Ascending Neural Pathways Flashcards
State how sensations are divided into categories
Divided into :
- Conscious (Somatic)
- Unconscious
State what conscious sensations are divided into
(Based on locations of receptors)
Exteroceptive (Superficial)
Proprioceptive (Deep)
State what the exteroceptive sensations are divided into
Touch
Pain
Temperature
Touch
Protopathic - crude touch
Epicritic - discriminative touch
Distinction between protopathic and epicritic touch
They are carried in different pathways.
One can be spared and vice versa
State what the proprioceptive sensations are divided into
Joint position
Vibration
Kinaesthesia (sensation originating from muscles)
2-Point Discrimination
Feature of unconscious sensations
Do not reach the cerebral cortex, do not reach the brain.
Therefore, we are not aware of these sensations, however these sensations end up in different parts of the CNS.
Cerebellum deals with it.
State what unconscious sensations are divided into
Proprioceptive (from the joints)
Visceral (from the organs)
Free Nerve Endings
Pain, temperature
Pacinian Corpuscles
Vibration
Rapidly adapting
Encapsulated nerve endings
Pacinian corpuscles
Meissner corpuscles
Merkels discs
Ruffini endings
Meissner corpuscles
Texture
Rapidly adapting
Merkel discs
Sustained pressure
Slowly adapting
Ruffini endings
Drag (Stretch)
Slowly adapting
Describe transmission of somatic senses
Sensations are relayed to the CNS by 3 neurones.
1st order neurones pick up sensations with their peripheral branches from the receptors/free nerve endings.
To the dorsal root ganglion.
The central extensions of the 1st order neurone, bring the sensations to the spinal cord or brainstem, where they synapse with 2nd order neurones.
2nd order neurones cross the midline and ascend to terminate in the thalamus.
3rd order neurone projects from the thalamus to the somatosensory cortex.
Where are sensory nerves found ?
Dorsal Root ganglion
Houses:
- Afferent/ Sensory/ 1st order neurones
Function of the peripheral branch of the 1st order neurone
Carries sensations from the receptor/ free nerve ending.
Function of the central branch of the 1st order neurone
Enters the spinal cord / brainstem via the dorsal root ganglion.
Where is the cell body of the 2nd order neurone found ?
Located in the grey matter of the spinal cord / brainstem on the same side.
Where is the 3rd order neurone found ?
The thalamus
State the locations of the 1st, 2nd and 3rd order neurones
1: Dorsal Root Ganglion
2: Spinal cord or Brainstem
3: Thalamus
What does sensory information travel to the brain via ?
The dorsal column-medial lemniscus system
The anterolateral system
Where do the dorsal column-medial lemniscus system and the anterolateral system come back together ?
Partially at the level of the thalamus
State the sensations that travel together
Conscious proprioceptive sensation
Vibration
Discriminative touch
What is the pathway that carries :
Conscious proprioceptive sensation
Vibration
Discriminative touch
called ?
Dorsal column medial lemniscus pathway
Describe the dorsal column-medial lemniscus pathway
Carries signals up to the medulla (brainstem) in the dorsal columns of the spinal cord.
Synapse
Cross to opposite side of medulla, become medial lemniscus.
Up the brainstem to thalamus (VPL) via medial lemniscus.
The axons of the 3rd order neurones travel to the cerebral cortex.
Sensory decussation
Axons that cross the midline
1st order neurones in the dorsal column-medial lemniscus pathway
Central branches of 1st order neurones enter the dorsal column and ascend to the medulla as fasciculus gracilis (3a) or cuneatus (3b)
2nd order neurones in the dorsal column-medial lemniscus pathway
Found in the ipsilateral gracile and cuneate nuclei in the medulla
State the 2 types of pain
Fast pain
Slow pain
Describe fast pain
- 0.1s after a painful stimulus
- carried by A-delta axons
- Not felt in deep tissues (felt in skin)
State some types of fast pain
Sharp pain
Stabbing pain
Prickling pain
Acute pain
Electric pain
Describe slow pain
- Begins >1s after a painful stimulus
- Increases slowly
- Carried by unmyelinated C axons
- Felt both in skin and deep tissue/organs
- Usually associated with tissue destruction
State some types of slow pain
Slow burning pain
Aching pain
Throbbing pain
Nauseous pain
Chronic Pain
What is nociception ?
Detection of stimuli that can cause tissue injury.
It can involve pain.
Describe unmyelinated type C axons
Not localised (dull pain)
- Respond to intense heat/cold
- Slow pain
- Dull, poorly localised
- Terminate in reticular formation
What is reticular formation ?
A network of cells and connections that are scattered all around the brainstem.
The nuclei can be found in the medulla/pons/midbrain etc.
No direct connection with the cortex.
Spinoreticular tract
Carries pain from the spinal cord to the reticular formation.
Describe finely myelinated Adelta axons
Ends up in the cortex
- Sharp, fast pain
- Well localised
- Terminate in NVPL (spinothalamic/ anterolateral tract)
What is the pathway that carries :
Pain
Temperature
Crude Touch
called ?
Anterolateral tract
Anterolateral tract
What does it carry ?
(i.e. what sensations)
Receptors: Nerve endings
Pain, temperature and crude touch
Describe the anterolateral tract
Enter the spinal cord via dorsal root nerves
Synapse w 2nd order neurones in the dorsal horns of spinal grey matter
Cross to the opposite side of the cord
Ascend through the anterior and lateral white columns of the cord
Terminate at all levels of the lower brainstem and thalamus.
State the 2 spinothalamic tracts
Anterior spinothalamic tract
Lateral spinothalamic tract
Anterior spinothalamic tract
Crude touch and pressure
Lateral spinothalamic tract
Pain and Temperature
Describe referred pain
Noxious stimuli originating in an organ are perceived as pain arising from a superficial part of the body (skin)
Mechanism of referred pain
Branches of anterior pain fibres synapse in the spinal cord on same 2nd order neurones that receive signals from the brain.
When anterior pain receptors are stimulated, pain signals from the viscera are conducted through some of the same neurones conducting pain signals from the skin.
So the person feels sensations originate in skin.
Do organs have pain receptors ?
NO !
They have nociceptors and stretch receptors.
Stretch - uncomfortable sensation, referred as pain
T10
Umbilicus
Summary of dorsal column-medial lemniscus
Conscious proprioception
Vibration
2-Point discrimination
Fine touch
Summary of anterolateral (spinothalamic) system
Pain
Temperature
Crude touch
Features dorsal column-medial lemniscus
Large, myelinated fibres
30-110 m/s
Discriminative mechanoreceptive sensation
High degree of spatial orientation
Unconscious Proprioception function
Essentail for smooth motor coordination
Very fast conduction is required
Features of anterolateral system
Smaller fibres
Up to 40 m/s
Broad spectrum of sensory modalities
Less spatial orientation
Unconscious Proprioception
Sensations do not reach the cortex, the cortex is not aware of what’s going on.
Cerebellum is the most important structure involved.
Describe unconscious proprioception
Afferent sensory information from muscle spindles and Golgi tendons terminate in IPSILATERAL cerebellum, rather than cerebral cortex.
Clarke’s nucleus
Found in T1 to L2 spinal cord segments
Where the spinocerebellar tracts originate
Anterior spinocerebellar tract
Carries input from the trunk, upper and lower limbs
Posterior spinocerebellar tract
Carries input from lower trunk and lower limbs
Cunocerebellar tract
Carries input from upper limbs
Stereognosis
Ability to recognise and identify objects by feeling them
Graphesthesia
Ability to recognise symbols written on the skin
Anaesthesia
Total loss of touch sensation
Hypoesthesia
Decrease in touch sensation
Hyperesthesia
Increase in touch sensation
Astereognosis
Loss of stereognosis
Analgesia
No pain
Thermanalgesia
Loss of temperature sensation
Sensory Ataxia
GAIT disorder resulting form sensory impairment
- severe swaying when eyes closed
- impaired joint sense and discriminative touch
- broad based gait
