Biology Notes Paper 2
B10 - THE HUMAN NERVOUS SYSTEM
Includes Principles of homeostasis, the structure and function of the nervous system, reflex
actions, the brain, the eye, common problems of the eye
Principles of homeostasis
● Homeostasis is the regulation of conditions in the body in order to maintain optimum
function
● The nervous system enables humans to react to their surroundings and to coordinate
their behaviour
● In the body, homeostasis controls blood glucose concentration, body temperatures
and water levels
● Stimulus → Receptors → Coordination Centres → Effectors
● A stimulus is a change in your environment which you need to react to (temperature,
moisture, humidity)
● A receptor is a cell that can detect changes in the environment
● Coordination centres (brain, spinal cord, pancreas) receive and process the
information from the receptors
● Effectors (Muscles and glands) these make the responses happen to change body
conditions
Structure and function of the nervous system
● The nervous system uses electrical impulses to enable you to react quickly to your
surroundings
● Stimulus → Receptor → Sensory Neurone → Relay Neurone → Motor neurone →
effector → response
● Once a receptor detects a stimulus, the information is passed as an electrical
impulse that passes along neurones
● Sensory neurones carry these impulse travels along the neurone until it reaches the
CNS (Central Nervous System)
● The CNS is made of the brain and spinal cord
● The PNS (peripheral nervous system) includes all the nerves outside the CNS and
are carried by motor neurones
● They involve involuntary responses such as heartbeat and breathing rate
● Axon is the neurone fibre that carries the impulse
● Dendrites are the ends of the neurone that receive or pass on a message
● Synapse is the gap when two neurones meet.
● Reflexes don't include the conscious parts of the brain
The brain
● The brain is made up of billions of interconnected neurones that control complex
behaviour
● The cerebral cortex controls consciousness, memory, intelligence and language
● The Cerebellum coordinates with muscular activities and balance
● The hypothalamus controls body temperature
● The medulla controls unconscious activities such as heart rate and breathing rate
, The Eye
●
● Sclera - tough and strong to make sure eyeball isn’t damaged
● Iris - controls size of the pupil
● Ciliary muscle - change the shape of the lens to fine focus light onto the retina
● When it is dark, the radial muscles contract and circular muscles relax which mean
the pupil gets bigger
● In bright light, the radial muscles relax and circular muscles contract which means
the pupil gets smaller
The pathway of light
● Light rays pass through the transparent front of the eye - the cornea - which starts
the focussing of the light rays
● They then pass through the pupil in the centre of the iris, which is the coloured part of
the eye
● They then pass through the lens, which focuses the light rays onto the back of the
eye, the retina, which contains receptor cells to detect light intensity and colour
● The receptor cells send electrical impulses down the optic nerve to the brain
● Cornea → Pupil → Lens → Retina → Receptors → Brain
Common problems of the eye
B10 - THE HUMAN NERVOUS SYSTEM
Includes Principles of homeostasis, the structure and function of the nervous system, reflex
actions, the brain, the eye, common problems of the eye
Principles of homeostasis
● Homeostasis is the regulation of conditions in the body in order to maintain optimum
function
● The nervous system enables humans to react to their surroundings and to coordinate
their behaviour
● In the body, homeostasis controls blood glucose concentration, body temperatures
and water levels
● Stimulus → Receptors → Coordination Centres → Effectors
● A stimulus is a change in your environment which you need to react to (temperature,
moisture, humidity)
● A receptor is a cell that can detect changes in the environment
● Coordination centres (brain, spinal cord, pancreas) receive and process the
information from the receptors
● Effectors (Muscles and glands) these make the responses happen to change body
conditions
Structure and function of the nervous system
● The nervous system uses electrical impulses to enable you to react quickly to your
surroundings
● Stimulus → Receptor → Sensory Neurone → Relay Neurone → Motor neurone →
effector → response
● Once a receptor detects a stimulus, the information is passed as an electrical
impulse that passes along neurones
● Sensory neurones carry these impulse travels along the neurone until it reaches the
CNS (Central Nervous System)
● The CNS is made of the brain and spinal cord
● The PNS (peripheral nervous system) includes all the nerves outside the CNS and
are carried by motor neurones
● They involve involuntary responses such as heartbeat and breathing rate
● Axon is the neurone fibre that carries the impulse
● Dendrites are the ends of the neurone that receive or pass on a message
● Synapse is the gap when two neurones meet.
● Reflexes don't include the conscious parts of the brain
The brain
● The brain is made up of billions of interconnected neurones that control complex
behaviour
● The cerebral cortex controls consciousness, memory, intelligence and language
● The Cerebellum coordinates with muscular activities and balance
● The hypothalamus controls body temperature
● The medulla controls unconscious activities such as heart rate and breathing rate
, The Eye
●
● Sclera - tough and strong to make sure eyeball isn’t damaged
● Iris - controls size of the pupil
● Ciliary muscle - change the shape of the lens to fine focus light onto the retina
● When it is dark, the radial muscles contract and circular muscles relax which mean
the pupil gets bigger
● In bright light, the radial muscles relax and circular muscles contract which means
the pupil gets smaller
The pathway of light
● Light rays pass through the transparent front of the eye - the cornea - which starts
the focussing of the light rays
● They then pass through the pupil in the centre of the iris, which is the coloured part of
the eye
● They then pass through the lens, which focuses the light rays onto the back of the
eye, the retina, which contains receptor cells to detect light intensity and colour
● The receptor cells send electrical impulses down the optic nerve to the brain
● Cornea → Pupil → Lens → Retina → Receptors → Brain
Common problems of the eye
