Health and Disease Week 7 Flashcards
(124 cards)
1
Q
What type of cells are neurones?
A
postmitotic
2
Q
define postmitotic
A
cells that are fully differentiated and unable to divide
3
Q
define soma
A
the cell body of a neurone, an expanded area of cytoplasm where nucleus and organelles are found
4
Q
Which organelle do neurones NOT have?
A
centrioles -> important in cell division, so don’t need them
5
Q
What is the structure and function of the myelin sheath?
A
made up of Schwann cells and they insulate the axon
6
Q
What are the 4 shape classes of neurones?
A
multipolar, bipolar, unipolar, anaxonic
7
Q
What are the 3 classes of neurones?
A
afferent, efferent, interneurone
8
Q
define afferent neurone
A
transmits signal from receptors to CNS
9
Q
define efferent neurone
A
transmits signal from CNS to effectors
10
Q
define interneurone
A
transmits signal from afferent to efferent neurones
11
Q
What is a resting membrane potential (RMP)?
A
an electrical charge across the plasma membrane, with the interior of the cells negative compared to exterior
12
Q
define chemical gradient
A
gradient based on concentration
13
Q
define electrical gradient
A
gradient based on charge
14
Q
What are the 2 types of movement across the plasma membrane involving proteins?
A
facilitated diffusion and active transporters (pumps)
15
Q
define facilitated diffusion
A
when ions diffuse down their concentration gradient and the channels are selectively permeable to different ions
16
Q
define active transport
A
when pumps move ions against their concentration gradient and create a concentration gradient across the membrane
17
Q
How do Na+ and K+ pumps maintain excitability?
A
active transporters exchange 2K+ in for every 3NA+ out
18
Q
What is the resting membrane potential in most neurones?
A
-70mV
19
Q
Which equation is used to calculate the equilibrium potential for an ion?
A
the Nernst equation
20
Q
give the Nernst equation
A
E ion = RT / zF x log [ion]outside / [ion]inside
21
Q
Which other equation is used to calculate the resting membrane potential?
A
Goldman equation
22
Q
define action potential
A
a brief change in the voltage across a membrane due to the flow of ions into and out of the neurone
23
Q
What does the ‘all or nothing law’ describe?
A
if a stimulus is strong enough, an action potential occurs, which is always a full response i.e. can’t be strong or weak
24
Q
What are the 5 phases of action potentials?
A
- hypopolarisation
- depolarisation
- overshoot
- repolarisation
- hyperpolarisation/undershoot
25
define hypOpolarisation
the initial increase of the membrane potential to the value of threshold potential
26
define depolarisation
the potential moving from the RMP to less negative values
27
define overshoot
the peak of the action potential being reached at about +40mV
28
define repolarisation
the potential moving back to the RMP (-70mV)
29
define hyperpolarisation/undershoot
the potential moves away from the RMP in a MORE negative direction, but the RMP is eventually restored due to K leak channel and sodium-potassium pump
30
action potential stage 1
membrane is at resting potential and VGNC and VGKCs remain closed
31
action potential stage 2
a stimulus causes depolarisation the threshold potential and VGNCs open
32
action potential stage 3
Na+ ions flow in and the membrane rapidly depolarises and more VG sodium ion channels open but VGKCs remain closed
33
action potential stage 4
VG sodium ion channels are inactivated and Na+ entry slows
34
action potential stage 5
VGKCs open and K+ begin to flow out, beginning repolarisation
35
action potential stage 6
VGNC channels fully close and VGKC remain open to give delayed hyperpolarisation -> eventually resting potential is restored
36
What are the properties of VGNCs?
1. open rapidly with depolarisation at around -55mV
2. moving away from -55mV causes inactivation
3. inactivated channels are blocked during continued depolarisation
4. inactivated channels move to a closed state during repolarisation
37
What are the properties of VGKCs?
1. K+ channels slowly open during depolarisation at about +30mV
2. they close slowly on repolarisation
38
What are the 2 classes of refractory period?
absolute refractory period, relative refractory period
39
What happens during the absolute refractory period?
action potentials cannot be generated as VGNCs are inactivated and can't be activated again until the membrane is repolarised and resting state is restored
40
When does the refractory period occur?
from the start of an action potential to the point that voltage first returns to RMP
41
What happens during the relative refractory period?
the membrane potential is hyperpolarised by VGKCs and action potentials CAN be generated if the stimulus is strong enough to overcome hyperpolarisation and reach threshold
42
What is action potential propagation?
the process by which an action potential travels across a neurone
43
How does action potential propagation work (local currents)?
1. stimulation at point A exceeds threshold
2. local currents spread along axon and exceed threshold
3. this opens VGNC and generate AP at point B
4. VGNC inactivation occurs and open VGKC prevent back-propagation
44
What 2 factors does the velocity of action potential propagation depend on?
1. axon diameter
2. myelination
45
How does axon diameter affect action potential propagation velocity?
the larger the diameter, the faster the propagation as there is more space for ions to travel
46
define saltatory conduction
the propagation of action potentials along myelinated axons from one node of Ranvier to the next, increasing velocity
47
What causes Guillain-Barre syndrome?
the destruction of Schwann cells in the peripheral nervous system
48
What causes multiple sclerosis (MS)?
a loss of oligodendrocytes in the brain and spinal column
49
What are the 2 types of graded potential?
excitatory and inhibitory
50
What do inhibitory graded potentials do?
take the membrane further away from the threshold potential
51
What are the 4 types of excitatory graded potentials?
1. temporal summation
2. spatial summation
3. no summation
4. spatial summation of EPSPs and IPSPs
52
define temporal summation
2 excitatory stimuli close in time causes EPSPs to add together
53
define spatial summation
2 simultaneous stimuli at different locations cause EPSPs to add together
54
define no summation
2 stimuli separated in time cause EPSPs that do NOT add together
55
define spatial summation of EPSPs and IPSPs
changes in membrane potential that cancel each other out
56
define synapse
the point at which an electrical signal moves from one nerve cell to another
57
What are the 2 types of synapse?
electrical and chemical
58
What is the structure of an electrical synapse?
the pre and post-synaptic neurones are directly connected by gap junctions
59
What is the structure of an chemical synapse?
the pre and post-synaptic neurones are physically separated by the synaptic cleft and chemical transmitter from pre-synaptic neurone binds to receptors on post-synaptic neurone
60
What are gap junctions?
channels formed by connexons in both cell membranes and allow direct passage of ions and small molecules through the channels
61
What are the features of chemical synapses?
1. synaptic vesicles filled with neurotransmitter on the inside of the presynaptic neurone
2. voltage-gated calcium ion channels in presynaptic neurone
3. neurotransmitter receptors on postsynaptic neurone
62
What are the 3 types of synapse in the CNS?
axo-dendritic, axo-somatic, axo-axonal
63
define axo-dendritic synapse
an axon synapsing onto a dendrite
64
define axo-somatic synapse
an axon synapsing onto a cell body
65
define axo-axonal synapse
an axon synapsing onto another axon or axon terminal
66
define neurotransmitter
a chemical messenger that is released from a pre-synaptic neurone
67
What are the sequence of events involved at a chemical synapse?
1. neurotransmitter is synthesised and stored in vesicles
2. AP arrives at presynaptic terminal
3. AP depolarises the terminal and VGCC opem
4. Ca2+ enter and trigger exocytosis
5. transmitter diffuses down synaptic cleft and binds to receptors
6. ion flow causes postsynaptic response
7. transmitter is removed by enzyme breakdown or reuptake
8. the vesicle is retrieved from the terminal membrane
68
What are the 4 key criteria for a substance being a neurotransmitter?
1. substance must be present within the presynaptic neurone
2. substance must be released in response to presynaptic depolarisation by an AP
3. specific receptors for the substance must be present on the postsynaptic cell
4. there must be a mechanism for removal and/or breakdown
69
What are the 2 types of neurotransmitter receptor?
ionitropic receptor, metabotropic receptor
70
What is an ionotropic receptor?
a ligand (transmitter) gated ion channel that opens to allow passage of ions through membrane in response to binding
71
What is a metabotropic receptor?
a g protein-coupled receptors -> binding activates g-protein which activates second messenger which can directly affect ion channels on membrane
72
What is a neuromuscular junction?
the synapse between a motor neurone and skeletal muscle
73
What is a neuromuscular junction also known as?
a motor endplate
74
Which neurotransmitter and receptor are used at neuromuscular junctions?
acetylcholine and nicotinic receptors
75
What type of receptor in the nicotinic acetylcholine receptor?
ionotropic or neurotransmitter-gated ion channel
76
How is acetylcholine synthesised?
in the presynaptic terminals by the enzyme choline acetyltransferase
77
How is acetylcholine broken down?
by acetylcholinesterase into acetate and choline
78
What is the main excitatory transmitter in the CNS?
glutamate
79
What type of receptor does glutamate activate?
both ionotropic and metabotropic receptors
80
What is the main inhibitory transmitter in the CNS?
GABA (G-aminobutyric acid)
81
What type of receptor does GABA work on?
a small family of ionotropic and metabotropic receptors
82
What type of potential does glutamate generate?
an excitatory postsynaptic potential (EPSP)
83
What type of potential does GABA generate?
an inhibitory postsynaptic potential (IPSP)
84
What do IPSPs do?
make a neurone less likely to generate an action potential
85
Which 2 main parts is the nervous system divided into?
the central and peripheral nervous systems
86
What is the central nervous system made up of?
the brain and spinal cord
87
define periphery
the area that is away from the centre of the body
88
define afferent neurone
a neurone that transmits an action potential from the periphery to the CNS
89
define efferent neurone
a neurone that transmits an action potential from the CNS to the periphery
90
define vertebrae
a stack of bones that surround the spinal cord
91
What are the 4 sections of spinal nerves that receive inputs and send outputs?
cervical, thoracic, lumbar, sacral
92
How do sensory inputs enter the CNS?
through the dorsal root into the spinal cord
93
What is the dorsal root ganglion?
where the cell bodies of axons are just outside the vertebrae in the spinal cord
94
What type of neurone are most sensory neurones?
unipolar -> have a cell body and one long axon
95
What is the simplest example of a connection between sensory neurone input and output back to the periphery?
the monosynaptic reflex
96
define monosynaptic
there is ONE synapse between the presynaptic and postsynaptic neurone
97
What type of neurone are most motor neurones?
multipolar
98
define reflex
when input is received by the periphery and the body provides output back to the periphery without any conscious thought
99
What do proprioceptors do?
sense position and movement
100
How does the knee jerk reflex work?
1. tap the tendon attached to the quadriceps
2. the tendon gets pulled, which stretches the quadriceps
3. this is sensed by the muscle spindle fibres (proprioceptors)
4. generates action potential
5. action potential goes through dorsal root to spinal cord
6. neurotransmitter is released in spinal cord
7. this causes an action potential in a motor neurone, which causes the quadriceps to contract
101
What is the pathway of a reflex arc?
1. receptor gives input to integrative centre
2. integrative centre gives output to effector
102
What is USUALLY the integrative centre?
the spinal cord
103
How do sensory neurones vary?
by thickness and myelination
104
What does the extent of myelination determine?
the speed of an action potential
105
define ascending pathway
neuronal input travelling from the spinal cord to the brain
106
give an example of an ascending pathway in proprioception
1. action potential comes into dorsal root
2. goes up the spinal cord to a synapse at the brain stem (medulla)
3. action potential crosses to the other side of the body
4. it reaches another synapse in the middle of the brain called the thalamus
5. eventually reaches the somatosensory cortex
107
define descending pathway
information going from the brain to the spinal cord
108
Where does all input from the periphery to the CNS BELOW the neck go to?
the spinal cord
109
Where does all input from the periphery to the CNS go to if ABOVE the neck?
the cranial nerves
110
define glial cell
a cell that is specialised to help neurones function but are NOT neurones
111
What are 2 examples of glial cells?
oligodendrocytes and astrocytes
112
What do oligodendrocytes do?
produce myelin -> there are different glial cells that do this in the peripheral nervous system called Schwann cells
113
What does astrocytes do?
act as a buffer to equalise concentrations of k+ ions -> there may be high concentrations of K+ ions if axons are generating many action potentials, so astrocytes 'suck them up' and move them to other parts of the brain
114
define the meninges
the 3 layers of membranes that cover and protect the brain and spinal cord
115
What is the outer membrane called?
dura mater
116
What is the inner membrane called?
the pia mater
117
What is the space between the inner and outer membranes called?
the sub arachnoid space
118
What is the sub arachnoid space filled with?
cerebrospinal fluid
119
What is the function of the choroid plexus?
it is a gland in the middle of the brain that produces cerebrospinal fluid
120
What does the cerebrospinal fluid contain?
salt and sugar -> high concentrations of Na+ and low K+ -> glucose and oxygen
121
What is the blood-brain barrier?
a semipermeable membrane separating the blood from the cerebrospinal fluid and brain
122
What is the structure of the blood-brain barrier?
tight junctions between the endothelial cells and blood vessel wall (tight junction is a seal between two cells that prevents leakage of content)
123
What does the blood-brain barrier do?
prevents substances leaking out of the blood vessels into the brain, including blood borne viruses and bacteria
124
Which cells acts as immune cells in the brain?
microglia
