Chapter 13 - Neuronal Communications Flashcards
1
Q
What are sensory receptors?
A
Specialised cells that can detect changes in our surroundings
- energy transducer that convert one form of energy to another
2
Q
What sensory receptors detect change in light intensity?
A
- Light sensitive cells (rods and cones) in the retina
(light -> electrical)
3
Q
What sensory receptors detect change in temperature?
A
- Temperature receptors in the skin and hypothalamus
(heat -> electrical)
4
Q
What sensory receptors detect change in pressure on the skin?
A
- Pacinian corpuscles in the skin
(movement -> electrical)
5
Q
What sensory receptors detect change in sound?
A
- Vibration receptors in the cochlea of the ear
(movement -> electrical)
6
Q
What sensory receptors detect change in movement?
A
- Hair cells in inner ear
(movement -> electrical)
7
Q
What sensory receptors detect change in length of muscle?
A
- Muscle spindles of skeletal muscles
(movement -> electrical)
8
Q
What sensory receptors detect change in chemicals in the air?
A
- Olfactory cells in epithelium lining the nose
(receptors detect the presence of a chemical and create an electrical nerve impulse)
9
Q
What sensory receptors detect chemicals in food?
A
- Chemical receptors in taste buds on tongue
(receptors detect the presence of a chemical and create an electrical nerve impulse)
10
Q
What is a Pacinian corpuscle?
A
- pressure sensor that detects change in pressure on the skin
corpuscle = oval-shaped structure that consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell.
11
Q
What is the corpuscle sensitive to ?
A
- ONLY to changes in pressure that deform the rings of connective tissues.
when pressure is constant, they stop responding
12
Q
Membrane stuff
A
- if channel proteins are permanently open the ions can diffuse across the membrane and will keep going till conc on both side of the membrane are equal
- if the channels can be closed, the action of the active pumps can create a conc gradient across the membrane
- sodium channels + potassium channels possess a gate that can open or close the channel
- sodium channels are sensitive to small movements of the membrane, so when the membrane is deformed by changing pressure, sodium channels open
- allows Na+ to diffuse into the cell, producing a generator potential
13
Q
What do the membranes contain? (generating nerve impulse)
A
- sodium/ potassium pumps actively pump sodium ions out of the cell and potassium ions into the cell
- 3 Na+ out for every 2 K+ in
- channel proteins closed = sodium pumps work to create a conc gradient
- conc of Na+ outside the cell increases, more than conc of K+ inside the cell
- movement of ions via the sodium-potassium pumps establishes an electrochemical gradient
-membrane is more permeable to K+ ions and less to Na+ ions - negatively charged on inside of axon
14
Q
What is the cell membrane when the cell is inactive?
A
- polarised
15
Q
How is a nerve impulse created?
A
- altering the permeability of the nerve cell membrane to sodium ions by opening sodium ion channels
- as Na+ channels open, membrane permeability increases and Na+ can move across the membrane
down conc gradient into the cell - creates a change in potential difference across the membrane
- inside of the cell becomes LESS NEGATIVE = depolarisation
- if a small stimulus is detected, only a few sodium channels will open
- the larger the stimulus, the more gated channels will open
- if enough Na+ enter the cell and enough gates are opened, potential difference across the cell membrane changes significantly + will initiate an action potential/ impulse
16
Q
What are the 3 different types of neurones?
A
- motor neurones
- sensory neurones
- relay neurones
17
Q
Motor neurones
A
- carry an action potential from the central nervous system (CNS) to an effector such as a muscle or a gland
18
Q
Sensory neurones
A
- carry the action potential from a sensory receptor to the CNS
19
Q
Relay neurones
A
- connect sensory and motor neurones
20
Q
What features do neurones have? (8)
A
- long so they can transmit the action potential over a long distance
- cell surface membrane has many gated ion channels that control the entry/exit of Na, K and Ca
- Na/K pumps uses ATP to actively transport 3 Na+ out the cell and 2 K+ into the cell
- maintain a potential difference across their cell surface membrane
- cell body contains the nucleus, mitochondria, ribosomes
- dendrites connect to other neurones: carry impulses towards the cell body
- axon carries impulses away from the cell body
- surrounded by a fatty layer that insulates the cell from electrical activity (composed of Schwann cells associated with the neurone)
21
Q
What are the differences between types of neurone?
A
- motor neurones have their cell body in the CNS + have a long axon that carries the action potential out to the effector
- sensory neurones have a long dendron carrying the action potential from a sensory receptor to the cell body, which is just outside the CNS
(short axon carrying the action potential into the CNS) - relay neurones connect the sensory + motor neurones together
(many short dendrites + short axon)
22
Q
What are myelinated neurones?
A
- insulated by an individual myelin sheath (is formed by specialised cells known as Schwann cells which wrap themselves around the axon)
23
Q
What make up the myelin sheath?
A
- Schwann cells
24
Q
What are the gaps in the myelin sheath called?
A
- nodes of Ranvier (each node is very short)
25
What does the myelin sheath do?
- it prevents the movement of ions across the neurone membranes, so it can only occur at the nodes of Ranvier
26
What are non-myelinated neurones?
- has no individual layer of myelin - so impulse travels more slowly as it moves through the entire length of the axon
27
How does action potential move in myelinated neurones?
- action potential jumps from node to node
28
How does action potential move in non-myelinated neurones?
- action potential moves along the neurone in a wave
29
What are the advantages of myelination?
- transmit an action potential much quicker than non-myelinated neurones
- myelinated neurones carry action potentials from sensory receptors to the CNS and from the CNS to effectors
- carry action potentials over long distances - increased speed of transmission= action potential reaches the end of the neurone much more quickly
30
What is it called when a neurone is not transmitting?
- action potential is said to be at rest
31
What is action potential doing while it is at rest?
- it is actively pumping ions across its cell surface membrane
32
How can an action potential be generated?
- when neurone is at rest, it maintains a conc gradient of Na+ across its plasma membrane
- Na+ channels open = Na+ will diffuse down conc gradient into cell from tissue fluid -> causes depolarisation of the membrane
- in the generator region, the gated channels are opened by the action of the synapse
33
What is a generator potential?
- gated channels open + allow Na+ into the cell and produce a small depolarisation
34
What is a voltage-gated channels?
- Na+ channels in a neurone are opened by changes in the potential difference across the membrane
35
What are the stages of an action potential?
- Membrane starts in its resting state - polarised with the inside being 60mV compared to the outside
⇡ conc of Na+ outside than inside
⇡ conc of K+ inside than outside
-Na+ channels open and some Na+ diffuse into the cell
- Membrane depolarises- becomes less -ve and reaches the threshold value of -50mV
- positive feedback causes nearby voltage-gated Na+ channels to open and many Na+ flood in -> as more Na+ enter, cell becomes +vely charged inside compared with outside
- A potential difference across the plasma membrane reaches +40mV : inside of the cell is +ve compared with outside
- Na+ channels close and K channels open
- K+ diffuse out the cell bringing the potential difference back to -ve inside compared with outside (repolarisation)
36
What is the refractory period?
- For a short time after each action potential it is impossible to stimulate the cell membrane to reach another action potential
- allows the cell to recover after an action potential
- ensures action potentials are transmitted in only 1 direction
- limits number of impulse transmission which prevents over reaction to stimulus
36
What are the steps in the formation of local currents + transmission of a nerve impulse?
- When an action potential occurs, the Na+ channels open at that point in the neurone
- open Na+ channels allow Na+ to diffuse across the membrane from the region of ⇡ conc. outside the neurone into the neurone
-conc. of Na+ inside rises at the point where the Na+ channels are open
- Na+ continue to diffuse sideways along the neurone, away from the region of ⇡ conc
- local current causes a slight depolarisation further along the neurone which affects the voltage-gated Na+ channels, causing them to open
- the open channels allow rapid influx of Na+ causing a full depolarisation further along the neurone
- action potential has moved along the neurone
37
What is a local current?
-the movement of charged particles:
38
What is saltatory conduction?
- when action potential appears to jump from one node to the next
39
What does a higher frequency of action potentials mean?
- a more intense stimulus -> more Na channels are opened in the sensory receptor -> produces more generator potentials -> more frequent action potentials in the sensory neurone -> more frequent action potentials enters the CNS
40
What is a synapse?
- a junction between 2+ neurones, where 1 neurone can communicate with, or signal to, another neurone
41
What does the action potential in the pre-synaptic neurone cause?
- release of a neurotransmitter that diffuses across the synaptic cleft + generates a new action potential in the post- synaptic neurone
42
What are cholinergic synpases?
- synapses that use acetylcholine as the neurotransmitter
43
What are 4 specialised features of a pre-synaptic bulb?
- many mitochondria
- large amount of SER, which packages the neurotransmitter into vesicles
- large number of vesicles cont. molecules of acetylcholine
- a number of voltage-gated ca+ channels on the cell surface membrane
44
What is acetylcholine?
- molecules of a chemical -> transmitter that will diffuse across the synpatic cleft
45
What does post-synaptic membrane contain?
- specialised Na+ channels that can respond to the neurotransmitter
- channels consist of 5 polypeptide molecules
- 2 have a special receptor site that is specific to acetylcholine + shape that is complementary to shape of acetylcholine molecule
- when acetylcholine is present in the synaptic cleft it binds to the 2 receptor sites + causes Na+ channel to open
46
How does transmission occur across the synaptic cleft (synapse)?
- action potential arrives at the synaptic bulb
- voltage-gated Ca+ channels open
- Ca+ diffuse into the synaptic bulb
- Ca+ cause the synaptic vesicles to move to + fuse with the pre-synaptic membrane
- acetylcholine is released by exocytosis
- acetylcholine molecules diffuse across the cleft
- acetylcholine molecules bind to the receptor sites on the Na+ channels in the post-synaptic membrane
- Na+ channels open
- Na+ diffuse across the post-synaptic membrane into the post-synaptic neurone
- generator potential is created
- if sufficient generator potentials combine = potential across the post- synaptic membrane reaches the threshold potential
- new action potential is created in the post-synaptic neurone
47
What are the final steps to transmission occurring across the synapse?
- Na+ channels open
- Na+ diffuse across the post-synaptic membrane into the post-synaptic neurone
- generator potential is created
- if sufficient generator potentials combine = potential across the post- synaptic membrane reaches the threshold potential
- new action potential is created in the post-synaptic neurone
48
What is acetylcholinesterase?
- it is an enzyme found in the synaptic cleft
- hydrolyses the acetylcholine to ethanoic acid (acetic acid) and choline
- stops the transmission of signals -> synapse doesn't continue to produce action potentials in the post-synaptic neurone
49
What happens to the ethanoic acid and choline?
- recycled
- re-enter the synaptic bulb by diffusion and recombined to acetylcholine using ATP from respiration in the mitochondria
- recycled acetylcholine is stored in synaptic vesicles for future use
50
What is the main role of syanpses?
- connect 2 neurones together so a signal can be passed from 1 to the other
51
What is an excitatory post-synaptic potential?
- acetylcholine molecules diffuses across the cleft produces a small depolarisation
52
What is summation?
- occurs when effects of several EPSPs are added together
53
What is a temporal summation?
- result from several action potentials in the same pre-synaptic neurone
54
What is a spatial summation?
- result from action potentials arriving from several different pre-synaptic neurones
55
What is inhibitory post-synaptic potentials (IPSPs)?
- reduce effect of summation + prevent an action potential in the post- synaptic neurone
56
Control of communication
- combo of several EPSP's could be prevented from producing an action potential by 1 IPSP
- 1 pre-synaptic neurone might diverge to several post-synaptic neurones -> allows 1 action potential to be transmitted to several parts of the nervous system - useful in a reflex arc -> 1 post-synaptic neurone elicits the response, while another informs the brain
- synapses ensure that action potentials are transmitted in the correct direction - only the pre-synaptic bulb cont. vesicles of acetylcholine
