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==What is Pain?==
==What is Pain?==
'''''Nociception''''' is the process of neurotransmission that transmits and processes information relating to tissue damage. It originates from sensory receptors known as ''nociceptors''. '''''Pain''''', on the other hand, is a conscious experience arising from nociception. It has previously been described as:
'''''Nociception''''' is the process of neurotransmission that transmits and processes information relating to tissue damage. It originates from sensory receptors known as ''nociceptors''. '''''Pain''''', on the other hand, is a conscious experience arising from nociception. It has previously been described as:
# "An unpleasant sensory or emotional experience associated with actual or potential tissue damage." (International Association for the Study of Pain, 1978).
# "An unpleasant sensory or emotional experience associated with actual or potential tissue damage." (International Association for the Study of Pain, 1978).
==Physiology and Pathophysiology of Pain Transmission==
==Physiology and Pathophysiology of Pain Transmission==
Two types of nocieptive fibres (neurons) exist. C-fibres are slow-conducting and unmyelinated, whereas A-delta-fibres are small, fast-conducting, myelinated structures. The cell bodies of these neurons are located in the dorsal root ganglion, and the neurons are bipolar. The sensory nerve endings conduct afferent impulses to the cell body, and fibres then extend to the dorsal horn of the spinal cord. Here, ascending information is transmited to the cortex via several "relay stations", including the [[Forebrain - Anatomy & Physiology|thalamus]], the reticular formation, the [[Hindbrain - Anatomy & Physiology#Pons|pons]] and the amygdala. These modulate the signal on its journey towards conscious perception. Local [[Reflex Arcs - Anatomy & Physiology|reflex arcs]] may also be stimulated in the dorsal horn, producing spinal reflexes such as the withdrawal reflex.
Two types of nocieptive fibres (neurons) exist. C-fibres are slow-conducting and unmyelinated, whereas A-delta-fibres are small, fast-conducting, myelinated structures. The cell bodies of these neurons are located in the dorsal root ganglion, and the neurons are bipolar. The sensory nerve endings conduct afferent impulses to the cell body, and fibres then extend to the dorsal horn of the spinal cord. Here, ascending information is transmited to the cortex via several "relay stations", including the [[Forebrain - Anatomy & Physiology|thalamus]], the reticular formation, the [[Hindbrain - Anatomy & Physiology#Pons|pons]] and the amygdala. These modulate the signal on its journey towards conscious perception. Local [[Reflex Arcs - Anatomy & Physiology|reflex arcs]] may also be stimulated in the dorsal horn, producing spinal reflexes such as the withdrawal reflex.
===Sensitisation===
===Sensitisation===
Hypersensitisation of the pain transmission can occur at any level of the neuraxis. This can result in two phenomena: '''hyperalgesia''', where an exaggerated response to a noxious stimulus is experienced, and '''allodynia''', where a non-noxious stimulus (such as gentle touch) elicits a painful response.
Hypersensitisation of the pain transmission can occur at any level of the neuraxis. This can result in two phenomena: '''hyperalgesia''', where an exaggerated response to a noxious stimulus is experienced, and '''allodynia''', where a non-noxious stimulus (such as gentle touch) elicits a painful response.
==Physiological Effects==
==Physiological Effects==
Pain has adverse physiological effects, which include metabolic and cardiac effects.
Pain has adverse physiological effects, which include metabolic and cardiac effects.
===Metabolic Effects===
===Metabolic Effects===
Pain may activate the stress response and hence hormone secretion from the pituitary glands, adrenal glands and pancreas. This leads to substrate mobilisation and catabolism, particularly protein wasting. These effects can impair wound healing, and in the long term result in immunosupression. They can also cause a negative energy balance, giving weight loss or poor growth in young animals. It is important to bear this fact in mind when considering the economics of analgesia in food animal production.
Pain may activate the stress response and hence hormone secretion from the pituitary glands, adrenal glands and pancreas. This leads to substrate mobilisation and catabolism, particularly protein wasting. These effects can impair wound healing, and in the long term result in immunosupression. They can also cause a negative energy balance, giving weight loss or poor growth in young animals. It is important to bear this fact in mind when considering the economics of analgesia in food animal production.
===Cardiovascular Effects===
===Cardiovascular Effects===
Pain can cause '''hypertension''' and '''tachycardia'''. This is of particular importance in surgical scenarios: poor peri-operative pain management will contribute to poor recovery from anaesthesisa and increase the risk of post-operative complications.
Pain can cause '''hypertension''' and '''tachycardia'''. This is of particular importance in surgical scenarios: poor peri-operative pain management will contribute to poor recovery from anaesthesisa and increase the risk of post-operative complications.
===Chronic Pain===
===Chronic Pain===
Severe or persistent pain can lease to pathophysiological "chronic" pain. Increased risks of auto-mutilation or wound biting are associated with this, proving proper peri-operative pain relief again to be very important.
Severe or persistent pain can lease to pathophysiological "chronic" pain. Increased risks of auto-mutilation or wound biting are associated with this, proving proper peri-operative pain relief again to be very important.
==Assessment of Animal Pain==
==Assessment of Animal Pain==
Assessment of pain in animals is neither easy nor, often, intuitive. Usually, vets make observations of behaviour in order to assess their patients' well-being. They must however bear in mind that pain is a subjective experience that varies greatly between individuals. The expression of pain behaviour is also highly species specific. Pain behaviour is influenced by many extrinsic factors, such as previous conditioning, social dominance and overall health status, which may contort the observations. Finally, since animals cannot verbally describe their pain, bias of the observer is inevitable. Therefore knowledge of an individual's behaviour and the assessor's observational skills and attitude towards pain will influence how pain is assessed and consequently managed.
Assessment of pain in animals is neither easy nor, often, intuitive. Usually, vets make observations of behaviour in order to assess their patients' well-being. They must however bear in mind that pain is a subjective experience that varies greatly between individuals. The expression of pain behaviour is also highly species specific. Pain behaviour is influenced by many extrinsic factors, such as previous conditioning, social dominance and overall health status, which may contort the observations. Finally, since animals cannot verbally describe their pain, bias of the observer is inevitable. Therefore knowledge of an individual's behaviour and the assessor's observational skills and attitude towards pain will influence how pain is assessed and consequently managed.