Intro to Motor Control: Lower Motor Neurons (9) EXAM 3 Material Flashcards
T or F: Movement is meaningful and motivated?
True
T or F: Movement is best understood by looking at the interaction of the person, task and environment?
True
What environments is movement guided by?
Internal and External
Do none, some, or all nervous system components influence movement?
All nervous system components
What type of movement happens when a doctor taps your knee and it pops up?
Reflex/Reaction
What type of movement happens when you touch something hot and jerk your arm back?
Reflex/reaction
Reflex/reaction
Occurs as a reaction to something
What is volitional movement?
With intention
What two types of volitional movement are there?
- Automatic
2. Cortical
What is cortical movement?
Requires conscious attention (like when learning to ride bike)
(Part of volitional movement)
What is automatic movement?
Requires little conscious attention, but does require continuous integration of information
(Part of volitional movement)
Where do spinal nerves exit?
Above/below the vertebrae
T or F: the Spinal cord is the same in different regions?
F, the spinal cord is NOT the same in different regions: Shape, size, proportion of white-to-gray matter change.
Where are motor neurons in the spinal cord?
Ventral horn
Internal Divisions of the spinal cord: Gray Matter areas
Dorsal Horn, Ventral Horn (motor neurons are in ventral horn)
Internal Divisions of the spinal cord: White Matter areas
Location of ascending and descending tracts
Do the tracts in the spinal cord ascend in white or gray matter?
White matter
Medial descending tracts of the spinal cord control what muscles?
Axial muscles
Lateral descending tracts of the spinal cord control what muscles?
Distal muscles
Lower Motor neurons directly innervate what?
Skeletal muscle fibers
Where are the cell bodies of LMN’s located?
In the SC or brainstem (CN’s)
Where do the upper motor neurons synapse?
On the LMN’s and/or interneurons in the brainstem or SC
Why do the UMN’s synapse on the LMNs or interneurons?
In order to convey commands for movement
Where do cell bodies of UMN’s originate?
Higher regions of the brain (cortex or brainstem)
What type of neuron are LMNs?
Multipolar (many dendrites)
Do many or little neurons synapse w the LMN’s?
Many (from higher centers and spinal afferents)
Once outside the vertebral column LMNs are part of the CNS or PNS?
PNS
Which are the ONLY neurons that send signals to extrafusal and intrafustal skeletal muscle fibers?
Lower motor neurons
Two types of LMNs:
- Alpha
2. Gamma
Alpha LMN:
Projects to extrafusal skeletal muscle, branching into many terminals.
Where are the cell bodies of alpha and gamma LMNs?
In the ventral horn of the spinal cord (gray matter)
Gamma LMN:
Projects to intrafusal fibers of the muscle spindle.
What are groups of LMNs in the SC whose axons project to a single muscle?
LMN pools
Neurons to a specific muscle are NEAR or FAR from each other in the ventral horn?
NEAR
ex: flexor muscle neurons would be together
Medial LMN Pools:
Axial/proximal muscles (head, neck)
Lateral LMN Pools:
Distal Muscles
Ventral LMN Pools:
Extensors (ex: triceps)
Dorsal LMN Pools:
Flexors (ex: biceps)
Which “pool” area of the ventral horn controls extensor muscles?
Ventral LMN pools
Which “pool” area of the ventral horn controls distal muscles such as the fingers?
Lateral LMN pools
Which “pool” area of the ventral horn controls the head and neck muscles?
Medial LMN pools
Which “pool” area of the ventral horn controls the flexor muscles?
Dorsal LMN pool
How many nerves supply each skeletal muscle?
One or more
What kind of fibers do nerves contain?
Both motor and sensory
An alpha motor neuron and all the muscle fibers it innervates
Motor unit
Motor unit can be:
Fast twitch or slow twitch
Fast Twitch
Faster speed of contraction (alpha motor neuron)
ex: gastrocnemius muscle when sprinting
Slow Twitch
Slower speed of contraction (alpha motor neuron)
ex: Trunk muscles
Innervation ratio:
The number of muscle fibers innervated by a single LMN
Example of low innervation ratio:
Eye, (one neuron to two muscle fibers for precision)
Example of high innervation ratio:
Calf (one neuron to hundreds of muscle fibers, not for precision)
End plate of neuromuscular junction
Highly excitable region of the muscle fiber’s membrane responsible for the initiation of AP’s across the muscle’s surface, causing the muscle to contract
Motor Neuron Lesion: Muscle Strength
Decreased ability to generate muscle force
Partial loss of voluntary muscle contraction
Paresis
Complete loss of voluntary muscle contraction
Paralysis
Hemiplegia
One side of the body experiences muscle loss (line down center of body)
Paraplegia
lower half of body paralyzed
Quadriplegia/Tetraplegia
paralysis of all four limbs
Atrophy
Loss of muscle bulk, wasting
Two types of atrophy:
- Disuse
2. Neurogenic
Disuse atrophy:
Type of decreased muscle bulk, person CHOOSES not to use muscles, but can
Neurogenic Atrophy:
Type of decreased muscle bulk due to motor neuron lesion. CANT recruit muscles in this atrophy .
Which happens faster, Neurogenic or Disuse atrophy?
Neurogenic because pathway is blocked.
Consequences of Motor Neuron lesions: (6 things)
Muscle Strength Muscle bulk Muscle contraction Muscle tone Muscle stiffness Reflexes
Muscle Tone
The force with which a resting muscle resists being stretched (also termed stiffness)
Range of muscle tone:
Normal, Hypotonia, Hypertonia
What does normal muscle tone allow for?
Maintenance of posture
Hypotonia
Abnormally low resistance to passive stretch (flaccidity)
How does hypotonia occur?
LMN lesions
Acute LMN lesion (ex: Stroke)
developmental disorders
Hypertonia
Atypically strong resistance to passive stretch; greater than normal muscle tension
Two types of hypertonia:
Spastic
Rigid
Which type of hypertonia is velocity dependent?
Spastic
if you try and move someone’s muscle slowly there is a better movement possibility than if you try and jerk it quickly
Which type of hypertonia is velocity independent?
Rigid
doesnt matter how fast or slow you try and move someone’s muscle
What does hypertonia occur from?
Chronic UMN lesion (stroke)
Some Basal Ganglia disorders (Parkinson’s)
Signs of a LMN disorder:
Muscles undergo:
- Wasting/atrophy
- Fasciculations
- Fibrillations (detectable by myography)
- Flaccid paralysis
- Loss of reflexes
Etiology of Polio (Poliomyelitis):
Viral illness: transmitted primarily through the ingestion of material contaminated with fecal matter.
Pathology of Polio:
Virus leaves digestion track and enters the blood stream, attacking the LMNs (in spinal cord and brainstem)
Asymptomatic Polio:
No symptoms (most people had this one)
Symptomatic Polio:
Symptoms range from mild to severe (death possible)
Spinal Polio:
LMN cell bodies attacked (only in ventral horn of spinal cord)
Bulbar polio:
CN (motor) cell bodies attacked (in brainstem)
Bulbospinal polio:
Combination of spinal polio and bulbar polio where cell bodies are attacked in spinal cord and in brainstem.
Polio: Axonal Sprouting
Survivors of polio recover some muscle strength as surviving neurons sprout new terminal axons and innervated the denervated muscle fibers.
(Mainly in bulbar polio)
Collateral Sprouting:
Sending off a shoot from a healthy axon
Iron Lung
Allows a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person’s ability.
Post-Polio syndrome possible symptoms:
Muscle weakness and atrophy
Joint and muscle pain
Fatigue
Breathing and swallowing problems
When does Post-Polio syndrome occur?
Years (decades) after the acute illness in some people who survive paralytic polio
Theory of post-polio syndrome:
Due to overextending of surviving neurons
Use it and (you will) lose it.
(wouldnt want to tell your patient to go to the gym and overexert)
ALS: Inherited or idiopathic?
Both, 1 in 10 cases is inherited, the others are idiopathic (dont know why you get it)
What does ALS cause the destruction of?
Somatic motor neurons (bilateral)
UMNs and LMNs
What is the progression in regards to muscles of ALS symptoms?
Progressive muscle weakness and atrophy –> paralysis
(Paresis, spasticity, hyperreflexia (overresponsive reflexes), atrophy, fasciculations (brief, spontaneous contraction of only a few muscle fibers) )
What is the LMN damage in regards to ALS?
CN damage, difficulty with breathing, swallowing and speaking
Prognosis of ALS:
Average life span following diagnosis is 3 years, usually caused by respiratory complications.
Myopathic Disorder
A disorder intrinsic to muscle
Duchenne’s Muscular Dystrophy:
Genetic disorder, X-linked
Duchenne’s Muscular Dystrophy: occurs mostly in girls or boys?
Boys (almost exclusively occurs in boys)
What is the most common form of childhood muscular dystrophy?
Duchenne’s
What is the cause of Duchenne’s Muscular Dystrophy?
A genetic deficiency of the protein dystrophin
Without dystrophin, muscles are not able to operate properly and will eventually suffer progressive damage.
Early symptoms of Duchenne’s MD:
Clumsy movement Difficulty climbing stairs Frequently trips and falls Unable to jump or hop normally Tip toe walking Gower's Sign
What is Gower’s Sign?
An early symptom of Duchenne’s MD where the person has difficulty getting up from a sitting or lying position on the floor.
Why would you see enlarged calf muscles in Duchenne’s MD?
Due to large amounts of fatty deposits that are replacing muscle.
What type of condition is Duchennes MD? (progressive, stable, etc..)
Progressive, first affects the muscles of the legs and pelvis, then progresses to the arms, neck and other areas of the body
When is a wheelchair usually needed by in Duchennes MD?
By age 12
By late teens, what happens in Duchennes MD?
Often have heart and lung problems
What happens to the sensory and autonomic functions in Duchennes MD?
Remain intact.
