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90 Cards in this Set

  • Front
  • Back

What are the two signs of MS that can be elicited on clinical examination?

Uhthoff’s sign
Lhermitte’s sign

What are the two investigations that should be done if MS is suspected? What is expected to be seen?

MRI ➙ Lesions


Lumbar puncture ➙ oligoclonal bands

What investigation distinguishes MS from GBS?

EMG leading to decreased conduction or conductivity speed in GBS and normal in MS

Name 7 functions of Type A nerves

Proprioceptor


Motor


Touch


Pressure


Muscle spindles


Pain


Temperature

Name 1 function of Type B nerves

Preganglionic

Name two functions of Type C nerves

Pain


Postganglionic

Differentiate Type A, B and C nerves in terms of diameters and myelination

Type A: large and highly myelinated


Type B: medium and weakly myelinated


Type C: small and not myelinated

Two clinical features of upper/lower motor neurone lesions

Upper: Reflex below the level of the lesion ➚ and spastic paralysis



Lower: Reflex below the level of the lesion ➘ and muscle wasting and weakness

How many ions and in what direction are transported by Na/K ATPase?

3Na+ out of the cell and 2K+ into the cells

Give the range of potentials in which voltage-gated sodium channels are in each of the three states.

Open in [-50mV ➙ +40mV]


Closed below -50mV


Inactivated in [+40mV ➙ -70mV].

Name the four phases of AP

Initiation

Upstroke

Repolarisation

Refractory period



Name three stimuli that can cause the changes in cations permeability that initiates the AP

Binding of neurotransmitter


Heat


Pressure

What current is responsible for the upstroke in the AP?

Sodium influx through voltage-gated sodium channels

What current is responsible for the repolarisation in the AP?

Potassium efflux through voltage-gated potassium channels

Use-dependent mechanism of action of local anaesthetics

Reversibly bind to open voltage-gated Na+ channels


⇒ Channels cannot return to closed state after inactivation


⇒ Action potential cannot propagate

Name one local anaesthetics

Lidocaine

Name one side effect of local anaesthetics

Nerve damage ⇒ prolonged numbness, feeling of pins and needles, respiratory depression

Relate gap junction, connexons and connexins

Gap junctions are made of 2 connexons each made of 6 connexins.

Name two types of synapse

Chemical and electrical

Differentiate chemical and electrical synapse in terms of: speed of propagation, directionality, and possibility to integrate signals.

Electrical: fast, bidirectional, no integration


Chemical: slow, monodirectional, integration

In which tissues are electrical synapses located?

Smooth and cardiac muscles

In which tissues are chemical synapses located?

Skeletal muscles

What ion channel is responsible for the eventual exocytosis of the neurotransmitter at the presynaptic membrane?

Voltage-gated calcium channels

Name 6 categories (molecules) of neurotransmitters

1) Amino acids


2) Monoamine


3) Opioids


4) Gas


5) Tachykinins


6) Secretins

Name 5 monoamine neurotransmitters

Catecholamines

Dopamine


Histamine


Serotonin


Melatonin

Name and differentiate two types of postsynaptic receptors

Ionotropic: ligand-gated ion channels


Metabotropic: receptor-coupled second messenger (e.g. G-protein)

What transport protein is responsible for the recovery and maintenance of the resting potential after the undershoot of repolarisation in an AP?

Na/K pumps

Three fates of neurotransmitter after exocytosis

(a) reuptake into presynaptic cell, (b) diffuse away from synaptic cleft, (c) undertake enzymatic breakdown

How is ACh synthesised (reaction)?

Acetyl-CoA + Choline ➙ Acetylcholine

What enzyme catalyses synthesis of ACh?

choline-O-acetyltransferase

What proteins mediating the exocytosis of vesicles do Ca2+ bind in the presynaptic neurone?

SNARE


What is the effect of botulinum on NMJ?

Cleaves SNARE proteins ⇒ Release of ACh is blocked ⇒ Paralysis known as botulism (including respiratory failure)

What series of events happens in the post-synaptic cell when ACh binds to nicotinic ACh receptors, leading to initiation of an action potential?

Membrane conductance to Na+ and K+ ➚


⇒ Depolarisation of the muscle fibres


⇒ End-plate potential (not yet an action potential, because the NMJ lacks voltage-gated channels)


⇒ Propagation of the end-plate potential by local circuit currents


⇒ Initiation of an action potential in the vicinity of the NMJ

Mechanism of action of depolarising blockers

Activates nicotinic ACh receptors ⇒ One action potential followed by sustained depolarisation ⇒ Paralysis

Name one depolarising blockers

Suxamethonium

Mechanism of action of non-depolarising blockers

Competitive antagonist of (binds to but does not activate) ACh receptors

Name one non-depolarising blocker

Tubocurarine

Two side effects of depolarising blockers

1) Initial spasms leading to post-operative muscle pain


2) Bradycardia

One side effect of non-depolarising blockers

Histamine release (contraindicated in asthmatics and allergies)

How can effects of non-depolarising blockers be reversed?

Inhibitors of acetylcholinesterase (e.g. eserine)

Name 3 applications of cholinesterase inhibitors

Diagnosis of myasthenia gravis


Treatment of myasthenia gravis


Reverse the effects of non-depolarizing blockers

Name 3 side effects of cholinesterase inhibitors

Bradycardia


Hypotension


Breathing problems



(By activating PNS)

Briefly outline the pathogenesis of myasthenia gravis

1) Antibodies destroy AChR at the NMJ


⇒ Muscle weakness


2) Antibodies destroy MuSK ⇒ Muscle weakness

Name one disease in which muscles get weaker and weaker as they are being used

Myasthenia gravis

Treatment of myasthenia gravis

Cholinesterase inhibitors

Two specific signs of MS

1) Worsening of symptoms when temperature ➚ (Uhthoff’s sign)


2) Electrical sensation running down the back elicited by bending head forward (Lhermitte’s sign)



What muscles are grouped into the category of striated muscles

skeletal and cardiac

Name the three levels of protection to the skeletal muscles



What is the equivalent names for cytoplasm, membrane and endoplasmic reticulum for myocytes

Myoplasm


Sarcolemma


Sarcoplasmic reticulum

What structure in myocytes allow the depolarisation of the membrane to quickly penetrate to the interior of the cell

T-tubules (invagination in the sarcolemma)

What are myofilaments and myofibrils?

Myofibrils are elongated contractile threads found in striated muscles. They are made of myofilaments (proteins)



Myofilaments < Myofibrils < Myofibre < Fascicle < Muscle


Name the two types of myofilaments and their principal constituent

Thin myofilament: made of actin


Thick myofilament: made of myosin

Besides actin, what other two key proteins do thin filaments contain?

Troponin


Tropomyosin

What does troponin bind and at what sites do they bind them?

Tropomyosin (T subunit)


Actin (I subunit)


Calcium (C subunit)

What does tropomyosin bind?

Actin and myosin

Outline the lines and bands of sarcomeres



In what region of the sarcomere do thin filaments attach

Z-line



(Think Zin filament)

In what region of the sarcomere do thick filaments attach

M-line

What does the action potential triggers once it has reached the interior of the cells via T-tubule?

Release of Ca2+ from sarcoplasmic reticulum through ryanodine receptors (RyRs) (that are Ca2+ channels coupled to the T-tubular system) to the myoplasm

Why is intra-cellular calcium in the thin filaments important to trigger muscle contraction?

Troponin C binds 4 Ca2+ ions causing conformational changes in tropomyosin which exposes binding sites and allows myosin and actin to interact to form cross-bridge cycling.

What happens to intracellular calcium in thin filaments when the muscle relaxes?

Ca2+ is pumped back into the the SR by Ca2+ ATPase

Explain how motion of filaments against one another (thick against thin) is modulated by ATP

1) ATP binds to myosin causing myosin head to dissociate from actin


2) Myosin hydrolyses ATP to ADP causing conformational change of the angle of myosin head


3) ADP (and Pi) released from myosin causing conformational change of the angle of myosin head

Mechanism of rigour mortis

After death, the absence of ATP causes muscle to remain contracted for 72 hours before protein degradation.

How does frequency of stimuli change force of muscle contraction ?

Train of stimuli leads to summation of tension as Ca2+ accumulate in cytoplasm.

By what mechanism does training increases force of muscle contraction?

Training increases cross-sectional area of myofibre but not their number.

What are isometric and isotonic contraction?

Isometric contraction: contraction of muscles without shortening




Isotonic contraction: shortening of muscles against constant load

How many calcium ions does troponin bind in muscles?

Skeletal: 4


Cardiac: 3

What basic principle differentiates Type 1 from Type 2 muscle fibres?

Type 1 are for long, resistant efforts

Difference between Type 1 and Type 2 fibres in terms of colour, contraction speed and conduction velocity

Type 1: Red, slow, slow


Type 2: White, fast, fast

Difference between Type 1 and Type 2 fibres in terms of metabolism, power and energy source

Type 1: aerobic, weak, TAGs


Type 2: anaerobic, powerful, ATC

Define motor unit

Group of muscle fibres (6 to 1000s) that a single lower motor neurone innervates

Name two ways in which the body can achieve stronger muscle contraction

Increasing frequency of action potentials or increasing the number of lower motor neurones recruited

In what order are motor neurones recruited when contracting a muscle

Size principle:


First: Small neurones (Type 1)


Second: Medium neurones (Type IIa)


Third: Large neurones (Type IIb)

Name two types of reflexes elicited in muscles

Stretch reflex opposes a rapid increase in muscle length




Golgi tendon reflex opposes an increase in muscle tension

Name the two types of sensory nerves from muscles and what they are sensitive to

Type Ia: absolute changes in muscle length and rate of changes




Type II: absolute changes in muscle length only

What are muscle spindles and what do they contain?

Sensory receptors within the belly of a muscle containing Bag1, Bag2 and chain fibres

What do nerves from the muscle spindles synapse with in the stretch reflex?

α and γ motor neurones

What do γ motor neurones do in the stretch reflex?

Contract the fibres in the spindle itself so they remain aligned with the muscle

What do α motor neurones do in the stretch reflex?

Contract the muscle itself to activate the reflex

Give a practical example of a Golgi tendon organ reflex

Place a bowling ball on a stretch arm. Muscles of the arm contract to avoid overstretching the tendon

Distinguish monosynaptic vs. polysynaptic reflex arches

Mono: no interneurone involved




Poly: 1 or several interneurones involved

Differentiate neurogenic and myogenic smooth muscle

Neurogenic: require nerve inputs


Myogenic: spontaneous activity

What functionally replaces troponin in smooth muscles?

Myosin light chain kinase

Compare smooth muscles and skeletal muscles in terms of number of nuclei, presence of T-tubules, and size of SR

Skeletal: multinucleate, T-tubules, Large SR


Smooth: mononucleate, no T-tubule, Small SR

Where do thin filaments in smooth muscles insert?

Dense bodies (not Z-line)

Compare the actin:myosin ratio in smooth and skeletal muscles

Skeletal: low


Smooth: high (⇒ greater degree of contraction)

Compare presence of gap junctions in smooth and skeletal muscles. Why is that important?

Skeletal: No gap junction


Smooth: gap junctions to allow coordinated contraction

What two coupling processes may lead to contraction of smooth muscles?

1) Excitation-contraction coupling


2) Pharmacomechanical coupling

What is the role of Pharmacomechanical coupling in smooth muscles?

Triggers contraction of smooth muscles even when membrane potential is at rest.

How does the pharmarcomechanical coupling work?

Ca2+ enters the smooth muscle cell by activation of ligand-gated Ca2+ channels or G protein coupled receptor and Ca2+ then activates myosin light chain kinase (MLCK)