Chapter Six - Nervous System and Hormones Flashcards
Draw and explain the components of the nervous system
Receptor is stimulated—>Information is sent from the receptor
- We have receptors to the central nervous system (brain
Sensitive to sight, and spinal cord) which is a
Sound, touch etc coordinator and determines what
response is required; info is then
Effector (usually a
Label diagram of structure and function of the eye
- conjunctiva - thin transparent protective outer covering
- Iris - controls how much light enters eye
- Lens - refracts/bends light
- Pupil - space in iris through which light passes
- Cornea - transparent front part of eye, allows light to enter; causes some refraction
- Retina - inner coat of eye where light sensitive cells are found
- Optic nerve - contains neurones carrying info to the brain
Explain the two humours in the eye
The clear fluid found in the front of the eye (aqueous humour) and in the back of the eye between the lens and the retina (vitreous humour) are needed to provide support to the eye and to allow light to pass through the retina
Explain the iris
Coloured part of the eye, consists of two types of muscle: radial muscles which are like the spokes of a bicycle wheel, and circular muscle which forms rings around the pupil
Iris muscles in bright light
Risk, action, effect on pupil and amount of light entering eye
Risk - bright light can damage the cells of the retina leading the blindness
Action of Iris muscles
Circular - contract
Radial - relax
Effect on pupil diameter - decreased
Amount of light entering eye - decreased
Iris muscles in dim light
Risk, action, effect on pupil and amount of light entering eye
Risk - low light levels can result in not enough light reaching retina to form an image
Action of Iris muscles
Circular - relax
Radial - contract
Effect on pupil diameter - increased
Amount of light entering eye - increased
What is accommodation?
Light is focused on the retina by changing the shape of the lens. This allows near and far objects to be seen clearly
Label eye focused on distant object
- lens thin
- light rays arrive parallel; cornea refracts rays; lens is thin as little additional refraction is necessary to focus light on the retina
Label diagram of eye focused on near object
- lens think
- light rays diverge; cornea refracts rays; lens is thicker as additional refraction is necessary to focus light on retina
Explain focusing on a near image
To focus on a near object a ring of muscle surrounding the lens (ciliary body) contracts. This allows the suspensory ligaments to become loose and the lens bulges out as it is not under pressure
Explain focusing on a distant object
The ciliary body relaxes. This causes suspensory ligaments to become taut, pulling the lens into a thinner, flattened shape
Adaptions of nerve cells
Nerve cells (neurones) are specially adapted to carry electrical impulses through the nervous system. These include;
- long length - to carry impulses long distances
- Insulating sheath - to allow rapid transmission of impulses
- Branching ends - to receive or pass impulses from of to many other nerve cells
What is a synapse?
The tiny gaps between nerve cells. For impulses to pass from one nerve 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.
Label diagram in a synapse
- synapse
- vesticles containing chemical transmitter
- direction of impulse
- chemical transmitter
Explain voluntary and reflex actions
Our nervous system allows two basic types of response. The first first of these are the voluntary actions - we have conscious control over these.
The second type of responses is reflex actions - we are not conscious of these actions. Reflex actions tend to be much faster as they use a special pathway of nerves called the reflex arc that does not include ‘thinking time’. The rapid nature of reflex actions means many are used by the body for protection.
Label diagram of the reflex arc
- association (connector) neurone - joins the sensory and motor neurones
- White matter
- grey matter
- sensory neurone - carries info from receptors for example a burn on the hand, to the spinal cord
- motor neurone - carries info from spinal cord back to muscle (effector) causing a response, for example moving the hand
The three neurones link in the grey matter (butterfly shaped part) of the spinal cord; the outer part is the white matter.
What are hormones?
Chemicals produced by special glands in the body that can travel through the blood to target specific organs in order to produce changes in the way the cells in the organ function
The role of insulin?
They key hormone in the control of blood glucose levels is insulin. Although glucose is needed for respiration, high blood glucose levels can result in damage to cells.
Diagram of how blood glucose levels are controlled by negative feedback
Pancreas releases insulin Blood glucose level increases
| /\
| | normal blood glucose level
Glucose by - increasing rate of
respiration in liver and muscles
- converting glucose to glycogen
for storage in liver
How are nerves and hormones similar as well as different
They are both involved in sensing and responding to changes in the environment (stimuli). The actions of nerves is faster and more short-lived than the action of hormones, which don’t act as quickly and have long lasting effects on the body.
Explain negative feedback
The mechanism insulin uses to control blood glucose levels. The action of insulin in reducing blood glucose levels means that less insulin is needed. When normal blood glucose levels are restored due to the action of insulin the pancreas no longer releases insulin.
The role of glucagon
Involved in increasing blood sugar levels during exercise or when blood glucose levels fall. Glucogen acts on the cells of the liver, causing them to convert glycogen back into glucose.
What is diabetes?
The condition where people fail to produce enough insulin or their cells fail to respond correctly
Symptoms of diabetes;
- high blood glucose levels
- glucose in the urine, excessive thirst, lethargy (tiredness) and a frequent need to urinate
Long term dangers of diabetes;
If left untreated
- kidney damage
- eye damage
- stroke
- heart disease
Why is the no. of people with diabetes increasing?
Varies reasons including;
- poor diet
- obesity
- lack of exercise
How is diabetes controlled?
People with diabetes must test their blood glucose levels and may need to inject insulin to correct them if levels are too high. If too much insulin is taken or enough food is not eaten at regular intervals, blood glucose levels can fall too low resulting in a ‘hypo’ (hypoglycaemic attack) and unconsciousness
Explain what phototropism is.
Parts of the plant above ground most often grow towards the light as this should increase their rate of growth as more photosynthesis can occur. This effect is known as phototropism.
The hormone responsible for phototropism is auxin. It is caused by auxin accumulating on the shaded side of a shoot and this causes more growth on that side.
Explain the action of auxin if light is hitting the shoot from all directions
- there will be even distribution of auxin
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\/
Due to the even distribution all cells will elongate at a similar rate
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\/ - the shoot will grow vertically
Explain the action of auxin when light is shining from one side
- there will be accumulation of auxin on the shaded side of the shoot
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\/ - cells on the shaded side elongate more rapidly than those on the illuminated side
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\/ - the increase of length on one side of the shoot causes it to bend towards the light
Commercial uses of plant hormones
Include: use, how it works and benefits
Selective weedkillers
How it works - hormone stimulates such a high rate of uncontrolled growth that plants disintegrate
Benefits - hormones used only act on broadleaved plants (weeds) but not on narrow leaved grasses and cereals
Rooting powder
How it works - hormone stimulates certain cells to develop features of root cells
Benefits - can be used in horticulture to allow growth of new plants from cuttings
Promoting flower and fruit formation
How it works - action of hormone causes flowers to develop - these flowers can be pollinated to allow development of seeds and fruit
Benefits - allows more fruit to be produced e.g if there are adverse weather conditions. Can also be used to produce seedless fruits
Tissue culture
How it works - hormones can stimulate growth of all types of plant cell from a mass of cells called callus
Benefits - allows species of plant that are very rare or difficult to breed to be produced more rapidly
