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.
