C3- The nervous system Flashcards
What does the CNS comprise of?
The brain and the spinal cord.
What is the name of the tough protective membrane that protects the brain and the spinal cord?
The meninges.
Describe the spinal cord.
- The white matter contains nerve fibres surrounded by myelin ( which are fatty so look white).
- The grey matter has less myelin and is composed mainly of nerve fibres of relay neurones and the cell body’s of relay and motor neurons.
What two nervous systems does is PNS comprised of?
The somatic nervous system and the autonomic system.
Describe the somatic nervous system.
- It contains pairs of nerves and their branches that originated in the brain or spinal cord.
- These nerves contain fibres of sensory neurons that carry impulses to the CNS and motor neurones that carry impulses from the CNS to effectors.
What is the autonomic nervous system?
It provides unconscious control of the functions of the internal organs, such as the heartbeat or digestion.
What is a reflex arc?
The neutral pathway taken by the nervous impulses of a reflex action.
Define a reflex action.
- A rapid automatic response resulting from nervous impulses initiated by a stimulus.
- The decision making area of the brain is not involved and this makes the response involuntary.
- They’re a protective function.
Identify the elements of a reflex arc.
Stimulus receptor sensory neurones relay neurones in the CNS motor neurone effector response
Name a reflex action that does not require a relay neurone.
When your knee jerks.
Briefly describe the evolution of the nervous system.
- Animals in the phyla who appear in early fossil records do not have a nervous system. They do have genes related to nerve formation though.
- Later animals have radial symmetry and their nervous system is a nerve net.
- Animals that have appeared even later have bilateral symmetry and a central nervous system.
Define a nerve net.
The simplest kind of nervous system, a diffuse network of cells that group into ganglia, but do not form a brain.
Name the two types of nerve net.
- Ganglion cells provide connections in several directions.
- Sensory cells detect stimuli.
What are the non-neuronal cells in the human nervous system called?
Glia.
What do glia cells do?
Protect and support the neurons, including generating the myelin sheath.
What type of nervous system does a hydra have?
A nerve net.
Why is the hydra used to study nerve nets?
- Has a simple pattern.
- Easy to manipulate in experiments.
- Regenerates rapidly e.g. when replacing lost tentacles
Where is the hydra’s net located?
It is in its ectoderm which is the outer of two layers of cells that make up its body wall.
What does they Hydra’s nerve net allow it to do?
- Sense light, physical contact and chemicals.
- In response it can contract, perform locomotion, hunt and feed.
- So even without a brain it shows complex movements.
What is the limitation of the nerve net found inside a Hydra?
It cannot detect the direction of a stimulus, although a larger stimulus can stimulate more cells and so triggers a larger response.
How many cell types does the Hydra’s nervous system have?
Two.
Does the Hydra’s nervous system have a myelin sheath?
No.
Compare the speed of the hydra’s nervous system to that of a human’s.
The human’s nervous systems significantly faster.
Can the Hydra’s nervous system regenerate neurones?
Yes.
What do each of the following neurones do?
- Sensory
- Motor
- Relay/ connector/ association
- Sensory- Carry impulses from the sense receptors or organs into the CNS.
- Motor- Carry impulses from the CNS to the effector organs (e.g. muscles or glands)
- Relay- receive impulses from the sensory neurones and transmit them to the motor neurones or other relay neurones.
Explain the functions of the following structures of a neurone…
- Cell body/ centron
- Cytoplasm
- Nucleus
- Cell body- Contains the nucleus and granular cytoplasm.
- Cytoplasm- It is granular and it contains many ribosomes.
- Nucleus- Holds the DNA.
Explain the functions of the following structures of a neurone…
- Nissl granules
- Dendrite
- Axon
- Nissl granules- Cytoplasmic granules comprising of ribosomes grouped on RER.
What does the following statement mean?
‘Neurones are excitable.’
They can change their resting potential.
What is the resting potential?
It is -70mV.
It is the potential difference across a neurones membrane.
What does an action potential do to the polarity of a nerve cell?
It reverses its polarity.
Describe the stages on a graph showing the phases of an action potential in relation to the potential difference of the cell.
resting potential → depolarisation → depolarisation → undershoot → resting potential
What is the fluid that runs through the axon?
axoplasm
Describe the overall charge inside a neurone at resting potential compared to outside the cell.
Inside the cell has an overall negative charge compared to outside the cell that has an overall positive charge.
Explain simply how an action potential is created.
By positive ions rushing in.
Describe the organic ions found in a nerve cell.
- They’re large.
- They remain within the cell.
- They are negatively charged amino acids.
How does K^+ move out of the cell?
Via potassium channels.
How does Na^+ move into the cell?
Via sodium channels.
How does Na^+ move out of the cell?
- Active transport
- Sodium potassium pump
