2. General Principles of Sensory Physiology

Question 1

Interaction between sensory system and motor system

Answer 1

Sensory receptors in the PNS generate an impulse
The CNS interprets the impulse
The PNS stimulates a response

Question 2

Sensory receptors

Answer 2

Some specialized structures activated by stimuli and convert a stimulus into neuronal activity

Question 3

Types of sensory receptors

Answer 3

1. Endings of afferent neurons (somatosensory and olfactory systems)
2. Specialized epithelial cells adjacent to an afferent neuron (visual, taste, and auditory systems)
3. Specialized structure associated with nerve terminals (Pacinian corpuscles)

Question 4

Simple receptors

Answer 4

Neurons with free nerve endings, work on somatosensory and olfactory systems

Question 5

Complex neural receptors

Answer 5

Nerve endings enclosed in connective tissue capsules, Pacinian corpuscles

Question 6

Special senses receptors

Answer 6

Cells that release neurotransmitter onto sensory neurons, initiating an action potential

Question 7

5 types sensory receptors

Answer 7

Mechanoreceptors, photoreceptors, chemoreceptors, thermoreceptors, nociceptors

Question 8

Mechanoreceptors

Answer 8

For touch, is a pacinian corpuscle and located on the skin
For audition, is a hair cell and located in the organ of corti
For vestibular, is a hair cell locating on macula, semicircular canal

Question 9

Photoreceptors

Answer 9

For vision, rods and cones are the receptors and located on the retina

Question 10

Chemoreceptors

Answer 10

For olfaction: olfactory receptors on olfactory mucosa.
For arterial Po2 on carotid and aortic bodies.
Fo pH of CSF on ventrolateral medulla

Question 11

Thermoreceptors

Answer 11

For temperture, receptors are cold receptors and warm receptors, on skin.

Question 12

Nociceptors

Answer 12

Detect stimuli causing tissue damage, can be thermal, mechanical or polymodal, located on skin.

Question 13

Receptor potential vs. action potential

Answer 13

Receptor potential = graded, non-propagated

Action potential = hyperpolarizing or depolarizing

Question 14

Sensory transduction

Answer 14

1. Stimulus -> ion channel opening
2. Current –> receptor potential
3. Depolarization -> voltage gated sodium channels, action potentials
4. Propagation -> NT release
5. Transmission to CNS through sensory afferent neurons (1st, 2nd, 3rd, and 4th order)

Question 15

Sensory unit

Answer 15

primary sensory neuron with all sensory receptors (endings or associated sensory receptor cells).
The smallest unit of sensory response.

Question 16

Receptive field

Answer 16

an area of the body surface that when stimulated results in a change in firing rate of a sensory neuron.

Question 17

What determinates the size of receptive field of a sensory neuron?

Answer 17

Terminal size and associated cells; Convergence

Question 18

Receptive field variation in size

Answer 18

The smaller the receptive field, the more precisely the sensation can be localized or identified.
The higher the order of the CNS neuron, the more complex the receptive field.

Question 19

Receptive field firing rate

Answer 19

Receptive field can be excitatory or inhibitory depending on the change in firing rate.

Question 20

Four aspects of a stimulus

Answer 20

Stimulus Modality: light, sound, temperature, taste, smell, pressure

Stimulus Intensity: strength of a stimulus

Stimulus Location: acuity, lateral inhibition

Stimulus Duration: adaptation

Question 21

Modality of mechanoreceptors

Answer 21

Stretch and pressure

Question 22

Modality of photoreceptors

Answer 22

Light

Question 23

Modality of chemoreceptors

Answer 23

Chemicals

Question 24

Modality of thermoreceptors

Answer 24

Cold, warm

Question 25

Modality of nociceptors

Answer 25

Stimuli causing tissue damage

Question 26

Adequate stimulus

Answer 26

Each sensory receptor is particularly sensitive to one stimulus type or modality

Question 27

Labeled line

Answer 27

the distinct anatomical pathways (including ascending pathways, specific neuronal circuits, from sensory receptors to a specific region of the CNS) associated with a particular stimulus modality.

Question 28

Do all receptors from same sensory unit respond to same modality?

Answer 28

Yes

Question 29

What encodes stimulus intensity?

Answer 29

1. The number of receptors that are activated. A stronger stimulus affects a larger area and recruit a larger number of receptors.
2. Differences in firing rates of sensory neurons in the pathway. An increased stimulus results in a higher frequency of action potential.
3. Activating different types of receptors. A light touch of the skin may activate only mechanoreceptors, while an intense damaging stimulus to the skin may activate mechanoreceptors and nociceptors.

Question 30

Lateral inhibition

Answer 30

The capacity of an excited neuron to reduce the activity of its neighbors
Further enhance sensory acuity

Question 31

Acuitity

Answer 31

Precision of stimulus location
Positively correlated with the density of sensory units
Negatively correlated with the receptive field size

Question 32

Adaptation

Answer 32

sensory receptors decrease in sensitivity to stimulus of constant strength
⇒ action potential frequency decreases

Question 33

Phasic sensory receptors

Answer 33

Phasic (rapidly adapting): generate a receptor potential and action potential at the onset (and offset) of a stimulus but very quickly cease responding; detect changes in the stimulus

Question 34

Tonic sensory receptors

Answer 34

Tonic (slowly adapting): maintain a persistent or slowly decaying receptor potential and continue firing during a constant stimulus; encode duration and intensity of a stimulus

Question 35

Microneurography

Answer 35

an invasive method used by neuroscientists to visualize and record the normal traffic of nerve impulses.

Question 36

Relay nuclei

Answer 36

Integrate converging information
Prominent in thalamus.
Contain local interneurons and projection neurons

Question 37

Topographic organiztaion

Answer 37

Neural maps
Somatosensory system: somatotopic map (sensory homunculus)
Visual system: retinotopic map
Auditory system: tonotopic map

Question 38

Decussation

Answer 38

The crossings of sensory (and motor) pathways in the spinal cord or in the brain.
Commissure: e.g. corpus callosum
Optic chiasm

Question 39

Classification of nerve fibres

Answer 39

Many! Look at table haha

Question 40

Sensory (ascending) pathways

Answer 40

A series of sensory afferent neurons travel in bundles of parallel pathways to pass on certain sensory information to the brain.
First-order neuron is the primary sensory afferent neuron.
Second-order sensory afferent neurons is located in relay nuclei in the spinal cord or in the brain stem. They cross at the midline (decussation).
Third-order neurons typically reside in relay nuclei in the thalamus.
Fourth-order neurons reside in the appropriate sensory area of the cerebral cortex.

Question 41

Divergence of Ascending Pathways

Answer 41

One primary sensory neuron synapses onto many higher-order neurons.

Question 42

Convergence of Ascending Pathways

Answer 42

A higher-order sensory neuron may receive inputs from more than one primary sensory neuron (information processed rather than just relayed).

Question 43

Where do ascending pathways terminate

Answer 43

Terminate in specific primary sensory areas
Somatic receptors ⇒ Somatosensory cortex
Eyes ⇒ visual cortex
Ears ⇒ auditory cortex
Nose (nasal cavity) ⇒ olfactory cortex

Further processing in associational cortical areas for complex integration.

Leads to perception of sensations

Question 44

Perception vs Sensation

Answer 44

Perception is an active process and sensation is a passive process.

Question 45

Influence of Desending Pathways

Answer 45

Descending pathways can inhibit (directly or indirectly) the transduction of sensory information to the brain. Not all sensory information reaches conciousness.