2.7 - The nervous system
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What does the human nervous system consist of?
Central nervous system (CNS) - brain, spinal chord. Peripheral nervous system - nerve cells carry info to or from CNS.
What are nerve cells also known as?
Neurones
What are neurones?
long cells that carry electrical signals along their length
Where two neurones meet there is a tiny gap called a …
Synapse - a chemical (diffusion) signal that travels across the synapse to the next neurone.
How does information flow from the receptors to the effectors?
Receptors –(sensory neurons)–> CNS —-(motor neurons)–> Effectors
What do are sense organs detect?
Changes in the world around us known as stimuli
What is a stimulus?
Something that sets of a reaction in the nervous system (light, temp, sound). These changes in environment are detected by receptors in an organism.
What do sense organs contain?
Groups of specialised cells called receptor cells which produce electrical impulses in response to specific stimuli.
What are the stimulus of these five sense organs? Skin Tongue Nose Eye Ear
Touch, temperature Chemicals (in food and drink) Chemicals (in air) Light Sound
What are effectors?
Parts of the body, such as muscles or glands, that produce a response to a detected stimulus.
Give examples of effectors in use?
muscle contracting to move an arm muscle squeezing saliva from salivary gland A gland releasing a hormone into the blood
What is the order of how information flows from receptors to effectors? Stimulus,_____,____ neuron,____ neuron, ____ neuron,_____, response
Stimulus -> receptor -> sensory neuron -> relay neuron -> motor neuron -> effector -> response
What is a reflex action?
A protective, automatic and rapid response to a stimulus
The nerve pathway followed by a reflex action is called a…
Reflex arc
What happens when you accidently touch something hot?
1) receptor in skin detects a stimulus (heat) 2) sensory neuron sends impulse to relay neuron in the spinal cord 3) The relay neuron connects to the motor neuron (and also sends a message to the brain) 4) motor neurons sends impulses to effector 5) effector produces a response ( muscle contracts to move hand away)
When there is a bright light in your eye what happens to your: Radial muscles Circular muscles Pupil
Radial muscles - relaxed Circular muscles - contracted Pupil - contracted (less light enters eye)
When there is a dim light in your eye what happens to your: Radial muscles Circular muscles Pupil
Radial muscles - contracted Circular muscles - relaxed Pupil - relaxed (more light enters)
The reaction of light in an eye is protective, involuntary and rapid. What do these words mean?
Protective - prevents harmful bright light from damaging the receptor cells at the back of the eye Involuntary - you don’t have to think about it, it happens automatically Rapid - the reaction happens very quickly
Once the stimulus is detected the following process occurs:
1) A receptor cell passes an electrical impulse along the sensory neurone. 2) The sensory neurone reaches the coordinator ( determines correct response to stimulus), the CNS. 3) The sensory neurone connects to a relay neurone, via a synapse, inside the CNS. 4) The relay neurone connects to a motor neurone, via a synapse, inside the CNS. 5) The motor neurone leaves the CNS and the impulse is carried to the effector.
What are the functions in the eye of the following structures? Cornea Iris Lens
Cornea - refracts light - bend it as it enters eye Iris - controls how much light enters pupil Lens - focuses light onto the retina
What are the functions in the eye of the following structures? Retina Optic nerve Sclera Pupil
Retina - contains the light receptors Optic nerve - carries impulses between the eye and brain Sclera - white, tough outer layer Pupil - small hole at center of Iris that allows light in eye