Nervous system Flashcards
What is a membrane potential?
Difference in the concentration of different ions across the cell
What ions contribute to the resting membrane potential
Na+
K+
A- - anions which have a negative charge due to amino acids
Concentration of ions inside cell
Na+ = 15mM K+= 150mM A- = 60mM
Concentration of ions outside the cell
Na+ = 150mM K+ = 5mM A- = 0
What contributes most to the membrane potential?
Potassium ions
What is resting potential?
-70mV
What are the stages of an action potential?
Resting potential Stimulus Threshold Action potential Repolarisation Hyperpolarisation Returns to resting
Sodium voltage gated channel proteins
have 2 separate gates - inactivation and activation
in resting state the inactivation gate is open but the activation gate is closed
Process of action potential generation
- Stimulus causes sodium ion channels to open and sodium moves into the cell
- Once threshold is reached the sodium voltage gated channel is activated and both gates open
- there is an influx of sodium ions
- causes depolarisation and more channels to open, increasing depolarisation
- Potassium channels open and there is an outflow of potassium ions
- Inactivation gate of voltage gated sodium ion channels close
Repolarisation
The leaky sodium ion channels and potassium ion channels allow outflow of sodium and potassium ions causing repolarisation
Hyperpolarisation
Outflow of potassium ions can be large enough to cause hyperpolarisation so the cell becomes more negative than resting potential. The potassium ion voltage gated channels close and the membrane potential is restored by the sodium/ potassium pump
Types of refractory period
- Absolute
2. Relative
Absolute refractory period
No stimulus can initiate a second action potential because the inactivated sodium gate is closed/ cannot reopen
Relative refractory period
period of time when a second action potential can only be initiated with there is a larger than normal stimulus are this is when the potassium channels are still open and so there is hyperpolarisation
How are action potentials propagated?
Influx of sodium ions causes adjacent voltage gated channels to open and cause the action potential to travel along the membrane
Continuous conduction
step by step depolarisation and repolarisation of the adjacent segment of the membrane . Occurs in unmyelinated neurons and muscle fibres
saltatory conduction
Occurs in myelinated neurons becaus there is an uneven distribution of voltage gated channel proteins - few where there is myelin sheath and many at nodes of ranvier
How does saltatory conduction work?
An electric current flows through the ECF surrounding the myelin and through the cytosol from one node to the next causing the sodium ion channels to open at the next node.
What is special about saltatory conduction
The action potential leaps from one node to the next and so is energy efficient as there are smaller regions of depolarisation
what factors affect the speed of propagation?
Myelination
axon diameter - larger diameter the faster rate of conduction due to larger surface area
temperature - quicker when warmer due to rate of diffusion
What are the different types of neurotransmitter?
Excitatory and inhibitory
Excitatory neurotransmitter
One that causes depolarisation of the post-synaptic membrane - brings it closer to threshold
Inhibitory neurontransmitter
Causes hyperpolarisation of the post synaptic membrane
Main neurotransmitters
Glutamate Serotonin Dopamine Histamine ATP Acetylcholine Noradrenaline Glycine Neuropeptides GABA
Glutamate
Main excitatory in CNS
GABA
Main inhibitory in adult brain
Glycine
Main inhibitory in spinal cord
Acetylcholine
excitatory at NMJ and inhibitory at heart
Receptors of acetlycholine
Nicotinic and muscarinic
Nicotinic at NMJ
Muscarinic is inhibitory only at heart muscle
Histamine
Excitatory
Noradrenaline
Excitatory and inhibitory
Receptors of noradrenaline
Alpha 1&2
Beta 1-3
Neuropeptides
excitatory and inhibitory - they assist neurotransmitters
ATP
Excitatory
Serotonin
Inhibitory and excitatory
How many receptors does serotonin have?
13 - all GPCRs except 5-HT3
main controller of mood
Dopamine
Excitatory and inhibitory
Dopamine receptors
D1-5 linked to schizophrenia and parkinsons
What neurotransmitter works in the sympathetic NS post-ganglionic?
Noradrenaline
Formation of noradrenaline
Tyrosine-DOPA-Dopamine-Noradrenaline
What controls the presynaptic levels of serotonin, noradrenaline, adrenaline and dopamine at the presynaptic membrane?
Monoamine oxidase
What neurotransmitter works at an adrenal medullary cell assisting adrenal catecholamine release?
Adrenaline
Formation of adrenaline
Tyrosine-DOPA-Dopamine-Noradrenaline-Adrenaline
What inhibits noradrenaline release?
Presynaptic reuptake
Catechol-o-methyltransferase (COMT) which breaks it down at postsynaptic neuron
Serotonin formation
Tryptophan-5hydroxytryptophan-5hydroxytryptamine (5-HT)
What does serotonin act on?
CNS
Gut
CVS
Blood
Serotonin role in CNS
Mood memory aggression appetite sleep addiction
Serotonin role in Gut
increased motility
emesis
Serotonin role in CVS
Vasoconstriction
increases heart rate
Serotonin role in blood
Platelet activation
Alpha 1 adrenergic receptor
Arterioles and bladder
Vasoconstriction and constriction
Affected by adrenaline and noradrenaline
Alpha 2 adrenergic receptor
Central and presynaptic Inhibition and inhibition of release of adrenaline and noradrenaline
Beta 1 adrenergic receptor
Heart
Increases heart rate and contractility. Affected by adrenaline and noradrenaline
Beta 2 adrenergic receptor
Bronchi and muscle blood vessels and uterus
causes bronchodilation and dilation of muscle blood vessels and relaxation of uterus
Affected by adrenaline only
Beta 3 adrenergic receptors
Fat cells - lipolysis
Thermogenesis
Affected by adrenaline and noradrenaline
Catecholamines
Adrenline and noradrenaline
GPCR classification
Gs
Gi
Gq
Gs receptor
Adrenergic Beta 1 and heart
Stimulates adenylate cyclase to increase cAMP concentration and activate protein Kinase A. Increases rate and strength of contractions
Gi receptor
cholinergic muscarinic 2 in heart . Inhibits adenylate cyclase decrease cAMP. Decreases rate and strength of contractions
Gq receptor
Adrenergic alpha 1 in blood vessels. IP3 opens calcium ion channels and activates protein kinase C. Causes vasoconstriction
Peripheral neurotransmitters
Acetylcholine
Noradrenaline
CNS neurotransmitters
Acetylcholine Noradrenaline Dopamine Serotonin GABA Glutamate Endorphins/ enkephalins Substance P Glycine
Role of acetylcholine
motor function regulation
emotion
arousal
Role of noradrenaline
memory
arousal
circadian rhythm
endorphin release in spinal cord which inhibits nociception
Role of dopamine
Motor function regulation
memory
emesis
regulation of hormone release
Role of serotonin
mood memory appetite sleep endorphin release in spinal cord and inhibits nociception
GABA receptors
GABA a - chlorine channel linked
GABA b - GPCR
Glutamate receptors
NMDA and non-NMDA - KA and AMPA
what do Endorphins/ Enkephalins do?
Inhibits nociception in dorsal horn of spinal cord
Substance P
amplifies nociception in the dorsal horn of spinal cord
What are the types of sensory cells/ receptors
Chemoreceptors Thermoreceptors Mechanoreceptors Photoreceptors Baroreceptors Hydroreceptors Magnetoreceptors Nociceptors Osmoreceptors Proprioceptors
Autonomic
regulates functions with little or no voluntary control, via a pair of opposing systems = sympathetic and parasympathetic
Parasympathetic NS
Comfort
Sympathetic NS
Crisis
What tissues can be innervated by the autonomic NS
smooth muscle cardiac muscle exocrine glands endocrine glands fat cells
What does the parasympathetic nervous system affect?
Pupils salivary glands heart rate bronchi gut bladder
What does PSNS do to pupils?
constricts
What does PSNS do to salivary glands?
stimulates
What does PSNS do to heart rate?
decreases
What does PSNS do to bronchi?
constricts
What does PSNS do to gut?
stimulates peristalsis and gastric acid secretion
What does PSNS do to bladder?
stimulates contraction, allows urine to be passed
What are the pathways of the parasympathetic NS?
Craniosacral
What does the sympathetic NS affect?
Arterioles sweat glands pupils salivary glands heart rate bronchi gut bladder
What does SNS do to arterioles?
constricts
What does SNS do to sweat glands?
stimulates via ACh receptors
What does SNS do to pupils?
dilates
What does SNS do to salivary glands?
inhibits
What does SNS do to heart rate?
increases
What does SNS do to bronchi?
dilates via circulating adrenaline
What does SNS do to gut?
inhibits peristalsis
What does SNS do to bladder?
inhibits contraction - cannot pass urine
What are the pathways of the sympathetic NS?
Thoracolumbar - only input between T1 and L2
Which cranial nerves are autonomic?
oculomotor, facial, glossopharyngeal and vagus
Parasympathetic pathway
2 neurones
long pre-ganglionic and short post-ganglionic
Sympathetic pathway
2 neurone pathway
short pre-ganglionic and long post-ganglionic
Ganglia of sympathetic NS
ascends to supply head, descends to supply pelvis
directly innervates adrenal medulla
directly from pre-ganglionic neurone
releases adrenaline
Horner’s syndrome
Damage to the sympathetic nerves of face causing miosis, ptosis, lack of sweating and facial flushing. could be a sign of cancer at the top of the thorax.
What is miosis?
Pupil constriction
What is ptosis?
Droopy eyelid
Autonomic neurotransmitterS
acetylcholine
noradrenaline
Muscarinic 1 receptor
autonomic ganglia, synaptic transmission
Muscarinic 2 receptor
stomach - acid secretion
Muscarinic 3 receptor
bronchi - constriction bladder - contraction gut - increases peristalsis eye - accommodation salivary glands - saliva secretion stomach - acid secretion
Muscarinic 4 receptor
CNS - multiple roles
Muscarinic 5 receptor
CNS - multiple roles
Atropine
blocks muscarinic receptor to increase heart rate
Isoprenaline
can be used to activate beta 1 receptors
how to treat Hyperhidrosis
can be treated locally by botox injections which prevent synaptic ACh release
Pilocarpine
selective M3 agonist used to treat glaucoma by constricting the pupil
Anaphylaxis
results in profound histamine induced hypotension and bronchospasm - adrenaline is used to treat it as it stimulates both alpha 1 and beta 2
Ear drum
Tympanic membrane
Middle ear
Made up of 3 bones oval window round window stapedius muscle tensor tympanic muscle eustachian tube
bones of middle ear
OSSICLES
malleus
incus
stapes
Membranes of ear
vestibular
basilar
tectorial
Organ of Corti
on top of the basilar membrane and beneath the tectorial membrane with hair cells on the surface which have stereocilia
the organ of corti is embedded in endolymph
Fluid spaces
Scala vestibuli - perilymph
Scala tympani - perilymph
Scala media - endolymph
electrochemical potential between the spaces
Hair cells
inner hair cells - responsible for transducing the mechanical energy
outer hair cells
stereocilia
How is an action potential generated in the ear?
waves of vibration in scala media causes membranes to move and hair cells bend - moving ions and creating an action potential
What happens in the hair cells when an action potential is generated in the ear
as the membranes move the hair cells move. The hair cells have thick bases containing potassium solution and stereocilia on the top which is bathed in endolymph which is rich in potassium ions. When the stereocilia move the tip links stretch and mechanical gates channels open and potassium diffuses, opening calcium ion channels to open and cause neurotransmitter release forming an action potential .
Pitch
Varied frequencies which are detected at different positions along the basilar membrane
Mechanism of damage from noise
damage to hair cells/ cilia
inflammation
excitotoxicity
Acoustic reflex
method to try and dampen the sound
tensor tympani attached to the tympanic membrane and stapedius to the stapes
the muscles contract in response to loud noise
contraction of stapedius pulls stapes and reduces the intensity of the sound reaching the cochlea
Ineffectiveness of acoustic reflex
muscles fatigue quickly
Rinnes test
normal result = air conduction>bone conduction
sensorineural deafness = air conduction>bone conduction
conductive deafness = bone conduction> air conduction
Webers test
normal = sound heard equally in both ears
sensorineural deafness = sound is louder on side of intact ear
conductive deafness = sound is louder on side of affected ear
vestibular apparatus
near to cochlea: semi circular canals utricle saccule contains endolymoh and perilymph
balance
rotation of head movements can be detected in all planes as the semi circular canals are in all 3 planes.each canal is an ampulla which contains the crista ampullaris
Crista ampullaris
the sensing mechanism linked to vestibular nerve
