Reflex Movement Flashcards
What are the 3 types of movement?
- Involuntary actions - reflex movement
- Semi-automatic actions - CPG in breathing
- Voluntary action
What are reflexes?
- No conscious element: involuntary actions
- Stereotyped responses
- Typically consist of a monosynaptic circuit
- Rapid, short latency/delay between sensory component and motor component
What is the basic pattern for an voluntary movement?
Motor cortex -> brainstem -> spinal cord -> muscle
Which neurotransmitter is released at the neuromuscular junction to cause muscle contraction?
Acetylcholine
What is the common final component in reflex pathways?
Motor neurons in spinal cord innervating muscle which causes muscle contraction
What does ‘monosynaptic’ mean?
Only one central synapse
Where are motor neuron cell bodies located?
In the spinal cord (somatic) or the brainstem (cranial nerves)
What are motor neurons activated by?
- Various brain regions (cortex)
- Various peripheral receptors (reflex)
What are the components in a reflex pathway?
Stimulus, receptor, afferent (sensory) neuron, synapse, (interneuron), efferent (motor) neuron, effector (muscle, gland), response
Describe tendon-jerk reflexes (type of receptor, afferents, motor neurons)
- Proprioceptor endings
- Group 1a muscle afferents
- Homonymous motor neurons
Describe cutaneous reflexes
- Mechanoreceptor endings
- Noiceptor endings
Describe the quadriceps (knee-jerk) reflex
- Tapping patellar tendon with a hammer
- Stretches the quadriceps muscle
- Initiates reflex arc: contraction of quadriceps muscle, causing extension of lower limb causing foot lift
- Group 1a muscle afferents wrap around individual fibres
- When fibrils are stretched: displacement of ionotropic channels within endings of primary afferents -> action potential occurs
- Aalpha axons synapse with alpha and gamma
Which axons have the largest diameter, highest degree of myelination and fastest conduction speed?
Aalpha
What does the knee-jerk reflex/quadriceps reflex aim to do?
Restore tension in the muscle (opposes the stretch)
What are the purposse of somatic reflexes?
- To maintain posture and tone
- Escape mechanism
- Prevention of muscle overloading
- Prevention of inadvertant foreign body ingestion
- Digestive aid 8 7
Describe the ankle-jerk reflex
- Hammer tap to the achilles tendon
- Stretches spindles in the gastrocnemius muscle
- APs conducted along Group 1a muscle afferents to spinal cord
- Monosynaptic activation of motor neurons of gastrocnemius muscle
- APs travel along Aalpha efferent/motor axon
- Gastrocnemius muscle contracts
- Foot extends
Describe the jaw-jerk reflex
- Hammer tap to chin
- Stretches spindles of jaw elevator muscles (masseter, temporalis and medial pterygoid)
- APs conducted along group 1a muscle afferents to brainstem
- Monosynaptic activation of motor neurons of jaw elevator muscles
- APs travel along Aalpha motor axon
- Jaw elevator muscles contract
- Jaw jerks upwards, mouth closes
What is the flexion withdrawal reflex?
- e.g. picking up a hot mug, reflex makes you move your hand away quickly
- Interneuron also involved (disynaptic or polysynaptic)
- Pain pathway is also stimulated for further response
What do Golgi tendon organs do?
- Prioprioceptive sensory receptors
- Important in initiating the inhibition of motor neuron axons
- Give rise to group 1a afferents
- Inverse of stretch reflex/inverse myotatic reflex
- Prevents overloading of the muscle
What prevents overloading in jaw muscles?
- Compression of the periodontal ligament
- No golgi tendon organs in the jaw muscles
- Bite force is controlled by increasing pressure on the periodontal ligament
- Inhibition of jaw elevator muscle motor neurons
Describe the pharyngeal (gag) reflex
- Tap back of person’s mouth - initate gag reflex
- Activate sensory fibres in the glossopharyngeal or trigeminal nerve
- APs conducted to lower part of medulla
- Project to and terminate in the spinal trigeminal nucleus
- Active 2nd order sensory neurons - project to upper part of the medulla
- 2nd order neurons split and innervate nucleus ambiguus on both sides
- Nucleus ambiguus contains motor nerves for the vagus nerve
- Innervates posterior oral and pharyngeal muscles - causes gagging
What is the aim of the gag reflex and when is it initiated?
- Protective: causes bilateral contraction of the throat
- Initiated if you have ingested a foreign body or if you tap on the back of someone’s throat
Which fibres are activated in the pharnygeal (gag) reflex?
Sensory fibres in the glossopharyngeal and trigeminal nerve
Where are action potentials from sensory fibres in the glossopharyngeal and trigeminal nerve conducted to in the pharyngeal reflex?
Afferents terminate in the brainstem (SpVn - spinal trigeminal nucleus)
Where do 2nd order projection neurons project from/to?
From the spinal trigeminal nucleus (SpVn) in the brain stem to the nucleus ambiguus (upper part of the medulla). These 2nd order projection neurons split to innervatethe nucleus ambiguus on both sides.
The nucleus ambiguus contains motor neurons for which cranial nerve?
X (Vagus)
What does the vagus nerve do in the pharyngeal (gag) reflex?
The vagus nerve innervates posterior oral and pharyngeal muscles - causes gagging
Briefly describe the pharyngeal (gag) reflex
- Tap at back of person’s throat
- Stimulates primary afferents of glossopharyngeal and trigeminal nerve
- APs are conducted to the spinal trigeminal nucleus (SpVn - in the brainstem) where they synapse with 2nd order sensory neurons.
- 2nd order sensory neurons project from SpVn to the nucleus ambiguus in the upper part of the medulla. They split in 2 causing bilateral innervation of motor neurons in the nucleus ambiguus (on both sides)
- Nucleus ambiguus contains motor neurons for vagus nerve (CN X)
- Vagus nerve innervates posterior oral and pharyngeal muscles (bilateral) - causing gagging
What is the effector in salivary reflexes?
Salivary glands
What are the stimuli for the salivary reflex?
Gustatory (taste) stimuli, visual stimuli, olfactory stimuli, chewing forces
What does the salivary reflex cause in response to a stimuli e.g. gustatory stimuli?
Increased salivary flow
What is the end result of the pharyngeal reflex?
Mass contraction of both sides of the posterior oral and pharyngeal musculature
