Topic 5- – Somatosensory System

Question 1

What is somatosensation?

Answer 1

Somatosensation is the sensory information received from the skin and musculoskeletal system.

Question 2

What are the two major systems involved in somatosensation?

Answer 2

1) cutaneous system and
2) proprioceptive system

Question 3

What is the primary function of the cutaneous system in somatosensation?

Answer 3

Detection of mechanical stimuli.

Question 4

What is the primary function of the proprioceptive system in somatosensation?

Answer 4

The primary function of the proprioceptive system in somatosensation is the detection of pain and temperature.

Question 5

Five Types of Mechanoreceptors in the Skin +1 sensory receptor

Answer 5

Meissner’s corpuscles, Pacinian corpuscles, Merkel’s disks, Ruffini’s corpuscles + Free nerve endings

Question 6

Meissner’s Corpuscles: Location and Function

Answer 6

Location: Found in the superficial layers of the skin, particularly in the fingertips and lips (areas that dont have hair)
Detection: Sensitive to light touch, low-frequency vibrations, and changes in texture/pressure

Question 7

Pacinian Corpuscles:

Answer 7

Location: Located deeper in the skin.
Detection: Sensitive to deep pressure and high-frequency vibrations. They detect rapid changes in pressure or vibration

Question 8

Merkel Cells (Tactile Discs):

Answer 8

Location: Found in the epidermal-dermal junction of the skin, associated with nerve endings.
Detection:involved in the perception of light touch and the shape and texture of objects. shapes and edges.

Question 9

Ruffini Corpuscles:

Answer 9

Location: Situated in the deep layers of the skin.
Detection: Respond to sustained pressure and skin stretch.

Question 10

Free Nerve Endings:

Answer 10

Location: Distributed throughout the skin and various tissues.
Detection: These receptors are not specialized for any specific type of mechanical stimulus. Serve as nociceptors, responding to pain, and thermal receptors, detecting temperature changes.

Question 11

What determines the quantity or strength of a stimulus in somatosensory afferents?

Answer 11

The quantity or strength of a stimulus is determined by the rate of action potentials generated in response to the stimulus

Question 12

What determines the quality of a stimulus in somatosensory afferents?

Answer 12

The quality of the stimulus is determined The quality of a stimulus in somatosensory afferents is determined by the specific type of sensory receptor activated by the stimulus and the specific area in the central nervous system (CNS) that processes the sensory information

Question 13

How does deformation around a neuron affect sensory transduction?

Answer 13

Deformation changes ion permeability, leading to depolarization in the cell, setting up summation and excitatory post-synaptic potentials.

Question 14

Where are somatosensory afferent receptors typically located, and where is the cell body in this system?

Answer 14

Somatosensory afferent receptors are often located in the periphery, such as the skin. The cell body is in the dorsal root ganglion, situated outside the brain and spinal cord.

Question 15

What is sensory neuron adaptation?

Answer 15

If stimulus persists without change in position or amplitude, the intensity of that stimulus diminishes

Question 16

Where does sensory neuron adaptation occur?

Answer 16

Sensory neuron adaptation takes place in both the central nervous system (CNS) and the peripheral nervous system (PNS).

Question 17

What are the two main ways sensory receptors can adapt to a stimulus?

Answer 17

Sensory receptors can adapt in two main ways: slowly adapting (tonic signal) and rapidly adapting (phasic response).

Question 18

Why is the phasic response important in sensory perception?

Answer 18

The phasic response is crucial for informing you when something begins or ends, allowing you to perceive both static and dynamic qualities of a stimulus.

Question 19

What characterizes a rapidly adapting signal in receptor adaptation?

Answer 19

A rapidly adapting signal, known as a phasic response, bursts and diminishes quickly. It is essential for signaling the onset and cessation of a stimulus

Question 20

What is a tonic signal in the context of sensory receptor adaptation?

Answer 20

A tonic signal refers to a slow adaptation in which the receptor response persists as long as the stimulus is present

Question 21

What characterizes slowly adapting receptors in terms of their response to stimuli?

Answer 21

Slowly adapting receptors exhibit persistent depolarization and continuous action potentials in response to stimuli.

Question 22

What is the primary characteristic of rapidly adapting receptors?

Answer 22

Rapidly adapting receptors only respond to changes in the intensity of a stimulus, such as increases or decreases, but not to constant or persistent stimuli.

Question 23

Receptive Field

Answer 23

specific area on the sensory receptor or sensory neuron’s surface from which a response can be generated in response to an adequate stimulus.

Question 24

How does the number of mechanoreceptors associated with a neuron affect the field of response and the information sent to the CNS?

Answer 24

The more mechanoreceptors associated with a neuron, the wider the field of response. This, in turn, impacts how much sensory information the central nervous system (CNS) receives from the periphery.

Question 25

How is the sensitivity of a sensory system measured?

Answer 25

Sensitivity is measured through a concept called two-point discrimination: determines the minimum distance required to perceive two distinct stimuli.

Question 26

What factors influence the sensitivity of a sensory system?

Answer 26

The concentration of receptors and the size of the field of response are factors that influence the sensitivity of a sensory system.

Question 27

How does the size of the field of response impact sensitivity in a sensory system?

Answer 27

A larger field of response allows the system to detect stimuli over a wider area, while a smaller field of response limits sensitivity to a more localized region.

Question 28

How does a high concentration of receptors affect sensitivity in a sensory system?

Answer 28

A high concentration of receptors in a region increases sensitivity, making that area more responsive to stimuli.

Question 29

How does the depth of receptors in the skin affect the size of their receptive field?

Answer 29

Receptors closer to the surface have smaller receptive fields, while deeper receptors have larger receptive fields.

Question 30

What are muscle spindles?

Answer 30

Muscle spindles are sensory receptors located in skeletal muscles.

Question 31

What type of changes do muscle spindles signal?

Answer 31

Muscle spindles signal changes in the length of skeletal muscles.

Question 32

What kind of information do muscle spindles provide about the body?

Answer 32

Muscle spindles provide information about the relative positions of body segments.

Question 33

What is the role of proprioceptors in the body?

Answer 33

Proprioceptors are responsible for monitoring the mechanical forces generated by our own musculoskeletal system.

Question 34

What are the three main components of a muscle spindle?

Answer 34

Intrafusal muscle fibers.
Sensory afferent endings (Large Myelinated Sensory Endings ex: (Primary and Secondary Endings).
Efferent motor endings (Small Myelinated Motor Endings (ex: Gamma Motor Neurons):.

Question 35

What are intrafusal muscle fibers?

Answer 35

Intrafusal muscle fibers are specialized muscle cells within the muscle spindle that respond to changes in muscle length.

Question 36

What is the role of sensory afferent endings in a muscle spindle?

Answer 36

Sensory afferent endings are nerve endings that detect and transmit information about muscle length and changes to the nervous system.

Question 37

What is the role of efferent motor endings in a muscle spindle?

Answer 37

Efferent motor endings are nerve endings that innervate and regulate the sensitivity of intrafusal muscle fibers within the muscle spindle.

Question 38

What are the two main types of intrafusal muscle fibers?

Answer 38

The two main types of intrafusal muscle fibers are nuclear chain fibers and nuclear bag fibers.

Question 39

What are the subtypes of nuclear bag fibers, and how are they classified?

Answer 39

Nuclear bag fibers have two subtypes: dynamic bag fibers and static bag fibers. They are classified based on their responsiveness to changes in muscle length.

Question 40

What sets dynamic bag fibers apart from static bag fibers?

Answer 40

Dynamic bag fibers monitor rate of change of length (type l whereas static bag fibers monitor the length of the muscle(type la and II)

Question 41

What are the two main types of sensory afferent endings in muscle spindles?

Answer 41

The two main types are the primary sensory ending (Group Ia, large, myelinated nerve fibers.) and the secondary sensory ending (Group II, smaller in diameter ).

Question 42

How does spindle density vary in different parts of the body?

Answer 42

Spindle density varies depending on the importance of movement accuracy needed for that area. Areas requiring fine motor skills, such as the hands, neck, and extraocular muscles of the eye, have a higher spindle density.

Question 43

What are muscle spindle receptors, and what happens when you stretch them?

Answer 43

Muscle spindle receptors are sensory nerve fibers wrapped around intrafusal muscle fibers. When you stretch them, their activity increases, leading to more action potentials.

Question 44

What is the effect of loading vs. unloading the muscle spindle?

Answer 44

Loading the muscle ( the muscle it is located in is stretched or put under tension.) spindle increases its sensitivityto changes in muscle length and responsiveness, while unloading it ( it means that the muscle it is located in is allowed to shorten or rela). decreases its sensitivity and responsiveness

Question 45

What is the function of gamma motor neurons in relation to muscle fibers?

Answer 45

Gamma motor neurons connect from the spinal cord to intrafusal muscle fibers, extending from the central nervous system (CNS) to the periphery.

Question 46

How do dynamic gamma motor neurons affect the sensitivity of muscle spindles?

Answer 46

Dynamic gamma motor neurons are responsible for increasing the sensitivity of primary sensory endings in muscle spindles (sensory receptors become more responsive to changes in muscle length,_

Question 47

What happens to the sensory ending (Ia) in the muscle spindle when the muscle stretches and contracts?

Answer 47

When the muscle stretches, the sensory ending (Ia) becomes excited, but it becomes less active when the muscle contracts. Gamma motor neurons help maintain its sensitivity during muscle contractions.

Question 48

What is alpha-gamma co-activation, and why is it important?

Answer 48

Alpha-gamma co-activation is the simultaneous activation of both alpha motor neurons (which control extrafusal muscle fibers responsible for force generation) and gamma motor neurons (which control intrafusal muscle fibers within muscle spindles) to ensure that muscle spindles remain sensitive during muscle contraction,

Question 49

What occurs when the muscle is contracted, and how does it affect the muscle spindle?

Answer 49

When the muscle is contracted, the muscle spindle becomes “saggy” and insensitive, leading to reduced Ia afferent output.

Question 50

What effect do static motor efferent neurons have on muscle spindle activity?

Answer 50

Static motor efferent neurons increase tonic activity in both primary and secondary endings of the muscle spindle ( making them more sensitive to maintain awareness of muscle length and position )

Question 51

How do static gamma motor efferents influence tonic activity in muscle spindles?

Answer 51

Static gamma motor efferents can change the tonic activity in muscle spindles.

Question 52

Why is coordination with the alpha motor system important for static gamma motor efferents?

Answer 52

Coordination with the alpha motor system is crucial to ensure that the tonic information provided by muscle spindles remains accurate and reliable

Question 53

What is the role of Golgi Tendon Organs (GTOs) in relation to muscle fibers?

Answer 53

Golgi Tendon Organs (GTOs) sit in series with muscle fibers and measure force generated by muscles.

Question 54

How does the activity of GTO afferents change with increasing muscle force?

Answer 54

As the force generated by active muscles increases, the afferent activity of GTOs going into the spinal cord also increases, resulting in a higher action potential rate.

Question 55

Is the relationship between GTO activity and force linear or non-linear?

Answer 55

The relationship between GTO activity and force is non-linear. The action potentials generated are not directly proportional to the amount of force produced.

Question 56

What’s the main job of Golgi Tendon Organs in muscle activity signaling?

Answer 56

Golgi Tendon Organs primarily signal changes in muscle force rather than giving an exact measure of constant muscle contractions. They inform the brain about how things are changing in the limbs, not the exact force.

Question 57

What are slow-adapting mechanoreceptors?

Answer 57

Slow-adapting mechanoreceptors, such as Ruffini endings and Merkel cells, maintain a continuous response to constant stimuli, making them suitable for sensing prolonged pressure, skin stretch, and limb position.

Question 58

What are rapidly adapting mechanoreceptors?

Answer 58

Rapidly adapting mechanoreceptors, like Meissner’s corpuscles and Pacinian corpuscles, respond strongly to changing stimuli but quickly stop responding to constant stimuli, helping detect fast touch or pressure changes.

Question 59

Describe the process of sensory transduction in somatosensory afferents

Answer 59

) Stimuli applied to skin changes the shape of receptor
2) This deformation triggers receptor potential through mechanical ion channels, leading to cell depolarization.
3) If the summation of excitatory postsynaptic potentials (EPSPs) in the trigger zone reaches the threshold, an action potential is generated.
3) AP travel down dorsal root ganglion sensory afferent to CNS​
4) The type of sensation (pressure, stretch, vibration) is determined by the specific receptor properties.