Homestasis (Nervous)

What is Homeostasis

The regulation of the internal conditions of a cell or organism to maintain the optimum conditions for it to function in response to internal or external changes

What does homeostasis do for enzymes

Maintains the optimum conditions for enzyme action

In the human body what conditions affect enzyme action

Blood glucose concentration, body temperature, water levels

What two systems might the body use to respond to a change

Chemical or nervous

What do all control systems include

receptors, coordination centres and effectors

What is a receptor

A cell that can detect stimuli

What are the 3 main coordination centres in the human body

Brain, Spinal cord and pancreas

What are the two types of effectors

muscles or glands

What does the nervous system do

It enables humans to react to stimuli and coordinate their behaviour

How do we respond to stimuli

An electrical impulse is passed from receptors through a sensory neurone to the central nervous system where the relay neurone passes the impulse through to the motor neurone which passes the impulse to the effector causing it to respond to the stimuli

What are the 2 ways the body can respond to a stimulus

Muscles contracting or glands secreting hormones

What is the stimulus response pathway

stimulus → receptor → coordinator → effector → response

What is the reflex arc

stimulus → receptor cell → sensory neurone → CNS → motor neurone → relay neurone → effector

What makes reflexes different from normal actions

They are rapid and automatic. This is because the impulse bypasses the brain and goes to the spinal cord instead so we don’t realise we are doing it until after we have completed the action

What area of the brain is this

Cerebral Cortex

What part of the brain is this

Cerebellum

What part of the brain is this

The Medulla

What does the cerebral cortex do

It control consciousness, intelligence, memory and language

What does the pituitary gland do

Produces hormones

What does the hypothalamus do

It controls body temperature, hunger, thirst and blood pressure

What does the pons do

Connects cerebellum to cortex

What does the cerebellum do

Muscular Coordination and balance

What does the spinal cord do

Coordinates reflexes

Why is it difficult to study the brain

It is complex and delicate, there are lots of neurons, synapses and neurotransmitters, encased by skull, difficult to treat illness and surgery is hard

What three ways can we study the brain

Studying the effect of injury, Electrical brain stimulation and MRI

How does electrical brain stimulation work

Exposing parts of the brain and stimulating it with an electrode

What are the pros of electrical brain stimulation

It links specific parts of the brain to their function

What are the cons of electrical brain stimulation

There is a risk to health with surgery

What is an MRI machine

A machine that takes photos of your brain using magnets

What are the pros of MRI’s

They are minimally invasive and it shows the whole brain

What are the cons of MRI’s

Expensive

Where is the cornea

On the front of the eye on top of the iris

Where is the iris

Under the cornea and sclera on the front of the eye

Where is the pupil

The pupil is a hole in the iris

Where is the lens

behind the pupil held in place by the suspensory ligaments and ciliary muscles

Where are the ciliary muscles

Next to the lens, holding it in place with the suspensory ligaments

Where are the suspensory ligments

They attach the ciliary muscles to the side of the eye

Where is the sclera

Around the outside of the eyeball

Where is the retina

At the back of the eye

Where is the optic nerve

On the retina, leading to the brain

Where is the vitreous humour

Inside the eye

What is the function of the retina

It contains rods and cones which are receptor cells for light and colour

What is the function of the optic nerve

The sensory neuron that transmits impulses to the brain

What is the function of the sclera

Protects the eye from injury

What is the function of the cornea

Refracts light onto the lens

What is the function of the iris

To change the size of the pupil

What is the function of the pupil

To allow light into the eye

What is the function of the lens

Refracts light onto the retina

What is the function of the ciliary muscles

They change the shape of the lens

What is the function of the suspensory ligaments

Help change the shape of the lens

What is the function of the vitreous humour

To maintain the shape of the eye

How does the eye respond to bright light

The pupil contracts

Why does the pupil contract when in contact with bright lights

To stop too much light getting in the eye and damaging the retina

How does the pupil contract

The circular muscles contract and the radial muscles relax

What does the eye do in dim light

The pupil dilates

Why does the pupil dilate in dim light

To allow more light into the eye so that we can see

How does the pupil dilate

The circular muscles relax and the radial muscles contract

What does the lens do when focusing on something far away

The lens becomes thin

How does the lens become thin when focusing on an object far away

The ciliary muscles relax and the suspensory ligaments contract

How does the lens change when focusing on an object close to you

Then lens becomes thicker

How does the lens become thicker when focusing on objects close up

The ciliary muscles contract and the suspensory ligaments relax

What are the 2 most common defects of the eye

Myopia and Hyperopia

What is myopia

Myopia, or nearsightedness, is when the lens is too thick or the distance between the lens and retina is too great so the image is in focus before the retina

What type of lens is used to treat myopia

A concave lens

What is hyperopia

Hyperopia or farsightedness, is when the lens is too thin or the distance between the len and the retina is too small so the image focuses behind the retina

What lens is used to treat hyperopia

A convex lens

How can myopia and hyperopia be treated

Glasses, contact lenses, laser eye surgery and lens replacement surgery

What are contact lenses

Contact lenses are small plastic lenses that sit on top of the eye and refract light in the same way glasses do

What are the pros of contact lenses

They are invisible and pain free

What are the cons of contact lenses

They are expensive, they are susceptible to infection and hard lenses require upkeep

What is laser eye surgery

When a laser is used to change the shape of the cornea

How are lasers used to treat myopia

The cornea is slimmed down reducing the refracting power

How are lasers used to treat hyperopia

The cornea’s shape is changed to increase the refracting power

What are the pros of laser eye surgery

Its permanent and invisible

What are the cons of laser eye surgery

Expensive, susceptible to infection, painful recovery

What is a lens replacement surgery

A surgery that replaces the lens with a plastic lens

What are the pros of lens replacement surgery

Permanent, invisable

What are the cons of lens replacement surgery

Expensive, risk of complication and invasive

What is an FMRI

A functional MRI

How is an FMRI different from a regular MRI

It shows brain activity

Why do the ciliary muscles push on the lens when contracted

Because their diameter decrease

If an impulse is weaker how does this affect the muscles

They relax

If an impulse is stronger how does this affect the muscles

The muscles contract