Nerve & Muscle Flashcards
Describe how a resting potential is maintained
K+ moves out of the cell via the K+ channels
Na+ moves into cell via Na+ channels
Na+/K+ ATPase actively pumps 3Na+ out of the cell and 2K+ into the cell to maintain concentration gradient
Final resting potential is approx -70mv
Describe how an action potential is generated
- Membrane is depolarised so its membrane
- Voltage gated Na+ channels allow Na+ into the cell
- Voltage gated Na+ channels start to inactivate
- Voltage gated K+ channels open allowing K+ to leave the cell causing repolarisation
- K+ and Na+ channels closed
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What’s the difference between chemical and electrical synapses?
Electrical synapses have a direct passage of current between neurones
Chemical synapses have to release vesicles containing neurotransmitter to affect the target cell
What are the features of an electrical synapse?
- more rapid
- can be bidirectional
- enable the synchronised activity of groups of cells
What are gap junctions?
Channels called connexons in the pre and post synaptic membrane join to form complexes creating electrical continuity between the two cells
What are the features of a chemical synapse?
Unidirectional
Slower than electrical
In a chemical synapse, how are neurotransmitters cleared from the synapse?
Enzymatic degradation
Reuptake by specific transporters
Diffuse out of the synapse
What are the two types of post synaptic receptors?
Ionotropic
Metabotropic
What type of post synaptic receptor is this?..
- open/close in response to the binding of the neurotransmitter
- fast acting
Ionotropic
What type of post synaptic receptor is this?
- requires G proteins (secondary messangers)
- slow and more persistent response
metabotropic
What is a neuromodulator?
It alters the strength of transmission between neurons by affecting the amount of neurotransmitter produced and released
What is the function and drug effect/pathology of acetyl choline?
Main parasympathetic neurotransmitter, involved in NMJ, learning and memory
Botox causes paralysis by blocking ACh release
What is the function and drug effect/pathology of noradrenaline?
Used by the sympathetic nervous system, alertness, mood
Beta adrenergic receptor blockers used to treat cardiovascular pathologies e.g. hypertension and heart faliure
What is the function and drug effect/pathology of GABA?
Main inhibitory neurotransmitter
Anti-anxiety drugs bind to GABA receptors suppressing overactive brain areas linked to worry
What is the function and drug effect/pathology of Glutamate?
Main excitatory neurotransmitter, learning, memory
High levels are associated with schizophrenia
What is the function and drug effect/pathology of serotonin?
Influences sleep, appetite, learning/memory and mood
Selective uptake inhibitors are used to treat depression
What is the function and drug effect/pathology of dopamine?
Pleasure neurotransmitter, influences learning/memory, motivation/behaviour, mood and movement
Drugs that increase dopamine are used in treating Parkinson’s
What does a single motor unit consist of?
A single motor neurone and all the skeletal muscle fibres innervated by that neurone
How is fine precision in the muscle enabled?
Smaller muscles having few muscle fibres in each motor unit
What are the features of a neuromuscular junction?
Chemical synapse
1:1 transmission
unidirectional
Inherent time delay (0.5-1ms)
Site for many diseases and action of many pharmacological drugs
Label this diagram
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Describe how acetylcholine is removed from the synapse
After ACh has bound to the receptor on the post synaptic cell it is hydrolysed by acetylcholinesterase
Choline is recycled back into the presynaptic terminals to make more ACh
Acetate quickly diffuses into the surrounding medium
Describe the structure of the nicotinic acetylcholine receptor
ACh gated Na+ channels
Made of 5 polypeptide subunits
(Two alpha, one each of beta, sigma and gamma)
2 ACh molecules are needed to stimulate the receptor
What does succinylcholine do and how is it used clinically?
Causes muscle paralysis by affecting ACh receptors
Used during surgery to relax skeletal muscle
Patient is requires to be artificially ventilated
What does succinylcholine do and how is it used clinically?
Causes muscle paralysis by affecting ACh receptors
Used during surgery to relax skeletal muscle
Patient is requires to be artificially ventilated
How does the toxin produced by clostridium botulinum affect the NMJ?
It prevents exocytosis of ACh from the synaptic vesicles
Therefore muscle does not contract
How can Botox be used clinically?
Can be used to relax muscles to help with strabismus (cross eyes), biepharospasm (eyelid spasms) or cerebral palsy
What are the symptoms of myasthenia gravis?
Muscle weakness that increases during periods of activity and improves after rest
Eye related issues
- Ptosis (drooping of upper eyelid)
- Diplopia (double vision)
Face and throat related issues
- Altered speech
- Dysphagia (difficulty swallowing)
- Loss of facial expression
What is myasthenia gravis?
Autoimmune condition
Caused by antibodies that competitively inhibit the nAChR on the motor end plate
NMJ less responsive to ACh - muscle weakness
What is the treatment for myasthenia gravis?
Long term acting anti-cholinesterases (neostigmine)
Prevent breakdown of ACh - more ACh available in the synapse to compete with the antibodies for the nAChR
What is Lambert-Eaton myasthenic syndrome?
Autoimmune disease
Antibodies formed against the voltage gated Ca2+ channels on the presynaptic nerve terminal at NMJ
Prevents ACh release
Condition is also associated with small cell lung cancer
What are the symptoms of Lambert Eaton myasthenic syndrome?
Weakness in muscle limbs, fatigue, autonomic dysfunction (e.g. blurred vision, dry mouth)
Symptoms almost always precede detection of cancer
What is the treatment for Lamert-Eaton myasthenic syndrome?
Using immunosuppressants
Use a K+ channel blocker - blocks K+ channels on presynaptic nerve terminal
This delays the repolarisation of the membrane so prolongs depolarisation of the presynaptic membrane
This enhances Ca2+ entry into the terminal so facilitates release of ACh improving neuromuscular transmission
What is the difference between the autonomic and somatic nervous system?
Autonomic - involuntary responses
Somatic - voluntary responses
What is the difference between the sympathetic and parasympathetic nervous system?
The sympathetic does fight/flight responses such as increased heart rate or dilated pupils
Parasympathetic does the opposite so relaxes e.g decreased heart rate or constricted pupils
Describe the structure of a multipolar neurone
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Describe the structure of a unipolar neurone
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Describe the structure of a bipolar neurone
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What is the difference between what white and grey matter in the brain are made from?
Grey matter contains more neuronal cell bodies
White matter contains more axons
What is the meninges?
3 membranes that overlie the brain and spinal cord
- dura mater
- arachnoid mater
- pia mater
What do the following terms mean?
- meningitis
- extradural, subdural, subarachnoid
- meningioma, metastasis
- infection of the meninges
- types of bleeds
- tumours of the meninges
What are glial cells?
Non-neuronal cells in the CNS and PNS
What are the roles of the glial cells?
- formation of myelin
- nutritional support
- structural support
- immune functions (some)
Are these neuroglial cells found in the PNS or CNS?
- ependymal cells
- oligodendrocytes
- astrocytes
- microglia
Central nervous system
Are these neuroglial cells found in the PNS or CNS?
- schwann cells
- satelite cells
Peripheral nervous system
What are the features of oligodendrocytes?
- Form myelin sheaths in CNS
- One oligodendrocytes can myelinate multiple axons
- Clinically important as they are the site of damage in demyelinating diseases (multiple sclerosis)
What are the features of microglia?
Resident immune cells of CNS, related to macrophages
General maintenance
- clear up damaged neurons
- prune unnecessary synapses
- scavenge amyloid plaques
What are the roles of astrocytes?
- Metabolic support for neurons
- Structural support
- Form blood-brain barrier with capillaries
- Repair ‘glial scar’ injuries
- Contribute to synaptic function
What are the features of ependymal cells?
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Lining cells of the ventricular system of the brain, central canal and spinal cord
Ciliated surface aids flow of cerebrospinal fluid
Modified ependymal cells contribute to CSF production
What are the features of Schwann cells?
They support neurones in the PNS
Responsible for myelin formation in the PNS
Some provide support without myelinating
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Surround cell bodies in PNS
Regulate extracellular environment of neurones in the ganglia
Express various ion channels and transporter es for neurotransmitters
How are peripheral cells classified?
Based on diameter and conduction velocity
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What are the two types of refractory periods and whats the difference?
Absolute refractory period - during the action potention
Relative refractory period - a large stimulus can still result in an action potential at this time
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How does it affect the action potentials if the stimulus is above the threshold?
It increases the frequency of APs but not the amplitude
What is amyotrophic lateral sclerosis?
The most prevalent form of motor neurone disease
What are the symptoms of motor neurone disease?
Progressive voluntary muscle weakness and paralysis
Which motor neurones does MND tend to affect?
Somatic motoneurones
(Leaves sensory and autonomic neurones intact)
What is the suspected cause of motor neurone disease?
Excessive levels of the neurotransmitter glutamate causes over excitation of the motoneurones leading to damage and death
What causes the build up of neurotransmitter glutamate in motor neurone disease?
Loss of glutamate transporters
Excess glutamate causes Ca2+ to flood ge cell which causes cell damage and can activate apoptosis
What cells are responsible for myelination in the PNS and CNS?
CNS - oligodendrocytes
PNS - Schwann cells
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What is the difference between how oligodendrocytes provide myelin than Schwann cells?
One schwann cell provides myelinaton for one segment of one axon
Oligodendrocytes can myelinate 3-50 neurones
How does a demyelinating disease affect the nervous system?
Nerve impulses slow/stop
Deficiency in sensation, movement, cognition
Axons and cell bodies degenerate
How are demyelinated diseases classified?
On basis of cause
- demyelinating leukodystrophic diseases (genetic cause)
- demyelinating myelinoclastic diseases (healthy myelin destroyed by a toxic agent)
What type of neurones does multiple sclerosis affect?
Sensory and motoneurones
How does multiple sclerosis work?
Autoimmune degenerative nerve disorder
(Immune system attacks the myelin sheath)
Results in areas of scarring - impedes nerve signalling
What are the symptoms of multiple sclerosis?
Difficulty walking
Blurred vision
Numbness or tingling in different parts of the body
Problems with balance and coordination
Problems with thinking, learning and planning
What is the cause of multiple sclerosis?
Exact cause is unknown
Molecular mimicry - virus triggers an autoimmune attack which destroys nerves
Basically when there is structural similarity between foreign and self molecules
What are the features of Guillain-Barre syndrome?
Demyelinating disease of the peripheral nervous system
Autoimmune disease (caused by biomimicry)
What are the symptoms of Guillain-Barre syndrome?
Symmetrical ascending muscle weakness and paraesthesia in arms and legs
Loss of sensation
Autonomic dysfunction
What do the following types of receptors mean what are tuned to detect sensory modalities?
- mechanoreceptors
- thermoreceptors
- photoreceptors
- chemoreceptors
- nociceptors
Mechanoreceptors - touch, pressure, vibration, stretch
Thermoreceptors - hot, cold, temperature change
Photoreceptors - light
Chemoreceptors - chemicals
Nociceptors - pain
