T16. SOMATIC GENERAL SENSITIVITY

Question 1

What are somatic senses?

Answer 1

Somatic senses are nervous mechanisms that collect sensory information from all over the body;

Question 2

How are somatic senses classified by physiology?

Answer 2

• Mechanoreceptive → tactile and position sensations
• Thermoreceptive → detect heat and cold
• Pain senses → activated by tissue-damaging factors

Question 3

Whhat does general sensitivity means?

Answer 3

General sensibility refers to senses distributed throughout the body like temperature, position, and movement, using simple receptors such as sensory neurons and free nerve endings.

Question 4

How are somatic senses classified by structure?

Answer 4

They are classified as unencapsulated or encapsulated nerve endings.

Question 5

What are unencapsulated nerve endings?

Answer 5

Nerve endings not wrapped in connective tissue; include free nerve endings, Merkel (tactile) discs, and hair receptors.

Question 6

What do free nerve endings sense?

Answer 6

Pain and temperature; found in skin and mucous membranes.

Question 7

What do tactile (Merkel) discs sense?

Answer 7

Light touch and texture; located at the base of the epidermis.

Question 8

What do hair receptors sense?

Answer 8

Movement of hair; wrapped around the base of hair follicles.

Question 9

What are encapsulated nerve endings?

Answer 9

Dendrites wrapped by glial cells or connective tissue to enhance sensitivity or selectivity; used for touch and pressure receptors.

Question 10

What do Meissner (tactile) corpuscles sense?

Answer 10

Light touch and texture; encapsulated receptors.

Question 11

What do Krause end bulbs sense?

Answer 11

Touch in mucous membranes.

Question 12

What do Pacinian (lamellated) corpuscles sense?

Answer 12

Deep pressure, stretch, tickle, and vibration; located in the dermis (phasic receptors).

Question 13

What do Ruffini (bulbous) corpuscles sense?

Answer 13

Heavy touch, pressure, joint movement, and skin stretch (tonic receptors).

Question 14

What is a receptive field?

Answer 14

The area of skin that changes the firing rate of a single sensory neuron when stimulated.

Question 15

What determines receptive field size?

Answer 15

The density of receptors in the region—fewer receptors (e.g., back/legs) → larger field; many receptors (e.g., fingertips) → smaller field.

Question 16

What does a large receptive field mean?

Answer 16

Less precise stimulus detection due to overlap/interference of stimuli.

Question 17

What does a small receptive field mean?

Answer 17

Very precise detection of stimulus due to high receptor density.

Question 18

What is the two-point touch threshold?

Answer 18

A test measuring the smallest distance at which two separate touches are felt as distinct; indicates receptive field size.

Question 19

What happens if two points fall within one receptive field?

Answer 19

Both touches are perceived as one.

Question 20

What happens if two points fall in different receptive fields?

Answer 20

Both touches are perceived as separate.

Question 21

What is lateral inhibition in somatic senses?

Answer 21

The most strongly stimulated receptors inhibit neighboring receptors to create sharp, well-defined sensations.

Question 22

What is the role of proprioceptive senses?

Answer 22

They provide position sense essential for equilibrium and posture.

Question 23

What is the muscle spindle apparatus?

Answer 23

Stretch receptors within muscle bodies that convey muscle length information to the CNS.

Question 24

What are the sensory components of muscle spindles?

Answer 24

Primary type Ia (spiral around muscle) and secondary type II sensory fibers.

Question 25

What do muscle spindle sensory fibers detect?

Answer 25

Stretch of muscle fibers (length change).

Question 26

What are the motor components of muscle spindles?

Answer 26

Gamma motor neurons (up to a dozen) and a few beta motor neurons activate fibers within the spindle.

Question 27

What is the static response of muscle spindles?

Answer 27

Slow stretch activates both primary and secondary endings; sends stimuli over several minutes.

Question 28

What is the dynamic response of muscle spindles?

Answer 28

Quick stretch activates only primary endings; stimuli sent during the stretch.

Question 29

What is the myotatic reflex?

Answer 29

Reflex muscle contraction in response to muscle stretch detected by spindles.

Question 30

What are Golgi tendon organs?

Answer 30

Receptors that monitor muscle tension and trigger relaxation to avoid excessive tension.

Question 31

How do Golgi tendon organs work?

Answer 31

Tension activates sensory neurons → stimulate spinal interneurons → inhibit motor neurons → reduce tension.

Question 32

Where does somatic sensory information enter the spinal cord?

Answer 32

Sensory information enters through the dorsal horn.

Question 33

Where do motor commands exit the spinal cord?

Answer 33

Motor output exits through the ventral horn.

Question 34

What are thermoreceptive senses?

Answer 34

Sensory receptors that detect temperature changes.

Question 35

Where are cold receptors located?

Answer 35

Close to the epidermis; stimulated by cold and inhibited by warmth.

Question 36

Where are warmth receptors located?

Answer 36

Deeper in the dermis; excited by warm temperatures and inhibited by cold.

Question 37

What are heat receptors?

Answer 37

Nociceptors (pain receptors) that detect hot stimuli via capsaicin receptors (ion channels for Na⁺ and Ca²⁺).

Question 38

What activates capsaicin receptors?

Answer 38

Heat or chemicals like capsaicin from chili peppers.

Question 39

What are nociceptors?

Answer 39

Pain receptors activated by chemicals from damaged tissues.

Question 40

What types of neurons transmit pain?

Answer 40

Myelinated neurons (Type III-A) for sharp pain; unmyelinated (Type IV-C) for dull, persistent pain.

Question 41

What are somatic pain receptors?

Answer 41

Pain from skin, muscles, and joints.

Question 42

What are visceral pain receptors?

Answer 42

Pain from organ stretch, chemical irritation, or ischemia—poorly localized.

Question 43

How is pain inhibited in the CNS?

Answer 43

Inhibitory interneurons prevent weak pain signals from reaching the brain unless strong pain inhibits them.

Question 44

How can pain be modulated?

Answer 44

Non-painful stimuli activate interneurons that reduce the perception of pain.

Question 45

What is referred pain?

Answer 45

Pain felt in skin from internal organ issues due to neural convergence (e.g., heart attack pain in arm).

Question 46

What is convergence theory of referred pain?

Answer 46

Visceral and somatic neurons share pathways; the brain misinterprets visceral pain as coming from the skin.

Question 47

What is the somesthetic (somatosensory) projection pathway?

Answer 47

Pathway from receptor to brain, usually involving 3 neurons: 1st order, 2nd order, and 3rd order.

Question 48

What is the 1st order neuron in somesthetic pathway?

Answer 48

Afferent neuron from body enters dorsal horn via spinal nerves; from head enters pons/medulla via cranial nerves.

Question 49

What is the 2nd order neuron in somesthetic pathway?

Answer 49

Decussates (crosses) to the opposite side in spinal cord, pons, or medulla; ends in thalamus (except proprioception, which ends in cerebellum).

Question 50

What is the 3rd order neuron in somesthetic pathway?

Answer 50

From thalamus to primary somesthetic cortex (postcentral gyrus of the cerebrum).

Question 51

Where does sensory decussation occur?

Answer 51

At the level of the spinal cord, pons, or medulla—opposite side of entry point.

Question 52

What is the somatosensory homunculus?

Answer 52

Brain representation of sensory input distribution across body regions.