Biology A2 level 3.8 the nervous system. These notes were formulated using class notes, the WJEC study guide and past papers. These notes helped me to achieve an A* at A level biology!
Brings about change rapidly Brings about change slower
Short-term response Long-term response
Information is carried by neurones to specific Chemicals carried by the blood throughout
target cells/organs the body, only target cells/organs respond
Transpors electrical impulses Transports hormones
Stimulus response model
● Describes how a system responds to a stimuli
● Stimulus ⇾ detector ⇾ coordinator ⇾ effector ⇾ response
○ A stimulus is a detectable change in the internal or external environment
○ A detector contains cells which detect stimuli, and convert energy from one form
into an electrical impulse (act as transducers)
■ e.g. visible light is detected by the retina, and light energy is converted to
an electrical impulse
○ The coordinator is the central nervous system, electrical energy travels along
neurone as a nerve impulse, coordinating a response
○ An effector brings about a response (either a muscle or a gland)
○ The response is the change in the organism
A human's nervous system
● Central nervous system
○ Made up of the brain and spinal cord
○ Processes information provided by a stimulus and coordinates a response
● Peripheral nervous system
○ Is made up of neurones
○ Has two parts;
■ The somatic nervous system, which consists of pairs of nerves branching
from the brain and spinal cord inc. sensory and motor neurones
■ Autonomic nervous system which controls involuntary actions e.g.
digestion, heart beat (myogenic)
Neurones
● Three types of neurones in humans;
○ Sensory neuron - carry impulses from receptors to the central nervous system
, ○ Relay / connector neuron - located within the CNS, receive impulses from
sensory or other relay neurones and transmit them onto motor neurones
○ Motor neurone - transmit impulses from the CNS to effectors
Structure Function
Cell body Contains granular cytoplasm with ribosomes (+ rough endoplasmic
reticulum) for protein synthesis
DNA is within the nucleus and acts as the site for transcription
Axon Long extension of cytoplasm from the cell body
Carries impulses away from the cell body
Myelin sheath Surrounds the axon (and dendron in sensory neurones), made of lipids
& protein, provides electrical insulation for faster impulse transmission
Schwann cell Surrounds the axon (and dendron in SN) and produce the myelin sheath
Nodes of Ranvier Gaps in the myelin sheath between Schwann cells where the axon
membrane is exposed, 1μm wide
Allow faster nerve impulse conduction (saltatory conduction)
Axon terminal Secrete a neurotransmitter which results in depolarisation of the
adjacent neurone
Synaptic end bulbs Swelling found at the end of an axon terminal where the
neurotransmitter is synthesised
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