Lecture 2-Exam 1 Flashcards
What are the subdivisions of the nervouse system?
What are the different horns and roots of the spinal cord? What horn is special and why?
Lateral horn – serves SNS. Only in thoracolumbar spinal cord
What are descending and ascending tracts?
What are each track for:
* Lateral corticospinal
* Dorsal columns
* Lateral spinothalamic
* Ventral spinothalamic
- Lateral corticospinal: motor
- Dorsal columns: Fine touch, propioception, vibration
- Lateral spinothalamic: pain and temperture
- Ventral spinothalamic: light touch
- The motor system is comprised of what?
- Muscle contraction only occurs in response to what? What does it constitute?
- The motor system is comprised of skeletal muscles and the neurons that control them.
- Muscle contraction only occurs in response to action potentials in alpha motor neurons, which originate in the ventral gray matter of the spinal cord (and brainstem nuclei of certain cranial nerves) and constitute the final common pathway for motor control
Where do Action potentials in alpha motor neurons originate in?
in the ventral gray matter of the spinal cord (and brainstem nuclei of certain cranial nerves)
What is the hierarchy of motor control within the CNS? What is the purpose of each component?
Association cortex and the basal ganglia
* determine the goal of movements.
Primary motor cortex and cerebellum
* determine the correct sequence of commands that will allow the goal to be achieved.
Neuronal circuits in the spinal cord
* implement descending commands
There are three inputs to alpha motor neurons that determine which muscle fibers will contract, explain
- Upper motor neurons from the cortex or brainstem regulate voluntary movements
- Spinal interneurons form an extensive circuitry within the spinal cord. Basic motor programs (e.g., walking) are encoded in spinal circuits known as central pattern generators.
- Sensory neurons from muscle proprioceptors provide feedback about muscle length and tension.-> (muscle spindle and tendon golgi)
What is the alpha motor neuron?
The final common path, to release Ach onto the muscle
* Somotic motor control
What influences the motor neurons?
Peripheral sensory input and spinal cord tracts that descend from the brainstem and the cerebral cortex influence the motor neurons
What does the cerebellum and basal ganglia contribute to?
The cerebellum and basal ganglia contribute to motor control by modifying the brainstem and the cortical activity.
What is a motor unit? What is the difference of high threshold motor unit and lower threshold motor unit?
a motor neuron and all the muscle fibers it innervates
* High: More AP needed to fire
* Lower: smaller motor neurons, less APs are needed to fire
Larger vs smaller motor units?
Larger motor units are harder to activate, so a greater stimulus is needed to activate the larger motor units. Thus, smaller motor units always get activated first in any movement.
- Motor unit consist of what?
- What is determined by the motor neuron?
- A motor unit consists of an α motor neuron and a group of extrafusal muscle fibers it innervates.
- Functional characteristics, such as activation threshold, twitch speed, twitch force, and resistance to fatigue, are determined by the motor neuron
Proprioception includes what? What are they derived from?
Proprioception includes conscious sensation derived from receptors in the skin and joint capsules (e.g., Pacinian corpuscles).
Unconscious sensation about muscle length and tension is relayed from what? (2)
from muscle spindles and Golgi tendon organs (GTOs)
Muscle spindles:
* What does it provided?
* What does it consist of?
* Expanded where?
- Provide information to the CNS about muscle stretch (length) and the speed with which muscle length is changing.
- Consist of specialized muscle fibers called intrafusal fibers contained in a fibrous capsule and are connected at both ends to the force-generating extrafusal muscle fibers.
- Expanded in the middle where sensory axons are wrapped around the intrafusal fibers. The sensory fibers are large myelinated axons (type Ia) and have very fast conduction speeds.
Muscle spindles
- What are gamma motor neurons?
- Where are their cell bodies located?
- provide the motor supply to contractile filaments within muscle spindles (referred to as the fusimotor system).
- The cell bodies of gamma motor neurons are located in the ventral gray matter of the spinal cord
- Contraction of intrafusal fibers alters what?
- What is an example?
- Contraction of intrafusal fibers alters the sensitivity of muscle spindles.
- For example, intrafusal fibers and extrafusal fibers must shorten at the same time to prevent the muscle spindles from becoming slack
- How are intrafusal and extrafusal muscles fibers organized? Muscle length is monitored by what?
*
- Intrafusal muscle fibers are arranged in parallel with the extrafusal muscle fibers.
- Muscle length is monitored by myelinated Ia afferent neurons coiled around the midsection of intrafusal fibers.
Gamma motor neurons contract what? What does this maintain?
Gamma motor neurons contract intrafusal fibers to maintain spindle tension when surrounding extrafusal fibers contract
* Allos the intrafusal muscle fibers to reset
- Golgi tendon organ arranged how?
- Sensory endings of Ib afferent neurons are arranged how?
- A Golgi tendon organ arranged in series with muscle fibers at the junction between the muscle and tendon.
- Sensory endings of Ib afferent neurons are intertwined with collagen filaments and detect the force of muscle contraction.
What is the myotatic reflex?