Neuromuscular etc Flashcards
What is a tendon Golgi?
Junction between tendon and muscle that monitors tension
What is the structure of a tendon Golgi?
Afferent nerve endings surrounding the collagen bundles in tendon
What does a muscle spindle do?
Monitors length of muscle
Structure of muscle spindle?
Afferent nerve endings surrounding muscle fibres
Intrafusal/Extrafusal?
Intrafusal - within spindle
Extrafusal - outside spindle
Name reflexes
Stretch
Withdrawal
Inverse stretch
Clasp knife reflexes
What is a stretch reflex?
A muscle contraction in response to stretch
Eg postural control
Lean to far to one side muscles contract to correct it
What is a withdrawal reflex
Protects body from damaging stimuli
Eg withdrawing hand from hot object
What is a inverse stretch reflex?
Also called Golgi tendon reflex
Causes relaxation before the tendon tension becomes high enough to cause damage
What is a clasp-knife reflex?
When a limb resists passive resistance but then suddenly gives way when more pressure is applied
What causes upper motor neuron weakness?
Corticospinal tract lesions
What causes lower motor neuron lesions?
Peripheral neuropathies
Anterior horn cell lesions
What causes weakness at neuromuscular junctions?
Myasthenia gravis
Where are upper motor neurons?
Motor neurons within the CNS (brain & spinal cord)
Above anterior horn cell
Where are lower motor neurons?
In PNS
From spinal cord to the rest of the body
Below anterior horn cell
Signs of upper motor neuron lesion?
Increased tone (spasticity) Hyperreflexia
Signs of lower motor neuron lesion?
Decreased tone (flaccidity)
Hyporeflexia
Fasciculations & atrophy
What happens at a neuromuscular junction?
- Action potential arrives at the presynaptic terminal causing Ca channels to open and Ca to go into the presynaptic bulb
- The Ca ions cause vesicles to release Ach from synaptic vesicles into the presynaptic cleft
- Ach diffuses across and binds to the ACH receptors on postsynaptic muscle fibre membrane
- Na ions go into postsynaptic terminal and K ions leave it
- This muscle cell results in depolarisation of membrane. An action potential is generated and propagates over muscle cell membrane
- Causes Ca to be released from sarcoplasmic reticulum and muscle contracts
What happens to the Ach after it has bound to the receptors?
It is broken down into acetic acid and choline by acetlycholinesterase
Reabsorbed back into presynaptic bulb and combines to form more Ach
What is a motor end plate?
The bit on the muscle where an axon of a motor neuron establishes synaptic contact with it
