Paper 2: Topic 5 Homeostasis & response - Nervous system (LV) Flashcards
Why do single-celled organisms not need a nervous system?
They can respond to changes in their environment easily and directly
Why does a multi-cellular organism need a nervous system?
- So that they can react to changes in their environment AND control and regulate changes in the different part of the body
- The nervous system allows cells to communicate with each other so a controlled response occurs
- A nervous system ensures co-ordinated behaviour
What structures are the main parts of the central nervous system?
- Brain
- Spinal cord
Describe how the central nervous system is connected to the other parts of the body?
Sensory and motor neurones
Define the term receptor
A cell that detects a stimulus (change in the environment)
AND
that can generate/produce a nerve impulse
State 4 different types of receptor
- Sound receptors
- Light receptors
- Chemical receptors
- Pressure receptors
Define the term effector
A muscle or gland that responds to nerve impulses and cause a response
State how muscles respond to nerve impulses
They contract
HINT: do NOT write they “contract AND RELAX” - the impulse only causes them to contract
State how glands respond to nerve impulses
Glands secrete a hormone into the plasma
State the function of the central nervous system
To receive and process information from the receptors AND
to co-ordinate the response
Write the pathway of a nerve impulse from stimulus to response (reflex arc)
Stimulus → receptor -→ sensory neurone → central nervous system → motor neurone → effector → response
Explain why not all multi-cellular organisms have a nervous system
Only large, multi-cellular organisms have a nevous system
Small multi-cellular organsims e.g. jelly fish rely on reflex reponses
State the function of a neurone
To transmit a nerve impulse
Define the term ‘synapse’
A junction between two neurones
Describe how a nerve impulse is transmitted across a synapse
- Neurotransmiters are released into the synapse from the synaptic knob
- The neurotransmitters diffuse across the synapse
- The neurtransmitters bind to receptors on the membrane of the next neurone
- And this then triggers the nerve impulse in the neurone
Define the term neurotransmitter
A specialised chemical that is released from the end of the axon of one neurone that can diffuse across a synapse to trigger a nerve impulse in the next neurone
Explain the purpose of reflex actions
To prevent damage or harm to the organism
State 5 examples of relex actions
- Blinking
- Coughing
- Sneezing
- Vomiting
- Knee-jerk
Describe a reflex arc
Hint: 6 main stages
- A change in the environment occurs (a stimulus)
- A receptor cell detects the stimulus
- A nerve impulse is sent along the sensory neurone to the CNS
- The nerve impulse is passed through the relay neurone in the CNS
- The nerve impulse is sent along a motor neurone to the effector
- The effector brings about a response
What is the role/function of a sensory neurone?
To transmit a nerve impulse from the receptor to the relay neurone
What is the role/function of a relay neurone?
To transmit a nerve impulse from the sensory neurone to the motor neurone
What is the role/function of a motor neruone?
To transmit a nerve impulse from the relay neurone to the effector
Explain the advantage of using reflex actions
- Quicker response time i.e. rapid response
- Which reduces damage and harm to the organism
Define a reflex action
Hint:
This is a similar question to “state the charcateristics of a reflex action”
A rapid, automatic response that does not involve the conscious part of the brain
Characteristics of a reflex action:
- rapid / fast
- involuntary response i.e. subconcious



