P1 Muscle Reflexes and Balance Flashcards
describe the reflex arc
The basic unit of integrated neural activity is the reflex arc. The arc consists of a sensory receptor, a sensory (afferent) neuron carrying impulses into the CNS, often one or more connecting neurons (interneurons within the CNS) and a motor (efferent) neuron supplying a specific organ (the effector). Reflex activity is involuntary.
describe the automatic reflexes
The autonomic nervous system, like the somatic, is organised on the basis of reflex arcs. Impulses starting in visceral receptors are relayed via afferent nerves to the CNS. Here the information is processed, integrated with information from elsewhere, and transmitted via efferent nerves of the autonomic nervous system to specific organs. Simple autonomic reflexes, such as contraction of the full bladder, operate through the spinal cord. More complex reflexes that regulate blood pressure and respiration are integrated in the medulla oblongata. Those that control pupillary responses to light and accommodation are integrated in the mid-brain.
pupillary light reflex:
bright light =
dim light =
pupillary light reflex:
bright light = PUPIL CONSTRICTS
dim light = PUPIL DILATES
When looking at a near object, the pupil is ________. When looking at a far object, the pupil is ________.
When looking at a near object, the pupil is CONSTRICTED. When looking at a far object, the pupil is DILATED.
describe the stretch reflex
The knee and ankle jerk reflexes are both stretch reflexes, meaning that they control the length (stretch) of our muscles. Stretch reflexes are monosynaptic (one synapse), where sensory neurons synapses directly to motor neurons in the spinal cord to produce a muscle response. For example, the knee jerk reflex is initiated when the patellar ligament is tapped, and the quadriceps muscle is stretched. Muscle stretch is detected by the sensory endings of afferent nerves attached to spindles embedded in the muscle. Stretching of the muscle spindles results in an increased rate of afferent action potential firing. The impulses travel to the spinal cord, where the sensory neurons synapse directly with motor neurons supplying the same muscle. Stimulation of the motor neuron causes the quadriceps muscle to contract and the foreleg to extend.
what is an electromyography and what does it measure
Electromyography (EMG) uses surface electrodes to record the sum of the muscle action potentials (a compound action potential) just before a muscle contracts. Electromyography can be used to measure:
• The strength of a reflex (indicated by the amplitude of the EMG trace)
• The response time of a reflex (indicated by the time between the hammer strike and the muscle contraction)
A monosynaptic reflex has…
a. interneurons between afferent and efferent neurons
b. a direct synapse between the motor neurons and extrafusal muscle fibres
c. a direct synapse between the afferent and efferent neurons
d. just one neuron in the pathway
C (a direct synapse between the afferent and efferent neurons)
in regards to the stretch reflex:
Stimulus: _____ –> Receptor: ____ –> afferent pathway: ___ –> control centre: ___ –> efferent pathway: ___ –> effect: ___
Stimulus: MUSCLE STRETCH –> Receptor: MUSCLE SPINDLE –> afferent pathway: SENSORY NEURON –> control centre: SPINAL CORD–> efferent pathway: MOTOR NEURON –> effect: MUSCLE CONTRACTION
What does an increase in amplitude on the EMG trace represent when a subject performs the Jendrassik manoeuvre during the stretch reflex?
a. more motor units have been recruited
b. the muscle spindles are responding more quickly
c. the neuronal conduction velocity has increased
d. the reflex is occuring more quickly
e. the strength of contraction has been reduced
A (More motor units have been recruited = the increased amplitude on the EMG trace indicates that there are more muscle action potentials, which will corresponds to a stronger muscle contraction)
Why is the response time for the ‘voluntary’ stretch longer than a regular stretch reflex?
Because it is first processed as an auditory stimulus, then it goes to the motor area, simulates a motor neuron = contraction (voluntary stretch involves multiple neurons = polysynaptic = longer response time)
Which sensory inputs regulate balance when we are standing with closed eyes?
Vestibular nuclei, proprioception, somatosensory
