In This Motor Control and Vestibular System Physiology MCQs Quizz, We will covers the physiology of motor units, the control of voluntary and reflex movements, and the role of the vestibular system in balance and posture through Multiple choice questions and answers with explanations to help remember the information.
The Concept of Lower and Upper Motor Neurons and Their Malfunction
1 Which of the following would not be considered an upper motor neuron?
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The ventral horn ฮฑ motor neurons are considered lower motor neurons, as they are located in the ventral horn of the spinal cord and directly innervate skeletal muscle. Upper motor neurons lie completely within the central nervous system and control lower motor neurons, such as the corticospinal, corticobulbar, and bulbospinal motor neurons.
2 You examine a dog that is unable to stand and bear weight on the right rear leg. The right rear leg is much smaller in diameter than the left rear leg. Pinching the toe on the left rear leg results in withdrawal of the left rear leg, but pinching the toe on the right rear leg results in no movement of the right rear leg. Where is this dogโs pathological lesion?
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The lack of movement in the right rear leg in response to toe pinching, combined with muscle atrophy, suggests damage to the lower motor neuron controlling that leg. Lower motor neuron lesions are often associated with decreased muscle tone, muscle atrophy, and the loss of reflexes in the affected limb.
3 You examine a dog that is bright, alert, and responsive. She can stand and bear weight on both front legs, but she cannot stand or bear any weight on the back legs. Her knee jerk and toe-pinch withdrawal reflexes are normal in all four legs. There is no atrophy. The proprioceptive positioning response is normal in the front legs but absent in both rear legs. Where is this dogโs pathological lesion most likely located?
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The absence of atrophy and normal reflexes suggest that the lower motor neurons are intact. However, the absence of proprioceptive positioning in the hind legs indicates that the lesion is located in the spinal cord between the front and rear limbs, likely in the thoracolumbar region.
4 You examine a cat that cannot bear weight on the hind legs. The cat is bright, alert, and responsive. Atrophy is present in the back legs. Knee jerk and toe-pinch withdrawal reflexes are absent in the hind legs. What is the most likely location for this catโs pathological lesion?
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The presence of muscle atrophy and the absence of reflexes in the hind legs suggest a lesion in the lower motor neurons that innervate those legs. Lower motor neuron lesions often lead to flaccid paralysis, muscle atrophy, and reduced reflexes.
5 You are presented with a horse that is unable to stand or support any weight on the hind legs. You electrically stimulate both the sciatic and the femoral nerves, but neither stimulation results in muscular contraction. However, direct stimulation of the gastrocnemius and the quadriceps femoris muscles results in muscular contraction. From these observations, what do you conclude to be the location of this horseโs pathological lesion?
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The absence of a response to nerve stimulation but a response to direct muscle stimulation suggests that the neuromuscular junction and muscles are functioning. The issue is likely with the lower motor neurons, which are not transmitting signals to the muscles.
6 Which of the following is a key sign of lower motor neuron disease?
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Lower motor neuron disease is often associated with muscle atrophy due to the loss of innervation to the muscles, leading to a decrease in muscle mass. This is in contrast to upper motor neuron disease, which may present with spastic paralysis but without muscle atrophy.
7 What characterizes the function of upper motor neurons?
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Upper motor neurons are located in the central nervous system and send signals to lower motor neurons, which then innervate skeletal muscles. This control allows for voluntary movement and reflex regulation.
8 What is a clinical sign of upper motor neuron disease?
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In upper motor neuron disease, reflexes are retained but often exaggerated due to the loss of inhibitory control from the upper motor neurons. This contrasts with lower motor neuron disease, where reflexes are diminished or absent.
9 Which motor neurons are involved in controlling the muscles of the limbs?
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Lower motor neurons that control the muscles of the limbs originate in the ventral horn of the spinal cord. These neurons directly innervate skeletal muscles and are responsible for motor responses.
10 What clinical sign differentiates upper motor neuron lesions from lower motor neuron lesions?
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Hyperreflexia, or exaggerated reflexes, is a hallmark of upper motor neuron lesions. Lower motor neuron lesions typically result in diminished reflexes (hyporeflexia) or absence of reflexes, along with muscle atrophy.
11 You examine a dog that has weakness and a spastic gait in the hind legs. Knee jerk and toe-pinch reflexes are exaggerated. There is no evidence of muscle atrophy. Where is the lesion most likely located?
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The spastic gait and exaggerated reflexes suggest a lesion in the upper motor neurons controlling the hind legs. The lack of muscle atrophy further supports this diagnosis, as lower motor neuron damage would typically result in atrophy.
12 What is the expected outcome of damage to lower motor neurons?
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Damage to lower motor neurons results in hyporeflexia (diminished reflexes) or areflexia (absence of reflexes), as these neurons are essential for the transmission of signals necessary for reflex actions. In contrast, upper motor neuron damage often results in hyperreflexia (exaggerated reflexes).
13 Which of the following is a typical finding in upper motor neuron lesions, but not in lower motor neuron lesions?
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Upper motor neuron lesions often result in exaggerated segmental reflexes because the inhibitory control exerted by the upper motor neurons is lost. Lower motor neuron lesions lead to the loss of these reflexes.
14 A dog presents with normal motor function in the front legs but paralysis in the hind legs. The knee jerk reflex is exaggerated in both hind legs, and there is no muscle atrophy. Where is the lesion likely located?
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The presence of paralysis without muscle atrophy, along with exaggerated reflexes, suggests an upper motor neuron lesion affecting the hind legs.
The Central Control of Movement
15 A motor neuron pool located most laterally in the ventral horn of the spinal cord is most likely to operate a muscle controlling movement of the:
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Motor neuron pools in the ventral horn of the spinal cord are organized somatotopically. Neurons that control distal limb muscles are located more laterally in the ventral horn, while those controlling axial and proximal muscles are positioned medially.
16 Which of the following is true regarding decerebrate rigidity?
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Decerebrate rigidity is caused by damage to the brainstem or forebrain, which disrupts the normal cortical control over brainstem motor pathways. This condition results in exaggerated antigravity muscle tone and a rigid, fixed posture, often seen in animals with severe brain injury.
17 Which of the following descending brainstem motor pathways controls distal limb musculature associated with skilled movement?
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The rubrospinal tract is responsible for controlling the distal limb musculature involved in skilled, voluntary movements, particularly flexor muscles. Other pathways, like the vestibulospinal and reticulospinal tracts, mainly control postural muscles.
18 The corticospinal (pyramidal) tract, in general, initiates what form of movement?
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The corticospinal tract is responsible for initiating fine, skilled, voluntary movements, particularly of the distal limb muscles, such as those involved in dexterous hand movements in primates.
19 You are presented with a dog with a weakness and proprioceptive placing reaction deficit in its left front and left back legs. A single pathological site could cause these signs if it were located in the:
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A lesion in the left side of the cervical spinal cord could directly affect the motor neurons serving both the left front and left hind limbs. Alternatively, a lesion in the right cerebral cortex could impair the motor control of the contralateral limbs due to the crossing of corticospinal tract axons at the pyramidal decussation.
20 The corticospinal tract simultaneously co-activates both the ฮฑ and the ฮณ lower motor neurons. If the initial coactivation fails to be sufficient to cause the intended shortening of the muscle, sensory neuron activity of the muscle spindle of that muscle will have what influence on the ฮฑ motor neurons to the same muscle?
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If the intended muscle shortening does not occur, the stretch on the muscle spindle will increase. This results in excitatory postsynaptic potentials (EPSPs) on the ฮฑ motor neurons through a stretch reflex mechanism, helping to increase contraction and adjust the muscle length appropriately.
21 Which descending motor pathway is primarily responsible for controlling antigravity muscles and maintaining posture?
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The vestibulospinal tract is involved in controlling the axial and proximal extensor muscles, which are essential for maintaining posture and resisting the pull of gravity. This pathway plays a key role in keeping the body upright.
22 The rubrospinal tract primarily controls which of the following types of movement?
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The rubrospinal tract is responsible for voluntary skilled movements, particularly of the distal limb flexors. It allows for more refined control of limb movements, especially in quadrupeds.
23 Which of the following motor system structures modulates movement but does not directly initiate it?
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The basal ganglia modulate motor activity, particularly by helping to select and suppress movement patterns. They do not directly initiate movement but play a crucial role in regulating motor output.
24 Damage to which of the following tracts would most likely result in a loss of skilled, voluntary movement in the distal limbs?
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The corticospinal tract is crucial for skilled, voluntary movements, particularly of the distal limb muscles. Damage to this tract can lead to profound deficits in fine motor control and dexterity.
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25 Which structure is responsible for coordinating the timing and smoothness of complex movements?
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The cerebellum plays a critical role in coordinating the timing and smoothness of movements by comparing sensory feedback with the motor plan and making adjustments as needed. Damage to the cerebellum results in uncoordinated and jerky movements.
26 Which of the following motor pathways is involved in reflex orientation of the head toward environmental stimuli?
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The tectospinal tract is involved in reflexively orienting the head in response to visual, auditory, or somatosensory stimuli. It plays a role in rapid head movements to align the gaze with a stimulus.
27 Which of the following components of the motor system hierarchy is primarily responsible for controlling voluntary movements of the face and head muscles?
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The corticobulbar tract controls the lower motor neurons in the brainstem that innervate muscles of the face and head. It is responsible for voluntary movements in these areas, similar to how the corticospinal tract controls limb movements.
28 What is the main function of the reticulospinal tract in the control of movement?
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The reticulospinal tract is primarily involved in regulating muscle tone, especially in the axial and proximal muscles. It plays a key role in maintaining posture and preparing the body for movement by controlling antigravity muscles.
29 Which type of motor neurons are responsible for maintaining muscle spindle sensitivity during voluntary muscle contraction?
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Gamma motor neurons adjust the tension in intrafusal muscle fibers to ensure that the muscle spindle remains sensitive to stretch even during muscle contractions, allowing the muscle to detect changes in length and make corrections.
30 Which of the following describes the corticospinal tractโs role in movement?
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The corticospinal tract, particularly the lateral corticospinal tract, is essential for controlling voluntary, skilled movements, such as fine motor skills in the distal limbs.
31 What is a key role of the supplementary motor cortex in the control of movement?
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The supplementary motor cortex is involved in planning and organizing complex sequences of movements, such as those required for tasks involving both limbs working together.
32 The medial descending brainstem motor pathways, such as the vestibulospinal and reticulospinal tracts, primarily control which muscles?
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The medial brainstem motor pathways, including the vestibulospinal and reticulospinal tracts, are critical for maintaining posture by controlling axial and proximal extensor muscles.
33 What function does the cerebellum perform in the motor system?
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The cerebellum plays a vital role in coordinating the timing and smoothness of complex movements, ensuring proper muscle contractions and adjustments during ongoing movements.
34 Which of the following accurately describes the function of the basal ganglia in movement control?
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The basal ganglia are involved in modulating motor activity, helping to select the correct movement pattern while suppressing others, ensuring smooth execution of motor tasks.
35 What is the primary role of the lateral vestibulospinal tract in movement?
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The lateral vestibulospinal tract helps maintain posture by activating antigravity extensor muscles, particularly in response to changes in balance.
36 The motor cortices consist of three different regions, including the primary motor cortex, supplementary motor cortex, and which other region?
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The motor cortices include the primary motor cortex, supplementary motor cortex, and premotor cortex. The premotor cortex is involved in preparing the body for movement, especially in orienting the limbs toward a target.
37 What is the primary difference between the lateral corticospinal tract and the ventral corticospinal tract?
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The lateral corticospinal tract primarily controls skilled voluntary movements of the distal limbs, while the ventral corticospinal tract controls muscles involved in postural adjustments, particularly the axial and proximal muscles.
38 What is the significance of the pyramidal decussation in the corticospinal tract?
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The pyramidal decussation is where the majority of the corticospinal tract axons cross to the contralateral side, allowing for the control of muscles on the opposite side of the body from the motor cortex.
The Vestibular System
39 What is the receptor organ that detects rotary acceleration and deceleration of the head?
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The ampulla of the semicircular duct contains a receptor organ called the crista ampullaris. This organ is responsible for detecting rotary acceleration and deceleration of the head by transducing mechanical stimuli caused by the movement of the endolymph within the semicircular ducts.
40 Which two of the following are not generally associated with the macula?
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The macula is associated with detecting linear acceleration of the head and contains hair cells whose cilia are embedded in a gelatinous layer with otoliths on top. The cupula is part of the crista ampullaris in the semicircular ducts, not the macula.
41 A dog presents with head tilt, compulsive circling, and spontaneous nystagmus. What is the most likely site of the pathological lesion?
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The vestibular system is responsible for maintaining balance and spatial orientation. Lesions in this system can result in symptoms such as head tilt, circling, and spontaneous nystagmus, which are characteristic of vestibular disease.
42 Which one of the following statements is false?
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This statement is false because, in the utricle, the hair cells are not all oriented in the same direction. The cilia of the hair cells are arranged in a pattern that allows them to detect changes in orientation and acceleration from various directions.
43 If a normal dog is sitting on a piano stool and the stool is spun to the right, which two of the following statements are false regarding the observed nystagmus?
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Nystagmus is caused by the lag of endolymph in the semicircular ducts during acceleration. However, once constant velocity is achieved, the endolymph movement catches up with the head movement, and nystagmus ceases. Therefore, statement C is false.
44 Which structure of the vestibular system is primarily responsible for detecting linear acceleration and static head tilt?
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The utricle and saccule, also known as otolith organs, are responsible for detecting linear acceleration and static tilt of the head.
45 Which ion is primarily responsible for the depolarization of hair cells in the vestibular system when the cilia are bent toward the largest cilium?
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Depolarization of the vestibular hair cells is caused by the influx of potassium ions (K+) through mechanically gated ion channels at the tips of the cilia. When the cilia are bent toward the largest cilium, these channels open, leading to depolarization and increased firing of the associated sensory neuron.
46 What is the primary role of the vestibulo-ocular reflex (VOR)?
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The vestibulo-ocular reflex (VOR) stabilizes vision by coordinating eye movements with head movements. As the head moves, the VOR ensures that the eyes remain fixed on a target, allowing for clear vision during motion. This reflex is essential for maintaining visual acuity.
47 Which of the following clinical signs is NOT typically associated with vestibular disease in animals?
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Vestibular disease is characterized by symptoms such as head tilt, circling, nystagmus, and ataxia. Loss of proprioception, however, is typically a sign of central nervous system or spinal cord pathology, rather than peripheral vestibular dysfunction.
48 What is the gelatinous structure within the ampulla that bends the hair cell cilia during head rotation?
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The cupula is the gelatinous structure found in the ampulla of the semicircular ducts. When the head rotates, the endolymph fluid lags behind due to inertia, causing the cupula to bend, which in turn bends the cilia of the hair cells, sending signals to the brain regarding the direction and speed of head rotation.
49 Which of the following functions is performed by the lateral vestibulospinal tract?
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The lateral vestibulospinal tract plays a critical role in maintaining posture by providing excitatory input to the gamma (ฮณ) and alpha (ฮฑ) motor neurons of antigravity muscles. These muscles, primarily in the trunk and limbs, help maintain balance and upright posture in response to changes in head position or linear acceleration.
50 Which of the following is a common pathological sign of vestibular syndrome in animals?
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Strabismus, a condition where the eyes are misaligned and fail to focus on the same point, is often seen in animals with vestibular disease. This can be caused by lesions affecting the nerves that control the extraocular muscles or the vestibular systemโs connections to these muscles. Other signs of vestibular disease include head tilt, ataxia, and nystagmus.
51 Which structure is responsible for detecting changes in head rotation?
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The crista ampullaris, located in the ampullae of the semicircular ducts, is the receptor organ responsible for detecting rotary acceleration and deceleration of the head. Hair cells within the crista ampullaris sense the movement of endolymph fluid during head rotation, allowing for the detection of changes in head position.
52 What is the primary function of the medial longitudinal fasciculus (MLF)?
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The medial longitudinal fasciculus (MLF) is a neural pathway that connects the vestibular nuclei with the motor nuclei controlling the extraocular muscles. This connection is crucial for coordinating eye movements, particularly during head movements, to ensure that the eyes remain fixed on a target (as part of the vestibulo-ocular reflex).
53 What are otoliths, and where are they located?
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Otoliths are small calcium carbonate crystals located within the utricle and saccule. These crystals rest on top of a gelatinous layer, and their movement in response to linear acceleration or head tilt causes the hair cells beneath them to bend, sending signals to the brain about the bodyโs orientation and movement.
54 Which fluid is found in the membranous labyrinth of the vestibular system?
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The membranous labyrinth of the vestibular system is filled with endolymph, a potassium-rich fluid that is essential for the proper functioning of the sensory receptors in the vestibular system. The perilymph, on the other hand, surrounds the membranous labyrinth and is found in the bony labyrinth.
55 The vestibular system is primarily involved in which of the following?
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The vestibular system plays a crucial role in maintaining balance and spatial orientation by detecting changes in head movement and position. It sends signals to the brain to coordinate movements that help maintain equilibrium and control reflexive eye movements.
56 What happens when the hair cell cilia in the vestibular system are bent in the direction away from the largest cilium?
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When the hair cell cilia are bent away from the largest cilium, the hair cell membrane becomes hyperpolarized, which decreases the release of neurotransmitters and reduces the firing rate of the associated sensory neurons. This hyperpolarization is the opposite of what occurs when the cilia bend toward the largest cilium.
57 Which of the following describes nystagmus observed during vestibular dysfunction?
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Nystagmus refers to involuntary, rhythmic eye movements that can occur horizontally, vertically, or torsionally. It is commonly seen in cases of vestibular dysfunction, where abnormal signals from the vestibular system affect eye movement control, leading to this characteristic sign.
58 What is the function of the otolith organs in the vestibular system?
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The otolith organs, consisting of the utricle and saccule, detect linear acceleration and static head tilt. The hair cells in these organs have cilia embedded in a gelatinous layer topped with otoliths. Movement of the otoliths due to gravity or acceleration causes the cilia to bend, sending signals to the brain about changes in position and movement.
59 Which cranial nerve transmits information from the vestibular system to the brain?
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The vestibulocochlear nerve (cranial nerve VIII) is responsible for transmitting sensory information from both the vestibular system and the cochlea (for hearing) to the brain. It carries signals related to balance, spatial orientation, and hearing.
60 The utricle and saccule differ in their orientation. How is the macula of the utricle oriented in relation to the body?
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The macula of the utricle is horizontally oriented, which makes it more sensitive to horizontal linear accelerations, such as when the body moves forward or backward. In contrast, the macula of the saccule is vertically oriented, making it more sensitive to vertical movements, like moving up or down.
61 What is the role of the medial vestibulospinal tract?
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The medial vestibulospinal tract helps coordinate movements of the head and neck, particularly in response to signals from the vestibular system. This pathway plays an important role in stabilizing the head during movements and maintaining balance.
62 Which of the following is NOT a characteristic of the crista ampullaris?
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The crista ampullaris detects rotary (angular) acceleration of the head, not linear acceleration. Linear acceleration is detected by the maculae of the utricle and saccule. The crista ampullaris, located in the ampulla of the semicircular ducts, responds to rotational movements.
63 What effect does the vestibulocollic reflex (VCR) have on an animal?
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The vestibulocollic reflex (VCR) acts to stabilize the head by activating the neck muscles, particularly during movement or when the body is subjected to external forces that could disturb balance. This reflex helps maintain the head in a stable position relative to the environment, aiding in balance and posture.
64 Which of the following reflexes is crucial for maintaining gaze stability during head movements?
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The vestibulo-ocular reflex (VOR) is critical for maintaining gaze stability during head movements. It ensures that as the head moves, the eyes adjust accordingly to keep a target in focus, which allows for clear vision even when the head is moving.
65 In which structure are the sensory receptors responsible for detecting changes in the bodyโs equilibrium and orientation located?
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The sensory receptors responsible for detecting changes in the bodyโs equilibrium and spatial orientation are located in the inner ear, specifically in the utricle, saccule, and semicircular ducts. These structures transduce mechanical stimuli into neural signals that are processed by the brain to maintain balance and orientation.
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