Sensory physiology: principles

Question 1

efferent nerves/ descending pathways: define

Answer 1

• somatic motor neurons/ autonomic moto neurons

- relay signals form CNS towards an effector (organ, muscle, gland)

Question 2

afferent nerves/ ascending pathways: define

Answer 2

• sensory neurons

- relay signals from sensory receptors in PNS towards the CNS

Question 3

general visceral afferents:

Answer 3

• provide input to brain about viscera

- processed mostly subconsciously for homeostasis

Question 4

special visceral afferents:

Answer 4

• nerves that develop in association w GIT and carry info from ‘special senses’ of smell and taste via CN I (olfactory), VII (facial), IX (glossopharyngeal), V (trigeminal), X (Vagus)

Question 5

general somatic afferents:

Answer 5

• transmit sensation arising from body surface (touch, pressure)
• proprioceptive info from mm, joints, skin, inner ear

Question 6

special somatic afferents:

Answer 6

• nerves carry info from special senses vision, hearing, balance via CN II (optic) and VIII (vestibulocochlear)

Question 7

sensory transduction: is

Answer 7

• conversion of physical/ chemical stimuli from int/ext environment into neural signals that can effect physiological/ behavioural response

Question 8

sensory transduction: features

Answer 8

• sensory receptors respond to specific modality (energy form)
• transduce stimulus into form used by nervous system
• can be simple (mechanical opening of ion channel)
• transduction process can have amplification stage, esp if transduction is mediated by metabotropic/ G protein coupled receptor (eg. olfactory receptors)

Question 9

sensory transduction: pathway

Answer 9

stimulus - receptor - transduction - transmission - perception

Question 10

adequate stimulus: modality define

Answer 10

• form of energy particular receptor can respond to

Question 11

adequate stimulus: define

Answer 11

• modality to which particular receptor responds best

Question 12

exteroceptors: are

Answer 12

respond to stimuli orginating outside body

Question 13

exteroceptors: list

Answer 13

• mechanoreceptors
• photoreceptors
• chemoreceptors
• thermoreceptors
• magnetoreceptors
• electroreceptors

Question 14

interoceptors: are

Answer 14

• respond to stimuli originating inside body

Question 15

interoceptors: list

Answer 15

• chemoreceptors (blood O2, CO2, pH)
• baroreceptors (BP)
• osmoreceptors (osmotic pressure - fluid balance)

Question 16

proprioceptors: are

Answer 16

provide info about posture and position of body

Question 17

proprioceptors: list

Answer 17

mechanoreceptors

• proprioception (joint/ limb position)
• vestibular system (balance/ motion)

Question 18

sensory receptor type 1:

Answer 18

• some sensory receptors formed from specialised ending on primary afferent sensory neuron
• stimulus cause membrane ion channel to open/ close
• graded potential (generator) -> can initiate AP in same cell
• depolarising potentials will increase rate of AP generation

Question 19

sensory receptor type 2:

Answer 19

• some sensory receptors are specialised cells separate from primary afferent neuron
• graded potential generate in receptor cell (non-spiking)
• voltage gated Ca channels open/ close and increase/ decrease rate of NT release
• depolarising/ hyperpolarising graded potential is induced in primary afferent neuron -> increase/ decrease rate of firing AP

Question 20

trigger zones:

Answer 20

• multipolar neurons: AP at axon hillock/ initial segment where axon joins soma
• primary sensory afferent typically psuedounipolar cells -> dendrites (peripheral sensory) and axon terminal (central synaptic end)
• trigger zone close to receptors/ dendrites (peripheral end)

Question 21

trigger zones: necessary why

Answer 21

graded potentials would not be able to travel all the way to soma (in dorsal root ganglion)

Question 22

receptor adaptation: features

Answer 22

• receptors transduce sensory stimuli and respond w graded potentials proportional to stimulus strength and duration
• some receptors respond w depolarisation of same magnitude for as long as stimulus is applied
• most receptors reduce magnitude if sustained stimulus

Question 23

receptor adaptation: types

Answer 23

• tonic (slow adapting)

- phasic (rapid adapting)

Question 24

tonic receptors: and eg

Answer 24

• provide continuous updates for long lasting stimulus
• muscle stretch (prevent over stretch)
• merkel’s (pressure)
• nociceptors

Question 25

phasic receptors: and eg

Answer 25

- signal changes in stimulus intensity - many respond to cessation of stimulus w off response - olfactory receptors - touch (pacinian)

Question 26

stimulus intensity: rate (frequency) coding

Answer 26

- larger stimulus - higher magnitude of potential - higher frequency of NT release

Question 27

stimulus intensity: population coding

Answer 27

- stronger stimulus activates more receptors (recruitment) - more receptors of same afferent sensory neuron stimulated simultaneously - receptors on additional afferent sensory neurons that converge on same area of brain simultaneously

Question 28

stimulus localisation:

Answer 28

- sensory systems organised spatiotopically (touch, vision) acuity will depend on - size of receptive field/ unit - density of sensory units (spatial coverage) - degree of overlap in receptive fields of adjacent units - lateral inhibition

Question 29

define receptive field:

Answer 29

- physical area within which receptors of single sensory unit can detect stimuli

Question 30

overlap of receptive field:

Answer 30

- stimulus falling on overlapping portion of RF of two sensory receptors will stimulate them both neurons simultaneously (population coding)

Question 31

lateral inhibition: features

Answer 31

- increases signal contrast for easy comparison - enhance transmission of focal signals, suppress transmission of diffuse signals - eg. of presynaptic inhibition

Question 32

lateral inhibition: centre surround RF

Answer 32

- creates functional RF that has: - excitatory centre - inhibitory surround

Question 33

eg. tactile acuity:

Answer 33

- ability to perceive two points pressed in skin - depends on density, RF size, overlap of tactile receptors (mechanoreceptors) - meissner's corpuscles, merkel's discs involved in fine touch perception and discrimination (small RF)

Question 34

two point discrimination threshold:

Answer 34

- min distance btw points required for tactile discrimination

Question 35

sensory afferent neuronal pathways have two routes:

Answer 35

- part of reflex arc | - relayed upward via ascending pathways -> further processing and possible conscious awareness

Question 36

sensory association areas of cortex:

Answer 36

- identification and interpretation sensory info provided by primary cortical area - integration, association (memory) and behaviour

Question 37

define perception:

Answer 37

- awareness and interpretation of sensory info

Question 38

perception: labelled lines

Answer 38

- sensory pathways that transmit info regarding particular modality are specific to that modality

Question 39

Muller's law (law of specific nerve energies):

Answer 39

- sensation invoked by signals generated in receptor is determined by part of brain that they ultimately activate

Question 40

law of projections:

Answer 40

- regardless of where a particular sensory pathway is stimulated along its course - conscious sensation generation is referred to location of receptor

Question 41

law of projections: eg.

Answer 41

- phantom limb pain - L arm and chest during heart attack - pain signals from visceral pain receptors converge on same spinal neurons as somatic pain receptors

Question 42

inadequate stimulus of sufficient strength may stimulate receptors to respond to inappropriate modalities:

Answer 42

- excessive pressure (mechanical energy) on eye stimulate retinal photoreceptors that normally detect light - visual phenomenon (seeing stars)

Question 43

consequences of Muller's law 2: synaesthesia

Answer 43

- stimulation of one sensory modality eg. vision, evokes perceptual experiences in another, eg. hearing - cross talk btw sensory pathways in brain (hearing colours, seeing or smelling sounds, seeing letters as colours)