c2.2 neural signalling

Question 1

What type of signal is a nerve impulse?

Answer 1

Electrical

Question 2

Cell body function

Answer 2

Contains nucleus and cytoplasm, associated with the production of proteins and neurotransmitters.

Question 3

Dendrite func

Answer 3

Carry electrical impulses towards cell body from other neurons in brain/spinal cord.

Question 4

Axon

Answer 4

Carry electrical impulses away from cell body to transmit nerve impulses along longer distances (tips of the finger to spinal cord).

Question 5

Define nerve impulse

Answer 5

The facilitated diffusion of positively charged ions across the nerve cell membrane.

Question 6

Resting potential

Answer 6

+ ve ion concentration is greater outside the membrane than inside (-70mV).

Question 7

Outline how action potential starts:

Answer 7

1) Na+ channels open
2) Na+ ions diffuse into the membrane across a concentration gradient.
3) Charge imbalance is reversed, membrane potential reaches +40mV
4) K+ channels open and they diffuse out.
5) MP falls back to -70
6) Na-K pumps re-establish Na+ and K+ conc gradients.

Question 8

Outline 3 ways that resting potential is maintained:

Answer 8

• Na-K pumps pump 3 Na+ outside per 2 K+ inside, so charge outside is higher.
• Differential permeability causes K+ to diffuse into the cell more.
• Organic anions contribute to overall -ve charge.

Question 9

Synapse

Answer 9

A 20-40um junction between a neuron and a post-synaptic membrane.

Question 10

Give 3 examples of a synapse

Answer 10

• Between 2 neurons in the brain/SC.
• Between a neuron and a sensory receptor cell
• Between a neuron and an effector cell (muscle fibre/gland cell).

Question 11

Outline the how NTs are released from pre-synaptic membrane:

Answer 11

1) Nerve impulse in transmitting neuron reaches the pre-s membrane.
2) The synaptic knob is depolarized, voltage gated Ca2+ channels open.
3) Influx of Ca2+ ions causes vesicles with NTs to move to Pre-S membrane, releasing them by exocytosis.
3) NTs that are not received are loaded into vesicles and pumped back from synaptic gap into pre-S membrane.

Question 12

What is the diameter of a human axon, and hence what is its speed

Answer 12

1 um, 1ms

Question 13

What are 2 factors that effect the speed of nerve impulses?

Answer 13

• The diameter of the axon: wider axon»less resistance»higher speed.
• Myelination: myelin is deposited by schwann cells that wrap around the axon and insulate it, nerve impulses increase as they jump from one node to another (up to 100ms).

Question 14

Outline excitatory post-synaptic potential:

Answer 14

1) NTs bind to a receptor on post-s membrane.
2) Na+ channels open Na+ ions diffuse down concentration gradient, potential rises to threshold potential.
3) Action potential is propagated away from synapse.
4) NT is broken down by enzymes or reabsorbed by pre-s membrane.

Question 15

At which synapses can AcH be found?

Answer 15

• Neuron-Neuron Synapses
• At neuromuscular junction synapses

Question 16

How AcH trigger a response?

Answer 16

1) Binds to receptors that act as Na+ ion channels.
2) Na+ channels open and Na+ ions diffuse into membrane.
3) Potential reaches action potential and a nerve impulse is propagated.

Question 17

How is a nerve impulse propagated along an axon?

Answer 17

• (inside): Na+ ions move from the depolarized (high c) area to the polarized (low c)
• Outside: Na+ ions move from the polarized (high c), to the depolarized (low c).

Question 18

State a device used to measure membrane potential:

Answer 18

Oscilloscope

Question 19

How does an oscilloscope measure membrane potential:

Answer 19

A microelectrode is placed on either side of the membrane and measures the charge difference that way.

Question 20

Exogenous chemicals

Answer 20

Chemicals that enter the body by an external source and either promotes or blocks synaptic transmission.

Question 21

Neonicotinoid

Answer 21

Synthetic compounds similar to nicotine that are used in pesticides (imidacloprid for ex).

Question 22

What do nicotinoids do:

Answer 22

• Bind to receptors in cholinergic synapses, prevent AcH from binding and blocks synaptic transmission.
• Acetylcholinesterase does not recognize them so doesn’t break them down, so permanent binding, causing paralysis and death.

Question 23

What does cocaine do:

Answer 23

• Acts at synapses were dopamine is a NT.
• binds to DPN re-uptake transporters, prevents DPN from being uptaken back to PRE-synaptic membrane.
• DPN builds up and causes continous post-synaptic transmission.
• causes feelings of euphoria with actions related to the release of dopamine.

Question 24

Ex of excitatory NT

Answer 24

AcH

Question 25

Ex of inhibitory NT

Answer 25

GABA

Question 26

EPSP vs ISPSP

Answer 26

• Depolarizes potential
• Makes membrane potential more negative.

Question 27

How does GABA inhibit a response?

Answer 27

1) Binds to receptor
2) Cl- channels open
3) Cl- ions diffuse into neuron and hyperpolarize the neuron.

Question 28

How does a post-synaptic membrane with mutiple pres regulate response?

Answer 28

• no response is triggered in the case of the single release an excitatory NT.
• response is triggered if several adjacent pres release an excitatory NT.
• response is triggered if 1 pre-s repeatedly releases a neurotransmitter.

Question 29

How does a post-synaptic membrane with mutiple pres regulate response in the case conflicting messages, bigger picture this:

Answer 29

• a response is triggered only if one type of NT outnumber the other.
• helps in integrating signals from different sources, helps with decision-making in CNS.

Question 30

How does the body start a sensation of pain:

Answer 30

• Pain on skin/other receptors detect external stimuli.
• channels of ions associated with the receptors open and the ions diffuse inside.
• Threshold potential is reached and nerve impulse passes to the spinal column from the sensory neuron.
• Interneurons in the SC carry the response to the cerebral cortex.
• then to pre-frontal cortex for evaluation.

Question 31

Conscious

Answer 31

A state of complex awareness of many things simultaneously.

Question 32

What to scientists agree on in terms of consciousness:

Answer 32

emerges from the interaction of individual neurons in the brain and spinal cord

Question 33

Consciousness is an…

Answer 33

emergent property