what did you learn ch. 16
A posterior root ganglion
attached to the posterior root located medial to the pedicles of the adjacent vertebrae
the posterior horns of the spinal cord
contain the axons of sensory neurons and the cell bodies of interneurons
lumbar cord part
Slightly larger than the thoracic part (11-13 mm in transverse diameter) Less oval, almost circular Relative amount of white matter is reduced both in proportion to gray matter and in comparison to cervical part Anterior and posterior horns are very large; small lateral horns present in first two sections of lumbar part only
Which of the following is not generally involved in a reflex?
inhibition of an effector by a stimulus from a motor neuron
The anterior horns of the spinal cord
primarily house the cell bodies of somatic motor neurons
a withdrawal reflex example
quickly pulling the arm away after touching something hot.
The gray matter in the spinal cord
s centrally located and shaped like an H or a butterfly
the main nerves of the sacral plexus
sciatic nerve, which divides into the tibial and common fibular nerves
The main nerves of the lumbar plexus
the femoral nerve and the obturator nerve.
Which nerve innervates the posterior thigh and leg muscles, plantar foot muscles, and skin of the sole of the foot?
tibial
sacral cord part
very small almost circular Proportion of gray matter to white matter is largest in this spinal cord part Anterior and posterior horns relatively large compared to the size of the cross section
coccygeal nerve
1 (Col)
The spinal nerves inferior to ____________ exit below the vertebra of the same number.
C8
horns
Gray matter regions on both sides are artificially separated into three projections
The anterior rami of spinal nerves T1-T11
are called intercostal nerves
the lumbar enlargement
contains the neurons that innervate the lower limbs.
thoracic nerves
12 (T1-T12)
pairs of spinal nerves
31 pairs
lumbar nerves
5 (L1-L5)
sacral nerves
5 (S1-S5)
cervical nerves
8 (C1-C8)
the cervical enlargement
Contains the neurons that innervate the upper limbs.
cervical cord part
Largest of all spinal cord parts Oval; slightly flattened on both anterior and posterior surfaces Large proportion of white matter compared to gray matter In superior segments (C1-C5), anterior horns are relatively small, and posterior horns are relatively large In inferior segments (C6-C8), anterior horns are larger and posterior horns are even more enlarged
polysynaptic reflexes
More complex neural pathways are observed which have a number of synapses involving interneurons within the reflex arc. a tad bit slower
thoracic cord part
Smaller than the cervical part (9-11 mm in transverse diameter) Oval; still slightly flattened anteriorly and posteriorly Larger proportion of white matter than gray matter Anterior and posterior horns are enlarged only in first thoracic segment; small lateral horns are visible
monosynaptic reflex
The afferent sensory axons synapse directly on the motor neurons, whose axons project to the effector. Interneurons do not function in this type of reflex
what does a posterior root ganglion contain
The cell bodies of the sensory neurons in the posterior root
the spinal cord enlargements
The cervical enlargement The lumbar enlargement
funiculi
The peripheral white matter
the three groups of funiculi in the white matter of the spinal cord
The posterior, lateral, and anterior funiculi
conus medullaris
The tapered inferior end of the spinal cord
Which statement is true about intercostal nerves?
They originate from the thoracic region of the spinal cord.
The word root commissura most nearly means
a stream
Which structure contains motor axons only?
anterior root
The radial nerve originates from the ________ plexus.
brachial
What is the collective name for all of the axons that project inferiorly from the spinal cord?
cauda equina
nerve plexuses from superior to inferior
cervical, brachial, lumbar, and sacral plexuses
What is the benefit of having an intricate nerve plexus, rather than a single nerve that innervates a structure
damage to a single segment of the spinal cord or damage to a single spinal nerve generally does not result in complete loss of innervation to a particular muscle or region of skin.
Between the dura mater and the inner walls of the vertebrae is the
epidural space
Axons cross from one side of the spinal cord to the other through a gray matter region called the
gray commisure
denticulate ligaments
help suspend and anchor the spinal cord within the middle of the vertebral canal, thus preventing potential lateral displacement of the spinal cord.
The anterior funiculi
interconnected by the white commissure.
if its receptor and effector are on the same side of the body, a reflex arc is termed ____________; if on opposite sides, it is ____________.
ipsilateral; contralateral
the gray commissure
part of the gray matter helps connect the right and left regions of gray matter a horizontal bar surrounds a narrow central canal