Lecture 17, Sensory Physiology (part 2)

Question 1

General Senses: Touch

Answer 1

stimulation of mechanoreceptors within the skin allow for the sensation of touch and pressure
◦ highly sensitive nerve endings that are
encapsulated in cellular structures
◦ some are slow-adapting and some are fast
adapting
- touch sensations provide information about shape or texture (if something is rough vs smooth)
- pressure sensations provide information about the degree and frequency of mechanical distortion (how much then skin of your tissue is distorted)
- there are millions of mechanoreceptors within the body, with the greatest diversity found in the skin

Question 2

tactile (meissner’s) corpsucles

Answer 2

• fine touch and pressure, and low-frequency vibration -
• phasic receptors

Question 3

tactile disks (merkel cells)

Answer 3

• fine touch and pressure
• very small receptive fields
• extremely sensitive tonic receptors

Question 4

lamellated (pacinian) corpuscles

Answer 4

• deep pressure, and high-frequency vibration
• phasic receptors

Question 5

ruffini corpuscles

Answer 5

• pressure and stretch of deep layers of the skin
• tonic receptors (very little adaptation)

Question 6

free nerve endings

Answer 6

◦ touch, pressure, pain and temperature
◦ the most abundant in the skin
◦ are tonic or phasic receptors
◦ either tonic or phasic receptors

Question 7

root hair plexuses

Answer 7

◦ monitors movement and distortion across the body surface
◦ when a hair is displaced, movement of the hair follicle distorts the sensory receptor and initiates a receptor potential
◦ phasic receptors

Question 8

General Senses: Pain

Answer 8

stimulation of nociceptors are activated by signals of tissue damage or potential tissue damage (mechanical deformation, temperature extremes, chemicals)
* free axon terminal of small-diameter afferent neuorn
* myelinated type A fibers provide sensations of fast pain or prickling pain
* unmyelinated type C fibers provide sensations of slow, burning or aching pain
referred pain: when the sensation of pain is experienced/perceived at a site other than the damaged tissue
* occurs because visceral and somatic afferents converge on the same interneurons within the spinal cord
* ex. during heart attack come in presenting with chest pain, back pain, arm pain (in other areas) - giving us sensations of the heart

Question 9

analgesia

Answer 9

hyperalgesia: hypersensitivity to painful stimuli
analgesia: the suppression of pain without effects on consciousness or other sensations
* inhibition of the pain signal transduction pathway
* during shock-induced analgesia, the body releases endogenous opioids, which block the transmission of the signal from the nociceptor to high centers of the CNS
* can also be induced via electrical stimulation of certain regions of the CNS
* is also thought to be the mechanism behind the pain-relieving effects of acupuncture
* shock prevents you from feeling extreme pain so you can still function

Question 10

General Senses: Temperature

Answer 10

temperature stimuli are sensed by small-diameter afferent neurons with little to no myelination (similar to nociceptors)
- originate in tissues as free nerve endings
the membrane of thermoreceptors contain ion channels that are directly responsive to changes in temperature
- these proteins are called transient receptor potential (TRP) proteins
- opening of TRP proteins causes an influx of ions (either Ca2+ or Na2+), inducing a change in the receptor potential
some TRP proteins are also sensitive to some chemicals
- capsaicin is a chemical found in chilli peppers interacts with TRP proteins and provides the sensation of warmth
- menthol is a chemical found in mint leaves interacts with TRP proteins and provides a cooling sensation

Question 11

General Senses: Proprioception

Answer 11

• proprioception refers to the signals our body provides about our position in space
  golgi tendon organs are mechanoreceptors that are located within the tendon of skeletal muscles
• GTOs are activated by deformation of the tendon, which occurs during muscle stretch and during muscle contractions
• provide information about the length of the muscle, which can be used to contribute to our perception of body position

muscle spindles stretch receptors are located within the skeletal muscle (are also activated muscle stretch (mechanical deformation), and monitor the rate of change in muscle length)

Question 12

General Senses: Proprioception (2)

Answer 12

• when a muscle is stretched or is undergoing a contraction, tension is exerted on the tendon
  ◦ causes distortion of the golgi tendon organs
• the tension exerted on a tendon tends to be greater during a muscle contraction than during a passive stretch
• the action potentials initiated from golgi tendon organs provide a lot of information enables for the conscious perception of muscle force

Question 13

Special Senses: Sight

Answer 13

the eye is a spherical structure that is composed of three layers, and is filled with fluid
* the outer layer is the sclera, which is a white, dense connective tissue capsule
◦ is the insertion point for muscles that move the
eye
* the second layer is the choroid, which forms the iris on the anterior aspect
* the inner layer of the eye is the retina, which contains photoreceptors that are activated by specific wavelengths of light

Question 14

cornea

Answer 14

clear dense area of the sclera at the anterior side of the eye that allows for light to reach the lens

Question 15

iris

Answer 15

coloured part of the eye that allows for pupillary dilation or constriction

Question 16

ciliary muscle

Answer 16

controls the shape of the lens, allowing for the eye to focus on objects

Question 17

Refraction of Light

Answer 17

light is electromagnetic radiation that travels in waves through space. different wavelengths of light are perceived as different colours
when light crosses from one medium (like air) to a denser medium (like glass or the cornea of your eye), the direction of the light changes
* the change in direction depends on the density of the medium, and the angle that the light hits the medium
* refraction of light is what allows the eye to focus an accurate image of an object onto the retina, where it can be sensed by photoreceptors
light is refracted so that it can converge at one point on the retina

Question 18

cililary muscles - distance, out of focus and in focus

Answer 18

cililary muscle control the shape of the lens
* objects at a distance do not need as much ciliary muscle contraction for proper focusing
* objects that are closer to that eye will converge at a location posterior to the retina, without ciliary muscle contraction (improper focusing)
* ciliary muscle contraction changes the shape of the lens, allowing the refracted light to converge at the retina (proper focusing)

Question 19

Myopia and Hyeropia

Answer 19

myopia is also known as nearsightedness
- due to the length of the eyeball, light converges anterior to the retina (elongated)
- can be corrected with a concave lens
hyperopia is also known as farsightedness
- due to the length of the eyeball, light converges posterior to the retina (more shorter in length)
- can be corrected with a convex lens

Question 20

Special Senses: Sight

Answer 20

the retina is an extension of the CNS, and contains an abundance of photoreceptors
- function: transducing light stimuli into signals that can be interpreted as visual information

there are two types of photoreceptors:
- rods - extremely sensitive photoreceptors that are active during dimly-lit environments
- cones - less sensitive photoreceptors that respond to very bright stimuli
- day-to-day we have a good balance between both
photoreceptors are supported by several different cell types in the retina that provide metabolic support and colour enhancement

Question 21

information passed through eye (path)

Answer 21

• sensory information is passed from photoreceptors in the retina to retinal ganglion cells
• the axons of retinal ganglion cells leave the retinal through the optic disk to the optic nerve, where it is relayed to the visual cortex
  ◦ the optic disk contains no photoreceptors r
  resulting in normal blind spot in your eye
• the macula lutea is a region of the retina that is relatively free of blood vessels
  ◦ within it is the fovea centralis, which contains a
  high density of cones
  ◦ the fovea centralis provides very high acuity;
  sharp central vision (very important for tasks like
  reading, driving, writing)
• like other sensory receptors, photoreceptors are also adaptable
  ◦ light adaptation vs dark adaptation

Question 21

information passed through eye (path)

Answer 21

• sensory information is passed from photoreceptors in the retina to retinal ganglion cells
• the axons of retinal ganglion cells leave the retinal through the optic disk to the optic nerve, where it is relayed to the visual cortex
  ◦ the optic disk contains no photoreceptors r
  resulting in normal blind spot in your eye
• the macula lutea is a region of the retina that is relatively free of blood vessels
  ◦ within it is the fovea centralis, which contains a
  high density of cones
  ◦ the fovea centralis provides very high acuity;
  sharp central vision (very important for tasks like
  reading, driving, writing)
• like other sensory receptors, photoreceptors are also adaptable
  ◦ light adaptation vs dark adaptation