IB Biology Topic C2.1.5 Localized and Distant Effects of Signalling Molecules Revision Notes (HL)

IB Biology Topic C2.1.5 Localized and Distant Effects of Signalling Molecules Revision Notes (HL) | RevisionDojo

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Signalling Range: Neurotransmitters Act Next Door, Hormones Reach Across the Body

Cells face the same problem you do in a crowded room: some messages are for the person beside you, others must reach everyone.
A neurotransmitter is released across a tiny gap onto one adjacent cell, so it acts locally.
A hormone is released into the blood and travels to distant target cells throughout the body.
The distance a molecule acts over sets a trade-off between precision and breadth of effect.

Definition

Signalling molecules

Signalling molecules are chemicals that transmit information between cells, triggering specific responses in target cells.

Analogy

To reach someone right beside you, you whisper.
To reach someone across the room, you use a microphone so everyone can hear.
Neurotransmitters are the whisper; hormones are the announcement carried by the blood.

Local Signalling: Neurotransmitters Cross a Single Synapse

Definition

Neurotransmitter

Neurotransmitters are chemical signals used by neurons to communicate across synapses, the tiny gaps between nerve cells or between nerve cells and other target cells.

An impulse reaches the end of the presynaptic neuron and neurotransmitter is released into the synaptic cleft.
The molecule diffuses across a very short gap, only about 20 to 40 nm wide.
It binds receptors on the postsynaptic cell only, so just that one adjacent cell responds.
It is then quickly broken down or reabsorbed, so the effect is fast and short-lived.
1. Because the range is tiny and the receptors are specific, the signal is highly precise but reaches very few cells.

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Note

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IB Biology Topic C2.1.5: Localized and Distant Effects of Signalling Molecules Notes

Signalling Range: Neurotransmitters Act Next Door, Hormones Reach Across the Body

Local Signalling: Neurotransmitters Cross a Single Synapse

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Signalling Range: Neurotransmitters Act Next Door, Hormones Reach Across the Body

Local Signalling: Neurotransmitters Cross a Single Synapse

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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic C2.1.5: Localized and Distant Effects of Signalling Molecules Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Signalling Range: Neurotransmitters Act Next Door, Hormones Reach Across the Body

Local Signalling: Neurotransmitters Cross a Single Synapse

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Signalling Range: Neurotransmitters Act Next Door, Hormones Reach Across the Body

Local Signalling: Neurotransmitters Cross a Single Synapse

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account