Sensory Physiology

Question 1

What is the purpose of senses?

Answer 1

1. Provide information about an environment (temperature, osmolarity, light)
2. Provide information about ourselves (energy storage, temperature, water ion balance)

Question 2

What are types of conscious senses?

Answer 2

Special senses: Vision, hearing, taste, smell, balance

Somatosensory: Touch (texture vibration), temperature, pain/itch, proprioception

Question 3

What is proprioception?

Answer 3

Awareness of limb position with or without movement.

Question 4

What are types of unconscious senses?

Answer 4

Somatic senses: muscle tension, proprioception

Visceral senses: Blood pressure, GI distension (swelling of belly), glucose, osmolarity, O2/CO2 content, etc.

Question 5

What are the 5 general properties of sensory systems?

Answer 5

1. Receptors are most sensitive to certain forms of energy/stimuli
2. Sensory transduction converts stimuli to graded potentials
3. Sensory neurons have receptive fields
4. CNS integrates sensory information
5. Coding and processing distinguish stimulus properties

Question 6

What are 4 major groups of receptors WRT stimulus specificity?

Answer 6

1. Chemoreceptors: respond to binding of ligands
2. Mechanoreceptors: respond to mechanical energy (pressure, vibration, gravity sound)
3. Thermoreceptor: respond to temperature
4. Photoreceptors: respond to light

Question 7

What are the differences between simple, complex and special sensory receptors

Answer 7

Simple: free nerve endings

Complex: nerve ending ensheathed with connective tissue.non-neuronal accessory cells

Special: specialized receptor cell synapses with sensory neurons.

Question 8

What are two ways that allow conversion of stimuli into graded potentials via transduction?

Answer 8

1. Opening or closing of ion channels converts energy directly into a change in membrane potentials
2. Transduction via signal transduction and second messenger systems initiate a change in membrane potential

Question 9

What is a receptor potential? What does it cause?

Answer 9

Graded potential caused by changing ion activity in the sensory receptor.

It may activate an action potential that travels along the sensory fiber to the CNS OR influence neurotransmitter secretion which alters activity in an associated sensory neuron.

Question 10

What is an adequate stimulus?

Answer 10

Preferred type of stimulus for a receptor (e.g. thermoreceptors are more responsive to temp than pressure)

Question 11

What is the receptor threshold?

Answer 11

Minimum stimulus required to activate a receptor and generate a receptor potential; differs per receptor

Question 12

What is a receptive field?

Answer 12

Specific physical area that activates somatosensory and visual neurons when stimulated. Usually associated with one sensory neuron, but neighbouring primary neurons may converge at a secondary neuron to allow summation.

Question 13

What is the telationship between receptive field and acuity?

Answer 13

The more convergence, the larger the receptive field, the lower the acuity. Found in most areas of the body.

The less convergence, the smaller the receptive field, the higher the acuity. Found in sensitive areas of the body.

Question 14

Why does convergence eliminate two point discrimination?

Answer 14

Two stimuli that fall within different receptive fields of primary sensory neurons that converge onto the same secondary sensory neuron will be perceived as a single point as only one signal goes to the brain.

Question 15

Where is sensory information processed?

Answer 15

1. Spinal cord or from cranial nerves to brainstem; visceral reflexes that do not reach conscious perception
2. Cortex processes consciously aware sensory info from sensory neurons directly, or from relay neurons that collect info from multiple sources

Question 16

What is the perceptual threshold?

Answer 16

level of stimulus necessary to be aware of a particular sensation

Question 17

What are the properties of a stimulus that is distinguished by coding and processing?

Answer 17

1. Modality
2. Location
3. Intensity
4. Duration

Question 18

What is modality and how is it distinguished?

Answer 18

Modality is the different ways information is perceived and processed by the human senses. It is distinguished by labeled line processing.

Question 19

What is labeled line processing?

Answer 19

Association of a signal from a certain group of receptors with a specific modality based on the neural pathway that brings it to the CNS.

Question 20

How does the location of the stimulus distinguished?

Answer 20

1. Which receptive fields are activated
2. Specific area in which they are projected and processed in the cerebral cortex
3. Lateral inhibition

Question 21

What is lateral inhibition and how does it work?

Answer 21

Secondary neuron suppresses response of secondary neurons lateral to it, which allows the sensation to be more easily localized.

Question 22

How is the intensity of a stimulus distinguished?

Answer 22

Number of receptors activated (population coding) and frequency of action potentials fired from receptors (frequency coding).

As stimulus intensity increases, receptor amplitude increases, and frequency of action potentials in primary sensory neuron increases.

Question 23

How is the duration of a stimulus distinguished?

Answer 23

Coded by duration of action potentials in the sensory neuron. A persisting stimulus will continue to fire action potentials (slow adapting), or will cease to respond (rapid adapting) in receptors that don’t adapt.

Question 24

What is the difference between tonic receptors and phasic receptors?

Answer 24

Tonic: slow to adapt; fire rapidly when first activated, then slow and maintain firing as long as stimulus is present

Phasic: rapidly adapting; fire rapidly when first activated, then cease if stimulus remains constant.

Question 25

What are Pacinian corpuscles?

Answer 25

Structure: Large, myelinated nerve endings in concentric layers of connective tissue creating larger receptor fields in deep layers of skin.

Function: respond to high-frequency vibrations and rapidly adapt.

Question 26

What are Merkel receptors?

Answer 26

Structure: Merkel cell that synapses onto enlarged nerve ending of primary sensory neuron in superficial layers of skin.

function: sense steady pressure and texture, responsible for high sensitivity of tactile reception in fingertips. Slow adapting.

Question 27

What is Meissner’s corpuscle?

Answer 27

Structure: Bare nerve ending wrapped in connective tissue in superficial layers of skin

Function: Activated by light touches (e.g. Fluttering, stroking), Rapidly adapt.

Question 28

What is Ruffini ending?

Answer 28

Structure: highly branched nerve endings encapsulated in connective tissue in deep layers of skin

Function: Detects stretch of skin to provide info about position of the hand. Slowly adapting.

Question 29

What are thermoreceptors?

Answer 29

Structure: Free nerve endings that terminate in the subcutaneous layers, and include cold and warm receptors.

Function: They stimulate action potentials in transient receptor potential channels which fire in response to a specific temperature. This may be in response to sensed temperature, or ligands that stimulate the same feeling.

Question 30

What is TRPV2?

Answer 30

Type of transient receptor potential channels that open in response to temperatures at 52ºC. They are stimulated by Arachadonic acid and prostaglandins which activate GPCR to cause graded potentials in nociceptive neurons.

Question 31

In terms of temperature, what do cold warm and pain receptors respond to?

Answer 31

Cold: activated below body temp

Warm: 37-45ºC

Pain: Above 45ºC

Question 32

What are nocireceptors?

Answer 32

Structure: Neurons with free nerve endings

Function: respond to a variety of strong noxious stimuli and stimulate the sensation of pain.

Question 33

What are the classes of somatosensory nerve fibres?

Answer 33

A-beta: from nociceptor to medium diameter myelinated to CNS = fast pain

A-delta: form nociceptor to small to medium diameter myelinated to CNS = fast pain

C-fibres: from nociceptor to Small unmyelinated to CNS = slow, intense pain

Question 34

What is the difference in the two sensory pathways?

Answer 34

Receptor to spinal cord to brainstem, SYNAPSE in brainstem as it crosses to thalamus, synapses to travel to cortex

Nociception/temp: Receptor to spinal cord, SYNAPSE in spinal cord as it crosses, straight to thalamus, synapses to travel to cortex