Sensory pathways and pain

Question 1

Sensory receptors are classified by different properties.

Answer 1

1. Function- Pain, temperature, touch, muscle length
2. Morphology- free nerve endings or encapsulated. – what do they look like
3. Conduction velocity - fast or slow
4. Location - skin, muscle, tendon
5. Rate of adaptation - slow or fast stop transmit (Rapid adapting & Slow adapting sensory fibres)

Question 2

Name the types of mechanoreceptors in the skin.

Answer 2

• Meissner corpuscle (surface)
• Pacinian corpuscle
• Ruffini’s corpuscles
• Merkel’s disks
• Free nerve endings

Question 3

Name the types of mechanoreceptors in the skin that are fast adapting.

Answer 3

• Meissner corpuscle (surface)

- Pacinian corpuscle

Question 4

Name the types of mechanoreceptors in the skin that are slow adapting.

Answer 4

• Ruffini’s corpuscles

- Merkel’s disks

Question 5

Somatic sensory pathways take information from sensory receptors to ____ area in the ____, and to the ____.

Each pathway consists of: ___, ___ and ___.

Answer 5

Somatic sensory pathways take information from sensory receptors to primary somatosensory area in the cerebral cortex, and to the cerebellum.

Each pathway consists of:
1) First order neuron – takes information from receptors to spinal cord

2) Second-order neuron – takes informaLon from brain stem and spinal cord to the thalamus
3) Third order neuron – takes information from the thalamus to the somatosensory cortex

Question 6

Decussation (crossing over) occurs in ____, where information from each side of the body is taken to the opposite side of the thalamus.

Answer 6

Second-order neuron

Question 7

Name the type of receptors in anterolateral (spinothalamic) pathways, and this pathway decussate in which region?

Answer 7

Receptors for pain, cold, warmth (temp), tickle, and itch

decussate in Medulla

Question 8

Name the type of receptors in Dorsal/ Posterior column– medial lemniscus pathway, and this pathway decussate in which region?

Answer 8

Receptors for touch, pressure, vibration, and proprioception

decussate in Midbrain

Question 9

Name the type of receptors in Trigeminothalamic tract, and this pathway decussate in which region?

Answer 9

Receptors for touch, pressure, vibration, pain, cold, warmth, itch, and tickle in the “face, nasal cavity, oral cavity, and teeth”

decussate in Pons and Medulla

Question 10

Name the four main types of pain

Answer 10

1) psychogenic pain- no physical cause, felt by mind only
2) nociceptive pain- arise from any body tissues apart from nerves (neuropathic pain)
3) neuropathic pain- arise from nerves
4) visceral pain- a type of nociceptive pain arise from stomach

Question 11

Name other classification of pain

Answer 11

1) according to type:
i) Intense pressure (e.g. caused by being struck or banging against something
ii) Tissue damage (due to a cut, bruise etc)
iii) Intense heat or cold

2) according to duration:
i) Acute pain
ii) Chronic pain

Question 12

Nociceptors (free nerve endings ) can be directly activated by:

Answer 12

• Heat or cold
• Intense pressure
• Chemical sLmuli
• Inflammatory mediators released from damaged tissue (cytokines,
bradykinin, serotonin, prostaglandins and H+

Question 13

Nociceptors can also be sensitised (i.e. acLon potenLals can be induced at lower levels of stimulation) by

Answer 13

inflammatory mediators

Question 14

Name the two types of nociceptive neurons.

Answer 14

1) Fast pain (typically sharp pain) - Aδ fibres Myelinated, large diameter, high conduction velocity

2) Slow Pain (typically ache) – C-fibres
Unmyelinated, small diameter, low conduction velocity

Question 15

Reason for referred pain.

Answer 15

Second order neurons are rarely specific for visceral pain.

Question 16

Explain the transmission and modulation of pain.

Answer 16

• The nociceptive neuron releases the neurotransmitter **GLUTAMATE at synapses in the spinal cord
» which causes an **“EPSP- excitatory post-synaptic potential” (and action potentials if the stimulus is great enough)

• One branch transmits the pain signal to the somatosensory cortex via the “spinothalamic pathway”

• Another branch transmits it to an
interneuron, and then to a motor
neuron

Question 17

Name the other type of descending neural pathway from the brain that can influence the sensation of pain- being subjective.

Answer 17

• originates in the “periaqueductal grey area” and forms synapses with interneurons in the spinal cord
• The descending neuron causes the interneuron to release the neurotransmitters ENKEPHALIN and GABA**
• These two neurotransmiiers have an *inhibitory effect on the transmission cell (taking the pain signal to the brain- thus feel less pain)

Question 18

Not only is there a descending influence from the brain, ____ receptors can also inhibit pain percepLon by activating the _____

Answer 18

touch receptors

spinal interneuron