Grey Matter Flashcards
What is a neurone?
A single cell, each one is a long nerve fibre which carries the nerve impulse
What is a nerve
Bundles of nerve fibres (neurones)
What are the 3 types of neurone?
- Sensory
- Motor
- Relay
State the role of dendrites and dendron.
To receive the impulse and transmit it towards the cell body.
State the role of the axon.
To transmit the impulse away from the cell body.
What is the myelin sheath made of?
Schwann cells
Describe the role of the myelin sheath.
Wraps around the axon or dendron to provide protection from damage. As it is composed of predominantly lipid membrane, it acts as an electrical insulator preventing depolarisation of the neurone in these areas.
Name the gaps between the Schwann cells.
Nodes of Ranvier
Describe the role of the Nodes of Ranvier.
They provide an area along the axon or dendron where depolarisation can occur. This enables the impulse to jump from node to node speeding up nervous impulse transmission
Which organsims have nodes of Ranvier?
Vertebrates only
Describe the reflex arc. e.g. for touching something hot
- Receptors detect a stimulus and generate a nerve impulse
- Sensory neurones conduct a nerve impulse to the CNS along a sensory pathway
- Sensory neurones enter the spinal cord through the dorsal route
- Sensory neurone forms a synapse with a relay neurone
- Relay neurone forms a synapse with a motor neurone that leaves the spinal cord through the ventral route
- Motor neurone carries impulses to an effector which produces a response. In this example the bicep contracts to raise the arm away from the flame
Explain the features of a reflec arc.
Rapid/fast – Only 3 neurones and 2 synapses are involved
Involuntary – The main impulse pathways does not travel to the brain for processing
Name the two muscles in the iris
Radial and circular muscles working as antagonistic pairs.
Which part of the nervous system controls the muscles in the iris?
The autonomic
Name the muscle that is ‘told’ to contract by the sympathetic nervous system?
Radial
Name the muscle that is ‘told’ to contract by the parasympathetic nervous system?
Circular
Describe the sequence of events that results in the narrowing of the pupil diameter due to high light intensity.
- High light intensity activates photoreceptors (rods) in the retina. Generator potentials are achieved. Bipolar cells depolarise and action potentials are created in the ganglion neurones.
- Impulses pass along the ganglion (sensory) neurones out of the eye through the optic nerve. They arrive at the pupil reflex coordinating centre in the midbrain.
- The ganglion neurones synapse with relay neurones, which then synapse with parasympathetic neurones within the midbrain.
- Impulses are sent down the parasympathetic neurones towards the optic nerve.
- The parasympathetic neurones synapse with motor neurones connected to the circular muscles in the iris.
- The circular muscles contract and the radial muscles relax. This causes the diameter of the pupil to constrict and reduce the amount of light entering the eye.
Describe the sequence of events that results in the dilation of the pupil diameter due to low light intensity.
- Low light intensity activates photoreceptors (rods) in the retina. Generator potentials are achieved. Bipolar cells depolarise and action potentials are created in the ganglion neurones.
- Impulses pass along the ganglion (sensory) neurones out of the eye through the optic nerve. They arrive at the pupil reflex coordinating centre in the midbrain.
- The ganglion neurones synapse with relay neurones, which then synapse with sympathetic neurones within the midbrain.
- Impulses are sent down the sympathetic neurones towards the optic nerve.
- The parasympathetic neurones synapse with motor neurones connected to the radial muscles in the iris.
- The circular muscles relax and the radial muscles contract. This causes the diameter of the pupil to dilate and increase the amount of light entering the eye.
