Lab 4 - muscles Flashcards
Where do motor neurons originate?
CNS
Mechanism of skeletal muscle AP:
Motor neurons release ACh at neuromuscular junctions (motor endplates) to generate an AP. This causes contraction. Usually voluntary; can be involuntary.
Limb movement:
Accomplished by coordinating the contraction/relaxation of antagonistic muscle groups. Tendons attach muscles to bones. CNS assists coordination using info from sensory receptors.
EMG:
Electromyogram: records electrical activity associated with skeletal muscle APs from surface of the body.
Muscle fibre:
Specialized receptors that convey info about muscle length to the CNS.
Stretch (myotatic) reflex:
Muscle stretch excites muscle spindles, resulting in a reflex contraction of the muscle.
Involve large diameter neurons and small number of synapses.
Monosynaptic pathway:
(Ex: stretch reflex)
Sensory afferent nerves enter the spinal cord and synapse directly with motor neurons, rather than with interneurons. Motor neurons trigger contraction of the muscle group. The same neuron synapses to an interneuron that connects to another motor neuron, which stimulates the antagonistic muscle group.
Experiment 1: EMG during Achilles’ reflex
Strike heel, record electrical activity. Take onset of hammer strike to peak of response.
Foot movement terms:
Plantar flexion - pointing toe.
Dorsiflexion - flexing foot.
Achilles’ tendon connects what to what?
Gastrocnemius muscle to tarsal bone
When measuring L for conduction velocity, assume…
Sensory-motor synapse is at spinal segments L5 and S1.
Why do you subtract synaptic transmission time?
Even though the stretch reflex is monosynaptic, the pathway also includes the neuromuscular synapse. 0.5 milliseconds.
Conduction velocity (m/s) equation:
Path length (m) / reflex time (s) – synaptic transmission time (s)
Experiment 2: grip strength
Use hand dynamometer to measure grip strength. EMG of forearm muscles.
Strength of striated muscle contraction depends on…
Amount of electrical activity.
