Neuroscience: Intracranial Part and Basal Ganglia
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Questions and Answers

Which cranial nerves have motor nuclei associated with them?

  • 3, 4, 5, 6, 7, 9, 10, 11, 12 (correct)
  • 1, 2, 8
  • 3, 5, 7, 9, 11
  • 4, 6, 8, 10

    • Where does the spinal cord end?

  • At the conus medullaris
  • At the lower border of the 2nd lumbar vertebra (L2)
  • At the lower border of the 1st lumbar vertebra (L1) (correct)
  • At the lower border of the 1st cervical vertebra (C1)

    • Which section of the spinal cord contains the largest number of segments?

  • Cervical (correct)
  • Lumbar
  • Thoracic
  • Sacral

    • What is the function of the cranial nerve nuclei located in the medulla?

    <p>Motor function</p> Signup and view all the answers

    In which anatomical area is the cerebellum located?

    <p>Behind the brain stem in the posterior cranial fossa</p> Signup and view all the answers

    What type of sensations does the dorsal column pathway primarily carry?

    <p>Fine touch and proprioception</p> Signup and view all the answers

    Which structure is responsible for decussating the first neuron of the anterior spinothalamic tract?

    <p>Anterior white commissure</p> Signup and view all the answers

    In the lateral spinothalamic tract, where does the first neuron synapse with the second neuron?

    <p>Gray matter of the same segment</p> Signup and view all the answers

    Which of the following sensations are transmitted by the lateral spinothalamic tract?

    <p>Pain and temperature</p> Signup and view all the answers

    What is the ultimate destination of the sensations carried by both the anterior and lateral spinothalamic tracts?

    <p>Somatosensory cortex</p> Signup and view all the answers

    What structure connects the two cerebral hemispheres?

    <p>Corpus callosum</p> Signup and view all the answers

    Which lobe of the brain is NOT one of the four lobes of the cerebral hemispheres?

    <p>Cerebellar</p> Signup and view all the answers

    What is the primary function of the basal ganglia?

    <p>Controlling movements and coordination</p> Signup and view all the answers

    Which condition is associated with neuronal loss in the caudate nucleus?

    <p>Huntington disease</p> Signup and view all the answers

    In which part of the brain are the basal ganglia primarily located?

    <p>Telencephalon</p> Signup and view all the answers

    Which disease is characterized by neuronal degeneration within the substantia nigra?

    <p>Parkinson disease</p> Signup and view all the answers

    What is the role of the outer gray matter in the cerebral cortex?

    <p>Contain neural cell bodies</p> Signup and view all the answers

    What clinical condition is associated with impaired function of the lentiform nucleus?

    <p>Wilson disease</p> Signup and view all the answers

    Where does the voluntary motor impulse primarily originate?

    <p>Motor area 4 in the cerebral cortex</p> Signup and view all the answers

    What is the role of the upper motor neuron (UMN) in the motor pathway?

    <p>To send motor impulses from the cerebral cortex</p> Signup and view all the answers

    What percentage of corticospinal tract fibers cross to the opposite side of the spinal cord in the lower medulla?

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

    Which structure is responsible for supplying cranial nerve motor nuclei?

    <p>Corticobulbar tract</p> Signup and view all the answers

    Which neurons are located in the anterior horns of the spinal cord?

    <p>Lower motor neurons</p> Signup and view all the answers

    What structure do the axons of lower motor neurons exit from?

    <p>Anterior roots</p> Signup and view all the answers

    Which part of the motor pathway directly communicates with voluntary muscles?

    <p>Neuromuscular junction</p> Signup and view all the answers

    What type of sensations include pain and temperature?

    <p>Somatic sensations</p> Signup and view all the answers

    Which neuron is always associated with the dorsal root ganglion (DRG)?

    <p>1st order neuron</p> Signup and view all the answers

    What is the function of the corticospinal tract?

    <p>To transmit motor impulses from the cerebral cortex to the spinal cord</p> Signup and view all the answers

    Where are all somatic sensations processed before reaching the cortical sensory area?

    <p>Thalamus</p> Signup and view all the answers

    Which type of sensations are conducted via cranial nerves?

    <p>Special sensations</p> Signup and view all the answers

    What type of sensations relate to internal organ signals, such as those from the heart and intestines?

    <p>Visceral sensations</p> Signup and view all the answers

    For superficial sensations, which is the correct pathway for pain and temperature?

    <p>1st order neuron in the dorsal root ganglion</p> Signup and view all the answers

    Which of the following is NOT a type of somatic sensation?

    <p>Smell</p> Signup and view all the answers

    Which of the following sensations is NOT categorized under deep sensations?

    <p>Touch</p> Signup and view all the answers

    Which cranial nerves do not have motor nuclei associated with them?

    <p>Cranial nerves 1, 2, and 8</p> Signup and view all the answers

    What is the correct upper boundary for the spinal cord's termination?

    <p>Lower border of the first lumbar vertebra (L1)</p> Signup and view all the answers

    What segments are found in the cervical region of the spinal cord?

    <p>8 segments</p> Signup and view all the answers

    Which part of the spinal cord comprises the lowermost segments?

    <p>Conus medullaris</p> Signup and view all the answers

    Which structure starts at the lower border of the first lumbar vertebra (L1)?

    <p>Cauda equina</p> Signup and view all the answers

    What mechanism leads to persistent muscle tone?

    <p>The muscle maintains a spontaneous local axon reflex due to slight stretch.</p> Signup and view all the answers

    What effect does upper motor neuron lesion (UMNL) have on muscle tone?

    <p>It causes increased muscle tone, resulting in spasticity.</p> Signup and view all the answers

    How is the deep reflex (tendon jerk) primarily activated?

    <p>By a sudden stretch from tapping the tendon.</p> Signup and view all the answers

    What role do the Pyramidal and Extrapyramidal systems play in muscle tone?

    <p>They inhibit the local axon reflex, reducing muscle tone.</p> Signup and view all the answers

    What happens to muscle tone at the level of a lower motor neuron lesion (LMNL)?

    <p>There is a decrease in muscle tone, leading to flaccidity.</p> Signup and view all the answers

    What is primarily regulated by the pyramidal system?

    <p>Initiation of voluntary motor activity</p> Signup and view all the answers

    Which function is associated with the extrapyramidal system?

    <p>Regulation of muscle tone</p> Signup and view all the answers

    Where does the cerebellar system primarily control motor activity?

    <p>The same side of the body</p> Signup and view all the answers

    Which structure is responsible for co-ordination of voluntary motor activity initiated by the pyramidal system?

    <p>Cerebellum</p> Signup and view all the answers

    What is the primary role of lower motor neurons (LMN)?

    <p>Transmission of motor impulses to voluntary muscles</p> Signup and view all the answers

    Which systems are involved in the inhibition of muscle tone?

    <p>Extrapyramidal and pyramidal systems</p> Signup and view all the answers

    Which components are included in the lower motor neuron structure?

    <p>Alpha motor neurons, peripheral nerves, and neuromuscular junctions</p> Signup and view all the answers

    What is a primary function of the extrapyramidal system?

    <p>Regulation of involuntary muscle tone and movement</p> Signup and view all the answers

    What structure physically connects the two cerebral hemispheres?

    <p>Corpus callosum</p> Signup and view all the answers

    Which lobe of the cerebral hemisphere is primarily responsible for processing visual information?

    <p>Occipital lobe</p> Signup and view all the answers

    Which basal ganglia component is associated with Huntington's disease due to neuronal loss?

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

    What type of axons are present in the inner white matter of the cerebral hemisphere?

    <p>Myelinated axons</p> Signup and view all the answers

    Which of the following conditions leads to impaired function of the lentiform nucleus due to copper accumulation?

    <p>Wilson's disease</p> Signup and view all the answers

    Which of the following is a consequence of a lesion in the subthalamic nucleus?

    <p>Contralateral hemiballismus</p> Signup and view all the answers

    Which area of the brain do the basal ganglia primarily occupy?

    <p>Telencephalon</p> Signup and view all the answers

    What is a primary characteristic of Parkinson's disease related to the basal ganglia?

    <p>Neuronal degeneration in the substantia nigra</p> Signup and view all the answers

    What is the muscle tone characteristic of upper motor neuron lesions (UMNL)?

    <p>Hypertonia below the level of the lesion</p> Signup and view all the answers

    How is clonus typically elicited?

    <p>Due to a sudden sustained stretch of the muscle tendon</p> Signup and view all the answers

    Which reflex behavior is observed with lower motor neuron lesions (LMNL)?

    <p>Decreased deep reflexes at the level of the lesion</p> Signup and view all the answers

    What distinguishes the deep reflex responses in UMNL from LMNL?

    <p>UMNL presents with hyperreflexia below the lesion, while LMNL shows hyporeflexia at the level of the lesion</p> Signup and view all the answers

    What happens to superficial reflexes in cases of upper motor neuron lesions?

    <p>They are lost if the lesion is above the segmental supply of the reflex</p> Signup and view all the answers

    What mechanism causes muscle wasting in lower motor neuron lesions?

    <p>Disuse atrophy due to prolonged inactivity</p> Signup and view all the answers

    What type of reflex response is indicated by positive Babinski sign in cases of UMNL?

    <p>Dorsiflexion of the big toe with fanning of other toes</p> Signup and view all the answers

    Which statement accurately describes clonus in the context of neurological assessment?

    <p>It ceases immediately upon stopping the sustained stretch</p> Signup and view all the answers

    Study Notes

    Intracranial Part

    • It consists of two cerebral hemispheres connected by the corpus callosum.
    • Each cerebral hemisphere is divided into four lobes: frontal, temporal, parietal, and occipital.
    • Cerebral cortex is composed of neural cell bodies and unmyelinated axons (outer gray matter) and conducts impulses to and from the cerebral cortex (inner white matter).

    Basal Ganglia

    • Group of nuclei located beneath the cortex.
    • Include:
      • Caudate nucleus: Molecular changes in Huntington disease lead to neuronal loss in the striatum.
      • Putamen: Wilson disease (hepatolenticular degeneration) leads to impaired function of the lentiform nucleus due to copper accumulation.
      • Globus pallidus: Wilson disease (hepatolenticular degeneration) leads to impaired function of the lentiform nucleus due to copper accumulation.
      • Subthalamic nucleus: Effect of lesion: contralateral hemiballismus.
      • Substantia nigra: Parkinson disease is characterized by neuronal degeneration in the substantia nigra.

    Brain Stem

    • Consists of different parts that contain cranial nerve motor nuclei:
      • Midbrain: Contains motor nuclei for cranial nerves 3 and 4.
      • Pons: Contains motor nuclei for cranial nerves 5, 6, and 7.
      • Medulla: Contains motor nuclei for cranial nerves 9, 10, 11, and 12.
    • Cranial nerves 1, 2, and 8 are sensory nerves and do not have motor nuclei as they are concerned with special sensation.

    Cerebellum

    • Located at the back and bottom of the cranium behind the brain stem.
    • Lies in the posterior cranial fossa.

    Spinal Part

    • It lies in the spinal canal and ends at the lower border of the 1st lumbar vertebra (L1).
    • Includes different segments:
      • Cervical: 8 segments
      • Thoracic: 12 segments
      • Lumbar: 5 segments
      • Sacral: 5 segments
      • Coccygeal: 1 segment
    • Conus medullaris: The lowermost 3 segments of the spinal cord (S3, 4, 5).
    • Epiconus: The 4 segments above the conus medullaris (L4, 5, S1, 2).
    • Cauda equina: A collection of lumbo-sacral roots that fills the lower part of the spinal canal.
    • It starts at the lower border of the 1st lumbar vertebra (L1).

    Motor Pathway

    • The voluntary motor impulse originates in the cerebral cortex and terminates on the voluntary muscle.
    • It involves:
      • Upper motor neuron (UMN): Pyramidal tract.
      • Lower motor neuron (LMN): Ant. horn cells, nerves, neuromuscular junction, muscles.

    Upper Motor Neuron (UMN)

    • Begins in the motor area (4) in the cerebral cortex.
    • Axons of these cells descend through the internal capsule in the brain stem and supply the motor nuclei of the cranial nerves on both sides, except for the lower 1/2 of the facial nucleus and all the hypoglossal nucleus, which are supplied only from the opposite pyramidal tract.
    • The corticospinal tract travels from the cerebral cortex to the anterior horn cells in the spinal cord.
      • In the lower medulla:
        • 85% of fibers cross (decussate) to descend in the white matter of the opposite side of the spinal cord.
        • 15% of fibers descend directly in the white matter of the same side of the spinal cord.

    Lower Motor Neuron (LMN)

    • Located in the anterior horns of the H-shaped gray matter of the spinal cord.
    • Receive the voluntary motor impulse from the corticospinal pyramidal tract.
    • Exit the spinal cord as the anterior roots.
    • Carry the motor impulse from the anterior horn cells to the voluntary muscles.
    • Involved in neuromuscular junction and voluntary muscles.
    • Fasciculations may be present in an irritative lesion of the anterior horn cells.

    Sensory System

    • Includes three types of sensations:
      • Somatic sensations: Conducted to the CNS via the somatic nerves. Includes pain, temperature, touch (superficial), vibration, muscle sense, joint sense, nerve sense (deep), tactile localization, two-point discrimination, stereognosis, and graphosthesia (cortical).
      • Visceral sensations: Conducted to the CNS via the autonomic nerves. Includes all sensations coming from the internal viscera.
      • Special sensations: Conducted to the CNS via the cranial nerves. Includes smell, vision, and hearing.

    Pathways of Somatic Sensations

    • All somatic sensations (superficial or deep) pass through three order neurons from receptors in the skin and deep structures to reach the cortical sensory area of the opposite side:
      • 1st order neuron: Always in the Dorsal root ganglion (DRG).
      • 2nd order neuron: Varies according to the type of sensation.
      • 3rd order neuron: Always in the thalamus of the opposite side.

    Pathway of Superficial Sensations

    • Pain and temperature: The 1st order neuron is in the dorsal root ganglion (DRG).

    Pathway of Cortical Sensations

    • These are a mixture of refined superficial and deep sensations arriving to the thalamus via the 1st and 2nd order neurons.
    • Conducted from the thalamus to the cortical sensory area (1, 2, 3) in the parietal lobe.

    Intracranial Part

    • Two cerebral hemispheres connected by the corpus callosum
    • Each cerebral hemisphere has four lobes: frontal, temporal, parietal, and occipital
    • Cerebral cortex: outer gray matter composed of neural cell bodies and unmyelinated axons
    • Cerebral cortex contains areas controlling specific functions
    • Depth of the cerebral hemisphere: inner white matter composed of myelinated axons, conducts impulses to and from the cerebral cortex

    Basal Ganglia

    • Group of nuclei beneath the cortex
    • Distributed over the telencephalon, diencephalon, and mesencephalon (midbrain)

    Basal Ganglia Components

    • Striatum:
      • Caudate nucleus
      • Putamen
    • Lentiform nucleus:
      • Putamen
      • Globus pallidus
    • Subthalamic nucleus
    • Substantia nigra

    Clinical Significance

    • Huntington disease: neuronal loss in the striatum
    • Wilson disease: impaired function of the lentiform nucleus due to copper accumulation
    • Lesion of the subthalamic nucleus: contralateral hemiballismus
    • Parkinson disease: neuronal degeneration in the substantia nigra

    Brain Stem

    • Contains cranial nerve motor nuclei:
      • Midbrain: cranial nerves 3 & 4
      • Pons: cranial nerves 5, 6, 7
      • Medulla: cranial nerves 9, 10, 11, 12
    • Cranial nerves 1, 2, and 8 are sensory nerves, not motor, and are concerned with special sensation

    Cerebellum

    • Located at the back and bottom of the cranium, behind the brain stem, in the posterior cranial fossa

    Spinal Part

    • Lies in the spinal canal
    • Ends at the lower border of the 1st lumbar vertebra (L1)

    Spinal Cord Segments

    • Cervical: 8 segments
    • Thoracic: 12 segments
    • Lumbar: 5 segments
    • Sacral: 5 segments
    • Coccygeal: 1 segment

    Spinal Cord Features

    • Conus medullaris: lowermost 3 segments of the spinal cord (S3, 4, 5)
    • Epiconus: 4 segments above the conus medullaris (L4, 5, S1, 2)
    • Cauda equina: collection of lumbosacral roots that fills the lower part of the spinal canal, starts at the lower border of the 1st lumbar vertebra (L1)

    Motor System

    Upper Motor Neuron (UMN) System

    • Origin: cerebral cortex (motor area 4 and premotor area 6)
    • Termination: anterior horn cells (AHCs) of the spinal cord at different levels
    • Control: opposite side of the body
    • Functions:
      • Initiation of voluntary motor activity
      • Inhibition of deep reflexes
      • Inhibition of muscle tone
      • Regulation of voluntary motor activity
      • Regulation of emotional and associated movements

    Extrapyramidal System

    • Origin: basal ganglia
    • Termination: AHCs of the spinal cord at different levels
    • Control: opposite side of the body
    • Functions:
      • Regulation of voluntary motor activity
      • Inhibition of muscle tone
      • Coordination of voluntary motor activity initiated by the pyramidal system

    Cerebellar System

    • Origin: cerebellum
    • Termination: AHCs of the spinal cord at different levels
    • Control: same side of the body
    • Functions:
      • Coordination of voluntary motor activity initiated by the pyramidal system
      • Maintenance of equilibrium

    Lower Motor Neuron (LMN) System

    • Origin: AHCs of the spinal cord at different levels
    • Termination: voluntary muscles via peripheral nerves (PN), neuromuscular junction (NMJ)
    • Functions:
      • Transmission of the motor impulse from the AHCs to the voluntary muscles

    Muscle Tone

    • Defined as a spontaneous local axon stretch reflex
    • Mechanism:
      • Persistent slight stretch of the muscle due to its length being shorter than the distance between the origin and insertion
      • The stretch persistently activates the local axon reflex
      • This leads to persistent contraction of the muscle, resulting in muscle tone

    Muscle Tone Implications

    • The Pyramidal and Extrapyramidal systems inhibit muscle tone.
    • UMNL (Upper Motor Neuron Lesion): loss of inhibition, leading to increased muscle tone (spasticity) below the level of the lesion
    • LMNL (Lower Motor Neuron Lesion): disruption of the reflex arc, leading to decreased muscle tone (flaccidity) at the level of the lesion

    Deep Reflex (Tendon Jerk)

    • An induced local axon stretch reflex
    • Mechanism:
      • Sudden stretch of the muscle by tapping the tendon with a hammer
      • Activates the local axon reflex (suddenly and temporarily)
      • Causes a sudden transient contraction of the muscle (jerk)

    Deep Reflex Implications

    • The Pyramidal system inhibits the deep reflex.
    • UMNL: loss of inhibition, leading to increased deep reflex (hyperreflexia) below the level of the lesion.
    • LMNL: disruption of the reflex arc, leading to decreased deep reflex (hyporeflexia) at the level of the lesion.

    Clonus

    • Rapid, rhythmic, regular contractions resulting from sudden sustained stretch of the muscle tendon
    • Indicates severe pyramidal lesion due to loss of inhibition on the stretch reflex
    • Elicited in: ankle, patella, and wrist
    • Stops when the stretch is stopped

    Differentiating UMNL and LMNL

    UMNL

    • Muscle Power: Paralysis or weakness below the level of the lesion
    • Muscle Wasting: No wasting, or if present, it is late and due to disuse atrophy
    • Muscle Tone: Hypertonia (spasticity) below the level of the lesion
    • Deep Reflexes: May be present, Hyperreflexia below the level of the lesion
    • Clonus: May be present
    • Superficial reflexes: Lost if the lesion is above the segmental supply of the reflex
    • Plantar response: Positive, dorsiflexion of the big toe ± fanning of the other toes

    LMNL

    • Muscle Power: Paralysis or weakness at the level of the lesion
    • Muscle Wasting: Early and marked wasting due to loss of muscle tone
    • Muscle Tone: Hypotonia (flaccidity) at the level of the lesion
    • Deep Reflexes: Hyporeflexia at the level of the lesion
    • Clonus: Absent
    • Superficial reflexes: Lost if the lesion involves the supply of the reflex
    • Plantar response: Plantar flexion of the toes, or no response

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    Description

    This quiz covers the structure and function of the intracranial parts of the brain, focusing on the cerebral hemispheres and basal ganglia. It delves into the implications of various diseases like Huntington's and Wilson's on the brain's nuclei. Test your knowledge on these essential components of neuroscience.

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