Neuroanatomy Sensory & Motor Pathways

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Questions and Answers

Which cranial nerve is responsible for motor functions only?

CN IX: Glossopharyngeal

CN VI: Abducens (correct)

CN X: Vagus

CN VII: Facial

What structure do axons from the spinal accessory nerve enter through?

Internal acoustic meatus

Jugular foramen

Foramen rotundum

Foramen magnum (correct)

Which cranial nerve conveys sensory information from the posterior one-third of the tongue?

CN IX: Glossopharyngeal (correct)

CN XII: Hypoglossal

CN X: Vagus

CN VII: Facial

In the autonomic nervous system, where is the first neuron located?

Lateral horn of the spinal cord Signup and view all the answers

The vestibulocochlear nerve is responsible for which type of function?

Sensory only Signup and view all the answers

Which cranial nerve exits the skull through the internal acoustic meatus?

CN VII: Facial Signup and view all the answers

Which of the following cranial nerves is not involved in autonomic functions?

CN XI: Spinal Accessory Signup and view all the answers

Where do postganglionic cells of the autonomic nervous system project to?

Smooth muscle, cardiac muscle, or glands Signup and view all the answers

Where does the 2nd neuron of the lateral spinothalamic tract cross the midline?

Anterior white commissure Signup and view all the answers

What is the destination of the 3rd neuron after it synapses in the VPL?

Primary somatosensory cortex Signup and view all the answers

Which tract mediates unconscious proprioception?

Dorsal spinocerebellar tract Signup and view all the answers

The 1st neuron of the dorsal spinocerebellar tract is located in which structure?

Dorsal root ganglion (DRG) Signup and view all the answers

What percentage of motor fibers cross over at the pyramidal decussation?

90% Signup and view all the answers

Which structure does the rubrospinal tract fibers descend through?

Brainstem Signup and view all the answers

Which tract is responsible for innervating lower motor neurons in the ventral horn?

Lateral corticospinal tract Signup and view all the answers

What differentiates the anterior corticospinal tract from the lateral corticospinal tract?

Percent of crossing fibers Signup and view all the answers

What is the initial input of the indirect pathway from the cerebral cortex?

Striatum Signup and view all the answers

Which part of the basal ganglia receives striatal inputs but does not participate in the indirect pathway?

Substantia nigra reticular part Signup and view all the answers

What is the effect of dopamine on the striatum according to the content?

Permissive Signup and view all the answers

Which cerebellar peduncle is solely comprised of inputs from the pons?

Middle peduncle Signup and view all the answers

Which cerebellar function is primarily associated with error detection and correction?

Spinocerebellum Signup and view all the answers

Which deep cerebellar nucleus is involved in motor planning and programming?

Dentate nucleus Signup and view all the answers

What structure projects from the striatum to the globus pallidus external segment?

Axonal pathways Signup and view all the answers

What tests the function of the spinocerebellum through motor signal correction?

Finger to nose test Signup and view all the answers

Which cranial nerve is responsible for taste information from the posterior one-third of the tongue?

CN IX Signup and view all the answers

What happens when the tympanic membrane vibrates?

It causes the ossicles to deflect. Signup and view all the answers

Which structure in the cochlea is responsible for the transduction of sound waves into neural impulses?

Organ of Corti Signup and view all the answers

How does the vestibular apparatus detect linear acceleration?

With the aid of the utricle and saccule. Signup and view all the answers

Which cranial nerve is responsible for controlling the stapedius muscle during loud noises?

CN VII Signup and view all the answers

What is the correct pathway for input from the cerebral cortex to reach the lateral corticospinal tract?

Cerebral cortex to cerebellum to dentate nucleus to VL of the thalamus to lateral corticospinal tract Signup and view all the answers

Which of the following statements correctly describes the function of the iris?

It constricts or dilates the pupil using smooth muscle. Signup and view all the answers

What occurs when the ciliary muscle relaxes?

The lens takes on a less convex shape, suitable for distance vision. Signup and view all the answers

Which cranial nerve is responsible for taste sensation in the anterior two-thirds of the tongue?

CN VII Signup and view all the answers

What happens to visual fields if the optic chiasm is cut?

Temporal vision is lost in both eyes. Signup and view all the answers

Which part of the eye is primarily responsible for bending light, enabling refraction?

Cornea and lens Signup and view all the answers

Where are the rods and cones located in the eye?

At the retina Signup and view all the answers

What is the role of the lacrimal apparatus?

Stimulates tear production and drainage. Signup and view all the answers

Study Notes

Sensory Pathways

Lateral Spinothalamic Tract: Carries pain and temperature sensations. Second neuron crosses the midline in the anterior white commissure, ascending as the lateral spinothalamic tract. Synapses on the third neuron in VPL of the thalamus, which then projects to the primary somatosensory cortex.
Dorsal Column-Medial Lemniscus Pathway: Carries touch, pressure, vibration, and proprioception. The second neuron crosses the midline in the medulla, ascending as the medial lemniscus. Synapses on the third neuron in VPM of the thalamus, which then projects to the primary somatosensory cortex.
Dorsal Spinocerebellar Tract: Carries unconscious proprioception. Never reaches the cerebral cortex. The second neuron ascends on the same side of the spinal cord and projects to the cerebellum via the inferior cerebellar peduncle.

Motor Pathways

Lateral Corticospinal Tract: Mediates voluntary motor function. Axons from the primary motor cortex descend through the internal capsule, cerebral peduncle, pons, and medullary pyramids. 90% of fibers cross over at the pyramidal decussation and descend as the lateral corticospinal tract, innervating lower motor neurons in the ventral horn.
Anterior Corticospinal Tract: Mediates voluntary motor function. The remaining 10% of fibers that do not cross over descend as the anterior corticospinal tract, crossing the midline at the spinal cord level to innervate lower motor neurons.
Rubrospinal Tract: Another mediator of motor function. Axons originate in the red nucleus of the midbrain and cross the midline as they descend through the brainstem, lying anterior to the lateral corticospinal tract fibers.

Cranial Nerves

CN V (Trigeminal): Mixed nerve. Sensory innervation for the face, including anterior ⅔ of the tongue. Motor innervation for muscles of mastication. Branches: V1 (ophthalmic) – superior orbital fissure, V2 (maxillary) – foramen rotundum, V3 (mandibular) – foramen ovale.
CN VI (Abducens): Motor only. Innervates the lateral rectus muscle of the eye. Originates in the abducens nucleus in the pons and exits through the superior orbital fissure.
CN VII (Facial): Mixed nerve. Sensory innervation for taste buds on the anterior ⅔ of the tongue. Motor innervation for facial muscles, including muscles of facial expression. Passes through the internal acoustic meatus.
CN VIII (Vestibulocochlear): Sensory only. Carries auditory and vestibular information. Passes through the internal acoustic meatus.
CN IX (Glossopharyngeal): Mixed nerve. Sensory innervation for taste buds on the posterior ⅓ of the tongue and general sensation from the pharynx. Motor innervation to pharynx. Passes through the jugular foramen.
CN X (Vagus): Mixed nerve. Sensory innervation for thorax, abdomen, and pelvis. Motor innervation to muscles of the palate, pharynx, and larynx. Passes through the jugular foramen.
CN XI (Spinal Accessory): Motor only. Innervates the trapezius and sternocleidomastoid muscles. Axons originate in the cervical spinal cord, enter the skull through the foramen magnum, and exit through the jugular foramen.
CN XII (Hypoglossal): Motor only. Innervates the tongue muscles. Originates in the hypoglossal nucleus and exits through the hypoglossal canal.

Autonomic Nervous System

Sympathetic Division: Preganglionic neurons are located in the intermediomedial column of the spinal cord between T1-L2.
Parasympathetic Division: Preganglionic neurons are located in the brainstem and sacral spinal cord.

Basal Ganglia

Direct Pathway: Facilitates movement. Cerebral cortex projects to the striatum, which then projects to the globus pallidus internal segment (GPi). GPi projects to the thalamus (VA/VL), then to the motor cortex.
Indirect Pathway: Inhibits movement. Cerebral cortex projects to the striatum, which then projects to the globus pallidus external segment (GPe). GPe projects to the subthalamic nucleus, which projects to GPi. GPi then projects to the thalamus (VA/VL), and then to the motor cortex.
Substantia Nigra: The compact part produces dopamine, which helps regulate the basal ganglia pathways. The reticular part receives striatal inputs and projects to the thalamus (VA/VL).

Cerebellum

Primary Fissure: Separates the anterior and posterior lobes, but anterior lobe is only ⅓ of the cerebellum.
Cerebellar Peduncles: Connect the cerebellum to the brainstem. Superior peduncle: connects to the midbrain and carries mostly outputs; Middle peduncle: comprised of only inputs from the pons; Inferior peduncle: connects to the medulla.
Deep Cerebellar Nuclei: Located within the white matter. Receive inputs from the cerebellar cortex and project to the brainstem and thalamus. These nuclei are: fastigial, globose, emboliform, and dentate.
Spinocerebellum (Medial Cerebellum): Involved in error detection and correction. Receives sensory input from the spinal cord and motor input from the pons. Projects to the red nucleus and then to the rubrospinal tract.
Cerebrocerebellum (Lateral Cerebellum): Involved in motor planning and programming. Receives input from the cerebral cortex and projects to the dentate nucleus, then to the thalamus (VL), and then to the lateral corticospinal tract.

Eye

Sclera: Outermost layer, composed of connective tissue. Forms the "white" of the eye.
Choroid: Vascular layer located between the sclera and cornea. Contains blood vessels supplying nutrients to the eye.
Cornea: Transparent, dome-shaped outer layer. Bends light entering the eye.
Iris: Colored part of the eye, containing muscle fibers that control the size of the pupil.
Lens: Flexible, transparent structure that focuses light onto the retina.
Ciliary Body: Structure containing muscles that control lens shape for focusing.
Lacrimal Apparatus: Produces and drains tears.

Light Transduction

Retina: Contains photoreceptor cells called rods (sensitive to low light) and cones (sensitive to bright light and color), which convert light into electrical signals.
Ganglion Cells: Receive signals from photoreceptor cells and send their axons to form the optic nerve.
Optic Nerve: Carries visual information from the eye to the brain.
Optic Chiasm: Point where optic nerves from both eyes cross over. Axons from the nasal half of each retina cross over, while axons from the temporal half stay on the same side.
Lateral Geniculate Nucleus (LGN): Relay center in the thalamus. Receives visual information from the optic chiasm.
Optic Radiation: Axons projecting from the LGN to the visual cortex.

Gustation (Taste)

General Sensation: Anterior ⅔ of tongue – CN V; Posterior ⅓ of tongue – CN IX; Epiglottis – CN X.
Taste: Anterior ⅔ of tongue – CN VII; Posterior ⅓ of tongue – CN IX; Epiglottis – CN X.

Taste Transduction

CN VII, IX, X: Carry taste information. Synapse in the medulla, then project to the gustatory cortex.

Audition (Hearing)

Tympanic Membrane (Eardrum): Vibrates in response to sound waves, causing the middle ear ossicles to move.
Ossicles: Three small bones in the middle ear (malleus, incus, stapes) that transmit vibrations from the tympanic membrane to the oval window of the cochlea.
Cochlea: Spiral-shaped structure in the inner ear containing the organ of Corti.
Organ of Corti: Contains hair cells that are stimulated by fluid movements in the cochlea, generating auditory signals.
CN VIII: Carries auditory information from the cochlea to the brainstem.
Dorsal and Ventral Cochlear Nuclei: Relay centers in the brainstem that receive auditory information from the cochlea.
Inferior Colliculus, Medial Geniculate Nucleus (MGN), Primary Auditory Cortex: Relay centers for auditory processing, eventually reaching the primary auditory cortex.

Vestibular System

Semicircular Canals: Three fluid-filled canals that detect angular rotation of the head.
Utricle and Saccule: Adjacent structures that detect linear acceleration. Utricle: detects horizontal acceleration; Saccule: detects vertical acceleration.

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Description

Test your knowledge of sensory and motor pathways in neuroanatomy. This quiz covers the lateral spinothalamic tract, dorsal column-medial lemniscus pathway, and more. Understand how these pathways function and their significance in the nervous system.