Biology 3.8: The nervous system Flashcards
How do organisms process stimuli?
Detect stimuli - process the information received about the stimuli - respond to the stimuli in a suitable way.
Where is information received?
Sensory cells and transferred to the nervous system to effector cells that carry out the response.
What is a reflex action
An inborn response to a stimulus and is rapid, automatic (doesn’t involve conscious part of the brain) and beneficial.
A coordinator is …
Either the brain or the spinal cord.
What’s the difference between reflex and voluntary actions?
Reflex is rapid and automatic whereas voluntary is slower and involves the conscious part of the brain.
What is the HYDRA?
An organism with simple behavioural patterns and therefore, only respond to a limited number of stimuli. They have few sense receptors and effector cells that communicate through a network of simple nerve cells linked together by short, branched communication pathways.
What does the sensory neurone do?
They carry nervous impulses from sensory cells to the CNS.
What does the coordinator neurone do?
They receive sensory information and coordinate which effectors are activated and communicate with the brain.
What does the motor neurone do?
They carry nervous impulses to effector organs - these are muscles or glands - so that the organism can respond to the stimuli they detect.
What is the myelin sheath?
It is a chemical synthesised by the Schwann cells that insulate the axon speeding up the transmission of the nervous impulse.
What type of impulse is the nerve impulse?
An electrochemical impulse.
Nervous impulses are transmitted by neurones. How does this affect the nervous impulse?
Nervous impulses are both directed and localised.
Why is nervous control unlike hormonal control?
It is precise rather than being diffuse.
What is a microelectrode?
A very fine, hollow, glass needle, filled with salt solution that conducts electricity.
What is the resting potential across the axon membrane?
-70mV, the membrane is said to be polarised.
How is the inside of the axon charged?
Negative with respect to the outside.
When the axon membrane is stimulated, what occurs to the potential difference across the membrane?
There is a local and temporary reversal of the resting potential difference.
Why is the impulse said to be unidirectional?
It always travels in the same direction.
How is the resting potential of -70mV maintained?
A combination of active transport and facilitated diffusion.
What is the threshold intensity?
The minimum value of a stimulus that will initiate an action potential.
What is meant by the propagation of a nerve impulse?
How an action potential is passed along an axon.
Myelinated neurones
They speed up the rate of transmission by increasing the distance over which the currents can bring about depolarisation.
Non-myelinated neurones
They conduct nerve impulses relatively slowly and do not, in general, transmit information to muscles.
How are myelinated neurones specialised?
Local currents can only occur at the nodes of ranvier - so the action potential ‘jumps’ from node to node instead of moving along and depolarising the whole of the axon membrane.
This is saltatory conduction and is much faster than in non-myelinated neurones.
