Section 3 - Sensory contribution to sensorimotor control (part 1) Flashcards
What are sensory receptors
provide input about the body and environment essential for interacting in a complex world
What are the 3 ways in which sensory systems are important for the control of movement
Visual, Vestibular, somatosensory
Define sensory feedback
The information (input) provided by the receptors of the different sensory systems
Describe the diagram of sensory feedback & integration
Behavior/action (eg. muscle contractions)
->
Sensory receptors (eg. eyes, muscle spindles)
-> GIVES FEEDBACK
-> Integration/ decision making (eg. brain, spinal cord circuit)
-> loops back around
Where does sensory feedback stem from
receptors in the head, muscles, joints and skin
Where does sensory feedback information get integrated (i.e., multi-sensory integration)
Within the central nervous system (and peripheral nervous system?)
components of neuronal
What are dendrites
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
What are Axons
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
Function of myelin sheath
Myelin insulates axon, speeds up transmission of the electrical signal, and reduces current leakage
Define Pre-Synaptic terminals
“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)
Define House vesicles
Contain neurotransmitters which are released into synaptic cleft (gap between neurons) because of action potentials
- Neurotransmitters cross the cleft to post-synaptic neuron
Define Post-synaptic neuron
Receptors on dendrites or cell body receiving neurotransmitters generate electrochemical signals that sometimes lead to an action potential
when are action potentials most likely
when postsynaptic neurons receive simultaneous inputs from multiple presynaptic neurons; thus, neurons are integrators of information.
What are the 4 functional components of a neuron that generate signals to transmit information & explain them
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
Define afferent neurons
carry information towards the spinal cord and brain; often associated with sensory neurons
Define efferent neurons
carry information down the spiral cord and out to the periphery; often associated with motor neutrons
define interneurons
neurons that connect other neurons, like an afferent and efferent neutron
- interneurons are abundant in the brain
- refer to figure page 3
explain 2 ways in which the frequency of an action potential is key
1) # of action potential
2) time intervals between action potentials
what determines the intensity of sensation or speed of movement
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.
what are the 4 pieces of information that the nervous system extracts from its receptors
1) Modality
2) Intensity
3) Duration
4) Location
Explain sensory receptor modality & what it relates to in the course
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.
Define sensory transduction
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
Define sensory receptor intensity and its relation
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
explain diagrams for frequency coding and population coding
page 8/9
compare the results of a strong vs weak stimulus
strong stimulus results in the activation of more receptor endings OR in the activation of more sensory neurons
Explain Sensory threshold
- 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
Define psychophysics
the study of how the quantitative aspects of physical stimuli correlate with the psychological sensations they evoke
explain graph of sensory threshold (right, left,middle) - Psychometric function
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.
Explain sensory receptor duration & what it relates to in the course & the 2 types of receptors in terms of their adaptation properties
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
t/f : you adapt (become desensitized) as a stimulus persists.
t
Explain sensory receptor location & what it relates to in the course
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.
Explain sensory receptive field
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
Define Cutaneous
of or relating to the skin
Explain spatial resolution in reference to sensory receptive field, what test is used for touch sensations spacial resolution
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
define the two point discrimination test
determines at what separation two closely spaced stimuli can be perceived as distinct
explain labelled lines
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.
how does the brain “know” about modality and location
labelled lines concept
“looking at figures that show the activity of neurons” - what do neurons use action potentials (spikes) for
to transmit information
“looking at figures that show the activity of neurons” - what is 1 tick/spike equivalent to
1 action potential
“looking at figures that show the activity of neurons” - What 2 ways can this be graphed & what is the x and y axis
1) neural activity can be plotted as individual spikes
2) or as a spike rate / discharge rate / impulse rate
x: Time
y: spikes/second
define somatosensory system
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.
Define proprioception
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
Define mechanoreceptor
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.
Define muscle spindles & what are they composed of
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
explain gamma motoneurons
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
define Intrafusal muscle fibres
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.
Label and identify figure of muscle spindles
page 13
“Muscle spindles signal position and movement” - how are static muscle lengths / position detected by muscle spindles
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
“Muscle spindles signal position and movement” - how are CHANGES in muscle length (or limb/muscle movement) detected by muscle spindles
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)
where are the highest spindle density muscles (3)
Extraocular (Eye muscles)
hand
neck
What is alpha-gamma co-activation and why is it necessary
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)
define passive movement muscle length changes
someone or something other than person moves limb
define active movement muscle length changes
person moves their own limb via alpha motoneuron activated muscles
Explain the difference between alpha and gamma motor neurons
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.
explain what happens during passive stretch (length ^) and the diagram
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)
explain what happens during a situation in which the gamma motoneuron does not contract the muscle spindle, active contraction (length down) and the diagram
- 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
explain what happens during a situation in which there is a normal active contraction (length down) & the diagram
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
t or f : the gamma motoneuron tightens the spindle and makes it more sensitive
t
Define eccentric contractions
lengthening
works with gravity
t or f : for voluntary contractions, spindles and muscle fibres are activated different amounts
f
input page 15 3a.4.2.5
How does the group la afferents respond to muscle lengthening & figure with release
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
How does the group ll afferents respond to muscle lengthening & figure with release
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
what do muscle spindles provide feedback of
the state of the muscle and therefore the position of the limb
Explain what is activated for voluntary muscle contractions vs passible limb movements
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.
t or f: muscle spindles can detect muscle length changes in both voluntary and passive limb movements
t
what is feedback from muscle spindles used for (3 answers)
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
Define monosynaptic stretch reflex & the diagram
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).
t or f : proprioceptors (eg. muscle spindles) can provide limb state and signal the length of the limb segment/absolute location in space
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.
Define Golgi tendon organs (GTO) , its location
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)
what type of information is relayed in the Golgi tendon organs & via which group
Sensory information relayed via group Ib afferents
what type of information are Golgi tendon organs sensitive to
Sensitive to tension/force changes in muscle and body
- (weight-bearing load information)
t or f: GTO have both afferent and efferent connections
f: GTOs have no efferent connections and thus are not under CNS modulation like muscle spindles
what is the mechanism of action of GTO
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)
what is the role of GTO/ what is the GTO feedback
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.
explain diagram: How Ib afferent from GTO responds to passive versus active muscle length changes:
Page 19
t or f: GTO does not need gamma motoneuron
t
where are joint receptors found
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.
define range fractionation & why its important
having multiple receptors activated in overlapping ranges
- important since it provides greater resolution about joint angles
explain joint receptors varying proprioception
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.
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.
t, related to range fractionation
what are _ techniques to study proprioception
1) Deafferentation (surgical or temporary)
-> Deafferentation results in proprioception being unavailable
2) sensory neuropathy
3) muscle/tendon vibration
explain surgical deafferentation, what is this a technique of
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
Explain temporary deafferentation, what is this a technique of
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
explain sensory neuropathy patients, what is this a technique of
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
Explain muscle/tendon vibration, what is this a technique of
- 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
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.
t
explain the growing nose pattern/pinocchio effect and what does it demonstrate
- 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.
what does proprioception facilitate
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
why are cutaneous receptors important
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
what are the 6 cutaneous receptors and what are they for
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
explain the connection between cutaneous receptors different receptive field sizes, depth, and adaptive properties
- 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
where are cutaneous receptors more concentrated in (hands) and feet & why
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
give an example of how we know that cutaneous receptors can contribute to proprioception
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.
how does somatosensory feedback reach the brain
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).
Explain somatosensory cortex
NEEDS TO BE UPDATED
- contains a map of sensory space (brain’s physical representation of the body)
-
explain somatotopy
correspondence of body area to a specific part of the brain such that adjacent body parts are represented near each other in the brain
explain retinotopy
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
why are somatotopy & retinotopy important
Somatotopy and retinotopy allow comparisons to be made over shorter distances in brain circuits, which is faster and more energetically efficient.
explain the somatotropin map visualized as a sensory “homunculus”
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
