A&P Exam 3 - ch 12

from the foramen magnum to L1

Spinal cord

• bone
• meninges
• CSF

• space between the vertebrae and the dural sheath (dura
• mater) filled with fat and a network of veins

• filled with CSF
• best place for spinal tap = cauda equina region

terminal portion of the spinal cord

fibrous extension of the pia mater; anchors the spinal cord to the coccyx

delicate shelves of menigeal tissue; attach the spinal cord to the vertebrae - entire length

31 pairs attach to the cord by paired roots (Compare to cranial nerves)

sites where nerves serving the upper and lower limbs emerge

collection of nerve roots at the inferior end of the vertebral canal

separates anterior funiculi (columns)

divides posterior funiculi (columns)

• soma
• unmyelinated processes
• neuroglia

connects masses of gray matter; encloses central canal

interneurons for sensory tracts

interneurons and somatic motor neurons

contain sympathetic nerve fibers (ANS)

• Dorsal half – sensory roots and ganglia;
• Ventral half – motor roots
• Dorsal and ventral roots fuse laterally to form spinal nerves
• Four zones are evident within the gray matter – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)

• ascending
• descending
• transversely

• posterior
• lateral
• anterior

• Each funiculus contains several fiber tracks
• –Fiber tract names reveal theirorigin and destination, eg. Corticospinal, spinothalamic
• –Fiber tracts are composed of axons with
• similar functions

Pathways decussate (Why is it important to know WHERE different pathways decussate?)

• Most consist of two or three neurons
• –First order: sensory receptor to
• spinal cord or brain stem (soma in ganglion)
• –Second order: from cord or brain
• stem to thalamus (soma in dorsal horn or medulla)
• –Third order: thalamus to somatosensory cortex (soma in thalamus)

Most exhibit somatotopy (precise spatial relationships)

Pathways are paired (one on each side of the spinal cord or brain)

• Dorsal column
• –Skin sensation & proprioception - Discriminative touch, pressure, limb & joint position
• –Cuneatus = upper limbs & trunk
• –Gracialis, lower limbs & lower trunk

• Spinocerebellar tracts
• –send impulses to the cerebellum and do not contribute to sensory perception - unconscious proprioception

• Spinothalamic tracts
• –Pain, temperature, crude touch

• Descending tracts deliver efferent impulses from the brain to the spinal cord, and are
• divided into two groups
• –Direct pathways equivalent to the pyramidal tracts
• –Indirect pathways, essentially all others

• Motor pathways involve two neurons (upper and lower motor neurons)
• –Upper = brain to spinal cord
• –Lower = spinal cord to effector muscle

• Direct pathways originate with the pyramidal neurons in the precentral gyrus (upper motor neuron)
• Impulses are sent through the corticospinal tracts and synapse in the anterior horn
• Stimulation of anterior horn neurons activates skeletal muscles via lower motor neurons
• Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei
• The direct pathway regulates fast and fine (skilled) movements

• Includes the brain stem, motor (basal) nuclei, and all motor pathways not part of the pyramidal system
• This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts

• Reticulospinal tracts – maintain balance
• Rubrospinal tracts – control flexor muscles (help regulate antagonistic movement, eg gait)
• Superior colliculi and tectospinal tracts mediate head movements

loss of motor function

severe damage to the ventral root or anterior horn cells

–Lower motor neurons are damaged and impulses do not reach muscles

–There is no voluntary or involuntary control of muscles

only upper motor neurons of the primary motor cortex are damaged

–Spinal neurons remain intact and muscles are stimulated irregularly

–There is no voluntary control of muscles

Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut

Paraplegia – transection between T1 and L1

Quadriplegia – transection in the cervical region

Partial transection? Only cut one side: is it above or below decussation point?

Destruction of the anterior horn motor neurons by the poliovirus

Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes

Sadly, motor neurons targeted are often involved in respiration.

Vaccines are available and can prevent infection. Polio is NOT eradicated. If you have not been vaccinated, you are susceptible.

Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract

Symptoms – loss of the ability to speak, swallow, and breathe, as well as walk & use arms/hands

Death occurs within five years

Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase - involved in protection of neuron health.