4.5 Homeostasis

Biology GCSE Higher P2

What is homeostatis?

The regulation of the conditions in our body maintaining stable internal environment at optimum levels

What does it do?

Responds to any change in internal or external conditions

What are the 3 main components in automatic control systems?

Receptors, coordination centres and effectors

What is a stimulus?

A change in your environment than requires a response

Give some examples of stimuli?

Light, sound, touch, pressure, pain, chemical or temperature

What do the receptors do?

Detect the stimulus when either temp or water is high or low

What happens after the receptors?

Receptors send messages to the cns which organise a response to the effector

Give examples of the central nervous system?

The brain or spinal cord

How is the CNS connected to the rest of the body?

Through sensory and motor neurones

What is an effector?

Muscles or glands that bring about a response

What do the muscles and glands do in response?

Muscles contract and glands secrete chemical substances(hormones)

What is a sensory neurone?

Neurones that carry information from the receptors to the cns

What is a relay neurone?

Neurones that carry impulses from the sensory to the motor neurones

What is a motor neurone?

Neurones that carry information from the cns to the effectors

What is the nervous system?

It is what allows you to react to your surroundings

What is a synapse?

It is the nerve signal being transferred by chemicals which move across the gap, sending a electrical signal to the next neurone

What is a reflex? Why are they important?

quick automatic response to a stimulus to avoid harm

Doesn't use conscious brain so faster

What is a reflex arc?

The passage of the information, that brings around a response

Process of Reflex Arc

1. Sensory receptor detects stimulus

2. Impulses is carried by sensory neurons to relay neurones

3. From spinal cord to motor neurons

4. Motor neurons causes muscles of effector to contract

5. Impulse is transferred to brain for conscious awareness of stimulus

What happens if the body temp is too low or high

1)Temperature receptors detect temp. is too high/low

2) Thermoregulatory centre receives info. from temperature receptors and triggers effectors automatically

3) Effectors produce a response and counteract change

Responses that reduce body temp-

Hairs lie flat, sweat and blood vessels get wide and more blood flows closer to the surface of the skin (vasodilation)

Helps transfer energy to environment

Responses that increase body temp-

Hairs stand up, no sweat, shivering and blood vessels constrict to close of skins blood supply(vasoconstriction)

Shivering needs respiration( as muscles are contracting) which transfers some energy to warm the body

What is the body's core temp?

37 degrees c

What is the sclera?

The tough supporting wall of the eye

What is the cornea?

Outer layer, bends light into the eye

What is the pupil?

The hole in the centre where light enters

What is the iris?

Controls the diameter of the pupil and how much light enters

What is the retina?

Contains receptor cells- one sensitive to light intensity and the other is colour

What is the lens?

Focuses the light into the retina

What is the ciliary muscles and suspensory ligaments?

Control shape of the lens

What is the optic nerve?

Carries impulses from the receptors on the retina to the brain

What happens when bright light enters?

Photoreceptors in retina detect change in light

The circular muscles contract and the radial muscles relax, reducing the amount of light that enters

What happens in dim light?

The radial muscles contact and the circular muscles relax which makes pupil wider

What is long sightedness?

lens or muscles not powerful enough to bring light to focus on retina. light vocal point is behind retina (convex lens)

bottom diagram is with corrective lenses

What is short sightedness?

naturally too powerful lens, unable to focus on distant objects, refracts light too much(concave lens)

bottom diagram is with corrective lenses

eye lenses when looking into distance

for distant objects the light does not have to be refracted by a big angle

Ciliary muscles relax so suspensory ligaments contract

This makes lens go thin

eye lenses for near objects

For near objects the light has to be refracted through a big angle. ciliary muscles contract making the lens thicker

Increases amount of refracted light

looks like a diamond on its side

Evaluation of contact lenses

Popular as they are lightweight and almost invisible

More convenient

Soft lenses are more comfortable then hard yet higher risk of eye infection

Evaluation of laser eye surgery

Laser used to vaporise tissue, changing shape of cornea.

Can precisely control and correct the vision

Risk of infection and vision becoming worse

Evaluation of replacement lens surgery

Natural lens of eye removed and artificial plastic lens inserted

Higher risks than laser eye surgery and can damage retina(loss of sight possible)

What is the brain made from?

Millions of interconnected neurones

What is the brain in charge of?

It is in charge of our complex behaviours, controls and coordinates everything we do

What is the cerebral cortex?

The outer wrinkly layer of the brain, controls consciousness, memory and language

What is the medulla?

The base, controls unconscious activities like breathing, movement in the intestines and heartbeat

What is the cerebellum?

At the back, responsible for muscle contraction & balance

what is the hypothalamas

controls homeostasis and pituitary gland

pituitary gland in head

Secretes hormones involved in homeostasis

How have scientists mapped the regions of the brain?

Studying patients with brain damage: If small part has been damaged, effect on patient can tell damaged part of the brain

Electrical stimulating: Pushing tiny electrode into tissue and giving zap. By observing what stimulating parts of brain does, possible to get idea of what those parts do

MRI scans: Produces highly detailed picture of brain

Used to find out what areas of the brain are active when people are listening to music etc.

What are the risks of investigating the brain?

It is incredibly complex and delicate so treatment is difficult

Also has physical risks, such as physical damage to brain or increased problems with brain function

What is reaction time?

The time it takes to respond to a stimulus

Required Practical: Reaction Time Method

Have someone catch a ruler from a set height three times

Calculate average for how fast they catch it depending on what cm mark and use a conversion table to convert ruler measurements to reaction times

Then give them caffeine and wait 10 minutes and repeat experiment

Calculate difference in average between the 2

Required Practical : Reaction Time Control variables

Person catching ruler uses dominant hand

Dropping same ruler same height and orientated the same direction with 0 facing down

If caffeine investigated, none should be consumed or if background noise, room is silent for first run.

What is reaction time affected by?

Age, drugs or gender

synapse

connection to neurone/gap

thermoregulatory centre of the brain

near hypothalamus, monitors temp of blood and will get info from the skin and surface temp

How do signals travel across a synapse?

Chemicals diffuse across the synapse from one neurone to the next

What are the differences between nerves and hormones?

Nerves:

Very fast action

Act for short time

Act on very precise area

Hormones:

Slower action

Act for long time

Act more generally

How is blood glucose regulated?

If too high, insulin secreted, glucose moves from blood into liver and muscle cells and insulin makes liver turn glucose into glycogen

If too low, glucagon secreted which makes liver turn glycogen into glucose.

How is water content controlled?

1) .The amount of water reabsorbed in the kidney nephrons is controlled by anti-diuretic hormone (ADH).