nervous system Flashcards
nervous system
consists of body’s nerves as well as the brain and spinal chord, to control your actions. All reactions happen in the same way. There are always stimuli, receptors and effectors which communicate with each other to bring about a response
chain of events
stimuli-changes that can be detected
receptors-detect changes
effectors- bring about a response
response-change that occurs
how nervous system works
most important part is the co Ordinator, part of system that receives the information( in the form of a nerve impulse) from nerve cells called sensory neurons and organize an appropriate response
does this because it determines what receptors link up with which effectors.
It then passes a nerve impulse through a motor neuron to reach the appropriate effector
co Ordinator are the brain and spinal chord which together form the central nervous system
responsible for our reactions and behavior
the eye
example of a receptor, specialized sense organ that contains light sensitive receptors, receives light and sends images to the brain where they are interpreted
watery fluid between cornea and lens, the aqueous humor, and between the lens and retina is the vitreous humor, keeping the lens shape and allows light through
optic nerve
carries nerve impulses to brain
lens
can change shape to focus light onto retina
Iris
controls the amount of light entering the eye by making the pupil bigger or smaller
conjunctiva
protects the cornea from damage and keeps it moist
Cornea
transparent layer which stops material entering eye and also aids focusing
pupil
a hole in middle of eye which allows light ot enter
retina
contains the receptor cells that are sensitive to light
controlling amount of light entering eye
important that not too much or too little light enters eye, the light receptors in the retina can be damaged
muscles or IRIS contract and relax to change size of pupil. this is an automatic reaction called the pupillary reflex
Dim light
radical muscles contract and the circular muscles relax which makes the pupil bigger
Bright light
the circular muscles contract and the radial muscles relax making the pupil smaller
Focusing
light entering eye is refracted as it passes through the cornea, with further bending of light taking place as it passes through the lens. This controls how focused an image will be
lens can be controlled to focus an image onto the retina. Done by changing thickness of lens . thicker the lens the more it will refract the rays of light
thicker
rays from a close object need more refraction to focus so lens is
thinner
rays from a distant object need less refraction to focus so lens is
accommodation
this process of lens changing shape to focus light on the retina
how does lens change shape
there is a ring of muscle surrounding the lens called ciliary muscles
lens is attached to ciliary muscle by suspensory ligaments
if ciliary muscle relaxes, suspensory ligaments pull the lens tight, making the lens thin
if ciliary muscles contract, suspensory ligaments are no longer tight and lens becomes fat
how the eye is able to focus on a close up object
lens becomes more convex( fatter) when looking at a close up object
suspensory ligaments slacken and the ciliary muscles contract
how the eye is able to focus on a distant object
lens becomes less convex( thinner) when looking at distant objects . The suspensory ligaments become taut and the ciliary muscles relax.
nucleus
controls activities of the neuron is surrounded by most of cells cytoplasm in cell body
Neurons
special cells that connect receptors such as eye and effectors such as muscles to the central nervous system
Axon
long extension of cytoplasm( can be up to 1 meter) so nerve impulses can be transmitted from central nerve system to extremeness of the body
Myelin shecith
fatty layer around axon produced by special cells. It acts as an insulator and helps speed up nerve impulses
Branched ends
Branched ends of the axon and small branching extensions from cell body allow the neuron to make junctions with many other nerve cells
reflex actions
a reflex pathway, the length of the nerve pathway, is kept as short as possible which has few a number of synapses between the neurons as possible
Synapses
Sensory and motor neurons don’t make direct contact in the brain or spinal chord.
Instead there are small gaps which impulses” jump” called synapses, where transmitter chemical is produced by the end of the neuron and if enough is produced, an impulse will be triggered. allowing lots of connections to be made and a greater degree of control at the junctions.
