Spinal Cord and Periphery Flashcards
What is the cross sectional anatomy of the spinal cord?
Has a central grey matter and peripheral white matter
The grey matter has on each side a dorsal and a ventral horn
The axons of sensory fibres enter through the dorsal root in the dorsal horn of grey matter.
Motor neurons have their cell bodies in the ventral horn
What is motor neurone disease?
Group of diseases affecting the motor neuron in the spinal cord.
(this neuron is called the Lower Motor Neuron)
The neutron dies and as a result muscle supplied by it atrophies
Progressive, incurable disease
Describe the white matter of the spinal cord
White matter is made up of tracts (axons transmitting information between higher centres in the brain and peripheral nerves)
Tracts are pathways
Different tracts carry different bits of information. Ascending pathways are sensory, descending pathways are motor.
The white matter is arranged as 3 columns (posterior, lateral and anterior). Each column has in it various tracts
Explain ascending spinal tracts
Carries sensory information to the brain (cerebral cortex and cerebellum)
Pathways reaching conscious level have common characteristics:
- There are 3 neurones between peripheral receptor and cortex)
- –1st, 2nd and 3rd order neuron
Describe the general route of ascending spinal tract
Receptor
First order neuron
- Dorsal route/ cranial nerve ganglion
- Paraunipolar neuron
Grey matter of spinal cord or nucleus in medulla
2nd order neuron
-Crosses over to contralateral side in spinal cord or medulla
Nucleus in contralateral thalamus
3rd order neuron
-Contralateral parietal cortex
What does the posterior/ dorsal column nerves carry?
Sensory information for:
- Fine touch
- Tactile localisation
- Vibration sense
- Proprioception
Posterior column of right side = Touch, pressure, proprioception from right side of body
What is the lateral spinothalamic tract?
Pain and temperature from contralateral side
lateral spinothalamic tract of right side = pain and temperature from left side of body
Describe motor/ descending tracts of spinal cord
Originate in the cerebral cortex and brainstem
Are concerned with control of movement, muscle tone, spinal autonomic functions
Tracts coming from cerebral cortex have 2 neurons in their pathway
They decussate to the opposite side in the brainstem
What is the route of motor/ descending tracts of spinal cord?
Upper motor neuron in primary motor cortex
Pyramidal decussation in medulla
Lower motor neurone in spinal cord/ cranial nerve neclei
Neuromuscular junction
What is the corticospinal/ pyramidal tract?
Control of voluntary skilled movements.
Posterior limb of IC (blood supply MCA).
Corticobulbar fibres go to contralateral cranial nerve nucleii
Corticospinal fibres mostly cross in decussation of pyramids (lateral corticospinal tract)
(anterior corticospinal tract)
Describe upper motor neuron and lower motor neuron
The lower motor neuron (LMN) is responsible for muscle tone and reflexes.
If the upper motor neuron (UMN) is damaged with LMN intact, then reflexes and tone are exaggerated
Why would sensory info not reach the brain?
Not all sensory information needs to be sent to the brain for decisions to be made.
In certain instances where an immediate response in needed, the spinal cord or other lower centres themselves can take these decisions
The make up some of our reflexes
What are reflexes?
A reflex is an involuntary stereotyped pattern of response brought about by a sensory stimulus.
Many reflexes are mediated at the level of the spinal cord (spinal reflexes)
Anatomically they may be monosynaptic (e.g. stretch reflex) or polysynaptic (e.g. flexor reflex)
What is the stretch reflex (+ reciprocal innervation)?
- Tendon stretched
- Intrafusal muscle fibres stimulated
- Sensory neutron activated
4a. Monosynaptic reflex arc
4b. Polysynaptic reflex arc to inhibitory interneuron
- Muscle contraction
What is the stretch reflex for?
Important in control or muscle tone and posture
What is the flexor (+ crossed extensor) reflex?
- Pain stimulus
- Sensory neutron activated
- Polysynaptic reflex arc
4a. Flexion and withdrawal from noxious stimulus
4a. Crossed extensor response to contralateral limb (only in weight bearing limbs)
Explain the effects of an upper motor neuron lesion
It is the lower motor neuron that was involved in both these reflexes
So a motor response was brought about (reflexively) without using the upper motor neuron
So even if the upper motor neuron is damaged, one still does have reflexes - which become EXAGGERATED
The muscle tone also increases -> leads to spasicity (as opposed to flaccidity)
i.e. with an upper motor lesion there is spastic paralysis with hyperreflexia
What should you think about when dealing with neurological lesions?
- Cortical problems - speech
- Motor paralysis/weakness
- Which side?
- Is it spastic/flacid
- What happens to reflexes? - What about cranial nerve weakness?
- Same or opposite side - Sensory defects
- Which side? for pain and temperature
- Which side? for touch vibration etc
What is Brown-Sequard Syndrome?
Herniated disc may cause
Hemisection of spinal cord left side
Pyramidal tract, spinothalamic tract, posterior column all abrupt on left side
What would Brown-Sequard Syndrome of the left side cause?
Right sided loss of temperature and pain
Left sided paralysis (spastic)
Left sided loss of touch, vibration sense
Reflexes on left side exaggerated
What is the basic organisation of ANS?
Autonomic nervous system refers to nerve cells within both cans and PNS concerned with innervation and control of visceral organs, smooth muscles and secretory glands.
It is not under voluntary control. Basic autonomic efferent pathway has 2 neurons in its pathway
Describe the route of ANS
Cell body in brainstem/ spinal cord
Preganglionic neuron
Autonomic ganglion
Postganglionic neuron
Target organ
How do sympathetic and parasympathetic outflow, preganglionic fibres and postganglionic fibres differ?
Outflow:
- Symp = thoracolumbar
- Para = craniosacral
Preganglionic fibres:
- Symp = ganglia near spinal cord
- Para = ganglia near target organ
Postganglionic fibres:
- Symp = target every cell in the body
- Para = target-> exocrine glands, heart, other selected organs
