6.5 Neurons and Synapses

Question 1

What do neurons do?

Answer 1

Neurons transmit electrical impulses

Question 2

What systems are used for internal communication of the body?

Answer 2

• endocrine system - nervous system

Question 3

What does endocrine system consist of?

Answer 3

The endocrine system consists of glands that release hormones

Question 4

What does the nervous system consist of?

Answer 4

consists of nerve cells called neurons. They help with internal communication by transmitting nerve impulses

Question 5

Explain how the nerve impulse passes along a neuron. (8 marks)

Answer 5

○ in resting potential ○ sodium is pumped out by the active transport and potassium in ○ a concentration gradient builds up electrical potential / voltage ○ negative inside compared to outside ○ in action potential ○ must pass threshold level ○ sodium channels open and ions diffuse into neuron ○ membrane depolarized ○ potassium diffuse out across membrane through ion channels ○ active transport of ions once more ○ slower in un-myelinated neuron than in myelinated ○ an action potential in one part of the neuron causes the action potential to develop in the next section

Question 6

What is a nerve impulse?

Answer 6

Is an electrical signal, an action potential starts at one end of neuron and propagates along the axon to the other end of the neuron

Question 7

Where do nerve impulses travel along in a neuron?

Answer 7

Neurons have narrow out growths called nerve fibres where impulses travel along.

Question 8

Explain how a nerve impulse is transmitted from a neuron to a muscle

Answer 8

• impulse reaches the motor end plates / synaptice knobs / boutons / synaptic terminals • synaptic vesicles contain neurotransmitter / acetylcholine • calcium enters through the presynaptic membrane • calcium causes the vesicle to move to and fuse with the membrane / causes exocytosis • neurotransmitter / acetycholine released into the synaptic cleft • crosses / diffuses across the synoptic cleft to the muscle fibre membrane / postsynaptic membrane • binds to receptor sites • causes depolarisation of the muscle fibre membrane / postsynaptic membrane • by opening sodium gates • threshold of stimulation must be reached / all or nothing effect • enzyme / acetylcholinesterase breaks down the neurotransmitter / acetylcholine • depolarisation causes sarcoplasmic reticulum to release calcium ions • calcium ions cause / enable muscle contraction

Question 9

What is a synapses?

Answer 9

Synapses are junctions between neurons and between neurons (meeting point between two neurons)

Question 10

What are the cells called that send the signals to another cell?

Answer 10

Pre-synaptic neuron

Question 11

What is a neurotransmitter?

Answer 11

A neurotransmitter is a chemical that sends signals across synapses.

Question 12

What is an example of a neurotransmitter?

Answer 12

Acetylcholine

Question 13

When nerve impulse (action potential) reaches the synaptic knob before it reaches the axon terminal, what happens?

Answer 13

The electrical impulse (depolarization) causes calcium channels to open.

Question 14

What happens when an electrical impulse in a pre-synaptic cell causes calcium channels to open?

Answer 14

Calcium ions diffuse into the axon terminal of the pre-synaptic neuron

Question 15

How does the neurotransmitter move across the synaptic cleft from the pre-synaptic neuron to the post synaptic neuron?

Answer 15

Through simple diffusion it moves across the synaptic cleft

Question 16

What are dendrites?

Answer 16

short branched nerve fibres used to transmit impulses between neurons like in the brain

Question 17

What are axons?

Answer 17

very long elongated nerve fibres for example those that transmit impulses from toes to spinal cord

Question 18

What is myelin?

Answer 18

Material that COAT along most the nerve fibre’s length which consists PHOSPHOLIPID BILAYER deposited by SCHWANN CELLS

Question 19

What do Schwann cells do?

Answer 19

deposit a layer of myelin by growing around the nerve fibre several times which creates Schwann cells and thus a myelin sheath

Question 20

What are the gaps called between the myelin?

Answer 20

Node of Ranvier

Question 21

How does the nerve impulse travel along a myelinated nerve fibre?

Answer 21

Jumps from one node of ranvier to the next. This is called Saltatory conduction

Question 22

Does a nerve fibre travel quicker on a myelinated or unmyelinated nerve fibre?

Answer 22

Saltatory conduction (myelinated) is faster than continuous transmission as it can jump.

Question 23

What is resting potential?

Answer 23

A neuron that is not transmitting a signal that has potential difference

Question 24

How is potential created?

Answer 24

An imbalance of positive and negative charges across the membrane

Question 25

How is RESTING Potential (imbalance of charge across membrane) created?

Answer 25

- Using sodium potassium pumps. - The ions pumped in and out are unequal - Concentration gradient created (2 K+ into the cell, while 3 Na+ go out) as different in concentration and charges - Membrane is more permeable to K+ ions, so Na+ concentration gradient is steeper (Na+ does not diffuse easily) - Negatively charged protein inside nerve fibre increase the charge imbalance - resting membrane potential is -70 mV

Question 26

How does action potential occur?

Answer 26

Rapid change in membrane potential from depolarization (negative to positive) and re-polarization (positive to negative) ONLY when THRESHOLD POTENTIAL is reached

Question 27

How does depolarization occur?

Answer 27

When local currents (natural polarization) occurs, and threshold of around -55 mV is reached: - SODIUM CHANNELS OPEN, so Na+ can diffuse down concentration gradient (into the cell) - this makes the charge inside as positive as the outside - membrane potential becomes +30 mV

Question 28

How does re polarization occur?

Answer 28

- rapidly happens after depolarization - Na+ channels close, K+ channels open - K+ ions diffuse down concentration gradient (move out of cell) - inside of cell becomes negative again - K+ channel remains open until -70mV potential difference - diffusion of K+ repolarizes neuron but does not restore RESTING potential (K+ and Na+ gradients are not the same)

Question 29

Why does the propagation of action potential occur?

Answer 29

ion movements that depolarize one part of a neuron, causing depolarization of a neighbouring neuron that is still polarized . (Na ions moving along axon due to concentration gradient )

Question 30

Can a nerve impulse travel in two directions?

Answer 30

No, can only be initiated at one terminal be passed to on by the other terminal. The period after depolarization also prevents action potential backwards

Question 31

What are local currents?

Answer 31

- Inside the cell, there is more Na+ in the depolarized part - Inside cell, Na+ diffuses from depolarized part to not yet polarized part to reduce potential difference from -70 mV to -50mV - Na+ channels open at threshold potential

Question 32

What is a synaptic cleft?

Answer 32

the gap between pre-synaptic neuron and post-synaptic neuron is called synaptic cleft and is 20 nm wide

Question 33

What does the influx of calcium in the pre-synaptic cell cause?

Answer 33

Vesicles containing neurotransmitters move to membrane and fuse

Question 34

How are neurotransmitters released into the synaptic cleft?

Answer 34

exocytosis

Question 35

What happens after neurotransmitters diffuse across the synaptic cleft?

Answer 35

Bind to to receptors on post-synaptic membrane which cause adjacent Na+ channels to open where Na+ ions can diffuse down concentration gradient into new neuron

Question 36

What is caused when Na+ ions diffuse from synaptic cleft into post-synaptic cell

Answer 36

Threshold potential is reached that triggers action potential which depolarizes along the neuron

Question 37

What happens to the neurotransmitters after they activate receptors?

Answer 37

-broken down and removed from synaptic cleft

Question 38

How are acetylcholin produced?

Answer 38

Produced by pre-synaptic cell by combining choline and acetyle group (held in vesicles of neuron)

Question 39

If a spider touches you compared to an elephant, how is the action potential different?

Answer 39

The strength is ALWAYS THE SAME, only the frequency increases to highlight urgency

Question 40

Why does acetylcholine only bind to the receptor for a short time?

Answer 40

enzymes in the synaptic cleft break acetylcholin down quickly.

Question 41

What happens to broken down choline?

Answer 41

Reabsorbed by presynaptic cell and converted back into active neurotransmitter

Question 42

When neurotransmitters are released into synapse, does this always cause threshold potential?

Answer 42

If not ENOUGH neurotransmitters are released, and ENOUGH Channels are opened, threshold potential cannot be reached

Question 43

What are the different areas of science that come together to research memory and learning?

Answer 43

medicine & physiology, engineering and optical microscopy, chemistry and biochemistry, genetics, molecular biology and neurobiology