Spinal Control Of Movement

Front 1

Lower motor neurons

Back 1

-Somatic motor neurons in the ventral horn of the spinal cord
-Directly command muscle contraction
-Final common pathway

Front 2

Upper motor neurons

Back 2

-Brain
-Supply input to spinal cord.

Front 3

Spinal nerve

Back 3

-Axons of lower motor neurons form ventral roots. Ventral roots join with dorsal roots to form these nerves.
-In notches btw vertebrae

Front 4

Mixed spinal nerves

Back 4

-Nerves contain both sensory and motor fibers

Front 5

Alpha Motor Neurons

Back 5

-Directly trigger the generation of force by muscles
-Combine with other AMN and muscle fibers to form a motor unit

Front 6

Motor neuron pool

Back 6

-Motor neuron = alpha motor neurons + muscle fibers
-Collection of AMNs that innervates a single muscle

Front 7

What are the 2 ways that the CNS controls muscle contraction?

Back 7

1. Varying action potential firing rate
2. Recruiting additional synergistic motor units

Front 8

What are the 3 sources of inputs to an alpha motor neuron?

Back 8

1. Dorsal root ganglion cells
2. Upper motor neurons in motor cortex/brain stem
3. Interneurons in spinal cord (largest source)

Front 9

Hypertrophy v. Atrophy

Back 9

Hypertrophy: Exaggerated growth of muscle fibers
Atrophy: Degeneration of muscle fibers

Front 10

Excitation Contraction Coupling

Back 10

-Action potential release Ca2+ from an organelle inside muscle fiber -> contraction of the fiber.
-Relaxation occurs when Ca2+ levels are lowered

Front 11

Sarcolemma

Back 11

-Excitable cell membrane enclosing muscle fibers

Front 12

Myofibrils

Back 12

-Cylindrical structures within muscle fibers which contract in response o an AP sweeping down sarcolemma.

Front 13

Sarcoplasmic Reticulum

Back 13

-Surrounds myofibrils
-Extensive intracellular sac that stores Ca2+

Front 14

T Tubules

Back 14

-Network of tunnels
-Inside fiber
-Inside out axons, continuous with extracellular fluid.

Front 15

Tetrad

Back 15

-Voltage-sensitive cluster of four calcium channels in the T tubule
-Linked to calcium release channel in the SR.

Front 16

Calcium Release Channel

Back 16

-Linked to tetrad
-Ca2+ flows through = myofibril contracts

Front 17

Z Lines

Back 17

-Divides myofibril into segments by disks

Front 18

Sarcomere

Back 18

-Segment comprised of 2 Z lines and the myofibril between.

Front 19

Thin filaments

Back 19

-Series of bristles anchored to each side of Z line

Front 20

Thick filaments

Back 20

-Series of fibers
-Between and among the two sets of thin filaments

Front 21

How does muscle contraction occur?

Back 21

-The thin filaments slide along the thick filaments, bringing adjacent Z lines towars one another
-aka Sarcomere is shorter

Front 22

Actin and myosin

Back 22

-Myosin binds to actin and undergo a conformation change that causes pivoting.
-Thick filament moves with respect to thin filament
-Myosin heads disengage and uncock so that the process can repeat itself = myosin heads walk along actin filaments.

Front 23

Troponin

Back 23

-Prevents myosin from interacting with actin when muscles are at rest
-Covers actin binding sites.

Front 24

Muscle spindles

Back 24

-Deep in skeletal muscles
-Stretch receptor
-Several types of specialized skeletal muscle fibers contained in a fibrous capsule

Front 25

Proprioreceptors

Back 25

-Component of somatic sensory system that is specialized for body sense or proprioception which informs us about how our body is positioned and moving space.

Front 26

Myotatic Reflex

Back 26

-When a muscle is pulled on it tends to contract.
-Stretch reflex

Front 27

Monosynaptic Myotatic reflex arc

Back 27

-The Ia axon and the AMNs on which it synapses constitute this
-One synapse separates the primary sensory input from the motor neuron input.

Front 28

Intrafusal fibers

Back 28

-Contained within muscle spindle
-Modified skeletal muscle fibers in fibrous capsule

Front 29

Extrafusal fibers

Back 29

-Outside spindle, and form bulk of muscle
-receive motor innervation by another type of lower motor neuron called a gamma motor neuron.

Front 30

Gamma Motor Neurons

Back 30

-Innervate extrafusal fibers at 2 ends of muscle spindle
-Causes a contraction of two poles of the spindle, thereby pulling on the noncontractile equatorial region and keeping the Ia axons active.

Front 31

Gamma Loop

Back 31

Gamma Motor Neuron->intrafusal muscle fiber->Ia afferent axon->alpha motor neuron->extrafusal muscle fibers

Front 32

Golgi tendon organ

Back 32

-Sensor in skeletal muscle
-acts like a strain gauge
-Monitors muscle tension or force of contraction
-In series (not in parallel)

Front 33

Reciprocal inhibition

Back 33

-the contraction of one set of muscles accompanied by the relation of the antagonist muscles. (Walking)

Front 34

Crossed extensor reflex

Back 34

-activation of extensor muscles and the inhibition of flexors on the opposite side
-stepping on tack

Front 35

Central pattern generators

Back 35

-Rhythmic motor activity
e.g. walking