5.1.3 - Neuronal Communication Flashcards
What do sensory receptors do?
Detect a stimulus/changes in the internal and external environments of an organism
How do receptors act as a transducer?
They convert different types of stimuli into electrical nerve impulses
Which receptors detect light?
Photoreceptors (rods and cones)
Which receptors detect heat?
Thermoreceptors (skin)
Which receptors detect pressure?
Mechanoreceptor (Pacinian corpuscle in skin)
Where are the Pacinian corpuscles found?
Deep in the skin mainly in fingers and feet or in joints
What is the structure of a Pacinian corpuscle?
It has a single neurone, the ending of which is surrounded by layers of tissue separated by a gel
How does the Pacinian corpuscle respond to the stimulus of change in pressure?
- The membranes of the pacinian corpuscle have stretch mediated sodium channels
- When pressure is applied it deforms the neurone plasma membrane and stretches and widens the sodium channels so sodium ions diffuse in which leads to the establishment of a generator potential
What are the 3 types of neurones?
- Sensory
- Relay
- Motor
What are the common features of all 3 neurones?
- Cell body: contains the organelles found in a typical animal cell including the nucleus and proteins and neurotransmitter chemicals are made here
- Dendrons: carry the action potentials to surrounding cells
- Axon: conductive, long fibre that carries the nervous impulse along the neurone
What is the function of a sensory neurone?
Transmits electrical impulses from sensory receptors to other neurones (relay, motor or brain)
What is the structure of a sensory neurone?
They have a long dendron which carries the impulse from the sensory receptor cell to the cell body of the neurone and then an axon to carry the impulse from the cell body to the next neurone
What is the function of a relay neurone?
Transmits electrical impulses from sensory neurones to motor neurones
What is the structure of a relay neurone?
They have multiple short axons and dendrons
What is the function of a motor neurone?
Transmits electrical impulses from the CNS to the effector (muscles or glands)
What is the structure of a motor neurone?
They have one long axon and multiple short dendrons
What are myelinated neurones?
They have Schwann cells which wrap around the axon to form the myelin sheath which is a lipid and so does not allow charged ions to pass through it
What is the function of a myelin sheath?
It acts as an electrical insulator speeding up the conduction of electrical impulses
What are the gaps in the myelin sheath called?
nodes of Ranvier
Why is the transmission of electrical impulses faster in myelinated neurones than in non-myelinated neurones?
The action potential jumps from node to node (saltatory conduction) which means the action potential travels along the axon faster as it doesn’t have to generate an action potential along the entire length, just at the nodes of Ranvier
What is the resting potential?
- When a neurone is not conducting an impulse there is a difference between the electrical charge inside and outside of the neurone
- There are more positive ions, Na+ and K+ outside compared to inside so the inside of the neurone is comparatively more negative
What is the potential difference when the neurone is in resting state?
-70mV
How is the resting potential established and maintained?
- The resting potential is maintained by a sodium potassium pump involving active transport and ATP
- The pump moves 2K+ ions in and 3Na+ ions out
- This creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
- The membrane is more permeable to K+ so more are moved out resulting in the -70mV
What is needed for an action potential to generate?
Stimuli need to reach a threshold potential