advance neuro lec 11

somatic motor sys function

voluntary movement

reflexive movement

itegration of signals

voluntary movement

conscious control

reflexive movement

unconscious control

integration of signals

bring signals in afferents from sensory organs

sends signals back efferents to muscles effectors

upper motor neurons UMN

begin in cortex or brainstem 

contained wi cns

synapse in spinal cord or brainstem

supply input to lower motor neruons

lower motor neruons lmn

cell bodies in spinal cord or brainstem

leave cns

directly innervate skeletal muscles

synapse w/ muscle fibers

lmn

innervate somatic musculature

only ones to directly command muscle contraction

axons budle to form ventral roots

include alpha and gamma

ventral roots

are lmn axons bundled together 

each joins w/ dorsal root to form mixed spinal nerve

mixed spinal nerve

ventral root joins w/ dorsal root

alpha motor neurons

connect cns to extrafusal fibers of skeletal muscle

large myelinated axons

efferent diviision of all muscle reflexes

alpha motor neruons cell body

in ventral horn of spinal cord and terminal endings synapse w muscle fibers nmj

alpha motor neurons are controlled by

local spinal cord circuitry and by descending commands from umn

lmn distrib

not distrib evenely

motor unit

directly trigger generation force by musclesamn and muscle fiber

motor neruon pool

all of amn that innervate a single muscle

muscle control

firing rate of amn

motor end plate

receiving end of nmj

realease ach onto nachr

cause epsp on muscle fiber (epp)

ap is evoked in muscle fiber

muscle contraction

1. ach binds to postsyanptic receptors

2. epsp

3. na and ca enter muscle cell

4. excitation contraction coupling ca is released from intracelular stores

5. ca binds to troponin

   1. troponin moves to allow myosin to walk along actin by atp

input to llmn

umn desending motor pthways top down 

due to dorsal root ganglion muscle spindle gto-spinal reflexes

interneruons

reflex

realtively sterotyped movement caused by peripheral stim

simple circuit in sc

carry signal into cns and back out to periphery

spinal circuitry and reflexes

occur wo/ awareness or cortical input

can be subject to conscious control

sensory stim to sc to motor response

gamma motor neurons

intrafusal and innervate specialized muscle fibers combined w sensory nerve fibers to form sensory organs

spindle

detects muscle stretch

gto

detects muscle contraction

gamma motor neurons

don’t execute spinal reflexes but modulate muscle contraction

myotatic reflex

contraction of muscle when it is stretched

knee jerk

monosynaptic reflex

monosynaptic

only one synapse sep primary sensory input form motor neuron output

knee jerk input

sensory stim from muscle

knee jerk output

motor amn

reciprocal innervation

muscles from agonsit/antagonist pairs to facilitate speed,direction and control of movement

reciprocal innervation

contraction of stretched muscle with simultaneous relaxation of antagonist muscle

sensory neruons form

monosynaptic excitatory connection with amn that innervate same muscle

via interneruons inhibitory connection w amn that innervate antagonist muscles

intteruneurons in sc

balance btw snesory and motor commands

recevie info form descending axons umn afferents and efferetns amn

can be excitatory or inhibitory

determine which muscles should relax or contract in reposnse to sensory stim

gto reflex

reduce muscle tension and aiding w/ stability

muscle contaction stretches and stim afferents in gto

afferents of gto reflex

stim inhibitory internuon that signals to amn of homonymous muscle casuing relaxation

stim an excitatory internuron that signals to amn to antagonist causing contraction

lmn syndrome lesion

set of symptoms casued by damage to amn in brainstem or spinal cord

casue = stroke tumors trauma guillain barre syndrome amyotrophic lateral sclerosis spinal muscular atrophy mg infections polio

lmn syndrome symptoms

wakeness/paralysis

atrophy

hypotonia

hyporflexia

fasciculations

fibrillations

amyotrophic lateral sclerosis

no known cause- genetec and envi factors

degen motor neurons

muscle weakness and paralysis

short life expectancy upon diagnosis

mg

autoimmune

diagnosed in adulthood

affect lmn

loss of nachr at nmj

eye deviatiion and drooping eyelid

muscle weakness

normal life expectancy