Spinal Cord Tracts Flashcards
what is the nervous system divided into morphologically?
CNS - brain and spinal cord
PNS (peripheral) - cranial nerves
- spinal nerves and autonomic nerve trunks with their associated ganglia
what neurons does the peripheral nervous system consist of?
afferent (sensory) - arriving to body
efferent (motor) -
what can the afferent neurones be divided into?
somatic - from skin - from retina - from membranous labyrinth
visceral - from thoracic and abdominal organs - from olfactory epithelium from taste buds
what are the efferent (motor) neurons divided into?
somatic - to skeletal muscle
visceral - to cardiac muscle - to smooth muscle - to exocrine glands
what does the gray matter consist of of the spinal cord?
somatic afferent neurons
visceral afferent neurons (1 and 2 from the dorsal horn)
Visceral efferent neurons
Somatic efferent neurons (3 and 4 form the ventral horn)
Dorsal root ganglion
where does the spinal cord conduct information?
to and from the brain through axonal tracts
when the spinal cord connects with spinal nerves - what information does it process?
it processes afferent information from muscles, tendons, joints, ligaments, blood vessels, skin and viscera AND discharges efferent commands that control muscles and regulate glands
what is the spinal cord and its function?
it is a reflex centre, producing subconscious responses of muscles and regulate glands
what do spinal pathways all involve?
A sequence of neurons
information carried to brain by?
motor commands
spinal pathways can either be … or …?
either ascending or descending
what is an ascending spinal pathway?
carrying information from receptors to the brain
what is a descending pathway?
conveying information from the brain to spinal cord neurons
what are tracts?
a bundle of functionally related axons in the CNS
where are tracts found?
in the white matter
ascending tracts?
carrying sensory information
descending tracts?
carrying motor commands
what are spinal pathways/tracts divided into?
divides into dorsal, lateral and ventral funiculus (or columns)
what are nerve tracts named according to?
their origin spinothalamic tract
what do the funiculi have in common?
common origin, destination and function
how can sensory receptors be classified?
external environment (exteroceptors)
internal environment (interoceptors)
receptors used in spatial orientation (proprioceptors)
describe the ascending spinal tracts:
begin with the primary afferent neuron - terminate in the brain
information about pain is carried in - spinothalamic tract
neurons of the spinothalamic pathway do what?
to spinal cord and synapses on the gray matter
information about pain is carried in?
the spinothalamic tract
what does the spinothalamic pathway begin with?
with the primary afferent neuron (first-order neuron)
where does the spinothalamic pathway terminate?
in the brain
where is the unipolar cell body found?
in the spinal ganglion and receptors
how is pain transmitted?
SPINOTHALAMIC pathway
from primary afferent axons to the spinal cord dorsal horn (marginal nucleus or nucleus proprius)
what is pain transmitted throughout?
the length of the spinal cord, projection neurons are concentrated in the marginal nucleus and nucleus proprius of the dorsal horn
what do the secondary neurons of the spinothalamic pathway do?
primary order neurons synapse with secondary neurons
what do the axons of the second-order neurons of the spinothalamic pathway do?
they cross the midline and join other axons that also carry pain sensation
these axons form the spinothalamic tract
what does the spinothalamic tract reach?
the contralateral thalamus (third-order neuron)
what do thalamic projection neurons do?
they send axons to the somesthetic area od the cerebral cortex
what do axons of the spinothalamic pathway that terminate in the lateral thalamus do?
they mediate discriminative aspects of pain
axons of the spinothalamic pathway that terminate in the medial thalamus do what?
they mediated the motivational-affective aspects of pain (emotional aspects of pain; attention of pain)
what is the spinocervicothalamic pathway concerned with?
transmission of superficial pain and tactile sensations, considered with the primary conscious pathway in carnivores
what is the spinoreticular tract primarily concerned with?
with deep pain and visceral sensations
first order neurons of the spinocervicothalamic pathway?
spinal ganglion
second order neurons of spinocervicothalamic?
marginal nucleus or nucleus proprius
axons of the second-order neurons of the spinocervicothalamic pathway do what?
they ascend ipsilaterally to the upper cervical spinal cord to synapse on third-order neurons located in the lateral cervical nucleus
axons from third order neurons of the spinocervicothalamic pathway do what?
they cross the midline and ascend to the contralateral thalamus to terminate on fourth-order neurons
axons of the fourth order neurons of the spinocervicothalamic pathway project to?
to the cerebral cortex
functions of the motor system?
maintain posture, gait and provide a stable platform for movement
voluntary movement and locomotion
visceral motor functions
what is somatic motor activity regulated by?
regulated by separate groups of nerve cells, designated the lower and upper motor neurons
nerve tracts are named according to?
their origin
caudally projecting neurons generally terminate on?
interneurons
what are the descending tracts?
rubrospinal tracts
vestibulospinal tracts
reticulospinal tracts
tectospinal tracts
corticospinal tracts
corticobulbar tracts
motor systems (descending tracts) often functionally grouped into what two categories?
Ventromedial motor system -
Dorsolateral motor system -
Dorsolateral motor system includes?
distal limb muscles, especially flexors
Ventromedial motor system includes?
axial and proximal limb muscles, especially extensors
where are lower motor neurons located within?
within the ventral column of the gray substance of the spinal cord and within the somatic motor nuclei of cranial nerves that contain somatic efferent components
where are the axons of the lower motor neurons conveyed within?
within the spinal and relevant cranial nerves to the skeletal muscles, where each terminates on a group of muscle fibres
what do lower motor neurons provide the efferent limbs with?
simple reflexes, but are mostly directed by upper motor neurons
what do the axons of the lower motor neurons project in to?
the peripheral nervous system via cranial or spinal nerves to connect with muscle
what is a reflex?
an inherent, subconscious, relatively consistent response to a particular stimulus
what does a reflex arc involve?
involves sensory input, connection in the CNS to the UMN, the LMN, neuromuscular junction and muscle
there are a number of different types of reflexes; what are two of them?
somatic; autonomic
what do reflexes utilise?
inputs from exteroceptors, interoceptors or proprioceptors
what nerves do reflexes use?
cranial or spinal nerves
what muscle do reflexes affect?
they affect striated or smooth muscle
all reflexes contain 5 basic components - what are they?
sensory receptor
sensory neuron
synapse in CNS
motor neuron
target organ (effector organ)
name some examples of spinal reflexes; involving spinal nerves and the spinal cord?
myotatic reflex (muscle stretch)
Withdrawal (flexor) reflex
Panniculus (cutaneous trunci) reflex
Perineal (anal constriction) reflex
describe the myotatic reflex:
muscle stretch is resisted by reflex contraction of the muscle
describe the withdrawal reflex:
limb flexes to withdraw from a noxious stimulus
describe the Panniculus reflex:
pricking skin triggers contraction of cutaneous trunci (panniculus) m.
describe the Perineal (anal constriction) reflex:
mild compression of the skin of the perineum or anus with forceps causes contraction of anal sphincter and flexion of the tail
patellar reflex is the most?
reliable pelvic limb reflex
stretch stimulus on the tendon travels via and how is impulse transmitted?
via the afferent neuron to the spinal cord
it is then transmitted to the efferent neuron, which stimulates the quadriceps muscle
myotatic reflex - patellar reflex?
muscle stretch is resisted by reflex contraction of the muscle
motor component of the myotatic reflex - patellar reflex arises from?
from L4-L6 in the spinal cord, which is the origin of the femoral nerve
where is the origin of the femoral nerve?
L4-L6 in the spinal cord
what does the femoral nerve innervate?
innervates the quadriceps muscle - effector muscle of this reflex
it also causes reciprocal inhibition
what does the myotatic reflex-patellar reflex evaluate?
the integrity of the spinal cord segments (L4-L6 and sensory/afferent and motor/efferent) as well as the femoral nerve
lumbar enlargement with a similar relationship to the lumbosacral plexus involves?
cord segments (L5-S1)
lumbar plexus is?
a complex, interwoven network of nerves
cord segments: L5-S1
what is the lumbar nerve plexus formed by?
by the ventral branches of spinal nerves L4, L5, L6, L7 and S1 (may reach S3)
spinal nerves of 2nd through the 7th leave through?
through foramina cranial to the vertebrae of the same number
Nerve 2C will leave where and why?
it will leave cranial to the second cervical vertebrae because it lacks corresponding vertebrae, C8 spinal nerve exits through cranial margin of vertebrae T1
withdrawal or flexor reflex is used to test for?
test primarily for the sciatic nerve and its spinal cord segments (L6,L7 and S1)
what type of neurons do most sensory neurones have?
unipolar
Sensory tracts that carry information about body position from joints tendons and muscles are called?
proprioception
what is not always a component of the reflex arc?
CNS interneuron
patellar reflex is also named?
monosynaptic myotatic (stretch) reflex
which spinal reflex is unique in that afferent neurons synapse directly onto efferent neurons?
patellar
what is the largest nerve in the body?
schiatic nerve
what may withdrawal reflex be used for?
to check the depth of the anestesia
motor cells can be - for the withdrawal reflex?
can be stimulated or inhibited
which motor tract is well developed in primates and humans?
corticospinal tract
corticospinal tracts also called?
pyramidal system
Are reticulospinal and vestibulospinal tracts are important keeping the body upright against the pull of gravity?
yes
how many order neurons are involved in spinocervicothalamic tract?
4
Somatosensory cortex: required for localisation of pain in which lobe?
parietal
pyramidal tract initiates?
skilled, voluntary movement
see in primates and carnivores
which descending tract is concerned with turning the head suddenly, auditory or visual stimuli?
tectospinal
in quadrupeds, the most prominent tract in the motor system is?
rubrospinal
