Biology - 10 The Human Nervous System

Homeostasis

the tendency to maintain a constant internal state

Why is temperature regulated?

to keep the enzymes of the body at their optimum temperature

What internal conditions are controlled? [3]

- body temperature
- water content of the body
- blood glucose concentration

Receptor

a cell that detects a change in a condition

Effector

an organ or cell that acts in response to a stimulus.

Stimuli

changes in the environment

Coordination centre

receives and processes the information then organises a response

Neurone

a cell that transmits electrical impulses in the nervous system

Nerve

a bundle of neurones

Central nervous system

brain and spinal cord

Sensory neurone

carries impulses from receptor to CNS

Motor neurone

carries impulse from CNS to effector

Nervous system process [7]

- stimulus
- receptor
- sensory neurone
- coordinator (CNS)
- motor neurone
- effector
- response

Reflex

an automatic response to a sensory stimulus

What do reflexes skip?

the conscious mind

What do reflexes do? [2]

- respond to dangerous stimuli
- control unconscious body functions

Relay neurone

short neurone that connects sensory and motor neurones

Where are most relay neurones?

in the spinal cord

Reflex arc

the nerve pathway involved in a reflex action

Reflex arc components [7]

- stimulus
- receptor
- sensory neurone
- relay neurone
- motor neurone
- effector
- response

Synapse

a junction where information is transmitted from one neuron to the next.

How does an impulse travel across a synapse?

neurotransmitters carry it across the gap

Neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

Cerebral cortex function [4]

- consciousness
- intelligence
- memory
- language

Cerebellum function [2]

- coordinating muscular activity
- balance

Medulla function [1]

- unconscious activities

Hypothalamus function [1]

- monitors and regulates conditions

Pituitary gland function [1]

- produces many hormones

How has the brain been investigated? [3]

- studying brain-damaged people
- electrically stimulating parts of the brain
- MRI scans

What does MRI stand for?

magnetic resonance imaging

What does an MRI do?

helps determine structure of brain to find tumours or abnormalities

Lens function

focuses light onto retina

Cornea function

allows light to enter the eye and refracts light

Pupil function

allows light to enter the eye

Iris function

controls the size of the pupil

Suspensory ligament function

slackens or tightens to control the thickness of the lens

Ciliary muscle function

relaxes or contracts to control the thickness of the lens

Focussing on a distant object [3]

- ciliary muscles relax, increasing diameter
- suspensory ligaments tighten
- lens thins

Focussing on a nearby object [3]

- ciliary muscles contract, decreasing diameter
- suspensory ligaments slacken
- lens thickens

Retina function

receive light that the lens has focused and converts to neural signals

Sclera function

protects eye and maintains its shape

Optic nerve function

carries impulses from the eye to the CNS

Blind spot

where the optic nerve meets the eye

Accomodation

the lens changes shape to focus

In bright light [3]:

- circular muscles contract
- radial muscles relax
- pupil constricts

In dim light [3]:

- circular muscles relax
- radial muscles contract
- pupil dilates

Myopia

short sightedness - where light is focused in front of the retina

Hyperopia

long sightedness - where light is focused behind the retina

Myopia causes [2]

- overly convex lens
- long eyeball

Hyperopia causes [2]

- overly flat lens
- short eyeball

Myopia treatment

glasses with a concave lens

Hyperopia treatment

glasses with a convex lens

Other treatments for myopia and hyperopia [3]

- contact lenses
- laser eye surgery
- replacement lenses

How does laser eye surgery work [2]

- for myopia, the cornea's thickness is reduce so light is refracted less
- for hyperopia, the cornea's curve is changed to refract light more effectively

Replacement lens types [2]

- permanent contact lens implanted; natural lens left in place
- faulty lens is replaced with artificial lens