Lecture 10

Question 1

special senses

Answer 1

specialised organ for detecting the sensory input

Question 2

sensory systems

Answer 2

specialised receptors convert stimuli into electrical signals (graded potentials). Each receptor has a ‘threshold’ minimum stimulus required for activation. Sensory neurons have a receptive field related to the degree of convergence (determines acuity). Size of receptive field varies. e.g fingers is small while back is large

Question 3

Convergence RF

Answer 3

large. There is a degree of overlap between the fields and the primary sensory neurons feed into a single secondary neuron that sums the two stimuli into one.

Question 4

Small RF

Answer 4

in more sensitive areas. No overlap therefore, each forms synapse with their respective secondary neuron. Same distance apart. High acuity

Question 5

chemoreceptors

Answer 5

O2, pH, various molecules like glucose

Question 6

mechanoreceptors

Answer 6

Pressure (baroreceptor), cell stretch (osmoreceptors), vibration, acceleration and sound

Question 7

photoreceptors

Answer 7

light photons

Question 8

thermoreceptors

Answer 8

varying degree of heat

Question 9

merkel receptors

Answer 9

pressure and texture

Question 10

meissners corpuscle

Answer 10

flutters/stroking volume

Question 11

Pacinian Corpuscle

Answer 11

vibrations

Question 12

Ruffini corpuscle

Answer 12

responds to skin stretch

Question 13

sensory neurons

Answer 13

carry signals to spinal cord

Question 14

free nerve endings

Answer 14

noxious stimuli, temp and hair movement

Question 15

Piezo 2

Answer 15

Excitatory (allows positive ions to move into cell for depolarisation) ion channel gated by mechanical forces detecting changes in membrane tension. Required for Merkel cell mechanotransduction.

Question 16

sensing temperature

Answer 16

cold receptors: <37
warm receptors: >45

there are far more cold receptors than warm. Adaptations occur between 20-40. detect change in temp rather than absolute temp. Rely on transient receptor potenital channels. Warm receptors activate pain receptors

Question 17

sensing pain

Answer 17

nociceptors are free nerve endings that respond to noxious stimuli. Found in many tissues, but not NS. Type depends on type of sensory fibres.

Question 18

Fast pain

Answer 18

A- delta fibres (myelinated)

Question 19

slow pain

Answer 19

C unmyelinated fibres

Question 20

itch

Answer 20

C fibres in skin stimulated by histamines

Question 21

TRPV1

Answer 21

Capsaicin (vanilloid) receptor. Heat-activated ion channel (>43), integrates inflammatory response

Question 22

TRPM8

Answer 22

Menthol receptor. Cold activated channel (<26)

Question 23

TRPA1

Answer 23

Wasabi receptor. chemoreceptor for environmental irritants and inflammatory agents

Question 24

properitoes of a stimulus relayed to CNS

Answer 24

Modality: Nature of stimulus
Location: where on body
Intensity: stimulus strength
Duration: length of stimulus

Question 25

modality

Answer 25

indicated by which sensory neurons are activated and where they terminate in the brain. Each receptor responds strongly to a particular stimulus. Each receptor associated with a specific modality (i.e labelled line coding)

Question 26

Location

Answer 26

indicated by which receptive fields are activated. Topographical organisation of receptors preserved in processing centres of the brain

Question 27

lateral inhibition

Answer 27

increase contrast between activated receptive fields and local non-activated fields. Increases acuity

Question 28

intensity

Answer 28

indicated by number of receptors activated (population coding), frequency of action potentials (frequency coding)

Question 29

duration

Answer 29

indicated by duration of action potential firings, Affected by receptor adaptation. Longer/ stronger stimulus = staying in depolarised state for longer = longer firing of action potentials.

Question 30

tonic receptors

Answer 30

slow to adapt e.g propioreceptors, good for dangerous situations

Question 31

phasic receptors

Answer 31

fast to adapt e.g some touch receptors, good for normal situations

Question 32

somatosensory pathways

Answer 32

1. Stimuli innervate primary neurons 2. Nociceptor, temp and coarse touch synapse in spinal cord where they cross over and send signals up to the thalamus 3. thalamus integrates it into system to determine where it should be sent 4. once determined, signal is sent to sensory cortex which will perceive signals 5. fine touch, proprioception and vibrations stimulus will come into spinal cord, but, synapse at medulla. 6. Once synapse is formed, secondary neuron crosses over and travels up to thalamus 7. Repeat 3-4

Question 33

Somatosensory cortex

Answer 33

Receives input from specific sensory tracts, each of which has a corresponding sensory field within the cortex. It is organised in a columnar arrangement, where different types of receptors from the same body part are grouped together in vertical columns. This area of the brain has a high capacity for plasticity, meaning it can reorganise itself in response to changes such as injury or increased use, resulting in heightened sensation in the affected area.