Section 3a Notes Flashcards
1
Q
Give the function of sensory receptors
A
provide in put about the body and environment essential for interacting in a complex world
- receptors are in the head, muscles, joints and skin
2
Q
What are the 3 sensory systems important for the control of movement?
A
visual, vestibular (inner ear), and somatosensory (proprioception)
3
Q
Define: sensory feedback
A
The information (or input) provided by the receptors of the different sensory systems
4
Q
What is the structure and function of dendrites
A
- branch off and resemble a tree
- other neurons connect to sites on dendrites for communication
5
Q
What is the structure and function of axons
A
- Propagates electrical signal (i.e., action potential)
- Most neurons have their axons surrounded by myelin and
interrupted by gaps known as nodes of Ranvier
6
Q
Describe the function of myelin
A
- Myelin insulates axon, speeds up transmission of the electrical signal, and reduces current leakage
7
Q
Describe the function and location of pre-synaptic terminals
A
- House vesicles containing neurotransmitters, which are released into synaptic cleft (gap between neurons) by action potentials
- Neurotransmitters cross the cleft to post-synaptic neuron
8
Q
Describe the location and function of the post-synaptic neurons
A
- Receptors on dendrites or cell body receiving neurotransmitters generate electrochemical signals that sometimes lead to an action potential
- Action potentials are most likely when postsynaptic neurons receive simultaneous inputs from multiple presynaptic neurons; thus, neurons are integrators of information.
9
Q
What are the 4 functional components of a neuron that generate signals to transmit information
A
- Local input (receptive) component: A sensory receptor ending or dendrite of a non-receptor neuron
- Trigger (summing or integrative) component: Sensory neurons = first node of Ranvier; Motor neurons & interneurons = axon hillock
- Long-range conducting (signaling) component: The axon that conducts an action potential
- Output (secretory) component: Pre-synaptic terminal where neurotransmitters are released
10
Q
Define: afferent neurons
A
carry information towards the spinal cord and brain; often associated with sensory neurons
11
Q
Define: efferent neurons
A
carry information down the spinal cord and out to the periphery; often associated with motor neurons
12
Q
Define: interneurons
A
neurons that connect other neurons, like an afferent and efferent neuron; interneurons are abundant in the brain
13
Q
What determines the intensity of sensation or speed of movement?
A
- frequency! ( which is equal to the # of action potentials and time intervals between each action potential)
- number of sensory receptors activated (aka population coding)
14
Q
What are some other names for frequency of an action potential?
A
- discharge, discharge activity, spike rate, or firing rate
15
Q
What is another word for the baseline frequency of neurons
A
discharge activity
16
Q
What 4 pieces of information does the nervous system extract from its receptors
A
- modality: sight, touch, sound, taste, smell
- intensity
- duration
- location
17
Q
Define: sensory transduction
A
converting a form of energy into changes in membrane potential (leading to receptor potentials).
18
Q
What information does this somatosensory system receptor detect?: cutaneous mechanoreceptors
A
touch
19
Q
What information does this somatosensory system receptor detect?: thermal receptors
A
temperature
20
Q
What information does this somatosensory system receptor detect?: nociceptors
A
pain
21
Q
What information does this somatosensory system receptor detect?: muscle mechanoreceptors
A
muscle force and length
22
Q
Define and explain: population coding
A
# of sensory receptors activated - a strong stimulus compared to a weak stimulus results in the activation of more receptor endings or in the activation of more sensory neurons
23
Q
Define: sensory threshold
A
- intensity at which stimulus can be perceived defined to be the stimulus intensity detected on 50% of trials
24
Q
Define: psychophysics
A
The study of how the quantitative aspects of physical stimuli correlate with the psychological sensations they evoke
25
Give some examples of factors that effect the relationship between stimulus intensity and the ability to detect that intensity
- fatigue
- practice
- context in which the stimulus is presented
26
Explain the different between slowly adapting receptors vs rapidly adapting receptors
- adaptation to consistent stimuli through decreasing frequency of the action potentials (see diagram in notes)
- slowly adapting receptors = static response (best suited for static stimuli like sustained pressure)
- rapidly adapting receptors = dynamic response (best suited for vibrating/moving stimuli)
27
Define: receptive field of a sensory neuron?
- a particular 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
- determine spatial resolution of the sensory system; greater the resolution = you can discriminate smaller stimuli
28
How can you test spatial resolution for touch sensations?
two point discrimination test
| - this test determines at what separation two closely spaced stimuli can be perceived as distinct.
29
What parts of the body have the greatest spatial resolution for touch?
- hands
- cheek
- upper lip
30
What parts of the body have the worst spatial resolution for touch?
- back
- thigh
- sole of feet
31
Explain the labelled line concept
- A hypothesis to explain how different nerves, all of which use the same physiological principles in transmitting impulses along their axons, are able to generate different sensations.
- sensory afferents carry information regarding a single type of receptor from a specific part of the body; the nervous system has an implicit understanding of what information is carried by what neurons.
32
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: muscle spindles, golgi tendon organs, joint receptors, and cutaneous (i.e., skin) mechanoreceptors
33
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
34
Receptors involved in proprioception send information about characteristics such as what?
limb movement direction, location in space, and velocity to the CNS
35
What are the most prominent sources of proprioceptive information?
- muscle spindles
- golgi tendon organs
- joint receptors
- others: vision, cutaneous mechanoreceptors, vestibular organs
36
Define and give the function of muscle spindles
- encapsulated spindle-shaped sensory receptors located in the muscle belly of skeletal muscles
- function: signal position and movement by detecting muscle length and changes in muscle length,
37
What are muscle spindles composed of?
- intrafusal muscle fibres
- sensory neuron endings
- gamma motor neuron endings
- see notes for more information
38
What do group 1a afferents sense vs group 2 afferents
group 1a: changes in muscle length (and muscle length)
| group 2: muscle length
39
When dynamic gamma motoneurons increase sensitivity, what do they detect?
muscle length changes (related to Ia afferents)
40
When static gamma motoneurons increase sensitivity, what do they detect?
static muscle length (related to II afferents)
41
Which muscles have the highest spindle density?
- extraocular (eye muscles), hand, neck
42
What is alpha-gamma co-activation and why is it necessary?
- gamma motoneurons and alpha neurons both fire at the same time (aka coactivation)
- if only alpha motor neurons were activated, only extrafusal muscle fibers contract, the muscle spindle becomes slack and no APs are fired. it is unable to signal further length changes
- when both gamma and alpha motoneurons contract, both extrafusal and intrafusal muscle fibers contract. tension is maintained in the muscle spindle and it can still signal changes in length
43
How do muscle spindle Ia afferents respond to passive versus active muscle length changes
passive stretch (length increases): no alpha or gamma motoneuron activity is present with passive stretch since the movement is externally generated by bodyweight; action potentials of Ia afferents occur once muscle length changes.
active contraction (length decreases): in a hypothetical situation where only alpha motoneurons are stimulated (and not gamma motoneuron activity) during muscle contraction, there is no ia afferent action potentials during the contraction. the spindle goes "slack" because there is no gamma motoneuron activity
active contraction (length decreases): in a normal situation (both alpha and gamma motoneurons fire), ia afferent action potentials are present and fire consistently during muscle contraction and after. the spindle remains tight
44
Describe the function of gamma motoneurons
keep spindles tight and makes it more sensitive (when holding a hair elastic, you are better able to detect changes in the length of the band with your eyes closed when the band is pulled taut vs slack
45
Fill in the blank: For voluntary contractions, spindle activation _____ the effort put into the contraction, and a ____ in gamma drive (i.e., activity) is directed only to the contracting muscle
- parallels
| - increase
46
Why do eccentric contractions generate very strong Ia afferent activity?
- muscle lengthening with gamma drive both individually increase Ia activity so the combined result creates even stronger firing
47
When is alpha-gamma co-activation most helpful?
when contractions are relatively slow or the muscle is working against a load
48
Unloaded rapid shortening movements are likely to show little increase in spindle
feedback. So how does the brain know how the muscle length is changing?
Presumably it gets
feedback from stretched (i.e., lengthened) antagonist muscles because each joint’s angle can be determined by the length of the flexors or the extensor muscles.
- E.g., biceps (agonist) contracts rapidly while triceps (antagonist) lengthens passively during elbow flexion; Ia afferents in triceps provide brain the needed information about muscle length changes
- Thus, the brain uses input from multiple muscle spindles from different muscles to sense limb position and movement
49
How do the group Ia and II afferents respond to muscle length?
- Group II afferents increase 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. gaps in action potentials occur during rapid unloading (shortening) of the muscle (example; tendon tap or muscle/tendon vibration or release of a lengthening muscle (see diagram)
- Group Ia afferents show dynamic response to muscle stretch (i.e., changes in muscle length). think about it as if the dynamic response fires to the slope of the stretch. for example in a linear stretch, the 1a response is low firing (same as baseline), high firing, then low-medium firing). low medium firing shows that it is not a purely dymamic response otherwise it would return to baseline firing. some static signal causes elevated frequency of action potentials
50
Feedback from muscle spindles is use do what? (2)
- Regulate muscle activity via the alpha motoneuron (elicits the stretch reflex)
- Signal higher centres (e.g., cortex, brainstem, cerebellum) about muscle length (and thus limb position) which helps the brain make decisions about how to move
51
Define: monosynaptic pathway
- one synapse causes contractions in response to stretch
- Ia afferent connects directly to the alpha motoneuron controlling the agonist, or homonymous, muscle
- example: doctor taps hammer on muscle tendon causing lower leg to move forward
52
How does a disynaptic pathway
- 2 synapses: 1 Ia afferent connects directly to the alpha motoneuron controlling the agonist, or homonymous, muscle. the Ia afferent connects to an inhibitory interneuron in the spinal cord, which then connects to an alpha motoneuron (inhibits antagonist muscle).
- Real-life example: when you step on uneven terrain, your ankle joint may rotate in an unexpected manner, stretching the muscles around it. Spindle feedback can then result in greater muscle activity of the muscle stretched, thus enhancing joint stability.
53
Define and give the function of : Golgi tendon organs (GTO)
- Tiny spindle-shaped receptors located at muscle-tendon junction. In series with the muscles and tendon. sensory information from GTO is relayed via group Ib afferents.
- Sensitive to tension/force changes in muscle and body
(weightbearing) load information
- GTOs have no efferent connections and thus are not under
CNS modulation like muscle spindles
- Mechanism of action: under force/load, collagen fibrils
pinch the axon of Ib afferent (thereby causing graded receptor potentials to the point of eliciting an action potential)
54
How do Ib afferent from GTO responds to passive versus active muscle length changes:
- passive: Ib afferent no change
| - active: no Ib afferent activity during muscle length shortening until after length change is done
55
Where are joint receptors found?
connective tissue, capsule, and ligaments of joints
56
What do joint receptors sense? (5)
```
joint pressure
angle
direction
velocity
twisting forec
```
57
Define: range fractionation
- multiple joint receptors in overlapping ranges because some joint receptors only response to a limited range of joint motion. this provides greater resolution about joint angles
58
Techniques to study proprioception (4)
* Surgical deafferentation
* Temporary deafferentation
* Sensory neuropathy
* Muscle/tendon vibration
59
Define: Surgical deafferentation
- Surgically cut or remove afferent neural pathways
- Deafferentation results in proprioception being unavailable.
- In animals, this results in less precision of well learned motor skills (such as climbing or
reaching in monkeys)
60
Define: Temporary deafferentation
- example: Blood pressure cuff inflated around a part of a limb until person can’t feel anything below. Portion of limb ‘falls asleep' but efferent paths still intact
- example: Can also give an injection around the nerve with an anesthetic to eliminate afferent feedback (nerve block)
- Deafferentation results in proprioception being unavailable
61
Define neuropathy
In these patients, peripheral afferent nerves in various parts of the body are not functioning
properly but 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; 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 with
remarkable accuracy. Can perform movements that don’t require somatosensory feedback control (E.g., discrete movements that happen rapidly and/or are very short in duration)
62
Give one cause of neuropathy
diabetes
63
How does high speed vibration applied to a muscle/tendon affect the muscle/tendon?
Distorts muscle spindle firing patterns and hence distorted proprioceptive feedback
– Preferentially affects group Ia afferents
Gives illusion of muscle lengthening
– Thus, causes compensatory movements (example: vibrating tibialis anterior which is responsible for dorsiflexion causes an illusory sensation of plantar flexion causing forward body sway)
- vibration on triceps surae causes backward sway
- vibration on hamstrings causes backward sway and knee bend (think like deadlift)
- vibration on quadriceps leads to no response (Quadriceps extension, hamstring extension leading to hip and knee extension)
64
Describe the Pinochio effect
- a blindfolded person holding their nose while having their biceps vibrated will feel like their arm is being extended and the fingers and/or nose are being elongated
- demonstrates that muscle spindle activity is sufficient for proprioception and body schema for body dimensions is extremely plastic
65
What does it mean when it is said that the body schema of the body's dimensions are extremely plastic?
- the internal model of the body (what the brain thinks the body looks like) can be modified
- this is a mechanism for adjustments needed during normal growth in childhood
66
What does proprioception facilitate?
- movement accuracy (provides kinematic and kinetic feedback)
- body and limb segment co-ordination (postural control and Spatial-temporal coupling between limbs and segments)
67
What can touch tell you? What receptors are responsible for touch? Why is this important (3)?
- Tactile information on texture, composition, and shape of surfaces and objects
- cutaneous receptors/mechanoreceptors on the skin
- object manipulation, precision, sensing body position
68
What type of cutaneous receptor detects: vibration
- Meissner corpuscle
| - Pacinian corpuscle
69
What type of cutaneous receptor detects: stroking
- Meissner corpuscle
| - hair follicles
70
What type of cutaneous receptor detects: skin stretch
- Ruffini's corpuscles
71
What type of cutaneous receptor detects: pressure
- Merkel's disks
72
What type of cutaneous receptor detects: pain
- free nerve endings
73
Describe the depth and receptive field of the following cutaneous receptor: Meissner corpuscle
- RA1 (close to surface and fast adapting)
| - smaller and more focal receptive field allowing for greater discrimination
74
Describe the depth and receptive field of the following cutaneous receptor: Merkel cells
- RA1 (close to surface and fast adapting)
| - smaller and more focal receptive field allowing for greater discrimination
75
Describe the depth and receptive field of the following cutaneous receptor: Pacinian corpuscle
- RA2 (far from surface and fast adapting)
| - broader receptive field
76
Describe the depth and receptive field of the following cutaneous receptor: Ruffini endings
- SA2 (far from surface and slow adapting)
| - broader receptive field
77
Why are cutaneous receptors more concentrated 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
78
True or false: skin stretch contributes to propioception
true! 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 (see panel B, right two bars)
79
Describe the pathways of the somatosensory system which consists of 3 neurons
primary: cell bodies of primary neurons are in the dorsal root ganglia and a single process extends fromthe cell body that splits into a peripheral and central axon. peripheral axon ends in skin or muscle or joint (cutaneous receptor, muscle spindles, GTOs, or joint receptors). central axon ends in the CNS (spinal cord)
secondary: exists in the spinal cord or brain stem
tertiary: cell body in the ventral posterior nucleus of the thalamus and terminates in the primary somatosensory cortex of the brain
80
Fill in the blank: Somatosensory information from peripheral receptors (e.g., cutaneous, muscle spindles) enters spinal cord via _______
dorsal roots
81
Give the function of: dorsal column – medial lemniscus tract
- Transmits touch, vibration, and conscious proprioceptive info to supraspinal centres
• Sent to somatosensory cortex
• Provides conscious awareness of body position
82
Define the function of spinocerebellar tracts
- Transmits unconscious proprioceptive information to cerebellum
• Transmits muscle spindle and GTO input
– Divided into ventral and dorsal tracts
83
Give the 2 ascending sensory tracts
- dorsal column – medial lemniscus tract
| - spinocerebellar tracts
84
Give the Brodmann area for the primary somatosensory cortex
BA area 3b
85
Define: 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
86
Define: retinotopy
mapping of visual input from the retina to neurons, particularly those neurons within the visual stream.
87
Why is the organization of somatotopy and retinotopy efficient?
inputs to adjacent parts of the skin or retina need to be compared to extract information like shape. Somatotopy and retinotopy allow these comparisons to be made over shorter distances in brain circuits, which is faster and more energetically efficient
88
Describe the sensory homunculus figure
The visualization of the somatotopic map
- latin for little man
- Representation size is proportional to number of receptors rather than area of skin, so more densely innervated skin appears magnified in the homunculus
- big head, big hands small shoulders, big lips and tongue
