Descending Motor Tracts (Spinal Cord)

descending spinal cord tracts

has to do with efferent (motor) information

• corticospinal pathway

• vestibulospinal tract

• tectospinal tract

• rubrospinal tract

• reticulospinal tract

corticospinal pathway

• voluntary contralateral muscle control (conscious)

• corticobulbar tract (cranial nerve branches)

• lateral tract decussates in medulla in the pyramids

• anterior tract decussates at spinal level

**information goes to skeletal muscles

vestibulospinal tract

(balance)

• from vestibular nucleus in pons and medulla oblongata to spinal cord

• input from inner ear concerning head position, body posture, and body balance

• output to postural and balance muscles

• ipsilateral control

NO CROSSING! just travels through anterior spinal cord region

tectospinal tract

• from tectum nuclei in midbrain

• tectum receives visual and auditory input

• output goes to skeletal muscles of the head and neck to respond to bright lights, sudden movements, and loud noises

• contralateral, decussates at the brainstem

rubrospinal tract

• from red nucleus in midbrain to cervical spinal cord

• limited motor control of upper extremity muscles

  • contralateral control; crosses at brainstem and facilitates upper extremity flexion

reticulospinal tract

• from reticular formation in brainstem to spinal cord

• input from all ascending and descending pathways, cerebrum, brain stem, and cerebellum

• output to muscles during an increase in alertness of the body

• ipsilateral control, NEVER CROSSES

somatic motor control

• complex motor control from the cerebral cortex

• simple reflexes in the brain stem and spinal cord

• when movement begins from the motor cortex, the basal nuclei and cerebellum evaluate and modify the movement control (higher level processing)

exteroceptors

external environment

interoceptors

internal environment

proprioceptors

body position and movement

mechanoreceptors

detect change in pressure and distortion

• baroreceptors are a type

ex: free nerve endings, merkel discs, root hair nerve endings

thermoreceptors

detect temperature change

chemoreceptors

detect change in chemicals

• carotid bodies and aortic bodies are a type that can sense issues in the heart that need to be addressed

photoreceptors

detect light

nocioreceptors

detect pain

unencapsulated mechanoreceptors with free nerve endings

located in the dermis

detect fine touch and some pressure

merkel disc unencapsulated mechanoreceptors

communicate with sense neurons to detect fine touch and pressure

root hair nerve ending unencapsulated mechanoreceptors

detects hair distortion (like in the wind)

Meissner’s corpuscles encapsulated mechanoreceptor

located in the dermis

detects light touch and movement

ruffini corpuscle encapsulated mechanoreceptors

detects pressure and skin tension; slow to accept info, has to have a lot of it

pacinian (lamelated) corpsucle encapsulated mechanoreceptors

rapid response, detects deep pressure

referred pain

perceived pain located in areas other than where the injury is located

like visceral pain: pain in organ but is perceived in a superficial area and the areas do not have to be close to each other

golgi tendon organ

• senses tension in tendon of muscles (gets excited when muscle tension is too high)

• sends inhibitory signal back to parent muscle to try and decrease muscle tension and tell it to stop contracting

• “safety mechanism” for muscles

muscle spindle

• senses muscle length, tension, and velocity of contraction

• nuclear bag with sensory neuron called the la affarent

• intrafusal fibers to control tension in bag via a gamma efferent motor neuron

• extrafusal fibers are muscle fibers in the muscle

**threshold is reached if too long or too fast, so the muscle spindle contracts

WE DO NOT WANT TO ACTIVATE THIS

reflex arc

the pathway or neural wiring that is responsible for an immediate involuntary response to a specific stimulus

• starts at receptor

• then goes to interneuron

• then goes to effector which is end target

classification of relfexes

• innate or acquired

• spinal or cranial (brain) - where it is processed

• somatic (motor/muscle) or visceral (organ) - end target, where the response is

• monosynaptic or polysynaptic (complexity of circuit, # of process points)

patellar reflex

monosynaptic reflex

checks the L1-L4 nerve roots that connect to quad;

hammer is stimulus, then muscle spindle is triggered, than the information travels through the dorsal root, goes back out the ventral root, contraction of muscle is the response

reciprocal inhibition reflex (cross extensor reflex)

• step on something painful (hurt leg flexes to get away, ipsilateral… normal leg stays extended, contralateral)

• monosynaptic

• flexors are stimulated and extensors are inhibited in hurt leg, information goes in through the dorsal root and out of the ipsilateral ventral side

• flexors are inhibited and extensors are stimulated in pain free leg, therefore a contralateral signal is sent so that it remains in extension