NAS W4 - DISORDERS OF MOTOR UNIT & ANAESTHETIC

Question 1

WHY RE-INNERVATION NOT ALWAYS SUCCESSFUL

Answer 1

outcompeted by other effector organs so nerve re-innervates effector that is dif. to original effector which leads to crocodile tears syndrome

Question 2

WAYS MOTONEURON CELL BODY DIES

Answer 2

infection of ventral horn of grey matter of spinal cord

Question 3

POLIO MYELITIS

Answer 3

• targets cell bodies of LMN of body & infects them
• death of motoneurons = denervation = paralysis of muscles they supply (dangerous if respiratory etc)
• toxic infection of cell body of neurones on ventral horn of spinal cord = death of dorsal horn of spinal cord (ventral horn looks visibly thinner)

Question 4

CAUSE OF MOTONEURON DISASE (UMN or LMN)

Answer 4

due to apoptosis where cell bodies of motoneurons suicide

Question 5

DISORDERS OF MOTONEURON AXON

Answer 5

• may not always lead to motoneuron death but leads to muscle denervation
• more distal the damage, more likely the chance of survival/re-innervation
• e.g. Guillain-Barre syndrome which demyelinates axons of sensory & motor neurons

Question 6

SIGNS OF DISORDERS OF SKELETAL MUSCLES

Answer 6

part of motor unit so disorders lead to LMN signs

Question 7

LMN SIGNS

Answer 7

damage to LMN (due to damage to axon, cell body or NMJ) = impairment of motor system

Question 8

HOW TO RECOGNISE NMJ

Answer 8

• presynaptic noticeable as has lots of vesicles

- postsynaptic noticeable as has folds (increase SA)

Question 9

BOTOX

Answer 9

causes paralysis (depletes presynaptic terminal of NMJ of its neurotransmitter)

Question 10

USES OF LOCAL ANAESTHETICS

Answer 10

dental work, stitching, eye operations

Question 11

HOW LOCAL ANAESTHETICS WORK

Answer 11

• reversibly block nerve conduction to brain when applied to restricted area of body to enable procedure to be carried out without loss of consciousness
• block ion channels when in ionised form

Question 12

NOCICEPTOR

Answer 12

• type of sensory receptors that detect harm to body & perceive it as pain (generate AP to brain)
• if we find way to stop these AP from travelling to brain (by interfering with voltage-gated Na+ channels) we can prevent feeling of pain

Question 13

ANAESTHETIC BLOCKING ION CHANNELS

Answer 13

can block ion channels when in ionised form (more pain = more open channels = more channels being blocked)

Question 14

HOW PH AFFECTS ANAESTHETIC EFFECTIVENESS

Answer 14

inflammation/infection = more acidic = more ionised form of anaesthetic = poor anaesthesia

Question 15

DIFFERENTIAL SENSITIVITY OF NEURONES TO ANAESTHETIC

Answer 15

motor neurones (much larger & myelinated) have FAR LOWER sensitivity to anaesthetic than small nociceptors & a-motoneuron axons

Question 16

LOCAL ANAESTHETIC ADMINISTRATION

Answer 16

more proximal the site of administration, the greater the area anaesthetised (closer to spinal cord = more anaesthetised as you anaesthetise all the nearby branches of nerves too)

Question 17

TOPICAL ANAESTHESIA

Answer 17

on surfaces e.g. skin but not effective as skin has many layers for it to diffuse through

Question 18

INFILTRATION ANAESTHESIA

Answer 18

injected into skin/area

Question 19

NERVE BLOCK ANAESTHESIA

Answer 19

injecting fairly proximally so we anaesthetise whole nerve & all axons in that area e.g. numbing whole jaw

Question 20

EPIDURAL ANAESTHESIA

Answer 20

inject into space surrounding vertebrae (epidural space) so that local anaesthetic bathes nerves exiting spinal cord to denervate whole lower body

Question 21

SPINAL ANAESTHETIC

Answer 21

inject into CSF & can affect any nerve in that space (anaesthetise large area of body e.g. major surgery)

Question 22

SIDE EFFECTS OF LOCAL ANAESTHESIA

Answer 22

• we add agents into LA to ensure no bacteria but these can lead to hypersensitivity/allergy reactions
• specific side effects e.g. high dose injected to blood vessels = lower BP

Question 23

OTHER DRUGS GIVEN WITH LOCAL ANAESTHETICS

Answer 23

vasoconstrictors - constrict blood vessels so harder for anaesthetic to affect blood vessels in that region (leads to less unwanted effects & longer duration of action so can give lower dose)

Question 24

LMN

Answer 24

have cell body in ventral horn of spinal cord or cranial nerve nuclei & its axon comes out & supplies skeletal muscle

Question 25

UMN

Answer 25

command LMN to bring about muscle contractions