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
What is phosphocreatine?
The energy store of the muscles
What happens to cation potentials generates in muscle cells?
They travel along the T-tubules and depolarisation leads to a structural change in the DHP receptor which is linked to the Ryanodine receptor. The ryanodine receptor opened and released calcium ions from the sarcoplasmic reticulum
What is most of the strength of a muscle controlled by?
Variations in the number of active motor units
What happens to cation potentials generates in muscle cells?
They travel along the T-tubules and depolarisation leads to a structural change in the DHP receptor which is linked to the Ryanodine receptor. The ryanodine receptor opened and released calcium ions from the sarcoplasmic reticulum
What does he strength of a muscle contraction depend on?
How many fibres are contracting and at what rate
What is tetanus?
At high frequencies, the muscle fibres are maximally contracted (when all your muscles are contracted)
What makes fast and slow twitch muscle fibres different?
These fibres express different myosin genes- with different rates of ATPase activity (cross-bridge cycle).
Fast twitch fibres (can react faster but doesn’t last as long) ca recycle their actin-myosin cross-bridges fasted than slow-twitch fibres.
Describe slow twitch muscle fibres
Also called oxidative or red muscle because they contain especially large amounts of myoglobin (binds oxygen molecules and stores it), have many
Mitochondria, and are well supplied with blood vessels
Describe fast twitch muscle fibres
Also called glycolytic or white muscle, have few mitochondria, little or no myoglobin, and fewer blood vessels. Their major energy source is glycolysis. They can develop maximum tension more rapidly than slow-twitch fibres can, and that maximum tension is greater. However fast-twitch fibres fatigue rapidly (so doesn’t last as long)
Muscles can build up force (tension) without changing its length. What is this called?
Isometric contraction
Is the muscles shortens what is this called? (The fords does not change during the contraction, but the entry of the muscle does)
Isotonic contraction
He muscle has elastic elements which can be parallel or in series e.g. titin, tendons. Shortening of the sarcomeres can stretch those elements leading to what?
Isometric contraction and increased tension
What does striated mean?
It has sarcomeres
What kind of contractions does smooth muscle cause?
Slow contractions of many internal organs
Why does smooth muscle look smooth?
Because the actin and myosin filaments are not as regular yardages as they are in skeletal ad cardiac muscle
In smooth muscle where is the calcium-mediated change? Where is it in skeletal and cardiac muscle?
Smooth: in myosin
Skeletal/ cardiac: on the actin-tropomyosin filament
What happens when a smooth muscle cell is depolarised by a neurotransmitter?
Calcium enters the cytoplasm from outside and binds to calmodulin, which in turn activates an enzyme that phosphorylates the myosin heads, causing them to bind to actin
What do chemoreceptors do?
Detect chemical signals (smell/taste)
What do mechanoreceptors do?
Detect mechanical stimuli (touch/sound)
What do photoreceptors do?
Detect light (vision) (electromagnetic stimulus)
What do thermoreceptors do?
Detect temperature (electromagnetic stimuli)
What do electroreceptors do?
Detect electrical stimuli
What do magnetoreceptors do?
Detect the magnetic field
What do nociceptors do?
Detect pain (chemical stimulus)
In sensory receptor cell what is the change in membrane potential called?
Receptor potential
In sensory neurons (afferent neurons): the change in the membrane potential upon stimulation of the receptor generates action potentials and is therefore termed what?
Generator potential
What do sensory receptor cells/ neurons do? What is this called?
Take incoming stimuli of various types and convey them into changes in the membrane potential. This is called transduction.
Explain dynamic range
Most sensory receptors are able to encode stimuli over a kites rage of stimulus intensities
What is threshold intensity?
The weakest stimulus that. Produces a response in a receptor 50% of the time
What is range fractionation?
Groups of receptors, each sensitive to a different range of the stimulus, work together to cover the whole range of the stimulus intensity (for example in the resting- different receptors detect different colours)
What does logarithmic coding allow?
A receptor to have a constant response to above percentage change in stimulus intensity
What do tonic receptors do?
Fire action potentials as long as the stimulus continues and can this provide information about how long a stimulus lasts. However, in most of these receptors, action potential frequencies decrease: receptor adaption
What are phasic receptors?
Adapt vey rapidly and depolarise only at the beginning of a stimulus. This allows animals (and us) to tune out factors in their environment that are not changing.
E.g. can detect at the beginning but the don’t notice it over time- smell, clothes, swimming water temp etc.)
What is the sense of smell called?
Olfaction
What are chemicals which are detected by the olfactory system called?
Odorants
What are odorants detected by?
Olfactory receptors/ odorants receptors
What is sense of taste called?
Gustation
What are chemicals that are detected by the gustatory system called?
Tastants
What do taste buds contain?
Chemoreceptors
What is flavour?
A combination of chemosensation by your tongue and the olfactory system
What are pseudogene?
Lost through evolution
What does logarithmic coding allow?
A receptor to have a constant response to above percentage change in stimulus intensity
What do tonic receptors do?
Fire action potentials as long as the stimulus continues and can this provide information about how long a stimulus lasts. However, in most of these receptors, action potential frequencies decrease: receptor adaption
What are phasic receptors?
Adapt vey rapidly and depolarise only at the beginning of a stimulus. This allows animals (and us) to tune out factors in their environment that are not changing.
E.g. can detect at the beginning but the don’t notice it over time- smell, clothes, swimming water temp etc.)
What is the sense of smell called?
Olfaction
What are chemicals which are detected by the olfactory system called?
Odorants
What are odorants detected by?
Olfactory receptors/ odorants receptors
What is sense of taste called?
Gustation
What are chemicals that are detected by the gustatory system called?
Tastants
What do taste buds contain?
Chemoreceptors
What is flavour?
A combination of chemosensation by your tongue and the olfactory system
What are pseudogene?
Lost through evolution
What does logarithmic coding allow?
A receptor to have a constant response to above percentage change in stimulus intensity
What do tonic receptors do?
Fire action potentials as long as the stimulus continues and can this provide information about how long a stimulus lasts. However, in most of these receptors, action potential frequencies decrease: receptor adaption
What are phasic receptors?
Adapt vey rapidly and depolarise only at the beginning of a stimulus. This allows animals (and us) to tune out factors in their environment that are not changing.
E.g. can detect at the beginning but the don’t notice it over time- smell, clothes, swimming water temp etc.)
What is the sense of smell called?
Olfaction
What are chemicals which are detected by the olfactory system called?
Odorants
What are odorants detected by?
Olfactory receptors/ odorants receptors
What is sense of taste called?
Gustation
What are chemicals that are detected by the gustatory system called?
Tastants
What do taste buds contain?
Chemoreceptors
What is flavour?
A combination of chemosensation by your tongue and the olfactory system
What are pseudogene?
Lost through evolution
What does logarithmic coding allow?
A receptor to have a constant response to above percentage change in stimulus intensity
What do tonic receptors do?
Fire action potentials as long as the stimulus continues and can this provide information about how long a stimulus lasts. However, in most of these receptors, action potential frequencies decrease: receptor adaption
What are phasic receptors?
Adapt vey rapidly and depolarise only at the beginning of a stimulus. This allows animals (and us) to tune out factors in their environment that are not changing.
E.g. can detect at the beginning but the don’t notice it over time- smell, clothes, swimming water temp etc.)
What is the sense of smell called?
Olfaction
What are chemicals which are detected by the olfactory system called?
Odorants
What are odorants detected by?
Olfactory receptors/ odorants receptors
What is sense of taste called?
Gustation
What are chemicals that are detected by the gustatory system called?
Tastants
What do taste buds contain?
Chemoreceptors
What is flavour?
A combination of chemosensation by your tongue and the olfactory system
What are pseudogene?
Lost through evolution
In snakes what is the Vomeronasal organ called? And where is it located?
Jacobson’s organ
Oral cavity
What do snakes use their tongues for?
To transfer pheromones to the vomeronasal organ by flicking its tongue into its mouth (so they use their tongues to smell the environment)
What are insect antennae covered with?
Hairlike projections of the cuticle: sensilla
What can sensilla detect?
Both chemical and mechanical stimuli
What does the taste bud (in vertebrates) consist of?
A pore containing sensory cells (receptor cells, not sensory neurons) and support cells. Both are epithelial cells. The apical surface contains microvilli (surface enlargement) which carry taste receptors
