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5115 > sensory receptors > Flashcards

sensory receptors Flashcards

1
Q

sensory transduction

A

process by which sensory receptors convert one kind of signal energy into another

Receptor neurons are modified axons that project to and synapse on specific destinations in CNS. The distal part (the receptor) converts stimuli into a neural event called generator or receptor potential. The receptor neuron conducts AP to the CNS. The receptor neuron encodes information from the receptive field. With the special senses a separate cell is the receptor which synapses on the sensory neuron.

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2
Q

labeled line principles

A

(parallel pathway) - receptor field in periphery is connected to an area in the brain

Each receptor generates information in response to a stimulus that conveys info about location and modality. A given pathway btwn a receptor and its destination in the cortex only transmits AP from one spot and for one modality.

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3
Q

receptive field

A

Restricted region of receptive surface - the area of skin where stimulation excites the receptor

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4
Q

absolute sensory threshold

A

lowest intensity stimulus that can be detected in 50% of trials

Sensation threshold coincides with the neuron threshold.

Changes in sensory threshold can often be due to changes in CNS

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5
Q

Weber’s Law

A

The larger the stimulus, the larger the increase has to be in order to be “noticed.”

Discrimination is best at low intensities

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6
Q

Adaptation

A

A process that occurs while a stimulus is in place. In the face of a continuous stimulus AP frequency may quickly or gradually change depending on the type of receptor.

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7
Q

tonic receptors

A

Slowly adapting
i.e. pain receptors, baroreceptors, muscle spindles
Keeps CNS up-to-date about events in the periphery (nociceptor)

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8
Q

phasic receptors

A

Deep touch receptor
i.e. Pacinian corpuscle
Rapidly adapting

Rate coding, reporting changes in stimuli

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9
Q

2-point discrimination

A

Spatial discrimination.

2 harp points of a caliper are applied to areas of the skin while subject is looking away. With high 2-point discrimination, the subject can distinguish two closely placed stimuli as two points rather than one. Areas with higher concentrations of receptors have a greater 2-point discrimination (i.e. the finger tips)

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10
Q

temporal and spatial summation

A

temporal - The build-up of an electrical charge on a membrane to create an AP as a result of more than one small successive inputs

spatial - the ability to achieve an AP potential in a neuron which receives input from several cells.

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11
Q

Mechanoreceptor

A

touch, pressure, vibration muscle and joint position (proprioception), hearing and balance.

Ex. Pacinian corpuscles, Ruffini corpuscles, Merkel disks

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12
Q

Thermoreceptors

A

changes in temperature and some chemicals

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13
Q

Nociceptors

A

pain from harmful or potentially harmful stimuli - tissue damage

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14
Q

Electromagnetic receptors

A

photoreceptors - detect light striking the retinas

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15
Q

Four main somatic modalities

A

tactile, proprioception, thermal, pain

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16
Q

Receptor generator potential vs. Action potential

A

RPs are a local potential. They are graded responses such that the greater the stimulus, the greater the receptor potential.

The stimulus (in the correct modality) opens or closes transduction gated channels. The channel event results in potential changes that can be either a depolarization or a hyperpolarization.

For an action potential to occur, the membrane HAS to depolarize (in order to reach threshold), but after action potential, there’s a short time where the membrane hyperpolarizes

In the somatic nervous system, the receptor is the specialized distal end of the axon. When the RP reaches the threshold of the adjoining neuron, AP occur in the neuron.

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17
Q

Transmission

A

generator potentials resulting in AP going to the CNS

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18
Q

Frequency coding

A

Greater increases in RP beyond threshold, result in greater frequencies of AP going to the CNS. Frequency coding is any increased stimulus intensity that increases AP

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19
Q

Size of receptive fields in 2-point discrimination

Finger tip vs. Palm vs. forearm

A

Fingertip - 1 mm
Palm - 10 mm
Forearm - 20 mm

20
Q

A-neurons

A

large, myelinated with high conducting velocities

alpha, beta, delta, gamma

21
Q

alpha neurons

A

innervate skeletal muscle
large, myelinated A neurons
Fast
Carry fast pain

22
Q

Beta neurons

A

medium sized neurons with medium conducting velocity which are associated with autonomic pathways

23
Q

C- neurons

A

small, unmyelinated neuron with slow conducting velocities which are associated with pain, itch, temp, crude touch pathways

24
Q

General sensory pathway

A

First order neurons transmits AP from the skin and muscles to the CNS (spinal cord or medulla)

Second order neurons cross on the midline (contralateral representation) and transmit AP to the thalamus

Third order neurons project to the parietal lobe (primary somatosensory cortex). Sensory info from the left side of the body goes to the right side of the brain.

25
Q

How does info get back to the CNS?

A

The somatic NS communicates with the CNS via spinal nerves. Spinal nerves are mixed nerves meaning they carry both sensory and motor information. The somatic sensory info returns to the spinal cord via the dorsal root.

26
Q

Dermatome

A

Area of skin innervated by a single dorsal root

Some overlap

Orderly arrangement of sensory circuitry

27
Q

Spinal cord - white and gray matter

A

White matter - myelinated axons

Gray matter - nerve cell bodies and synapses

28
Q

Dorsal column pathway/medial leminiscal

A

large fibers, high conduction velocity

  1. First order neurons ascend spinal cord in dorsal columns

Information from the lower body enters the sacral and lumbar spinal levels, travels in the fasciculus gracilis tracts in the medial dorsal column, ascend the spinal cord and synapse in the brainstem nucleus gracilis.

Information from the upper body enters the thoracic and cervical levels, travels in the fasiculus cuneatus tracts in the lateral dorsal columns, ascend the spinal cord and synapse in the brainstem nucleus cuneatus.

  1. Second order neurons cross at medulla and the fibers travel in bundles through medial lemniscus and project to the thalamus
  2. Third order neurons project to the somatosensory cortex in the parietal lobe and information is mapped in a sensory homunculus in the cortex
29
Q

Anterolateral system/Spinothalamic tract

A

Smaller, slower fibers

  1. First order neurons enter the dorsal root and synapse in the dorsal horn.
  2. Second order neuron crosses and ascends spinal cord in spinothalamic tract, projecting to the thalamus and RAS
  3. Third order neuron projects from thalamus to the somatosensory cortex in the parietal lobe - information also mapped in sensory homunculus but the mapping is not as precise as the dorsal column pathway
30
Q

Modality conveyed in dorsal pathway

A

fine touch, vibration, position, mechanoreceptors

High spatial organization, discrete mechanical stimulation, highly localized

31
Q

Info/modality convey in anterolateral pathway

A

pain and temp, crude touch, pressure, tickling, itching, sexual

32
Q

Brown-Sequard syndrome

A

caused by damage to one half of the spinal cord, resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion.

33
Q

Stereogenesis

A

Ability to pick up an object (without looking at it) and figure out what it is

If a person can’t figure out the object, indicates degermation in parietal lobe

34
Q

Why is the thalamus a filter?

A

Sensory information thus travels to the thalamus and is routed to a nucleus tailored to dealing with that type of sensory data. Then, the information is sent from that nucleus to the appropriate area in the cortex where it is further processed. making sure that the information gets sent to the right place

35
Q

Reticular activating system

A

piece of the brain that starts close to the top of the spinal column and extends upwards around two inches. It has a diameter slightly larger than a pencil. All of your senses (except smell, which goes to our brain’s emotional center) are wired directly to this bundle of neurons that’s about the size of your little finger.

it’s the gatekeeper of information that is let into the conscious mind. This little bit of brain matter is responsible for filtering the massive amounts of information your sensory organs are constantly throwing at it and selecting the ones that are most important for your conscious mind to pay attention to.

36
Q

Lateral inhibition and resolution

A

Inhibits the sides the most, intensifying the center, thereby allowing for edge detection.

Not present at the level of the receptor but starts at the dorsal column nuclei and is found at each subsequent relay step.

In the CNS, the center cells are exited and are surrounded by a rind of inhibited cells. This helps with resolution, precise location and edge detection.

37
Q

Where is the somatosensory cortex?

A

Anterior part of the parietal lobe

38
Q

What is involved in stimulus perception?

A

Sensation with context

39
Q

How are the body areas represented in the cortex?

A

Sensory cortex is laterally mapped to body regions called somatotopic representation

The map is represented according to two point discrimination.

Somatic regions with a higher two-point discrimination have greater representation in the cortex (hands and face).

Homunculus

40
Q

How is information in the cortex localized?

A

Fast pain is more localized via fast nuclei

A delta fibers

41
Q

In what ways does the somatosensory cortex interpret sensory information?

A

The cortex has 6 layers of cells that permit connections with other brain areas. Different modalities are from a given area of the body are grouped together in modality specific pathways

The mapping in the cortex enables the CNS to localize the information well

  1. Location of a stimulus via labeled line theory
  2. Intensity determined by frequency of AP
  3. Modality determined by pathway to the cortex
  4. Resolution - density of receptive fields
42
Q

What is the function and cause of pain?

A

Pain is a protective mechanism

Acute pain is a physiologic adaptation that ells the organism something is wrong. Acute pain is classified as somatic, visceral or referred.

Somatic pain can be fast or slow.

43
Q

Nociceptors

A

Tonic receptors that adapt very little. They can actually become more sensitive (hyperalgesia)

unencapsulated or free nerve endings found in skin, periosteum, vessel and gut walls, joint surfaces, and dura btwn brain hemispheres.

Polymodal - they can be stimulated by more than one kind of stimulus

Extreme heat or cold, tissue damage and release of certain chemicals, ischemia, or mechanical stimuli like muscle spasms

44
Q

Compare/contrast fast and slow pain in terms of pathway, speed of transmission, interpretation at the CNS

FAST PAIN

A

Stimulus - Noxious levels of thermal or mechanical stimulation

Receptor - A delta fibers - myelinated and fast

Conduction velocity - Conducts AP at 5-30 m/sec

NTZ - glutamate

Evolutionary name - neospinothalamic

Pathway - First order neuron enters the spinal cord and synapses at the level of entry. The second order neuron crosses at the midline and ascends via the contralateral spinothalamic tract. Most fibers project to the thalamus where the info is filtered. The third order neuron relays the info to the cortex.

Characteristics - sharp, electric, stabbing pain that is well localized

45
Q

IF the somatosensory cortex were missing or damaged, could a person still sense pain?

A

Ppl engage in guarding behavior, elevated HR with painful stimuli even with severe cerebral damage.

46
Q

What is the role of endogenous opiates in pain modulation?

A

Work at all levels of pain processing

Nociceptor inhibited through binding of endogenous opioids (e.g. enkephalin). The release of substance P is prevented.

5115 (8 decks)

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