Topic 15

Stimulus

a condition or signal that causes a response, a change in the internal or external environment that is detected by a receptor.

Myelin

a fatty molecule that insulates the nerve fibre and so increases the speed of transmission of the impulse.

Axon

a long fibre, often myelinated, that transmit impulses to te axon terminals and then to other cells at the synapse.

Convection

best in gases and liquids, carries heat away from the body.

Conduction

best in lipids and solids.

Hormones

chemical messenger (proteins or lipids) secreted in response to a stimulus. Often secreted by endocrine glands in the bloodstream and bring about a response in an effector.

Coordination centre

comprises the action of the central nervous system and endocrine system.

Cell body

contains the cell nucleus that controls neuron function and organelles.

Receptors

enable the body to detect changes that occur in both the external and internal environment.

Radiation

heat energy in the form infrared heat rays lost from the surface of a warm body, best in a vacuum.

Dendrites

highly branched extensions of a neuron that receive signals from other neurons or receptors.

Interneuron

in the CNS; transmit impulse from one neuron to the next in the CNS via synapses; usually have many axons and dendrites.

Evaporation

loss of water in vapour form, uses heat from the surface.

Homeostasis

maintenance of a relatively stable internal environment, within narrow limits.

Response

mechanisms put into place by an organism to maintain homeostasis.

Effector

muscles or glands.

Negative feedback

occurs when the response to a stimulus reverses the direction of change of the stimulus.

Endothermic

organisms whose body heat is generated from internal metabolic sources. (birds & mammals)

Ectothermic

organisms whose body temperature is governed by external heat source. (reptiles)

Poikilothermic

refers to an organism having a body temperature that can vary greatly with changes in the external environment. (fish)

Homeothermic

refers to an organism that is able to maintain a constant body temperature within narrow limits.

Motor neuron

transmit impulses from CNS to effectors via the PNS. Collections of motor neurons form a motor nerve.

Sensory neuron

transmit impulses from the sense organs (Ex. En.) and the internal organs (In. En.) to the CNS