Motor and Sensory Pathways Flashcards
tracts of NS can be divided into…
ascending (sensory) and descending (motor) tracts
commissure
bundle of fibres crossing from one side of the body to the other at the same level (straight across) - e.g. corpus callosum is the largest commissure of the body also an anterior and posterior commissure, hippocampal commissure, etc.
- Good for communication between hemispheres
decussation
‘crossing over’ - fibres descending from the brain down the spinal cord and they cross over obliquely (form an x-shape)
are descending tracts sensory or motor?
motor
are ascending tracts sensory or motor?
sensory
UMN
nerves in CNS (brain and spinal cord)
- Stroke, tumour, etc. indicate damage
LMN
nerves in PNS (outside of brain)
- Includes cranial nerves as they are outside of the brain
descending pyramidal tracts we need to know
lateral and ventral corticospinal tracts
corticobulbar tract
what is a pyramidal tract?
axons cross over at the medullary pyramids
role corticospinal tract
carry conscious motor control from primary motor cortex down spinal cord via UMN
where does corticospinal tract decussate?
medullary pyramids
are pyramidal tracts conscious or unconscious
conscious
are extrapyramidal tracts conscious or unconscious
unconscious
route of corticospinal tract
conscious motor control from primary motor cortex
decussation in medullary pyramids
UMN passes into corticospinal tract in white matter of spinal cord and tract descends until level at which signal is due to leave spinal cord
UMN passes into grey matter and synapses with LMN, which exit the spinal cord to form peripheral nerves and travel to muscle
lateral corticospinal tract contains…
signals responsible for moving the muscles of the limbs
lateral corticospinal tract decussates where?
medullary pyramids
ventral corticospinal tract contains…
signals that will innervate the muscles of the trunk
ventral corticospinal tract decussates where?
not at the medullary pyramids - from the primary motor cortex signals enter the lateral corticospinal tract on same side and descend to the level they are due to leave at on the spinal cord where they decussate to the other side and leave immediately.
corticobulbar tract role
motor pathway connecting the primary motor cortex to the medulla
conscious motor innervation to muscles of face, head and neck region (not eyes)
corticobulbar tract contains…
UMN that will synapse with motor cranial nuclei of the cranial nerves
extrapyramidal motor tracts to know
rubrospinal
reticulospinal
vestibulospinal
tectospinal
rubrospinal tract
cervical area of spinal cord
fine-tuning movements of upper limbs
originates in the red nucleus of the midbrain
reticulospinal tract and vestibulospinal tract
posture, balance and coordinating movements
vestibulospinal tract is an uncrossed pathway
tectospinal tract
orientating eyes and head towards sounds as part of auditory and visual reflexive pathways
where are LMN found?
peripheral nerves connecting signal from UMN to target muscle
part of spinal cord LMN leaves in motor route
ventral horn
part of spinal cord LMN enters in sensory route
dorsal horn
dorsal horn receives…
sensory info
ventral horn has…
motor neurons
lateral horn in what levels only…
thoracic
central canal of spinal cord contains…
CSF
what connects sides of spinal cord?
Ventral white commissure and the grey commissure
grooves between the hemispheres of the spinal cord
Dorsal median sulcus and ventral median fissure
Vertebral foreman
where the spinal cord runs through
role of UMN
motor innervation of LMN
inhibitory effect on muscle stretch reflex
role of LMN
motor component in peripheral nerve
example of UMN lesion
stroke
CNS tumour
example of LMN lesion
peripheral nerve laceration
peripheral tumour
UMN lesion and fasciculations
absent
LMN lesion and fasciculations
present
UMN lesion and muscle wasting
present after some time due to lack of use (physiologic muscle atrophy)
LMN lesion and muscle wasting
present due to loss of neurotrophic factors at the LMN (neurogenic muscle atrophy)
quicker onset
muscle tone and UMN lesion
hypertonia - loss of inhibitory pathways
muscle tone and LMN lesion
hypotonia
power and UMN lesion
reduced power
power and LMN lesion
reduced
reflexes and UMN lesion
hyperreflexia
LMN lesion and reflexes
hyporeflexia
UMN lesion and babinski sign
positive
LMN lesion and babinski sign
negative
UMN lesion and clonus
present
LMN lesion and clonus
absent
what is muscle tone
natural resting contraction of the muscles
what is atrophy
muscle wastage
what are fasciculations
muscles twitching
what is babinski sign?
type of reflex
- UMN lesion: toes go up (dorsiflexion) (positive)
- LMN lesion: toes go down (plantarflexion - normal) negative
what is clonus?
differences in the knee reflex test
- UMN lesions: present
- LMN lesions: absent
where can UMN lesions occur?
any part of descending motor tracts - pyramidal susceptible as span length of CNS and pass internal capsule
if lesion is found on left or right corticospinal tract before level of decussation at the medulla effects will be seen where?
contralaterally - opposite side
damage to corticobulbar tract results in…
mild muscle weakness due to bilateral nature of tract (except facial palsy)
why is there hypertonia in UMN lesions?
due to disinhibition of alpha and gamma neurons
Brown Sequard syndrome
- Hemisection of SC
- Paralysis and loss of proprioception on the same side as the injury
- But loss of pain and temp sensation on the opposite side as lesion
LMN describe…
damage to alpha motor neurons found in peripheral NS innervating skeletal muscles
occur anywhere from the anterior horn to the peripheral nerves neuromuscular junction
what type of neurons are sensory neurons?
bipolar
where are sensory neurons nuclei found?
dorsal root ganglion
what is in the dorsal root ganglion
sensory nuclei
sensory pathways
sensory signals travel from sensor organ or tissue up axon of peripheral sensory nerve
nuclei in DRG
first order neuron
one axon travels from sensor organ to DRG which projects an axon towards the spinal cord and synapses in the dorsal horn of the spinal cord
second order neuron
travel up spinal cord in sensory tracts of white matter and synapse in thalamus
third order neuron
synapses with thalamus and projects into sensory cortex
where is primary somatosensory cortex
post-central gyrus in parietal lobe of cerebrum
sensory pathways carry info about…
touch (fine and crude)
pain
temp
proprioception
special sense (audition, vision, olfaction, taste)
ascending tracts to know
dorsal columns
spinocerebellar tracts
spinothalamic tracts
dorsal columns are what kind of tract
sensory - ascending
spinocerebellar tracts are what type of tract
sensory - ascending
spinothalamic tracts are what type of tract
sensory - ascending
dorsal columns carry info about…
fine touch - two point discrimination
vibration
conscious proprioception
where do dorsal columns decussate
medulla
neurons in dorsal columns
- 2nd order neuron crosses over (in medulla - medial lemniscus) not the dorsal columns
- 1st order neuron in dorsal column, 2nd order neuron in medulla decussates taking info to thalamus, 3rd order neuron to somatosensory cortex (post-central gyrus)
spinocerebellar tracts
unconscious proprioception and balance
ventral and dorsal tract
spinothalamic tracts sense…
pain
temp
gross touch/pressure
how many spinothalamic tracts
2 (lateral and ventral)
where do spinothalamic tracts decussate
at the level of the spinal cord (roughly where the sensory neuron enters)
what are spinal reflexes and their role?
- Automatic, involuntary and rapid
- Protective function
- Can be used to test for level of deficit
- Sensory (central and peripheral deficit)
- Damage to spinal cord at a level
- Damage to brain (brainstem reflexes)
what happens at posterior horn of spinal cord?
sensory/afferent signals arrive at the cord
what happens at anterior horn of spinal cord?
motor signals leave the cord
example reflex - standing on a pin
nociceptors in skin transduce mechanical energy into electrical energy in form of AP.
AP passes up somatic sensory nerves in foot and leg towards spinal cord
sensory neurons passes into dorsal horn of spinal cord and synapses in grey matter with a control centre (relay/interneuron)
interneuron relays electrical signal directly to motor neuron which leaves ventral horn and travels down spinal nerve to target muscle.
foot is drawn away from the pin.
biology behind a reflex to prevent damage
prevent muscles from damage by stretching too much - muscle spindle receptors in muscle detect stretch and send afferent neurons to spinal cord which synapse directly with efferent neurons to innervate muscle fibres to connect. (occurs at spinal cord level)
reflexes can be…
brisk
normal
absent
bicep tendon reflex root level
C5 C6
Triceps tendon reflex root level
C7 C8
knee tendon reflex root level
L3 L4
ankle tendon reflex root level
S1 S2
reflex loss (hyporeflexia/absent) indicates…
peripheral neuropathy
LMN lesion
hyperreflexia indicates…
damage to motor pathway in brain
e.g. stroke or tumour
damage to spinal cord above reflex
e.g. compression, inflammation, trauma
UMN issue
signs or cerebellar damage
dysdiadochokinesia
ataxia
nystagmus
intention tremor
slurred speed
hypotonia
dysdiadochokinesia
uncoordinated movements (like touching back of hand and then palm, alternating quick)
ataxia
wide gait (walking differences)
nystagmus
eyes rapidly moving
intention tremor
can’t do things like touching your nose and then touch an outstretched finger etc
slurred speech
staccato speech
hypotonia
tone goes down
dermatome
area of skin innervated by a single spinal cord level
myotome
muscles served by a spinal nerve route
