Nervous System And Hormones Flashcards
Differences between nerves and hormones
Nerves are faster and shorter lived than hormones which don’t act quickly and have lasting effects on the body
They are both involved in sensing and responding to changes in the environment (stimuli)
Receptors
Receives/detects the stimulus (pressure sensors in the skin)
Co-ordinator
Determines the response (the brain and spinal cord)
Effector
Carries out the response (biceps muscles)
Advanced receptor
The eye is an example of an advanced receptor
- it contains a number of cells types that a fe sensitive to light
Aqueous and vitreous humour
Aqueous: front of eye
Vitreous: back of eye
Both are needed to provide support to the eyeball and also allows light to pass through the eye to the retina
The iris
It is the coloured part of the eye
It consists of two types of muscles:
-radial muscle (spokes on a wheel)
-circular muscle (form rings around pupil)
Risk to the eye in bright light
Bright light can damage the cells of the retina leading to blindness
Risk to the eye in dim light
Dim light can result in not enough light reaching to form an image
Action of iris muscle in bright light
Circular: contract
Radial: relax
Action of iris muscle in dim light
Circular: relax
Radial: contract
Effect on pupil diameter in bright light and in dim light
Bright light: decreased
Dim light: increased
Amount of light entering the eye in bright light and in dim light
Bright light: decreased
Dim light: increased
Adaptations to nerve cells (neurone) to carry out electrical impulses through nervous system
Long length: to carry impulses long distances
Insulting sheath: to allow rapid transmission of impulses
Branching ends: to receive or pass impulses from/to many other nerve cells
What are synapses
These are tiny gaps between nerve cells
For impulses to pass from one cell to the next a transmitter chemical must diffuse across the synapse at a high enough concentration to trigger an impulse in the next cell
What happens when an impulse reaches a synapse (8 steps)
- ) The impulse reaches the synaptic bulb (the end of the neurone)
- ) Vesicles containing the transmitter move towards the cell membrane at the synapse
- ) Vesicles release release their neurotransmitter into the gap between the two cells
- ) Neurotransmitter diffuses across the gap
- ) The neurotransmitter reaches the membrane of the next cell
- ) When enough neurotransmitter reaches the membrane of the next cell an impulse will occur (threshold)
- ) The impulse travels along to the next cell
- ) The used neurotransmitter is broken down by an enzyme
Voluntary actions
We have conscious control over these
Reflex actions
We are not conscious of these actions
These tend to be much faster than voluntary actions as they use a special pathway of nerves called reflex arc that does away with ‘thinking time’
The rapid nature means they can be used as protection
What are hormones
Hormones a re chemicals produced by special glands in the body that can travel through the blood to target organs in order to produce temporary changes in the way cells function
How is blood glucose levels controlled
The key hormone is insulin.
Although needed for respiration Hugh glucose levels can result in damage to cells
How does insulin decrease blood glucose
When a meal rich in carbs is ingested blood glucose levels rise and the pancreas releases insulin.
Insulin decreases blood glucose by:
-increasing rate of respiration in liver and muscle
-converts glucose to glycogen for storage in liver and muscles
What is glucagon?
Release from the pancreas
It is involved in increasing blood glucose levels during exercise or when glucose levels falls
Glucagon acts on the cells of the liver causing the time o convert glycogen back to glucose
Negative feedback
This mechanism is used by insulin to control blood glucose levels.
It inseparable that changes are reversed and returned back to the set
level
