Neuronal Communication Flashcards
1
Q
What are neurons
A
- specialised nerve cells
- transmit electrical impulses rapidly around the body so that an organism can respond to changes in its internal and external environment
2
Q
Outline the structure of a neuron
A
- cell body; contains a nucleus surrounded by cytoplasm which contains large amounts of mitochondria and endoplamsic reticulum which are involved in the production of neurotransmitters
- dendron; short extensions which divide into dendrites and transmit electrical impulses towards the cell body
- axon; singular, elongated nerve fibres that transmit impulses away from the cell body, it is long and has a cylindrical shape consisting of a narrow region of cytoplasm surrounded by a plasma membrane
3
Q
Name the 3 types of neuron
A
- sensory - transmits impulses from sensory receptors to the CNS
- relay - transmits impulses between sensory neurons and motor neurons
- motor - transmits impulses from CNS to effectors
4
Q
What are myelinated neurons
A
- neurones surrounded by a myelin sheath which is made from Schwann cells
- acts as an insulating layer which allows myelinated neurons to conduct the electrical impulse at a much faster speed
- gaps in between the myelin sheath are the nodes of ranvier
5
Q
How do the nodes of ranvier contribute to the speed of an impulse?
A
- they allow the impulse to jump from one node to the next node as it travels along the neurone which causes it to be transmitted much faster rather than it transmitting continuously along the nerve fibre which would be slower
6
Q
What are sensors receptors?
A
- transducers which detect stimuli and convert it into a nerve impulse, producing a generator potential
- each specific to a single type of stimulus
7
Q
Give the 4 main examples of sensory receptors in animals
A
- mechanoreceptors ; detect pressure and movement, found in the skin (e.g Pacinian Corpuscles)
- chemoreceptors ; detect chemicals, found in the nose (e.g olfactory receptors)
- thermoreceptors ; detect heat, found in the tongue (e.g end-bulbs of Krause)
- photoreceptors; detect light, found in the eyes (e.g cone cell)
8
Q
Outline what Pacinian Corpuscles are
A
- sensory receptors which detect mechanical pressure
- found deep within the skin
- contain a sensory nerve ending
9
Q
How do sensory receptors work?
A
- during resting potential, when a stimulus is detected the cell
membrane is excited and becomes more permeable allowing more ions to move in/out of the cell, altering the potential difference - this change in potential difference caused by a stimulus is known as the generator potential
- the bigger the stimulus, the bigger the generator potential produced
- if the generator potential reaches the threshold then an action potential will be triggered
10
Q
Describe how Pacinian Corpuscles work
A
- during resting state, the stretch mediated sodium ion channels in the sensory neurone membrane are too narrow for ions to pass through
- when pressure is applied to the Pacinian Corpuscles, it changes shape and causes the membrane surrounding its neurone to stretch
- this widens the sodium ion channels and ions diffuse into the neurone
- the influx of positive sodium ions changes the potential of the membrane; it becomes depolarised and results in a generator potential
- generator potential creates an action potential which is transmitted along neurones to the CNS
11
Q
What is resting potential?
A
- usually -70mV
- when the outside of the membrane is more positively charged
- the membrane is polarised due to the difference in charge
12
Q
How is a resting potential created?
A
- Sodium ions are actively transported out of the axon and Potassium ions in using the sodium potassium pump (an intrinsic protein)
- every 3 sodium ions pumped out, 2 potassium ions are pumped in
- there are more sodium ions outside of the membrane than in the axon cytoplasm so sodium ions diffuse back into the axon down the electrochemical gradient
- the gated sodium channels close and potassium channels open so potassium ions can diffuse out of the axon
- there are more positively charged ions outside of the axon creating a resting potential
13
Q
What is an action potential?
A
- the sequence of events that occur due to the rapid movement of sodium and potassium ions across the axon membrane through voltage gated ion channels
14
Q
Name the 5 stages involved in an action potential
A
- stimulus
- depolarisation
- repolarisation
- hyperpolarisation
- resting potential
15
Q
Discuss the first stage of an action potential
A
- stimulus
- excites the cell membrane causing some sodium ion channels to open, means the membrane becomes more permeable to sodium ions so sodium ions diffuse down their electrochemical gradient into the neurone, making the inside of the neurone less negative