Reflexes Flashcards
All reflexes are monosynaptic. T/F?
False
The magnitude of a reflex can be modulated by higher brain centres. T/F?
True
Fibres within a muscle spindle are termed ‘intramural’. What is the term for the contractile muscle fibres outwit the muscle spindle?
Extrafusal
What type of sensory neuron innervates muscle spindles?
Ia sensory neuron
How does the lengthening of a muscle affected the discharge rate of Ia sensory neurons?
Stretching (due to muscle lengthening) in the middle third of the intramural fibres leads to the increased depolarisation of the Ia axon endings due to opening of mechxnosensitive ion channels
Sensory Ia efferent have an excitatory synapse in the spinal cord with what type of motor neuron?
Alpha motor neuron
Gamma motor neurons innervate the contractile portions at the end of intramural muscle fibres, to cause these poles of the intramural fibre the contract when the extrafusal fibres contract. Why is this important?
This means that when the extrafusal fibres contract, the spindle does not become slack, which allows Ia sensory neurons to report information about muscle length
What type of sensory neuron innervates Golgi tendon bodies?
Ib sensory neuron
What is the name of the structures found at the junction between muscle and tendon which are innervated by Ib sensory neurons?
Golgi tendon organs
How does the firing rate fo Ib afferent fibres change when the tendon organ is stretched?
The firing rate increases
Ib sensory afferents, which transmit information from Golgi tendon organs, have excitatory synapses with alpha motor neurons. T/F?
False - these are inhibitory synapses
Tendon organs form part of a reflex circuit which inhibits homonymous and synergist neurons. What is the term for this system?
The inverse myotactic reflex
Describe the flexion withdrawal reflex.
This protects the limbs against potentially noxious stimuli detected by cutaneous structures. the flexors of the affected limb contract and the extensors are relaxed to draw the limb away from the noxious stimuli. At the same time the crossed extensor reflex is elicited in the contralateral limb to contract the extensors and relax the flexors in order to provide postural support during the withdrawal of the stimulated limb
Why is a positive Babinski’s sign commonly seen in infants?
The corticospinal tract is not yet fully myelinated in infants
What cranial nerve innervates the Jaw jerk reflex?
Trigeminal nerve
What spinal roots innervate the biceps reflex?
C5/6
What spinal roots innervate the triceps reflex?
C6/7/8
What spinal roots innervate the brachioradialis reflex?
C5/6
What spinal roots innervate the knee jerk reflex?
L3/4
What spinal roots innervate the ankle jerk reflex?
S1/2
Describe how reinforcement measures work to recruit more motoneurons into the reflex response?
Reinforcement measures use higher brain centre modulation to slightly depolarise some of the motoneurons in the pool to bring them closer to threshold and make them easier to excite
The tendon jerk reflex is useful clinically but it is a response to an artificial stimulus. What is its normal function?
Acts to produce prolonged contraction when there is prolonged stretch of the muscle to maintain a constant muscle length and to control muscle tone
Highly sensitive areas of skin such as on the hands and lips have lots of small receptive fields as compared to less sensitive areas such as the trunk which has fewer, bigger receptive fields. T/F?
True
What must happen for two sensory stimuli on the skin to be perceived as separate?
These stimuli must activate different receptors i.e. they must ‘land’ in different receptive fields
Explain the differences in two point discrimination between highly sensitive areas such as the hands, and less sensitive areas such as the trunk?
In the more sensitive areas there are multiple, small receptive fields whereas on the trunk there are fewer, bigger receptive fields. Stimuli must act on separate receptive fields to be perceived as separate. therefore, stimuli can be much closer together and still perceived as separate on areas such as the hand compared to areas such as the trunk
What is kinaesthesia?
sense of movement
speed of movement
direction of movement
Rufini endings, Golgi endings and free nerve endings are rapidly adapting. T/F?
False - they are slow adapting
Paciniform endings are rapidly adapting. T/F?
True
Subcutaneous receptors may discharge during movement to provide the sense of proprioception. T/F?
True
Primary muscle spindle endins respons to changing length and to tapping or vibrating of the tendon. T/F?
True
Opposing muscles at a joint (e.g. biceps and triceps) provide complementary information about joint flexion/extension. T/F?
True
In the experiment, if vibration was applied to the biceps tendon of the right arm with the eyes closed and the subject asked to match the level of elbow flexion in the left arm to that of the right arm, the subject will extend their left arm further. Why is this?
the vibration is creating an artificial stimulus on the biceps muscle spindles which creates the impression that the muscle is longer than it actually is which accounts for why the subject would extend their arm further than they should on the left side
Platinum grid array electrodes are used for seizure monitoring and brain mapping on subdural cortical surface in conscious patients. This is an invasive procedure. Name to non-invasive methods of brain stimulation?
Transcranial electrical stimulation
Transcranial magnetic stimulation
