Nervous system questions Flashcards
What part of the nervous system does the somatic system refer to?
The point where voluntary motor outputs begin to be stimulated from - can also mediate some involuntary responses
What does the Blood Brain Barrier do?
Restricts transport of products to the CNS, acting as a gatekeeper.
This prevents 98% of drugs reaching the brain
Molecules generally have to be lipid soluble and less than 400 Da to cross the BBB.
Which part of the brain links the endocrine and nervous system?
The hypothalamus
Describe the structure of the neuron
Functions of the neuron?
- Obtain input via neurotransmitters acting on receptors in dendritic spines
- Depolarisation
- Action potential generation and propagation
- Neurotransmitter release to signal to Neurons, glands and muscles.
How does the neuron have a membrane potential?
There is higher sodium concentrations outside than inside and higher Potassium concentrations inside than outside.
There is a net Negative membrane potential (inside negative to outside).
Due to the balance of Sodium and Potassium, there is a ELECTRICAL and CHEMICAL force Inwards for sodium. But for potassium, there is a chemical force outwards but an inwards Electrical force.
This causes the membrane potential to be formed.
Na+/K+ ATPase pumps are responsible for maintaining these gradients.
The nodes of Ranvier have a higher….
Sodium concentration
Why does the refractory period occur?
By this stage the sodium channels are closed and the Potassium channels are lagging to close.
Afferent neurons go from…
Sensory receptors to the CNS
Efferent neurons go from…
The CNS to the Autonomic system reaching the glands and smooth muscle, or the somatic system, reaching the skeletal muscle.
function of myentric and submucosal plexus
Myenteric - motor functions
Submucosal - Sensory functions.
How many cell types does the brain have?
Neurones, astrocytes, microglia, and oligodendrocytes
How do spinal cords receive input?
Peripheral afferent inputs occur via the dorsal horn
Efferent input via the ventral horn.
What receptors does glutamate act upon?
NMDA, AMPA, Kainate and Metabotropic.
GABA acts on which receptors?
GABA-a and GABA-b
Describe the process of neurotransmission
What is required for neurotransmitter release?
Calcium ions.
How does cholinergic neurotransmission occur?
Acetyl-Coenzyme A and choline are converted into Acetylcholine via Choline acetyl transferase enzyme.
Once the membrane is depolarised, calcium channels are activated and calcium enters the cell, the calcium enters the synapse and prompts the release of the neurotransmitters.
Acetylcholinesterase converts acetylcholine back to choline and acetate, allowing the choline carrier to let the choline back in
What methods are available to uptake Noradrenaline
Presynatic uptake, whereby NA gets recycled
Postsynaptic uptake, which mops up any remaining NA
What is co-transmission?
Transmission through a single synapse by more than one transmitter
Examples include ATP, Neuropeptide Y, Dynorphin, NO
How does presynaptic modulation of synaptic transmission occur?
Synaptic Transmission primarily inhibits neurotransmitter release but can enhance it.
Autoreceptors - these act on its own presynaptic terminal to reduce release. E.g. mGlu2 modulation of glutamate release.
Heteroreceptor - neurotransmitter acting to modulate release other than its own ligand. GABA acting on GABA-B to reduce glutamate release.
Antagonists and agonists can have the same physiological effect
Yes it can - this depends on receptor location. E.g. Hysocine and Morphine in the GI tract would both reduce the muscle contractions and reduce the rate of peristalsis.
How do GABA-a receptors act?
They act via influx of chloride ions and have a hyperpolarising effect on the membrane potential
How do G-proteins get activated
Why are GPCR’s so important
Involved in numerous physiological processes
Target for >50% of all prescribed medicines
Why do we need reflexes?
Maintain Body homeostasis
Detect and react to changes in environment e.g. temp, toxins
Protect the body from noxious stimuli.
Examples of Simple Reflex
Knee-jerk reflex (Monosynaptic)
Pain withdrawal reflex (polysynaptic)
Learned Reflexes
No specific norm, can be learned and improved - Somatic involvement
Can exercise improve reflexes?
Although evidence is limited, there are some specific training methods which can improve reflexes.
These can be particularly useful following stroke, spinal cord injury etc.
Why are sensory systems required?
Maintain homeostasis.
Detect and react to changes in environment
Protect the body from noxious stimuli.
Examples of nociceptors
Mechanoceptors - Activated by Intense pressure on skin - A-delta fibres
Thermoceptors - Activated by extreme temperature (A-delta fibres)
Polymodal - Activated by high intensity mechanical, chemical, and thermal stimuli - C fibres
Pain transmits via A-delta and C..
These fibres have slightly unique methods of inducing pain.
A-delta causes pain in the first instance and mediates a sharp pain - these types of fibres are myelinated
C fibres - relatively slow fibres which end up mediating longer lasting second pain - these fibres are unmyelinated.
Where is the synapse for nociceptors?
Synapse is located in the dorsal horn of the spinal cord.
Glutamate is the excitatory neurotransmitter, modulated by many others.
How are nociceptive pathways projected to the brain?
Via spinothalamic tracts - descending inhibition and perception.
Where can pain signals be interrupted in the spinal cord?
The substantia gelitanosa.
How do local anaesthetics block sodium channels?
Unionised local anaesthetic enters the cell - the LA becomes ionised once inside the cell, and blocks the sodium channels, resulting in a reduction of pain signalling.
What is Aspirin’s mechanism of action?
Aspirin was the first NSAID and is the only one which irreversibly binds and inhibits COX-1
How does the metabolism of paracetamol work?
How does codeine metabolism work?
What are the transport mechanisms at the BBB?
