Lecture 4 Flashcards
How do whiskers work?
hair follicle mechanoreceptors, in which a nerve ending is wrapped around the base of a hair, the movement of a hair stimulates the nerve ending
What can noxious stimuli (pain) be activated by?
extreme hot/cold
intense pressure
chemical irritants
What is a brief history of attitudes regarding pain?
1860s - 30% of amputations on humans patients were performed without anaesthesia/analgesia
1980 - no analgesics were given to laboratory animals recovering from surgery
21st century - large proportion of lab rodents don’t receive sufficient analgesia
What percentage of french veterinarians are moderately or extremely concerned about recognition and alleviation of pain?
96%
What are the top two reasons provided for lack of analgesics?
difficulties in recognizing pain
lack of knowledge about appropriate therapy
What is the prediction for lameness in cattle vs the actual lameness in cattle?
5.73% farmer estimate of lameness
22.11% actual lameness
What are some examples of painful procedures animals undergo?
tail docking, ear cropping
declawing
castration
dehorning/branding
beak trimming
surgery
What are the 2 components of pain?
- nociception: physical hurt or discomfort caused by injury or disease
- emotional suffering/feeling pain
How can pain alter an animals physiology?
Changes the animals physiology and behaviour to reduce or avoid damage, to reduce the likelihood of recurrence and to promote recovery
theory of analogy?
similarity of function between structures that have different origins
e.g. primitive areas of the brain to process nociceptive information medulla, thalamus, limbic system and cortex
What does the theory of analogy allow us to conclude about animal behaviour?
does NOT allow us to conclude all being experience identical feelings, but we can use the strength of the similarities to justify inferences about that individuals subjective state
What is nociception?
detection and reflex response to damage, to distinguish it from feeling pain
What are nociceptors?
specialized sensory receptors responsible for
- the detection of extreme pressure or temp, as well as certain chemicals that damage animal tissue, noxious stimuli
- transforming the stimuli into electrical signals which then travel to cns
What is a free nerve ending caused by?
activation of very small diameter of free nerve
What is a mediator
When tissue is damaged, chemical substances released that stimulate these fibers directly - inflammatory mediators
What are the five types of nociceptors?
- mechanical nociceptors respond to intense pressure
- thermal nociceptors respond to extreme hot or cold temperatures
- mechano-thermal nociceptors respond to both thermal and mechanical stimuli
- polymodal nociceptors respond to noxious mechanical, thermal and chemical stimuli and typically have small unmyelinated C fibers that conduct impulses at a velocity of less than 3 m/s
- silent nociceptors are activated by chemical stimuli and respond to mechanical and thermal stimuli onyl after theyve been activated, the use small unemyelinated C fibers
What fibers do mechanical, thermal and mechano-thermal nociceptors have?
myelinated A fibers, collectively, these 3 types of nociceptors are called A-nociceptors
Draw the chart for the primary afferent fibers
slide 36
What are the two types of nociceptive nerve fibres?
fast pain pathway: stimulation and transmission of nerve impulses over of A delta fibres (triggers withdrawal reflex)
slow pain pathway: stimulation and transmission of nerve impulses over non-myelinated fibres
What is the spinal cord?
continuation of the brain
major reflex center
cushioned and protected by meninges
What are some characteristics of the gray matter of the spinal cord?
looks like a butterfly in cross-section
has posterior projections called dorsal horns and two anterior projections called ventral horns
surround the central canal of cord that contains CSF
What are dorsal root ganglion
cell bodies of sensory neurons, near, but outside, spinal cord
What are ventral horns?
cell bodies of motor neurons of somatic ns
What are some characteristics of the white matter of the spinal cord?
composed of myelinated fiber tracts
What are the three regions of the white matter of the spinal cord?
dorsal column: contains only ascending tracts
lateral column: both ascending and descending tracts
ventral column: both ascending and descending tracts
Where do axons that convery fine touch ascend through?
dorsal column
Where do axons that carry pain/temperature info enter through
dorsal root
What is the spinthalamic tract?
afferent neurons ascend in the contralateral spinothalamic tract to nuclei within the thalamus and some projections to the midbrain
What is the spino-reticular tract?
afferent neurons ascend in the contralateral spino-reticular tract to reach the brainstem reticular formation before projectin got the thalamus and hypothalamus, other projections to the cortex
What are the perceptual and behavioural effects of pain
sensory component
immediate emotional consequences of pain
long-term emotional implications of chronic pain
What is the gate control theory?
inhibitory pain modulation at the spinal cord level
by activating Abeta with tactile, non-noxious stimuli inhibitory interneurons in the dorsal horn are activated, leading to an inhibition of pain signals transmitted C fibres
What are some important areas involved in descending inhibitory modulation?
midbrain
medulla
dorsal horns
these areas contains high concentration of opioid receptors (infusion of morphine in these areas = analgesic)
What are some ways to recognize pain?
pain and nociceptive stimuli are stressors, physiological pain response is confounded by the physiological and behavioural stress response to tissue damage and handling stress
what are some physiological responses to pain?
cardiovascular: elevations in hr
respiratory: elevations in rr
endocrine: various changes in stress hormones
What are the three main classes of behavioural changes?
pain specific behaviour
decline in the frequency or magnitude of certain behaviours
choice or preference tests
How can preference tests indicate pain?
lame birds showing preference for drugged feed
What are certain attential shifts seen in animals with pain?
changes in motivation
motivational changes act by way of altering the attention of animal away from pain
What is visceral pain?
pain arising from internal organs
viscera are largely innervated by c fibres
What is visceral pain associated with?
autonomic changes such as nausea, vomiting, changes in hr/bp
What is visceral pain triggered by?
smooth muscle contraction, ischaemia, necrosis, irritation by chemicals produced during inflammation
