Spinal cord and the Periphery Flashcards
Spinal Cord is composed of
Central grey matter
Peripheral white matter
Where is the dorsal and ventral horn located in the spinal cord
In the grey matter
What is the pathway of sensory fibres in the spinal cord
Enter through dorsal route into the dorsal horn of the grey matter
Where is the motor neurones cells bodies located
In the ventral horn
Where is the sensory neurones cell body located
In the dorsal root ganglia of the spinal cord
How is the white matter arranged and what is it composed of
Arranged into three columns, Posterior, lateral and anterior, with each column having its various tracts
What is function of tracts in the white matter
Act as pathways as axons transmit information between higher centres and the peripheral nerves
What are ascending pathways
Pathways that carry sensory information to the brains cerebral cortex and cerebellum via the spinal cord
What is the common characteristic of ascending pathways
3 neurones between peripheral receptor and cortex
always cross over at 2nd order neurone
Common pathway -
1st order:
From receipts travels via dorsal root ganglia and synapses in grey matter of spinal cord of nucleus medulla
2nd order:
Crosses over to contralateral side in spinal cord or medulla and synapses in nucleolus in contralateral thalamus
3rd order:
Travels to contralateral parietal cortex
- pathways may have different route to get to parietal cortex
What are the two tracts in the ascending pathway
Posterior/dorsal column
Lateral spinothalmic tract
What sensory information is the posterior/dorsal column responsible for
Fine touch
Vibration sense
proprioception
tactile localisation
(touch and pressure receptors located in the skin)
What is the pathway os posterior/dorsal column
1st order neurones pick up sensory impulses from receptors in skin
travels into spinal cord through dorsal route
the enters posterior column of the dorsal part and travels upwards
Synapses in the medulla in the gracille and cuneate nuclei
The second neurone then crosses over to opposite side and travels up to pons via medial lemniscus
Then synapses in the VLPL nucleus in the thalamus
the 3rd order neurone then travels to post central gyrus in parietal lobe
Why is the thalamus called the relay station
as is a group of nuclei that all sensory information synapse in then the thalamus modulates
Where does the posterior dorsal column cross over
2nd order neurone in the gracille and cuneate nuclei in the medulla
What sensory information is the lateral spinothalmic tract responsible for
Pain
Temperature
(nociceptors and thermoreceptors)
What is the pathway of the spinothalmic tract
1st order neurones pick up sensory impulses nociceptor/thermoreceptor in the skin
travels into spinal cord through dorsal route and synapse and level of entry
The second order neurone then crosses over at level of entry to the lateral white matter of the spinal cord
Then synapses in the VPL nucleus of the thalamus
and 3rd order neurone travels to the post central gyrus of parietal lobe
How does the right side of the brain process pain and temperature from the left side of the body
Due to 2nd order neurone crossing over at the level entry to reach the lateral coloumn in the spinal cord to so carries pain and temperature from the opposite side of the body
Why is the dorsal column thicker than the lateral spinothalmic tract
Due to more sensory fibres being present
Where does the spinothalmic tract cross
2nd order neurone at the spinal cord level of entry
What is descending pathways
Tracts coming from cerebral cortex with motor impulses concerned with voluntary control of movement, muscle tone, reflexes and spinal autonomic function
What is the characteristic of the descending pathway
Originate from cerebral cortex
Have two motor neurones in there pathway:
Upper motor neurone
- primary motor cortex –> spinal cord
Lower motor neurone
Spinal cord –> skeletal muscle
Upper motor neurone crosses to the opposite side of the bodying brainstem (pyramidal decussation in medulla)
What is the name of the descending motor pathway
Pyramidal tracts:
Corticospinal
Corticobullar
What is the pathway of the corticospinal tract pathway
Starts in motor homunculus on primary motor cortex on opposite side
neuronal cell bodies sit in grey matter of precentral gyrus and axons radiates through white matter to posterior limb of internal capsule and into the midbrain whose internal capsule becomes cerebral peduncles and travels through the white matter of the cerebral peduncles called the crus cerebri
Then travels through pons to medulla and forms pyramidal tracts, the first order neurone crosses at the lower part of the medulla = decussation of pyramids
(most cross)
Travels in white matter of spinal cord then enter ventral horn of grey matter in spinal cord and synapses with lower motor neurone at the levels of the skeletal muscles its going to innervate
What are the two corticospinal tracts and how are they different
Lateral corticospinal tract - due to fibres crossing in decussation of pyramids
anterior corticospinal tracts - due to not crossing in decussation of pyramids (only 10-15)
What is the function of the corticobulbar tract
Motor pathway connecting the motor cortex in the cerebral cortex to the Medullary pyramids,
Primarily involved in carrying the motor function of the non-oculomotor cranial nerves.
What is the pathway of the corticobulbar tract
Two neurone pathway identical to corticospinal tracts until crus cerebri
then the corticobulbar fibers exit at the appropriate level of the brainstem to synapse on the lower motor neurons of the cranial nerves on contralateral side
Define reflexes
An immediate response brought by sensory stimulus mediated at the level of the spinal cord and doesnt go through cerebral hemisphere
What is an example of a monosynaptic and polysynaptic reflex
mono - stretch reflex
poly- flexor reflex
What occurs in a stretch reflex
Tendon stretches
Intrafusal muscle fibres stimulated
Sensory neurone activates
monosynaptic reflex arc causing agonist muscle stimulated to contract
additionally
Polysynaptic reflex arc to inhibitory interneurone casing reciprocal innervation of antagonist muscle to relax
What is the importance of the stretch reflex
important in control of muscle tone and posture
What occurs in flexor reflex
Pain stimulus
sensory neurone activates goes through polysynaptic reflex arc
causing flexion withdrawal from stimulus
and crossed extensor response to contralateral (only in weight bearing limbs)
What motor neurone is involved in stretch and flexor reflex
what does this show
The lower motor neuron (LMN) as is responsible for muscle tone and reflexes
motor response can occurs can without UMN involvement
What is the importance of the flexor reflex
Help protect the body from painful stimuli
What occurs if upper motor neurone is damaged and lower motor neurone is intact on reflexes and tone
reflexes and tone are exaggerated
Why do you investigate in a neurological lesion
Cortical problems - speech?
Motor paralysis/wekaness
- which side
- spastic/flaccid
- what happens to reflexes
Cranial nerve weakness
- same side or opposite
Sensory defects
- which side for pain and temp
- which side for touch and vibration
What occurs in a lesion of the upper motor neurone
LMN works without UMN
But causes increased tone = spastic paralysis
and exaggerated reflexes = hyperflexia
What occurs in a lesion on the lower motor neurone
paralysed muscle
arefexia - reflexes lost
flaccid paralysis - lack of tone
What causes brown-sequard syndrome
Hernaited disc
If a lesion occurs in the left side of the spinal cord what is the symptoms and why?
Left side paralysis, and loss of touch and vibration sense
( as posterior dorsal column hasn’t crossed yet)
Right sided loss of temperature and pain (as spinothalmic tract has already crossed)
Reflexes in left side exaggerated (as corticospinal tract hasn’t crossed yet)
What is the basic autonomic efferent pathway
Cell body in brainstem/spinal cord
Travels are preganglionic neurone
synapses in autonomic ganglion
travels as post ganglionic neurone to target organs where it synapses again
What is the division of the peripheral nervous system
Somatic
autonomic
What is the division of the autonomic nervous system
Sympathetic
Parasympathetic
