Section 3 - Sensory contribution to sensorimotor control (part 1)

Question 1

What are sensory receptors

Answer 1

provide input about the body and environment essential for interacting in a complex world

Question 2

What are the 3 ways in which sensory systems are important for the control of movement

Answer 2

Visual, Vestibular, somatosensory

Question 3

Define sensory feedback

Answer 3

The information (input) provided by the receptors of the different sensory systems

Question 4

Describe the diagram of sensory feedback & integration

Answer 4

Behavior/action (eg. muscle contractions)
->
Sensory receptors (eg. eyes, muscle spindles)
-> GIVES FEEDBACK
-> Integration/ decision making (eg. brain, spinal cord circuit)
-> loops back around

Question 5

Where does sensory feedback stem from

Answer 5

receptors in the head, muscles, joints and skin

Question 6

Where does sensory feedback information get integrated (i.e., multi-sensory integration)

Answer 6

Within the central nervous system (and peripheral nervous system?)

Question 7

components of neuronal

Question 8

What are dendrites

Answer 8

Component of neurons Processed that branch off and resemble a tree
- other neurons connect to sites on the dendrites known as “dendrites spines” for communication

Question 9

What are Axons

Answer 9

Component of neurons
Propagates electrical signal (i.e action potential)
- Most neurons have their axons surrounded by myelin & interrupted by gaps known as nodes of Ranvier

Question 10

Function of myelin sheath

Answer 10

Myelin insulates axon, speeds up transmission of the electrical signal, and reduces current leakage

Question 11

Define Pre-Synaptic terminals

Answer 11

“terminal” in the sense of being the ends of axons
- The presynaptic terminal is at the end of an axon and is the place where the electrical signal (the action potential) is converted into a chemical signal (neurotransmitter release)

Question 12

Define House vesicles

Answer 12

Contain neurotransmitters which are released into synaptic cleft (gap between neurons) because of action potentials
- Neurotransmitters cross the cleft to post-synaptic neuron

Question 13

Define Post-synaptic neuron

Answer 13

Receptors on dendrites or cell body receiving neurotransmitters generate electrochemical signals that sometimes lead to an action potential

Question 14

when are action potentials most likely

Answer 14

when postsynaptic neurons receive simultaneous inputs from multiple presynaptic neurons; thus, neurons are integrators of information.

Question 15

What are the 4 functional components of a neuron that generate signals to transmit information & explain them

Answer 15

1) Local input (receptive) component
- A sensory receptor ending or dendrite of a non-receptor neuron

2) Trigger (summing or integrative) component
- Sensory neurons = first node of Ranvier; Motor neurons & interneurons = axon hillock

3) Long-range conducting (signaling) component
- The axon that conducts an action potential

4) Output (secretory) component
- Pre-synaptic terminal where neurotransmitters are released

Question 16

Define afferent neurons

Answer 16

carry information towards the spinal cord and brain; often associated with sensory neurons

Question 17

Define efferent neurons

Answer 17

carry information down the spiral cord and out to the periphery; often associated with motor neutrons

Question 18

define interneurons

Answer 18

neurons that connect other neurons, like an afferent and efferent neutron
- interneurons are abundant in the brain
- refer to figure page 3

Question 19

explain 2 ways in which the frequency of an action potential is key

Answer 19

1) # of action potential
2) time intervals between action potentials

Question 20

what determines the intensity of sensation or speed of movement

Answer 20

not the magnitude (which is always the same) or the duration of individual action potentials, but their frequency

• Many neurons have a baseline frequency (or discharge activity). What is important is the relative change in that frequency (or activity) when communicating with other neurons. Thus, a neuron that decreases its activity when stimulated by another neuron (or by a physical stimulus) still conveys meaningful information within the nervous system.

Question 21

what are the 4 pieces of information that the nervous system extracts from its receptors

Answer 21

1) Modality
2) Intensity
3) Duration
4) Location

Question 22

Explain sensory receptor modality & what it relates to in the course

Answer 22

relates to: 1/4 pieces of information the nervous system extracts from its receptors

def: what was the stimulus? (sight, sound, taste)
- Each of these modalities has submodalities.

• A sensory receptor transforms different types of physical energy (e.g., mechanical, thermal, and chemical) to a language that the nervous system understands. Sensory transduction = converting a form of energy into changes in membrane potential (leading to receptor potentials). These signals are then sent to different areas of the CNS, which then uses them to coordinate a response.

Question 23

Define sensory transduction

Answer 23

converting a form of energy into changes in membrane potential, leading to receptor potentials

• online: Sensory transduction is defined as energy transformation from the external world to the internal world

Question 24

Define sensory receptor intensity and its relation

Answer 24

Relates:1/4 pieces of information the nervous system extracts from its receptors

def: how much we feel or seen the stimulus depends on the strength of the stimulus

Intensity is encoded by:
1) # of sensory receptors activated
- Called population coding

2) Frequency of action potentials
- called frequency coding

Question 25

explain diagrams for frequency coding and population coding

Answer 25

page 8/9

Question 26

compare the results of a strong vs weak stimulus

Answer 26

strong stimulus results in the activation of more receptor endings OR in the activation of more sensory neurons

Question 27

Explain Sensory threshold

Answer 27

• There is a certain intensity at which a stimulus can be perceived
• The sensory threshold is usually defined as the stimulus intensity detected on 50% of trials
  -> his ensures that the likelihood of an individual actually perceiving the stimulus is above chance in an experiment where you have to answer yes or no to whether a stimulus was present at a certain time

Question 28

Define psychophysics

Answer 28

the study of how the quantitative aspects of physical stimuli correlate with the psychological sensations they evoke

Question 29

explain graph of sensory threshold (right, left,middle) - Psychometric function

Answer 29

Relationship between the stimulus intensity and the ability to detect that intensity
- For example, the psychometric curve can shift to the left to a lower threshold due to practice. This means an individual can detect a lowerintensity stimulus. It can shift to the right to raise threshold with injury. This means an individual can detect a stimulus only when presented at a higher intensity.

Question 30

Explain sensory receptor duration & what it relates to in the course & the 2 types of receptors in terms of their adaptation properties

Answer 30

Relates:1/4 pieces of information the nervous system extracts from its receptors

• How long you perceive a stimulus depends on how long the stimulus is present and the intensity of the stimulus.
• Generally, you adapt (become desensitized) as a stimulus persists.
• For stimuli that rise and then plateau, slowly adapting receptors continue to fire during the plateau.
  -> better represents static stimuli (sustained pressure)
  -> static response
• While stimuli ramp up, rapidly adapting receptors keep firing because the intensity is always rising above the level to which they just adapted
  -> better represents time varying stimuli (vibrating or moving)
  -> dynamic response

Question 31

t/f : you adapt (become desensitized) as a stimulus persists.

Answer 31

t

Question 32

Explain sensory receptor location & what it relates to in the course

Answer 32

Relates:1/4 pieces of information the nervous system extracts from its receptors

• Where is the stimulus? This may seem obvious at first, but it depends on the receptive field of the sensory neuron.

Question 33

Explain sensory receptive field

Answer 33

The receptive field of a sensory neuron is the spatial domain in the sense organ where stimulation excites or inhibits the neuron.

Said a different way, a receptive field of a single sensory neuron is a region of sensory space (such as the location on the skin,) in which a stimulus activates that neuron, causing receptor potentials and possibly action potentials.

• Sensory receptive fields provide information about the spatial location of a stimulus. They also determine the spatial resolution of the sensory system

Question 34

Define Cutaneous

Answer 34

of or relating to the skin

Question 35

Explain spatial resolution in reference to sensory receptive field, what test is used for touch sensations spacial resolution

Answer 35

Greater special resolution:
- Smaller receptive field (perceived as multiple points)
- means you can discriminate smaller stimuli
- Lower threshold, more sensitive

test: two-point discrimination test

Question 36

define the two point discrimination test

Answer 36

determines at what separation two closely spaced stimuli can be perceived as distinct

Question 37

explain labelled lines

Answer 37

sensory afferents carry information regarding a single type of receptor from a specific part of the body.

For example, the pattern of action potentials arriving in the visual cortex does not have to start with a code for visual info; neurons are connected there in circuits to process visual information.

That is, the nervous system has an implicit understanding of what information is carried by what neurons.

Question 38

how does the brain “know” about modality and location

Answer 38

labelled lines concept

Question 39

“looking at figures that show the activity of neurons” - what do neurons use action potentials (spikes) for

Answer 39

to transmit information

Question 40

“looking at figures that show the activity of neurons” - what is 1 tick/spike equivalent to

Answer 40

1 action potential

Question 41

“looking at figures that show the activity of neurons” - What 2 ways can this be graphed & what is the x and y axis

Answer 41

1) neural activity can be plotted as individual spikes

2) or as a spike rate / discharge rate / impulse rate

x: Time
y: spikes/second

Question 42

define somatosensory system

Answer 42

This system conveys information about the body and its interaction with the environment. - It includes proprioception and touch.
- Receptors of this system relevant to this course are muscle spindles, golgi tendon organs, joint receptors, and cutaneous (i.e., skin) mechanoreceptors.

Question 43

Define proprioception

Answer 43

The sensation and perception of limb, trunk, and head position
– Where they are in space and in relation to your other limbs/body

Receptors involved in proprioception send information about characteristics such as limb movement direction, location in space, and velocity to the CNS

The most prominent sources of proprioceptive information are muscle spindles, golgi tendon organs, and joint receptors
- However, cutaneous mechanoreceptors and vestibular organs can also contribute
- Vision can also tell you where your limbs are in space and relative to one another

Question 44

Define mechanoreceptor

Answer 44

Mechanoreceptors are a type of somatosensory receptors which relay extracellular stimulus to intracellular signal transduction through mechanically gated ion channels. The external stimuli are usually in the form of touch, pressure, stretching, sound waves, and motion.

Question 45

Define muscle spindles & what are they composed of

Answer 45

Muscle spindles are encapsulated spindle-shaped sensory receptors located in the muscle belly of skeletal muscles

Intrafusal muscle fibres
- Nuclear bag (dynamic bag1 and static bag2) and chain fibres
- Note: extrafusal fibres are regular muscle fibres (muscle is composed of many muscle fibres)

Sensory neuron endings
- Group Ia and Group II afferents
- Wrap around central regions of intrafusal fibres
- Carry sensory input from spindle to the spinal cord

Motor neuron endings (efferent control)
- Activate polar contractile regions of intrafusal fibres
- Two types: static and dynamic gamma motoneurons
- Spindles are unique as somatosensory receptors because they have this efferent part

Question 46

explain gamma motoneurons

Answer 46

Motor neuron endings (efferent control)
Activate polar contractile regions of intrafusal fibres
Two types: static and dynamic gamma motoneurons
Spindles are unique as somatosensory receptors because they have this efferent part

• contract spindles to make them tighter

Question 47

define Intrafusal muscle fibres

Answer 47

Intrafusal fibres are a specialised cell population in skeletal muscle, found within the muscle spindle. These fibres have a mechano-sensory capacity, forming part of the monosynaptic stretch-reflex arc, a key component responsible for proprioceptive function.

Question 48

Label and identify figure of muscle spindles

Answer 48

page 13

Question 49

“Muscle spindles signal position and movement” - how are static muscle lengths / position detected by muscle spindles

Answer 49

via static bag2 & chain fibres
- sensed mostly by group ll afferent

• static gamma motoneurons increase sensitivity to detect static muscle length (which is signalled by group II afferents)
• note: Note that Ia afferents also wrap around the static bag2 and chain fibres, so they also sense static muscle length; the main driver of their firing, however, is dynamic changes in length

Question 50

“Muscle spindles signal position and movement” - how are CHANGES in muscle length (or limb/muscle movement) detected by muscle spindles

Answer 50

via dynamic bag1 fibres
- sensed by la afferent

• Dynamic gamma motoneurons increase sensitivity to detect muscle length changes (which is signalled by group Ia afferents)

Question 51

where are the highest spindle density muscles (3)

Answer 51

Extraocular (Eye muscles)
hand
neck

Question 52

What is alpha-gamma co-activation and why is it necessary

Answer 52

Recall: alpha motoneuron innervates the muscle (not the muscle spindle) and contracts the extrafusal muscle fibres

note: Gamma motoneuron activity contracts spindle to maintain sensitivity of group la and ll afferent to muscle length changes

• if only alpha neurons were activated: only the extrafusal muscle fibres contract. the muscle spindle becomes slack and no APs are fired. it is unable to signal further length changes
• purpose of ay coactivation: normally ay coactivation occurs. Both extrafusal and intramural muscle fibres contract. Tension is maintained in the muscle spindle and it can still signal changes in length. (AP are firing)

Question 53

define passive movement muscle length changes

Answer 53

someone or something other than person moves limb

Question 54

define active movement muscle length changes

Answer 54

person moves their own limb via alpha motoneuron activated muscles

Question 55

Explain the difference between alpha and gamma motor neurons

Answer 55

Motor neurons are divided into two groups. Alpha motor neurons innervate extrafusal fibers, the highly contracting fibers that supply the muscle with its power. Gamma motor neurons innervate intrafusal fibers, which contract only slightly.

Question 56

explain what happens during passive stretch (length ^) and the diagram

Answer 56

PAGE 15

• the spindle responds to passive lengthening stretch
• because movement is generated by weight, there is no alpha or gamma motoneuron activity

diagram:
no alpha or gamma motoneurons (MN) activity is present with passive stretch

• spindle afferent la
• afferent activity: consistent ticks
• muscle length: stretch (flat to upward slope & plateau)

Question 57

explain what happens during a situation in which the gamma motoneuron does not contract the muscle spindle, active contraction (length down) and the diagram

Answer 57

• spindle becomes floppy/slack
  -The alpha motoneuron causes the muscle to contract (shorten), but group Ia neurons don’t discharge

diagram:
- afferent activity: (la?), consistent ticks with a large gap
- muscle force: hill due to contraction

Question 58

explain what happens during a situation in which there is a normal active contraction (length down) & the diagram

Answer 58

the gamma motoneuron co-active (thus pulling the spindle tight) with the alpha motoneuron. In this case, group Ia neurons discharge during the change in muscle length. Whenever the muscle is actively contracted, the muscle spindle is as well. In other words, the brain sends a command via alpha and gamma motoneurons simultaneously.

• normally whenever there is alpha motoneuron activity, there is gamma motoneuron activity

diagram:
- afferent activity: consistent ticks, with la response “filled in”
- muscle force: hill for contraction

Question 59

t or f : the gamma motoneuron tightens the spindle and makes it more sensitive

Answer 59

t

Question 60

Define eccentric contractions

Answer 60

lengthening
works with gravity

Question 61

t or f : for voluntary contractions, spindles and muscle fibres are activated different amounts

Answer 61

f

Question 62

input page 15 3a.4.2.5

Question 63

How does the group la afferents respond to muscle lengthening & figure with release

Answer 63

PAGE 16

• Group Ia afferents show dynamic response to muscle stretch (i.e., changes in muscle length)
• Also show change in firing rate with amount of static stretch similar to group II afferents; thus, can signal static muscle length a bit too
• One way to think about a dynamic response is that it fires to the slope or derivative of the stretch. The slope of the linear stretch below is [zero, one, zero] and the Ia response is [low firing (no change from baseline firing), high firing, low-medium firing]
• If the Ia afferent had a pure dynamic response, it would return to baseline, but instead it contains some static information, and its firing rate remains elevated when stretch is at a plateau.
• during release slope 0,-1,0: GAP OCCURS DURING RAPID UNLOADING (muscle shortening) of muscle

Question 64

How does the group ll afferents respond to muscle lengthening & figure with release

Answer 64

PAGE 16

• Group II afferent activity increases proportionally with amount of stretch

-Though it looks like these respond to changes in muscle length, think of them as taking instantaneous “snapshots” of static muscle length during this period

release:
- no gap

Question 65

what do muscle spindles provide feedback of

Answer 65

the state of the muscle and therefore the position of the limb

Question 66

Explain what is activated for voluntary muscle contractions vs passible limb movements

Answer 66

For voluntary muscle contractions: cortical commands (mostly via interneurons) activate alpha motoneurons to contract the muscle and gamma motoneurons to pull the spindle tight

For passive limb movements: there is no cortical command, and no alpha or gamma motoneuron activation. However, spindle can still detect muscle length changes.

Question 67

t or f: muscle spindles can detect muscle length changes in both voluntary and passive limb movements

Answer 67

t

Question 68

what is feedback from muscle spindles used for (3 answers)

Answer 68

Regulate muscle activity via the alpha motoneuron – Feedback from Ia afferents can trigger the activity of an alpha motoneuron (which is normally activated by descending commands from the brain)

Elicits the stretch reflex
– Nervous system can use information about muscle length to adjust how active a muscle is at a given moment in time (which is important for precise muscle control, like when buttoning your shirt)

Inform higher centres (e.g., cortex, brainstem, cerebellum) about muscle length (and thus limb position)
– This information can help the brain to make decisions about how to move

Question 69

Define monosynaptic stretch reflex & the diagram

Answer 69

Used to regulate muscle length (i.e., tries to maintain desired muscle length OR joint position)

• The muscle spindles sense this change in muscle length. The muscle contracts in response to the stretch. The circuit uses a monosynaptic pathway to cause contraction. It is monosynaptic because there is only one synapse (Ia afferent connects directly to the alpha motoneuron controlling the agonist, or homonymous, muscle).

Question 70

t or f : proprioceptors (eg. muscle spindles) can provide limb state and signal the length of the limb segment/absolute location in space

Answer 70

f, While proprioceptors (e.g., muscle spindles) can provide limb state, they can’t signal the length of the limb segment (or absolute location in space)

Brain must have knowledge of the body’s dimensions to infer the location of the extremities from joint angles. Note that such dimensions change gradually during development and rapidly when we don thick-soled shoes or hold tools.

Question 71

Define Golgi tendon organs (GTO) , its location

Answer 71

Tiny receptors located at muscle-tendon junction

Description automatically generatedGTO is in series with the muscle and tendon (as opposed to in parallel like the muscle spindle)

Question 72

what type of information is relayed in the Golgi tendon organs & via which group

Answer 72

Sensory information relayed via group Ib afferents

Question 73

what type of information are Golgi tendon organs sensitive to

Answer 73

Sensitive to tension/force changes in muscle and body
- (weight-bearing load information)

Question 74

t or f: GTO have both afferent and efferent connections

Answer 74

f: GTOs have no efferent connections and thus are not under CNS modulation like muscle spindles

Question 75

what is the mechanism of action of GTO

Answer 75

under force/load, collagen fibrils pinch the axon of a Ib afferent (thereby causing graded receptor potentials to the point of eliciting an action potential)

Question 76

what is the role of GTO/ what is the GTO feedback

Answer 76

The role of the GTO depends on the state (or task) and the limb

GTO feedback can lead to either inhibition or excitation of muscles (i.e., it can regulate muscle force).

Overall, the effects of GTO feedback are complex: This is because Ib afferents connect to a complex neuronal circuit filled with neurons arising from different areas.

Question 77

explain diagram: How Ib afferent from GTO responds to passive versus active muscle length changes:

Answer 77

Page 19

Question 78

t or f: GTO does not need gamma motoneuron

Answer 78

t

Question 79

where are joint receptors found

Answer 79

Joint receptors are found within the connective tissue, capsule, and ligaments of joints.

Several types exist. Depending on the type, they sense joint pressure and angle, direction and velocity, or twisting force.

Question 80

define range fractionation & why its important

Answer 80

having multiple receptors activated in overlapping ranges

• important since it provides greater resolution about joint angles

Question 81

explain joint receptors varying proprioception

Answer 81

Joint receptors contribute to the perception of our position in space (proprioception) at some joints more than others.

Research suggests that information from muscles, tendons, skin, and joints are combined to provide estimates of joint position and movement.

For example, when the hip joint is replaced — removing all joint receptors — the ability to detect the position of the thigh relative to the pelvis is not lost. At joints of the fingers, joint receptors play a much larger role in providing proprioception.

Question 82

t or f : Some joint receptors appear sensitive only at extreme ranges of motion. Some groups of joint receptors respond to limited ranges of joint motion.

Answer 82

t, related to range fractionation

Question 83

what are _ techniques to study proprioception

Answer 83

1) Deafferentation (surgical or temporary)
-> Deafferentation results in proprioception being unavailable

2) sensory neuropathy

3) muscle/tendon vibration

Question 84

explain surgical deafferentation, what is this a technique of

Answer 84

Surgically cut or remove afferent neural pathways

In animals, this results in less precision of well learned motor skills (such as climbing or reaching in monkeys)

• technique to study proprioception

Question 85

Explain temporary deafferentation, what is this a technique of

Answer 85

Blood pressure cuff inflated around a part of a limb until person can’t feel anything below

Portion of limb ‘falls asleep’ (lose sensation)
Efferent paths still intact

Can also give injection around nerve with anesthetic to eliminate feedback (i.e., nerve block)

• technique to study proprioception

Question 86

explain sensory neuropathy patients, what is this a technique of

Answer 86

Diabetes is one of a number of causes of neuropathy
- In these patients, peripheral afferent nerves in various body parts are not functioning properly – Efferent pathways intact (strength is normal)

Unless these patients can see their limbs, they cannot sense their position nor detect motion of joints, because these sensations are mediated primarily by receptors in muscles and joints supplied by large-diameter fibres

Tactile sensation is also impaired
- Hence, manual dexterity is severely impaired in these patients even in habitual tasks such as writing and buttoning clothes

Nevertheless, they can perform a surprising range of pre-programmed finger movements that don’t require somatosensory feedback with remarkable accuracy
E.g., discrete movements that happen rapidly and/or are very short in duration

• technique to study proprioception

Question 87

Explain muscle/tendon vibration, what is this a technique of

Answer 87

• High-speed vibration applied to a muscle/tendon
• Distorts muscle spindle firing patterns and hence distorts proprioceptive feedback – Preferentially affects group Ia afferents
• Gives illusion of muscle lengthening
  Thus, causes compensatory movements
• technique to study proprioception

Question 88

t or f: with muscle/tendon vibrations, the compensatory response is generally opposite of the illusory perception caused by vibration and under normal circumstances would help maintain balance equilibrium.

Answer 88

t

Question 89

explain the growing nose pattern/pinocchio effect and what does it demonstrate

Answer 89

• vibration of the biceps & blocked vision
• this creates illusions of muscle stretch
• The brain interprets it as change in joint angle, biceps vibration feels like elbow extension
• this creates a conflict: the fingers are touching the nose, but the arm is felt to be extended
• The brain’s solution is that the fingers or nose or both have elongated.

demonstrates:
- This example demonstrates that muscle spindle activity is sufficient for proprioception and that the “body schema” (or “internal model”) of the body’s dimensions is extremely plastic.

Question 90

what does proprioception facilitate

Answer 90

1) movement accuracy
- Proprioception provides kinematic (position/speed) and kinetic (force) feedback

2) Helps your brain know where and how your limbs are moving, which allows it to correct the trajectory of a movement and ensure distance accuracy
- Deafferentation causes several movement deficits

3) Co-ordination of body and limb segment
- including Postural control : E.g. ankle muscle length changes tell the nervous system which direction and by how much you are swaying about the ankle joint while standing

4) Neuropathy causes increased postural sway
- Spatial-temporal coupling between limbs and segments

5) Knowing the joint angle and how fast a limb is moving is important because it allows the nervous system to adjust the timing/onset of different muscles that act across different joints to ensure smooth movement
- In this sense, proprioception helps solve the serial-order problem

Question 91

why are cutaneous receptors important

Answer 91

touch relies on cutaneous receptors

• Tactile information on texture, composition, and shape of surfaces and objects – Relies on receptors in the skin (i.e., cutaneous mechanoreceptors)
• Important for:
  Object manipulation
  Precision
  Sensing body position

Question 92

what are the 6 cutaneous receptors and what are they for

Answer 92

1) Meissner corpuscle = stroking & vibration

2) Pacinian corpuscle = vibration

3) Ruffini’s corpuscle = skin stretch

4) Merkel’s disk = Pressure

5) Free nerve endings = Pain

6) Hair follicles = stroking

Question 93

explain the connection between cutaneous receptors different receptive field sizes, depth, and adaptive properties

Answer 93

• Rapid adapting = neural spike is dense then gap
• slow adapting = dense then gradual consistent spikes

depth is related to the receptive field:
(1) higher on skin surface =smaller receptive field
- allows for greater discrimination

(2) deeper in the skin = broader receptive fields

Question 94

where are cutaneous receptors more concentrated in (hands) and feet & why

Answer 94

cutaneous receptors are concentrated more around the lateral edges, heel, and forefoot/toes on the bottom of the feet

• This allows the nervous system to detect the edges of the BOS to better regulate the COP and hence body COM

Question 95

give an example of how we know that cutaneous receptors can contribute to proprioception

Answer 95

PAGE 25
-Elbow flexion naturally stretches elbow skin.

• When skin stretch is applied in the same direction as muscle stretch via vibration, there is an increase in the perceived sensation of movement above and beyond that produced when each is applied alone
• This shows that input from skin stretch contributes to proprioception.

Question 96

how does somatosensory feedback reach the brain

Answer 96

Sensory information from muscle spindles, golgi tendon organs, joint receptors, and cutaneous receptors is carried to the spinal cord via afferent neurons
- where it ascends via other neurons to the brain (primary somatosensory cortex and cerebellum).

Question 97

Explain somatosensory cortex

Answer 97

NEEDS TO BE UPDATED

• contains a map of sensory space (brain’s physical representation of the body)

-

Question 98

explain somatotopy

Answer 98

correspondence of body area to a specific part of the brain such that adjacent body parts are represented near each other in the brain

Question 99

explain retinotopy

Answer 99

in visual cortex:
- visual space is mapped retinotopically
- This kind or organization is efficient because inputs to adjacent parts of the skin or retina need to be compared to extract information like shape

Question 100

why are somatotopy & retinotopy important

Answer 100

Somatotopy and retinotopy allow comparisons to be made over shorter distances in brain circuits, which is faster and more energetically efficient.

Question 101

explain the somatotropin map visualized as a sensory “homunculus”

Answer 101

Different body parts have different size representations in the somatosensory cortex

• Representation size is proportional to NUMBER OF RECEPTORS rather than area of skin, so more densely innervated skin appears magnified in the homunculus