Reflexes Flashcards
Are reflexes voluntary or involuntary?
involuntary
How many synapses do stretch reflexes make?
usually only one -monosynaptic
What is the common final motor pathway?
recruitment of motor neurones
Where can motor cell bodies be found?
ventral horn of spinal cord (somatic)
brainstem (cranial nerves)
What can motor neurones be activated by?
various brain regions (cortex)
various peripheral receptors due to reflex
What are the intrafusal muscle fibres wrapped in?
sensory endings
What do the sensory nerve endings (mechanoreceptors) fuse together to form?
a-Alpha axons
What are the steps of the spinal reflex pathway? (knee jerk)
- Stimulus (hammer to knee)
- Receptor activation (mechanoreceptor- sensory endings around intrafusal muscles)
- Stimulus transduction
AP conduction along sensory axon (Aa) - Synaptic transmission in the spine
- Motor neuron recruitment
AP conduction along motor axon (Aa) - Synaptic transmission
(Effector recruitment )
Response (knee contract and lifts up)
What muscles are stretched in the jaw-jerk reflex?
jaw elevators - temporalis, medial pterygoid, masseter
Why is the latency for the jaw jerk reflex shorter than for the ankle jerk reflex?
the neural pathway for the jaw jerk reflex is shorter than that for the ankle jerk
What is the amplitude?
Measure of electrical activity in skeletal muscle
Why is the amplitude for the jaw jerk reflex less than for the ankle jerk reflex?
Masseter = smaller muscle than gastrocnemius
Recruitment of muscle fibrils in masseter less than for gastrocnemius
Smaller amplitude of response
What receptors and nerve fibres do tendon-jerk reflexes include?
Proprioceceptor endings
Group 1alpha muscle afferents
Why are protective mechanisms of somatic reflexes important?
- Escape mechanism
- Prevention of muscle overloading
- Prevention of inadvertent ingestion of a foreign body
- Digestive aid
How many synapses does a flexion withdrawal reflex have?
two synapses (disynaptic)
In the flexion withdrawal reflex, what prevents instant reflex which may cause further harm via inhibition (i.e not throw pot of boiling water)?
interneuron which allows momentary control over situation and inhibits harmful action
In the flexion withdrawl reflex, what are two responses that can occur?
can inhibit or stimulus different spinal regions through many inter-neurons to maintain balance or protect against further injury
What triggers the flexion withdrawl reflex?
pain (mechanical or heat)
What are golgi tendon organs?
proprioceptors that are located in the tendon
What are inverse stretch reflexes?
golgi tendon organs activated by stretch and contraction
afferent signals cause inhibiton of motor neurons
prevents overloading of muscle
Does an increase in synapses affect latency?
yes more synapses increased latency
What protects the mouth from increased bite force?
no golgi tendon organs therefore controlled by increased periodontal loading which sends afferent signals which inhibit elevation of jaw muscles
What does anaesthetisation of molars cause?
increased bite force as periodontal ligament cannot send feedback loop
Where do interneurones project in the pharyngeal reflex to cause mass contraction?
nucleus ambigious (motor control)
