Reflex and voluntary movements Flashcards
What are reflexes
No conscious element; involuntary
* Stereotyped response
* Rapid: short latency (delay)
* Centred on:
-Brainstem (cranial nerves)
-Spinal cord (spinal nerves)
* Monosynaptic circuit
What are the 3 movements we can initiate
Involuntary actions - reflexes
Voluntary actions
Semi-automatic actions
Where are motor neurons found
spinal chord (somatic - ventral horn)
brainstem (cranial nerves)
What activates motor neurons
Influences from cortical regions
Peripheral receptors
What is the stretch reflex pathway (knee jerk)
Sensory neuron stimulated group 1a muscle afferent fibre (hammer)
Projectes into spinal chord into ventral horn where it activates and recruites motor neuron
What are muscle spindles composed of
Intrafusal fibres wrapped in sensory endings
What type of axons are associated with group 1a muscle afferents
A alpha axons
What happens when a muscle is streched
intrafusal fibres stretched too which distorts sensory endings within muscle spindles generating AP and when activated fire a high frequency train of action potentials which is conducted along muscle fibre
What happens when muscle is relaxed
No generation of AP
What are the steps in the knee jerk reaction
Tapping patella tendon causes tendon to pull on quad muscle which activates the muscle spindles, mechanoreceptors then transduce the mechanical signal into an electrical signal and the AP conducts along afferent fibre to ventral horn where it synapses with motor axon and then leads to inervation of muscle and causing a release of ACH which acts upon muscle fibres causing contraction - EXTENSION OF LOWER LEGS
What is the summary of the stretch reflex pathway
- Stimulus
- Receptor activation (mechanoreceptor)
- Stimulus transduction
AP conduction along sensory axon (Aa) - Synaptic transmission
- Motor neuron recruitment
AP conduction along motor axon (Aa) - Synaptic transmission
(Effector recruitment ) - Response
What reflexes can we use to test integrity of central nervous system
Biceps jerk reflex
Tricep jerk reflex
ankle jerk reflex
rectus abdominis reflex
How does the jaw jerk reflex work
- Hammer tap to chin
- Stretches spindles of jaw elevator muscles
(masseter, temporalis, medial pterygoid) - Action potentials conducted along
group 1a muscle afferents to brainstem (Aa) - Monosynaptic activation of motor neurons
of jaw elevator muscles - Axon potentials travel along motor axon (Aa)
- Jaw elevator muscles contract
- Jaw jerks upwards, mouth closes
What are the steps to the ankle jerk reflex
- Hammer tap to Achilles’ tendon
- Stretches spindles within gastrocnemius
- Action potentials conducted along group
1a muscle afferents to spinal cord (Aa) - Monosynaptic activation of motor neurons
of gastrocnemius muscle - Axon potentials travel along motor axon (Aa)
- Gastrocnemius muscle contracts
- Foot extends (plantar extension)
What is the lag on an EMG between stimulus and response
Latency of response
What are the two features to look for on an EMG
Latency of response
Amplitude of response
What are the axons in the afferent and efferent in stretch reflex pathways
A alpha - no difference in speed of conduction
Why is the latency of the jaw jerk reflex less than that for the ankle jerk reflex
Because the neural pathway for the jaw jerk reflex is shorter than that for the ankle jerk
Which jerk reaction (jaw/ankle) has a greater amplitude of response
Ankle - greater recruitment of muscle fibrils in gratrocnemius than masseter
What are the components of tendon-jerk reflexes
Proprioceceptor endings
Group Ia muscle afferents
Homonymous motor neurons
What are the purpose of tendon jerk reflexes
Maintenance of posture and muscle tone
What type of reflexes use mechanoreceptor and nociceptor endings
Cutaneous reflexes
What protective mechanisms can reflexes provide
Escape mechanism
Prevention of muscle overloading
Prevention of inadvertent ingestion of a foreign body
Digestive aid
What is the flexion withdrawal reflex a response to
Noxious stimulus
