The Spinal Cord and the Periphery Flashcards
How is the grey matter arranged?
Central
How is the white matter arranged?
Peripheral
What does the grey matter have on each side?
Dorsal and ventral horn
What enters through the dorsal root into the dorsal horn of the grey matter?
The axons of sensory fibres enter through the dorsal root into the dorsal horn of grey matter.
Where do motor neurones have their cell bodies?
Ventral horn
What is motor neuron disease?
- Group of diseases affecting the motor neuron in the ventral horn of spinal cord. (This neuron is called as the Lower Motor Neuron.)
- The neuron dies and as a result muscle supplied by it atrophies.
- Progressive, incurable disease.
What is white matter made up of?
White matter is made up of tracts.(axons transmitting information between higher centres in the brain and peripheral nerves)
What are tracts?
Pathways
How do tracts differ?
Different tracts carry different bits of information. Ascending pathways are sensory, descending pathways are motor.
What are the 3 columns of the white matter?
The white matter is arranged as 3 columns – posterior,lateral & anterior. Each column has in it various tracts.
What do the ascending spinal tracts carry?
Carries sensory information to the brain (cerebral cortex and cerebellum)
What are the common characteristics of pathways reaching conscious level?
- There are 3 neurons between peripheral receptor and cortex.
- 2nd order neuron nucleus in grey matter of spinal cord or medulla
- Crosses over to contralateral side in spinal cord or medulla (2nd order neuron)
- 3rd order neuron nucleus in contralateral thalamus
What is the posterior/dorsal column responsible for?
- Fine touch
- Tactile localisation
- Vibration sense
- Proprioception
What is the lateral spinothalamic tract of the right side responsible for?
Pain and temperature from Left side of body
What is the posterior column of the right side responsible for?
Touch, pressure, proprioception from Right side of body.
Where do the motor/descending tracts of the spinal cord originate from?
Cerebral cortex and brainstem
What are motor/descending tracts of the spinal cord responsible for?
Are concerned with control of movement, muscle tone, spinal autonomic functions.
How many neurons do ascending sensory tracts have in their pathway
3
Where do the motor/descending tracts of the spinal cord decussate?
They decussate to the opposite side in the brainstem.
What is the corticospinal/pyramidal tract responsible for?
Control of voluntary skilled movements.
Where do corticobulbar fibres go?
Corticobulbar fibres go to contralateral cranial n nucleii.
Where is the decussation of corticospinal fibres?
Corticospinal fibres mostly cross in decussation of pyramids (Lateral corticospinal tract).
Where is the corticospinal/pyramidal tract located?
Posterior limb of Internal Capsule (blood supply MCA).
What is the LMN responsible for?
The lower motor neuron (LMN) is responsible for muscle tone and reflexes
What happens if the UMN is damaged with the LMN intact?
If the upper motor neuron (UMN) is damaged with LMN intact, then reflexes and tone are exaggerated
What is a reflex?
A reflex is an involuntary stereotyped pattern of response brought about by a sensory stimulus.
Where are many reflexes mediated?
Many reflexes are mediated at the level of the spinal cord (spinal reflexes).
How can reflexes differ anatomically?
Anatomically they may be monosynaptic (eg: stretch reflex) or polysynaptic (eg: flexor reflex).
When is some sensory information not sent to 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.
- These make up some of our reflexes.
What is stretch reflex important in the control of?
Stretch reflex is important in control of muscle tone and posture.
Briefly describe the steps in the stretch reflex (and reciprocal innervation).
- Tendon stretched
- Intrafusal muscle fibres stimulated
- Sensory neuron activated
- Monosynaptic reflex arc
- Polysynaptic reflex are to inhibitory interneuron
- Muscle contraction
- Reciprocal innervation
What does the flexor reflex help to do?
Flexor reflex helps protect the body from painful stimuli.
Briefly describe the steps in the flexor (and crossed extensor) reflex.
- Pain stimulus
- Sensory neuron activated
- Polysynaptic reflex arc
- Flexion and withdrawal from noxious stimulus
- Crossed extensor response to contralateral limb (only in weight bearing limbs
Why does someone have exaggerated reflexes with an UML?
- 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
What are the characteristics of UMN lesions?
- Exaggerated reflexes
- Increased muscle tone (spasticity)
At the spinal cord level what tracts are crossed/uncrossed?
- Pyramidal tract crossed
- Spinothalamic tract crossed
- Posterior column uncrossed
What would hemisection of spinal cord on the left side result in?
- Pyramidal tract, spinothalamic tract, posterior column all abrupted on left side
- Right sided loss of temperature and pain
- Left sided paralysis (spastic)
- Left sided loss of touch, vibration sense
- Reflexes on left side exaggerated
What are the divisions of the motor PNS?
- Somatic motor (skeletal muscles)
- Autonomic motor (smooth muscle, cardiac muscle, glands)
What does the autonomic nervous system refer to?
Autonomic nervous system refers to nerve cells within both CNS & PNS concerned with innervation & control of visceral organs,smooth muscles & secretory glands.
What is the outflow of the sympathetic system?
Thoracolumbar
What is the outflow of the parasympathetic system?
Cranisacral
Where are the preganglionic fibres in the sympathetic system?
Ganglia near spinal cord
Where are the preganglionic fibres in the sympathetic system?
Ganglia near target organ
Where are the postganglionic fibres in the sympathetic system?
Target - every cell in body
Where are the postganglionic fibres in the parasympathetic system?
Target- exocrine glands, heart, other selected organs
How many neurons do the descending motor tracts have in their pathway?
2
