The Motor System and Motor Cortex
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Questions and Answers

What is the main function of the corticospinal tracts?

  • Regulating autonomic functions
  • Processing sensory information
  • Facilitating reflex actions
  • Controlling voluntary motor activity (correct)

    • How do motor neurons in the spinal cord transfer signals?

  • They project their axons contralaterally
  • They use chemical signals exclusively
  • They have no direct connections to muscles
  • They project their axons ipsilaterally (correct)

    • Which structure is responsible for transmitting signals from the cerebral cortex to the brainstem or spinal cord?

  • Upper motor neuron (correct)
  • Corticobulbar tract
  • Anterior horn cell
  • Lower motor neuron

    • What characterizes a monosynaptic reflex?

    <p>Involves a single synapse between sensory and motor neurons (B)</p> Signup and view all the answers

    What is the main function of the lower motor neuron?

    <p>To transmit motor signals to the muscle (D)</p> Signup and view all the answers

    Which area is primarily associated with sensory information processing?

    <p>Post-central gyrus (C)</p> Signup and view all the answers

    What distinguishes upper motor neuron lesions from lower motor neuron lesions?

    <p>Upper lesions can result in spastic paralysis (C)</p> Signup and view all the answers

    What percentage of fibers decussate at the level of the medulla?

    <p>85% (A)</p> Signup and view all the answers

    In the context of motor pathways, how is the term 'extrapyramidal' best described?

    <p>Involves coordination and posture control (B)</p> Signup and view all the answers

    Which part of the internal capsule contains the corticobulbar tracts?

    <p>Genu (B)</p> Signup and view all the answers

    What is the primary role of the internal capsule?

    <p>It serves as a major pathway for neural signals between the cortex and the brainstem (A)</p> Signup and view all the answers

    How is the body represented on the motor cortex?

    <p>In an inverted manner (D)</p> Signup and view all the answers

    What is the primary function of the primary sensory cortex?

    <p>To perceive sensory information (D)</p> Signup and view all the answers

    What structure is primarily involved in coordinating voluntary movements?

    <p>Cerebellum (D)</p> Signup and view all the answers

    Where is the primary motor cortex located in relation to the central sulcus?

    <p>Anterior to the central sulcus (D)</p> Signup and view all the answers

    What does the term 'motor homunculus' refer to?

    <p>A graphical representation of the motor cortex's mapping (A)</p> Signup and view all the answers

    What is the primary role of the medial reticulospinal tracts in the spinal cord?

    <p>Involved in locomotion and postural control (A)</p> Signup and view all the answers

    Which condition is likely to show hyper-reflexia?

    <p>Upper motor neuron lesion (B)</p> Signup and view all the answers

    What is the result of a diminished patellar reflex response?

    <p>Compatibility with a lower motor neuron lesion (D)</p> Signup and view all the answers

    What does the term 'paresis' refer to in a clinical context?

    <p>Partial loss of motor function (D)</p> Signup and view all the answers

    Multiple Sclerosis primarily affects which part of the neuronal structure?

    <p>Myelin coating on neurons (C)</p> Signup and view all the answers

    Which of the following best describes hemiplegia?

    <p>Loss of function in one side of the body (A)</p> Signup and view all the answers

    The patellar tendon reflex tests which aspect of the nervous system?

    <p>Integrity of sensory, CNS and motor reflex arc (C)</p> Signup and view all the answers

    In motor neuron disease, which motor neurons can be affected?

    <p>Both upper and lower motor neurons (A)</p> Signup and view all the answers

    What does a positive Babinski sign indicate?

    <p>Upper motor neuron lesion (C)</p> Signup and view all the answers

    In which age group is the Babinski sign commonly present as a normal reflex?

    <p>6 months to 2 years (B)</p> Signup and view all the answers

    What characteristic is NOT associated with lower motor neuron lesions?

    <p>Hyperreflexia (B)</p> Signup and view all the answers

    Which cranial nerve has mixed function among all motor cranial nerves?

    <p>VII - Facial (D)</p> Signup and view all the answers

    Which statement about the innervation of cranial motor neurons is true?

    <p>Most receive bilateral innervation from both hemispheres (C)</p> Signup and view all the answers

    What is the consequence of an upper motor neuron injury to the facial nerve?

    <p>Wrinkling of forehead is spared (A)</p> Signup and view all the answers

    Which of the following conditions is typically related to lower motor neuron lesions?

    <p>Paresis (A)</p> Signup and view all the answers

    What clinical sign indicates reduced resistance to passive stretching?

    <p>Hypotonicity (A)</p> Signup and view all the answers

    What type of lesion results in paralysis of the lower right side of the face?

    <p>Left-sided upper motor neuron lesion (B)</p> Signup and view all the answers

    Which part of the brain is primarily involved in the pyramidal system for upper motor neurons?

    <p>Cerebral cortex (D)</p> Signup and view all the answers

    Which type of movement is the extrapyramidal system primarily responsible for?

    <p>Fine-tuned movement (D)</p> Signup and view all the answers

    What is the primary role of the rubrospinal pathway?

    <p>Control of tone in flexor muscles (A)</p> Signup and view all the answers

    Which structure is NOT part of the basal ganglia?

    <p>Cerebellum (C)</p> Signup and view all the answers

    What is the primary function of the tectospinal tract?

    <p>Reflex movements in response to visual stimuli (D)</p> Signup and view all the answers

    Which of the following statements correctly describes the extrapyramidal system?

    <p>It includes connections to various brain nuclei such as the basal ganglia. (C)</p> Signup and view all the answers

    What characterizes a right-sided lower motor neuron lesion of the facial nerve?

    <p>Paralysis of the entire right side of the face (B)</p> Signup and view all the answers

    What is the main pathway used by the motor neurons for sending signals to the same side of the body?

    <p>Ipsilateral pathway (A)</p> Signup and view all the answers

    Which type of motor neuron lesion typically results in muscle atrophy and flaccid paralysis?

    <p>Lower motor neuron lesion (C)</p> Signup and view all the answers

    In the context of reflex actions, how many neurons are involved in the efferent pathway?

    <p>Two neurons (D)</p> Signup and view all the answers

    Which structure is the initial point for the upper motor neurons of the pyramidal system?

    <p>Cerebral cortex (A)</p> Signup and view all the answers

    What is the role of the internal capsule in the motor system?

    <p>Transmitting signals from the cortex to the brainstem and spinal cord (D)</p> Signup and view all the answers

    What is the primary distinction between corticobulbar and corticospinal tracts?

    <p>Corticobulbar tracts are associated with cranial nerves. (D)</p> Signup and view all the answers

    Which area of the brain is primarily involved in generating voluntary motor commands?

    <p>Pre-central gyrus (A)</p> Signup and view all the answers

    Which reflex is exemplified by monosynaptic neurons responding directly to a stimulus?

    <p>Patellar reflex (C)</p> Signup and view all the answers

    What role does the lower motor neuron play in the motor pathway?

    <p>To transmit signals to muscles directly (B)</p> Signup and view all the answers

    Which structure is located posterior to the central sulcus and primarily involved in sensory processing?

    <p>Post-central gyrus (A)</p> Signup and view all the answers

    At what anatomical location do the upper motor neuron fibers decussate in the pyramidal system?

    <p>Pyramids of the medulla (B)</p> Signup and view all the answers

    Which motor pathway is primarily associated with involuntary or automatic movements?

    <p>Extrapyramidal pathway (C)</p> Signup and view all the answers

    What is meant by the term 'bulb' in the context of the pyramidal system?

    <p>It is an outdated term for the medulla. (A)</p> Signup and view all the answers

    Which structures are considered components of the basal nuclei?

    <p>Lentiform nucleus and caudate nucleus (A)</p> Signup and view all the answers

    What is the primary function of the superior colliculus?

    <p>Controlling reflex movements based on visual input (A)</p> Signup and view all the answers

    Where do the upper motor neurons of the pyramidal system originate?

    <p>Cerebral cortex (C)</p> Signup and view all the answers

    Which of the following statements is true regarding the extrapyramidal system?

    <p>It largely influences involuntary motor pathways. (A)</p> Signup and view all the answers

    Which area of the brainstem is involved in both homeostatic and reflex functions?

    <p>Tectum (A)</p> Signup and view all the answers

    What defines the primary pathway of the upper motor neurons in the pyramidal system?

    <p>They pass through the pyramids of the medulla. (D)</p> Signup and view all the answers

    Which nucleus is NOT included in the lentiform nucleus?

    <p>Caudate nucleus (D)</p> Signup and view all the answers

    Which of the following is primarily associated with reflexive movements in response to auditory input?

    <p>Inferior colliculus (C)</p> Signup and view all the answers

    What is supplied by the anterior perforating arteries in the brain?

    <p>Internal capsule (A)</p> Signup and view all the answers

    What do the anterior perforating arteries originate from?

    <p>Middle cerebral artery (A)</p> Signup and view all the answers

    In which part of the pyramidal motor pathway does the corticobulbar tract primarily reside?

    <p>Genu of the internal capsule (D)</p> Signup and view all the answers

    What is the primary effect of a unilateral upper motor neuron lesion in the cerebral hemisphere?

    <p>Contralateral weakness (B)</p> Signup and view all the answers

    What percentage of fibers decussate in the lateral corticospinal tracts?

    <p>85% (C)</p> Signup and view all the answers

    What condition is characterized by spasticity and increased resistance to muscle stretching?

    <p>Upper motor neuron lesion (A)</p> Signup and view all the answers

    What is described as a rhythmic series of muscle contractions induced by stretching the tendon?

    <p>Clonus (B)</p> Signup and view all the answers

    What aspect of the pyramidal motor pathway corresponds to the decussation near termination for anterior corticospinal fibers?

    <p>Spinal cord (D)</p> Signup and view all the answers

    What is the main role of the superior colliculus?

    <p>Facilitating reflex movements in response to visual input (B)</p> Signup and view all the answers

    Which of the following correctly defines the tegmentum?

    <p>Located anterior to the aqueduct of Sylvius and present in all three parts of the brainstem. (A)</p> Signup and view all the answers

    What anatomical feature distinguishes tectum from tegmentum?

    <p>Tectum is posterior to the aqueduct of Sylvius, whereas tegmentum is anterior. (D)</p> Signup and view all the answers

    Which brain structure is responsible for reflex movements in response to auditory stimuli?

    <p>Inferior colliculus (C)</p> Signup and view all the answers

    Which statement about the tegmentum is correct?

    <p>It plays a role in both homeostatic and reflexive pathways. (A)</p> Signup and view all the answers

    What type of tracts does the tegmentum contain?

    <p>Both corticospinal and corticobulbar tracts (A)</p> Signup and view all the answers

    What is the primary function of the reticulospinal tract mentioned in relation to the tegmentum?

    <p>It is involved in maintaining postural control and reflexes. (C)</p> Signup and view all the answers

    In which part of the brainstem is the tegmentum located?

    <p>In all three parts of the brainstem (C)</p> Signup and view all the answers

    Study Notes

    The Motor System

    • The motor system is responsible for movement and is controlled by both the central nervous system (CNS) and peripheral nervous system (PNS).
    • The simplest motor response is a monosynaptic reflex which is triggered by a stimulus and causes a muscle to contract without conscious control (e.g., knee jerk, biceps reflex).
    • Motor neurons in the spinal cord and cranial nerves are ipsilateral, meaning they project their axons to the periphery on the same side of the body.
    • Controlled responses to stimuli require a more complex pathway involving sensory (afferent) and motor (efferent) neurons.
      • Afferent neurons carry information from the periphery to the CNS.
      • Efferent neurons carry commands from the CNS to the periphery.

    Motor Cortex and Pathways

    • The pre-central gyrus is the primary motor cortex where voluntary movements are initiated.
    • The motor homunculus is a distorted representation of the body on the motor cortex, reflecting the relative amount of cortical area dedicated to controlling different body parts.
    • The pyramidal motor pathway is responsible for conscious voluntary movements.
      • Upper motor neurons (UMN) originate in the cerebral cortex and project to the brainstem or spinal cord.
      • Lower motor neurons (LMN) originate in the brainstem or spinal cord and project to muscles.
      • Most (85%) of the corticospinal tract fibers cross over (decussate) in the medulla forming the lateral corticospinal tracts.
    • The internal capsule is a white matter structure that carries axons from the cerebral cortex to the brainstem and spinal cord.
      • The genu of the internal capsule carries the corticobulbar tract, which controls cranial nerve nuclei.
      • The posterior limb carries the corticospinal tract, which controls spinal motor neurons.
    • Damage to the pyramidal tract can result in weakness, paralysis, wasting of muscles, fasciculations, and hypotonia.

    Motor Cranial Nerves

    • Cranial nerves III, IV, VI, XI, and XII are primarily involved in motor control, while V, VII, IX, and X are mixed, containing both motor and sensory components.
    • The facial nerve (VII) has bilateral innervation for the upper face, meaning it receives input from both hemispheres.
    • Injury to the upper motor neuron (UMN) of the facial nerve will result in paralysis of the lower face on the contralateral side of the body, but the forehead will be spared.
    • Injury to the lower motor neuron (LMN) of the facial nerve will result in paralysis of the entire face on the ipsilateral side of the body.

    Extrapyramidal System

    • The extrapyramidal system is responsible for fine-tuning movements, regulating muscle tone, and controlling posture.
    • The basal ganglia are a group of subcortical nuclei that play a key role in the extrapyramidal system.
    • The rubrospinal tract originates in the red nucleus of the midbrain and helps control the tone of flexor muscles.
    • The tectospinal tract originates in the superior colliculi and controls reflex movements in response to visual stimuli.
    • The vestibulospinal tract originates in the vestibular nuclei and controls the tone of extensor muscles, maintaining posture and balance.

    Clinical Considerations

    • UMN lesions can result in hyperreflexia, spasticity, clonus, and a positive Babinski sign.
    • LMN lesions can result in hyporeflexia, flaccid paralysis, muscle atrophy, and fasciculations.
    • Neurological exams can help assess the integrity of the motor system by testing reflexes, muscle tone, and strength.

    Additional Information

    • Stroke is a common cause of UMN lesions, leading to weakness or paralysis on the contralateral side of the body.
    • Poliomyelitis (polio) is a viral infection that damages anterior horn cells, leading to LMN lesions.
    • Multiple sclerosis is an autoimmune disease that damages the myelin sheath of neurons, affecting both UMNs and LMNs.
    • Motor neuron disease is a group of disorders that affect motor neurons, leading to progressive muscle weakness and atrophy.

    Key Terms

    • Hyporeflexia (hypo) Reduced reflex response.
    • Hyperreflexia (hyper) Increased or exaggerated reflex response.
    • Fasciculations: Small, localized, involuntary twitches in muscle fibers.
    • Spasticity: Increased muscle tone and resistance to stretching.
    • Clonus: Rhythmic, involuntary muscle contractions often seen in response to sudden stretching.
    • Babinski sign: Dorsal extension of the big toe in response to stroking the bottom of the foot.
    • Palsy: Paralysis.
    • Paralysis: Complete or partial loss of motor function.
    • Paresis: Weakness or partial loss of motor function.
    • Paraplegia: Paralysis of the lower limbs.
    • Hemiplegia: Paralysis of one side of the body.
    • Monoplegia: Paralysis restricted to one limb.

    Motor System Function

    • The corticospinal tracts are a group of upper motor neurons that start in the cortex and end in the spinal cord.
    • The corticobulbar tracts are a group of upper cranial motor nerves that start in the cortex and end in the brainstem.
    • Upper motor neurons begin in the cerebral cortex.
    • Lower motor neurons begin in the brainstem or spinal cord.
    • Monosynaptic neurons are the simplest motor neurons, they respond to stimuli directly without any control.
    • The internal capsule is a part of the brain that is supplied by the anterior perforating arteries.
    • The anterior perforating arteries enter the brain through the anterior perforated substance and are branches of the middle cerebral artery.

    Motor Pathway Anatomy

    • Cerebral peduncles are the pathways that connect the cerebrum to the brainstem.
    • Pyramids are the bulges on the ventral surface of the medulla.
    • The pyramidal decussation occurs when 85% of the fibers cross to the opposite side in the medulla
    • Fibers in the anterior corticospinal tract decussate near the termination of the spinal cord.
    • The substantia nigra and red nuclei are located in the tegmentum of the midbrain.
    • The tectum is located in the midbrain posterior to the cerebral aqueduct.
    • The superior colliculus controls reflex movements from visual input.
    • The inferior colliculus controls reflex movements from auditory input.
    • The tegmentum is located in the brainstem and connects the thalamus to the brainstem, it is involved in homeostatic and reflex pathways.

    Upper and Lower Motor Neuron Lesions

    • An upper motor neuron lesion results in contralateral weakness or paralysis.
    • If the lesion occurs in the spinal cord, then the weakness or paralysis is ipsilateral.
    • Lower motor neuron lesions result in ipsilateral weakness or paralysis, atrophy, fasciculations, and hyporeflexia.

    Comparing Pyramidal and Extrapyramidal Systems

    • The pyramidal system consists of upper motor neurons that travel through the pyramids of the medulla and are responsible for conscious movement.
    • The extrapyramidal system consists of neurons that start in other brain regions and fine-tune movement.

    Other Extrapyramidal Tracts

    • The reticulospinal tract originates from the pons and medulla.

    Clinical Presentation

    • Spasticity is increased resistance to stretch of muscles, with a clasp-knife component.
    • Clonus is a rhythmic series of muscle contractions that occurs when stretching the tendon.
    • Flaccidity is a loss of muscle tone, can be caused by a lower motor neuron lesion.
    • Fasciculations are spontaneous muscle twitching, can also be caused by a lower motor neuron lesion.
    • Hyporeflexia is a decrease in reflexes, can also be caused by a lower motor neuron lesion.

    Key Structures

    • Basal nuclei include the lentiform nucleus (putamen + globus pallidus), caudate nucleus, and substantia nigra.
    • The lentiform nucleus is a large nucleus located in the forebrain that is involved in motor control.
    • The caudate nucleus is a curved structure that is involved in planning and executing movement.

    Motor Neuron Pathways

    • Motor areas are located in the pre-central gyrus and are responsible for controlling voluntary movement.
    • The internal capsule contains the corticospinal and corticobulbar tracts.
    • The genu of the internal capsule contains the corticobulbar tracts, which innervate the muscles of the head and face.
    • The posterior limb of the internal capsule contains the corticospinal tracts, which innervate the muscles of the trunk and limbs.
    • The crus cerebri is the part of the cerebral peduncles that is located in the midbrain.
    • The spinal cord conveys motor signals to the muscles.

    Remember

    • "Bulb" is an outdated word for the medulla.

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    Description

    Explore the fundamentals of the motor system, including its structure, function, and key pathways. This quiz covers reflex actions, motor neuron roles, and the motor cortex's involvement in voluntary movement. Test your understanding of how motor responses are executed in the nervous system.

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