Spinal Cord and Processing One Flashcards
What does the grey matter of the spinal cord look like?
A butterfly
Describe the divisions of the grey matter of the spinal cord;
Shaped like a butterfly with the head representing the anterior side:
Pos. grey horn Lateral grey horn Ant grey horn and pos. and ant. grey commisures.
With regards to the structure of the grey matter of the spinal cord, where are the nuclie?
Sensory nuclie are in the post grey horn
Motor nuclie are in the ant grey horn
These nuclie are both divided into somatic and visceral regions.
What feeds into the post grey horn?
The dorsal root ganglion
Please refer to your notes to learn the nuclie structures of the white matter in the spinal cord
now please
What sensory pathways are in the spinal cord?
(6)
- Fasiculus Gracalis
- Fasiculus Cuneatus
- Ant. Spinothalamic tract
- Lat. spinothalamic tract
- Ant. Spinocerebellar tract
- Post. Spinocerebellar tract
What motor pathways are in the spinal cord?
- Ant. Corticospinal tract
- Lat. Corticospinal tract
- Rubrospinal tract
- Reticulospinal tract
- Vestibulospinal tract
- Tectospinal tract
What is the function of the somatosensory system?
Sensory activity that conveys information about that state of body proper and its immediate environment.(excludes special senses)
How does the somatosensory system work?
Receptors in the periphery receive information about the environment that signal to the 1 somatosensory cortex, which is processed and allows for the appropriate response
What are the type of receptors in the somatosensory system?
Nocioreceptors
Propioreceptors
Thermoreceptors
Mechanoreceptors
How are the somatosensory tracts separated / arranged in the spinal cord?
Separated by:
1) Sensory Modality (i.e tracts only carry 1 type of sensory fibre)
2) Somatotopic arrangement
3) Medial-lateral arrangement (The fibers that have further to go are more medial in position)
What is special about first order neurons in somatosensory pathway?
First order = Afferent, Pseudounipolar, Takes info from the periphery into the spinal cord.
What is the structure of a psuedounipolar neuron?
Single elongated neuron.
- Cell body off to one side of this.
Do all sensory fibres carry information at the same speed?
No, depends on the thickness of the fiber in the myelon.
What is the erlanger-gasser classification of sensory fibres?
1a = Aa = 80-120ms (Receptors of muscle spindles) 1b = Aa = 80-120ms (golgi tendon organs) 2= Ab = 33-75ms (mechanoreceptors) + Receptors of muscle spindles) 3= Ad = 3-30ms (FNE , cold recptors, nocioceptors) Thin myelon 4= C = (not myelonated) 0.5-2.0ms (warmth receptors, nocioceptors)
Whats a common feature of somatosensory pathways?
Decussation
Whats the purpose of decussation?
It can occur in the spinal cord or the brain stem
Allows separation of tracts
More robust against wiring errors
What do mechanorecptors sense?
Mechanical pressure or distortion of the skin
What are the two mechanoreceptor pathways?
Discriminitive and non-discriminitve
Whats an example of the non-discriminitve and discriminitive pathways?
Discriminitve = (dorsal) Posterior column-medial laminiscus pathway
Non-discriminitve = Ant. spinothalamic tract
What do the Ant. Spinothalamic tract and Post column-medial laminiscus pathways have in common?
Both comprise of 3rd order neurons (1,2,3)
Describe the neuron anatomy of the Posterior column-medial laminiscus pathway:
1st order neuron = Enters the spinal cord via the dorsal root ganglion, travels up the dorsal column and terminates on the nucleus gracalis or nucleus cuneatus
2nd order neuron = Project from these nuclei and decussate at the level of the brainstem before terminating on thalamic nuclie
3rd order neurons project from the thalamus through the internal capsule and terminate in the primary somatosensory area
Describe the anatomy of the anterior spinothalamic tract
1st order neuron : Terminates in the dorsal grey horn
2nd order neuron: decussates immediately and follows the ant spinothalamic tract and terminates on the thalamic nueclie
3rd order neuron: Projects into the primary somatosensory area
Are all mechanorecptors the same?
No there are different types for different sensitivity and sensation
What are the sensations that can be detected/?
Fine touch
Pressure and vibration
Deep Pressure
What detects fine touch?
(light skin touch)
Free nerve endings
Tactile disc
(Initial contact with hair)
Root hair plexus
What detects pressure and vibration?
Tactile Corpuscle (low Hz vibration) Lamellated Corpuscle (high Hz vibration)
What detects deep pressure?
Ruffini Corpuscle
Merkle cells?
What enables these different receptors to sense different sensations?
They have different activation thresholds
With regards to mechanoreceptors, what is adaptation?
How quickly the receptors returns to basal firing level
What are slow adapting receptors useful for?
Detecting touch and pressure
What are fast adapting receptors useful for?
Detecting texture and vibration
In regards to mechanorecptors what does receptive field allow?
Two point touch discrimination
Breast = 40mm
Finger =
What do thermoreceptors do?
Convey information about temperature from the periphery to the brain
What are some thermoreceptors?
Free Nerve Endings
Transient Receptor Protein Channels
What tract carries afferent thermoreceptor fibers?
Lateral spinothalamic tract
non-discriminative
How does the body involuntarily respond to thermoception?
Through the ANS
- Sweat glands
- Shivering
- Vasodilation
What do nocioceptors respond to?
Mechanical, temperature, and chemical stimuli that are noxious
Relative to other receptors what size of stimulus do nocioceptors require?
A larger one to evolve a response
What fibres carry pain?
Ad fibres and C fibres
What are types of pain information pathways?
Sensory discriminative
Affective emotional
What pathway does the sensory discriminative pain information use?
Lateral spinothalmic tract (Involved in voluntary responses to pain)
What is the affective emotional pain pathway involved with?
Fear, anxiety, learning associated with painful experiences.
What does the affective emotional pathway effect?
Descending pain pathways to regulate pain sensation
What does the descending pain pathway input onto?
The descending pain pathway inputs onto the raphe nuclie in the spinal cord.
Which innervates the dorsal horn
Which connects to the inhibitory circuits and decreases pain by releasing encephalin- which inhibits signalling between C-fibres and the dorsal horn.– these are the [pain pathway
What is the gate theory?
The gate theory is that by rubbing your foot/ stimulating mechanoreceptors in the area of pain, you can cause the local circuit in the spinal cord to activate inhibitory neurons and stop pain signals from the c fibres.
What does discrimination i.e discriminative pathway mean?
That you can localize the sensation in fine detail
except in the pain pathway where it means you can localize it to a part of the body. Affective motivational pathways cant.
What is propioception?
Sense of movement and body position
What are the two types of propioception
Conscious = Dorsal column pathway
Unconscious = Spinocerebellar pathway
Why do we have propioceptors?
So that the body can have constant feedback to generate smooth movement
What are two examples of propioceptors?
Golgi tendon organ
Neuromuscular spindle
What is the function of the Golgi tendon organ proprioceptor?
Monitor tension, pressure and joint movement
What is the function of the neuromuscular spindle?
Detect rate and size of changes in the length of muscle (stretch reflex)
What is special about the spinocerebellar tracts?
The decussate twice
What do the spinocerebellar tracts convey information about?
Unconcious propioceptive information
What are the two spinocerebellar tracts?
Posterior ( carries information from limbs to body)
Anterior (Intergrates propioceptive information from the limbs and body
How many neurons are in the spinocerebellar pathway?
Two
What do the anterior spinocerebellar fibres synapse with?
They synapse with spinal border cells, integrating information from the lower limbs, descending tracts and reflex arcs.
What pathway carries crude touch?
Anterior spinothalamic
What tract carries fine touch info from the lower limbs?
Gracalis = lower limbs, grass = feet
