Nervous System + Eyes Flashcards
Stimulus
A change in an animals surroundings
Receptors
Detect changes in the environment called stimuli
Effector (2 examples)
Any part of the body that produces the response
Muscles contracting
A gland releasing a hormone into blood
Order of response to stimulus
Stimulus Receptor Coordination Effector Response
Transduction
When energy is changed from one form to another, all receptors are transducers of energy
Types of neurones
Sensory
Relay
Motor
Nerve fibre
Bundles of nerve cells that pass on electrical impulses to the brain
Sensory neurone
Carries impulses from the receptors to spinal cord
Relay neurone
Carries impulses from the spinal cord to brain
Motor neurone
Carries impulses from the brain to effector
4 features of the nervous system
Fast speed of conduction
Message carried by neurones
Short duration of response
Electrical impulses
Example of the coordinator for normal responses
Cerebellum in the brain
What does the cerebellum contain and what they do (2)
Sensory areas for receiving a processing information
Motor areas where voluntary actions originate
Why might some areas of the body be more sensitive than others
Higher density of receptors
Thickness of skin
What are reflex actions
A rapid automatic response to a stimulus
What is the nerve pathway of a rapid automatic response called
Reflex arc
Where does the nerve pathway not go to for reflex actions
The brain
Where is the signal processes for reflex actions
The spinal cord via the relay neurone
What is the coordinator for reflex actions
Relay neurones in the spinal cord
What is a synapse
A gap between two neurones
How are the “messages” carried across a synapse
5 steps
- Electrical impulses arrive at a synapse
- Ends of branches of the axon secrete a chemical called a neurotransmitter
- Neurotransmitter diffuses across synapse to the membrane of the second neurone
- Electrical impulses start again in second cell
- Neurotransmitter is broken down by an enzyme
What is the difference between the speed of the diffusion of neurotransmitter and electrical impulses along a neurone
Diffusion of neurotransmitter is slower
What can a reflex action in the eye control
The amount of light entering the eye
Iris
Controls the amount of light entering the eye by changing the size of the pupil
Which two muscles form the iris and what pattern do they form
Circular muscles for ring shapes
Radial muscles are like spokes of a wheel
What happens to the eye in bright light and why
Pupil is constructed
Circular muscles contract
Radial muscles relax
Prevents damage to retina
What happens to the eye in dim light and why
Pupil is dilated
Circular muscles relax
Radial muscles contract
Can see a clearer image
What does the retina contain
Contains light sensitive rod and cone cells which convert light energy into a nerve impulse (transduces energy)
What are rods for (2)
Dim light
Black and white
What are cones for (2)
Bright light
Red, green, blue
What is accommodation
The lens has to change shape in order to focus on near and distant objects
How is the lens controlled
By ciliary muscles and suspensory ligaments
Ciliary muscles
Changes shape of the lens by altering the tension of suspensory ligaments
What happens in the eye when focusing on a distant object
Lens is made flat (less convex)
Ciliary muscles relax
Suspensory ligaments are pulled tight
What happens in the eye when focusing on a nearby object
Lens is made more rounded (convex)
Ciliary muscles contract
Suspensory muscles are slackened
Cornea
Refracts/ bends light entering the eye
Lens
Changes shape to focus on an object
Pupil
Hole which allows light into the eye
Fovea
Area where light is most focused, very sensitive to colour
Optic nerve
Transmits nerve impulses to the brain
Sclera
Outer protective layer of the eye
Choroid
Contains blood vessels (and prevents light from exiting the eye?)
