block D - CNS Flashcards
what are the functions of the CNS?
they’re the primary unit of integration
- help to keep the body environment constant (homeostasis),
- helps with the bodies perception (sight, taste, smell and hearing),
- movement and coordination, intellect and emotions
what are the cellular components of the CNS?
neurons, glia and blood supply
what are glia?
theyre cells that are ‘others’
helper cells
what are myelinated axon bundles?
they wrap the cell body to protect it
what are astrocytes?
they connect with neurons and blood cells
they keep the junctions between endothelial cells tight in central arterioles
they also make sure that nothing that’s not allowed into the arterioles get in
what are olgiodendrocytes?
theyre myelin sheaths in the CNS
they help to more effectively transmit electrical impulses
what are microglia?
theyre cells like phagocytes and scavengers
what are ependymal cells?
they’re line ventricles, spinal canal and CSF circulation
what are the major subdivisions of the brain?
forebrain
midbrain
hindbrain
what are the two main parts of the forebrain and what do they consist of?
outer- cerebrum, corpus striatum and hippocampus
inner- thalamus and hypothalamus
what sections make up the midbrian?
basal ganglia including substantia nigra
what parts make up the hindbrain?
cerebellum, medulla oblongata, pons and reticular formation
why is the brain wrinkled?
it increases surface area
what is the hippocampus important for?
memories and emotions
what is grey matter made of?
cell bodies
what is white matter made up of?
its made up of mostly cell axons
what are the 4 lobes of the outer forebrain?
frontal lobe
parietal lobe
temporal lobe
occipital lobe
what does the central sulcus help to do?
it helps us discriminate different parts of the brain
what is the occipital lobe important for?
vision
what is the corpus striatum?
its part of basal ganglia and it coordinates body movements
what system is the hippocampus part of? and what is it important for?
limbic system and its important in pleasure, hostility, anger and instincts, its also involved in memory
what does the thalamus do?
it is the relay center and receives all sensory input, which gives it to the cerebrum and relays cerebrum motor output to other areas
what does the hypothalamus do?
it regulated autonomic and endocrine systems
these are essential for hunger, thurst, osmotic balance, body temperature and metabolic rate
what is the subratntia nigra?
its part of the basal ganglia and coordinates body movements
what does the hindbrain do?
it is a continuation of the spinal cord and has acending and decending nerves from the forebrain, its in control of veceral refelexes like heart rate, digestion and breathing
what happens if the hindbrain is damaged?
DEATH
what is the brain stem reticulum formation?
its within the brainstem and it modulates levels of wakefulness and sleep
what is the 2nd biggest structure in the brain?
the cerebellum
what does the cerebellum control?
fine coordinated movemets
what is the spinal cord surrounded by?
ascending and decending nerve tracts
what is the Ventral root?
motor/efferent nerves leaVing cord and innerVate effectors (innervate = supply)
what is the dorsal root?
its sensory and efferent nerves entering the cord
what is the dorsal root ganglion?
its a cluster of nerves coming out of the dorsal root
the nerves are sensory nerve cell bodies
what is the blood brain barrier between?
it is between the blood vessels and cerebral ventricles, these are around the brain and brainstem
and between the blood vessels and the interstitial fluid adjacent to neurons
what is the CSF-ISF interface?
its where there is some movement of fluid because of a permeable interface between the cerebrospinal fluid and the interstitial fluid (between the brain and the spinal cord)
what does the fluid which is separate from the blood do?
supplies metabolites
physically protects the brain
provides appropriate chemical environment for neuronal function
removes waste
how much of your energy does your brain burn?
1/5
how does the CNS get energy?
it relies on blood glucose and O2 supply to function, it receives 15% of all the blood pumped by the heart and 20% of the body’s total O2 usage
what is the difference between a central areteriole and a peripheral arteriole?
central arterioles have astrocytes to keep them together so nothing unwanted can get into them as they go up to the brain buit peripheral arterioles dont have these astrocytes to keep them together so theyve got tiny pores that allow things into them
what are the structural specialisations of central arterioles?
- tight junctions between endothelial cells
- astorcytes - 2nd barrier
what do central arterioles let into them and what do they stop from getting in?
they allow small ionised lipid-soluble compounds like O2, CO2 and hormones, they also allow in substrates for specific transporters e.g. glucose, essential amino acids and ions
they block the entry of proteins, substances bound to plasma proteins, toxins, pathogens and most drugs
what does BBB stand for?
Blood-Brain Barrier
what causes injury and inflammation like meningitus?
BBB breakdown and when the CNS is exposed to harmful substances
what does the cerebrospinal fluid fill?
4 chambers
2x layteral, 3rd and 4th ventricles and spinal cord canal
what is the point of cerebral spinal fulid?
it cushions the brain and spinal cord from physical forces and it aids the removal of waste to the venous system
can cerebral spinal fluid flow anywhere it wants to in the brain?
no, it follows a specific path through the brain and it only flows in one direction
it flows from ventricles to surround brain and spinal cord and a small amount goes into the spinal cord canal and then exits through one-way valves to veins
how is cerebral spinal fluid produced?
by choroid plexus (ependymal cells + capillary bed)
it produces ~20ml CSF/hr for physical support and buffer
the ependymal cells actively secrete Na+ into ventricle and Cl- follows passively, this increases the osmotoc pressure which drives into venticle
what does the cerebral spinal fluid carry?
glucose transporters have low efficiency so CSF glucose is about 66% of blood glucose and it has less K+ than blood (a net reverse transport of K+)
what are chemical messengers?
theyre general properties of neurotransmission and you get non-peptide ones and peptide ones
what are non-peptide neurotransmitters involved in?
they’re involved of synthesis, storage, release, mimicry, antagonists and inactivation
they’re also involved in pathways and are the main CNS types
what are the structural properties of neurotransmitters?
they have a presynaptic axon, post-synaptoc cell body and post-synaptic recpetors
what does calcium do at the synapse?
it activates and changes some of the vesicles and then they fuse and dump out neurotransmitter into the synapse for it to then bind to the post synaptic membrane
what are examples of monoamines?
noradrenaline,
dopamine,
5-hydroxytryptamine (5HT/ serotonin),
histamine
what are some examples of amino acid non-peptide neurotransmitters?
GABA, glutamate and glycine
what are some other non-peptide neurotransmitters?
acetylcholine, ATP and nitric oxide
what is the criteria for identification of a neurotransmitter? (theres 6)
- synthesised within the neuron
- stored in nerve terminal
- released by nerve stimulation in Ca2+ dependant manner
- specific mechanisms exist for inactivation
- exogenously applied substances mimic endogenous response to neurotransmitter
- antagonist inhibits both neurotransmitter and exogenously applied substance
what are the steps of dopamine as a neurotransmitter?
- its synthesised within the neuron
- its stored in the nerve terminal
- its released by nerve stimulation in Ca2+ - dependant matter
- specific mechanisms
- mimicry
- inhibition by antagonist
what happens to dopamine after its caused a spike of neurotransmitter?
its rapidly degraded, if its not you would just be hyper all the time
what happens in ‘mimicry’ of dopamine as a neurotransmitter?
cAMP is measures in straitum after nerve stimulation or adding dopamine
how is noradrenaline distributed in the brain?
its distributed from the brain stem to the cortex, then to the libic system, cerebellum and brain stem
what are the physiological functions of noradrenaline?
its part of the reward system and mood, state of arousal (alertedness) and blood pressure regulation
how is dopamine distributed in the brain?
SN to basal ganglia then to VTA to limbic system and cortical forebrain hypothalamus and then finally to pituritary
what are the physiological functions of dopamine?
motor control
reward system
mood
motivation
prolactin secretion
how is 5-HT distruibuted around the brain?
from brain stem to cortex to limbic system, thalamus, hypothalamus and cerebellum
what are the physiological functions of 5-HT?
sleep
wakefulness
temperature regulation
mood
what is the physiological functions of acetylcholine and how is it distributed?
arousal, learning and motor control
distribution - long and short projections from basal forebrain, interneurons in basal ganglia
how is glutamate distributed in the brain and that are the physiological functions of it?
functions- memory, epilepsy, relay of sensory information
distribution - widespread, mainly present as interneurons
how is GABA distributed in the brain and that are the physiological functions of it?
functions-epilepsy and anxiety
distribution - widespread, mainly present as interneurons
how is glycine distributed in the brain and that are the physiological functions of it?
distribution - spinal cord interneurons, modulates NMDA receptors
function- epilepsy (not all forms)
what are neuropeptides?
they’re 5->30 amino acids
they have many different function’s from classical neurotransmitters
what are the similarities between classical neurotransmitters and neuropeptides?
- stored in vesicles, in specific regions
- Ca2+ dependant release
- effect > 2nd messengers / change in ion channel activity`
what are the differences between neuropeptides Vs classical neurotransmitters ?
- synthesised in cell body, part of large precursor protein
- transported to terminal
- processed to active peptide
- released at lower concentrations
- mechanism of inactivation unclear
- removed slowly from synaptic cleft
- longer action
what what is involved in indirect, slow neurotransmission?
its via G-proteins and cytoplasmic 2nd messengers
what are some examples of ligands of GCPR?
dopamine, NA, 5HT, aCh- musccarenic, clutamate metatrophic
how fast is ‘slow neurotransmission’?
secs to mins
how fast is ‘fast neurotransmission’?
10’s of miliseconds
what is direct, fast neurotransmisson via?
receptor-operated ion channels
what are some examples of receptor-operated ion channels?
nicotinic ACh receptors
glumate ionotropic receptors
P2X receptors
what causes inhibitory post-synaptoc potential (IPSP) and what causes exitatory post-synaptic potential (EPSP)?
IPSP- Cl-
EPSP-Na+ and K+
if theres not enough stimulation to hit the neurotransmission threshold, what happens?
nothing. it just fizzles out and doesnt lead to anything
how do pre-synaptic inhibition by fast neurotransmitters work?
the inhibitory neuron is the one affecting the pre-synaptic synapse
what senses are sensed by the sensory reception?
vision
somatic sensory/ touch
gustatory / taste
olfaction / smell
auditory / hearing
balance /movement propricoception
why is sensory reception important?
it maintains homeostasis
detects and reacts to changes in environment
protects the body from noxious (damaging) stimuli
what are the different types of sensory receptors?
- cuteneous receptors - touch, pressure, temperature and pain
- proprioceptors - body position
- special senses- sight, hearign, taste and smell
what do sensory afferent nerves sense?
they only sense their own one specific stimulus
what do free nerve endings sense?
pain and temperature
do the same receptors sense hot and cold?
no, theres 2 different neurons that are sensitive to the different temperatures
how does skin sense pressure?
theres is lots of different nerve endings to sense different pressures and theyre all covered in connective tissue layers
what are some names of nerve endings that detect touch?
merkel’s disk
meissner’s corpuscle
Ruffini’s ending
what happens if the stimulus strength is: sub-threshold; moderate; strong?
sub-thershold- no action potentials are produced
moderate - a few action potentials are generated
strong- lots of action potentials are generated
what happens if there’s a strong continuous signal created?
they start ignoring the information sent because they’ve already detected it and created a response
give examples of 1st, 2nd and 3rd order neurons?
1st - goes from the stimulus to the spinal cord
2nd- goes from spinal cord to thalamus
3rd - goes from thalamus to cortex
do 2 signals coming from the same place to the same place have to follow the same pathway?
no, there can be 2 different pathways for the same pathway
what does the dorsal column system palthway transmit signals for?
fine touch
pressure
propriception
what does the spinothalamic system transmit signals for?
pain
temperature
coarse touch
what does decussation mean?
it means pathways that have to cross to the other side of the brain- thus sensory info is processed on the other side of the brain
where do the signals continuously sensed go to in the brain?
they go to the post centural gyrus
what are the two types of nociceptor fibres and what do they sense?
Aδ- these sense fast, sharp pain myelinated
C fibres- slow, dull aching pain unmyelinated
what are the characteristics of thermoreceptors?
theyre activated by extreme temperatures (>45 degrees, <15 degrees) theyre found at Aδ fibresq
what are the characteristics of mechanireceptors?
theyre activated by intense pressure and are found at Aδ fibres
what are the characteristics of polymodal nociceptors?
theyre activated by high intensity mechanical, chemical and thermal (both hot and cold) stimuli
what is referred pain?
its pain perceived to come form one part of the body but it actually comes from another part
how does spinal cord modulation of pain carried by C fibres?
interneurons that release enkaphalins on either descending stimuli from CNS or localised 5HT to activate pre- and post-synaptic opiate receptors at spinal sensory synapse; GPCRs coupled to Gi leading to decreased cAMP, reduced PKA activity, modulation of K+ conductance thus decreasing neuronal excitability
its part of the spinothalamic pathway
what is the gate control theory of pain?
its where theres a dampening down of the pain signals and the C fibre can turn off the neurons so strong signals dont go to the thalamus
how is pain carried by Aδ fibres modulated?
Aδ fibres synapse in different area of spinal cord
No interneurons that release enkephalins
No opiate receptors morphine ineffective
Sharp pain harder to treat
how is the sense of pain different for everyone?
the more your exposed to continuous stress, the less you may feel pain
its modulated by previous experiences
what are some non-steroidal anti-inflammatory drugs and what do they do?
they block COX-1 and COX-2 which block inflammation
- aspirin, ibuprofen
what does lidocane block?
the generation of action potentials
how do local anasthetics work?
they’re injected locally and block Voltage-dependant Na+ channels to block action potentials
how do opiods treat pain?
they bypass the primary nociceptive afferent pathway and inhibits discharge of 1 degree
