Download Control of Motor Movement

Motor Output
 
Control of Body Movements
Keri Muma
Bio 6
Spinal Cord Trauma: Paralysis
 
 
Paralysis – loss of motor function
Flaccid paralysis – severe damage to the
ventral root or anterior horn cells
 
 
Descending tracts – axons
carrying motor commands
from the brain to the PNS,
majority are anterior and
lateral, usually involve two
neurons
  Upper neuron – extends
from motor cortex or
motor nuclei in the
cerebrum to the anterior
horn
  Lower neuron – lie in
anterior horn and travel to
the effectors in the
periphery
Spinal Cord Trauma: Paralysis
 
Spastic paralysis – only upper motor neurons
of the primary motor cortex are damaged
 
Lower motor neurons are damaged and impulses
do not reach muscles
There is no voluntary or involuntary control of
muscles
 
 
Reflex Activity
Reflex Activity
 
 
Reflex – rapid predictable motor response to a
stimulus
 
 
 
Occur at the spinal cord or brain stem
May be inborn or learned
Important clinically, exaggerated or absence of reflex
responses may indicate neurological problems
Spinal neurons remain intact and muscles are
stimulated irregularly
There is no voluntary control of muscles
Exaggerated reflexes
Components of a reflex arc
 
 
 
 
 
Receptor – detects stimulus
Sensory neuron – relays info to CNS
Integration – may be monosynaptic or polysynaptic
Motor neuron – carries response away form CNS to
effector
Effector – muscle or gland
1
 
Reflexes
Monosynaptic vs. Polysynaptic
Spinal Reflexes
Stretch Reflexes
Somatic reflexes mediated by the spinal cord
 
Stretch reflexes – muscle spindles are stretched
and excited, afferent impulse is sent to the spinal
cord where it synapses directly with a motor
neuron that triggers the muscle to contract (serial)
 
The sensory neuron also synapses with an
interneuron that inhibits the motor neurons of
antagonist muscles, this is called reciprocal
inhibition
Stretch Reflexes
Spinal Reflexes
 
Flexor reflex – initiated by painful stimulus and
causes withdrawal of the body part
 
 
Examples: touch something hot, abdominal reflex
Superficial reflexes – initiated by cutaneous
stimulation
 
Example: plantar reflex
2
Autonomic Reflexes
3