Changes occur all the time both inside and outside an organism
A successful organism can adapt to these changes
The ultimate goal of any organism is to maintain a stable internal environment.
This stable environment is called homeostatis.
The way an organism achieves homeostasis is by regulation. This Dynamic Equillibrium MUST be maintained in order for the organism to survive.

Neuron - another name for a nerve cell

See if you can label the parts of this neuron. Nerve cells will conduct impulses or messages in one direction only. If the impulse was a car it would be just like a one-way street.

The order that the impulse travels will be:
Dendrite-->Cell Body (with nucleus)-->Axon-->Terminal Branches (that secrete neurotransmitters)-->Synapse The space between structures

Remember "DCATS" the order of the path of the impulse.

These neurotransmitters, like Acetylcholine (Ach), the most important neuromuscular transmitter, will move across the synapse and send the impulse to the next structure. This could be another neuron or an effector, such as a muscle or gland. Amphetamines or speed inhibits the enzymes that turns off this reaction. This is why it feels like you have so much energy.

A stimulus is a change that brings about a response.

A Releaser Is something that elicits a stereotyped response. Such as the red belly of the stickleback


Adaptations for Regulation


Unicellular so NO neurotransmitters are needed because they are unicellular. They do have chemoreceptors and photoreceptors

Coelenterates (HYDRA)

A nerve net that allows impulses to move in MANY directions.


Dorsal brain with ventral nerve cord (know your anatomical direction)


Dorsal brain with ventral nerve cord and elaborate sensory apparatus such as compound eye, antennae and a tympanum.

Did you know that a fly can "taste" with it's feet!


Humans use both the Nervous and Endocrine systems to achieve Homeostasis. The endocrine system secretes hormones. These are slow long termed reactions.

Central Nrevous system with brain and spinal cord (CNS) These are very fast short termed reactions.
The Brain consists of:

Peripheral Nervous System (PNS) this consists of the Somatic or VOLUNTARY part and the Autonomic or INVOLUNTARY part.
This is further subdivided into the Symapthetic (stress) (SPNS) and the Parasympathetic (peaceful) (PPNS)

So as an example
Getting ready to run away from a lion might be under the control of the sympathetic autonomic peripheral nervous system. On the other hand, relaxing by playing mellow music during dinner will be under the control of the parasympathetic autonomic peripheral nervous system.

Open Ended Questions