B3.1 the nervous system Flashcards
What is the nervous system made up of?
Neurones (nerve cells), which go to all parts of the body.
What is a stimulus?
A stimulus is a change in the environment.
What detects a stimulus?
Sensory receptors
What receptor cells are found and what is their stimulus for the following sense organs:
a) eye
b) tongue
c) skin
d) nose
a) receptor cell-light; stimulus-light
b) receptor cell-taste; stimulus-chemical
c) receptor cells-pressure(touch), temperature; stimuli- pressure, heat
d) receptor cells-smell, taste; stimuli- chemical (for both)
Describe the stages in a nervous response.
The receptor cells detect the stimulus. When a stimulus is detected by receptors, the information is sent as nervous (electrical) impulses along sensory neurones to the central nervous system (CNS) which consists of the brain and the spinal chord. The CNS coordinates the response (so decides what to do about the stimulus and tells something to do it). The CNS send information to an effector (muscle or gland) along a motor neurone. The effector then respond accordingly - eg. a muscle May contract or a gland may secrete a hormone.
What are the three types of neurones?
Sensory neurones
Replay neurones
Motor neurones
Describe the role of sensory neurones
Its role is to carry electrical impulses from receptor cells to the CNS
Describe the role of the relay neurones.
They carry impulses from sensory neurones to motor neurones
Describe the role of motor neurones
They carry impulses from the CNS to effectors
What is the role of the axon?
Electrical impulses are passed along the axon of a neurone
Why do neurones have dendrites?
Neurones have branched endings (dendrites) so they can connect with lots of other neurones
What is the myelin sheath?
The myelin sheath acts a an electrical insulator, speeding up the electrical impulse.
As well as the myelin sheath how else do the neurones speed up the impulse?
Neurones are long, which also speeds up the impulse (connecting with other neurones slows the impulse down, so one long neurones is much quicker than lots of short ones joined together).
What is a synapse?
The connection between two neurones.
Explain what happens in the synapse.
The electrical impulse triggers the release of transmitter chemicals, which diffuse across the gap.
These chemicals bind to receptor molecules in the membrane on the next neurone. This sets off a new electrical impulse.
What are reflex reactions?
Reflex actions are automatic (involuntary) reactions as they occur without thinking. By missing out the brain, your body can react even faster.
They often have a protective role
Give basic example of reflex actions.
Breathing
Heart rate
Digestion
Describe the cornea and its function.
It is a transparent coating on the front of the eye.
Its function is to protect the eye by refracting light into the eye.
Describe the pupil and its function
It is a central hole in the iris
Its function is to allow light to enter the eye
Describe the iris and its function
It is a coloured ring of muscle tissue
Its function is to alter the pupil size by contracting or relaxing
Describe the lens and its function
It is a transparent biconvex lens
Its function is to focus light clearly onto the retina
Describe the ciliary body and its function
It is a ring of muscle tissue attached to suspensory ligaments
Its function is to alter the shape of the lens