Chapters 4-6 Flashcards
(146 cards)
1
Q
What are neurons?
A
There are approximately 100 billion neurons in the human brain, and each individual neuron is part of the vast interconnected communications network that forms the human nervous system. Each neuron is analogous to a single computer that is connected to the millions or billions of other computers on the Internet.
2
Q
Structure of neurons include?
A
Cell body Dendrites Axon (nerve fibre) Action potential Myelinated neruons Unmyelinated neurons Synapse Neurontransmitters
3
Q
What are Cell body?
A
contains various organelles (for e.g., mitochondria) as well as the cell nucleus.
4
Q
What are Dendrites?
A
branches (extensions) of the cell body that receive stimulation from other neurons.
5
Q
What are Axon (nerve fibre)?
A
carries information (action potentials) away from the cell body of the neuron.
6
Q
What are Action potential?
A
the “all or none” electrical impulse that travels through a neuron or skeletal muscle cell.
7
Q
What are Myelinated neruons?
A
are neurons in which the axon of the neuron is covered with a fatty, sheath-like insulating substance known as myelin. Myelin increases the transmission speed of action potentials (nerve impulses) along the axon.
8
Q
What are Unmyelinated neurons?
A
are neurons in which the axons are not covered by myelin. Therefore, the transmission of nerve impulses in unmyelinated fibres is lower.
9
Q
What are Synapse?
A
refers to the place of close contact between neurons
The synapse is where information is transmitted from one neuron to another, and is often used to refer to the connections between neurons (for e.g., the term monosynaptic means one synapse or connection).
10
Q
What are Neurontransmitters?
A
are chemical substances that are released at the presynaptic nerve terminal (or axon terminal). Neurotransmitters are chemical messengers that transform and carry the information conveyed by the action potential across the synapse to the dendrite of the receiving neuron.
11
Q
Types of neurons? (3)
A
- Sensory (afferent) neurons
- Motor (efferent)
- Interneurons
12
Q
What are sensory (afferent) neurons?
A
these nerve cells send neural impulses (action potentials) from a sensory receptor (such as a pain receptor or touch receptor in your skin) towards the CNS.
13
Q
What are motor (efferent) neurons?
A
these nerve cells send neural impulses (e.g., motor commands from the brain) away from the CNS and toward the skeletal muscle fibres.
14
Q
What are interneurons?
A
these specialized nerve cells originate and terminate in the brain or spinal cord. One of their important functions is to provide a link between sensory neurons and motor neurons in the spinal cord. These connections in the spinal cord are known as reflexes and are important for the spinal control of movement.
15
Q
What is the spinal cord?
A
- Once the impulse reaches the spinal cord, it enters through a structure known as the dorsal root (there are right and left dorsal roots), which is located at the back (or dorsal) part of the cord.
- The spinal cord is composed of two sections known as gray matter and white matter
- From the dorsal root, the action potentials travel through the dorsal horn of the gray matter and up the spinal cord in specialized tracts (a network of nerves) located in the white matter known as the dorsal (or posterior) columns.
o Because these tracts carry incoming information from the peripheral nervous system up the spinal cord to the brain, they are known as ascending tracts.
o somatosensory cortex and other specialized areas of the brain
• The tracts which are responsible for transmitting motor information down the spinal cord (i.e., from the brain to skeletal muscle fibres) are
known are descending tracts.
o These tracts form the sensory and motor pathways through which the central nervous system controls movement.
16
Q
What is the anterolateral system?
A
These sensory tracts are located at the front (anterior) and sides (lateral) of the spinal cord (as opposed to the back of the cord in the case of the dorsal columns).
• These tracts transmit sensory information to different parts of the brain such as the thalamus and cerebellum.
17
Q
What is the Anterior spinocerebellar tract?
A
Connects the spinal cord to the cerebellum and is located on the anterior aspect of the cord.
18
Q
What is the Lateral spinothalamic tract?
A
Connects the spinal cord to the thalamus and is located on the lateral aspect of the cord.
The typical route taken by neural impulses as they travel up the dorsal column and spinocerebellar tracts respectively, and through different parts of the brain on their way to the somatosensory (or sensory) cortex, which is an important part of the brain for processing sensory information.
19
Q
Explain the Dorsal Column Pathway?
A
Dorsal column → Brainstem → Hypothalamus → Thalamus → Somatosensory cortex
20
Q
Explain the Spinocerebellar Pathway?
A
Spinocerebellar tract → Brainstem → Cerebellum → Somatosensory cortex
21
Q
The primary descending (motor) tract is the pyramidal (or corticospinal ) tract which is located what part of cord?
A
on the lateral aspect of the spinal cord.
22
Q
As with the sensory pathways, there are additional motor pathways that transmit information away from the brain. Explain them.
A
- Collectively, these pathways are known as the extrapyramidal tracts (or system) and can be found on the anterior aspect of the cord.
- Some examples of these secondary pathways are the rubrospinal tract and the vestibulospinal tract .
- Once the motor commands reach the appropriate spinal level, they exit at the front of the cord through a structure known as the ventral root.
23
Q
What is a Volitational Act?
A
- is usually intended to achieve a specific objective (i.e., movements are goal-directed)
24
Q
What is Synaptic Proliferation?
A
after a few months dramatic changes in the control of movement begin to occur as the brain continues to develop and form new connections
25
What is Typical Motor Pathway?
Cortical Motor Neuron → Upper Motor Neuron → Interneuron → Lower Motor Neuron
26
What is Gray matter?
is a gray coloured, butterfly-shaped looking central portion of the spinal cord. It contains the cell bodies of interneurons that lie in the centre of the cord.
27
What is White matter?
is the white-coloured, peripheral part of the spinal cord that surrounds the gray matter. It contains the myelinated axons of sensory and motor neurons, which give it its white appearance.
28
What is Dorsal root?
is the structure through which sensory information enters the spinal cord.
29
What is Ventral root?
is the structure through which motor information exits the spinal cord.
30
What are Dorsal (posterior) columns? (What does it do in terms of sensory information?)
transmits information about proprioception, touch, and pressure to the somatosensory cortex and other parts of the brain.
31
What sensations does Anterolateral system deal with? What tracts does it have?
contains the spinocerebellar and spinothalamic tracts which transmit pain, temperature, pressure, and touch information to the thalamus and cerebellum.
32
What is the Pyramidal tract system?
is the primary motor pathway through which neural impulses reach skeletal muscles from the brain.
33
What are Extrapyramidal tracts?
are secondary pathways carrying efferent information.
34
What sections are the brain organized into?
1. the brainstem,
2. the cerebellum
3. the cerebrum.
35
What is the brainstem?
- in evolutionary terms, the brainstem is the older, more "primitive" part of the brain, which is located at the top of the spinal cord. It is responsible for regulating basic "life-support" physiological processes such as breathing, heart rate, blood pressure and digestion
36
What is the cerebellum?
is located at the base of the cerebrum and just posterior to the brainstem. The cerebellum is frequently called the "little brain" and is an important centre for balance control and movement. One of its functions is to process (i.e., match and compare) the outgoing motor commands with the incoming sensory feedback that occurred as the result of the movement.
37
What is the cerebrum?
is the primary brain structure that consists of the right and left cerebral hemispheres. The cerebrum is covered with a highly dense layer of neurons known as the cerebral cortex.
38
What are the main areas in the brainstem involved in motor control?
a. reticular formation
b. pons
c. medulla oblongata (see below for further information).
d. The brainstem is also an important centre for the monitoring and regulation of reflexes.
39
What is the cerebral cortex?
the cortex covers the right and left cerebral hemispheres with an undulating, wrinkly, gray surface. The cortex is where the higher brain functions such as cognition (thinking, intelligence, decision-making, planning) and information processing (e.g., sensory perception) occur.
40
What is the Reticular Formation?
Provides an important link between sensory input and motor output, in that its primary function is as an integrator of sensory and motor information (for e.g., it can regulate motor output based on the sensory input it receives).
41
What is the Pons?
The pons is involved in the control of automatic movements such as breathing, chewing and swallowing, and may also play a role in the control of balance.
42
What is the Medulla oblongata?
Acts as a regulatory agent for internal physiological processes such as the control of heart rate and respiration. Most significantly, it is also the point at which sensory and motor tracts cross over to the other side of the body (i.e., the sensory and motor fibres from the left side of the body cross over to the right side at the level of the medulla oblongata, to be controlled by the right side of the brain, and vice versa). This crossing over is called a decussation.
43
What is the Hypothalamus?
• Some of its primary functions are to control the endocrine system (hormones) and to regulate body homeostasis (for example, it regulates body temperature, hunger, thirst and the physiological response to stress).
44
What is the Thalamus?
Is an important relay station for sensory input on its way to the higher brain centres. It functions very much like the central post office of a city, which receives all the mail for that city, and then sorts it and sends it to the appropriate local post office so it can reach its destination. The thalamus also play an important role in the control of attention
45
What is the Frontal Lobe?
Contains the motor cortex, which is the primary centre for the production of movement. The frontal lobe is involved with planning, coordinating and executing behaviour.
46
What is the Parietal lobe?
Interacts with the motor cortex and the supplementary motor area (SMA). It contains the somatosensory cortex which is the primary centre for receiving and processing sensory information.
47
What is the Occipital lobe?
Is an important centre for processing visual input.
48
What is the Temporal lobe?
Is an important centre for memory and language.
49
What is the Somatosensory cortex?
It forms part of the cerebral cortex and is located posterior to the central sulcus, which separates the parietal lobe from the frontal lobe. It includes several specific regions that receive sensory information transmitted via the sensory nerves that are specific to that type of information (for example, proprioception).
50
Collectively, the hypothalamus and thalamus form what is known as?
The diencephalon
51
The motor areas are?
* Primary motor cortex
* Premotor area
* Supplementary motor area (SMA)
52
What is the Primary motor cortex?
Is the primary motor centre responsible for the production of movement. It sends neural impulses (motor commands) down the pyramidal system (corticospinal tracts) to the α -motor neurons that travel to the skeletal muscle fibres.
53
What is the Premotor area?
Is involved in planning and movement preparation and plays an important role in rhythmic coordination.
54
What is the Supplementary motor area (SMA)?
Is also involved in movement planning, particularly in relation to the planning and preparation of sequential movements.
55
What does redundancy mean?
that if one centre is incapacitated and can no longer function, there is enough overlap that other centres may be able to compensate
56
Two other important centres of the brain that are responsible for controlling movement are?
1) the cerebellum
| 2) the basal ganglia.
57
What does the cerebellum do?
the cerebellum plays an important role in the production of coordinated movement and the control of balance. In general, it functions as an error detection and correction system which assists in the production of smooth, coordinated movements.
o It is believed that a copy of the motor commands (called an efference copy) is sent by the motor cortex to the cerebellum, so that the cerebellum can "predict" the sensory feedback that will be generated as a result of performing the movements.
o When the "real" sensory feedback reaches the cerebellum (via the spinocerebellar tract), it is thought that the cerebellum compares the actual sensory feedback to the predicted sensory feedback.
o If the outcome (real feedback) is inconsistent with the intended movement (predicted feedback), then the cerebellum provides error correction information to the motor cortex (to make the necessary adjustments) so that the movement will become more efficient and coordinated.
58
What does the basal ganglia do?
this structure is made up of 4 large clusters of neurons. Collectively, the basal ganglia are involved in movement initiation, control of muscle force and muscle antagonist activity. The basal ganglia are most commonly associated with the disease known as Parkinson's disease. Parkinson's disease is a neuromotor disorder which is caused by a lack of dopamine (a neurotransmitter) in the basal ganglia. It is characterized by tremors, rigidity and very slow movements (bradykinesia).
59
The names of the 4 clusters of neurons that make up the basal ganglia are?
o Putamen
o Caudate nucleus
o Substantia nigra
o Globus pallidus
60
The nervous system also contains two different types of motor neurons which are? (Motor neurons)
1) alpha (α) motor neurons
| 2) gamma (γ) motor neurons.
61
What are alpha (α) motor neurons?
innervate extrafusal muscle fibres (i.e., skeletal muscle cells)
62
What are gamma (γ) motor neurons?
What is a motor unit?
innervate intrafusal fibres (muscle fibres that lie within muscle spindles)
A motor unit is the basic functional unit of the neuromuscular system. It consists of all the skeletal (extrafusal) muscle fibres that are innervated by a single α-motor neuron
63
Motor unit recruitment is an important mechanism used by?
the CNS to control muscle tension (and therefore, movement).
64
There are several important structures associated with the point of connection between α-motor neurons and skeletal muscle fibres. What are they?
Motor Endplate
Neuromuscular junction (NMJ)
Synaptic vesicle
65
What is the Motor Endplate?
is the name given to the distal branch of the axon that lies parallel to the skeletal muscle fibre
66
What is the Neuromuscular junction (NMJ)?
is the point of connection between the axon terminal and the sarcolemma of the muscle fibre
67
What is the Synaptic vesicle?
are specialized structures located in the axon terminal which contain neurotransmitters (in this case, the neurotransmitter acetylcholine)
68
Explain low force levels of motor recruitment?
At low force levels (approx. 10 – 30% of MVC*), only the smaller motor units (which contain Type I or slow oxidative muscle fibres) will be recruited.
69
Explain medium force levels of motor recruitment?
At medium force levels (approx. 30 – 70% of MVC), intermediate motor units (which contain Type IIa or FOG muscle fibres) will be recruited. Note: At these force levels, both the small and the intermediate motor units will be recruited.
70
Explain high force levels of motor recruitment?
At higher force levels (approx. 70 – 100% of MVC), the largest (Type IIb fast glycolytic) motor units will be recruited. Note: At these force levels, both the small, intermediate and large motor units will be recruited
71
What is *MVC?
maximum voluntary contraction
72
What is size principal?
This order of motor unit recruitment
73
What is frequency coding?
This mechanism refers to the number of times (i.e., the frequency) that muscle fibres are stimulated by the alpha-motor neurons.
• The greater the stimulation, the greater the force associated with the contraction of that particular muscle fibre (the contraction of a single muscle fibre is known as a twitch).
74
The frequency coding mechanism is summarized as?
o Frequency coding refers to the rate of action potential transmission (measured in number of impulses per second).
o Motor neurons can stimulate skeletal muscle fibres at frequencies ranging from approx. 3 – 50 Hz (1 Hz = once per second).
o A single action potential produces a muscle contraction known as a twitch.
o A train (i.e., sequence) of neural impulses produces a summation of twitches, which creates a sustained period of contraction in the fibre known as tetanus. The tetanus can be either fused or unfused depending on the frequency of stimulation (fused tetanus occurs at the highest frequencies).
75
What does the CNS employ?
The CNS employs a distributed system in which multiple centres (i.e., the motor cortex, cerebellum, brainstem, basal ganglia, etc.) carry out the different functions needed for voluntary movement to occur.
76
As a hierarchical system, the control of voluntary movement occurs at three levels?
Highest level – involves intentions, decisions and other aspects of goal-oriented behaviour (i.e., choosing what to do); for e.g. deciding to pass the puck instead of taking a shot.
Middle level – involves planning and selection (i.e., planning to carry out a specific action); e.g., planning a fake to go around a defender.
Lowest level - implementation (executing the action); e.g. carrying out the fake and passing the ball to a teammate.
77
What is coordination?
refers to specific patterns (sequences) of body and/or limb movements that are preferable to others. Typically, these movements are highly efficient.
78
What is degrees of freedom?
refers to the number of variables or components in a system that can change (for example, the number of terms in an equation). In the context of movement, degrees of freedom is often used to refer to the number of directions of movement that are possible at a specific joint. For example, the elbow joint has very limited (or restricted) degrees of freedom compared to the shoulder.
79
What is prehension?
Reaching and grasping.
80
What is Open-Loop Control?
In an open-loop control system, specific instructions are sent to accomplish a specific objective. An example would be sending a package through a courier such as UPS.
81
There are three components in an open-loop control system which are?
1. a command (or control) centre (BRAIN),
2. the commands (instructions) themselves (ACTION POTENTIALS) and
3. the effector (the agent that carries out the instructions) (SKELETAL MUSCLES).
In the UPS analogy, you can think of:
1. as the store where you send the package,
2. are the forms you fill out to tell UPS where to deliver the package and
3. is all the individuals and transportation vehicles that carry out the instructions.
82
Pathway of movement?
Movement Control Center -> Movement Commands -> Movement Effectors
83
What is the purpose of feedback?
What would happen without feed back and why?
The purpose of feedback is to provide information to the control centre about the outcome of its commands.
* Without this, no adjustments to those commands can be made.
* Without feedback, it is impossible for the control centre to do anything else other than repeat the same action over and over again.
* Feedback is information, and mechanisms must be built into the system to obtain this information so the system can adapt.
* In the context of movement, feedback is sensory information, and the process of making adaptations to the motor commands that travel to the muscles is called motor learning.
* This is a very important point to make about the importance of sensory feedback; i.e., without it, no motor learning (i.e., skill improvement) can take place.
84
What is sensory feedback?
o Vision
o Proprioception (also known as kinesthesia)
o Vestibular feedback
o Auditory feedback (not in all cases, but in some cases)
85
The theories of motor control that will be presented in this section are?
1) Motor Program Theory
| 2) Dynamical Systems Theory.
86
What is the motor program theory?
In motor program theory, the basic idea is that the brain stores motor commands in memory as programs, that are selected and activated at the appropriate time (i.e., if you need to throw a ball, you search for the program in memory that applies to throwing).
87
Motor program theory consists of two key ideas, which are?
1) that generalized motor programs ( GMPs) are used to control movement
2) that specific movement parameters have to be added to the GMP to modify the movement in different situations
88
What is Generalized Motor Program (GMP)?
is a memory based construct that controls a class of actions.
* For example, all the different ways in which a person can throw constitutes a class of actions; i.e., throwing a baseball, a football, a discuss, etc.
* A class of actions does not represent a specific movement. Rather, it is a template for a class of movements that need to be modified according to specific criteria.
89
What does the motor program theory envision?
that each class of actions contains invariant features. This means that regardless of the type of throw required, certain aspects of all throwing movements are identical, and can therefore be applied by the GMP to every throwing situation.
90
Examples of invariant features that are controlled by the GMP are?
The component sequence
Relative force
Relative timing
91
What is component sequence?
(i.e., the specific sequence of joint rotations or limb movements).
92
What is Relative force?
(i.e., the amount of force applied by certain muscles relative to other muscles). The idea is that the ratio of the different muscle forces does not change, even though the amplitudes of the individual muscles may.
93
What is Relative timing?
This refers to the specific coordination pattern; i.e., the timing of one joint motion relative to another.
94
Another important idea in motor program theory is the way in which movement specific parameters are selected for the purpose of modifying the GMP for different situations. Examples of movement parameters include?
The total force required
The movement duration or speed of the movement
95
How does the CNS select the right set of parameters for each movement condition?
o The answer involves another idea or theory, which is known as schema theory.
o The term schema refers to a set of rules that are used to make a decision.
• One of the most popular ways to write code in computer programming is to use what are known as "if...then" statements. This is a very simple rule-based way of processing information. For example, in your code you may tell the computer that if x > 6, then y = 0, and if x < 6, then y = 1.
96
What is the schema theory?
is the abstract application of a set of rules that are used to make decisions
97
What is the motor response schema?
refers to the application of schema theory to the control of movement; i.e., the CNS uses specific rules (schema) to make decisions about the application of movement parameters to the GMP
98
What is the Movement specific parameters?
They are added to the GMP depending on the context and task specific conditions in which the movement takes place.
99
What is the Dynamical Systems Theory (Chaos theory or dynamic pattern theory?
It is a multidisciplinary science which studies the behaviour of complex systems. The "systems" in question are usually either physical or biological, and dynamical systems theory involves a branch of physics which is known as non-linear dynamics.
100
What are Non-Linear Dynamics?
* Non-linear equations are needed to explain very complex relationships.
* Non-linear systems are not predictable, and they are not easy to model mathematically (simple linear equations won't work).
* it will exhibit highly "unpredictable" behaviour. It is this unpredictability that is a characteristic feature of non-linear, chaotic systems.
101
Chaos, in this context, refers to two things which are?
1) complexity
| 2) unpredictability.
102
What is the Dynamical systems theory?
is the multidisciplinary study of the behaviour of complex systems (physical or biological).
103
What is the Non-linear dynamics?
refers to changes in a system over time that do not follow a linear progression.
104
What is the Chaotic Systems?
They can change from being in a predictable, steady-state, to being in an unpredictable, chaotic state, quite quickly and unexpectedly. This changing of states is known as a phase transition.
105
What is the non-linear systems?
exhibit chaos; i.e., predictable (linear) behaviour can become chaotic (unpredictable).
106
What is self organization?
given a certain set(s) of conditions, stable patterns of behaviour will emerge
107
What is the Dynamical Systems Theory and Human Movement?
Ex. Imagine you're in a gym walking on a treadmill at a nice comfortable speed. Now imagine that your personal trainer comes over and tells you that you need to walk faster and increases the speed. For most people, a comfortable walking speed is about 3 miles an hour. Let's say the trainer increased the speed to 3.4 miles per hour. You would now have to walk faster, but very little in terms of the mechanics of the movement would change, other than a small increase in the stride length and stride rate. After several minutes, the trainer decides to increase the speed again, to 3.8 mph. The same thing will happen. You will still be walking, but just a little bit faster than before. The trainer could continue to increase the speed in this way for quite some time and the changes that would occur would be very predictable. However, at a certain critical point (usually around 4.5 - 5.0 mph for most people), a very interesting phenomenon will occur. All of a sudden, you'll get the feeling that walking doesn't seem to work anymore, and that walking at this speed feels awkward and uncomfortable. You will find yourself changing your gait from a walk to a very slow jog. It is important to point out that this phenomenon was completely unpredictable based on what happened previously, and as such is consistent with how non-linear systems behave (i.e., unpredictably).
* Changes from one state to another (e.g., from stable to unstable) are called phase transitions.
* In this example, walking represents a steady-state, predictable pattern of behaviour which is consistent with a specific coordination pattern.
* Running represents a different, steady-state predictable pattern of behaviour (i.e., a brand-new coordination pattern), that is completely different from walking.
* To go from one stable steady-state to the other, we have to go through a phase transition in which the behaviour is chaotic, or unpredictable.
* he movement behaviour of locomotion in this specific instance is chaotic (unpredictable).
108
What are attractors (or attractor states)?
in the case of human movements, represent the most stable energy efficient coordination patterns.
109
What are states?
Patterns of behaviour in complex systems.
These patterns of behaviour (states) frequently change from stable (predictable) to unstable (unpredictable).
110
What is phase transition?
refers to a change in states (i.e., a change in the pattern of behaviour); predictable steady-state behaviour is usually followed by a phase transition to an unpredictable state, which is then followed by a new energy efficient pattern (a new predictable, steady-state).
111
What are control parameters?
parameters that control the behaviour of the system. Ex. in human movement, speed.
112
What are angle-angle Diagrams?
If we plot the motion of one joint relative to another.
113
What are order parameters?
- measuring the motion of one joint (or limb) relative to another.
* When measured, will reveal the inherent order (or pattern of behaviour) of the system.
* For example, measuring the angle of the motion at the knee relative to the motion at the hip will reveal the coordination pattern of the leg when walking or running.
114
Application of dynamical systems theory to the control of human movement? Process of joint coupling?
• In attempting to establish the order or patterns inherent in the movement of different joints, the concept of joint coupling has become popular in dynamical systems theory through the measurement of what is known as the phase angle.
115
What is the phase angle?
quantifies the degree to which the motion of one joint (or limb) is in-phase (or coupled) to the motion of another.
116
What is in-phase?
the two joints move at exactly the same time
117
What is out-of-phase?
they move in opposition to each other.
• Example is finger movements.
118
Evidence to Support Dynamical Systems Theory of Control?
o Changes in control parameters (such as movement speed) produce dramatic changes in coordination patterns that, at the present time, are not sufficiently explained by any other theory (including the motor program theory).
o Certain characteristics of coordinated movement behaviour, such as the phase transitions that occur between attractor states, cannot be explained by motor program theory (for e.g., why the transition from walking to running occurs just at the point where walking is no longer energy efficient).
119
What is touch?
The sensation we experience in our brains when we make contact with objects in the external world
This sensation arises when a special kind of sensory receptor called a mechanoreceptor, is stimulated.
120
What are • Mechanoreceptors?
specialized endings of sensory nerves which transduce
121
What are Cutaneous Mechanoreceptors?
specific mechanoreceptors responsible for the sensation of touch are located in the skin and provide sensory input to the CNS which creates the sensation of touch.
122
There are several different kinds of cutaneous mechanoreceptors responsible for producing the sensation of touch. They are?
1. Meissner's corpuscle (light touch)
2. Pacinian corpuscle (pressure)
3. Merkel's corpuscle/disk (touch)
4. Ruffini ending (temperature)
123
What are Nociceptors?
free nerve endings in the skin and that their function when stimulated is to create the sensation of pain.
124
What is proprioception?
the sensation of body and/or limb position and movement (e.g., limb movement direction, location in space, speed of movement) that is produced as a result of sensory information sent to the brain by different mechanoreceptors located in the joints, muscles, ligaments, tendons and skin.
One of the most important sensations humans have in relation to movement is called proprioception.
125
T OR F: It is important to note that in most cases the terms proprioception and kinesthesia are used synonymously (i.e., they are used to mean the same thing)?
TRUE
However, this is not always the case, as the term proprioception is sometimes used to refer specifically to the sensation of joint and/or limb position, whereas kinesthesia is used to refer to the sensation of joint and/or limb movement.
126
The mechanoreceptors that are responsible for sending proprioceptive feedback to the brain are?
Muscle spindles
Golgi tendon organs (GTO)
Cutaneous mechanoreceptors
Ligament and joint capsule receptors
127
What are Muscle spindles?
are specialized mechanoreceptors that detect changes in muscle length (as well as the rate of change of muscle length). They play an important role in the reflex control of movement because they trigger the stretch reflex.
128
What are Golgi tendon organs (GTO)?
embedded within the tendons of skeletal muscles.
129
What are Cutaneous mechanoreceptors?
located within the skin (many of the same receptors responsible for touch contribute to proprioception as well).
130
What are Ligament and joint capsule receptors?
e.g., Pacinian corpuscles, Ruffini endings) - these mechanoreceptors are stimulated as joints move and ligaments are stretched (for e.g., these receptors fire every time you bend your hip and knee to take a step).
131
Two different types of sensory neurons (afferents) are associated with muscle spindles which are?
1) Type Ia fibres
| 2) Type II fibres.
132
What are Type Ia fibres?
are low threshold (i.e., very sensitive) velocity sensors (they detect the rate of change in muscle length). Type Ia afferents are responsible for triggering the stretch reflex.
o The stretch reflex occurs when, at a certain threshold, the muscle spindles sense that the muscle is being stretched, and as a result, the Type Ia afferents stimulate (via the spinal cord) the muscle to contract involuntarily, as in the case of the knee jerk reflex
133
What are Type II fibres?
are higher threshold (i.e., harder to stimulate) static stretch receptors. Their stimulus does not diminish with stretch and is inhibitory rather than excitatory.
For example, when you are doing stretching exercises properly and hold the stretch for approximately 10 seconds, the Type II spindle afferents will cause the muscle to relax (i.e, the CNS accommodates to the new resting length), and this reflex response helps to facilitate the stretch by relaxing the muscle.
134
What are Golgi Tendon Organ Receptors?
is found in the tendons that attach muscles to bones. GTO is a force sensor that detects changes in muscle tension during isometric (no change in length), eccentric (lengthening) or concentric (shortening) contractions. (Type 1b afferent).
135
Stimulation of the GTO causes?
an inhibitory response in the muscle (which is sometimes called an inverse stretch reflex).
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GTOs play an important role in?
protecting muscles from producing too much force and in inhibiting antagonist muscle activity (reciprocal inhibition), so that the agonist is free to move the joint in the intended manner (i.e., when flexing the elbow, the GTO of the contracting biceps muscle helps to inhibit the antagonist triceps so it does not interfere with the movement).
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What is the dominant modality? Why?
Human beings are predominantly visual creatures, and as such vision is the dominant sensory modality. Consequently, vision is critical for motor control.
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What are rods and cones?
Light Sensitive Receptors
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Where is the visual cortex?
located in the occipital lobe of the brain
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Vision contributes to motor control in two specific ways which are?
1. Feedforward control
| 2. Feedback control
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What is Feedforward control?
defined as the process of movement planning and preparation that takes place prior to movement initiation.
• The schematic indicates that before any motor commands are issued by the brain, the brain has to plan and prepare the movement, and it relies almost exclusively (but not entirely) on visual input to do this.
* your brain will process (subconsciously) what it sees in front of it, so it can start planning the movements
* Based on the visual input it receives, your brain will try to make an estimate so it can activate the right muscles to the right degree (i.e., it has to figure out how many motor units to recruit in each muscle).
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Vision plays a critical role because?
it enables the brain to acquire information about objects at a distance so that movements can be planned in advance
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The brain also uses visual feedback to make corrections in terms of movement by? (Online Control)
The brain also uses visual feedback to make corrections to movements while the limbs and joints are moving. This is sometimes called online control, to refer to the fact that corrections can be made to movements while they are happening.
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What is feedback control?
happens after the movement has occurred (On occasion, the movement predictions the brain makes based on visual input are wrong, and the brain quickly corrects the situation once feedback is received from the touch and proprioceptive systems.)
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We also use visual perception to provide clues to the brain about how objects are moving in the external world. How does this occur?
(Ex. car braking).
• your brain has to rely on other sources of information. In this case, your brain recognizes that the car in front of you is stopping very quickly if the size of the image on the retina starts to increase very rapidly. Your brain knows that the closer an object is the bigger it appears. Therefore, if an object of a given size starts to increase its size very quickly, the brain "perceives" that this is not an actual increase in the size of the object, but rather a consequence of the rapidly shrinking distance between you and the object, which makes it appear larger.
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What is tau?
the rate of change of the size of an image on the retina. From this, the brain can estimate the speed of approaching objects.
