Biology GCSE AQA Year 10: Homeostasis - Nervous System

What is homeostasis?

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

Why do living organisms need to respond to changes in their environment?

To maintain optimal conditions for enzyme action and all cell functions

What needs to be kept constant in our bodies?

. blood glucose concentration

. body temp

. water levels

What types of responses may these automatic control systems involve?

. nervous responses

. chemical responses

What do all control systems include?

. cells called receptors which detect stimuli

. coordination centres (such as the brain, spinal cord, and pancreas) that receive and process information from receptors

. effectors: muscles or glands which bring about responses which restore optimum levels

How do glands respond?

By secreting chemical substances such as hormones or enzymes (e.g salivary glands release saliva at smell of food cooking)

How do muscles respond?

By contracting and relaxing

What type of signal is in the nervous system?

electrical impulses

How does the signal in the nervous system travel?

passes along neurones

How fast is the signal in the nervous system?

very fast

how long does the signal in the nervous system last?

short - 1ms

What type of signal is in the hormonal system?

hormones

How does the signal in the hormonal system travel?

carried by the blood

How fast is the signal in the hormonal system?

slower

How long does the signal in the hormonal system last?

long-lasting

What are the sense organs for the 5 senses?

. eyes

. ears

. tongue

. nose

. skin

What is the function of neurones?

to transmit electrical impulses from one part of the body to another to bring about a response to a stimulus

What are some adaptations of neurones?

. Long thin axons and dendrons - carry impulses over long distances

. Numerous branched nerve endings (dendrites) - allow the neurone to receive and pass on messages to other cells

. Insulatory myelin sheaths - speeds up the impulse

. Nucleus - to control all the chemical reactions in the cell

. Many mitochondria - provide energy through respiration

What is the function of the nervous system?

Enables humans to react to their surroundings and to coordinate their behaviour

How does the CNS work?

. Information from receptors passes along neurones as electrical impulses to the CNS (central nervous system)

. The CNS is the brain and spinal cord

. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones

What are the steps of a nervous response?

stimulus -> receptor -> coordinator -> effector -> response

What is the function of the sensory neurone?

Carries electrical impulses from the receptors to the CNS

What is the function of the relay neurone?

Transmits electrical impulses from the sensory to the motor neurone

What is the function of the motor neurone?

Carries electrical impulses from CNS to effectors

What is a synapse?

. Junction between any 2 neurones in the nervous system

. gap = synaptic gap

. electrical impulse can't jump it

What happens at a synapse?

. synapse = a junction between 2 neurones

. there is a gap between the 2 neurones at a synapse

. the electrical impulse can't jump the gap

. the first neurone releases chemicals (neurotransmitters) into the gap

. the chemicals diffuse across the gap and bind to receptors on the second neurone

. Which causes an electrical impulse to be sent through the second neurone

What is a reflex action?

. An automatic and rapid response to a stimulus

. Does not involve the conscious part of the brain

. minimises any damage to the body from potentially harmful conditions

What is the brain?

. controls complex behaviour

. made of billions of interconnected neurones

. has different regions that carry out different functions

What is the function of the cerebrum / cerebral cortex?

controls consciousness, intelligence, memory, personality, emotions, and language

What is the function of the cerebellum?

controls balance, coordination of movement, and muscular activity

What is the function of the medulla oblongata?

Controls unconscious activities, such as the heartbeat, movements of the gut, and breathing

What is the function of the pituitary gland?

. master endocrine gland

. produces many different chemicals (hormones) which play a big part in coordinating and controlling body systems

What is the function of the hypothalamus?

. part of the brain

. controls body temp and water balance in the body

What are the difficulties associated with brain medicine?

. Brain is a very complex and not fully known how it works

. delicate so easily damaged

. We don't know what effect surgery could have until it's too late

. Damage done in surgery can seriously affect the patient's quality of life

. Many drugs won't pass from the blood into the brain

. Does not easily repair itself

. Surgery may cause irreversible damage

. Each case is unique, complicating understanding and treatment

How do MRI scans help scientists understand the brain?

. Uses strong magnetic fields and radio waves to show details of brain structure and function

. patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active while tasks are carried out

. Can be used to scan brain after a stroke to see where the damage is

What is EBS and what does it tell us?

. Electrical Brain Stimulation is when scientists remove the top of the skull and apply weak electric currents to different parts of the brain

. As there are no sensory nerve endings in the brain this can be done on conscious patients who can say what they feel (hunger, anger, paralysis, etc.) while it happens

How did doctors in the past begin to understand what different parts of the brain did?

. Doctors studied people with brain damage

. Able to note what part of the brain was damaged and so knew that part was responsible for any changes (like personality)

. Often not until after death

What is the eye?

a sense organ containing receptors sensitive to light intensity and colour

What is the function of the blind spot?

. Point where the optic nerve attaches to the eye

. No light sensitive cells found here

What is the function of the sclera?

Tough white protective layer around whole eye

What is the function of the ciliary muscle?

Attached to the suspensory ligaments which pull on the lens to make it thin

What is the function of the cornea?

Transparent layer; curved to bend the rays of light

What is the function of the iris?

Coloured layer of muscle that controls the amount of light entering the eye

What is the function of the lens?

Rubbery structure that bends the light; thickness can be altered

What is the function of the optic nerve?

Carries nerve impulses to the brain

What is the function of the pupil?

Hole in the iris through which light passes to enter the eye

What is the function of the retina?

Inner light sensitive layer that contains rod cells and cone cells that detect light

What is the function of the suspensory ligaments?

Hold the lens in place and pull on it to change thickness

What is accommodation?

the process of changing the shape of the lens to focus on near or distant objects

What changes in the eye to focus on a near object?

. ciliary muscles contract so have a smaller diameter

. suspensory ligaments loosen

. the lens is then thicker and refracts light rays strongly

What changes in the eye to focus on a distant object?

. ciliary muscles relax so have a larger diameter

. suspensory ligaments are pulled tight

. the lens is then pulled thin and only slightly refracts light rays

What are cones used for?

colour vision

What are rods used for?

night vision

What is the pupil reflex?

. Iris controls the amount of light that reaches the retina

. Iris contains 2 muscles that alter the size of the pupil: circular muscles and radial muscles

. The amount of light entering the eye is controlled to prevent damage to the retina by bright light

What happens to the eye in bright light?

. circular muscle contracts so diameter is smaller

. radial muscle relaxes

. pupil size = smaller

. coloured image focused on retina

. cones active

What happens to the eye in dim light?

. circular muscle relaxes so diameter is larger

. radial muscle contracts

. pupil size = larger (dilated pupil)

. black and white image focused on retina

. rods active

What do you call only being able to see things close to you well?

myopia (short sightedness)

What do you call only being able to see things far from you well?

hyperopia (long sightedness)

In normal vision, where is the image formed and why?

. on retina

. light is refracted by cornea and lens in eye

In myopia, where is the image formed and why?

. forms in front of the retina

. either because the eyeball is too long for the strength of the lens or the lens is too sharply curved

. light is being refracted too much

How can myopia be corrected?

. by placing a concave lens in front of the eye

. this diverges the rays of light

In hyperopia, where is the image formed and why?

. focused behind retina

. either because eyeball is too short or lens is too flat and thin and has lost elasticity

. light not refracted enough

How can hyperopia be corrected?

. placing a convex lens in front of the eye

. converges rays of light

What are contact lenses?

. lenses placed on surface of the eye

. do same job as glasses but can't be seen and make life easier for playing sport and general activities

Pros and cons of hard contact lenses

. last a long time

. can sometimes provide sharper vision

. have to be removed overnight and kept sterile to prevent infection

. can be uncomfortable to wear

Pros and cons of soft contact lenses

. more comfortable

. don't last as long

How does laser eye surgery treat myopia?

. lasers are used to reduce thickness of cornea so it refracts light less strongly

. means lens now focuses distant light on retina instead of in front of it

How does laser eye surgery treat hyperopia?

lasers are used to change curve of cornea so it refracts light from close objects more effectively

Who can have laser eye surgery?

adults once their eyes have stopped growing and their vision has become stable

What are replacement lenses?

adding another lens inside the eye to correct the visual defect permanently

What are the 2 main techniques for replacement lenses?

1) a permanent contact lens is implanted into the eye and the natural lens is left in place

2) the faulty lens is replaced by an artificial lens

What are the risks of replacement lenses?

. damage to retina

. cataracts developing if the natural lens remains in place

. infections