spinal cord

spinal cord

• links peripheral body to brain

• distributes impulses along peripheral nerves

• carries sensory and motor impulses

• location: enclosed by vertebrae in the vertebral canal

foramen magnum to L1-2

spinal cord begins at _______ ______ where it meets the medulla, and ends at intervertebral disc between regions ____

conus medullaris

• tapered, cone-shaped

• distal portion of spinal cord

cauda equina

• strands of fibers: “horse’s tail”

• extends from the distal end of the spinal cord

• composed of nerve roots

filum terminale

• extension of pia mater

  • long, thin strip of CT

• extens inferiorly from conus medullaris

• anchors cord to coccyx

cervical and lumbar enlargements

• thickened regions of the spinal cord

• additional neurons to supply limbs

subarachnoid space

located between arachnoid and pia mater

• contains cerebrospinal fluid (csf) — ultrafiltrate of plasma produced in ventricles of the brain

• characteristics: clear, colorless, odorless

• cushions brain

• provides nourishment to and carries waste away from CNS

choroid plexuses

• clusters of specialized capillaries

• produce CSF

• located in cerebral ventricles (spaces in brain)

epidural space

• located external to dura mater

• contains fat & blood vessels which supply the spinal cord

subdural space

• deep to dura, between dura and arachnoid

• nothing found here normally

lumbar puncture

collect cerebrospinal fluid from the subarachnoid space for analysis or drainage

order of structures

1. skin

2. subcutaneous tissue

3. muscle

4. ligaments

5. dura mater

6. arachnoid mater

pain management

injection of anesthesia into epidural space

white matter

• contains bundles myelinated axons

• lipids in myelin sheath → white color

gray matter

• contains unmyelinated cell bodies of neurons

• forms “butterfly” shaped regions

• no myelin → gray color

ventral gray horn

cell bodies for motor neurons

dorsal gray horn

cell bodies for sensory neurons

dorsal root/rootlets

enter/exit cord carrying sensory impulses

ventral root/rootlets

enter/exit cord carrying motor impulses

dorsal root ganglion

contains cell bodies of sensory neurons

spinal nerve

short segment carrying ALL sensory and motor impulses at certain level of spinal cord

dorsal ramus

nerve of skin & axial muscles of back

carries all sensory and motor impulses

ventral ramus

anterior/lateral body wall and all limbs

carries all sensory and motor impulses

spinal nerves

31 pairs, pass through intervertebral foramina throughout spine

• cervical - 8

• thoracic - 12

• lumbar - 5

• sacral - 5

• coccygeal - 1

spinocortical tract

1. origin: sensory nerves

2. pathway: up spinal cord

3. decussation: cross opposite side in medulla

4. destination: brodmann areas 3,1,2 - somatosensory cortex

dorsal column medial lemniscus pathway

• fine touch & proprioception

• two bundles in dorsal (posterior) spinal cord

fasiculus cuneautus

sensory from upper body

fasiculus gracilis

sensory from lower body

corticospinal tract

1. origin: brodmann area - 4 motor cortex

2. decussation: crosses at medulla

3. travels down to spinal cord

4. then onto skeletal muscle

upper motor neuron

• starts in brain, ends in spinal cord

• cell body located in gray matter of cortex (precentral gyrus)

• axon synapses on lower motor neuron in spinal cord

lower motor neuron

• aka. peripheral motor nerve

• starts in spinal cord and ends in muscle

• cell body is in brain stem or ventral gray horn in spinal cord

• its axon synapses on skeletal muscle fibers

babinski sign

• upper motor neuron normally keeps sensory impulse from spreading to other nerve roots

• normal stimulation of sole: baby - hallux extension

  • adults - all toes curl and adduct

• damage = impulse distribution not controlled, adult responds like infant

poliomyelitis

• viral infection

• in extreme cases, motor neurons destroyed

• flaccid paralysis

  • reflexes absent

  • muscles atrophy

spinal reflexes

• rapid, unconscious & automatic response to a stimulus

• sensory stimulus triggers a motor response in the spinal cord, NOT from the brain

simple stretch reflex

1. muscle spindle receptor in muscle tendon responds to stimulus and initiates impulse

2. sensory neuron in dorsal root ganglion transmits impulse to cns (spinal cord)

3. motor neuron in ventral gray horn of spinal cord transmits impulse from cns to pns (via spinal nerve)

4. effector — skeletal muscle responds to motor neuron impulse

polysynaptic withdrawal reflex

1. pain receptor responds to stimulus and initiates impulse

2. sensory neuron in dorsal root ganglion transmits impulse to cns (spinal cord)

3. interneuron links between sensory and motor neurons

4. motor neuron in ventral gray horn of spinal cord transmits impulse from cns to pns (via spinal nerve)

5. effector — skeletal muscle responds to motor neuron impulse

absent reflex

• lower motor neuron issue

• stimulation cannot elicit motor response

exaggerated response

• upper motor neuron issue

• poor or no inhibition of lower motor neuron