1
Q
What is the overall function of the nervous system?
A
It is a communication and control network that allows an organism to interact with its environment.
2
Q
What are the two main sections of the nervous system, and what does each include?
A
Central Nervous System (CNS): The processing center, which includes the brain and the spinal cord. Peripheral Nervous System (PNS): The rest of the nervous system, consisting of nerves and ganglia (groups of nerve cell bodies outside the CNS). It serves the limbs and internal organs.
3
Q
What are the two divisions of the Peripheral Nervous System (PNS), based on the direction of information flow?
A
The Afferent Division (carries information towards the CNS). The Efferent Division (carries information from the CNS).
4
Q
What is the Afferent Division (or Sensory System)?
A
It is responsible for sending afferent info towards the nervous system. It carries info from: The external environment (e.g., light, sound). The internal environment (e.g., blood pressure).
5
Q
What is the Efferent Division (or Motor Division)?
A
It sends information from the nervous system to the organs of the body. The organs then carry out the appropriate response.
6
Q
What are the three general functions of the nervous system?
A
Sensory detection (by the afferent/sensory division). Information processing (by the CNS/brain). Expression of behavior / motor control (by the efferent/motor division).
7
Q
Where is the spinal cord located and what are its boundaries?
A
It is the most caudal portion of the CNS. It is located in the vertebral column. It extends from the base of the skull to the first lumbar vertebra.
8
Q
How many segments and pairs of spinal nerves make up the spinal cord?
A
There are 31 segments, which correspond to 31 pairs of spinal nerves. Breakdown (from Slide 3): 8 Cervical, 12 Thoracic, 5 Lumbar, 5 Sacral, 1 Coccygeal.
9
Q
What type of information do the 31 pairs of spinal nerves contain?
A
They contain both sensory (afferent) nerves and motor (efferent) nerves.
10
Q
What is the function of the sensory (afferent) nerves in the spinal cord?
A
They carry information TO the spinal cord from the skin, joints, muscles, and visceral organs in the periphery. They enter via the dorsal root and cranial nerve ganglia.
11
Q
What is the function of the motor (efferent) nerves in the spinal cord?
A
They carry information FROM the spinal cord TO the periphery. They innervate skeletal muscle, cardiac muscle, smooth muscle, glands, and secretory cells.
12
Q
What are the two main pathways for information traveling within the spinal cord?
A
Ascending pathways. Descending pathways.
13
Q
What is the function of the Ascending pathways?
A
They carry sensory information from the periphery to higher levels of the CNS.
14
Q
What is the function of the Descending pathways?
A
They carry motor information from higher levels of the CNS to the motor nerves that innervate the periphery.
15
Q
What is the overall function or “nickname” of the spinal cord (from Slide 3)?
A
It is the “information highway of the body” that connects the various organs of the body to the brain.
16
Q
What is the composition and microscopic appearance of White Matter?
A
Composition: Contains high concentrations of axon pathways. Appearance: Brighter under a microscope because the myelin sheaths are highly refractive to light.
17
Q
What is the composition and microscopic appearance of Gray Matter?
A
Composition: Contains high concentrations of neuron cell bodies and dendrites. Appearance: Dark color under a microscope. Structure: It forms a continuous column running the length of the cord, typically in an ‘H’ or butterfly shape.
18
Q
How are the “butterfly wings” of the gray matter divided?
A
They are divided into dorsal and ventral horns. These horns are separated by an intermediate zone.
19
Q
Where exactly do the cell bodies of Sensory Neurons reside?
A
They reside in the Dorsal Root Ganglion (DRG). Crucial Detail: They do not reside in the dorsal horn itself.
20
Q
What is the specific function of the Dorsal Horn?
A
It is the major recipient of incoming sensory info. It is the main source of ascending sensory pathways.
21
Q
Where do Motoneurons reside and what is the function of that region?
A
Location: They reside in the Ventral Horn. Function: The ventral horn is the main target of descending motor pathways from the brain.
22
Q
How is a Spinal Nerve formed and where does it emerge?
A
Formation: Formed by the combination of nerve fibers from the dorsal and ventral roots. Emergence: It emerges from the spinal column through an opening called the intervertebral foramen.
23
Q
What is the functional difference between the Dorsal Root and the Ventral Root?
A
Dorsal Root: Carries afferent sensory info into the CNS. Ventral Root: Carries efferent motor axons to the periphery.
24
Q
What are the two main components of the efferent division (motor system)?
A
The Somatic Nervous System (SNS). The Autonomic Nervous System (ANS).
25
What is the Somatic Nervous System (SNS), and what is its alternative name?
Function: It is associated with the voluntary control of body movements. Effectors (from Slide 5): It controls skeletal muscles. Alternative Name: It is also called the voluntary nervous system.
26
What is the Autonomic Nervous System (ANS), and what are its alternative names?
Function: It functions largely below the level of consciousness and controls visceral functions. Effectors (from Slide 5): It controls smooth muscles, cardiac muscles, and glands. Alternative Names: It is also called the involuntary nervous system or visceral nervous system.
27
What is the difference in control between the SNS and ANS?
SNS: Voluntary motor system, under conscious control. ANS: Involuntary, functions largely below the level of consciousness.
28
What is the difference in the number of neurons in the pathway from the CNS to the effector?
SNS: Uses a single neuron pathway. ANS: Uses a two-neuron pathway (preganglionic and postganglionic).
29
What is the difference in neuron location between the SNS and ANS pathways?
SNS: The single motor neuron is located in the CNS. ANS: The first neuron (preganglionic) is located in the CNS. The second neuron (postganglionic) is in a ganglion (a mass of neuron bodies outside the CNS).
30
What are the effector organs (targets) for the SNS vs. the ANS?
SNS: The effector organ is skeletal muscle. ANS: Effector organs include smooth muscle, cardiac muscle, and glands.
31
What are the specific neurotransmitters and receptors used in the SNS?
SNS: Motoneurons release ACh (Acetylcholine). This binds to nAChR (nicotinic ACh Receptors) on the skeletal muscle.
32
What are the specific neurotransmitters and receptors used in the ANS?
ANS: At the Ganglion: Preganglionic neurons release ACh that binds to nAChR on the postganglionic neuron. At the Effector: Postganglionic neurons release either: ACh (which binds to mAChR - muscarinic ACh Receptors) OR Norepinephrine (which binds to $\alpha$ or $\beta$ adrenoceptors).
33
What is the basic functional unit of movement in the Somatic Nervous System?
The Motor Unit.
34
What are the two components that define a single "motor unit"?
A single motoneuron. The skeletal muscle fibers that it innervates.
35
What is the relationship between the precision of muscle control and motor unit size?
Precision is related to the number of muscle fibers innervated by an axon. For finely controlled muscles (e.g., eye muscles), a motoneuron innervates only a few muscle fibers.
36
What is the motor unit size like for large postural muscles?
For postural muscles involved in large movements (e.g., the quadriceps femoris), a single motoneuron may innervate thousands of muscle fibers.
37
What are the two main "rules" of motor unit innervation?
Each muscle fiber is supplied with only one motor neuron. One motor neuron may innervate many muscle fibers (from 5 to >1,000).
38
What happens when a single motoneuron discharges (fires an action potential)?
All of the muscle fibers belonging to that motor unit contract.
39
Does a single muscle (like the biceps) consist of one or many motor units?
A given muscle may include several motor units.
40
What is a "muscle unit"?
The muscle fibers that belong to a given motor unit are called a muscle unit. It is part of the motor unit.
41
What are the two types of motoneurons and what do they generally innervate?
alpha-motoneurons: Innervate extrafusal muscle fibers. gamma-motoneurons: Innervate intrafusal muscle fibers.
42
What are the physical properties of alpha-motoneurons?
They are large, multipolar neurons. Size: Up to 70 µm in diameter. Their axons leave the spinal cord through the ventral roots.
43
What are Extrafusal Muscle Fibers and what is their function?
They are the standard skeletal muscle fibers that constitute the majority of the muscle. Function: They generate tension, allowing for skeletal movement. Types: Fast fibers and slow fibers.
44
How are Extrafusal fibers innervated and activated?
Innervation: Each fiber is innervated by a single alpha-motoneuron. Mechanism: AP in motoneuron to release of Acetylcholine (ACh) to binds to AChR to AP in muscle fiber to Muscle Contraction.
45
What are the physical properties of gamma-motoneurons?
They are smaller than alpha-motoneurons. Size: Soma diameter of about 35 µm. They supply specialized intrafusal fibers embedded within extrafusal fibers.
46
What are Intrafusal Muscle Fibers and why don't they generate movement?
They are narrower than extrafusal fibers and do not run the full length of the muscle. Reason: They are too weak to contribute significantly to muscle tension or directly cause changes in overall length.
47
How does the innervation of Intrafusal fibers differ from Extrafusal fibers?
Unlike extrafusal fibers (single innervation), intrafusal fibers are multiply innervated. They receive both sensory and motor innervation.
48
What is the Muscle Spindle and what is its orientation?
It is a proprioceptive organ formed by intrafusal fibers encapsulated in sheaths. Orientation: It runs parallel to the extrafusal fibers.
49
What is the overall function of the muscle spindle and the gamma-motoneuron's specific role?
Function: To sense muscle length. gamma-role: To adjust the sensitivity of the muscle spindles so they respond appropriately as the extrafusal fibers contract and shorten.
50
What are the physical size and target fibers of alpha-motoneurons?
Size: Large. Target: They form synaptic junctions with extrafusal muscle fibers.
51
What are the physical size and target fibers of gamma-motoneurons?
Size: Small. Target: They form synaptic junctions with intrafusal muscle fibers.
52
How does the innervation pattern differ between extrafusal and intrafusal fibers?
Extrafusal Fibers: Each fiber is innervated by a single alpha-motoneuron. Intrafusal Fibers: Each fiber is multiply innervated by both sensory and gamma-motoneurons.
53
What is the difference in force generated by stimulating alpha vs. gamma motoneurons?
alpha-motoneuron stimulation: Induces contraction of extrafusal fibers to generate large force. gamma-motoneuron stimulation: Induces contraction of intrafusal fibers to generate weak contraction.
54
What is the primary function (type of movement) controlled by alpha vs. gamma motoneurons?
alpha-motoneurons: Control muscle contraction involved in voluntary movement. gamma-motoneurons: Control muscle contraction in response to external forces, inducing involuntary, reflexive movement called the stretch reflex.
55
What is the specific, detailed function of gamma-motoneurons in relation to the muscle spindle?
They adjust the length of intrafusal fibers to maintain an appropriate level of tension on the muscle spindle receptor. This control is independent of the length of the extrafusal fibers. This allows the spindle to maintain high sensitivity over a wide range of muscle lengths, acting as a means of encoding muscle length.
56
What is a Muscle Spindle and what is its primary function?
Definition: A proprioceptive receptor (or stretch receptor). Composition: It is composed of very fine intrafusal fibers located within the extrafusal fibers of skeletal muscle. Function: It senses the length of the muscle and can help prevent further muscle stretch.
57
What is the location and orientation of intrafusal fibers?
Location: They are embedded within the extrafusal fibers. Orientation: They run parallel to the extrafusal fibers. Result: When the extrafusal fibers are stretched, the intrafusal fibers of the spindle stretch as well.
58
What are the two main types of intrafusal fibers, and how are they named?
Nuclear Chain Fibers. Nuclear Bag Fibers. Name Origin: They are named based on the arrangement of their nuclei.
59
What are the properties of Nuclear Chain Fibers?
Size: Smaller. Nuclei: Arranged in rows ("chains"). Abundance: More plentiful (typically 5 or 6 nuclear chain fibers per muscle spindle).
60
What are the properties of Nuclear Bag Fibers?
Size: Larger. Nuclei: Accumulated in a central "bag" region. Abundance: Less plentiful (typically 2 nuclear bag fibers per muscle spindle).
61
What are the two sub-types of Nuclear Bag Fibers?
Dynamic Nuclear Bag₁ Fibers (bag1). Static Nuclear Bag₂ Fibers (bag2).
62
What is the specific function of Dynamic Nuclear Bag₁ (bag1) Fibers?
They are sensitive to the rate of stretch, or changes in stretch
63
What is the specific function of Static Nuclear Bag₂ (bag2) Fibers?
They are sensitive to the amount of stretch, or stationary, steady-state stretch.
64
What two general types of innervation do intrafusal fibers (muscle spindles) receive?
Intrafusal fibers are multiply innervated and receive both: Sensory (afferent) innervation. gamma-Motor (efferent) innervation.
65
What are the properties and targets of the Group Ia (Primary) sensory fibers?
Number: A single group Ia afferent fiber. Size/Speed: Among the largest nerves in the body, with the fastest conduction velocities. Ending: Forms "primary endings" in a "spiral-shaped terminal". Targets: The central region of BOTH nuclear bag and nuclear chain fibers.
66
What are the properties and targets of the Group II (Secondary) sensory fibers?
Number: A variable number of group II afferent fibers. Size/Speed: Intermediate diameters and intermediate conduction velocities. Ending: Forms "secondary endings". Targets: Primarily on nuclear chain fibers and static nuclear bag₂ fibers (but not on dynamic bag₁ fibers).
67
What are the two types of gamma-motor (efferent) innervation?
Dynamic gamma-motoneurons. Static gamma-motoneurons.
68
What is the specific target of Dynamic gamma-motoneurons?
They synapse on the dynamic nuclear bag fibers (bag₁ fibers).
69
What are the specific targets of Static gamma-motoneurons?
They synapse on nuclear chain fibers AND static nuclear bag fibers (bag₂ muscle fibers).
70
How are muscle spindles able to sense muscle stretch?
They lie in parallel with the extrafusal fibers. Therefore, they are stretched or shortened right along with the main muscle.
71
What is the specific transduction mechanism that senses stretch in the spindle?
A change in the tension of the intrafusal fibers is sensed by the mechanosensitive cation channel Piezo2. Piezo2 is expressed in the terminals of the spindle afferent fibers and activates them.
72
How do both Group Ia and Group II fibers respond to steady-state (static) stretch?
Under steady-state conditions, their firing rate reflects the amount of muscle stretch. Stretched: Firing rate increases in proportion to the amount of stretch. Shortened: Firing rate decreases proportionately.
73
What is the main difference in sensitivity between Group Ia and Group II fibers?
Group Ia fibers: Sensitive to both the amount of muscle stretch and its rate (the speed of change). Group II fibers: Respond chiefly to the amount of stretch (static length).
74
What is the "dynamic response" of Group Ia fibers?
While muscle length is changing, the Group Ia firing also reflects the rate of stretch. It "overshoots" (fires rapidly) during the stretch. It "undershoots" (and possibly ceases firing) during muscle shortening (release).
75
What kind of stretches are Group Ia fibers especially sensitive to?
Due to their dynamic sensitivity, they are much more sensitive to transient and oscillatory stretches (like a "tap" or vibration).
76
What is the basic reflex arc that muscle spindles trigger?
Afferent fibers carry the stretch information into the spinal cord. They signal alpha-motoneurons located in the ventral horn. The alpha-motoneurons fire, causing contraction of the muscle.
77
What is the function of this reflex arc, and what does it maintain?
It is a negative feedback reflex. The muscular contraction induced by the stretching works against further muscle stretch. This mechanism helps to maintain proper muscle tension or tone.
78
What do muscle spindles detect, and what do they NOT detect?
Muscle spindles detect changes in muscle length (and the rate of change of length). They do not detect muscle tension.
79
What is the state of afferent fibers under steady-state conditions (constant muscle length)?
Afferent fibers fire at a certain constant rate.
80
What is the sequence of events when a muscle is stretched (e.g., by a reflex hammer)?
Extrafusal fibers are lengthened $\rightarrow$ Intrafusal fibers are also lengthened (due to parallel arrangement). This increase in length activates Group Ia sensory afferent nerves. Afferent activation stimulates $\alpha$-motoneurons in the spinal cord. These $\alpha$-motoneurons cause the homonymous (same) muscle to contract.
81
What happens to the muscle spindle without gamma-motoneuron activity during contraction?
Muscle contraction leads to unloading of the tension across the muscle spindle (it becomes slack). This happens because the intrafusal muscle does not contract. Result: The afferent fiber stops firing. This loss of feedback causes the extrafusal fibers to relax.
82
What is Alpha-Gamma Coactivation and what is its result?
Definition: The simultaneous stimulation of alpha and gamma-motoneurons. Action: Causes shortening of BOTH extrafusal and intrafusal fibers. Result: There is no unloading of the spindle; the afferent fiber maintains its spontaneous activity all the time.
83
What is the ultimate function of gamma-motoneurons in this reflex?
To regulate the sensitivity of the intrafusal muscle fibers. They keep the muscle spindle taut even during muscle contraction. This ensures the spindle remains sensitive to stretch over a wide range of muscle lengths.
84
What are the three different roles a muscle can play during a coordinated movement?
Agonist: The muscle that initiates and is the prime cause of the movement. Synergist: Muscles that act similarly to the agonist. Antagonist: Muscles whose activity opposes the action of the agonist.
85
What is a "reflex" and what is a "reflex arc"?
Reflex: An involuntary and nearly instantaneous movement in response to a stimulus, without you having to think about it. Reflex Arc: The neuronal circuit that directs the reflex.
86
What are the components of a typical reflex arc?
Sensory Receptors. Sensory Afferent Nerves (carry info to the spinal cord). Interneurons in the spinal cord (in most cases). Motoneurons (direct the muscle to contract or relax).
87
Stretch Reflex (Knee-jerk): Synapses, Stimulus, Afferent, and Response?
Synapses: Monosynaptic (one synapse). Stimulus: Stretch (lengthening) of the muscle. Afferent Fiber: Group Ia. Response: Contraction of the muscle.
88
Golgi Tendon Reflex (Clasp-knife): Synapses, Stimulus, Afferent, and Response?
Synapses: Bisynaptic (two synapses). Stimulus: Contraction (shortening/tension) of the muscle. Afferent Fiber: Group Ib. Response: Relaxation of the muscle.
89
Flexion (Withdrawal) Reflex: Synapses, Stimulus, Afferent, and Response?
Synapses: Polysynaptic (multiple synapses). Stimulus: Noxious stimuli (e.g., pain, temperature, touching a hot stove). Afferent Fiber: Groups II, III, and IV. Response: Flexion on the ipsilateral side and extension on the contralateral side.
90
What is the Stretch (Myotatic) Reflex and what are its main functions?
Definition: A group of motor responses elicited by the stretch of a muscle. Functions: Crucial for the maintenance of posture. Helps to overcome unexpected impediments during a voluntary movement. Acts as a negative-feedback system to maintain the muscle at a constant length.
91
What is the primary reflex arc for the agonist (homonymous) muscle, and why is it "monosynaptic"?
Muscle stretch (e.g., from a reflex hammer on the patellar tendon) activates Group Ia afferent fibers in the muscle spindle. The Ia afferents enter the spinal cord and synapse directly on alpha-motoneurons. It is called monosynaptic because it has only one synapse between the sensory afferent (Ia) and the motor efferent (alpha-motoneuron).
92
What is the result of the monosynaptic activation of the alpha-motoneuron?
The activated alpha-motoneurons cause contraction of the homonymous (same) muscle that was originally stretched. When the muscle contracts, it shortens, decreasing the stretch on the muscle spindle. The firing rate of the Group Ia afferents then returns to baseline.
93
In a stretch reflex, what happens simultaneously to the antagonist muscle?
Information is sent from the Ia afferent to an inhibitory interneuron in the spinal cord. This interneuron inhibits the alpha-motoneuron of the antagonist muscle (e.g., the Semitendinosus/Hamstring), causing it to relax.
94
What is the Phasic Stretch Reflex?
Response: Occurs in response to a rapid, transient stretch of the muscle. Examples: A tap from a reflex hammer or an unexpected impediment to a movement. Function: Crucial for the maintenance of posture.
95
What is the Tonic Stretch Reflex?
Response: Occurs in response to a slower or steady stretch applied to the muscle. Example: Can be elicited by the passive bending of a joint. Function: Its activity contributes to muscle tone and the ability to maintain a posture.
96
What is the clinical importance of the stretch reflex?
Pathological alterations in this reflex (e.g., hyper- or hypoflexia) are important signs of neurological diseases.
97
What is the Golgi Tendon Reflex (or Inverse Myotatic Reflex) and how many synapses does it have?
It is the inverse of a stretch reflex. It is a disynaptic spinal cord reflex, meaning it has two synapses in its arc (e.g., sensory neuron to interneuron to motor neuron).
98
What stimulates this reflex, what sensory receptor detects it, and what afferent fiber is used?
Stimulus: Muscle contraction (shortening), which creates tension. Sensor: The Golgi Tendon Organ (GTO), a stretch receptor found in the tendons. Afferent Fiber: Group Ib afferent fibers.
99
What is the reflex arc for the homonymous (same) muscle and what is the result?
Muscle contracts/tension increases to GTO activates the Group Ib afferent. The Ib afferent synapses on an INHIBITORY interneuron. The interneuron INHIBITS the $\alpha$-motoneuron to the homonymous muscle. Result: Relaxation of the muscle that was originally contracted.
100
What happens simultaneously to the antagonist muscle during this reflex?
The Ib afferent also synapses on a separate group of (excitatory) interneurons. These interneurons ACTIVATE the alpha-motoneurons that innervate the antagonist muscles. Result: Contraction of the antagonist muscles.
101
What are the two main functions of the Golgi Tendon Reflex?
To maintain the muscle at a constant tension. To act as a protective feedback mechanism to cause relaxation before the tendon tension becomes high enough to cause damage.
102
What is the "clasp-knife reflex" and when does it occur?
It is an abnormal reflex (an example of the Golgi tendon reflex). It occurs when there is an increase in muscle tone (hypertonia), often from upper motor neuron damage.
103
What is the mechanism of the "clasp-knife reflex"?
A joint is passively flexed, and the opposing muscles initially resist the movement. Tension increases, activating the Golgi tendon reflex. This causes the resisting (opposing) muscles to suddenly relax. The joint then closes rapidly, like a pocketknife snapping shut.
104
What is a Golgi Tendon Organ (GTO) and where is it located?
Definition: It is a proprioceptive receptor. Location: It is located within the tendons found on each end of a muscle.
105
What is the physical composition of a GTO?
It is composed of extrafusal muscle fibers that enter a funnel-like capsule. This capsule is filled with collagen fiber bundles.
106
What type of nerve innervates the GTO and how is it activated?
Innervation: Group Ib afferent nerve endings are entwined throughout the collagen fibers. Activation: The nerve endings are triggered when tension in the muscle (from contraction) is transferred to the collagen fibers.
107
How is the GTO arranged in relation to the muscle, and how does this contrast with a muscle spindle?
GTO: Arranged in series with the extrafusal muscle fibers. Muscle Spindle: Arranged in parallel.
108
What is the GTO more sensitive to (contraction or stretch) and why?
It is more sensitive to muscle contraction than to muscle stretch. Reason: This is due to its "in series" arrangement and its stiff structure.
109
What does the GTO detect, and how does this primary function differ from a muscle spindle?
GTO: Detects and responds to changes in muscle tension. Muscle Spindle: Detects and responds to changes in muscle length.
110
What is the main result of activating the GTO?
It inhibits further muscle contraction. It provides negative feedback control to maintain muscle tension at a constant level.
111
What is the protective function of the GTO?
It protects against muscle damage that could be caused when muscle contraction and tension become excessive.
112
What is the Flexion Reflex (or Flexor-Withdrawal Reflex) and what type of reflex is it?
It is a reflex that causes withdrawal of a limb from a painful stimulus. It is a polysynaptic reflex, meaning the afferent fibers synapse on multiple interneurons in the spinal cord.
113
What specific stimuli activate the flexion reflex, and which afferent fibers carry the signal?
Stimuli: Tactile, painful, or noxious stimuli (e.g., touching a hot stove). Fibers: Signals are carried by Group II, III, and IV fibers. Name: These are collectively called Flexion Reflex Afferent (FRA) fibers.
114
What is the specific mechanism that occurs on the ipsilateral (painful) side?
1. Excitatory interneurons activate alpha-motoneurons supplying the flexor muscles (causing contraction). 2. Inhibitory interneurons inhibit alpha-motoneurons supplying the antagonistic extensor muscles (causing relaxation). Result: This produces flexion (withdrawal) on the ipsilateral side.
115
What is the Crossed-Extension Reflex and where does it occur?
It occurs on the contralateral side (opposite to the pain). Reflexes evoke the opposite pattern of activity: Extensor muscles contract. Flexor muscles relax. Result: This produces extension on the contralateral side.
116
What is the functional purpose of the Crossed-Extension part of the reflex?
It helps in maintaining balance. It enables the contralateral limb to support the additional load transferred to it when the flexed (painful) limb is lifted.
117
Example Scenario: If a painful stimulus occurs on the left leg, what happens to both legs?
Left Leg (Ipsilateral): Will flex (withdraw). Right Leg (Contralateral): Will extend to support the body's weight.
118
What is the general importance of spinal reflexes?
They are important for posture maintenance and involuntary movement in response to some stimuli.
119
Do spinal reflexes work alone to control posture and movement?
No. Posture and movement depend on a combination of: Involuntary reflexes coordinated by the spinal cord. Voluntary actions controlled by higher brain centers.
120
Stretch Reflex: Receptor and Sensory Nerve Fibers?
Receptor: Muscle spindle (in the intrafusal fibers). Nerve Fibers: Group Ia and Group II.
121
Neurons in the arc and Activation stimulus?
Neurons: A sensory neuron and a motor neuron (Monosynaptic). Activation: Muscle stretch. Function: Senses muscle length; prevents further muscle stretch.
122
Golgi Tendon Reflex: Receptor and Sensory Nerve Fibers?
Receptor: Golgi Tendon Organ (in the tendon). Nerve Fibers: Group Ib.
123
Golgi Tendon Reflex: Neurons in the arc and Activation stimulus?
Neurons: A sensory neuron, a motor neuron, and an interneuron (Disynaptic). Activation: Muscle contraction or tension. Function: Senses muscle tension; prevents further muscle tension.
124
Flexion Reflex: Receptor and Sensory Nerve Fibers?
Receptor: A variety of sensory receptors in the skin. Nerve Fibers: A variety of afferent fibers (Group II, III, and IV).
125
Flexion Reflex: Neurons in the arc and Activation stimulus?
Neurons: A sensory neuron, a motor neuron, and multiple interneurons (Polysynaptic). Activation: Tactile or noxious stimuli. Function: Senses noxious stimuli; maintains balance and protects the body from damaging stimuli.
126
What is Muscle Tone?
It is the firmness or state of muscle contraction at rest. Healthy muscles are never fully relaxed; they retain a certain amount of tension and stiffness.
127
What causes muscle tone and what drives it?
Cause: Low levels of contractile activity in some motor units. Driven by: Reflex arcs from the muscle spindles.
128
What is the function of muscle tone?
It keeps muscles firm, healthy, and ready for action.
129
What is Flaccidity (or Flaccid Paralysis)?
A state where muscle tone is abolished. Cause: Interruption of the reflex arc, such as by nerve damage (e.g., sectioning the sensory afferent fibers). Appearance: Flaccid muscles are loose and flattened rather than rounded.
130
What is Hypotonia and what are its causes?
Definition: The medical term for decreased muscle tone (flaccidity is an example). Causes: Damage to lower motoneurons, the neuromuscular junction (NMJ), or muscle diseases.
131
What is Hypertonia and what are its causes?
Definition: A condition with too much muscle tone, making limbs stiff and difficult to move. Causes: Damage to upper motoneurons or decreased inhibition of motoneurons.
132
What is a "Lower Motoneuron" (clinically speaking)?
This term refers to the normal alpha-motoneurons that directly innervate skeletal muscle.
133
What is an "Upper Motoneuron" (clinically speaking)?
They are not actually motoneurons. They are descending interneurons that connect neurons in the brain to the alpha-motoneurons (the lower motoneurons).
