Neurones, synapses and transmitters

Question 1

How many neurons are in the brain?

Answer 1

100 billion

Question 2

How many neurons in the neocortex?

Answer 2

22.8 billion in men, 19.3 billion in women

Question 3

How long are all the nerve fibres in our brain?

Answer 3

150,000-180,000km

Question 4

How many synapses in the cortex

Answer 4

150,000 billion

Question 5

At what rate are neurones lost?

Answer 5

1 a second or 86,000 a day

Question 6

What is the ratio of glia to neurones?

Answer 6

10 glia for each neurone

Question 7

What do glia offer neurones?

Answer 7

Physical support
Metabolic support
Electrical insulation
Guiding connections (in development)

Question 8

Do glial cells send signals?

Answer 8

Yes

Question 9

What is the central nervous system?

Answer 9

The brain and spinal cord

Question 10

What is the peripheral nervous system made up of?

Answer 10

Sensory nervous system
Motor system
Autonomic nervous system

Question 11

What is the autonomic nervous system made up of?

Answer 11

Sympathetic
Parasympathetic
Enteric

Question 12

What is the opposite of the autonomic nervous system?

Answer 12

The somatic nervous system

Question 13

What is the definition of the peripheral nervous system?

Answer 13

Neurones that extend from the CNS

Question 14

How are neurones specialised for communication?

Answer 14

Dendrites - receive input from other neurones
Axon - impulse conduction
Synaptic bouton - release of neurotransmitter

Question 15

How are neurons classified?

Answer 15

Number of processes coming off the cell body: uni-, bi-, multi-polar
Dendrites: shape, spines
Connections: motor, interneurons
Axon length: golgi type I or II
Neurotransmitter (can’t be seen on microscope)

Question 16

What is a unipolar neurone?

Answer 16

Single axonal process

Question 17

What is a bipolar neurone?

Answer 17

Two axonal processes

Question 18

What is a multipolar neurone?

Answer 18

Multiple axonal processes

Question 19

What is a pseudo-unipolar neurone?

Answer 19

Single axonal processes, cell body is on a stem

Question 20

What is an electrical synapse?

Answer 20

(also known as gap junction)
Fastest and most primitive means of communication
Bi-directional transfer of information

Question 21

How do gap junctions work?

Answer 21

A pore between two cells, it allows ions to move between two cells

Question 22

What does a gap junction do?

Answer 22

Allow synchronous activity between neurons
Relatively rare (present in development)
Present in glia-neuron, glia-glia communication (cardiac myocytes)

Question 23

What is a chemical synapse?

Answer 23

A uni-directional transfer of information

Question 24

What is a synaptic cleft?

Answer 24

The gap between the pre and postsynaptic elements

Question 25

What is an efferent neuron?

Answer 25

Information going out

Question 26

What is an afferent neuron?

Answer 26

Information coming in

Question 27

Explain what happens in a chemical synapse

Answer 27

Action potential invades nerve terminal Depolarisation triggers Ca2+ channel opening Ca2+ influx (chemical gradient) Vesicle containing neurotransmitter moves to cell membrane and fuses Neurotransmitter leaves cell Diffuses across the synaptic cleft Binds to receptor

Question 28

How can a signal be terminated in a chemical synapse?

Answer 28

By re-uptake or enzymes in the synaptic cleft

Question 29

Explain how re-uptake occurs

Answer 29

Presynaptic neurone takes up neurotransmitter and either repackages it or breaks it down with enzymes

Question 30

Explain how enzymatic breakdown occurs

Answer 30

Enzymes present in the synaptic cleft breakdown the neurotransmitter

Question 31

What are the 4 categories of neurotransmitters?

Answer 31

Amino acids: glutamate, GABA Monoamines: noradrenaline, 5-HT Acetylcholine Neuroactive peptides

Question 32

What are the two classifications of neurotransmitters?

Answer 32

Inhibitory | Excitatory

Question 33

What are the receptors in synapses?

Answer 33

Membrane spanning protein molecules | Specific to a neurotransmitter

Question 34

How do the receptors cause a signal?

Answer 34

Transmitter binding causes structural change, structural change = signal

Question 35

How many receptors does a neurotransmitter have?

Answer 35

Several subtypes

Question 36

How do we classify receptors?

Answer 36

Localisation: post or pre synaptic | What it responds to: autoreceptor, heteroreceptor

Question 37

How do we name multiple receptor sub-types?

Answer 37

Based on most potent, selective agonist | e.g. for glutamatergic receptors we have: AMPA, NMDA, Kainate

Question 38

Name the receptor signalling mechanisms

Answer 38

Ionotropic | Metabotropic

Question 39

How does an ionotropic receptor work?

Answer 39

Ionotropic is receptor operated (ligand gated channels) | Transmitter binds: conformational change, channel opening, ion movement (Na+ in excitatory or Cl- in inhibitory)

Question 40

How quick is an ionotropic receptor?

Answer 40

Fast

Question 41

How does a metabotropic receptor work?

Answer 41

``` "G-coupled protein receptors" Transmitter binds Conformational change Activates G-protein Activates effector systems Has an indirect effect on excitability ```

Question 42

How quick is a metabotropic receptor?

Answer 42

Slow, but its effect lasts longer

Question 43

What can activated G-proteins do?

Answer 43

Open or close ion channels | Stimulate or inhibit enzymes/ secondary messenger systems