Somatosensation

Question 1

What are the nerves that receive somatosensory
inputs (soma- referring to the body, in the same
way the cell body is also called the soma)?

Answer 1

somatic nervous system

Question 2

What does the somatic nervous system do?

Answer 2

give us the ability to detect information
about the body

Question 3

What does the somatic nervous system sense?

Answer 3

These nerves can sense a wide variety of physical stimuli, including pressure,
stretch, vibration, heat, and pain.

Question 4

What is labelled line
principle?

Answer 4

When sources of information are carried in separate but parallel paths

Question 5

What is somatotopic organization?

Answer 5

specific points on the body map to specific neural populations

Question 6

What is the somatosensory homunculus?

Answer 6

The somatosensory homunculus shows which parts of the body are heavily represented in the somatosensory cortex, like the hands or mouth. This observation indicates that certain areas of the body are more densely packed (lips, fingertips) with sensory neurons compared to others (shoulders, trunk).

Question 7

What are Cutaneous mechanoreceptors?

Answer 7

responsible for sensing mechanical changes to the skin, such as pressure or stretch.

Question 8

How do mechanoreceptors detect changes at the skin?

Answer 8

Using mechanically-gated ion channels. These
transmembrane proteins are specialized for
detecting the physical distortion of the channel,
similar to the channels found in the stereocilia of
the hair cells or vestibular cells. When pressure
is applied to these proteins, the cation channel
opens and Na+ moves down its electrochemical
gradient into the neuron, causing depolarization.

Question 9

What is slowly-
adapting mechanoreceptors?

Answer 9

Slowly-adapting mechanoreceptors change their action potential
firing rate as long as the stimulus is present. For example, imagine the stimulus of a coin that is sitting in the palm of your hand. The
slowly-adapting sensory neurons may increase
their firing rate as long as the coin is in your
palm.

Question 10

What is rapidly-
adapting mechanoreceptors?

Answer 10

Rapidly-adapting mechanoreceptors only
change activity at the moment there is a change
in stimulus. A rapidly-
adapting sensory neuron will change its action potential firing properties only at two timepoints:
the moment the coin lands in your hand, and the
moment that coin is removed.

Question 11

What are tonic receptors?

Answer 11

When they return to their baseline firing rate

Question 12

What’s the difference between slowly-adapting mechanoreceptors and rapidly-adapting mechanoreceptors?

Answer 12

Slowly-adapting mechanoreceptors
modify their action potential firing as long as
a stimulus is present, while rapidly-adapting
mechanoreceptors do so only at the moments
when a stimulus is changed.

Question 13

What are thermoreceptors?

Answer 13

they are the cutaneous
receptors that sense temperature.

Question 14

what are low-threshold
thermoreceptors?

Answer 14

they detect innocuous, non harmful temperatures in the range of 15 to 45 degrees C.

Question 15

what are High-threshold thermoreceptors?

Answer 15

they detect painful
and potentially damaging temperatures hotter
than 45 C or colder than 15 C.

Question 16

Where are thermoreceptors located?

Answer 16

Thermoreceptors are located in a class of cutaneous receptors called free nerve endings.

Question 17

What are free nerve endings?

Answer 17

Compared to the mechanoreceptors, free nerve
endings are found closest to the surface of the
skin. Like mechanoreceptors, the free nerve
endings are the sensory end of the pseudounipolar
neurons which have their cell somata in the dorsal
root ganglion.free nerve
endings are found closest to the surface of the
skin.

Question 18

Which receptor detects cold sensations and how are they activated?

Answer 18

TRPM8 - activated by menthol, a chemical isolated from peppermint that produces a cooling sensation.

Question 19

Which receptor detects warm sensations and how are they activated?

Answer 19

TRPV1 - activated by the
chemicals capsaicin, the compound that makes
spicy peppers feel hot, and allyl isothiocyanate,
which is found in wasabi.

Question 20

How are pain detection carried out?

Answer 20

nociceptors - detect a variety of noxious stimuli, ranging from crush to acid and high heat. expressed on free nerve endings

Question 21

Many pain-detecting neurons respond to more
than one type of noxious stimulus, and these are
called…?

Answer 21

polymodal nociceptors

Question 22

What are cation
channels that respond to low pH conditions in the
dermis, which is usually seen in inflammation,
which is often downstream of tissue injury?

Answer 22

Acid-sensing ion channels

Question 23

Imagine you are reaching into your
bookbag, and accidentally stick your fingertip
with the sharp end of a pencil. Within half a
second, the _______causes a series
of muscular changes which moves your hand
away from the pointy end.

Answer 23

withdrawal reflex

Question 24

How does the withdrawal reflex work?

Answer 24

This motor response
is driven by a circuit of neurons in the spinal
cord, and is mediated completely independently
from descending motor control from the brain.
The nociceptive input from the sensory neurons
enters the spinal cord through the dorsal horn
where it forms a synapse onto an excitatory
interneuron. This interneuron then signals to two
other populations.

Question 25

What is proprioception?

Answer 25

When your nervous system
has mechanisms that inform you about the
location and position of your body parts, including
how much your joints are bent.

Question 26

What are muscle spindles?

Answer 26

They are wrapped around the intrafusal skeletal
muscle fibers and are a series of nervous structures which detect the
status of the muscle. When a
skeletal muscle is flexed, it widens in diameter,
becoming shorter and thicker. the
muscle spindle wrapped around it also changes
in shape.

Question 27

How do the muscle spindles communicate?

Answer 27

The muscle spindles communicate this
information to the nervous system through the
action of nonselective-cation mechanoreceptors
that respond to physical distortion - muscle
stretching increases firing rate, while muscle
flexion decreases firing rate.

Question 28

What is the stretch reflex?

Answer 28

a spinal cord-
mediated response to muscle stretch that causes flexion to prevent excess stretching, which can
cause damage to the muscles.

Question 29

What is the knee-jerk reflex?

Answer 29

the patient sits on the end of the exam table with their knee
bent and their lower leg dangling freely over
the edge. The examiner uses a pointed rubber
hammer to gently tap on the tendon that connects
the kneecap (patella) to the muscle in front of the
shin bone. When tapped, it causes a stretch of the
quadriceps, the muscle on the top of the thigh.

Question 30

What are Golgi tendon organs?

Answer 30

Made up of collagen fibers, GTOs are
found at the insertion site between muscles
and tendons. Signals from the GTO convey
information about the amount of the tension that
each set of skeletal muscles is experiencing as
we move around.