CSAD 334 Motor Control

for quiz 4

somato

means joints, skin, and skeletal muscle

viscero

means vessels, glands, smooth muscle, and cardiac muscle

efferent systems

involve motor information going to a muscle; a 2-neuron system; the 2 neurons depend on whether the system is somatic or autonomic

2 neurons of somatic system

upper motor neurons (UMNs) and lower motor neurons (LMNs)

2 neurons of autonomic system

preganglionic and postganglionic neurons

afferent system

involves sensory information coming in from the environment and going to the cortex; a 3-neuron system: first-order, second-order, and third-order

gray spinal cord matter

horns in the center of the spinal segment; dorsal and ventral

dorsal horns

sensory; the top set

ventral horns

motor; the bottom set

white spinal cord matter

the outer part of the spinal segment

autonomic nervous system

the motor control system for homeostasis; a 2-neuron pre-ganglion and post-ganglion system

principal transmitters of the autonomic nervous system

acetylcholine and norepinephrine

where the parasympathetic system emerges

from the brainstem/cranial nerves and some spinal sacral regions

where the preganglionic parasympathetic fibers originate

four chief nuclei in the brainstem - edinger-westphal of CN III, superior and inferior salivatory of CN VII and CN IX, and dorsal motor nucleus of CN X

where parasympathetic preganglionic cells project to

project to ganglion near the bladder, reproductive organs, the colon and the rectum

role of sensory inputs in motor system

provide real-time information about the body’s current state to M1

direct motor system

includes the cerebral cortex (pre-motor cortex, supplementary motor cortex, and M1) and the brainstem; UMN projects from cortical or brainstem areas and connects directly with the LMN

indirect motor system

includes the basal ganglia and cerebellum; does not directly communicate with the LMN; only communicates with the UMN in the cortex

two types of sensorimotor pathways

can be pyramidal and extrapyramidal systems

pyramidal system

motor cortex → brainstem → LMN; voluntary, fine motor movements; conscious and controlled by the individual (e.g., finger movements used during typing)

extrapyramidal system

brainstem → LMN; automatic and nonconscious; postural support - supports volitional movements of the pyramidal system (e.g., back, shoulder, and arm stability and position that allow typing to occur)

descending pyramidal tracts

include the corticospinal tract and corticobulbar tract

descending extrapyramidal tracts

rubrospinal tract, reticulospinal tract, vestibulospinal tract, and tectospinal tract

indirect sensorimotor pathway

(subcortical circuitry) informs both extrapyramidal and pyramidal pathways, so damage to subcortical circuitry may also impact both

corticospinal tract

originates in motor cortex and descends spinal cord; responsible for voluntary, skilled movement especially in the distal limbs

corticobulbar tract

originates in the motor cortex and goes to CN nuclei in the brainstem

UMN of corticospinal tract

cortex → medulla → pyramidal decussation → travel down spine to LMN; mostly unilateral, decussating in the medulla to have contralateral innervation

corticobulbar tract functions

innervates all LMN responsible for speech articulation (labial, lingual, velar, mandibular), vocal sound source production, facial expression, feeding/chewing, and swallowing

corticobulbar tract innervation

innervates majority of cranial nerve motor nuclei bilaterally; has unilateral innervation for some cranial nerves - those that serve the lower face and tongue

descending motor pathways of brainstem

extrapyramidal system pathways; UMN originates in the brainstem; name of tract tells you where UMN originates and where LMN picks up

UMN of rubrospinal tract

red nucleus

LMN of rubrospinal tract

spinal cord (rubro)

function of rubrospinal tract

influences activation of LMN innervating flexor muscles of the human body; more influential in non-human primates, acting as a functionally parallel system to the corticospinal tract in these animals; has an uncertain involvement in speech

what damage to rubrospinal tract causes

myoclonus in speech musculature

UMNs of reticulospinal tract

reticular formation - pons and medulla

LMN of reticulospinal tract

spinal cord (reticulo)

pontine reticulospinal tract

facilitates LMN activation of proximal extensor muscles of lower limbs; increases muscle tone

medullary reticulospinal tract

inhibits proximal voluntary movements and decreases muscle tone

general function of reticulospinal tract

helps to maintain balance and posture; innervates CNs and plays a role in swallowing reflex

UMN of tectospinal tract

superior colliculus

LMN of tectospinal tract

spinal cord (tecto)

function of tectospinal tract

influences LMNs and interneurons related to control of the neck, head, upper body, and shoulders; coordinates head posture with eye movements

UMNs of vestibulospinal tract

vestibular nuclei (medial and lateral)

LMNs of vestibulospinal tract

spinal cord (vestibulo)

two segments of vestibulospinal tract

medial and lateral vestibulospinal tracts

vestibulospinal tract function

transmits descending balance and vestibular-related signals to axial muscle systems of the head, neck, and extensor muscle of the limbs; engaged when you are starting to lose your balance and beginning to fall

lower motor neurons

final common pathway for development of muscle contraction during an action; smallest functional unit controlled by neuromotor system to generate voluntary force; one motoneuron can innervate many to thousands of fibers, and each muscle fiber is innervated by a single motoneuron at the NMJ

innervation ratio

number of muscle fibers innervated by one motoneuron

low IRs

great capacity for fine skill

IR for speech

15 fibers to one axon

high IRs

for gross movement

IR for walking

500 fibers per one axon

size principle of motor unit recruitment

as the need for force increases during a behavior, motor units are recruited in an orderly manner based on size

how the motor system varies force

as force levels fluctuate, the motor system can adjust, up or down, the firing rates of already active motor units, and can add or subtract motor units of increasing or decreasing size

LMN features

receives a vast quantity of convergent input from various sources; action potentials generated by them represent the summation and integration of all inputs synapsing onto them

where LMNs receive input from

motor and sensory cortical areas of the brain, local interneurons in the spinal cord and brainstem, modulary systems that originate in the brainstem, and sensory endings in the periphery

LMNs innervating striated muscle

come in two different forms and serve two different purposes - alpha motor neurons and gamma motor neurons

alpha motor neurons

innervate skeletal muscle and synapse onto these fibers via the NMJ; heavily myelinated; large diameter; innervate extrafusal (contractile) muscle tissue, contracting the muscle; part of lateral motor systems

gamma motor neurons

synapse upon contractile elements within the muscle spindle sensory receptor; lightly myelinated and have a smaller diameter than alphas; innervate muscle spindles; maintain the sensitivity of stretch receptors during muscle contractions - monitoring muscle tone; part of medial motor system