MO3: Spinal Cord; Reflexes

Cervical Vertebrae #

7

Thoracic Vertebrae #

12

Lumbar Vertebrae #

5

Inferior bone 1

Sacrum (5 fused vertebrae)

Inferior bone 2

Coccyx (3-5 fused vertebrae)

Vertebral foramen

Location of spinal cord

Intervertebral foramen

Spinal nerves exit vertebral column here

Cervical enlargement

Houses neurons that innervate muscles of upper extremity

Lumbar enlargement

Houses neurons that innervate muscles of lower extremity

Why is the cervical enlargement larger?

Greater control over fine musculature in upper limbs

Conus medularis

Most inferior portion of spinal cord

What level does the conus medularis fall at

Around L1

Cauda equina

Bundle of spinal nerves extending from inferior region of spinal cord

Dorsal root ganglion (DRG)

Enlargement of dorsal root near spinal nerve, houses sensory neuron cell bodies

Dorsal root

Entrance for sensory info

Ventral root

Exit for motor neurons

Spinal nerve

Merging of dorsal and ventral roots

Type of info carried by spinal nerves

Sensory and motor

Dorsal ramus

Carries sensory/motor info to posterior trunk

Ventral ramus

Carries sensory/motor info to extremities and anterior trunk

White matter (columns)

Regions composed primarily of myelinated axons

Gray matter (horns)

Regions with many cell bodies and dendrites

Dorsal (posterior) horn

Responsible for sensory processing

Ventral (anterior) horn

Sends motor signals to skeletal muscles

Lateral horn

Only found in thoracic region, central component of sympathetic nervous system

Central canal

Located in center of spinal cord, contains cerebrospinal fluid (CSF)

Anterior spinal artery

1 artery, supplies anterior 2/3 of spinal cord

Posterior spinal artery

2 arteries, supplies posterior 1/3 of spinal cord

Ascending pathways

In columns, carry sensory information up to the brain

Descending pathways

Carry motor commands from the brain

Decussation

Crossing to contralateral side of where a pathway originated

Dorsal column medial lemniscus pathway (DCML) carries?

Fine, discriminative touch and light pressure

DCML Pathway

Enters through dorsal root, cell body in DRG, travels to dorsal horn, travels in dorsal column, ascends to brainstem, decussates, synapses

Anterolateral System Pathway (ALS) carries?

Pain, temp, crude touch

ALS pathway

Enters dorsal root, cell body in DRG, to posterior horn, synapses w/2nd order neuron, immediately decussates at level of spinal cord entrance, enters column on opposite side, ascends to brain

Spinocerebellar pathway carries?

Proprioceptive and muscle sense info

Spinocerebellar pathway

Enter dorsal root, cell body in DRG, synapses in posterior horn, decussates 0 or 2x (info always ipsilateral)

Upper motor neurons

Originate in brain and descend through spinal cord until reaching the level the pathway exits the spinal cord. Responsible for exciting/inhibiting lower motor neuron

Lower motor neurons

Originate in anterior horn of spinal cord, travel through ventral root to join spinal nerve on the way out to skeletal muscle

Corticospinal tract is responsible for?

Motor control

Corticospinal tract pathway

Begins in cortex of brain, decussates in brainstem, descends into lateral horn, descends until exit level reached, reaches anterior horn and synapses w/lower motor neuron

Monosynaptic stretch reflex

Muscle spindle receptor activated when skeletal muscle is stretched. Causes direct contraction of muscle

Golgi tendon reflex

Inhibition of lower motor neurons in response to too much tension (sensed by golgi tendon organ)

Polysynaptic withdrawal reflex

Sensory receptors in skin sense early signs of tissue damage, innervate muscles needed to pull away nad inhibits muscles that would oppose

Spinal cord lesions symptoms in DCML are…

Ipsilateral

Spinal cord lesion symptoms in ALS are…

Contralateral

Spinal cord lesion symptoms in corticospinal are…

Ipsilateral