Anatomy of the Spinal Cord, Motor System and Spinal Reflexes Flashcards
What are extrafusal muscle fibers?
the large fibers actually involved in moving the muscles
What are extrafusal muscle fibers?
the large fibers actually involved in moving the muscles
What are intrafusal muscle fibers (spindle)?
Little tiny modified muscle fibers are sensory organ inside the muscle
What are the motor neurons going to extrafusal muscle fibers?
Alpha, fast conducting, called lower motor neurons.
What does white matter contain?
axons and glial cells
what does grey matter contain?
cell bodies of neurons
What is gamma motor neurons?
small motor neurons because of the Ag range of size and speed.
Where is the interneuron located?
center of spinal cord
Where does the spinal cord end?
L1 level
What is cauda equina?
The spinal column is longer than the spinal cord. Lower lumbar and sacral nerve roots have to descend for quite some distance before exiting the spine -> forming a cluster
What is lumbar cistern and what is its relationship with CSF?
dura and arachnoid matter continue down into the sacrum. There is then a pocket of fluid below the spinal cord in which the nerve roots reside.
What divides the grey matter?
ventral, lateral, and dorsal feniculus: divide the grey matter into three parts
Where is the grey matter large?
In the lumbar area
In which region the dorsal horn are pointy?
cervical
What is the major neuron type in ventral horn
alpha
Did you study the dermatome map?
No, you did not
Is alpha or gamma neuron more myelinated?
alpha, conducting velocity is much higher than gamma
what is type II sensory fiber for?
touch, joint, pressure, vibration,etc (cutaneoous mechanoreceptor)
What is type Ia sensory fiber for?
receptor is at muscle spindle
What is type Ib sensory fiber for?
receptor is at golgi tendon organ
What is type III sensory fiber for?
Fast nociceptorl cold thermoreceptor
What is type IV sensory fiber for?
Slow nociceptor; warm thermoreceptor
What is muscle pool?
cluster in ventral horn - going to a single muscle. Damage to a single root produce weakness of muscle, not paralysis.
What are intrafusal muscle fibers (spindle)?
Little tiny modified muscle fibers are sensory organ inside the muscle
What are the motor neurons going to extrafusal muscle fibers?
Alpha, fast conducting, called lower motor neurons.
What does white matter contain?
axons and glial cells
what does grey matter contain?
cell bodies of neurons
What is gamma motor neurons?
small motor neurons because of the Ag range of size and speed.
Where is the interneuron located?
center of spinal cord
Where does the spinal cord end?
L1 level
What is cauda equina?
The spinal column is longer than the spinal cord. Lower lumbar and sacral nerve roots have to descend for quite some distance before exiting the spine -> forming a cluster
What is lumbar cistern and what is its relationship with CSF?
dura and arachnoid matter continue down into the sacrum. There is then a pocket of fluid below the spinal cord in which the nerve roots reside.
What divides the grey matter?
ventral, lateral, and dorsal feniculus: divide the grey matter into three parts
Where is the grey matter large?
In the lumbar area
In which region the dorsal horn are pointy?
cervical
What is the major neuron type in ventral horn
alpha
Did you study the dermatome map?
No, you did not
Is alpha or gamma neuron more myelinated?
alpha, conducting velocity is much higher than gamma
what is type II sensory fiber for?
touch, joint, pressure, vibration,etc (cutaneoous mechanoreceptor)
What is type Ia sensory fiber for?
receptor is at muscle spindle
What is type Ib sensory fiber for?
receptor is at golgi tendon organ
What is type III sensory fiber for?
Fast nociceptorl cold thermoreceptor
What is type IV sensory fiber for?
Slow nociceptor; warm thermoreceptor
What is muscle pool?
cluster in ventral horn - going to a single muscle. Damage to a single root produce weakness of muscle, not paralysis.
The neurons located most laterally supply?
hand muscles; distal muscles
The neurons located most medially supply?
axial muscles; proximal muscles
Extensors muscles are more ventral or dorsal?
ventral
Flexor muscles are more ventral or dorsal?
relatively dorsal
What is a motor unit?
all of the muscle fibers innervated by a single motor neuron; the axon typically has collateral structures
how is dexterity related to the size of motor unit
the finer the action it is, the smaller the motor unit
What happens to the motor units when slowly build up muscle contraction to a maximum?
A single motor unit -> recruitment -> all motor units within the muscle are firing at a relatively high rate
What are the differences between Type I (red) and Type II (white) muscle fibers?
Size: type 1 small
Neuron size: type 1 small
Speed of contraction: type 1 moderate, type 2 very fast
Tension/fiber: type 1 low
Aerobic metabolism: type 1 high
Fatigue: Type 1 resistant.
The red = myoglobin, lots of mitochondria
3 classical spinal cord reflex
- Muscle strech (myotatic, “deep tendon”) 2. Inverse myotatic 3. Flexion reflex
What is muscle stretch/myotatic/deep tendon reflex?
Stretching a mucle results in contraction; tested with reflex hammer
What is inverse myotatic muscle?
Stretch the muscle to maximum, about to tear -> relaxation of muscle, protective reflex -> activation of antagonist muscle
What is the flexion/withdrawl relex?
Painful stimulus of a limb
Which two reflexes requires muscle receptor for stretch and tension?
Muscle stretch and inverse myotatic
What are the two types of muscle receptors?
Muscle spindle and Golgi tendon organ
How is the muscle spindle afferent (type 1A, fastest, heavily myelinated) is activated?
- Deformation of annulospiral endings (the nucleus part of the intrafusal muscle fiber stretches)
- Activation of gamma motor neuron.
What is annulospiral ending?
The sensory nerve endsing that wrapping around the central portion of the intrafusal muscle fiber.
What is the intrafusal muscle fiber?
= modified skeletal muscle fiber = muscle spindle
What is the extradusal muscle fiber?
Real muscle fiber that produce the contraction and movement
What is the result of knee flex?
Very sudden and rapid stretch (extension) of the quadriceps.
How is the extent “brisk” determined?
Excitability of the motor neurons
How is the sensory affarent type 1A synpasing?
- Directly with the motor neuron for the quadriceps, activating it.
- Synpase with interneuron that (1) inhibit the antagonist muscle (2) facilitate other agonist muscles
What is the knee reflex used for?
Stabilize the leg in a particular position.e.g. if I am standing with my knee extended, and somene knocked into the back of my knee -> this reflex prevents me from collapsing to the floor.
What are the functions of gamma motor neurons (2)?
- Firing when the intrafusal muscle fibers shortened, aligning the muscle spindl with the new position of the muscle.
- A baseline of firing during muscle relaxation.
Principle of alpha-gamma co-activation
When extrafusal muscle fibers contract, activation of gamma motor neurons align the muscle spindle (intrafusal muscle fibers) with the new position of muscle, restoring its ability to detect any stretch from this new position.
Once the muscle spindle within a muscle are set….
muscle spindle will help prevent any movement from that point…then automatic control of alpha motor neurons.
Two ways to command voluntary muscles.
- Command an alpha-motor neurons to direct muscle stretch.
- activate a small group of gamma motor neuronss going to the biceps - put tension onannulospiral endsing -> activate muscle stretch afferent nerve fibers -> activate target agonist muscles and inhibits angonist muscle.
The second method (gamma loop) is more efficient from a bioenergy perspective.
What is spasticity?
gamma motor neurons are overactive and result in excessively sensitive stretch reflex. If someone is spastic, the attempt to move away from a particular position will be resisted. The faster the attempt to move, the more resistance there is (more you activate the stretch reflex).
What is the cause of spasticity?
Typically due to loss of descending inhibitory pathway.
Where are golgi tendon organ?
1b afferent neuron sandwiched between muscle fibers and tendon (within CT).
What does GTO detect?
muscle tension, resistance, unconcious proprioceptor - lots of effort in to coordinate movement.
Why is GTO not a strong stretch receptor?
tendon is relatively inelastic unless gets to maximum, where CT is stretched; muscle belly has most stretch.
How does contraction activate GTO?
As the muscle contracts, it becomes stiff and starts to pull the tendon.
What happens when the stretch of GTO reach maximum?
Inverse myotatic reflex; negative feedback regulation of muscle tension; protective response
How is the negative feedback regulation of muscle tension by GTO related to spasticity?
Pt who have spasticity has excessively active negative feedback - “clasp-knife”, difficult to initiate.
What is the result of flexion reflex/withdrawal reflex?
One limb flexion, the counterlateral limb undergoes extension.
What is Babinski reponse?
Overactive withdrawal reflex
Toe extension…
Is a physiological withdrawal reflexion, can be a sign of overactive reaction
Interneuons…
pattern reflexes and also pattern many routine and repetitive movements.
