Midterm 1 Flashcards
What are the exit/entrance points of efferent and afferent fibres?
Efferent exit through the ventral root
Afferent enter through the dorsal root
What are the morphological features of the motor neuron?
- large dendritic tree
- soma
- axon
- presynaptic terminal
Define motor pool
Motor pool : a collection of motor neurone that all innervate a particular muscle
What is a Collection of motor units that all innervate a particular muscle?
Motor neuron pool
Describe the concept of cervical enlargement
Cervical enlargement explains that there are motor neuron pools for the arms, legs (lumbar), etc. Proximal muscles are closer to the spinal cord, while distal muscles are more lateral
Define motor unit
Motor unit: the motor cell and all of the fibres that it innervates
What is the term for a motor cell and it’s innervated fibres?
Motor unit
Define innervation ratio
Innervation ratio: the number of muscle fibres innervated by a single motor neuron. Varies for different muscles
What is the name for the number of muscle fibres that is innervated by a single motor neuron
Innervation ratio
List the different innervation ratios for gastrocnemius, eye muscles, and hand muscle
Gastrocnemius = 1:1900
Eye muscle = 1:15
DI = 1:342
What are the three types of muscle fibres and their conduction speeds
Slow twitch = 50 m/s
Fast fatigue resistant = 80m/s
Fast fatiguable = 110m/s
What size of muscle is typically innervated by fast twitch fibres?
Large muscle groups. They take more stimulation to be activated
What are some characteristics of slow twitch motor neurons?
Speed = 50m/s
High input resistance, easier to excite
Longer refractory period
Define rheobase and input resistance
Input resistance : measures the changes in the potential of the membrane
High in small motor neurons
Rheobase: direct measure of the current required to fire a neuron
Low in small motor neurons
Define twitch
Twitch: a physiological, quanta response of a motor unit to stimulation. This is a force time to a single motor unit
- contraction time of 50 ms
What is a physiological, quantal response of a single motor unit to stimulation?
Twitch
What is the time for a twitch contraction?
50ms
What happens to discharge frequency when force increases?
Discharge frequency increases
Explain fused vs unfurled tetanus
Tetanus: prolonged contraction of a muscle
Fused = smooth contraction wave due to increased discharge frequency
Unfused= bumpy contraction wave due to decreased discharge frequency
How can we differentiate the types of motor units by their characteristics?
Contraction time
- slow = Long contraction
- FO = medium contraction
- FG = quick contraction
Peak
- slow = low peak 2g (1s)
- FO = medium peak 10g ()
- FG = high peak at 60 g ()
Half relaxation time
- slow = long
- fo - medium
- fg = very short
What is the behaviour of the motor unit dependent on?
The fibre AND the neuron it is connected to
Motor unit definition
motor unit: the muscle cell and it’s innervated fibres
What two methods can be used to record motor units?
- Metal microelectrode - needle
- Fine wires - uses ultrasound
On an EMG, what would the motor units look like? Draw them out
(Motor units average +-0.75 volts)