Lectures 4,5 amd 6 Flashcards
What do the spinal nerves do?
Send information to and from the periphery
What does the dorsal tract do?
Receives sensory information from the periphery (afferent pathway)
What does the ventral tract do?
Sends information to muscles/ organs (efferent tract)
What does glutamate do?
Lead to an entry of sodium ions into the cells. If depolarisation is high enough it will stimulate an action potential
Give examples of some excitatory neurotransmitters
Glutamate and serotonin
Give some examples of inhibitory neurotransmitters
Gamma amino butyric acid (GABA) and glycine
Give some examples of some excitatory and inhibitory neurotransmitters
Acetylcholine Epinephrine (adrenaline) Norepinephrine (noradrenaline) Dopamine Endorphins
What are ionotropic receptors?
Ion channels which open upon binding of the neurotransmitter
What are metabotropic receptors?
Couples to intracellular signalling proteins (G-proteins) which then open ion channels. Depending on the repertoire of ion channels targeted by these proteins (e.g. sodium, potassium or chlorine) The is can lead to an EPSP or an IPSP
What is GABA?
The most important inhibitory neurotransmitter in the CNS
What are GABA A receptors? How do they work?
Chloride channels. Binding of GABA to the receptor opens the channel, leading to an entry of chloride ions. This hyperpolarises the postsynaptic membrane, leading to an IPSP
What does low GABA levels lead to?
Restlessness, anxiety and irritability
What does pharmacological enhancement of GABA receptors lead to?
Reduces anxiety and mild tranquilisation
What is glutamate?
The most abundant excitatory neurotransmitter in the vertebrate CNS
What are the three subtypes if iontropic glutamate receptors?
AMPA, Kainate and NMDA
What is the subtype of ionotropic glutamate receptors, NDMA receptors unusual?
It is blocked by Mg2+ - thereby preventing ions to pass through the channel even if glutamate is bound.
When the membrane depolarises what happens to NDMA receptors?
Mg2+ is electrostatically forced out of the channel and allows ions (Na2+ and Ca2+) to pass through
What is long term potentiation important in?
Memory and learning
What is the alternate name for serotonin?
5-HT (5-hydroxy tryptamine)
What does serotonin regulate?
Emotions, body temperature, sleep cycle and the digestive system
What are serotonin imbalances involved in?
Depression, impulsive behaviour or sleep disorders
There is a large variety of serotonin receptors. what are most of them?
Metabotropic
What are nicotine can acetylcholine receptors?
They are sodium channels. They are the major receptors in skeletal muscle cells and in the autonomous nervous system
What are nicotinic acetyl choline receptors (nAChR) activated and inhibited by?
Activated by nicotine and inhibited by alkaloid arrow poisons (Curare)
How were nicotinic acetylcholine receptors discovered?
Electric rays
What are muscarinic receptors coupled to? Where are they the major receptors?
Coupled to G-proteins
Are the major receptors in many organs controlled by the parasympathetic nervous system
What do the muscarinic acetylcholine receptors control?
In your eyes the iris sphincter (pupil size). Atropine inhibits the receptors leading to large pupils (considered as beautiful=belladonna)
What are dopamine receptors?
They are metabotropic (G-coupled) receptors
What is dopamine involved in?
The coordination of movement in the basal nuclei system as well as emotional balance (cortex and limbic system).
Also involved in pleasurable reward
What are reduced And high levels of dopamine associated with?
low levels are associated with Parkinson’s disease. High levels are associated with Schizophrenia
How do some drugs (e.g. cocaine) increase the action of dopamine?
By preventing its removal from the synaptic cleft
What are neurotransmitters used for?
Signalling between neurons (or e.g: muscles)
What is noradrenaline an important transmitter of?
The peripheral nervous system
What does adrenaline trigger?
Stress responses
Describe skeletal muscle
Fibres are large multinucleate cells that appear striped or striated under the microscope
Describe cardiac muscle
Fibres are striated but they are smaller, branches and uninucleate. Cells are joined in series by junctions called intercalated disks
Describe smooth muscle
Fibres are small and lack striations
What do thick filaments mainly consist of?
Myosin molecules which are connected by the tail and with heads extending radially
What are thin filaments mainly?
Actin
Thick and thin filaments in association with structural proteins comprise what?
The sarcomere
What is each thin filament anchored by?
The Z-disc (protein CapZ) and called at the end by tropomodulin.
What are thick filaments held in position by?
The elastic molecule Titin
What are thick filaments surrounded by? What does this increase?
Multiple thin filaments, increasing interaction with myosin heads
What are Z discs rich in?
CapZ
Describe what happens in the action-myosin interaction/ the cross-bridge cycle
- ATP binds, causing myosin to detach
- Detachment of myosin causes ATP to be hydrolysed to ADP and Pi which remain bound by myosin
- Hydrolysis causes myosin to attach to actin
- Release of phosphate promotes power stroke
- ADP is released
What is a power stroke?
When the myosin heads pull the actin filaments
Describe the sliding filament theory
Drug contraction the myosin heads pull the actin towards the centre of the myosin filament. The A band (myosin filaments) do not change size/width. Whereas the I band (unoccupied actin becomes narrow (it is pulled to the centre)
During the cross-bridge cycle, myosin heads interact with actin, what prevents this interaction and what is it controlled by?
Prevented by tropomyosin (which covers the myosin-binding sites). Tropomyosin is controlled by Troponin- which can bind calcium ions
What happens what calcium binds to Troponin?
The position of Tropomyosin changes, thereby exposing the myosin-binding sites of actin.
What is the sarcoplasmic reticulum?
A tubular network within the muscle fibre that is a store for calcium
What does the sarcoplasmic reticulum contain? What does this do?
Calcium pumps which pump calcium ions from the cytoplasm into the sarcoplasmic reticulum. (This process requires ATP)
It also contains a “lid”, the ryanodine receptors, which can release calcium into the cytoplasm when opened
At rest ATP is combined with creatine to form what?
Phosphocreatine