Chapter 13.1 : The Spinal Cord Flashcards
Functions of the Spinal Cord
Conduction, Locomotion, Reflexes
local neural circuits (central pattern generators)
are pools of neurons located at each segment of the spinal column that help to control of flexors and extensors which cause alternating movements of the lower limbs // brain sends command but local neural circuits carry out the actual movements
The spinal cord passes through the
vertebral foramen
The inferior margin of the brain ends at __ or a little beyond
L1
Spinal cord size
averages 1.8 cm thick and 45 cm long
Spinal cord occupies the upper ______ of the
vertebral canal
two thirds
At each segment of the bony spinal column, a pair of
axon exit the spinal cord. These are the ______ _____
that connect the cord to muscles and other organs..
spinal nerves
The spinal cord gives rise to __ pair of spinal nerves
31
The first pair of spinal nerve passes between the skull and C1. All other pass through the ________ _________
intervertebral foramen
medullary cone
(conus medullaris)
cord tapers to a point inferior to
lumbar enlargement
cauda equina
bundle of nerve roots that occupy the vertebral canal
from L2 to S5
terminal filum
extension of pia matter from medullary cone which
anchors spinal cord to inferiorly to coccyx
Longitudinal grooves on anterior and posterior surface
of spinal cord
anterior median fissure and posterior median sulcus
Spinal cord divided into the
cervical, thoracic, lumbar, and sacral regions
Two areas of the cord are thicker than elsewhere
- cervical enlargement – nerves to upper limb
- lumbar enlargement – nerves to pelvic region and
lower limbs
Lateral horns located only at
thoracic and lumbar segments
The Meninges of the Spinal Cord
Three fibrous connective tissue membranes that
enclose the brain and spinal cord
– separate soft tissue of central nervous system from
bones of cranium and vertebral canal
– from superficial to deep
* dura mater
* arachnoid mater
* pia mater
The Meninges of the Spinal Cord from superficial to deep
- dura mater
- arachnoid mater
- pia mater
DAP
Dura Mater
Forms loose fitting sleeve around
spinal cord // dura mater around
brain is fused to periosteum
Dura mater is tough, collagenous
membrane with an epidural space
between dura mater and
periosteum. This space is filled
with adipocytes.
An epidural anesthesia is often
injected into the epidural space
during childbirth.
arachnoid membrane
Layer of simple squamous epithelium lining dura mater and a loose mesh of collagenous and elastic fibers spanning the gap between the arachnoid membrane and the pia mater
subarachnoid space
gap between arachnoid membrane and the pia mater /// filled with cerebrospinal fluid (CSF)
lumbar cistern. What does it contain?
subarachnoid space inferior to medullary cone that contains cauda equina and CSF
Pia Mater
delicate, translucent membrane that follows the contours
of the spinal cord
terminal filum
fibrous strand of pia mater that extends
beyond the medullary cone within the lumbar cistern
coccygeal ligament
formed from fusion of terminal filum and dura mater // anchors the cord and meninges to vertebra Co1
denticulate ligaments
pia mater extends through the
arachnoid mater to the dura mater // anchors spinal cord
to limit side to side movement
Connective tissue from axon to spinal nerve order
Axon, myelin sheath, endoneurium, perineurium (surround fascicle), fascicles and blood vessels make up a spinal nerve that is covered in epineurium around entire nerve.
gray matter shaped like a
butterfly
white matter in _ columns // white areas = ____
3 ; tracts
gray matter
neuron cell bodies with little myelin // site of information processing – synaptic integration // grey matter = horns
white matter
abundantly myelinated axons // carry signals from one part of the CNS to another
Posterior grey horns
cell bodies and axons of interneurons + incoming sensory neurons form dorsal root ganglion
Anterior grey horns
somatic motor nuclei to skeletal muscles (LMN /// local motor neurons)
Lateral grey horns
only in thoracic and upper lumbar / contain autonomic motor nuclei / regulate smooth muscle – cardiac muscle - glands
Grey commissure
connects right and left sides // punctured by a central canal lined with ependymal cells and filled with CSF
White matter is
bundles of axons that course up and down the cord (i.e. arranged in fasicles)
Provide pathway of communication between CNS and
PNS target tissues
columns
or funiculi – three pair of these white
matter bundles
- Posterior columns (dorsal)
- Anterior columns (ventral)
- Lateral columns
tracts or fasciculi
subdivisions of each column
ascending tracts
carry sensory information up the spinal cord
descending tracts
carry motor information down the spinal
cord // all nerve fibers in a given tract have a similar origin,
destination, and function
decussation
as the fibers pass up or down the brain stem and
spinal cord they cross over from the left to the right side and vise versa
contralateral
when the origin and destination of a tract are on opposite sides of the body
ipsilateral
when the origin and destination of a
tract are on the same side of the body // does not
decussate
ascending tracts carry
sensory signals up the spinal cord // sensory to the brain
sensory signals travel across _ neurons from origin in receptors to the destination in the sensory areas of the brain // typical pattern
3
– first order neurons – detect stimulus and transmit
signal to spinal cord or brain-stem
– second order neurons – continues to the thalamus at
the upper end of the brain-stem
– third order neurons – carries the signal the rest of the
way to the sensory region of the cerebral cortex
first order neurons
detect stimulus and transmit
signal to spinal cord or brain-stem
second order neurons
continues to the thalamus at
the upper end of the brain-stem
third order neurons
carries the signal the rest of the
way to the sensory region of the cerebral cortex
Major Ascending Tracts
- cuneate fasciculus (above T6)
- gracile fasciculus (below T6)
- spinothalamic tract
- spinoreticular tract
- spinocerebellar tracts - posterior and
anterior
Cuneate Fasciculus // Ascending
carries signals for vibration, visceral pain, deep and
discriminating touch, and proprioception from lower
limbs and lower trunk
What is proprioception? Called the forgotten sensation
non-visual sensation for the position and movement
of the body from receptors located in skeletal muscles /
CF is a conscious pathway
Gracile Fasciculus // Ascending
carries signals for vibration, visceral
pain, deep and discriminating touch,
and proprioception from lower limbs
and lower trunk
medial lemniscus
formed
from the second-order neurons
of gracile and cuneate systems
that decussate in the medulla
Spinothalamic Pathway // Ascending
pain, pressure,
temperature, light touch, tickle, and itch
Spinoreticular Tract // Ascending
carries pain signals resulting from tissue injury
ascends the cord // end in reticular formation
reticular formation
loosely organized core of gray matter in the medulla
and pons
Spinocerebellar Tracts // Ascending
carry proprioceptive signals from limbs and trunk to the cerebellum
first-order neurons originate in the ______ and ______ // end in ____________________
muscles ; tendons ; posterior horn of the spinal cord
Spinocerebellar Tracts provide cerebellum with feedback needed to _______ ______ _____ // subconscious knowledge of muscle’s actual performance
coordinate muscle actions
The Descending Motor Tracts
Carry motor signals down the brain-stem and spinal cord
What are the two pathways of descending motor tract?
pyramidal pathway VS extra-pyramidal pathway
Pyramidal
voluntary // origin = precentral gyrus = motor strip
Extrapyramidal
involuntary // origin = subcortical nuclei
Pyramidal and extrapyramidal pathways use two neurons between their origin and their destination (skeletal muscles)
upper motor neuron and lower motor neuron
upper motor neuron. Where does it originate? Where does it terminate?
originate in cerebral cortex or brainstem // terminates on
a lower motor neuron (cranial nerve or soma in anterior horn)
lower motor neuron Where does it originate?
originate in brainstem or spinal cord // the upper motor
neuron synapse on LMN that leads the rest of the way to the muscle or other target organ
Descending “Pyramidal” Tract
Tracts from precentral gyrus carry action potentials downward through the brainstem and spinal cord. Pathways from precentral gyrus are voluntary pathways used to control skeletal muscles /// consist of upper and lower motor neurons
Two upper motor neuron tracts // synapse on lower motor neurons
– Corticospinal = upper motor neuron /// synapse with anterior horn neurons = lower motor neuron // innervate muscles below neck
– Corticobulbar = upper motor neuron / synapse with cranial nerves = lower motor neuron /// innervate skeletal muscles in head and neck
Corticospinal
upper motor neuron /// synapse with anterior horn neurons = lower motor neuron // innervate muscles below neck
Corticobulbar
upper motor neuron / synapse with cranial nerves = lower motor neuron /// innervate skeletal muscles in head and neck
About lower motor neurons for corticospinal tract
LMN somas in the anterior horn // LMN called common pathway
About lower motor neurons for corticobulbar tract
LMN somas are cranial nerves’ nuclei in brainstem // LMN called common pathway
Corticospinal Tracts // Descending or Motor
from cerebral cortex for precise, finely
coordinated movement of our skeletal
muscles in arms and legs
pyramids
ridges on anterior surface
of the medulla oblongata formed from
fibers of this system
UMN // These nuclei
originate in medulla
oblongata
- tectospinal tract
- vestibulospinal tract
- rubriospinal tract
- reticularspinal tract
Tectospinal tract
begins in midbrain region (tectum)
– crosses to contralateral side of midbrain
– reflex turning of head in response to sights and sounds
Reticulospinal tract
– originate in the reticular formation of brainstem
– controls muscles of upper and lower limbs // especially
those for posture and balance // send signals to “gama
fibers” of the muscle spindle to adjust “sensitivity” of the
muscle spindle in the “stretch reflex” - how the CNS can
influence the “stretch reflex”
– contain descending analgesic pathways // reduce the
transmission of pain signals to brain
Rubiospinal tract
It is one of the pathways for the mediation of
voluntary movement. The tract is responsible for large muscle movement as well as fine motor control, and it terminates primarily in the cervical spinal cord, suggesting that it functions in upper limb but not in lower limb control. It primarily facilitates flexion in the upper extremities
Vestibulospinal tract
begins in brainstem vestibular nuclei receives impulses form vestibular organs of balance from inner ear controls extensor muscles of limbs for balance control. Responsible for the trip response // activates extensor muscles in the arms and legs.
paraplegia
paralysis of lower limbs
quadriplegia
paralysis of all four limbs
hemiplegia
paralysis of one side of the body only
respiratory paralysis
loss of sensation or motor control respiratory paralysis
spina bifida
congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord
What reduces the risk of spina bifida?
folic acid (a B vitamin) as part of a healthy diet for all women of childbearing age reduces risk
– defect occurs during the first four weeks of development, so folic acid
supplementation must begin 3 months before conception
