Descending Tracts Flashcards
Voluntary Movement
Descending Motor Tracts: Pathway for brain’s communication w/ the body
Two Motor Neuron System
• Upper Motor Neuron
o Sits w/i cerebral cortex - w/i (precentral/postcentral) gyrus = w/i primary (motor/sensory) area and brainstem
o Neurons in CNS that terminate on other neurons in CNS
____ stem (cranial nerves)
____ cord (spinal nerves)
• Lower Motor Neuron
o Neurons in CNS whose axons terminate on (other neurons/effector organs)
Ex. Skeletal muscles, cardiac muscle, glands, neurons in PNS
• Upper and lower motor neurons need to synapse, work together and coordinate to produce voluntary movement
precentral; motor; brain; spinal; effector organs
Primary Motor Cortex (M1)
• Sits w/i (precentral/postcentral) gyrus
• Devises (motor/sensory) programs
o Not responsible for “flex your elbows” “curl your fingers”
o Responsible for “go lift something”
The rest of the coordination comes at the spinal cord level
o Synergistic program hardwired into the motor cortex
Not micro-managing
Big picture movements
precentral; motor;
• Somatotopic organization
o Similar to somatotopic organization of the sensory cortex
o Larger cortical regions for regions where finer (motor/sensory) control is required
Large number of motor neurons
o Homunculus
Cortical representation in the motor cortex
The more fine control movements required –> the more representation w/i primary (motor/sensory) area because need more motor units
• Ex. Quadriceps straightens out knee vs. Hand
o Don’t need as many players to do straight knee
o Need more players for fine-tuned control motions in hand
Face and hand take up (smaller/larger) representation w/i the motor gyrus
• More motor units needed b/c there’s more muscles in each
Geographic region may be small but the amount of movement and coordination needed is large
motor; motor; larger
Two Major Motor Tracts for Voluntary Movement
• Pathways that are used to carry information from brain down to end organs
1. Corticospinal Tracts
a. Information from the cortex down to the spinal cord levels
b. Limbs and trunk musculature, axial neck, axial trunk, pelvic limbs
c. Lateral corticospinal tract
i. Conscious control over the (limbs/trunk)
d. Anterior corticospinal tract
i. Conscious control over the (limbs/trunk)
2. Corticobulbar tracts
a. Information from (medial/lateral) most aspect of cortex to the _____ stem
b. (Cranial/Spinal) nerves of brainstem
c. Responsible for conscious control over eye, jaw and face muscles
limbs; trunk; lateral; brain; Cranial
• Upper Motor neurons coming from cortical region
o Sits w/i (gray/white) of the cortex
• Lower Motor Neurons sitting w/i (brain/cord) level
1. Corticospinal tracts come down from the cortex to 3 anatomic structures
2. Go down into the (midbrain/hindbrain)
3. Crosses into the ______ peduncle
a. Sits on outermost aspect of the brainstem at the midbrain
4. Continues down the most outermost aspect of the brainstem through to the medulla oblongata
5. Distal 2/3 of medulla oblongata –> lateral corticospinal tracts cross over onto contralateral side and posterior
a. Decussation happens at the medulla at the level called the _____
b. Corticospinal tracts cross through the _____
i. So corticospinal tracts are also known as _______ tracts
ii. Pyramidal region = where cross over occurs
c. Anterior corticospinal tract (responsible for trunk)
i. (DOES/DOES NOT) crossover at the level of the medulla
ii. Continues down into the cord and crosses over and stays anterior once it gets to target segment
iii. Stays at the (midline/lateral) of the white region
1. Midline b/c anterior corticospinal tract is responsible for trunk musculature
gray; cord; midbrain; cerebral; pyramids; pyramids; pyramidal; DOES NOT; midline
Structures involved w/ the corticospinal tracts
1. Corona Radiata
a. Comes down into where the _____ ganglia sit
b. Funnels into (midbrain/hindbrain)
i. Internal Capsule = the funneling region
c. Sits w/i _____ region
2. Internal Capsule
a. Sits w/i cortical region
3. Crus Cerebri
a. Sticks on the (inside/outside) of the midbrain/brainstem region
b. Travels through the medulla into medulla oblongata
4. Pyramidal tracts
Once Signal comes down at the target cord level
• Lateral corticospinal tract
o Takes up large part of the white area
o Essentially in dorsal aspect of cord
o Limbs sits on (medial/lateral) aspect of cord
• Anterior corticospinal tract
o Comes and sits on the midline
o On anterior aspect of cord
o Trunk musculature sits medial aspect of the cord
Posture control and maintain vertical
basal; midbrain; cortical; outside; lateral;
Reminder • White Matter categorized as columns o Dorsal column = (Motor/Sensory) o Lateral Column = (Sensory/Mix) Motor: Mostly limb control o Ventral Column = Mostly (motor/sensory) Some sensory cross over fibers Motor: mostly trunk/postural control
sensory; mix; motor;
• Cortico-spinal tract
o Cortex to the (Mid/hind) brain to the (basal ganglia/medulla) (lateral tract crosses over) to the (brain/spinal cord ventral horn) (anterior crosses over at the level of the spinal segment)
• Cortico-bulbar tract
o Responsible for (spinal/facial) nerves
o Cortex to Mid brain: some leave here , to the Medulla: some leave here
o Decussation before they leave (similar to anterior corticospinal tract)
o Synapsing with the cranial nerve nuclei: lower motor neuron.
mid; medulla; spinal cord ventral horn; facial
Motor Unit
• For each muscle fascicle = (one/two) lower motor neuron to control that fascicle
• When we perform an activity only some of these fascicles will be turned on
• Strengthening overload process
o First 2-6 weeks = (neural adaptation/hypertrophy)
o 6-8 weeks = (neural adaptation/true muscle hypertrophy)
Through training, practicing recruiting more motor units
• Not recruiting muscles at a 100%
o If we were, we wouldn’t need neural adaptation
o Elite athletes –> fire 98-99%
o Non-trained individuals –> fire roughly 80%
Reduction in central activation or central drive = (increase/decrease) in muscle fiber recruitment after an injury
• The drive from either the cortex or the cord not able to recruit 100% of muscle fibers
• Need to spend more time trying to recruit all the muscle fibers
• If not 90%-100% fascicles are activated = not getting overload regardless of how hard you’re working
one; true muscle hypertrophy; decrease;
Measuring Central Activation and Determining Central Activation Failure (CAF)
• Individual pushes into dynamometer w/ maximum effort
• Maximal volitional isometric contraction (MVIC) = plateau
• Once hit plateau, deliver a super maximal electrical stimulation to the quadriceps
o If muscle is working at 100% and all fascicles are turning on –> (No increase/increase) in strength
o Not recruiting 100% –> (no increase/increase) in strength
• Volitional activation (MVIC) / total activation after stimulus = Central activation ratio (CAR)
o Top chart: CAR = 1
individual has no central activation deficits
o Bottom chart: MVIC/ total activation after stimulus = 0.83
Some Central activation failure
Roughly turning on 80% of motor units
• An indirect method of measuring how much central output is getting to the end organ muscle fibers
No increase; increase;
Need Intact Lower Motor Neuron System
• NMES is stimulating the (axon/GTO) of the lower motor neuron
o So that the lower motor neuron releases acetylcholine into the neuromuscular junction
o Leads to chemical excitation of the muscle
• If Lower motor neuron is denervated to the muscle (laceration, injury to spinal cord) –> (able/unable) to function
o Even with NMES (electrical stimulation)
• NMES Direct Current
o Stays on if turned on
o Has a much (smaller/larger) current density than an alternating current
o In denervated individuals
Not stimulating lower motor neuron
Using (Alternating/Direct) current because of the magnitude of the current density
Getting the sarcolemma of the muscle to release calcium –> results in muscle contraction
• Actual muscle stimulation when using (alternating/direct) current
axon; unable; larger; Direct; direct
Nerve Palsies and Direct Current
• Spinal cord injury w/ not much chance for reinnervation –> use of direct current may be questionable
• Nerve palsies
o Lost (lower/upper) motor neuron temporarily
o Able to come back
o Can use (alternating/direct) current to try to keep muscle active and reduce atrophy
o Important for facial muscles
Muscles much smaller so atrophy could be detrimental
lower; direct
Motor Tracts
• (Involuntary/Voluntary) motor tract:
o Lateral + Anterior Corticospinal and Corticobulbar
• (Involuntary/Voluntary) Motor tracts (extrapyramidal tracts)
o Consists of four tracts involved in subconscious motor control
o Originate from the ____ stem w/i the midbrain and pons level
1. Vestibulospinal tracts
2. Tectospinal tracts
3. Reticulospinal tracts
4. Rubrospinal tracts
Voluntary; Involuntary; brain;
Tectospinal Tract
• Comes in from the (hindbrain/midbrain)
• Tectum
o 4 distinct lumps on the outer posterior aspect of the midbrain
o Superior Colliculi: receives (auditory/visual) information
Receives information from the optic nerve
Used to coordinated movement
The two top bumps
o Inferior colliculi: receives (auditory/visual) information
In order for you to respond to auditory information
The two lower bumps
• Location of cranial nerve nuclei and exiting cranial nerves
o Not part of the tectospinal tract
o Just be aware from a midbrain perspective
• Tectospinal tracts exits at C_ - C_
o Not going to see tectospinal tracts in the (cervical/thoracic) region because only responsible from (cervical/thoracic) spine musculature
• Function of the Tectospinal tracts
o Coordinates (head/foot) and (eye/nose) movements
o Turning of the head to visual or auditory stimuli
Involuntary circuitry
• Don’t always move head when moving eyes because there are superior inhibition controlling for that
Survival mechanism
o Crosses over (immediately/latently)
• Close eyes and can feel subtle suboccipital muscle contraction when moving eyes
midbrain; visual; auditory; C1-C4; thoracic; cervical; head and eye; immediately
Red Nucleus
• (Rubrospinal/Vestibulospinal) tract originates from here
• Receives input from the:
o (Basal ganglia/Cerebellum) (quality control center of the brain/comparator)
Takes (motor/sensory) output that you are currently performing and compares to what the cerebral cortex wants it to do to keep things on tract
o Cerebral cortex
• More active in quadrupedal animals and infants
• Pediatric relevance:
o While cerebral cortex has not developed much –> a lot of involuntary tracts have primitive movement control that are important to babies
o Not fully developed cerebral cortex = movement not well-refined
o –> Reliant on (involuntary/voluntary) circuitry to carry out motion
• Role in motor control (increases/reduces) as cortex develops
o BUT can play a backup role
Cortical lesion (stroke, brain tumor, traumatic brain injury)
• Can start to lose cortical input and refined motor drive from cortical input
• Involuntary tracts start to take over to aid in movement
Rubrospinal; Cerebellum; motor; involuntary; reduces;
Vestibulospinal tracts
• Vestibular system: equilibrium
• Send information from the inner ear to monitor position of the (head/feet)
• Vestibular nuclei respond by altering muscle tone for neck muscle contraction + limbs for posture and balance
• Falling backwards:
o Don’t want to hit head
–> vestibular system picks up quick acceleration of the head
Activates (ligaments/muscles) to try to stop the fall
From a neck muscle perspective –> going to duck your head
• Falling forwards:
o Same thing as falling backwards, just opposite
• All these muscles come in to play depending on the magnitude of perturbance
• 2 Vestibulospinal tracts:
o Lateral vestibulospinal tracts
Responsible for (limbs/trunk) and (flexors/extensors) of the leg
(Crossed/Uncrossed)
o Medial Vestibulospinal tracts
(Head and neck/Feet and toes) control (only found in (cervical/sacral) region)
(Crossed/Uncrossed)
Reminder:
• Anterior portion of the white is (MOTOR/SENSORY)
• (Lateral/Medial) tracts = trunk and postural
head; muscles; trunk and extensors; uncrossed; Head and neck; cervical ; crossed ; MOTOR; Medial
Reticular formation
• Resides w/i (pons and medulla/trunk and feet)
• Functions:
o Collection of multiple nuclei (100 or so)
o Pain modulation, alertness, arousal, consciousness, and motor control (We’re focusing on arousal and motor control)
Also sleep, and cardiovascular control
• Think back to the stepping on a glass bottle scenario
o Flexor withdrawal and crossed extensor
Hamstring firing on involved foot + Quadricep firing on stance foot
o Brain is alerted that a threat is detected
Recruits the gluteal muscles and trunk muscles to resist from falling over
o Because the anterolateral system goes into reticular formation + reticular formation is responsible for arousal and motor control
We think some of these corrections in balance and falling over stimulus occur at the reticulospinal tract
• Starts w/i reticular spinal region –> terminates on the (motor neurons/interneurons) in the (dorsal/ventral) horn
o Synapses (dorsal/ventral) horn and influences alpha and gamma motor neurons
o Different from simple reflex because
involving alpha and Gamma co-activation
• Gamma fibers
o Responsible for pulling the intrafusal fibers taught
So that there is always tension w/i spindles
and maintaining proprioceptive input from the 1a fibers
• 2 Reticulospinal tracts:
o Medial (from pons)
Inhibits (flexors/extensors) + excites *flexors/extensors)
Stays on (ipsilateral/contralateral) side
o Lateral (from medulla)
Inhibit (flexors/extensors) + excites (flexors/extensors)
Cross over onto (ipsilateral/contralateral) side
o Basic motions, NOT refined motions
Refined motion is from the _____
But keeps person from falling
pons and medulla; interneurons; ventral; ventral; flexors; extensors; ipsilateral; extensors; flexors; contralateral; cortex
