaxation** caused by?

Answer 27

Inhibition of the motor neuron.

Question 28

How are **muscle contractions** formed? ## Footnote *What does their strength depend on?*

Answer 28

Formed when the axon of the motor neuron connected to the muscle fires. ## Footnote *The strength of the muscle contractions depends on the rate of firing of the axons of the motor neuron that control it.*

Question 29

What is **an action potential?**

Answer 29

An electrical signal that travels down the axon of a neuron.

Question 30

What must happen when an **action potential arrives at the terminal?** ## Footnote *How is this achieved?*

Answer 30

The action potential must be transferred to another neuron or to tissue. ## Footnote *To acheive this, the action potential must cross the synapse.*

Question 31

What is a **neurotransmitter?**

Answer 31

A chemical substance that plays an important part in the workings of the nervous system by transmitting nerve impulses across a synapse.

Question 32

What is a **synapse?**

Answer 32

The conjunction of the end of the axon or one neuron and the dendrite or cell body of another.

Question 33

What does the **synapse** consist of?

Answer 33

* The end of the pre-synaptic neuron * Membrane of the postsynaptic neuron * The gap inbetween these two neurons

Question 34

What is the **synaptic gap?**

Answer 34

The physical gap between the pre-synaptic and postsynaptic cell membranes.

Question 35

**The physical gap between the pre-synaptic and postsynaptic cell membranes,** is known as what?

Answer 35

The synaptic gap.

Question 36

What is at the **end of an axon of a nerve cell?**

Answer 36

A number of sacs known as synaptic vesicles.

Question 37

What are **synaptic vesicles?**

Answer 37

The sacs at the end of an axon of a nerve cell.

Question 38

What do **synaptic vesicles contain?**

Answer 38

Chemical messengers/neurotransmitters that assist in the transfer of the impulse across the synaptic gap.

Question 39

What happens as the **action potential** reaches the **synaptic vesicles?**

Answer 39

Their contents are released through a process of exocytosis.

Question 40

What is **exocytosis?**

Answer 40

The process of moving materials from within a nerve cell to the exterior of the cell (the synaptic gap).

Question 41

Once the **neurotransmitter** is released, what happens to it?

Answer 41

It diffuses across the gap between the pre- and post synaptic neuron. Then, it binds to specialised receptors on the surface of the cell that recognise it and are activated.

Question 42

Once **neurotransmitters** have activated **specialised** **receptors**, what happens?

Answer 42

The receptor molecules produce either excitatory or inhibitory effects on the postsynaptic neuron.

Question 43

Describe the process of **synaptic transmission:**

Answer 43

* An action potential arrives at the terminal button at the end of the axon. * This causes the synaptic vesicles to release their contents through exocytosis. * Released neurotransmitters diffuse across the synaptic gap and bind to specialised receptors on the postsynaptic neuron. * These activated receptors produce either excitatory or inhibitory effects.

Question 44

What is **synaptic transmission?**

Answer 44

Refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron to another.

Question 45

Where do **neurotransmitters diffuse?**

Answer 45

Across the synaptic gap, onto specialised receptors on the postsynaptic neuron.

Question 46

In synaptic transmission, where are **specialised receptors found?**

Answer 46

On the postsynaptic neuron.

Question 47

How long does the process of **synaptic transmission last?**

Answer 47

Only a fraction of a second

Question 48

Where do the **effects** of synaptic transmission **terminate?**

Answer 48

The effects terminate at most synapses by a process called 're-uptake'.

Question 49

Describe the process of **re-uptake:**

Answer 49

*Occurs after synaptic transmission.* The neurotransmitter is taken up again by the presynaptic neuron, where it is stored and made available for later release *(it is recycled)*.

Question 50

(After synaptic transmission), what determines the **length** of the the **effects** on the postsynaptic neuron?

Answer 50

How quickly the neurotransmitters return to the presynaptic neuron - *the speed of re-uptake.* ## Footnote *The quicker they are taken back, the shorter the effects on the postsynaptic neuron.*

Question 51

Explain how **some antidepressants** prolong the action of the neurotransmitter:

Answer 51

They inhibit the re-uptake process, so the neurotransmitters can not return to the pre-synaptic neuron.

Question 52

Apart from re-uptake, what else can happen to **neurotransmitters?**

Answer 52

They can be 'turned off' after they have stimulated the postsynaptic neuron.

Question 53

What can happen to **neurotransmitters** once they have stimulated the postsynaptic neuron?

Answer 53

* Re-uptake * Be 'turned off'

Question 54

How are **neurotransmitters 'turned off'?**

Answer 54

Through the actions of enzymed produced by the body, which make the neurotransmitters ineffective.

Question 55

What can **neurotransmitters** be **classified as?**

Answer 55

Excitatory or inhibitory in their action.

Question 56

Give **examples** of **excitatory neurotransmitters:**

Answer 56

Acetylcholine and noradrenaline.

Question 57

What do **excitatory neurotransmittors do?**

Answer 57

Increase the liklihood that an excitatory signal is sent to the postsynaptic cell, which is then more likely to fire.

Question 58

Give **examples** of **inhibatory neurotransmitters:**

Answer 58

Serotonin and GABA.

Question 59

What do **inhibitory neurotransmitters do?**

Answer 59

Decrease the liklihood that an excitatory signal is sent to the postsynaptic neuron, and so decrease the liklihood of the neuron firing.

Question 60

What are **inhibitory neurotransmitters** generally responsible for?

Answer 60

Calming the mind and body, inducing sleep and filtering out unnecessary excitatory signals.

Question 61

An **excitatory neurotransmitter** binding with a **postsynaptic neuron** causes **what**? ## Footnote *What does this result in?*

Answer 61

Causes an electrical change in the membrane of that cell. ## Footnote *This results in an excitatory postsynaptic potential (EPSP).*

Question 62

What is an **EPSP?**

Answer 62

Excitatory post-synaptic potential.

Question 63

What does an **EPSP** lead to?

Answer 63

An increased liklihood that the postsynaptic cell will fire.

Question 64

An **inhibitory neurotransmitter** binding with a postsynaptic receptor, results in what?

Answer 64

An inhibitory postsynaptic potential (IPSP).

Question 65

What will an **IPSP do?**

Answer 65

Make it less likely that the postsynaptic cell will fire.

Question 66

What determines the **likelihood** of a cell firing?

Answer 66

The summation of IPSPs and EPSPs.

Question 67

What is the difference between spatial and temporal summation?

Answer 67

* In spatial summation, large number of EPSPs are generated by different synapses on same postsynaptic neuron at the same time. * In temporal summation, large number of EPSPs are generated at the same synapse by a series of high-frequency action potentials on presynaptic neuron.