7). Basal Ganglia, Thalamus, and Somatosensory Pathways

A set of 60 vocabulary flashcards covering the thalamus, basal ganglia, somatosensory tracts, trigeminal sensory system, and descending motor pathways based on the provided lecture transcript.

Thalamus

A small, egg-shaped structure in the brain that acts as a relay station for most sensory information (except smell), processing and transmitting it to the cerebral cortex for interpretation.

Lateral Geniculate Nucleus (LGN)

A thalamic nucleus through which all visual information from the retina travels via the optic tracts before being sent to the primary visual cortex in the occipital lobe.

Superior Colliculi

Paired dorsal midbrain structures involved in:

• Processing optical stimuli,

• Orienting attention

• Coordinating eye and head movements

Basal Ganglia

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

Caudate

One of the subcortical nuclei comprising the basal ganglia involved in reward, emotional, and motor circuitry.

Putamen

A nucleus of the basal ganglia that forms part of the subcortical motor control and emotional circuits.

Globus Pallidus

A subcortical structure of the basal ganglia that plays a role in regulating voluntary movement pathways.

Substantia Nigra

A basal ganglia structure located in the midbrain involved in motor control, whose degeneration is characteristic of Parkinson's disease.

Subthalamic Nucleus

A subcortical cell cluster that is part of the basal ganglia motor circuitry.

Nucleus Accumbens

Known as the “center of joy” in the central nervous system, it helps explain how motivation and emotion influence visual attention, learning, and therapeutic engagement.

Limbic System

A neural system that influences emotions, visceral responses to emotions, motivation, mood, pain, and pleasure, integrating raw visual data with memory and behavior.

Posterior Column–Medial Lemniscus System (DC/ML)

An ascending sensory pathway responsible for fine discriminative touch, pressure, proprioception, and vibration perception.

Anterolateral System (ALS)

An ascending sensory pathway, also known as the spinothalamic tract, responsible for conveying pain, temperature, and crude touch.

Spinocerebellar Tracts

Ascending sensory pathways that transmit unconscious proprioceptive information directly to the cerebellum.

Trigeminal Sensory System

The sensory pathway responsible for transmitting tactile, proprioceptive, pain, and temperature signals from the head to the CNS.

Mechanoreceptors

Cutaneous sensory receptors that includes:

• Merkel's disks

• Meissner's corpuscles

• Ruffini endings

• Pacinian corpuscles

Nociceptors

Sensory receptors consisting of free nerve endings that respond to painful or tissue-damaging stimuli.

Thermoreceptors

Specialized nerve endings dedicated to sensing thermal changes and temperature.

Proprioceptors

Sensory receptors located deep in muscles and joints that provide body awareness by sensing position and movement of body parts.

First-Order Neuron

The initial sensory neuron that carries signals from peripheral sensory receptors to the central nervous system.

Dorsal Root Ganglion

The peripheral sensory ganglion containing the cell bodies of first-order neurons that convey somatic sensation from the body.

Trigeminal Ganglion

The sensory ganglion containing cell bodies of first-order sensory neurons that transmit tactile, pain, and temperature signals from the face.

Second-Order Neuron

An interneuron that relays sensory signals from the first-order neuron to the thalamus.

Third-Order Neuron

A neuron that transmits sensory signals from the thalamus to the primary somatosensory cortex in the postcentral gyrus.

Ventral Posterolateral (VPL) Nucleus

The thalamic nucleus that receives second-order somatosensory signals from the body and projects them to the postcentral gyrus.

Ventral Posteromedial (VPM) Nucleus

The thalamic nucleus that receives second-order somatosensory signals from the face and relays them to the cerebral cortex.

Secondary Somatosensory Area

A somatosensory processing region located within the parietal operculum.

Somatosensory Homunculus

A somatotopic map depicting the relative anatomical representation of body parts along the primary somatosensory cortex.

Muscle Spindle

The major stretch receptor within skeletal muscles that senses changes in muscle length and stretch.

Golgi Tendon Organs

Proprioceptive receptors located in muscle tendons that monitor tension and mechanical stress at tendons and joints.

$A\alpha$ Nerve Fibers

Large myelinated sensory fibers with diameter $12-20\,\mu m$ and conduction velocity $70-120\,m/s$ responsible for proprioception and motor innervation.

$A\beta$ Nerve Fibers

Myelinated nerve fibers with diameter $5-12\,\mu m$ and conduction velocity $30-70\,m/s$ that convey pressure and touch sensations.

$A\gamma$ Nerve Fibers

Myelinated motor fibers with diameter $3-6\,\mu m$ and conduction velocity $15-30\,m/s$ that innervate muscle spindles.

$A\delta$ Nerve Fibers

Myelinated fibers with diameter $2-5\,\mu m$ and conduction velocity $12-30\,m/s$ responsible for touch, cold temperature, and fast pain.

$B$ Nerve Fibers

Small myelinated fibers with diameter $< 3\,\mu m$ and conduction velocity $3-15\,m/s$ serving autonomic nervous system functions.

$C$ Nerve Fibers

Unmyelinated nerve fibers with diameter $0.3-1.3\,\mu m$ and conduction velocity $0.7-2.3\,m/s$ responsible for autonomic functions and slow pain.

Contralateral Organization

The structural principle whereby one side of the cerebral cortex processes sensory inputs from or controls motor outputs to the opposite side of the body.

Ipsilateral Organization

The functional organization where neural processing occurs on the same side of the body, as observed in cerebellar proprioceptive pathways.

Ophthalmic Division ($V_1$)

The first primary sensory branch of the trigeminal nerve supplying upper facial structures, including the forehead and eye region.

Maxillary Division ($V_2$)

The second primary sensory branch of the trigeminal nerve supplying middle facial structures, including the upper lip and nose area.

Mandibular Division ($V_3$)

The third primary division of the trigeminal nerve supplying lower facial structures, lower teeth, and motor innervation to muscles of mastication.

Mesencephalic Trigeminal Nucleus

A brainstem nucleus associated with the trigeminal system that processes proprioceptive information from masticatory muscles and teeth.

Main Trigeminal Nucleus

A pontine nucleus in the brainstem that receives tactile and pressure inputs from the face.

Spinal Trigeminal Nucleus

A extended brainstem nucleus processing pain and temperature inputs from the head and face.

Trigeminal Motor Nucleus

The motor nucleus in the brainstem, also called the masticator nucleus, that innervates muscles involved in mastication.

Periodontal Ligament (PDL)

An oral structure containing mechanoreceptive and nociceptive endings, with Ruffini endings serving as its primary mechanoreceptor.***

Corneal Blink Reflex

A polysynaptic brainstem reflex connecting the trigeminal nerve (CN $V$) and facial nerve (CN $VII$) used to test trigeminal system integrity.

Trigeminal Neuralgia

A disorder producing brief ($< 1\text{ minute}$), excruciating, electric shock-like facial pain without sensory loss, most commonly affecting $V_2$ or $V_3$.

Stretch Reflex

A monosynaptic reflex elicited by tapping a muscle tendon, causing involuntary contraction of the corresponding muscle fibers.

Withdrawal Reflex

A polysynaptic reflex that rapidly pulls a body part away from a painful or harmful stimulus, such as a hot surface.

Pyramidal Tracts

Descending motor pathways originating in the cerebral cortex responsible for voluntary motor control, consisting of corticospinal and corticobulbar tracts.

Extrapyramidal Tracts

Descending motor pathways originating in the brainstem responsible for involuntary control of muscle tone, posture, balance, and coordination.

Corticobulbar Tract

A pyramidal motor path innervating brainstem cranial nerve nuclei bilaterally (except lower CN $VII$) to control voluntary head and face movements.

Lateral Corticospinal Tract

A motor pathway formed by the $85\%$ of corticospinal fibers that decussate in the lower medulla to control limb movement.

Anterior Corticospinal Tract

A motor path formed by the $15\%$ of corticospinal fibers that remain uncrossed through the medullary decussation.

Upper Motor Neuron (UMN)

A motor neuron originating in the cerebral cortex that terminates in the brainstem or spinal cord; damage results in spastic paralysis.

Lower Motor Neuron (LMN)

A motor neuron originating in the spinal cord or brainstem that directly innervates skeletal muscle;

Damage leads to flaccid paralysis. ***

Babinski's Reflex

An abnormal reflex characterized by extension of the great toe and fanning of other toes upon stroking the sole, indicating corticospinal path damage.

Decorticate Rigidity

An abnormal posture marked by flexion of elbows/wrists with extension of legs/feet, caused by cerebral lesions above the red nuclei.

Decerebrate Posture

An abnormal posture marked by rigid extension of all limbs, hyperreflexia, and opisthotonus, caused by lesions between the red and vestibular nuclei.