Lecture 4.1 Flashcards
what forms the neural plate
the thickening of the ectoderm
what forms the neural groove
the folding of the neural plate
what forms the neural tube
the closing of the neural groove
neurulation
the process that forms the neural tube
when does neurulation occur
third and fourth weeks of gestation
ectodermal folding
ectoderm thickening to form the neural plate
formation of the neural tube
anterior (rostral) end of the tube expands and differentiates into brain, while the posterior (caudal) end becomes the spinal cord
three types of spinal bifida
spina bifida occulta < meningocele < myelomeningocele
secondary neuralation
occurs at the caudal end of the developing embryo; becomes the lower part of the spinal cord
- involves mesodermal cells rather than ectodermal cells
ascending tract of spinal cord tract function
brings sensory info from the PNS to the brain
what are examples of ascending tracts in the spinal cord
what are examples of ascending tracts in the spinal cord
spinothalamic tract, the dorsal columns
what do the descending tracts of the spinal cord do
motor commands from the brain to muscles and glands
example of spinal cord descending tract
corticospinal tract
functions of the spinal cord
controlling the repetitive, coordinated actions required for walking and other forms of movement
- center for processing reflex actions
where does the spinal cord connect to the brain
medulla section
approximately how long is the adult spinal cord
45 cm
approximately how many neurons and glia does the spinal cord have
100 million neurons and 500 million glia
where does the spinal cord begin/end
begins at the foramen magnum in the skull (at the interface with the medulla oblongata) and ends at the L1 - L2 vertebral bone level at the conus medullaris
what are the two thickened areas of the spinal cord
cervical enlargement and lumbar enlargement
how many spinal cord segments are there
31 segments
cervical enlargement
supplies nerves to upper extremity
lumbar enlargement
supplies nerves to lower extremity
cauda equina
the nerve fibers coming from spinal cord segments lumbar 2 - 5, sacral 1 - 5, and coccygeal 1 which exit the vertebral column below the conus medullaris
where in the spinal cord is there more white matter than gray
rostral end
which end of the spinal cord has more gray matter than white matter
caudal end
what causes the spinal cord enlargements
the large number of nerve fibers that innervate the upper and lower limbs
what is the shape of the cervical segment
oval or almost circular shape
what is the shape of the thoracic segment
more rounded and have smaller dorsal and ventral horns
afferent neurons
carry sensory info from receptors in skin/other organs —> central nervous system
where are afferent neuron cell bodies located
outside of the spinal cord
efferent neurons
carry motor info from brain —> peripheral nervous system
- aka motor neurons
where are efferent neuron cell bodies located
ventral horn of spinal cord
SADDAVE
sensory = afferent = dorsal
dorsal = afferent, ventral = efferent
dorsal root
transmits sensory info
ventral root fibers
the axons of motor and visceral efferent fibers
cervical nerves
C1 - C8
thoracic nerves
T1 - T12
lumbar nerves
L1 - L5
sacral nerves
S1 - S5
coccygeal nerve
Co1
cord dermatome
body map of spinal segment innervation
cervical dermatomes
C2 - C8: back of the head, neck, shoulders, arms, and hands
thoracic dermatomes
T1 - T12: chest, abdomen, and back
lumbar dermatomes
L1 - L5: associated with the lower back, hips, and the anterior and medial aspects of the legs
sacral dermatomes
S1 - S5: cover the buttocks and posterior legs
the problem with convergence
sensory afferents carrying pain info from the skin and from the organs can converge onto the same dorsal horn neuron; leads to “referred pain”
posterior horn function
contains sensory interneurons and projection neurons for ascending sensory tracts
- present at every level of the spinal cord
intermediate gray matter function
involved in the autonomic nervous system
- present at every level of the spinal cord
anterior horn function
contains lower motor neurons that send motor output to skeletal muscles, controlling voluntary and involuntary movements
- present at every level of the spinal cord
Lissauer’s tract
white matter made up of both myelinated and unmyelinated axon fibers
- convey primarily pain, temperature, and light/crude touch information
what does Lissauer’s tract synapse with
second-order interneurons in Rexed lamina I (the marginal zone) and lamina II (substantia gelatinosa)
where is Lissauer’s tract found
posterior horn
marginal zone location
at the tip of the dorsal horn
marginal zone function
relays info about pain and temp sensation to the brain
marginal zone presence
all spinal levels
marginal zone associated rexed lamina
lamina I
substantia gelatinosa location
at the top of the dorsal horn
substantia gelatinosa function
relays information about pain and temp sensations to the brain
substantia gelatinosa presence
found at all segmental levels of the spinal cord
substantia gelatinosa associated rexed lamina
lamina II
nucleus proprius location
in the neck of the dorsal horn
nucleus proprius function
relays info about proprioception and light/crude touch to the brain
nucleus proprius presence
found at all spinal levels
nucleus proprius associated rexed lamina
laminae III or IV
light touch
poorly localized, crude touch (pressure, tickle, itch)
light touch DELETE
poorly localized, crude touch (pressure, tickle, itch)
fine touch
discriminative touch
dorsal nucleus of clarke location
medially at the bottom of the dorsal horn, corresponding to the medial part of Rexed lamina VII
dorsal nucleus of Clarke function
relays unconscious sensory info about proprioception to the brain (particularly to cerebellum)
dorsal nucleus of Clarke presence
found only in the thoracic to lumbar spinal segments: T1 - L2
intermediolateral nucleus location
in the lateral horn within Rexed laminate VII
intermediolateral nucleus function
relays motor and sensory info between the viscera (internal organs) and the brain
-controls autonomic neurons that give rise to the sympathetic nervous system
intermediolateral nucleus presence
found between the first thoracic spinal segment (T1) and the third lumbar segment (L3)
lateral motor neurons location
located in the ventral horn
lateral motor neurons function
relays motor info from the brain to the viscera and skeletal muscles of the limbs
lateral motor neurons presence
all spinal levels
medial motor neurons location
ventral horn
medial motor neuron function
relays motor info from the brain to the viscera and skeletal muscles of the trunk and neck
medial motor neuron presence
all spinal levels
rexed lamina
divides the gray matter into 10 layers based on the distribution of different types of neurons
dorsal/posterior sensory laminae (I - III) function
primarily involved in pain signaling
deeper laminae (IV - VII) function
involved in non-painful as well as painful sensation and proprioceptive info
ventral/anterior laminate (VII - IX) function
carry motor info from the brain out to the visceral and skeletal muscles
lamina I function
contains neurons that send info about noxious and temp sensory input to the brain
lamina I location
thin layer at the tip of the dorsal horn
- overlaps with the marginal zone nucleus
lamina I presence
found at all spinal levels
lamina II location
corresponds to the substantia gelatinosa nucleus
lamina II function
relay both noxious and non-noxious sensation info to the brain
- modulate sensory input to contribute to brain’s interpretation of incoming signals as painful or not
lamina II presence
all spinal levels
laminae III and IV location
contain nucleus proprius
laminae III and IV function
input is from fibers that convey proprioceptive and light touch sense
laminae III and IV presence
all spinal levels
lamina V function
relay both noxious and visceral sensory stimuli to the brain
lamina V presence
all spinal levels
lamina VI location
deep layer of the dorsal horn
lamina VI function
responds to proprioceptive signals from joints, muscles, and skin
lamina VI presence
all spinal levels
lamina VII location
large zone that contains the cells of Clarke’s as well as the intermediolateral nucleus, and a large portion of the lateral and ventral horns
lamina VII function
relaying proprioception and motor info to and from the brain to the viscera
lamina VII presence
T1 - S4
lamina VIII and IX location
motor neuron groups in the ventral/anterior gray horn
- medial portion (medial motor nucleus)
- lateral portion (lateral motor nucleus)
laminae VIII and IX function
- medial portion innervates muscles of trunk and neck
- lateral portion innervates distal muscles of the arms and legs
laminae VIII and IX presence
all spinal levels
lamina X location
small neurons around the central canal
lamina X function
relaying motor info from one side of the spinal cord to the other bc axons decussate in the gray commissure
lamina X presence
all spinal levels
white matter ascending tracts
carry sensory info up the spinal cord to areas of the brain (eventually terminating in cerebrum or cerebellum)
white matter descending tracts
carry motor info from brain down to levels of spinal cord, eventually terminating on skeletal muscles
reflex
simple, unvarying, unlearned response to sensory stimuli such as touch, pressure, and pain
- most are centered entirely within the spinal cord & don’t involve the brain
spinal reflex arcs
produced by the spinal cord and peripheral neurons only
what does a monosynaptic arc consist of
- a receptor organ (muscle spindle)
- a sensory (peripheral) neuron with sensitive endings
- a spinal cord motor neuron
- an effector organ (muscle)
what does a polysnaptic reflex arc consist of
- a receptor organ (skin)
- a sensory (peripheral) neuron with cutaneous receptor nerve endings
- a spinal cord interneuron
- a spinal cord motor neuron
- an effector organ (muscle)
