Lecture 5.1 Flashcards
decussate definition
cross over from one side of the CNS to the opposite side
ipsilateral definition
the same side
contralateral definition
the opposite side
afferent definition
ascending, input (sensory)
efferent definition
descending, output (motor)
spinal somatic sensory systems function
mediate touch, limb position senses, pain, itch, and temp senses
spinal somatic sensory system first stage
sensory neurons or specialized sensory receptor cells of the body detect changes in the body and environment
spinal somatic sensory systems stage two
sensory information is sent to the central nervous system through the spinal cord and brainstem
spinal somatic sensory system stage 3
sensory info is relayed through the thalamus to the primary sensory cortex in the parietal lobe or cerebellum
what do stimuli characteristics do receptors encode?
nature (modality), location, intensity, and duration of stimuli
what sensations are encoded from sensory receptors?
5 senses, balance, position, pain, sensory info from internal organs
kinds of sensory receptors
chemoreceptors, photoreceptors, mechanoreceptors, nociceptors
chemoreceptors
“chemical sensory”, smell, taste, internal stimuli like pH
photoreceptors
“light sensors,” visual receptors of the retina
mechanoreceptors
most varied type, respond to physical deformation, cutaneous receptors for touch, muscle length and tension, auditory and vestibular
nociceptors
pain receptors, noxious or obnoxious
what general categories can the sensory receptors be in?
- a neuron that has a free nerve ending (dendrites) embedded in a tissue (fine touch/pain/temp)
- a neuron that has dendrites encapsulated in connective tissue (crude touch/pressure)
- specialized receptor cell w/ distinct structural components that interpret a specific type of stimulus (specialized for light)
accumulation of axons
- greater distribution of white matter ascending the spinal cord
- more sensory axons added from periphery; fully intact motor tracts that have not branched off yet
descending white matter tracts
pyramidal tracts, extrapyramidal tracts
ascending white matter tracts
dorsal column medial lemniscus system, spinocerebellar tracts, spinothalamic tract
two pyramidal tracts
lateral corticospinal tract, anterior corticospinal tract
four extrapyramidal tracts
rubrospinal tract, reticulospinal tract, vestibulospinal tract, tectospinal tract
two dorsal column medial lemniscus system tracts
gracile fasciculus, cuneate fasciculus
three spinocerebellar tracts
posterior spinocerebellar tract, anterior spinocerebellar tract, cuneocerebellar tract
two spinothalamic system tracts
lateral spinothalamic tract, anterior spinothalamic tract
what three anatomical principles are neurons in the sensory tract arranged according to
- sensory modality
- somatotropic
- medial-lateral rule
sensory modality
different types of sensory info travel through distinct sensory pathways
sensory modality DELETE
different types of sensory info travel through distinct sensory pathways
somatotropic anatomical principle
ascending tracts are organized according to site of origin (body map)
medial-lateral rule
sensory neurons that enter a low level of the spinal cord are more medial within the spinal cord/ sensory neurons that enter at a higher level of the spinal cord are more lateral within the spinal cord
which three neurons do ascending sensory signals travel through
- first order
- second order
- third order
where do spinocerebellar tracts terminate
in the cerebellum rather than traveling to the thalamus and cortex
where do dorsal column medial lemniscus and spinothalamic tracts travel
thalamus and cortex
where does the gracile fasciculus transmit info from
lower body, all spinal levels
where does cuneate fasciculus transmit info from
upper body, only cervical
what kind of information does the dorsal (posterior) column medial lemniscus (DCML) pathway transmit
- conscious proprioception (joint position)
- vibration
- discriminative (fine) touch
where does DCML pathway terminate
somatosensory cortex
what does the DCML third order neuron synapse with
the ventral posterolateral thalamus (VPL)
where do 2nd order DCML neurons synapse in
dorsal column nuclei (gracile or cuneate nucleus) in the medulla (brainstem), and decussates to contralateral side
where does decussation occur for DCML pathway, if it occurs
medulla
characteristics of DCML tracts
only two separate tracts within the spinal cord; they decussate in the brainstem and travel as one pathway (the medial lemniscus) up to the thalamus and to the cortex
- carry the same kind of info in the spinal cord
what distinguishes the two DCML tracts
the origin of their input from the PNS
what are the spinothalamic tracts (anterolateral system) responsible for
transmitting crude touch, pressure, temp, pain
where do the anterior spinothalamic and lateral spinothalamic tracts decussate
in the spinal, cord, but at different locations
what kind of info does the anterior spinothalamic tract carry
pressure, light/crude touch
what kind of info does the lateral spinothalamic tract carry
pain, temp
what is the path the anterolateral system takes
brainstem –> thalamus in the same column –> somatosensory cortex
where is the 2nd order anterolateral system neuron found
spinal cord
where do the 2nd and 3rd order neurons synapse FOR WHAT????
ventral posterolateral thalamus (VPL)
where does the anterolateral system terminate
the contralateral somatosensory cortex
somatotopic organization
where the secondary neuron in the thalamus project to in the somatosensory cortex depends on where the corresponding sensory neuron in the body originated
what are the spinocerebellar tracts responsible for
transmitting unconscious proprioception from muscles, tendons, joints; muscle tone; balance
posterior spinocerebellar tract origination
lower body
posterior spinocerebellar tract decussation characteristics
stays ipsilateral to the side of the body that it enters
- uncrossed tracts enter the cerebellum via the inferior cerebellar peduncles (medulla)
cuneocerebellar tract origination
upper bod
cuneocerebellar tract decussation characteristics
stays ipsilateral; uncrossed tracts enter cerebellum via inferior cerebellar peduncles (medulla)
anterior spinocerebellar tract origination
lower body
anterior spinocerebellar tract decussation characteristics
decussates in the spinal cord at the level of entry but decussates again in the brainstem to return to the ipsilateral side of the brain
- enters cerebellum via superior cerebellar peduncles
posterior spinocerebellar tract neuron locations
1st order: enters spinal cord (lower body), 2nd order: within spinal cord (Clarke’s nucleus); no 3rd order neuron
cuneocerebellar tract neuron locations
1st order neuron: enters spinal cord (upper body), 2nd order neuron: medulla
anterior spinocerebellar tract neuron locations
1st order neuron: enters spinal cord (lower body), 2nd order neuron: within spinal cord, no 3rd order neuron
why do the spinocerebellar tracts not have 3rd order neurons
all tracts terminate in the ipsilateral cerebellum (not the cortex), so no 3rd order neurons
characteristics of descending tracts
- the pathways by which motor signals are sent from upper motor neurons in the cortex to lower motor neurons
- lower motor neurons then directly innervate muscles to produce movement
descending pathway synapses
no synapses within the descending pathways
- at the termination of the descending tracts, the first order upper motor neurons synapse with a lower motor neuron within the brainstem or spinal cord
where are the lower motor neuron cell bodies
within the CNS
- send fibers out into the PNS to make direct connections with muscles, glands, etc
where do the pyramidal tracts originate
cerebral cortex
pyramidal tracts function
- carrying motor fibers to the brain stem and spinal cord
- responsible for the voluntary control of muscles
extrapyramidal tract origination
brain stem
extrapyramidal tract function
- carrying motor fibers to the spinal cord
- responsible for the involuntary and automatic control of muscles (muscle tone, balance, posture, and locomotion)
what are the pyramidal tracts
corticospinal tracts, corticobulbar tracts
corticospinal tracts
lateral corticospinal tract, anterior corticospinal tract
what are the extrapyramidal tracts
vestibulospinal, reticulospinal, rubrospinal, tectospinal
vestibulospinal tracts
medial and lateral
reticulospinal tracts
medial/pontine and lateral/medullary
why are the pyramidal tracts named that way
they pass through the pyramids in the medulla
what are the pyramidal tracts responsible for
voluntary control of the muscles of the face and body
corticospinal tracts function
supply muscles of the body
corticobulbar tracts function
supply muscles of the head, neck, and face
corticospinal tracts path
cerebral cortex –> internal capsule –> brainstem
where does the corticospinal tract divide into two
most caudal part of the medulla
lateral corticospinal tract path after dividing from the corticospinal tract
decussates in the pyramids –> spinal cord –> terminates in ventral horn –> lower motor neurons of the spinal cord supply distal muscles (limbs)
medial corticospinal tract path after dividing from the corticospinal tract
spinal cord –> decussates in the cord –> terminates in ventral horn –> supply proximal muscles (trunk)
where do the lateral corticospinal tract neurons project to
distal muscles (limbs)
where do the medial corticospinal tract neurons project to
proximal muscles (trunk)
where do corticobulbar tracts arise from
the lateral primary motor cortex
where do corticobulbar tract fibers converge
internal capsule –> brainstem
where do corticobulbar neurons terminate
bilaterally on the motor nuclei of the cranial nerves in the brainstem
where do corticobulbar tract neurons synapse
with lower motor neurons that transmit to muscles of the head, face, and neck
where do the extrapyramidal tracts originate
brainstem
where do the extrapyramidal tracts carry motor fibers to
spinal cord
what are the extrapyramidal tracts responsible for
involuntary and automatic control of muscles (muscle tone, balance, posture, and locomotion)
which extrapyramidal tracts do not decussate and have ipsilateral innervation
vestibulospinal, reticulospinal
which extrapyramidal tracts decussate and have contralateral innervation
rubrospinal, tectospinal
where do the vestibulospinal pathways arise from
the vestibular nuclei
vestibular nuclei
receives inputs from the organs of balance in the inner ear and CN8
what is the vestibulospinal tract responsible for
upright posture and head stabilization
- detects small movements of the body, motor signals are sent via the vestibulospinal tract to specific muscles to counteract these movements to stabilize the body
medial vestibulospinal pathway projection
from medial vestibular nucleus to the cervical spinal cord
medial vestibulospinal pathway function
stabilizing head position by innervating the neck muscles
- bilateral
lateral vestibulospinal pathway projection
lateral vestibular nucleus to motor signals to extensor muscles in the legs
lateral vestibulospinal pathway function
helps maintain upright and balanced posture
- stays ipsilateral
what do the reticulospinal tracts do
coordinate automatic/involuntary movements of locomotion and posture control
where do the reticulospinal tracts originate
different parts of the reticular formation of the brainstem
medial reticulospinal tract (MRST) origination
reticular formation in the pons
lateral reticulospinal tract (LRST) origination
reticular formation in the medulla
characteristics of both reticulospinal and vestibulospinal tract decussation
both remain ipsilateral and terminate at different levels in the spinal cord
what kind of information does the MRST carry
info for controlling extensor motor neurons, enabling the extension of the legs to maintain postural support and contributes to patterned movements (eg stepping)
what kind of information does LRST carry
info for controlling flexor motor neurons, inhibiting the MRST extensor muscles and enabling modulating of the stretch reflex
where does the tectospinal tract originate
the superior colliculus in the midbrain
what composes the tectum
superior and inferior colliculi
what kind of information does the superior colliculus receive
input from optic nerves
where do the tectospinal tract neurons decussate
at the level of the midbrain
where does the tectospinal tract terminate
cervical levels of the spinal cord
what is the function of the tectospinal tract
coordinates movements of the head in relation to visual stimuli
where does the rubrospinal tract originate
red nucleus in the midbrain
where do the rubrospinal tract fibers decussate
level of the midbrain and descend into the cervical spinal cord with a contralateral innervation
what function does the rubrospinal tract fibers have
fine control of hand movements
which descending tracts originate in the cortex?
pyramidal tracts: corticospinal tract (lateral corticospinal tract, anterior corticospinal tract), corticobulbar tracts
other name for primary motor cortex
precentral gyrus
other name for primary sensory cortex
post-central gyrus
which important areas of motor association cortex lie anterior to the primary motor cortex
supplemental motor area and the premotor cortex
what are the supplemental motor area and the premotor cortex involved in
higher order motor planning and they project to the primary motor cortex
where are the primary sensory and motor areas located
on either side of the central sulcus
primary motor cortex function
execution of movement
supplemental motor cortex function
execution of sequences of movement (attainment of motor skills - in coordination with the cerebellum)
premotor cortex function
planning of movement
