Muscle function Flashcards
1
Q
Define muscle agonists/antagonists/synergists
A
- agonists- “primary mover”
- responsible for the initiation and execution of a specific action at a joint
- e.g. brachialis flexes the elbow
- antagonists
- oppose or reverse the action of the primary mover
- e.g. triceps oppose the brachialis
- synergists
- assist the primary mover in its action
- e.g. biceps/brachioradialis assist brachialis
2
Q
What is the concept of reciprocal inhibition?
A
- ensures the smooth movement of a joint
- skeletal muscles typically function in pairs for maximal muscle efficiency, speed, and control
- pair needs to coordinate their contraction to avoid muscle injury
- requires neurological input
3
Q
What is the neurological pathway of reciprocal inhibition?
A
- in neurologically intact patients
- one branch of the 1a afferent enters the spinal cord and synapses on the alpha motor neuron (causing the agonist muscle to contract)
- the other branch of the 1a afferent synapses on the 1a inhibitory interneuron which synapses on the alpha motor neuron of the antagoinst (preventing contraction of that muscle group)
- in neurologically compromised patients
- they lack reciprocal inhibition which causes spasticity (agonist and antagonist “fighting each other”)
4
Q
What are the planes of movement?
A
- frontal/coronal
- divides body into anterior and posterior
- e.g. abduction, adduction
- sagittal
- divides the body into right and left
- e.g. flexion and extension
- transverse/horizontal
- divides the body into top and bottom
- e.g. internal and external rotation
5
Q
What are the 3 types of muscle contractions?
A
- isometric
- muscle length remains the same
- isotonic
- concentric (muscle shortens)
- eccentric (muscle elongates)
6
Q
Which type of muscle contraction is capable of producing the greatest amount of force?
A
**isotonic eccentric contractions;
- require less metabolic energy
- with maximal contraction they can generate much higher tension levels (up to 50% higher) when compared to concentric contractions
- important concept in the rehabilitation of tendinopathies; eccentric contraction workouts (e.g. heal lifts/dips off the stairs) generate more force and stimulate collagen growth factors
7
Q
How can you clinically evaluate muscle function?
A
-
manual muscle testing (structural unit)
- typically tests groups of muscles, not an isolated muscle (all agonists/antagonists)
- tests planes of movement (helps evaluate the integrity of the nerves; the patient may move in a different plane which can help diagnose; e.g. unintential inversion during dorsiflexion)
- electromyography (EMG) and nerve conduction studies (functional unit)
- detailed evaluation of muscle and nerve function/interaction
8
Q
Describe the use of EMG and nerve conduction studies clinically
A
- **Used to diagnose certain disease processes such as _nerve compression, hereditary/acquired diseases, and myopathy (_which alter the normal recorded electrical signals and recruitment patterns)
- EMG tests skeletal muscle fibers (mostly type 1, slow twitch, muscle fibers)
- Nerve conduction studies test motor, sensory, and mixed nerves (standard studies are evaluating large myelinated nerve fibers)
9
Q
What is a motor unit? How is it recruited?
A
- motor unit= the muscle fibers that are all innervated by a single axon
- all the muscle fibers innervated by one motor unit are of the same muscle fiber type
- # of muscles : 1 axon= innervation ratio
- varies widely between muscles
- low ratio for fine motor (e.g. extraocular muscles)
- high ratio for gross motor (e.g. soleus)
10
Q
What is MUAP?
A
**Motor unit action potential
- depolarization of all the fibers in a motor unit creates an electrical potential called the MUAP
- analysis of the MUAP (size, complexity, firing frequency) and assessment of baseline electrical signal at rest serves as the foundation for EMG
- MUAP generated by contraction of an individual muscle can be recorded by using a surface or needle electrode
11
Q
What is the Henneman size principle?
A
- to generate more force the firing rate and recruitment (smallest to largest) of more motor units must be increased
- in practice, this means that slow-twitch, low-force, fatigue-resistant muscle fibers are activated before fast-twitch, high-force, less fatigue-resistant muscle fibers
- patterns of recruitment indicate neuropathic (reduced) versus myopathic (early) conditions
12
Q
Describe the basics of a nerve conduction study
A
- nerve conduction studies are a component of EMG (they asses the integrity of the PNS)
- evaluate peripheral nerve function;
- compound motor action potentials (CMAP)
- sensory nerve action potentials (SNAP)
13
Q
How does a nerve conduction study look? There are two lines of signal; what do they represent?
A
- flexors on top (signal during flexion, silent during extension)
- extensors on bottom (signal during extension, silent during flexion)
**isometric contraction shows simultaneous signal in both lines
14
Q
What are the signs of an upper motor neuron syndrome?
A
- overactivity or “positive” signs
- hyperreflexia
- spasticity
- due to the loss of descending inhibition
- e.g. hemiparetic gait, clonus
- underactivity or “negative” signs
- weakness
- NO inherent muscle atrophy
**MORE than just motor and sensory loss!
15
Q
What is spasticity? When does it occur?
A
- spasticity= a condition in which certain muscles are continuously contracted
- velocity dependent increase in tonic stretch reflex (muscle tone)
- hyperexcitability of the stretch reflex
- decreased reciprocal inhibition
- **occurs commonly as a “positive sign” of upper motor neuron syndromes
