Lecture: Reflexive and Voluntary Movement

Flashcards testing knowledge on spinal cord and brain control of movement, monosynaptic and polysynaptic reflexes, cortical motor areas, subcortical structures, and descending pathways.

How does a withdrawal reflex operate when a sensory neuron detects a noxious stimulus?

A sensory neuron receiving a high heat noxious stimulus sends a high firing rate of action potentials to the spinal cord, activating a motor neuron via an interneuron circuit to send an excitatory signal to the arm muscle, causing it to contract and withdraw without brain input.

How can the brain voluntarily inhibit a spinal reflex, such as when carrying a hot casserole?

The brain sends an inhibitory signal to the relay point between the sensory and motor neurons in the spinal cord to prevent dropping the object.

What are single muscle fibers composed of?

A single muscle fiber consists of a bundle of myofibrils, which are overlapping strands of proteins called actin and myosin.

What cellular event triggers muscular contraction?

Depolarization of a muscle fiber triggers contraction by allowing myosin to slide or row along actin.

What determines the strength of a muscular contraction?

The average rate of firing of various motor neurons associated with a particular muscle fiber, known as motor units.

What is the monosynaptic stretch reflex and its primary function?

It is the simplest level of motor integration consisting of a single synapse on the spinal cord; its primary function is to help maintain posture and adjust and maintain body positions.

How does the patellar reflex operate as a monosynaptic stretch reflex?

Tapping the patella when the leg dangles stretches the quadricep, activating a monosynaptic circuit that causes the quadricep muscle to contract and produce a kicking motion.

What pathway do afferent impulses follow in a monosynaptic stretch reflex?

Afferent impulses starting at the muscle pass through the dorsal root of the spinal column to terminal buttons in the gray matter of the spinal cord, which synapse directly on a motor neuron that passes through the ventral root to innervate the same muscle.

How does leaning forward standing straight activate a monosynaptic circuit?

Leaning forward stretches the relaxed calf muscle, activating a monosynaptic circuit that causes the calf muscle to contract to control posture and keep the body upright.

What is the key difference between a monosynaptic reflex and a polysynaptic reflex?

A monosynaptic reflex involves a single synapse on the spinal cord, whereas a polysynaptic reflex involves multiple synapses.

How does a withdrawal reflex differ from a pain reflex?

A withdrawal reflex is triggered directly by a noxious stimulus in the spinal cord before pain is perceived, whereas a pain reflex involves pain perception in the brain and results in slower movement.

What is the Maru reflex and how is it tested?

The Maru reflex is a polysynaptic reflex test used in babies around 32 of age or older to test brain stem functioning; holding a baby by its back and giving the sensation of falling causes the baby to spread its arms out and startle.

What postsynaptic effect do terminal buttons produce on motor neurons in polysynaptic reflex circuits?

Terminal buttons produce inhibitory postsynaptic potentials in the motor neurons via interneurons.

What is somatotopic organization in the primary motor cortex?

An arrangement represented by a somatotopic homunculus where more neurons control body areas capable of finer movements (such as hands) compared to areas with less movement (such as the belly).

What effect does non-invasive transcranial magnetic stimulation have when applied to the finger area of the primary motor cortex?

It applies a strong but small electromagnetic pulse on the scalp over the finger area, resulting in hand twitching.

Where are the supplementary motor area and premotor cortex anatomically located?

The supplementary motor area is located on the medial surface of the brain, and the premotor cortex is located mostly on the lateral surface of the brain.

Where does movement planning originate in the cortex?

Movement planning begins in the prefrontal cortex, where goals and decisions are formed based on input from perceptual systems.

What are the specific functional roles of the supplementary motor area and premotor cortex?

The supplementary motor area is involved in learning and performing movement behaviors consisting of sequences guided by sensory information, while the premotor cortex is involved in learning and executing responses signaled by arbitrary stimuli and in imitation.

What is the function of the reticular formation in motor processing?

It is involved in regulating muscle tone, controlling posture and locomotion, and exerting control over specific behaviors.

What motor controls are managed by the cerebellum?

It controls repetitive movements requiring accurate aiming and timing, smoothly guides movements, stops movements at the correct time and position, and integrates sequences of movements.

What are the inputs and primary functions of the basal ganglia?

It receives input from all regions of the cerebral cortex and the substantia nigra, influencing movements under primary motor cortex control and controlling inhibition of unwanted movements.

What is the lateral group pathway and what type of movement does it control?

It is a descending pathway whose axons travel down the lateral side of the spinal cord, primarily involved in controlling independent limb movements, especially in the hands and fingers.

What is the ventromedial group pathway and what type of movement does it control?

It is a descending pathway whose axons travel down the middle and ventral side of the spinal cord, primarily involved in controlling automatic movements such as gross muscle movements of the trunk and coordinated movements for posture and locomotion.