motoneurons and muscle recruitment - neuro

motoneuron function is matched to what to allow what

muscle properties to allow functional endurance or power

reflex circuits are located where

spinal cord

what do reflex circuits produce

automated responses that are adaptive for typical situations

what governs many muscle recruitment patterns, within and between limbs, including walking

spinal circuits

define spinal segment

the spinal tissue associated with a spinal root level

what does each spinal segment have

dorsal root, ventral root, and associated gray and white matter

spinal segments are _____ symmetrical

bilaterally

in a spinal cord segment, there is more white matter _____

rostrally

in what sections of the spinal cord is the gray matter enlarged

cervical and lumbosacral

which horn is always present in the SC

ventral horn

what is in the ventral horn of the SC segments

LMNs

ventral horn function

motor output

what is the lateral horn

The lateral expansion of ventral horn in the cervical and lumbosacral enlargements

3 important structures of white matter

dorsal fasciculus, ventral fasciculus, lateral fasciculus

where is gray matter in SC

center

Rexeds lamina are labeling by ____

cytoarchitecture

Lamina I-VI are in

dorsal horn

Lamina VII is in the

intermediate zone

Lamina VIII is in the

ventromedial gray

define motor pool

group of LMNs (alpha MN) in SC that innervate a single muscle

lamina IX contain what (location)

motor pools

which lamina are in dorsal horn

I - VI

lamina IX is also located in the ____ cell column

intermediolateral

in the cervical and lumbar enlargements, what is special about rexeds lamina

the lateral horn (of the ventral horn) is evident; it contains lamina VII, lamina IX (motor pools), and lamina VIII (medially)

define motor pools - buford

group of cell bodies in the SC whose axons project to a spinal muscle

which horn are motor pools located in

ventral horn

medial motor pools innervate

axial and proximal mm

lateral motor pools innervate

distal mm

anterior motor pools innervate

extensors

posterior motor pools innervate

flexors

LMNs directly control what

skeletal mm

where are the cell bodies of LMNs

SC or brain stem

UMNs arise where

cerebral cortex or brain stem

where do the axons of UMNs travel

descending tracts to synapse with LMNs and/or interneurons in brainstem or SC

where are the cell bodies of LMNs (in the SC)

ventral horn

how do axons travel in LMNs

leave via ventral root, travel in the spinal nerve, and then peripheral nerve to reach the muscle

2 kinds of LMNs

alpha and gamma MNs

gamma MN size and characteristic

medium, myelinated LMNs

what do gamma MNs project to

intrafusal fibers (muscle spindles)

alpha MN size and characteristic

large, myelinated LMNs

what do alpha MNs project to

extrafusal fibers (skeletal m)

define motor unit

an alpha motor neuron and all of the muscle fibers it innervates

when an alpha motor neuron is activated it releases a ____ to all of its neuromuscular junctions so all of the mm fibers it innervates are activated

neurotransmitter

how are motor unit fibers distributed

throughout a broad region of muscle

how are motor units termed depending on the speed of muscle contraction in response to an electrical stimulus

slow or fast twitch

what determines if a motor unit is fast or slow

the neuron innervating the muscle fibers of a motor unit

every muscle fiber in a motor unit will have the same ___ ___

fiber type

type 1 motor units AKA

slow twitch, slow resistant

speed/conduction velocity and size of type 1 MU

slow, small

innervation ratio, twitch tension, firing frequency of alpha MN of type 1 MU

small innervation ratio, low twitch tension, low firing frequency of alpha MN

innervation ratio define

number of muscle fibers innervated by a single motor neuron

oxidative capacity of type 1 MU

excellent

type IIa MU AKA

fast resistant, fast oxidative glycolytic

speed/conduction velocity and size of type IIa MU

medium and medium

innervation ratio, twitch tension, firing frequency of alpha MN of type IIa MU

medium

glycolytic and oxidative capacities of type IIa MU

excellent glycolytic and moderate oxidative

type IIb MU AKA

fast fatigable, fast glycolytic

innervation ratio, twitch tension, firing frequency of alpha MN of type IIb MU

high

glycolytic and oxidative capacities of type IIb MU

excellent glycolytic and poor oxidative

which twitch muscle fibers are activated first and why

slow twitch m fibers because small neurons (slow oxidative alpha MNs) are easier to excite with synaptic current than larger neurons (fast glycolytic alpha MNs)

define Henneman size principle

order of motor unit recruitment is from smaller to larger alpha motor neurons

order of types of MU activated

SO, FOG, FG

what is the training effect for MU

oxidative capacity of the MU is determined by its pattern of use

slow MU are suited for ___ and ___ activities

endurance, posture

fast MU are suited for ___ activities

power

Postural control muscles have many ____ innervated by one neuron (each MU in those muscles has a low innervation ratio - constant low force activation)

fibers

Gastrocnemius has an average of ____ muscle fibers innervated per motor neuron

2000

Muscles of precise control have ___ fibers innervated by each neuron (Muscles of precise control have many small motor units, each innervating only a few fibers)

few

Lateral extraocular eye muscle has an average of ___ muscle fibers innervated per motor neuron

2.5

what happens as drive to motor pool increases

MU increase their firing rate then additional MU are recruited (and each MU adds more force)