Sensory and Proprioception: Module 3.1-3.2

Question 1

What type of information is Sensory Input?

Answer 1

Afferent

Question 2

What type of information is motor output?

Answer 2

Efferent

Question 3

Are autonomic neurons affernet or efferent?

Answer 3

Both

Question 4

What are the different sensory systems and their receptor classes and cells?

Answer 4

Question 5

What are sensory modalities?

Answer 5

Include the familiar ones of seeing, hearing, touching, smelling, and tasting as well as our senses of pain, balance, body positionk and movement.

Also, intricate sensory systems of which we are not conscious monitor the internal milieu and report on the body’s chemical and metabolic state.

Question 6

Sensory receptors convert ____ into ____.

Answer 6

Sensory receptors convert environmental energy into neural signals.

Question 7

What are the 3 major functions of the somatosensory system?

Answer 7

1. Proprioception (Sense of Onself): Receptors in skeletal muscle, joint capsules, and the skin generated a conscious awareness of the posture and movements.
2. Exteroception (Direct Interaction with External World): Sensory Modalities = Touch, Pain
3. Interoception (Sense of the function of the major organ systems/internal state): Primarily Chemoreceptors (Blood Gases and pH)

Question 8

What are the primary sensory afferent cells of the somatosensory system?

Answer 8

DRG (Dorsal Root Ganglia) Neurons

The cell bodies of neurons tha tbring sensory information from the skin muscles, and joines lie in the DRG.

Question 9

Where is the DRG located?

Answer 9

Found adjacent to the spinal cord.

The neurons are bifurcated into peripheral and central branches. the central branch enters the dorsal portion of the spinal cord.

Question 10

What are the 5 functional zones of the DRG?

Answer 10

1. Distal Terminals: contain specialized receptor-channels that convert specific types of stimulus energy (mechanical, thermal,, or chemical) into a depolarizing receptor potential (graded potential).
2. Spike Generation Site: Contains Nav and Kv channels, located near the initial segment of the axon. conversion of the receptor potentials in APs.
3. Peripheral Nerve FIber (Branch): Transmits action potentials from the spike initiation site to the DRG cell body.
4. Cell Body: Contained within DRGs
5. Spinal or Cranial Nerve: Connects the DRG or trigeminal neuron to the ipsilateral spinal cord of brain stem.

Question 11

DRG neurons are _____.

Answer 11

DRG neurons are pseudo-unipolar.

Question 12

What is the function of the Thalamus?

Answer 12

The Thalamus links sensory receptors and the cerebral cortex for all modalities exept olfaction.

Also Acts as a gatekeeper for information to the cerebral cortex, prevening or enhancing the passage of speciic information depending on the behavioral state of the animal.

Question 13

What nerves do Vision and Taste sensory input use?

Answer 13

Cranial Nerves

Question 14

What nerves do Somatosensory input use?

Answer 14

Spinal Nerves

Question 15

What are the 2 pathways in which somatosensory information from the limbs and trunk ascend from?

Answer 15

1. Dorsal Column-medial lemniscal system.
2. Anterolateral System

Question 16

Explain the Dorsal Column Medial Lemniscal System.

Answer 16

Touch and limb proprioception signals are conveyed to the spinal cord and brain stem by large-diameter myelinated nerve fibers and transmitted to the thalamus. The second order fibers, cross the midline in the medulla and ascend in the contralateral medial lemniscus toward the thalamus, where they terminate in the lateral and medial ventral posterior nuclei (tactile and proprioceptive information).

Question 17

Explain the Anterolateral System.

Answer 17

Pain, itch, temperature, and visceral information is conveyed to the spinal cord by small diameter myelinated and unmyelinated fibers that terminate in the ipsilateral dorsal horn. Second order neurons cross the midline and transmit to the brain stem and the thalamus in the contralateral anterolateral system.

Question 18

How is the somatosensory cortex organized?

Answer 18

Somatotopically Organized

Amount of surface area of cortex devoted to each body part proportional to density of innvervation of sensory fibers (fineness of discrimination in the body).

Lower limb sensation is mediated by neurons near the midline of the brain. Sensations from the upper body are mediated y neurons located laterally.

Question 19

How are sensory nerves classified?

Answer 19

Classified into functional groups based on properties related to axon diameter and myelination, conduction, velocity.

Question 20

What are the different classification of sensory fibers?

Answer 20

Question 21

What do the different types of fibers innervate and how are they activated?

Answer 21

Aa: in muscle, nerves innervate muscle spindle receptors and Golgi tendon organs (proprioception).

AB: innvervate secondary spindle ending and receptors in joint capsules (proprioception).

AD: the smallest myelinated muscle afferents.

C Fiber: signal trauma or injuries in muscle and joints that are sensed as painful

Aa and AB activation are barely perceptible and involved in proprioception. Larger Nerve shocks will activate all types of fibres.

Question 22

Activation of what fibers result in pain?

Answer 22

Ad and C fibers.

Question 23

Neuronal communication depends on PSP with ligand gated channels

What does sensory transduction depend on?

Answer 23

Receptor Potentials mediate by the effect of an environmental stimulus acting on a receptor molecule.

Question 24

What type of channels are many types of sensory transduction mediated by?

Answer 24

TRP Channels (Transient Receptor Potential)

Question 25

What are TRP Channels and its characteristics?

Answer 25

Thermal Receptors

Plays central roles in sensory transduction pathways (pain, itch, heat, taste, and touch).

Genetic subfamily: vanilloid (V), melastatin (M), and ankyrin (A).

• Are cation non-selective channels, composed of 4 subunits (tetramers), each containing 6 transmembrane domains. The pore region is between S5 and S6. May be permeable to Ca.
• Some (TRPV1 and TRPM8) have a voltage-sensor.
• TRPs are tetramers (4 subunits)
• Different sensitivity to heat or cold.

Question 26

What can TRP channels can be activated by?

Answer 26

Question 27

What is proprioception and how does it work?

Answer 27

Sense of Onself

Receptors in skeletal muscle, and joint capsules, and the skin enable us to have conscious awareness of the posture and movements of out own body, particularly the four lumbs and the head.

Measures activity and joint positions.

Question 28

Can people move body without sensory propriceptor feedback?

Answer 28

Yes, however movements are clumsy if there is no visual aid.

Question 29

Where do group 1 and 2 sensory muscle fibers innervate and what are they sensitive to?

Answer 29

Group I: in muscle nerves innervate muscle spindle receptors and Golgi tendon organs (proprioception). Group II: innervate secondary spindle endings and receptors in joint capsules (proprioception).

Question 30

What are muscle spindles?

Answer 30

Small encapsulated sensory receptors.

They signal changes in the length of the muscle in which they reside.

They sense changes in length associated to changes in joint angles that the muscle cross.

Muscle spindles are used by the central nervous system to sense relative positions of the body.

Question 31

The Muscle Spindles run ____ to the extrafusal muscle fibers.

Answer 31

The Muscle Spindles run parallel to the extrafusal muscle fibers.

Question 32

What are the 3 components of Muscle Spindle?

Answer 32

1. A group of specialized intrafusal muscle fibers with noncontractile central reigions.
2. Sensory fibers that terminate on the cntral regions of the intrafusal fibers
3. Motor axons that terminate on the contractile polar regions of the intrafusal fibers.

Question 33

What type of neuron adjusts the sensitivity of muscle spindles?

Answer 33

Gamma Motor neurons

Question 34

The CNS can independently adjust the ____ and ____ sensitivity of sensory endings.

Answer 34

The CNS can independently adjust the dynamic and static sensitivity of sensory endings.

Question 35

Explain the loading and unloading of muscle spindle.

Answer 35

Stretching a muscle, stretches the intrafusal fibers, which also stretches the sensory
endings, which increase their firing.

When a muscle shortens, the spindle is unloaded and the activity decreases.

The intrafusal muscle fibers are innervated by gamma motor neurons (small-diameter myelinated axons). Activation of gamma motor neurons causes shortening of the polar regions of the intrafusal fibers. This in turn stretches the central region from both ends, leading to an increase in firing rate of the sensory axons or to a greater likelihood that the axons will fire in response to stretch of the muscle.

Question 36

Activation of Gamma motor neurons during active muscle contraction ____ muscle spindle ____ to muscle length.

Answer 36

Activation of Gamma motor neurons during active muscle contraction maintains muscle spindle sensitivity to muscle length.