The Anterolateral System Flashcards
(49 cards)
1
Q
______________ is #1 reason patients seek care from primary care physician for a problem
A
Persistent or chronic pain
2
Q
_____ of Americans suffer from chronic pain at some point during life
A
50%
3
Q
Definition of pain:
A
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
- complex, cognitive perception of a sensory stimulus in the context of the environment, previous experiences and emotions
- a product of brain’s abstract interpretation of a sensory experience
4
Q
Anesthesia:
A
lack of sensation
5
Q
Analgesia:
A
lack of pain
6
Q
Athermia:
A
lack of thermal sensation
7
Q
Hyperalgesia:
A
increased pain from normally painful stimulus
8
Q
Allodynia:
A
pain from a normally non-painful stimulus, light touch
9
Q
Hypoalgesia:
A
decreased pain from normally painful stimulus
10
Q
Paresthesia:
A
- unpleasant, abnormal sensation
- tingling, pricking, tickling
11
Q
Pruritus:
A
itching
12
Q
Acute vs. Chronic Pain:
A
Acute pain: Serves critical protective function
- Warning that injury should be avoided or treated
Chronic or persistent pain: When pain does not go away or adapt.
- Pain continues after healing or in absence of apparent injury
- Serves no useful purpose
- Difficult to diagnose and treat in absence of obvious physical damage
13
Q
What happens without acute pain?
A
Congenital insensitivity to pain
14
Q
What is nociceptive pain? What are the properties of nociceptive pain?
A
Pain resulting from tissue damage
- Well-localized, throbbing quality
15
Q
How is nociceptive pain initiated?
A
- Activation of nociceptors in skin, muscle, joint, bone or viscera in response to tissue injury or inflammation
- Inflammatory chemicals are released from immune cells and vasculature
- Chemicals act on receptors on bare nerve terminals of unmyelinated (C-fiber) nociceptors
16
Q
How is nociceptive pain treated?
A
- Typically responds to NSAIDs (non-steroidal anti-inflammatory drugs) and opioid drugs.
- For example, prostaglandins are synthesized from arachidonic acid
- Indomethacin, aspirin NSAIDs (non-steroidal anti-inflammatory drugs) block synthesis of prostaglandins
17
Q
What are examples of mild forms and severe forms of nociceptive pain?
A
- Mild forms: sprained ankle, infected cut, diaper rash
- More severe: rheumatoid arthritis, tumor that invades skin or soft tissue, bone fracture
18
Q
What is neuropathic pain?
A
Direct damage to nerves in the peripheral or central nervous system.
- Often has burning, lancinating, electrical quality
- Pain felt along distribution of nerves
- Allodynia common
19
Q
How is neuropathic pain treated?
A
- Tricyclic antidepressants, anticonvulsants
- Often resistant to NSAIDs or opioid meds
20
Q
What are some examples of neuropathic pain?
A
Examples:
- Post herpetic neuralgia following shingles
- Diabetic neuropathy
- entrapment neuropathy
- e.g. carpal tunnel syndrome
21
Q
What is the primary function of the anterolateral system?
A
Conveys info about pain and temperature to brain to higher brain levels
22
Q
Damage to anterolateral pathway reduces _______________.
A
pain and temperature sensation
23
Q
What is the input of the anterolateral system?
A
Noxious mechanical, thermal or chemical stimulus to free nerve endings of myelinated (Aδ) or unmyelinated (C-fiber) nociceptors in body (neck on down)
24
Q
Aδ fibers (myelinated):
A
mediate first pain:
- immediate
- short-lasting
- pricking quality
25
C fibers (unmyelinated):
mediate **second pain:**
* delayed
* long lasting
* burning quality
26
Central process of nociceptors:
* **enter** spinal cord **dorsal horn** (lateral part)
* **synapse onto 2nd order spinal neurons in Lamina I/II** (marginal zone and substantia gelatinosa)
* Some nociceptors synapse in the lateral edge of spinal cord (Lamina V)
* A few near the central canal (Lamina X)
* Chemical synapse involves **glutamate** and **substance P**
27
2nd order spinal neurons:
* **cross** to **contralateral side** of spinal cord within 2-3 segments rostral
* **ascend** in anterolateral quadrant tracts (**Ventral Lateral Funiculus**)
28
Major differnece between **anterolateral pathway** vs. the **dorsal column system:**
* **Dorsal Column:**
* Carries **non-nociceptive** mechanical information.
* **Remember:**
* Dorsal column afferents enter spinal cord and **ascend on ipsilateral side until lower medulla where they cross.**
29
What will lesion of the anterolateral tract at the spinal cord level cause?
* Contralateral loss of pain and temperature
* Loss is complete by 2-3 segments below the lesion
30
What are the pathways for termination in higher brain centers?
1. Spinothalamic tract
2. Spinoreticular tract
3. Spinomesencephalic tract
* other pathway: spinohypothalamic tract
31
Spinothalamic Tract:
* **Majority of 2nd order ascending fibers terminate in the thalamus** (on to **3rd order thalamic neurons**)
* Best known, **most prominent** pain pathway
\* **Mediates discriminative aspects of pain and temperature sensation**
* i.e. **location and intensity** of the noxious stimulus
32
In thalamus, axons terminate in:
* VPL (Ventral Posterior Lateral) Nucleus of the thalamus
* Central Lateral Nucleus of the thalamus (an intralaminar nucleus)
33
VPL (Ventral Posterior Lateral) Nucleus of the thalamus:
* 3rd order axons **project to ipsilateral SI cortex (areas 3b, 1, 2)**
* **Principal relay nucleus for discriminative somatosensory information** from body (neck-toes)
* Helps **localize** where
noxious stimulus on body occurs
34
How is the VPL somatotopically organized?
* VPL **receives** both **spinothalamic** and **dorsal column medial lemniscal** inputs
* Axons from the 2 systems **synapse on different VPL neurons**
35
Central Lateral Nucleus of the thalamus (an intralaminar nucleus):
⇒ 3rd order axons project to many areas of cortex, particularly **limbic cortex** (affect/emotion)
⇒ Involved in **emotional suffering**
⇒ CL nucleus is **not somatotopically organized**
36
Functions of thalamus:
1. Process nociceptive information. Crude pain and temperature sensation is beginning to be appreciated and emotional reactions (suffering) to pain are initiated.
2. Relay information to the cerebral cortex by 3rd order neurons that pass through posterior limb of internal capsule and corona radiata to the SI cortex.
* Spinothalamic tract is similar to dorsal column system: in that it projects to VPL of thalamus, is somatotopically-organized, and discriminates and localizes stimulus.
37
Spinoreticular Tract:
* Many **2nd order** axons **ascend from spinal cord** and **terminate in the medulla and pons** in a region called the **reticular formation**
* Other axons then **relay info from reticular formation to thalamus** and diffuse to many areas of the cortex.
* **Mediates changes in level of attention to painful stimuli**
* Also involved in **forebrain arousal** and **effective response to noxious stimulus**
38
Spinomesencephalic Tract:
* Some 2nd order axons **terminate in the midbrain in the superior colliculus** and in a region of gray matter surrounding the cerebral aqueduct called the:
* **Periaqueductal Gray (PAG)**
* \*\***Activation of it leads to stimulating the central modulation of pain**
* Stimulates **descending control pathways** that project back down to spinal cord
39
When the dorsal columns are completely lesioned, why is there still some crude touch sensation?
Anterolateral tract also carries some crude touch sensation
40
Anterolateral Tract Mnemonic:
When you step on a tack with left foot:
* **Spinothalamic tract** enables you **to realize** **"Something sharp is puncturing the sole of my left foot!"**
* ***Spinoreticular tract*** allows you ***to feel*** ***"Ouch! That hurts!"***
* ***_Spinomesencephalic tract_*** involves ***_pain modulation_***, eventually allows you to think ***_"Ahh, that feels better"_***
41
Cortex:
Thalamic neurons project to:
1. 1) **Somatosensory cortex:**
* SI areas **3b, 1, 2**, and also **SII**
* Helps **localize stimulus** on body
2. **Cingulate gyrus:**
* part of limbic system
* process the **emotional component of pain** of fear, anxiety, depression, anger, attention
3. **Insular cortex:**
* **Processes information on the internal, autonomic state** of body
* (heart races, breathing rapid, mouth dry, muscles tense, can’t sleep).
* Insular cortex thought to **integrate sensory**, **affective and cognitive components of pain** and all are **necessary for normal responses** to pain.
42
What will lesions of insular cortex result in?
**Asymbolia** for pain:
* Patients **can perceive noxious stimuli as painful and localize the pain** to body part,
* **Don't display appropriate emotional responses to pain** (indifferent, laugh, etc.)
43
Central control of pain:
Descending pathways that inhibit pain:
* Painful stimuli can be suppressed by endogenous pain control systems
* Reticular formation has prominent role
44
What is the role of of the PAG?
* Neurons that have cell bodies in the Periaqueductal Gray (PAG) (Central gray area) **in the midbrain send axons down to the Raphe nuclei** **in medulla**
* PAG neurons **also project down to neurons in the Locus Ceruleus of the pons**
45
What is the role of the Raphe Nuclei and Locus Ceruleus?
Neurons in the Raphe Nuclei and Locus Ceruleus:** **
* **Send axons down to spinal cord where they synapse on inhibitory interneurons or directly on to spinothalamic tract projection neurons**
* **Suppress transmission of noxious information toward thalamus and cortex**
46
What is referred pain?
* **Visceral pain** is often difficult to localize and is **referred to somatic tissues**
47
How can visceral pain aid in the diagnosis of the source of pain?
Fairly consistent from patient to patient:
* Area to which the pain is referred **corresponds to the dermatome innervated** by the spinal segment to which the visceral afferents project
48
Why is visceral pain referred?
Hypothesis:
* Visceral pain fibers at a given level of spinal cord **converge on to the same 2nd order spinothalamic tract neurons that receive input from somatic pain fibers** from that level.
* Because **somatic stimuli are more frequent** than visceral stimuli, the **brain interprets any spinothalamic tract impulses as stimuli from the somatic region** of the dermatome
49
Landmark Dermatomes:
* Diaphragm
* C3-C4
* Heart
* T1-T4 (mainly left)
* Stomach
* T6-T9 (mainly left)
* Gallbladder
* T7-T8 (right)
* Duodenum
* T9-T10
* Appendix
* T10 (right)
* Reporductive organs
* T10-T12
* Kidney, ureter
* L1-L2
