NAS W4 - DISORDERS OF MOTOR UNIT & ANAESTHETIC Flashcards
WHY RE-INNERVATION NOT ALWAYS SUCCESSFUL
outcompeted by other effector organs so nerve re-innervates effector that is dif. to original effector which leads to crocodile tears syndrome
WAYS MOTONEURON CELL BODY DIES
infection of ventral horn of grey matter of spinal cord
POLIO MYELITIS
- 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)
CAUSE OF MOTONEURON DISASE (UMN or LMN)
due to apoptosis where cell bodies of motoneurons suicide
DISORDERS OF MOTONEURON AXON
- 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
SIGNS OF DISORDERS OF SKELETAL MUSCLES
part of motor unit so disorders lead to LMN signs
LMN SIGNS
damage to LMN (due to damage to axon, cell body or NMJ) = impairment of motor system
HOW TO RECOGNISE NMJ
- presynaptic noticeable as has lots of vesicles
- postsynaptic noticeable as has folds (increase SA)
BOTOX
causes paralysis (depletes presynaptic terminal of NMJ of its neurotransmitter)
USES OF LOCAL ANAESTHETICS
dental work, stitching, eye operations
HOW LOCAL ANAESTHETICS WORK
- 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
NOCICEPTOR
- 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
ANAESTHETIC BLOCKING ION CHANNELS
can block ion channels when in ionised form (more pain = more open channels = more channels being blocked)
HOW PH AFFECTS ANAESTHETIC EFFECTIVENESS
inflammation/infection = more acidic = more ionised form of anaesthetic = poor anaesthesia
DIFFERENTIAL SENSITIVITY OF NEURONES TO ANAESTHETIC
motor neurones (much larger & myelinated) have FAR LOWER sensitivity to anaesthetic than small nociceptors & a-motoneuron axons
LOCAL ANAESTHETIC ADMINISTRATION
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)
TOPICAL ANAESTHESIA
on surfaces e.g. skin but not effective as skin has many layers for it to diffuse through
INFILTRATION ANAESTHESIA
injected into skin/area
NERVE BLOCK ANAESTHESIA
injecting fairly proximally so we anaesthetise whole nerve & all axons in that area e.g. numbing whole jaw
EPIDURAL ANAESTHESIA
inject into space surrounding vertebrae (epidural space) so that local anaesthetic bathes nerves exiting spinal cord to denervate whole lower body
SPINAL ANAESTHETIC
inject into CSF & can affect any nerve in that space (anaesthetise large area of body e.g. major surgery)
SIDE EFFECTS OF LOCAL ANAESTHESIA
- 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
OTHER DRUGS GIVEN WITH LOCAL ANAESTHETICS
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)
LMN
have cell body in ventral horn of spinal cord or cranial nerve nuclei & its axon comes out & supplies skeletal muscle
UMN
command LMN to bring about muscle contractions
