Top answers

During the cardiac cycle , there is a delay between the excitation of the atria and excitation of the ventricles. Explain how this is achieved and why this delay is essential.

Excitation from SAN (sino-atrial node) spreads across atria , causing them to contract first. The excitation is conducted to the AV (atrio-ventricular) node, which introduces a 0.12s delay . This refractory ...
JE
Answered by Jane E. • Biology tutor
15829 Views

Describe how a synapse works

- An electrical impulse travels down the axon of a pre-synaptic neurone . - The movement of this electrical impulse initiates the release of chemical messengers which are called neurotransmitters . - The neu...
SI
Answered by Saira I. • Biology tutor
3462 Views

How does a signal move from one neurone to another and how does this process change for different motor responses?

The transmission of an action potential- the signal- from one neurone to another occurs over the synapse. The structure of a synapse is as follows; there is a presynaptic bulb, a post synaptic bulb and the s...
AH
Answered by Amy H. • Biology tutor
3413 Views

What is natural selection?

Natural selection is when certain characteristic are 'selected' for. Each species have simiar characteristics but differences in genes means that their characteristics can vary for example individual birds o...
AM
Answered by Anna M. • Biology tutor
3276 Views

Explain the process of muscle contraction in a myofibril following nervous stimulation.

Muscle contraction can be explained using the 'Sliding Filament Hypothesis'. Following nervous stimulation, a nerve impulse will be transmitted to a neuromuscular junction. This will cause a release of the n...
LM
Answered by Lydia M. • Biology tutor
7941 Views