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Biology - Module 5.4 Cheat Sheet (DRAFT) by

neuronal communication

This is a draft cheat sheet. It is a work in progress and is not finished yet.

The nervous system and the endocrine system

organisms must respond to internal and external enviro­mental changes for survival
organisms may respond to enviro­mental changes using either the nervous system or the endocrine system
the nervous system
- uses electrical impulses sent through neurons
- transfer signals locally between synapses using neurot­ran­smi­tters such as acetyl­choline
the endocrine system
- uses hormones sent through the blood stream
- transfer signals aross large distances
thse commun­ica­tions (function of cells, organs and system) must be coordi­nated to operate effect­ively and maintain homeos­tasis


A neuron is a specia­lised cell in the nervous system that is the basic building block of the brain, spinal cord, and nerves. Neurons are respon­sible for transm­itting inform­ation through electrical and chemical signals, allowing the body to respond to stimuli.
structure of the neuron
- the soma is the body of the cell which contains the nucleus surrounded by cytoplasm with lots of ER and mitoch­ondria
synthesise neurot­ran­smi­tters
- short extentions coming from the soma which branch out into dendrites
transmit electrical impulses towards the soma
- single elongated nerve fibres that vary in length
- narrow region of the cytoplasm surrounded by plasma membrane
transmit electrical impulses away from the soma
myelinated sheath
- the myelinated sheath is made of schwann cells which are lipids and is sometimes found wrapped about 20 times around the dendron and axon
used for electrical insulation of the neuron
allows the electrical impuls to trasnmit faster as it can perform slatatory conduction
nodes of ranvier
- gaps between the schwann cells
areas that arent electr­ically insulated so the electrical impulse can jump from node to node
there are 3 types of neuron...
1. sensory neuron
- the sensory neuron carries the action potntial from the sensory receptor to the relay neuron in the CNS (brain and spinal cord)
- the sensory neuron has the soma in the middle between the dendron and axon.
- the sensory neuron has a dendron
2. motor neuron
- the motor neuron carries the action potential from the relay neuron in the CNS to the effector (muscle or gland)
- the motor neuron has the soma at the end of the neuron
- the motor neuron has no dendron - the dendrites connect directly to the soma
3. relay neuron
- the relay neuron is found in the CNS an carries the action potential from the sensory neuron to the motor neuron
saltatory conduction
only some neurons have myleinated sheaths. the neurons which do are used for rapid rections because they can then peform saltatory conduction - saltatory conduction is the process by which the electrical impulse jumps from node to node to produce a quick reaction as the elctrical impulse doesn't have to pass through the whole neuron. unmyel­inated neurons are used for rsponses that don't have to be immediate such as digestion.
other fators that affect the speed of action potentials are...
axon diameter
wider axons cause faster action potential since there is less resitance of flow for ions
as temper­ature increases ions diffuse faster meaning that the action potential is faster

coordi­nation in animals

internal changes may include
- core temper­­ature
- blood glucose concen­­tr­ation
- water potential
- cell pH
external changes may include
- enviro­nmental temper­­ature
- touching something hot
- light intensity
the importance of coordi­­nation in animals
the commun­­ic­a­tions (function of cells, organs and system) must be coordi­­nated to operate effect­­ively and maintain homeos­­tasis

coordi­nation in plants

plants dont have a nervous system however, they still must respond to changes in internal and external enviro­mental changes so therefore, they must commun­icate with hormones
internal changes may include
- water potential of cells
nutrient levels
external changes may include
- water availa­bility
- nutrient availa­bility
- soil pH
- light intensity
- temper­ature
- oxygen levels