2-NSc-Handout-F14

Question 1

somato-sensory system

Answer 1

1. principles
2. pain
3. proprioception
4. touch
5. temperature

Question 2

special senses

Answer 2

1. vision
2. hearing
3. balance
4. taste
5. smell

Question 3

nervous system

Answer 3

governs actions and reactions involving 3 basic functions

1. detection of a stimulus and transmission to CNS via afferent neurons (sensory)
2. processing info and decision making - interneurons (association neurons)
3. transmission of response via effector or efferent neurons (motor)

Question 4

THE SOMATO-SENSORY SYSTEM

Answer 4

… is comprised of peripheral sensory receptors, ascending tracts and central processing centers to produce 4 sensory modalities:
TOUCH, PROPRIOCEPTION, PAIN and TEMPERATURE.

Question 5

the somato-sensory concept??

Answer 5

specific stimulus in a BODY part (e.g. pain)triggers an electrical change or graded potential in its specific receptor = receptor STIMULATION TRANSDUCTION of signal into action potentialsTRANSMISSION via ascending neurons/tracts to a designated brain
area within the Somato-
Sensory CORTEXallows correct
interpretation and localization of
the stimulus = Conscious PERCEPTION

Question 6

RECEPTOR STIMULATION & TRANSDUCTION

Answer 6

Stimulation leads to changes in ionic channels, which alter ionic flow, typically leading to depolarisation of the receptor membrane = Graded Potential
–> stimulating energy is transformed into electric energy = TRANSDUCTION

Question 7

THe somato-sensory cortex –> cerebral cortex is responsible for?

Answer 7

the conscious experience of the incoming stimulus = Perception
(also for conscious movement and cognitive skills)

Question 8

The (somato-) sensory projection neurons (3rd order neurons) end in designated locations of the cortex –>

Answer 8

each area is dedicated to the perception of one sense = CORTICAL MAP

Question 9

Important body areas are disproportionately represented because they contain more sensory receptors; depends on a species’ life style —>

Answer 9

SomatoSensory Map or “Humunculus”

Question 10

adaptation

Answer 10

An organism has to primarily react to changes in the environment –> many receptors react only to initial change in stimulus strength and then adapt to it

Question 11

RAPID Adaptation = Phasic receptors

Answer 11

Sensory receptors adapt within seconds or milliseconds

–> geared towards registering quick changes in stimulus strength, e.g. touch, smell, thermoreception

Question 12

SLOW Adaptation = Tonic receptors

Answer 12

Sensory receptors continue to transmit impulses as long as stimulus exists,
and frequency decreases only slightly
–> keep CNS apprised of status of the body, e.g. proprioception, baroreceptors, chemical composition of blood

Question 13

Pain

Answer 13

is an unpleasant sensory and emotional experience associated with actual or potential tissue damage

Question 14

purpose of pain

Answer 14

Part of the body’s protection mechanism to withdraw from damage, to protect from further damage during healing and to avoid damage in the future

Question 15

Nociception sensory receptors

Answer 15

transduce a noxious stimulus = process of NOCICEPTION, and transmit stimuli via 2. / 3. order neurons to the brain for CONSCIOUS PERCEPTION = PAIN.
Nociceptors also transmit stimuli to LMNs to initiate withdrawal reflexes (without conscious perception of pain

Question 16

Nociception are?

Answer 16

Pain Neurons with free nerve endings

• are present in all tissues except the brain
• are more numerous in the skin (somatic superficial pain) than in deeper tissues like muscles and joints (somatic deep pain) or in organs (visceral pain)
• as first-order neurons, pain fibers run in peripheral nerves to the spinal cord/dorsal horn, respectively via Cranial Nerves (V, VII, IX, X) to the brain stem

Question 17

NOCICEPTOR ACTIVATION

Answer 17

• are triggered by high threshold chemical/mechanical/thermal energytissue disruption
• are poly-modal chemoreceptors = carry several types of receptors / transduction channels

Question 18

Common noxious stimuli include

Answer 18

ATP Nerve Growth Factor 
H+ Intense heat / cold 
K+ Intense pressure
Lipids Prostaglandins !! 
Bradykinin Histamine 
Serotonin Substance P(ain) 
Leukotriens Endothelin

Question 19

1. Pain (“generation of pain”)

Answer 19

Painful impulse is triggered by initial mechanical force
of injury –> damaged cells release many chemicals –> activate nociceptors –> transduction & transmission via small myelinated A-delta fibers –> perceived as sharp / immediate / stinging / bright / localized pain = First Pain

Question 20

2. Pain (“maintenance of pain”)

Answer 20

Activated nociceptors release additional chemicals, i.p. Substance P and Calcitonin- Gene-Related Peptide (CGRP); both:

–> Cause more pain, and
–> stimulate release / production of inflammatory
mediators from tissue macrophages & WBCs, e.g. histamine, prostaglandins, bradykinin, cytokines aka the “Inflammatory Soup”
The “Inflammatory Soup” activates nociceptors and maintains a burning / diffuse / nagging / throbbing / nauseating / long-lasting pain sensation via un- myelinated C fibers = Second Pain

Question 21

SENSITIZATION to Pain (=“enhancing pain”)

Answer 21

The Inflammatory Soup, i.p. prostaglandins, can lead to temporary changes in transduction channels:
- achieved via phosphorylation of channel proteins –> widening of channels, extended opening of channels
- via gene expression –> insertion of new channels and receptors
Both facilitate ionic flow & amplification of signal transmission = nociceptors become more sensitive to stimuli (increases protection of the affected area).

Question 22

Two forms of sensitization:

Answer 22

1. HYPERALGESIA
   an exaggerated pain response to a noxious stimulus
2. ALLODYNIA
   a pain response to a non-noxious stimulus, e.g. a gentle touch

Question 23

When does sensitization typically resolve?

Answer 23

as the injury heals. If it persists in the absence of injury –> chronic pain

Question 24

PAIN TRANSMISSION & ASCENDING PATHWAYS

Answer 24

Nociceptive afferent fibers (A delta and C fibers) enter spinal cord
via dorsal root –> dorsal horn –> synapse with 2.order neurons, using excitatory Neurotransmitters, e.g. Substance P, Glutamate –>
axons enter the SPINOTHALAMIC TRACT (STT) in the Lateral Funiculus: - always contralateral in primates
- ipsi- and contralateral in domestic animals

Question 25

The STT projects to various brain regions:

Answer 25

1. to Somatosensory Cortex via Thalamus (relay) for acute perception and localization of pain = discriminative pain pathway; receives input mostly from A delta fibers; aka Neo-STT = a “new” evolutionary tract 2. to Reticular Formation and Limbic System; receives input mostly from C fibers; aka Paleo-STT >evokes dull, aching, burning, diffuse pain >evokes autonomic responses, e.g pulse, blood pressure, sweat >evokes emotional & behavioral responses, e.g. fear & avoidance >maintains arousal / wakefulness

Question 26

Pain is also carried in many other tracts....

Answer 26

in the Fasciculus proprius

Question 27

Pain can be moderated / inhibited via descending ANALGESIA Pathways:

Answer 27

- originate in the cortex, thalamus and brain stem and descend in the lateral funiculus - are activated by incoming pain (also by high sympathetic tone/ excitement / danger) - form multiple synapses with ascending pain neurons and end on inhibitory interneurons in the dorsal horns - interneurons use a variety of inhibitory neurotransmitters where they synapse with incoming pain fibers to block transmission of pain signals (from 1. to 2. order pain neurons), i.p. the ENDOGENOUS OPIOIDS Enkephalins, Endorphins, and Dynorphins; also GABA, Glycine - Endorphins are also released into blood by hypothalamus

Question 28

chronic pain

Answer 28

- aka Pathological Pain or 'Bad Pain" ( vs acute, physiological or good pain) - serves no physiological purpose & persists IN THE ABSENCE OF TISSUE INJURY - is characterized by hypersensitivity of the pain transmission system = Hyperalgesia and Allodynia (see2.2.4), which can last months or years

Question 29

Underlying mechanism (of “neuroplasticity”)

Answer 29

Strong stimulationaltered signaling pathways (e.g. phosphorylation) and altered gene expression of c-fos, transcription factors, kinases --> induce neuron-remodeling with profound changes in receptors, channels, neurotransmitter production & release, cellular proliferation --> amplification of pain signals; two forms: 1. Peripheral Sensitization: Nociceptor re-modeling as discussed (2.2.4); induced by inflammatory mediators 2. Central Sensitization: aka 'Wind-Up"; hyper-excitability of neurons within the CNS upon strong stimulation; triggered by bursts of nociceptor activity, e.g. during surgical incisions

Question 30

The key to preventing chronic pain?

Answer 30

is preemptive analgesia

Question 31

Unmanaged pain / chronic pain can be debilitating, causing multiple stress responses, such as

Answer 31

- reduced food/water intake - reduced healing / prolonged recovery times - impaired immune system function - cardio-respiratory effects (high blood pressure, tachycardia, tachypnoe) - renal effects (reduced GFR, salt & water retention)

Question 32

“Is the animal in pain?”

Answer 32

Observation of behavior, expression, responsiveness, vital signs; Pain expression differs greatly depending on species with prey animals typically showing less obvious signs

Question 33

“Can the animal feel pain?” (neurological examination)

Answer 33

- skin prick for detection of superficial pain sensation (runs largely in the Spinothalamic tracts) - pinching digits / joints strongly with fingers or hemostat for detection of deep pain (runs in deeper tracts, e.g. Fasciculus Proprius)

Question 34

Because of different neurotransmitter (NT) pattern in different pain pathways with a wide variety of ...

Answer 34

excitatory and inhibitory NTs, multimodal analgesia is used to combat most / all pain transmission >CNS, via descending analgesia system, affecting pre- and/or post-synaptic transmission: - Opiods - Alpha 2 agonists - Serotonin (via re-uptake inhibitors) - Paracetamol ? >Axon Transmission local anesthetics (block Na-voltage gated channels) > Nociception NSAIDs, e.g. ibuprofen, salicylic acid via inhibition of Prostaglandin production

Question 35

Proprioception: Sense of Body Position and Movement

Answer 35

>Gives continuous and detailed information about positions of limbs relative to the body and their rate of movement > Is essential for accurate, coordinated, purposeful movements and gait > Receptors constantly monitor: - muscle length / tension via muscle spindles - tendon length / tension via tendon organs - joint angulation / rotation via joint receptors >stimuli ascend via spinal cord to cerebellum (unconscious proprioception) and cerebral cortex (conscious proprioception) >loss of unconscious a/o conscious sense of proprioception will lead to incoordinated movements = ATAXIA Note: full sense of orientation in space also requires the sense of equilibrium = special sense (= head position relative to ground)