7: Q&A: Basal Ganglia, Thalamus, Somatosensory, and Motor Pathways

Flashcards created from lecture notes covering the thalamus, basal ganglia, somatosensory pathways, trigeminal sensory system, and motor pathways.

What sensory modality does NOT relay through the thalamus?

Smell.

How is the thalamus described in terms of structure and function?

It is a small, egg-shaped structure in the brain that acts as a relay station for most sensory information and transmits it to the cerebral cortex for interpretation.

Which thalamic nucleus acts as the visual relay for information coming from the retina?

Lateral Geniculate Nucleus (LGN).

To which brain lobe is visual information transmitted after processing in the Lateral Geniculate Nucleus (LGN)?

Occipital lobe (primary visual cortex).

What are the superior colliculi and what are their functions?

They are paired dorsal midbrain structures involved in processing optical stimuli, orienting attention, and coordinating eye and head movements.

How are the basal ganglia defined?

A subcortical collection of interacting clusters of cell bodies involved in reward, emotional, and motor circuits.

What six structures make up the basal ganglia list provided in the notes?

1. Caudate, 2. Putamen, 3. Nucleus Accumbens, 4. Globus Pallidus, 5. Substantia Nigra, 6. Subthalamic Nucleus.

How can disorders of the basal ganglia, such as Parkinson's disease, affect a patient's vision?

By disturbing motor control, including eye movements, which affects the patient's ability to scan and focus effectively.

Which structure is designated as the "Center of Joy" in the central nervous system (CNS)?

Nucleus Accumbens.

Why is understanding the nucleus accumbens crucial for optometry students?

It helps explain how motivation and emotion influence a patient's visual attention, learning, and therapeutic engagement.

What is the primary role of the limbic system regarding visual data?

It gives "meaning" to what the eyes see by integrating raw visual data with emotions, memory, and behavior.

What sensory functions are carried by the Posterior column–medial lemniscus system (DC/ML)?

Fine discriminative touch, pressure, proprioception, and vibration perception.

What sensory modalities are transmitted via the Anterolateral system (ALS / Spinothalamic tract)?

Pain, temperature, and crude touch.

Which mechanoreceptor is identified as the primary mechanoreceptor in the periodontal ligament (PDL)?

The Ruffini ending.

Which mechanoreceptors are listed as present in the periodontal ligament (PDL)?

Meissner corpuscles, Pacinian corpuscles, and Ruffini endings.

What receptor type constitutes nociceptors?

Free nerve endings.

Where are proprioceptors located and what is their function?

Located deep in muscles and joints, they sense the position and movement of body parts to provide body awareness to the brain.

Where are the cell bodies of first-order sensory neurons located for the body versus the face?

Body: Dorsal root ganglion; Face: Trigeminal ganglion.

What is the role of a first-order sensory neuron?

It begins the sensory journey by carrying signals from sensory receptors to the central nervous system (CNS).

Where are the cell bodies of second-order sensory neurons located for sensory signals from the body?

Dorsal horn of the spinal cord or medullary nuclei.

Where are the cell bodies of second-order sensory neurons located for sensory signals from the face?

Trigeminal sensory nuclei in the brainstem.

What is the function of a second-order sensory neuron?

Relays the signal from the first-order neuron to the thalamus.

Where do third-order sensory neurons relay signals for the body versus the face?

Body: Ventral posterolateral (VPL) nucleus of the thalamus to the cerebral cortex; Face: Ventral posteromedial (VPM) nucleus of the thalamus to the cerebral cortex.

What is the progression of cortical regions in the somatosensory cortex pathway?

Primary somatosensory cortex -> secondary somatosensory cortex (parietal operculum) -> posterior parietal lobule (5 & 7).

Where do second-order neurons cross in the discriminative touch system (DC/ML)?

High in the medulla.

Where do second-order neurons cross in the pain system?

Low in the spinal cord.

On what side basis does the proprioceptive pathway to the cerebellum function?

Ipsilateral (same side) basis.

Why do sensory systems going to the cerebral cortex cross over to the contralateral side?

Because the cerebral cortex operates on a contralateral (opposite side) basis.

What is the major stretch receptor within muscles?

The muscle spindle.

From which type of afferent nerve fibers does the spinocerebellar tract primarily arise?

$A\alpha$ (A alpha) afferents, which are the largest and fastest axons.

According to the lecture table, what are the diameter and conduction velocity of A alpha fibers?

Diameter: $12\text{--}20\,\mu\text{m}$; Conduction Velocity: $70\text{--}120\,\text{m/s}$.

What are the diameter, conduction velocity, and main functions of C fibers?

Diameter: $0.3\text{--}1.3\,\mu\text{m}$; Conduction Velocity: $0.7\text{--}2.3\,\text{m/s}$; Functions: Autonomic and slow pain.

What are the three main branches of the trigeminal nerve?

Ophthalmic ($V_1$), Maxillary ($V_2$), and Mandibular ($V_3$).

What are alternative names for the trigeminal ganglion?

Semilunar ganglion or Gasserian ganglion.

What are the four nuclei associated with the trigeminal system?

1. Mesencephalic nucleus, 2. Sensory nucleus, 3. Motor nucleus, 4. Spinal nucleus.

What is the pathway of second-order neurons for touch and proprioception in the trigeminal system?

Main sensory nucleus -> Medial lemniscus / dorsal trigeminal tract / Ventral Trigeminal TRACT -> VPM nucleus of thalamus.

What is the pathway of second-order neurons for pain and temperature in the trigeminal system?

Spinal Trigeminal nucleus -> Spino-thalamic tract -> VPM nucleus of thalamus.

How is the corneal blink reflex mediated and which cranial nerves are involved?

Mediated by poly-synaptic connections in the brainstem between the trigeminal (CN V) and facial (CN VII) nerves.

What is Trigeminal Neuralgia (TN) also known as, and what are its pain characteristics?

Also known as Tic Douloureux; produces excruciating, lightning strikes of facial pain lasting less than $1\,\text{minute}$ near the nose, lips, eyes, or ears, with no sensory loss.

In which trigeminal branches is pain most commonly distributed in Trigeminal Neuralgia?

Maxillary ($V_2$) or Mandibular ($V_3$) branch.

What is the typical age of onset and gender prevalence for Trigeminal Neuralgia?

Onset age is after 40, and it is more common in women.

How do stretch reflexes and withdrawal reflexes differ in terms of synaptic circuit structure?

Stretch reflexes are monosynaptic, whereas withdrawal reflexes are polysynaptic.

What are the two pyramidal motor tracts and their specific motor controls?

Corticobulbar tract (controls voluntary muscles of head and face) and Corticospinal tract (controls voluntary movement of trunk and limbs).

What cranial nerve nuclei are innervated by the corticobulbar tract?

Cranial nerve nuclei 5, 7, 12, and nucleus ambiguus (9+10).

What is the key exception to the bilateral innervation pattern of the corticobulbar tract?

Cranial nerve nuclei 7.

What percentages of corticospinal tract axons form the Lateral Corticospinal tract versus the Anterior Corticospinal tract?

$85\%$ decussate in the lower medulla to form the Lateral Corticospinal tract; the remaining $15\%$ uncrossed fibers form the Anterior Corticospinal tract.

What clinical deficits characterize Upper Motor Neuron (UMN) damage versus Lower Motor Neuron (LMN) damage?

UMN damage leads to spastic paralysis and exaggerated reflexes; LMN damage leads to weakness, muscle twitching, and muscle atrophy (flaccid paralysis).

What is Babinski's reflex and what does its presence signify?

Occurs when the great toe flexes toward the top of the foot and other toes fan out after stroking the sole; signifies damage to the corticospinal tract.

What characterizes decorticate rigidity and where is its causative lesion?

Characterized by flexion of elbows and wrists with extension of legs and feet; lesion is located above the red nuclei (usually diffuse cerebral damage).

What characterizes the decerebrate state and where is its causative lesion?

Characterized by rigid extension of limbs, hyperreflexia, and opisthotonus; lesion is located in the brainstem between the red nuclei and vestibular nuclei.