Somatosensory and Motor Function

Comprehensive practice flashcards covering sensory receptors, somatosensory pathways, motor cortical areas, descending motor tracts, basal ganglia, cerebellum, cranial nerves, and spinal reflex arcs from Lesson 4.

What are the three fundamental functions of the nervous system?

Sensory input (monitoring internal and external changes), integration (processing and interpreting sensory input), and motor output (activating muscles or glands to produce a response).

How do the somatic and autonomic divisions of the motor nervous system differ in function?

The somatic nervous system controls voluntary movements, whereas the autonomic nervous system controls involuntary responses.

What are the roles of the sympathetic, parasympathetic, and enteric divisions of the autonomic nervous system?

The sympathetic division drives "fight or flight" responses, the parasympathetic division directs "rest or digest" functions, and the enteric nervous system governs the gastrointestinal tract.

What is the structural and functional difference between a nerve and a nerve tract?

A nerve is a bundle of fibers conveying impulses between the brain or spinal cord and the body in the peripheral nervous system, whereas a nerve tract is a bundle of myelinated fibers with the same function and origin running within the brain or spinal cord.

What is a nerve fibre?

A process, axon, or dendrite of a nerve cell, referring specifically to the axon along with its myelin sheath.

What are the four major classes of sensory receptors based on stimulus modality?

Mechanoreceptors (detecting mechanical deformation such as touch, vibration, position, and pressure), chemoreceptors (chemical stimuli), photoreceptors (light in the eye), and thermoreceptors (temperature changes in the skin and CNS).

What is sensory transduction?

The physiological process by which environmental stimuli cause local changes in membrane potential that, upon reaching threshold, trigger an action potential in afferent nerve fibers.

What is a receptive field, and how is its density assessed on the skin?

A receptive field is the specific physical area where a stimulus is detected by a single sensory neuron; its density is determined experimentally using the two-point touch threshold.

How many segments compose the spinal cord, and what emerges from each segment?

The spinal cord is divided into $31$ segments, each giving rise to a pair of spinal nerves that supply a specific region of the body.

What is a dermatome?

A specific area of the body surface whose sensory input is served by a single pair of spinal nerves, exhibiting overlapping receptive fields with adjacent segments.

What is the primary functional difference between the dorsal and ventral roots of the spinal cord?

The dorsal root transmits incoming sensory (afferent) signals into the dorsal horn, whereas the ventral root carries motor (efferent) signals originating from motor neurons in the ventral horn out to effectors.

What role does the muscle spindle play in motor regulation?

It is a mechanoreceptive proprioceptor arranged parallel to skeletal muscle fibers that senses muscle stretch and triggers reflex muscle contraction.

How does the Golgi tendon organ function as a protective motor brake?

It monitors increases in muscle tension and prevents excessively vigorous contractions by sending inhibitory impulses to motor neurons in the spinal cord.

Which ascending pathway is shown here, and what sensations does it carry?

The dorsal column lemniscal pathway; it conducts fine touch, vibration, pressure, and proprioception sensations from the body.

Where do the first- and second-order neurons synapse in the dorsal column lemniscal pathway?

The first-order neuron synapses in the medulla oblongata, and the second-order neuron crosses the midline and synapses in the thalamus before projecting to the primary somatosensory cortex.

Which sensations are transmitted via the spinothalamic tract, and where do its first-order neurons synapse?

It transmits crude touch, temperature, itch, tickle, and pain; its first-order neurons enter via the posterior root ganglion and synapse in the posterior gray horn of the spinal cord.

What are the anatomical locations and functions of the primary motor cortex and primary somatosensory cortex?

The primary somatosensory cortex is situated in the postcentral gyrus and receives sensory input from the body; the primary motor cortex is located in the precentral gyrus and plans and executes voluntary motor commands.

What specific contributions do the prefrontal cortex and premotor cortex make toward voluntary motor action?

The prefrontal cortex responds to sensory cues and calculates predictable outcomes to plan actions, whereas the premotor cortex prepares for movement, integrates body posture and position, and organizes direction in space.

What are the motor functions of the supplementary motor cortex and the posterior parietal cortex?

The supplementary motor cortex organizes rapid sequences of movements, while the posterior parietal cortex integrates visual information to guide hand-eye coordination.

What destinations do the dorsolateral and ventromedial corticospinal tracts innervate?

The dorsolateral corticospinal tract controls peripheral extremities (hands and toes), while the ventromedial corticospinal tract innervates proximal and axial muscles (shoulders, neck, and trunk).

What are the consequences of damage to the cerebellum?

Damage causes ataxia (loss of coordination), tremors, postural instability, and difficulty executing rapid movements requiring precise aiming and timing, such as hand-clapping, speaking, or writing.

What are the three main anatomical structures comprising the basal ganglia?

The putamen, caudate nucleus, and globus pallidus.

By what mechanism does the basal ganglia select a specific movement?

The basal ganglia selects and initiates a movement by ceasing to inhibit it (disinhibition).

Which motor pathologies result from dysfunction within the basal ganglia?

Parkinson's disease (characterized by loss of movement and resting tremor) and chorea (characterized by excessive, involuntary, uncontrolled movements).

How many pairs of cranial nerves enter/exit the brain, and what types of functional fibers can they carry?

There are $12$ pairs of cranial nerves; individual pairs can be purely sensory, purely motor, or mixed (both sensory and motor).

What are the functional roles of cranial nerves V (trigeminal) and VII (facial)?

Cranial nerve V (trigeminal) mediates facial sensation and mastication motor control; cranial nerve VII (facial) directs muscles of facial expression and sensory taste from the anterior tongue and soft palate.

What mixed functions are served by the vagus nerve (cranial nerve X)?

Motor innervation to the heart, lungs, bronchi, and gastrointestinal tract, and sensory input from the thoracic and abdominal viscera, pharynx, larynx, and external ear.

What five structural components constitute a somatic reflex arc?

1. Sensory receptor; 2. Sensory neuron; 3. Integrating center within the CNS; 4. Motor neuron; 5. Effector (muscle or gland).

How does reciprocal inhibition operate in the patellar stretch reflex ("knee jerk")?

Sensory neurons from the stretched quadriceps monosynaptically activate motor neurons to contract the quadriceps while simultaneously exciting inhibitory interneurons in the spinal cord that suppress motor output to the antagonist hamstring muscle.

What responses define the infant grasp, Babinski, and rooting reflexes?

The grasp reflex causes hands or feet to close around an object, the Babinski reflex causes the big toe to extend and other toes to fan out when the sole is stroked, and the rooting reflex causes the head to turn and suck when the cheek is touched.