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)
How is muscle force controlled?
Two major physiological methods
1. Recruit more motor units
2. Increase discharge frequency
What was discovered by Denny-brown in 1938?
Denny brown reported that the performance of a particular movement always appeared to be accomplished by the activation of motor units in a set sequence (orderly recruitment)
- motor unit #1 is activated and remains that way as long as the force doesn’t decrease, and then more motor units are added as the force increases
What is henemans’s size principle
States that motor units are recruited by size as force increases
Due to variations in motor unit size
Define recruitment threshold and derecruitment
Recruitment threshold: the minimum force that sustains the activation of fibres
DeRecruitment: sequential inactivation of fibres
Why recruit motor units in an orderly fashion?
Because big motor units recruited at the end will provide a big jump in net force. Since the sequence is predetermined, the brain doesn’t have to work with 500 switches, but instead can control the level of the input to the motor pool
With this, however, there is an inability to activate the units out of order
What is the relative contribution of recruitment for the adductor pollicis, first dorsal interosseus, and biceps brachii
Adductor pollicis and first dorsal interosseous – all motor units are recruited when the force reaches 50% of the max
Biceps brachii – motor unit recruitment continues until 85% max
What is the shape of the force frequency relationship?
Sigmoidal or S shaped
Draw the curve for the peak force and frequency as well as the graph for peak force percentage of maximum and frequency
What is double discharge?
Refers to two discharges in succession that result in a big jump in force production. Becomes more frequent with fatigue and the discharge is typically between 7 to 35 Hz (30-140ms after ap)
Define synchrony
The degree to which motor units within a muscle fire together at the same time
What might be the reason for short term synchronization?
Short term synchronization is likely due to a common presynaptic input, meaning that they receive the input from the same spot and converge into one neuron for a quicker synchronization
What occurs more frequently in large contractions and fatigue?
Synchrony
What does synchrony look like in musicians and normal people?
Musicians and the dominant hand of normal people both have less synchrony
Define neuromuscular Compartmentalization, how many compartments are in biceps brachialis and extensor digitorum?
Subdivisions of the muscle that can be activated singly or in combination. Each compartment contains motor units that activate a certain part of the muscle. Biceps brachii has two compartments and extensor digitorium has four
How does immobilization affect recruitment?
With immilization there are alterations in recruitment, and a lack of steady contractions. Motor units are no longer asynchronous.  In the case study the immobilized group how much longer contractions before fatigue.
Describe the behaviour of the motor neuron during prolonged submaximal contractions
We see that motor units switch off inactivity instead of overlap. Signifies that hennemen’s size principal isn’t a constant linear line but instead has a switch off between units.
Define sensory modulation
Sensory modulation: the ability to respond appropriately to sensory info and remain at an appropriate level of alertness
Describe the changes in the recruitment of a low threshold and high threshold
When you get a massive jolt of sensory input the the low threshold raises the recruitment threshold. In the high threshold it drops the recruitment threshold. (afferent input can modify the selection of motor units)
Describe the notion behind imagined muscle training and why it might be successful
What is accomplished early on in training involves the setting of reflexes within the spinal cord. Building better motor programs for lifting and learning how to selectively activate appropriate muscles.
What is high density surface EMG?
It is a method of examining muscle fibres. It’s an electrode that has dots about 4 mm apart and can get roughly 20 to 40 micro recordings of muscle activation and action potentials.
Define Interoceptor
Interoceptor: send information within the body
Define Exteroceptor
Exteroceptor: send information from the environment
Define proprioceptor
Proprioceptor: send information about the relative position of body segments
Where are motor cell bodies located?
They are located in the dorsal root ganglion
What is A pseudo – unipolar neuron?
Pseudo – unipolar neuron: T shaped neuron
What are the different types of afferent fibres and how are they classified
Go from one to four with one being the largest and for being smallest they are labelled based on cross-sectional diameter. Number one sub divides into one a and 1B
What characteristic of afferent fibres affects conduction speed
Diameter. Larger diameter results and faster Conduction
How do you cells communicate with one another?
Synaptic potential and postsynaptic potential
How are excitatory postsynaptic potential different from action potentials?
- EPSP is a local and graded
Not propagated - EPSP is not followed by a refractory period
They can summate
How are excitatory postsynaptic potential difference from action potentials?
- EPSP is a local and graded
Not propagated - EPSP is not followed by a refractory period
They can summary
What interplay between two things determines if the neuron will fire an action potential
The interplay between EPSP and PSP determines this
What is the resistance like for different sizes of motor neurons?
Small motor neurons have high inputs of resistance. It takes very little current to make it fire since it has a low threshold. The same synaptic input onto small motor neurons causes larger potential changes in larger EPSP
What are some characteristics of the typical muscle spindle receptor? What does it look like what is its position?
- Spindle/fusiform shaped receptors found in most muscle
- lie parallel with large force producing muscle
- different muscles have different numbers of spindles
- hand muscles have higher density of spindles
What are some characteristics of the muscle spindle
- 1 cm in length
- Equatorial or middle region is covered by a connective tissue capsule
- Polar or end region has myofilament contractile components
- Two types of intrafusal fibres - bag or chain
How are bag and chain fibres different
- Bag fibres are longer than train fibres and are further divided into bag one and bag 2
- There are 2 to 20 intra-fusal fibres per spindle, 2 to 3 big fibres and 3+ chain fibres
What are the two types of sensory afferent innervation of the muscle spindle
- Afferent Primary 1A
Spiral around bag 1 bag 2 and all chain fibres -  afferent 2
Innervate Bag 2 and chain fibres never Bag 1
Which bag is dynamic in which bag is static
Bag 1 is dynamic, bag 2 is static
What is the term for the efferent system of muscle spindles
Who fusimotor or gamma system
Define Mechano-receptor
Mechano-receptor: a type of receptor which relays sensory information about touch pressure stretching and motion
How is muscle stretch information sent
Stretch muscle = stretch of ending membrane = increased leakiness = graded potential
What is the difference between rapidly adapting and slow adapting receptor behaviour
Slow adapting provides static info
rapidly adapting provides dynamic info
What are the different afferent spindle types sensitive to
1A
- sensitive to speed and velocity of stretch as well as length.
- Tabs and vibrations and can start firing on release
2
- Sensitive to length change
Define dynamic index
Text: the difference between the peak and steady rate of a contraction
Define dynamic index
Text: the difference between the peak in steady rate of a contraction
What is a method used to record a muscle sympathetic nerve activity
Micro neurography
Define monosynaptic reflex
Monosynaptic reflex: a reflex arc that provides direct communication between sensory and motor neurons
A.k.a. deep tendon reflex/muscle stretch reflex
Information goes to the dorsal root and loops right back down to the muscle bypassing the CNS
What happens when we activate gamma static and gamma dynamic during a stretch
Gamma static, when activated decreases dynamic response
- sensitive to length
Gamma dynamic, when activated increases dynamic response
- sensitive to velocity
Results in a better stretch?
What does the fusi motor system do
Turning on the gamma system prevents the spindle from becoming unloaded or shortened during contractions and keeps it sensitive to stretch. Makes dynamic spindle more sensorive to the velocity and static more sensitive to length
What are the two systems for ascending pathways
- Medial lemniscus system - Relays information for discriminative aspects of sensation
- Spinothalamic system - relays information for conscious perception of pain, temperature and less discriminative tactile touch
How information is sent through the medial lemniscus system
- First order neurons enter the spinal cord and turn rostrally, or superior
- All fibres make a first connection with nuclei in the lower medulla
- Second order neurons cross the midline at the lower medulla and ascend to the medial lemniscus to reach the thalamus
- Third order neurons from the thalamus reach the somatosensory cortex
Describe how information is sent through the spinothalamic system
- First order neurons enter the spinal cord in dorsal root
- Fibres make a synapse in the dorsal gray horn
- Second order neurons decussate in ventral white commisure and turn rostrally
4. Second order neurons ascend in the ventro lateral white matter to reach the thalamus - Third order neurons from the thalamus reach the somato sensory cortex
Describe how information is sent through the spinothalamic system
- First order neurons enter the spinal cord in dorsal root
- Fibres make a synapse in the dorsal gray horn
- Second order neurons decussate in ventral white commisure and turn rostrally
4. Second order neurons ascend in the ventro lateral white matter to reach the thalamus - Third order neurons from the thalamus reach the somato sensory cortex
GTO location/morphology
- 1mm x 0.1mm
- GTO are at the end of the muscle, after contractile fibres, at the tendon
- spindles lie parallel, but GTO are in series
How are afferent fibres involved in GTO
- 1b afferent fibre hooks up the GTO to innervate it
How many GTO are innervated by 2 Ib afferent fibres.?
2%
What do GTO code for?
Muscle tension! A lot of tension = a lot of pinching of the golgi tendon
Describe the activation required for GTO
Passive stretching - 2 newtons required to activate GTO
Vs Activation of a single fibre = 30-90 mnewtons
Therefore GTO is incredibly sensitive to actively generated forces vs passive ones. Contracted muscle = a lot of ap. Stretched muscle = some ap
Describe the graph for force and discharge rate of GTO
Scales linearly with increasing muscle force
What does GTO code for
Force
What are the types of joint receptors
Type I, II, III = mechanoceptor
Type IV = nociceptors
Where are joint receptors located?
In joint capsules, loose tissue and ligaments
Where are joint receptors NOT located
Cartilage or synovial membranes
Describe the morphology of the type I joint receptor
Type I - low threshold, slow adapting
- detects displacement, angular velocity, intraarticular pressure of the joint
- globular or ovoid capsules (ruffini receptors)
- located in mainly superficial layers of joint capsule
- more densely populated in proximal joints
- weak velocity coding
- myelinated until branch off
Describe ent morphology of type II joint receptors
- low threshold but rapidly adapting
- elongated cylindrical receptors (Pacinian)
- detects acceleration of the joint
- deep layers of joint capsule
- more dense in distal
- bare nerve ending at the end of the core
- if we stretch the tissue and hold it, it’ll fire again at the release
Describe the morphology of type III joint receptors
- high threshold, low adapting
- detect tension
- fusiform corpuscles
- identical to muscle GTO, but are in a ton of collagen
- located in intrinsic and extrinsic joint ligaments
- maintains firing rate but has a high threshold
What is the neural code for joint receptors
They respond primarily at the limits of joint movements and respond to joint pressure
Describe the relationship with joint receptor responses and the joint angle
What is the joint receptors connection to higher order neurons.,
Strong connection, due to strong somatosensory response to joint afferent signals
What connection is weak between joint receptors?
not sure
What kind of fibre has more of an effect on low threshold joint receptors?
Y fibres (gamma)
Because there is a strong connection between gamma and joint receptors, what does it mean for their response?
Joint receptors, because of their strong connection, can evoke strong inhibitory or excitatory signals. Through the gamma reflexes, receptors can indirectly influence muscular control and proprioception
