Component 3 - The Nervous System Flashcards
What is the nervous system
The nervous system enables animals to respond to changes in the external or internal environment, also known as stimuli
What is the pathway for a nervous pathway
Stimulus → Receptor → Sensory neurone → Co-ordinator → Motor neurone → Effector → Response
What part of the nervous system is the coordinator located in
The Central Nervous System
What part of the nervous system are the motor and sensry neurone located in
The peripheral nervous system
What is a reflex action
A reflex action is a fast, automatic response to a stimulus that has a protective function
How do reflex actions occur to protect the body
Receptors detect the harmful stimulus and
send impulses through sensory neurones to a relay neurone in the spinal cord.
This sends an impulse through a motor neurone to an effector,
which responds to protect the body
What does grey matter contain
Nuclei and cell bodies
What does white matter contain
Myelinated cells
What is the spinal cord surrounded by
Membranes called the meninge
In a Hydra, what is the CNS
A Nerve Net
In a Hydra, in which direction can impulses travel
Both
What stimuli can be detected by receptors on Hydra
- Light
- Chemicals
- Physical contact
What is the function of a dendrite
Transmits impulses into the cell body
What is the funcition of Nodes of Ranvier
Gaps in the myelin sheath that form long local circuits with the next node, speeding up transmission
What is the function of schwann cells
wrap around the axon and form the myelin sheath, an electrical insulator
What is the function of the Axon
Transmits the impulse to the axon endings away from the cell body
Where is the cell body located in a motor neurone
At the dendrites
Where is the cell body located in a sensory neurne
On the axon away from the Dendrites
Where is the cell body located in a relay neurone
At the dendrites
Where is the cell body located in a relay neurone
At the dendrites
What is resting potential
-70mV
How is resting potential maintained
- The axon is more negative than the outside of the cell
- Na+ channels are closed, K+ channels are open
- A Na+/K+ pump uses ATP to pump 3Na+ out of the axon and 2K+ in
- K+ diffuses out but Na+ can’t diffuse in causing a charge difference
How does depolarisation occur
- A stimulus above the threshold (-40mV) causes Na+ channels to open
- Na+ ions diffuse rapidly into the axon
- The membrane depolarises to +40 mV
How does repolarisation occur
- Na+ channels close and K+ channels open
- K+ diffuse out rapidly
- Overshoot causes hyperpolarisation
- Resting Potential is restored
What is the All or Nothing Law
If the stimulus is below the threshold (-40 mV) then no action potential occurs and the membrane is not depolarised.
How does the action potential travel along a neurone in terms of sections
Depolarisation of the membrane sets up a local circuit with the next section. More voltage gated sodium channels open in the next section open causing further depolarisation.
What is the refractory period
During repolarisation the membrane can’t form an action potential due to Hyperpolarisation (-90mV)
What is the significance of the Refractory period
The impulse only travels foward in one direction
What 3 factors affect transmission speed of an impulse in a neurone
- Axon Diameters
- Temperatures
- Myelinated or unmyelinated neurones
How do larger axon diameters affect transmission speed
Larger axon diameters increase transmission speed due to less resistance
How do higher temperatures affect transmission speed
Higher temperatures increase transmission speed due to an increased rate of diffusion
How do myelin sheaths affect rate of transmission
Myelin sheaths speed up transmission because depolarisation can only happen at nodes of Ranvier. The local circuits are longer. Action potentials jump from one node to the next. - Saltatory conduction
What is a synapse
The gap between 2 nerve cells. The axon terminals of one neurone meet an effector or another neurone.
How does a nerve impulse travel through a synapse
- Depolarisation of the axon membrane causes Ca2+ channels to open
- Ca2+ diffuse into the synaptic knob
- Ca2+ cause vesicles containing neurotransmitter to fuse with the presynaptic membrane
- Neurotransmitter is released into the synaptic cleft by exocytosis
- Neurotransmitter diffuses over the synaptic cleft and binds to receptors on the post synaptic membrane.
- The binding causes Na+ channels on the postsynaptic membrane to open
- The postsynaptic membrane depolarises
- An enzyme breaks the neurotransmitter down and the products are taken into the synaptic knob and resynthesised and packaged
What is the name of a neurotransmitter
acetylcholine
What is an Antagonist
Antagonists affect synapses by preventing postsynaptic depolarisations
What is an Agonist
Agonists cause more postsynaptic depolarisations
What 3 ways could an antagonist work
- preventing Ca2+ channels opening and thus preventing exocytosis
- blocking receptors
- hyperpolarising the post-synaptic membrane so it is harder to reach threshold
