Module 9: Labour Physiology Ll

Front 1

Types of nociceptors typically stimulated during labour?

Back 1

Mechano-nociceptors (as they respond to extreme mechanical stress- pressure, stretch, rubbing and tearing). Maybe polymodal nociceptors too as they respond to mechanical stress.

Front 2

Locations of nociceptors triggered in labour?

Back 2

Cutaneous (exteroceptors)- skin

Somatic (proprioceptors) – skeletal muscles, ligaments and bones

Visceral (interoceptors) – within viscera

Front 3

Types of noxious stimuli?

Back 3

Increased:

- Stretching

- Tearing

- Tugging

- Pressure

- Rubbing

Decreased blood flow (restriction/pressure of blood vessels and associated temporary ischemia).

Front 4

Describe the sensory pathway for pain, including referred pain:

(Be able to list the neurons involved in the pathway & identify where each neuron in the pathway begins and end)

Back 4

Primary neuron: originate at nociceptors and terminates in the dorsal horn of the spinal cord.

There are two types of nociceptive nerve fibers (primary sensory neurons):

• A fibers: large diameter fibers that are myelinated, transmitimpulses rapidly (sharp).

• C fibers: smaller diameter, unmyelinated fibers, transmit impulsesmore slowly (dull).

Secondary neuron: synapse with the primary neuron in the dorsal horn of the spinal cord and terminates within the thalamus

Tertiary neurons: Originate in the thalamus and one terminates in the primary somatosensory cortex and the other terminates in the limbic system.

Front 5

Describe the sensory pathway for pain, including referred pain:

(Be able to describe what referred pain is and how that integrates into the pain pathway)

Back 5

Referred pain: pain felt in locations other than where it originates (i.e. where the noxious stimuli actually is).

This is due to visceral primary nociceptors synapsing with secondary neurons within somatic/cutaneous spinal cord tracts.

Eg. uterine & cervical pain is typically felt in the lower back, thighs and buttocks.

Front 6

Outline the perception of pain & relate physiological aspects of labour to pain intensity:

(Identify which parts of the brain are involved in the perception of pain and distinguish what aspects of pain are perceived by each of these brain areas)

Back 6

Primary somatosensory cortex: Location, intensity, type of stimuli (eg. stretching, pressure etc.), and type of pain (A fiber sharp or C fiber dull).

Somatosensory association area: Associates current stimuli with memories/experiences of past pain.

Limbic system: Emotional response to pain. Prefrontal cortex: Rationalization of pain and moderation of appropriate response. h

Front 7

Outline the perception of pain & relate physiological aspects of labour to pain intensity:

(The intensity of pain during labour increases due to?)

Back 7

The intensity of pain in labour is due to the increased intensity of contractions.

Front 8

Differentiate between pain thresholds and pain tolerance?

Back 8

Pain threshold: the intensity (amount of damage) of a noxious stimuli required to generate action potentials in a nociceptive (primary sensory) neuron. The greater the intensity of the stimulus, the greater the number of APs fired, the greater the intensity of pain felt.

Pain tolerance: the subjective unpleasantness of pain sensations. Much of an individual’s pain tolerance relates to previous pain experiences as well as numerous physical, emotional, social and mental aspects of the situation. During labour, pain tolerance is influenced by the mental, physical and emotional state of the woman, the birthing environment, stress and anxiety, the support she has for herbirth, etc

Front 9

Distinguish between the three physiological mechanisms regulating pain and relate to recommendations for pain alleviation during labour?

(Be able to identify the three pain regulatingmechanisms and describe how each of these mechanisms work to regulate/reduce pain (i.e. reduce the number of action potentials received)

Back 9

1) Gate Control Theory: Non nociceptive mechanoreceptor stimulation (touch/pressure) sends signals via primary sensory neurons into dorsal horn, which then communicate with the secondary neuron in pain pathway and stimulate inhibition of secondary neuron (i.e. hyperpolarizes the secondary neuron).

Enhance: stimulate nonnociceptive neurons (eg. massage, backrubs, acupressure, heat)

2) Descending regulation: Other brain areas, particularly in thebrainstem, send descending signals down to dorsal horn area currently receiving pain signals and suppresses activity at the primary-secondary nociceptive synapse.

3) Endorphins: Chemicals released from neural tissue which inhibit action atnociceptive synapses

Enhance: through use of drugs

Front 10

Outline the tissue damage that can occur during vaginal births?

Back 10

Stretching, bruising, tearing, grazing of pelvic area structures.

Front 11

Distinguish between the four degrees of perineal tears

Back 11

First degree tear: fourchette

Second degree tear: fourchette, perineal body, superficial perineal muscles

Third degree tear: fourchette, perineal body, superficial perineal muscles, external anal sphincter

Fourth degree tear: fourchette, perineal body, superficial perineal muscles, external anal sphincter, anal mucosa, internal anal sphincter

Front 12

Identify procedures, which intentionally cause tissue damage during labour?

Back 12

C-section and episiotomy

Front 13

Outline the tissue damage that occurs during a Caesareansection?

Back 13

Laceration of skin, CT, abdominalmuscles, peritoneum, smooth muscle of uterus, endometrium (within LUS), bloodvessels and nerves are also damaged.