3. Sensory Overview

Question 1

Afferent Nerve Fibers

Answer 1

Carry sensory info to CNS

Question 2

Afferent Neuron (components)

Answer 2

Peripheral process extending to sensory receptor

Centra process entering CNS through dorsal root/cranial nerve

Question 3

Sensory Transmission (steps)

Answer 3

Sensory receptors
First order neuron
Second order neuron
Third order neuron
Fourth order neuron

Question 4

First Order Neuron

Answer 4

Primary sensory afferent neuron

Cell body in dorsal root ganglion

Question 5

Second Order Neuron

Answer 5

In spinal cord or brainstem

Interneurons can modify here (excitatory or inhibitory)

Question 6

Third Order Neuron

Answer 6

Typically in thalamus

Question 7

Fourth Order Neuron

Answer 7

Sensory cerebral Cortex

Question 8

Types of Sensory Receptors

Answer 8

• Specialized peripheral ending of primary afferent neuron (free naked nerve ending)
• Accessory sensory cell (transmits info to primary afferent neuron)

Question 9

Adequate Stimulus

Answer 9

Form of stimulus energy that a receptor is most sensitive

Not absolute (can respond to other stimuli) (think eyes closed and pressure)

Question 10

Classification of Sensory Receptors

Answer 10

Classified by:

• the kind of stimulus they are sensitive to
• location in body

Question 11

Mechanoreceptors

Answer 11

Respond to mechanical energy

Touch, pressure, vibration

Question 12

Thermoreceptors

Answer 12

Respond to temperature changes

Warm and cold receptors

Question 13

Photoreceptors

Answer 13

Respond to light energy

Question 14

Chemoreceptors

Answer 14

Respond to circulating or applied chemicals

Question 15

Exteroreceptors

Answer 15

Detect stimuli affecting external surface of the body

mechanoR, thermoR

Question 16

Interoreceptors

Answer 16

Lie inside the body

taste, olfaction, things that effect gut

Question 17

Proprioceptors

Answer 17

Located in internal mass of body

muscles, joints, tendons

Question 18

Special Receptors

Answer 18

Vision, audition, taste, olfaction, balance

Question 19

Superficial Receptors

Answer 19

Touch, pressure, flutter, vibration, tickle, warmth, cold, pain, itch

Question 20

Deep Receptors

Answer 20

Position, kinesthesia, deep pressure, deep pain

Question 21

Visceral Receptors

Answer 21

Hunger, nausea, distention, visceral pain

Question 22

Nociceptors

Answer 22

Receptors associated with pain sensations

Question 23

Sensory Receptor (function)

Answer 23

Transduce/translate energy from one form to another

End result: train of impulses (APs) which carries info about the stimulus applied

Question 24

Sensory Trandsuction

Answer 24

1. stimulus energy
2. receptor
3. receptor/generator potential
4. action potentials

Question 25

Impulse Initiation

Answer 25

1. Stimulus activates R 2. Local, graded potentials occur across membrane (generator or receptor) 3. In afferent nerve fiber, separate local potentials summed at first node of Ranvier 4. AP generated when membrane reaches threshold

Question 26

Generator Potential

Answer 26

Graded potential Receptor is modified afferent nerve ending

Question 27

Receptor Potential

Answer 27

Graded potential Receptor is a separate cell

Question 28

Neural Encoding

Answer 28

Process by which information is transmitted from periphery to brain

Question 29

Sensory Information

Answer 29

Transmitted by sensory R Coded as AP - Modality (quality/nature of sensation) - Location - Intensity - Duration

Question 30

Modality

Answer 30

Sensations that are referred to a single type of receptor

Question 31

Doctrine of Specific Nerve Energies

Answer 31

Sense organ is sensitive to many forms of energy Sensation is always that of adequate stimulus - despite what form of energy was applied

Question 32

Labeled Lines

Answer 32

Modality of a sensation depends upon which particular cell, pathway, nucleus or lobe is activated by the stimulus Pathways of sensory neurons dedicated to that modality

Question 33

Location

Answer 33

Ability to locate the side of stimulation and discriminate between two closely spaced stimuli Encoded by receptive field of sensory neurons

Question 34

Receptive Fields

Answer 34

Area of the body that when stimulated results in a change in firing rate of sensory neuron Areas supplied by different sensory units will overlap More complex moving from primary to secondary etc neurons

Question 35

Receptive Fields: Increase in stimulus intensity ...

Answer 35

Stimulus will spread

Question 36

The smaller the receptive field ...

Answer 36

The greater the density of receptors - more precisely the sensation can be localized

Question 37

Two Point Discrimination Test

Answer 37

Minimal distance between two detectable stimuli Better discrimination where receptive fields are very small and densely innervated

Question 38

Receptive Field: Secondary Neurons

Answer 38

Determined by: - summed inputs from primary neurons - input from interneurons

Question 39

Intensity

Answer 39

Methods of transmission: 1. Frequency code 2. Population code 3. Intense stimuli activate different types of receptors

Question 40

Frequency Code

Answer 40

As stimulus intensity rises, firing frequencies of sensory neurons rise More APs (number of AP per unit time)

Question 41

Population Code

Answer 41

Intense stimuli recruit greater numbers of nerve fibers to fire Bigger stimulus - more neurons activated

Question 42

Duration

Answer 42

Encoded in the way sensory nerve fibers change their firing frequencies over time Phasic vs. Tonic

Question 43

Phasic Receptors

Answer 43

Rapidly adapting Signals only onset and cessation of stimulation

Question 44

Tonic Receptors

Answer 44

Slowly adapting Continuously signal a persistent signal (fires as long as the stimulus is present)

Question 45

Sensory Dysfunction: Negative

Answer 45

Taking something away Due to disruption of nerve activity Numbness Loss of cold or warmth Blindness Deafness

Question 46

Sensory Dysfunction: Positive

Answer 46

Gain sensation (in a way we don't want) Due to excitation or disinhibition Pain Paresthesias (tingling, pins and needles) Visual sparkles Tinnitus