TOPIC 6.5 NEURONS & SYNAPSES€¦ · Understandings U1: Neurons transmit electrical impulses. IB...

TOPIC 6.5 – NEURONS & SYNAPSES

6.5 – A - Neurons

INTRO

IB BIO – 6.5 The nervous system is the

organ system that carries

signals throughout the body.

It is divided into two sections:

• Central nervous system –

nerve tissue in the brain and

spinal cord

• Peripheral nervous system –

nerve tissues outside the

central nervous system

3

https://ka-perseus-images.s3.amazonaws.com/f7fa1bdddc896c2c635a1929c6578b745a6030c2.png

Understandings

U1: Neurons transmit electrical impulses.

IB BIO – 6.5

Key Terms

Neurons

The nervous sytem is made up of cells called neurons, which

transmit electrical impulses. The general structure of is

shown here. Key structures include…

4

https://denisezannino.files.wordpress.com/2014/09/neuron1.jpg

Understandings


IB BIO – 6.5

Key Terms

Axon

Dendrites

• Axon – a long, narrow

‘arm’ that carries electric

signals (like wires)

5

https://askabiologist.asu.edu/sites/default/files/resources/plosable/Brain_Speed/connected-neurons.jpg

• Dendrites – short, branched

fibers that transmits signals

to other cells

Understandings


IB BIO – 6.5

Key Terms

Cell Body

• Cell Body – contains the nucleus and majority of the

organellels and cytoplasm

6

https://upload.wikimedia.org/wikipedia/commons/e/ed/Neuron_Cell_Body.png

Understandings

U2: The myelination of nerve fibers allows for saltatory conduction.

IB BIO – 6.5

Key Terms

Myelin

Nodes of Ranvier

Nerve fibers function by transmitting

signals over long distances very

quickly.

To facilitate this, some nerve axons

are covered by a myelin sheath

which is produced by Schwann cells.

Gaps between the myelin sheaths

are called nodes of Ranvier.

7

https://classconnection.s3.amazonaws.com/811/flashcards/141811/jpg/neuron21320853416098.jpg

Understandings


IB BIO – 6.5

Key Terms

Nodes of Ranvier

Saltatory Conduction

8

http://antranik.org/wp-content/uploads/2012/04/conduction-in-a-myelinated-nerve-fiber-saltatory-conduction.jpg

Electric impulses traveling down

the axon are able to jump

between the nodes.

This ‘skipping’ is called saltatory

conduction and allows impulses

to travel up to 100 m/s.

Understandings

U3: Neurons pump sodium and potassium ions across their membranes to generate a resting potential.

IB BIO – 6.5

Key Terms

Na+/K+ Ion Pump

Sodium/Potassium ion pumps are embedded in the membrane of

axons and move ions against their concentration gradient using ATP.

9

http://reader14.docslide.net/store14/html5/392015/5571ffce49795991699e26b8/bg12.png

• THREE Na+ ions are

pumped out of the cells

• TWO K+ ions are pumped

into the cells

Understandings


IB BIO – 6.5

Key Terms

Na+/K+ Ion Pump

After being pumped, Na+ ions and K+ ions are able to diffuse

across the membrane. However, K+ diffuses much more quickly

than Na+.

10

http://slideplayer.com/slide/7069457/24/images/10/Figure+11.8:+The+basis+of+the+resting+membrane+potential,+p.+399..jpg

As a result:

• The Na+ gradient

is much is greater

than the K+

gradient.

• A charge imbalance

is created across

the membrane

Understandings


IB BIO – 6.5

Key Terms

Resting potential

This imbalance of of charges results in a potential difference

(voltage) across the membrane. This is called resting potential and

has a value of approx. -70 mV.

11

http://slideplayer.com/slide/7069457/24/images/10/Figure+11.8:+The+basis+of+the+resting+membrane+potential,+p.+399..jpg

VID

EO

SIB BIO – 6.5

• Crash Course – The Nervous System, Pt 1https://www.youtube.com/watch?v=qPix_X-9t7E

• 2-Minute Neuroscience – The Neuronhttps://www.youtube.com/watch?v=6qS83wD29PY

• Khan Academy – Resting Potentialhttps://www.youtube.com/watch?v=4htSVI5E9AQ

12

https://www.youtube.com/watch?v=qPix_X-9t7E

https://www.youtube.com/watch?v=6qS83wD29PY

https://www.youtube.com/watch?v=4htSVI5E9AQ

REVIE

WIB BIO – 6.5 1. Outline the role of the nervous system and its

primary subdivisions.

2. Identify the following structures:

13

https://s3.amazonaws.com/classconnection/399/flashcards/2562399/png/1280px-neuronsvg-151C0DCC5994F4DC02E.png

REVIE

WIB BIO – 6.5 1. Outline the role of the nervous system and its

primary subdivisions.

2. Identify the following structures:

14


REVIE

WIB BIO – 6.5 3. Describe nodes of Ranvier and their role in

transmitting impulses.

4. State the number of K+ and Na+ ions transported

by Na+/K+ pumps.

5. Outline how the resting potential is formed.

15


6.5 – B – Action Potential

INTRO

IB BIO – 6.5 Recall that neurons have axons that are able to transmit signals in

the form of electrical impulses. These signals travel in the form of

action potentials.

17

https://s-media-cache-ak0.pinimg.com/originals/b0/61/7c/b0617c59b5b5dc7bcd4760f3447349d4.jpg

INTRO

IB BIO – 6.5 Na+ and K+ voltage-gated ion channels are embedded in

the membrane of the axon. When open, these allow ions to diffuse

across the membrane. This affects the local potential.

18

https://cnx.org/resources/09ab17c9199ed6fb925c5fae201df4bcfac9b846/Figure_35_02_01.jpg

Understandings

U4: An action potential consists of depolarization and repolarization of the neuron.

IB BIO – 6.5

Key Terms

Action potential

Polarization

Repolarization

Action potentials occur when there is a rapid change in the

membrane potential. In has two phases as shown here:

19

https://s-media-cache-ak0.pinimg.com/originals/f9/53/59/f95359a8d685edcaaaaae66d6e43c510.jpg

1

2

1. Depolarization –

Na+ channels open,

allowing Na+ to diffuse

inside the neuron. The

Potential becomes +30mV

2. Repolarization –

Na+ channels close and

K+ channels open. K+

diffuses outwards. The

potential returns to

-70 mV

Understandings


IB BIO – 6.5

Key Terms

Action potential

Polarization

Repolarization

Repolarization happens quickly after depolarization. The diffusion

of K+ changes the potential from positive to negative, often

overshooting the resting potential. This is hyperpolarization.

20

https://s-media-cache-ak0.pinimg.com/originals/f9/53/59/f95359a8d685edcaaaaae66d6e43c510.jpg

Understandings

U5: Nerve impulses are action potentials propagated along the axons of neurons.

IB BIO – 6.5

Key Terms

In order to communicate

with other cells, action

potentials are propagated

along axons.

Nerve impulses travel in one

direction from the receiving

terminal to the other end.

The propagation of action

potentials has many steps…

21

http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-13/13_11.jpg

Understandings

U6: Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.

IB BIO – 6.5

Key Terms

22

https://s-media-cache-ak0.pinimg.com/736x/36/16/fb/3616fb33b2765be22faaec1bffd52679.jpg

Propagation

1. Membrane is at resting

potential.

2. An action potential causes Na+

channels to open and Na+

diffuses into the cell.

Na+ inside the cell diffuses

toward the neighboring region.

3. When the threshold potential is

reached, nearby Na+ channels

open, resulting in

depolarization.

Understandings


IB BIO – 6.5

Key Terms

23


Propagation

4. K+ ion channels open in the

original region, allowing K+

ions to diffuse outward.

This repolarizes the local

region, which returns to the

resting potential.

5. This process repeats allowing

the action potential to move

forward.

Understandings


IB BIO – 6.5

Key Terms

24


Action Potential Propagation

Understandings

S1: Analysis of oscilloscope traces showing resting potentials and action potentials.

IB BIO – 6.5

Key Terms

Oscilloscope

Oscilloscopes are devices

that can visualize oscillations

in electric potential.

To do this, they have two

electrodes that can be placed

on each side of the

membrane.

25

https://cdn-shop.adafruit.com/1200x900/468-06.jpg

Skills


IB BIO – 6.5

Key Terms

Oscilloscope

As shown here, oscilloscopes can be used to observe changes in

membrane potential as an action potential is propagated.

A narrow spike from -70mV to +30mV is seen during depolarization.

Then, the potential quickly drops back during repolarization.

26

https://online.science.psu.edu/sites/default/files/biol141/Propagation_of_Action_Potential.jpg

VID

EO

SIB BIO – 6.5

• Crash Course – The Nervous System, Pt 2https://www.youtube.com/watch?v=OZG8M_ldA1M

• 2-Minute Neuroscience – Action Potentialhttps://www.youtube.com/watch?v=W2hHt_PXe5o

27

https://www.youtube.com/watch?v=OZG8M_ldA1M

https://www.youtube.com/watch?v=W2hHt_PXe5o

REVIE

WIB BIO – 6.5 1. Define action potential.

2. Identify the types of ion channels embedded in the

axon membrane.

3. Differentiate between depolarization and

repolarization.

4. Outline the propagation of an action potential down

an axon.

28

REVIE

WIB BIO – 6.5 Action Potential Graph

Draw the graph of an action potential (potential vs.

time). Be sure to:

- Label the x and y axis

- Include specifica potential values

- Label regions of the graph correspond to:

- Depolarization

- Repolarization

- Hyperpolarization

29

REVIE

WIB BIO – 6.5 Action Potential Graph 30

https://opentextbc.ca/anatomyandphysiology/wp-content/uploads/sites/142/2016/03/1221_Action_Potential.jpg

6.5 – C - Synapses

INTRO

IB BIO – 6.5 Recall that the role of the nervous system is to carry signals

throughout the body. To do this, neurons must be able to pass

signals (action potentials) between them.

32

https://denisezannino.files.wordpress.com/2014/09/simple-network.jpg

Understandings

U7: Synapses are junctions between neurons and between neurons and receptor or effector cells.

IB BIO – 6.5

Key Terms

Synapse

Neurotrans-mitter

Synapses are the junctions

between neurons or between

neurons and receptor/effector

cells.

They are the places where signals

are transferred through chemicals

called neurotransmitters.

The gap between cells

is called the synaptic

clef.

33

https://www.ncbi.nlm.nih.gov/projects/pmh/PMH_Authoring/media/Images/originals/Fig8.1Neurons.jpghttps://www.ncbi.nlm.nih.gov/projects/pmh/PMH_Authoring/media/Images/originals/Fig8.1Neurons.jpg

Understandings

U8: When presynaptic neurons are depolarized they release a neurotransmitter

into the synapse.

IB BIO – 6.5

Key Terms

Pre-synaptic

Post-synaptic

34

http://openneuronproject.org/wp-content/uploads/2016/08/synapse.png

When a signal is being passed

between neurons, two types of cells

are involved:

• Presynaptic cell – the neuron

transitting a signal and releasing

neurotransmitters into the

synaptic cleft

• Post-synaptic cell – the neuron

receiving the signal by detecting

the presence of

neurotransmitters

Understandings


into the synapse.

IB BIO – 6.5

Key Terms

Synapse

Synaptic Cleft

When an action potential

reaches a dendrite, it

depolorizes the area

This causes the release of

neurotransmitter into

the synaptic cleft.

35

https://cnx.org/resources/75ab19a5b7c2945555083964780a2159caa68856/1225_Chemical_Synapse.jpghttps://cnx.org/resources/75ab19a5b7c2945555083964780a2159caa68856/1225_Chemical_Synapse.jpg

Understandings


into the synapse.

IB BIO – 6.5

Key Terms

Synapse

Synaptic Cleft

Synaptic Transmission 36

http://www.mrhorrocks.com/wp-content/uploads/2016/02/synaptic_transmission_med.jpg

1. An action potential propagate down an axon and reaches the

synapse.

2. Depolarization causes

Ca2+ ions to open, which

allows Ca2+ to diffuse

into the cell.

3. Vesicles containing

neurotransmitters

merge with the cell

membrane

This releases the

neurotransmitter into

the synaptic cleft.

Understandings


into the synapse.

IB BIO – 6.5

Key Terms

Synapse

Synaptic Cleft

Synaptic Transmission 37

http://www.mrhorrocks.com/wp-content/uploads/2016/02/synaptic_transmission_med.jpg

4. Neurotransmitters diffuse across the synaptic cleft towards the

post-synaptic cell.

5. Neurotransmitters bind

to receptors on the

post-synaptic cell.

This opens Na+ ion

channels and causes

depolarization and

triggers an action

potential.

6. This potential propagates

down the cell towards

the cell body.

Understandings

U9: A nerve impulse is only initiated if the threshold potential is reached.

IB BIO – 6.5

Key Terms

Threshold potential

In order for an action potential to be propagated in a post-

synaptic neuron, the threshold potential must be reached.

This is the potential at which voltage-gated ion channels open. The

graph above shows two failed attempts before the threshold is met.

38

http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_07_17_labeled.jpg

Understandings


IB BIO – 6.5

Key Terms

Threshold potential

When neurotransmitters bind to recepters on the post-synaptic

neuron, the influx of Na+ ions increases the membrane potential.

If the threshold potential is not reached, an actional potential will

not be initiated and propagated.

39


Understandings


IB BIO – 6.5

Key Terms

Threshold potential

When the threshold potential is reached, the action potential is

propagated down the post-

synaptic cell and the signal is carried.

40


REVIE

WIB BIO – 6.5 1. Define synapse.

2. Differentiate between pre-synaptic and post-

synaptic cells.

3. Outline the process of how a signal is transmitted

between two neurons (synaptic transmission).

4. Define the threshold potential.

41

6.5 – D - Acetylcholine

INTRO

IB BIO – 6.5 Recall that pre-synaptic cells release neurotransmitters in

order to communicate with other neurons or effector cells.

43

http://www.compoundchem.com/wp-content/uploads/2015/07/Chemical-Structures-of-Neurotransmitters-2015.png

Applications

A1: Secretion and reabsorption of acetylcholine by neurons at synapses.

IB BIO – 6.5

Key Terms

Acetylcholine

Acetylcholine is a neurotransmitter used in many synapses, most

notably between neurons and muscle fibers. After it is secreted, it

diffuses towards receptors on the post-synaptic cell.

44

http://www.nature.com/nature/journal/v436/n7050/images/436473a-f1.2.jpg

Applications


IB BIO – 6.5

Key Terms

Acetylcholine

Acetylcholine molecules only

bind for a short period of time

and only cause one action

potential in the post-synaptic

cell.

While in the synaptic cleft, it is

broken down by

acetylcholinesterase.

The products of this are choline

and acetate molecules.

45

https://classconnection.s3.amazonaws.com/801/flashcards/3736801/jpg/ace_enzy-1446A6ABC875C206CE2.jpg

Applications


IB BIO – 6.5

Key Terms

Acetylcholine

The choline and acetate molecules are reabsorbed by the pre-

synaptic cell via endocytosis. Inside the cell, they are converted

back into acetycholine by recombining with an acetyl group.

46

http://www.dokimiscience.com/uploads/4/6/9/2/46925269/939160450.gif

Applications

A2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.

IB BIO – 6.5

Key Terms

Neonicitonoids

Neonicotinoids are synthetic molecule that can bind to acetylcholine

receptors in the central nervous system of insects. It is not broken

down by acetylcholinesterase and so does not unbind from

receptors.

47

https://upload.wikimedia.org/wikipedia/commons/thumb/2/26/R-nicotine.svg/2000px-R-nicotine.svg.png

Applications


IB BIO – 6.5

Key Terms

Neonicitonoids

Since the binding is irreversible, neonicitinoids block synaptic

transmissions in cholinergic synapes. This cause paralysis and

death, making it an effective pesticide.

48

https://oregonsustainablebeekeepers.files.wordpress.com/2013/03/bad.jpg

Applications


IB BIO – 6.5

Key Terms

Neonicitonoids

49

http://www.compoundchem.com/wp-content/uploads/2015/04/Neonicotinoid-Pesticides-Their-Effect-on-Bee-Colonies-The-Facts.png

REVIE

WIB BIO – 6.5 50U1: Neurons transmit electrical impulses.




U5: Nerve impulses are action potentials propagated along the axons of neurons.


U7: Synapses are junctions between neurons and between neurons and receptor or effector cells.

U8: When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.





TOPIC 6.5 NEURONS & SYNAPSES€¦ · Understandings U1: Neurons transmit electrical impulses. IB...

Documents

Transcript of TOPIC 6.5 NEURONS & SYNAPSES€¦ · Understandings U1: Neurons transmit electrical impulses. IB...