Chapter 10 Flashcards
What does well coordinated or learned movement require?
a continuous integration of visual, somatosensory and vestibular information with motor processing
What is feedforward?
anticipatory use of sensory information to prepare for movement
What is feedback?
refers to the use of sensory information during or after movement to make corrections either to the ongoing movement or to future movements
What does neural activity begin with?
a decision made in the anterior part of the frontal lobe
What is the second step in motor planning?
motor planning areas are activated, followed by control circuits
What regulates the activity in upper motor neuron tracts?
control circuits, consisting of the cerebellum and basal ganglia
Where do upper motor neuron tracts deliver signals?
to spinal interneurons and lower motor neurons (LMN)
What does the LMNs do?
signals directly to skeletal muscles, eliciting the contraction of muscle fibers that move the upper limbs and fingers
How is voluntary movement controlled?
from the top down (the brain, to the spinal cord, to the muscle)
What four systems make essential and distinct contributions to motor control:
- local spinal and brainstem circuits
- Descending control pathways
- the cerebellum
- basal ganglia
Motor cortex
planning, initiating, and directing voluntary movements
Brainstem centers
basic movements and postural control
Basal ganglia
gating proper initiation of movement
Cerebellum
sensory motor coordination of ongoing movement
When is muscle contraction produced?
when actin slides relative to myosin
What does the resistance to stretch muscles depend on?
the length
What determines the total resistance to muscle stretch?
active contraction, titin and weak actin-myosin bonds
What is muscle tone?
resistance to a passive stretch in a resting muscle
How is muscle tone assessed clinically?
passive rotation of a limb through a range of motion
What happens when muscle tone is normal?
resistance to passive stretch is minimal
What is normal resting muscle tone provided by?
weak actin-myosin bonds
When do sarcomeres disappear from the ends of myofibrils?
when healthy innervated muscle is continuously immobilized in a shortened position
When will the muscle add new sacromeres?
if the muscle is immobilized in a length position
What is cocontraction?
refers to the simultaneous contraction of antagonist muscles, increasing the joint’s resistance to movement
What does cocontraction do?
stabilizes joint
What does cocontraction do in the upper limbs?
enables precise movements
What does cocontraction do in the lower limbs?
allows an individual to stand on an unstable surface
What are two types of LMSs
alpha and gamma
What do alpha and gamma neurons do?
only neurons that convey signals to extrafusal and intrafusal skeletal muscle fibers
Where do axons of alpha motor neurons project?
extrafusal skeletal muscle, branching into numerous terminals as they approach muscle
Where do axons of gamma motor neurons project?
to intrafusal fibers in the muscle spindle
What to gamma motor neurons consist of?
medium sized myelinated axons
What is alpha-gamma coactivation?
alpha and gamma motor neurons function simultaneously
Why does alpha-gamma coactivation occur?
- sources of input to alpha MN have collaterals MN
- less excitation needed to reach threshold gamma MN
Motor unit:
An alpha motor neuron AND the muscle fibers it innervates”, constituting a functional entity
Features of Motor units:
vary in degree of fatigability
in speed of contraction
in size
How are motor units classified:
slow-twitch fibers
fast-twitch fibers
Slow twitch fibers:
innervated by smaller-diameter, slower-conducting alpha motor neuron; involved in standing
Fast twitch fibers:
innervated by larger-diameter, faster-conducting motor neuron; involved in walk and run etc
In most movements, which fibers are activated first?
slow twitch fibers are activated first due to smaller cell bodies
What is the Size Principle?
The order of recruitment from smaller to larger motor neurons
When are movements generated?
when somatosensory information is integrated with descending motor commands in the spinal cord
What are LMN pools?
groups of cell bodies in the spinal cord whose axons project to a single muscle
What do medially located pools innervate?
axial and proximal muscles
What do laterally located pools innervate?
distal muscles
What do anteriorly located pools in ventral horn innervate?
extensors
What do posteriorly located pools innervate?
flexors
What is reciprocal inhibition?
the inhibition of antagonist muscles during agonist contraction
How is reciprocal inhibition achieved?
by interneurons in the spinal cord that link lower motor neurons into functional group
What is central pattern generators?
basic pattern of coordinated rhythmical activity (walking) wired into the spinal cord circuits
What is a stretch reflex?
a mechanism to monitor and maintain muscle length
What does a stretch reflex stimulate?
stretch of the muscle
What is the senor of a stretch reflex?
spindles
What does a stretch reflex involve?
alpha (and gamma) motor neurons, local circuit interneurons, and afferent somatic sensory input
What is the golgi tendon organ reflex?
a system that monitors and maintains the muscle force
What is the stimulus of the golgi tendon organ reflex?
tension due to muscle contraction
What is sensor for the golgi tendon organ reflex?
golgi tendon organ
What is a flexion withdrawal reflex?
a system for withdrawing the limb from a harmful stimulus
What is the activation of the flexion withdrawl reflex?
activation of nociceptor
What is the sensor of flexion withdrawal reflex?
sensor endings in skin, etc
How is the golgi tendon organ reflex a negative feedback?
Functionally, the system can protect potential damage and prevent muscle fatigue
What is the Hoffman or H-reflex?
Are monosynaptic reflexes elicited by electrically stimulating a nerve
What is the purpose of the Hoffman or H-reflex?
to quantify the level of alpha motor neuron facilitation or inhibition
