6.5 Neurons and synapses: Neurons transmit the message, synapses modulate the message.

Nature of science: Cooperation and collaboration between groups of scientists—biologists are contributing to research into memory and learning.

Understandings: Neurons transmit electrical impulses. The myelination of nerve fibres allows for saltatory conduction. Neurons pump Na+1 and K+1 ions across their membranes to

generate a resting potential. An action potential consists of depolarization and repolarization

of the neuron. Nerve impulses are action potentials propagated along the

axons of neurons. Propagation of nerve impulses is the result of local currents that

cause each successive part of the axon to reach the threshold potential.

Synapses are junctions between neuron; between neurons and receptor or effector cells.

When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.

A nerve impulse is only initiated if the threshold potential is reached.

Applications and skills:• Application: Secretion and

reabsorption of acetylcholine by neurons at synapses.

• Application: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.

• Application: The social effects of the abuse of psychoactive drugs could be considered, as could the use of the Botox for cosmetic treatments.

• Skill: Analysis of oscilloscope traces showing resting and action potentials.

Utilization: An understanding of the workings of neurotransmitters and synapses has led to the development of numerous pharmaceuticals for the treatment of mental disorders.

Topic 6: Human physiology (20 hours)

Biology Journal 3/16/2015

6.5 Application:

Discuss the social effects of the abuse of psychoactive drugs, the causes of addiction, including genetic predisposition, social factors and dopamine secretion.

What does the myelin sheath do for a neuron?

The myelin sheath speeds up and protects the electrical signal (action potential)

What is a neurotransmitter?

A neurotransmitter is any substance that is released by a neuron at it’s terminal, and effects the action potential of other neurons.Many drugs (both legal and illegal) mimic neurotransmitters, or manipulate their distribution.

1. What will the effect of an excitatory molecule be?2. What will the effect of an inhibitory molecule be?

1. An excitatory molecule will make the neuron its connected to more likely to have an action potential.

2. An inhibitory molecule will make the neuron its connected to less likely to have an action potential.

What are some of the functions of acetylcholine?

Acetylcholine is a neurotransmitter involved in many subconscious functions (heart rate,

digestion…), as well as being instrumental in muscle contraction.

Label this diagram

5

8

6

3

27

1

4

Label this diagram

Neurotransmitters

Receptor (for neurotransmitters)

Vesicle

Dendrite

Synapse

Transport protein

(for reuptake of neurotransmitters)

Axon terminal

Mitochondrion

Methamphetamine is a drug that goes into the axon terminal of neurons and forces out dopamine from the dopamine vesicles. This dopamine is then released from the axon and causes overstimulation of the dopamine receptors of the dendrite. Meth directly effects the reward system of the brain, making it one of the most addictive drugs known.1. Is meth a stimulant or a depressant?2. Is meth inhibitory or excitatory on neurons?

1. Meth is a stimulant.2. Meth is excitatory.Meth makes neurons more likely to have an action potential, especially in the pleasure and reward (addiction) systems of the brain.

1. What is the charge inside of an axon when it is polarized?

2. What is the charge inside of an axon when it is depolarized?

3. What is the charge inside of an axon when it is repolarized?

Polarized: (-) inside axon. This is the starting, or “resting” potential.Depolarized: (+) inside axon. This occurs when the Na+1 diffuses into the axon.Repolarized: (-) inside axon. This happens when the K+1 diffuses out of the axon.

Label this neuron cell1

4 6

2

8

53

7

Label this neuron cell

Dendrites

Myelin sheath Schwann cell

Cell body (soma)

Axon terminals

AxonNucleus

Node of Ranvier

Pesticides called neonicotinoids block acetylcholine transport proteins that re-absorb acetylcholine from the synapse. What would be the effects of neonicotinoid poisoning on a human?If acetylcholine (ACh) is trapped in the neurotransmitter and keeps ACh receptors firing, the results would be…• Convulsions• salivation and tearing of eyes• involuntary urination and defecation• eventual death by asphyxiationPesticides such as neonicotinoids are used to increase crop yields. However, these chemicals are killing natural bees, and entering the food chain and into our bodies.

1. Are neonicotinoids a stimulant or a depressant?2. Are neonicotinoids inhibitory or excitatory on neurons?

1. Neonicotinoids are a stimulant.2. neonicotinoids are excitatory.Neonicotinoids make neurons more likely to have an action potential.

Which parts of an action potential involve passive transport?

A B D E

A. When Na enters the neuronB. When K leaves the neuronC. When the Na/K pump is moving ionsD. Depolarization

E. RepolarizationF. The reuptake of neurotransmitters by transport proteinsG. The exocytosis of neuro-transmitters into the synapse

What step on the graph…A. is the resting potential?B. does Na diffuse into the neuron?C. is repolarization?D. does the Na/K pump re-position the ions?E. is the inside of the axon positive?

01452 and/or 3

When does the inside of an axon have a negative charge? (write all correct letters)

A C D F G

A. When it is polarizedB. When it is depolarizedC. When it is repolarizedD. Resting potential

E. After sodium diffuses inF. After potassium diffuses outG. After the Na/K pump has reset the ions following an action potential

Based on this picture, what are the effects of cocaine on neurons?

Cocaine blocks dopamine transporter proteins (also known as re-uptake proteins), thus dopamine stays in the synapse, overstimulating the dopamine receptors in the receiving neuron, exciting it..