Lecture 16

Question 1

What is the function of Meissner’s Corpuscles?

Answer 1

• In hairless areas mostly
• Fine touch
• Pressure
• Vibration

Question 2

What is the function of Pacinian corpuscles?

Answer 2

• In all skin (deeper), interosseous membranes, viscera
• Deep pressure
• Vibration
• Large receptive fields

Question 2

What is the function of Ruffini endings/corpuscles?

Answer 2

• In all skin (deeper)
• Deep pressure
• Skin stretch

Question 2

What is the function of Merkel’s discs/corpuscles?

Answer 2

• Fine touch
• Small receptive fields
• Info about shape and texture

Question 3

What are Proprioceptors crucial for?

Answer 3

• Stretch reflex
• Tension reflex
• Planning and monitoring movement

Question 4

List the 4 features of a stimulus

Answer 4

• Modality
• Intensity
• Duration
• Location

Question 5

Explain Modality

Answer 5

Type receptor which was activated

Question 6

Explain Intensity

Answer 6

Frequency of action potentials in sensory axon

Question 7

Explain Duration

Answer 7

Pattern and length of action potentials to end or begin a stimulus

Question 8

Explain Location

Answer 8

Spatial mapping to somatosensory cortex (receptive field)

Question 8

What is the primary role of the somatosensory system?

Answer 8

To provide the brain with information about the body’s internal state and external environment, supporting behavior and homeostasis

Question 8

Which types of sensations are processed by the somatosensory system?

Answer 8

• Touch
• Pressure
• Vibration
• Proprioception
• Pain
• Temperature
• Chemical stimuli

Question 9

What types of sensory information are not processed by the somatosensory system?

Answer 9

Special senses—vision, hearing, balance, taste, and smell

Question 10

What are mechanoreceptors responsible for detecting?

Answer 10

• Touch
• Vibration
• Pressure
• Proprioception

Question 11

What do thermoreceptors detect?

Answer 11

Changes in temperature

Question 12

What stimuli activate nociceptors?

Answer 12

• Mechanical
• Thermal
• Chemical noxious stimuli (pain)

Question 13

What is the role of proprioceptors?

Answer 13

To provide information about limb position and movement

Question 14

What do chemoreceptors detect in the body?

Answer 14

Chemical composition, such as blood gases (O₂, CO₂, H⁺)

Question 15

What is a receptive field?

Answer 15

The area in which a stimulus will activate a sensory neuron

Question 16

How does receptive field size affect sensory discrimination?

Answer 16

Smaller fields = better location discrimination

Question 17

What is the function of lateral inhibition?

Answer 17

• Increase the accuracy of sensory information
• Localises sensation to a restricted area of skin

Question 18

What is the somatotopic map (homunculus)?

Answer 18

A cortical map representing the body, with larger areas for regions with high receptor density

Question 19

Is the somatotopic map fixed or changeable?

Answer 19

It is plastic; changes with use or injury (e.g. musicians, amputees)

Question 20

Which pathway carries fine touch and vibration?

Answer 20

Dorsal Column Pathway

Question 21

Where does the dorsal column pathway cross the midline?

Answer 21

In the Medulla

Question 22

What is the order of neurons in the dorsal column pathway?

Answer 22

Receptor → Medulla → Thalamus → Somatosensory Cortex

Question 23

Which sensations are transmitted via the anterolateral (spinothalamic) pathway?

Answer 23

- Pain - Temperature - Some touch

Question 24

Where does the anterolateral pathway cross the midline?

Answer 24

In the Spinal Cord

Question 25

What is the order of neurons in the anterolateral pathway?

Answer 25

Receptor → Spinal Cord → Thalamus → Somatosensory Cortex

Question 26

What do Myelinated axons detect?

Answer 26

Temperature

Question 27

What do Unmyelinated or Thinly Myelinated axons detect?

Answer 27

- Nociceptors - Mechanical - Thermal - Chemical

Question 28

Where are Mechanoreceptors located?

Answer 28

- Muscles and tendons - Stretch receptors in skin (Ruffini endings)

Question 29

What do Interoceptors/Visceroceptors include?

Answer 29

- Mechanoreceptors (eg bladder distension) - Chemoreceptors (eg blood gases) - Nociceptors – visceral pain (eg intestine/bladder distension)

Question 30

List the 2 types of Chemoreceptors

Answer 30

1) Peripheral Chemoreceptors 2) Central Chemoreceptors

Question 31

Describe Peripheral Chemoreceptors

Answer 31

- Aortic & carotid bodies detect pCO2, and [H+], (and O2) in blood - Crucial in control of breathing

Question 32

Describe Central Chemoreceptors

Answer 32

- On surface of medulla - Detect pH of CSF

Question 33

What types of axons are present in Skin Mechanoreceptors?

Answer 33

Myelinated

Question 34

Where are the receptors in the Sensory Unit?

Answer 34

Peripheral processes (dendrite) - Span of receptive area = receptive field - Nerve ending can be free or encapsulated

Question 35

Where is the Cell body in a sensory unit?

Answer 35

Dorsal root ganglia, or cranial nerve ganglia

Question 36

Where does the Central Process enter?

Answer 36

CNS

Question 37

What does the Sensory Unit release?

Answer 37

Neurotransmitters into synapses between sensory unit and secondary sensory neuron (Location of synapse depends on type of signal being transduced)

Question 38

What is Receptor Adaptation?

Answer 38

A decrease in receptor sensitivity - Decrease in action potential frequency in afferent neuron despite continuous presence of stimulus

Question 39

What are Rapidly adapting receptors important for monitoring?

Answer 39

- Rapidly moving or changing sensory stimuli (eg vibration) - Persistent stimuli that don’t need to be monitored closely

Question 40

What are Slowly adapting receptors important for monitoring?

Answer 40

Stimuli that need to be constantly monitored (eg muscle and joint receptors for maintaining balance)

Question 41

What does Receptor ending overlap lead to?

Answer 41

Activity being triggered in multiple sensory units

Question 42

What is Lateral Inhibition mediated by?

Answer 42

Inhibitory interneurons

Question 43

When is Lateral Inhibition used?

Answer 43

When accurate location of stimulus is required

Question 44

What sensations does the Dorsal Column Pathway (DCP) carry?

Answer 44

Fine touch and Vibration

Question 45

What happen to the 1st neuron in the DCP?

Answer 45

Axons enter dorsal roots and ascend in the spinal cord **dorsal columns** to make synaptic contact on neurons in the **medulla**

Question 46

What happen to the 2nd neuron in the DCP?

Answer 46

Neurons in the **medulla** project **across the midline** to ascend to the **thalamus**

Question 47

What happen to the 3rd neuron in the DCP?

Answer 47

Thalamic neurons project to somatosensory cortex

Question 48

What happen to the 1st neuron in the AP?

Answer 48

Axons enter via dorsal root and synapse on neurons in spinal cord

Question 49

What happen to the 2nd neuron in the AP?

Answer 49

Spinal cord neurons project across the midline and ascend to neurons in the **thalamus**

Question 50

What happen to the 3rd neuron in the AP?

Answer 50

Thalamic neurons project to somatosensory cortex

Question 51

Where does the Somatosensory information from the head and face enter through?

Answer 51

The brainstem directly via the cranial nerves