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22 Cards in this Set

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lower motor neurons are _______ to the mm they innervate
ipsilateral
lower motor neurons are _______ and _______ motor neurons in spinal chrd
alpha and gamma
What does alpha motor neuron look like
very large, long, heavy branches, multipolar
motor nerves
stimulate activity in other cells. In corticospinal tract we are talking only about skeletal mm.
alpha motor neurons
nn in spinal cord, axons are found in peripheral nn. Synapse and cause contraction of skeletal mm
gamma motor nn
axons stimulate small mm, called 'intrafusa' mm, inside mm spindles.
muscle spindles
measure stretch of mm therby giving information about proprioception to brain.
Lower motor neurons
Definition
cause skeletal mm to contract e.g. ALPHA MOTOR

Counterparts in brainstem will be discussed separately.
Organization of alpha motor neurons in spinal cord
Founed in Rexed lamina IX.

Can be for single mm w/in one spinal level or more commonly among several.

Proximal and extensor mm are more medial in cord.
Distal and flexor mm are more lateral in position.
Spinal reflexes often involve _________ and proproception
muscle spindles
__________________ is caused by damage to or death of alpha motor neuron injury
lower motor neuron injury
Upper motor Neurons
Definition
Nerve cells whse axons directly affect the lower motor nerves causing either exitation or inhibition
Orginization of Upper Motor Neurons
Tracts that originate in brainstem

These include CORTICOSPINAL TRACT (MOST IMPORTANT), RUBEROSPINAL TRACT, RETICULOSPINAL TRACT, VESTIBULOSPINAL TRACT, AND TECTOSPINAL TRACT
Corticospinal Tract
Origin
entire precentral gyrus
Motor humunculus
Pyramidal cells in precentral gyrus send out axons to spinal cord (imputs from premotor cortex, basal ganglia and cerebellum will be discussed later)
Corticospinal tract: Brain to spinal cord
Axons originating rom precentral gyrus pyramidal cells continue down to POSTERIOR LIMB OF INTERNAL CAPSULE to middle third of the BASIS PEDUNCULUS in midbrain to BASILAR PONS to PYRAMIDS OF MEDULLA (hense common name for CST--pyramidal tract).
{LEGS LATERAL , ARMS MEDIAL}
At the DESUCATTION OF THE PYRAMIDS (85%) of motor axons cross over ipsilateral to the mm they innervate to the LATERAL CORTICOSPINAL TRACT. A minority of fibers (15%) remain contralateral and travel in the ANTERIOR CORTICOSPINAL TRACT. They decussate at the point where they need to innervate an alpha motor neuron.
Corticospinal tract is more important in _______ and _______ muscles.
flexor and fine movement
Postural muscles are innervated by _________ systems
extrapyramidal
Reticulospinal pathway
origin? contralateral, ipsilateral, bilateral?
Function?
From reticular formation of pons and medulla (central nuclei. Axons predominantly bilateral, may elicit delayed movement in proximal and/ or prexial limbs. -- helps in balance if someone pushes you from behind.
Vestibulospinal Pathwas
from lateral vestibular nucleus
Arise and descend ipsilaterally to affect postural mm, particularly deep back mmm but some proximal limb extensors.
Ruberospinal pathway
Input from cerebellum and cerebral cortex. With some fibers to cerebellum and inferior olivary nucleus, project contralaterally to spinal cord controlling upper limb
Tectospinal tract
arising superior colliculus
end in cervical region
fx in coordination of eye, neck mvmt
UMN injury
loss of consious motor control
leaves reflex intact
Initial shock will create FLACID PARALYSIS then SPASTIC PARALYSIS (exaggerated reflex activity present)
SIGNS:
Babinsky sign
Spacicity
Paresis