Perception and Sensorimotor Control

Question 1

state what it is meant by the key term - perception

Answer 1

perception is the process of obtaining information about the internal/external environment via sensory stimulation

Question 2

state 3 basic facts to expand upon the definition of perception

Answer 2

1) can be unconscious or conscious (i.e. - sensation) process
2) relies on specialised nerve cells which convert mechanical, visual, acoustic, or chemical energy into a neural signal
3) brings information into the brain (afferent signals) for controlling, planning, and deciding

Question 3

give 3 additional (different to the basic) facts to help explain what perception actually is

Answer 3

1) often multimodal (integrates multiple senses)
2) can be modulated by the CNS (i.e. - how much a sensor responds to a stimulus)
3) involves motor behaviour (i.e. - move to perceive & perceive to move)

Question 4

state what it is meant by the key term - Receptors

Answer 4

Receptors absorb energy and convert that energy into a neural signal. They are classified based on the source of the stimulus

Question 5

state the 5 types of receptors

Answer 5

1) Photoreceptors - sensitive to light
2) Mechanoreceptors - sensitive to mechanical input
3) Chemoreceptors - sensitive to chemical substances
4) Thermoreceptors - sensitive to thermal energy
5) Nociceptors - can fall into one or more of these categories - sensitive to pain

Question 6

depending on the origin of the signal, the five types of receptors can be classified into what 3 types?

Answer 6

1) Exteroceptors - respond to signals coming from the environment
2) Interoreceptors - respond to stimuli from within the body
3) Proprioceptors - give information about the position of the body elements in space

Question 7

what are the two types of sensory adaptation speeds ?

Answer 7

Tonic (slow) or Phasic (fast) adapting receptors

Question 8

state 4 facts about sensory adaption

Answer 8

1) the stronger the stimulus, the higher the firing rate in the afferent axon
2) response tends to decrease over time if the stimulus remains constant

• slow adapting: the decline is slow
• fast adapting: the decline is fast

Question 9

state what it is meant by the key term - Somatic Receptors

Answer 9

Somatic Receptors are located in the skin or in MSK tissues and process information about stimuli acting on the body surface of deeper structures

Question 10

what are the three sib-systems that somatic receptors process information about

Answer 10

1) Cutaneous - fine touch, vibration, pressure
2) Proprioception - muscle, tendon, joints
3) Pain - painful stimuli, coarse touch

Question 11

what are the four types of Somatic Sensory Afferents?

Answer 11

1) T1 / Aa
2) T2 / AB
3) T3 / Ao
4) T4 / C

Question 12

state the following for T1 somatic sensory afferents:

1) function
2) type
3) myelin?
4) diameter (um)
5 conduction speed (m/s)

Answer 12

1) Proprioception
2) Muscle Spindle
3) Yes
4) 13 - 20 um
5) 80 - 120 m/s

Question 13

state the following for T2 somatic sensory afferents:

1) function
2) type
3) myelin?
4) diameter (um)
5 conduction speed (m/s)

Answer 13

1) Touch
2) Cutaneous
3) Yes
4) 6 - 12 um
5) 25 - 75 m/s

Question 14

state the following for T3 somatic sensory afferents:

1) function
2) type
3) myelin?
4) diameter (um)
5 conduction speed (m/s)

Answer 14

1) Pain, Touch
2) Free Nerve Endings
3) Yes
4) 1 - 5 um
5) 5 - 30 m/s

Question 15

state the following for T4 somatic sensory afferents:

1) function
2) type
3) myelin?
4) diameter (um)
5 conduction speed (m/s)

Answer 15

1) Pain, Touch
2) Free Nerve Endings
3) No
4) 0.2 - 1.5 um
5) 0.5 - 2 m/s

Question 16

state what it is meant by the key term - Musculotendineous Receptors

Answer 16

Musculotendineous Receptors are mechanoreceptors of five different types, situated in the various soft tissues of the MSK system

Question 17

what are the 5 types of Musculotendineous Receptors ?

Answer 17

1) Muscle Spindle - in muscles; stretch sensor (amount & speed)
2) GTO - at MT junction; force sensor
3) Golgi, Ruffini, Paciniform - connective tissue of joints (Ruffini, Paciniform) or ligaments (Golgi); similar to cutaneous sensors; position sensory (limit detectors)

Question 18

what are Golgi Tendon Organs ? (2 points)

Answer 18

• a bundle of collagen fibres innervated by afferent axons

- axons branch out into the fine spaces in the collage mesh

Question 19

how do GTO’s work ? (2 points)

Answer 19

• when a force is applied, the collagen is stretched which causes depolarisation of the sensory unit causing an action potential
• in certain ranges of force (typically between 0.5 - 25 N), are proportional to the force applied

Question 20

where are GTO’s located, and what is the function of this ?

Answer 20

• at the interface between muscle fibres and the tendon
• NOT within the tendon itself –> makes them sensitive, especially to the force developed by active force contraction and passive stretch of the muscle

Question 21

are GTO’s fast or slow adapting receptors ?

Answer 21

Slow Adapting Receptors - sensitive to the overall amount of force applied, and not the rate of force application

Question 22

what are Muscle Spindles?

Answer 22

Muscle Spindles are Stretch Receptors

Question 23

what is the location of Muscle Spindles, and how does this enable them to do their job?

Answer 23

Muscle Spindles run parallel to the muscle fibre; they have a resting fibre potential which generates a firing rate as the muscle elongates and elongates the spindle with it

Question 24

what is the overall structure of Nuclear Bag and Nuclear Chain muscle spindles ? (2 points)

Answer 24

1) vary between 0.1 mm - 1 cm in length

2) a capsule of connective tissue (fusiform in shape) with several inter-connected fibres (3 - 18)

Question 25

what is the difference between nuclear bag and nuclear chain fibres structure ?

Answer 25

1) Nuclear Bag Fibres (one static, one dynamic) --> have nuclei in the middle 2) Nuclear Chain Fibres --> have nuclei along the whole fibre

Question 26

what information do Muscle Spindles give?

Answer 26

give information about muscle fibre length and rate of change in length (they do not directly produce force!)

Question 27

how are Muscle Spindles innervated ?

Answer 27

Muscle Spindles are innervated by the CNS and can control them through gamma motor neurones, type 1a and type 2 afferent axons

Question 28

explain what type 1a Afferent Neurones are: 1) function 2) how they work 3) how they work 4) origin/location

Answer 28

- primarily respond to the rate of change in muscle length - when muscle lengthening ceases, the firing rate returns to almost resting rate (fast adaptation - phasic) - increases AP's in a slow stretch, but not as frequent as a fast stretch - originates from static nuclear bag fibres, the nuclear chain fibres, but also wraps around the dynamic nuclear bag fibre

Question 29

explain what type 2 afferent neurones are: 1) function 2) how they work 3) origin/location

Answer 29

- APs remain in high frequency for the whole duration of the stimulus - slow response - sensitive to the overall length status of the muscle fibre - not the rate of stretch - originates from the static nuclear bag fibre and the nuclear chain fibre

Question 30

state what it is meant by the key term - Vestibular System

Answer 30

the Vestibular System processes sensory information related to head position, spatial orientation (with respect to gravity), and movement

Question 31

give 2 basic facts about the vestibular system

Answer 31

1) "6th Sense" - we are unaware of it | 2) key for the control of balance, eye movement, and perception of orientation in the environment while moving

Question 32

what 3 things does the Labyrinth consist of?

Answer 32

- 5 sensory neurones - 3 semilunar canals (approx. 3 mm diameter) - 2 otolith organs (utricle & saccule)

Question 33

All elements of the Labyrinth contain a fluid. What is this fluid, and what is its function?

Answer 33

- Endolymph - when the head moves, it causes nerve receptors in the membraneous labyrinth to signal to the brain about the body's motion

Question 34

what are key sensitive elements for the Labyrinth?

Answer 34

Hair Cells are the key sensitive elements in the structure of the Labyrinth and are located in the Pulis, Canals, and the Auto Leeth Organs

Question 35

what is the main part of the vestibular system?

Answer 35

an elaborate set of interconnected chambers called the Labyrinth (continuous and like the cochlea)

Question 36

where are the Labyrinth located ?

Answer 36

Labyrinth are located deep in temporal bone

Question 37

how do Labyrinth do their job?

Answer 37

Labyrinth are derived from optic placode of embryo and uses hair cells to transduce physical motion as neural stimuli

Question 38

what do the utricle & saccule function to do? what do the semilunar canals function to do?

Answer 38

the Utricle & Saccule specialise in translational movements of the head and static positions relative to the gravitational axis the Semilunar Canals respond to head rotations

Question 39

what is between the walls of the Labyrinth?

Answer 39

Perilymph (similar to cerebrospinal fluid)

Question 40

what is the function of Hair Cells ?

Answer 40

Hair Cells function is based on the detection of the 'Kinocilium' (longest hair) and the 'Sterocilia' (smaller hair) they transduce minute displacements into receptor potentials --> provides a basis for vestibular function

Question 41

how do Hair Cells function ? (3 points)

Answer 41

- when there is a movement of the Sterocilia towards the Kinocilium, there is a depolarisation of the membrane - during the movement of the Kinocilium towards the Sterocilia, there is hyperpolarisation of the cell membrane - no response occurs when there are other types of deflection in a perpendicular motion

Question 42

what does the 'Biphasic Nature' of the hair cells mean?

Answer 42

- means transduction channels are open in the absence of stimulation --> hair cells tonically release transmitter --> generates spontaneous APs in nerve cells - consequence --> firing rates of vestibular fibres can inc^ or dec^ in a manner that mimics the receptor potentials generated by Hair Cells --> mediated by Ca2+ entering through mechanoelectrical transduction and voltage gated ion channels --> allows hair cells to continue to signal small changes in head position, despite much larger tonic forces of gravity

Question 43

where are Hair Cells located, and what are their surroundings ?

Answer 43

- located in Ampulla - clustered in Crista; protected by gelatinous substance which forms a diaphragm between two different halves of the canal (capula)

Question 44

explain, using 3 points, how Hair Cells function

Answer 44

- when head moves it causes angular acceleration & canals actually respond to angular accelerations of the head - whenever the head is rotated, the canal moves together, and alongside the fluid inertia will generate deformation of the capula which will, in turn, deflect your hairs - depending on the direction, this will mean depolarisation (inc^ AP firing rate) or hyperpolarisation (dec^ AP firing rate)

Question 45

Explain what events occur when you tilt your head to the left in the canals

Answer 45

- fluid presses right side of capula - therefore, sterocilia move towards kinocilium - inc^ AP rate - as continues left, reaches steady velocity, so no more effect of fluid inertia, so firing rate returns to resting value - at some point, left movement will have to stop due to mobility & return to static position - this causes deceleration - therefore, canal walls move clockwise & place pressure on left of capula - causes kinocilium to move towards sterocilia & hyperpolarise membrane, dec^ AP firing rate

Question 46

what is the semilunar canal geometry ?

Answer 46

one horizontal, and two at 45 degree inclinations (the head can therefore respond to different rotations)

Question 47

the capula-endolymph system smooths transduction of angular accelerations into neural signals. This results in what two things?

Answer 47

1) results in a velocity signal at low frequencies | 2) results in an acceleration signal at high frequencies

Question 48

where are Hair Cells located ?

Answer 48

Hair Cells are located in a patch of epithelium called the 'Macula'

Question 49

state what it is meant by the key term - Otolith Inertia

Answer 49

Otolith Inertia is the deformation of the otolithic membrane, causing deflection of hairs

Question 50

state what it is meant by the key term - Otolith

Answer 50

Otolith are calcium carbonate crystals which are fused together and adhere to the top of the gelatinous membrane

Question 51

where do Hair Cells project from?

Answer 51

there is a gelatinous sheet (falitic membrane) where the hairs project from

Question 52

Hair Cells have a very complex distribution and orientation. Explain it using 4 points

Answer 52

- curved thread like identification that runs across the Macula - the Striola - hairs in Otolith point towards Striola, but in Succula they point away from the Striola - so, macula of the striola is about in the sagittal plane when the head is upright - the macula of the Otricol is perpendicular to the sagittal plane, and is tilted approx 20 - 30 degrees to the horizontal when the head is in an upright position

Question 53

what is the function of the Otolith Organs (Utricle & Saccule)?

Answer 53

the Utricle & Saccule detect tilting & translational movements of the head

Question 54

how do the Otolith Organs detect changes in head position ? (3 points)

Answer 54

- Hair Cells embedded in Otolithic Membrane embedded in Otoconia - Otoconia makes otolithic membrane heavier than structures & fluids surrounding it - head tilt = gravity = membrane shifts relative to macula - resulting shearing motion displaces hair bundles, generating receptor potential

Question 55

Striola form an axis of mirror symmetry such that hair cells on opposite sides of the Striola have opposing morphological polarisations. What 2 things does this mean?

Answer 55

- head tilt along striola axis excites hair cells on one side whilst inhibiting hair cells on the other side - the saccular macula is oriented vertically and the utricular macula horizontally, with continuous variation in the morphological polarisation of the hair cells located in the macula