Lecture 9 NROB60 Question And Answer

These flashcards encapsulate key concepts from the lecture on somatosensory pathways and descending motor control systems, designed to foster understanding and retention of the material for exam preparation.

What are the major somatosensory pathways discussed in the lecture?

Anterolateral System for pain and temperature, Dorsal Column-Medial Lemniscus pathway for fine touch.

How many orders of neurons are involved in the dorsal column-medial lemniscus pathway?

Three orders of neurons.

Where are the cell bodies of the first-order neurons located in the dorsal column-medial lemniscus pathway?

In the dorsal root ganglia (DRG).

What is the role of the second-order neurons in the dorsal column-medial lemniscus pathway?

Their cell bodies are in the dorsal column nuclei.

Where do the axons of the second-order neurons cross the midline in the dorsal column-medial lemniscus pathway?

At the level of the medulla.

What fibers carry fine touch information from the lower body?

Fasciculus Gracilis and Gracile nucleus.

What fibers carry fine touch information from the upper body?

Fasciculus Cuneatus and Cuneate nucleus.

What does somatotopic organization in the primary somatosensory cortex refer to?

A map of skin body areas transmits to the cortex in proper spatial order.

What happens if there is a lesion at a specific point in the dorsal column-medial lemniscus pathway?

Loss of fine touch sensation from the contralateral side of the body.

How is the somatosensory cortex organized?

Neurons with similar response properties cluster into functional columns.

What occurs in the somatosensory cortex immediately following a lesion?

The affected cortical region for a specific digit becomes unresponsive.

What happens in the somatosensory cortex after repeated practice of a task using specific fingers?

Expansion of cortical regions for those fingers at the expense of others.

What are the two main types of pain pathways within the anterolateral system?

Sensory-discriminative (first pain) pathway and affective-motivational (second pain) pathways.

What do nociceptors respond to?

They respond to stimuli that cause tissue damage or pose a threat of damage.

How do nociceptors produce action potentials?

They release peptides and neurotransmitters when activated.

What are the main receptors involved in nociception?

Free nerve endings.

What temperature threshold is associated with pain from heat stimuli?

43°C.

What are the characteristics of first pain sensation?

Early perception of sudden, sharp pain.

What characterizes second pain sensation?

A later sensation of a duller, burning quality.

What is the function of the TRPV1 receptor?

Detects drastic rises in temperature and signals burning.

What is the role of the TRPM8 receptor?

Responds to cool temperatures and binds menthol.

What are the two types of corticospinal tracts mentioned?

Lateral corticospinal tract and anterior corticospinal tract.

What type of movements is the lateral corticospinal tract involved with?

Skilled movements of distal limb muscles.

What movements does the anterior corticospinal tract support?

Posture, balance, and locomotion of axial and proximal limb muscles.

Where do upper motor neurons reside?

In the primary motor cortex (precentral gyrus).

What are the two major roles of lower motor neurons?

To contract muscles and transmit motor messages.

What happens during a stretch reflex?

Muscle contraction in response to its stretch.

What can cause lower motor neuron syndrome?

Damage to lower motor neurons or their peripheral axons.

What is flaccid paralysis?

Loss of muscle tone and reflexes due to lower motor neuron damage.

What can acute damage to upper motor neurons lead to?

Immediate flaccid paralysis followed by spastic paralysis.

What is hypertonia?

Increased muscle tone resulting from upper motor neuron damage.

What is the difference in input to the lower and upper face from motor cortex?

The lower face receives unilateral input while the upper face receives bilateral input.

What might a unilateral lesion in the corticobulbar tract affect?

It can result in different facial expressions depending on the location of the lesion.

What happens to corticospinal axons at the medulla-spinal cord junction?

About 90% of axons cross midline (pyramidal decussation).

What is the impact of damage to the lateral corticospinal tract?

Upper motor neuron syndrome affecting the level of the lesion and below.

What is the role of the premotor cortex?

It directs movements in response to external cues.

How does the supplementary motor area contribute to action?

It is important for planning internally generated movements.

What is the function of the pyramidal system?

Carries voluntary skilled movements from motor cortex to the brainstem/spinal cord.

Where do the brainstem cranial motor nuclei send axons?

To innervate muscles of the head and neck.

What part of the CNS do motor neurons represent?

The final common pathway for muscle control.

What do muscle fibers depolarize in response to?

Acetylcholine released by motor neurons.

What structure connects muscles to bones?

Tendons.

How is the arrangement of muscles characterized?

In reciprocal fashion.

What neurotransmitter is primarily released at the neuromuscular junction?

Acetylcholine.

What happens within reflex arcs with respect to interneurons?

They suppress activity in antagonistic muscle motor neurons.

What indicates that a muscle has been denervated?

Atrophy due to long-term disuse.

How does damage to the corticobulbar tract affect muscle control?

Influences facial expressions and movements.

What is the condition known as congenital insensitivity to pain (CIP)?

A genetic condition where individuals cannot feel physical pain.

What is 'spinal shock' characterized by following an upper motor neuron injury?

Flaccid paralysis of affected muscles.

What information does the spinothalamic tract carry?

Pain and temperature information to the primary somatosensory cortex.

What does the term 'neuroplasticity' refer to in the context of somatosensory pathways?

The ability of the somatosensory cortex to remap following changes in sensory experience.

How does the body signify pain as a social signal?

Expression of pain elicits caregiving behaviors from others.

What are the characteristics of the 'pain-proof' phenomenon as exemplified by Arthur Plumhoff?

Demonstrates high pain tolerance through training and possibly dissociation.

What can trigger nociceptors to respond?

Tissue injury or the risk of injury.

What are the possible symptoms of lower motor neuron syndrome?

Paralysis, hypotonia, and atrophy.

What is the mechanism of action for local circuit neurons in response to stretch reflex?

Activate motor neurons to contracted muscles and inhibit antagonistic muscles.

What type of information is carried in the anterior white matter tract?

Postural and proximal muscle control.

What happens to reflexes after damage to lower motor neurons?

Reflexes are abolished on the affected side.

How do the two major tracts of the pyramidal system differ in function?

Corticobulbar tract controls head/neck, corticospinal tract controls limbs.

What part of the CNS can be affected by upper motor neuron syndrome?

The entire area below the level of the lesion.

What influences the somatotopic organization of the motor cortex?

The finer motor control required for certain body parts, like hands.

What is the function of C-fibers in the context of pain perception?

They are responsible for transmitting dull, aching pain.

How does practice affect the representation of motor areas in the brain?

It can expand the area related to frequently used muscles.

What can predict which direction an arm will be moved based on neural discharge?

Directional sensitivity in primary motor cortex neurons.

What might be the clinical signs following a unilateral lesion to the dorsal column-medial lemniscus pathway?

Loss of fine touch on the contralateral side of the body.

Where do third-order neurons of the spinothalamic tract project to?

To the primary somatosensory cortex in the postcentral gyrus.

What is the result of excitation of lower motor neurons connected to muscle fibers?

Muscle contraction occurs.

What correlation exists between action potentials and perception of pain intensity?

Higher firing rates usually correlate with increased pain intensity.

What anatomical pathway signifies the lateral corticospinal tract?

It descends through the lateral column of the spinal cord.

What causes the increase in firing rates in response to specific movements?

Neurons exhibit directional tuning.

What impact can damage to the hypoglossal nucleus have?

It can impair tongue movements.

What kind of outcomes may result from interruption of the corticobulbar projections?

Facial weakness specific to upper or lower facial muscles.

What assists in transmitting signals from the motor cortex to the muscles?

Myelinated axons of motor neurons.

What sensory information does the spinothalamic tract primarily transmit?

Discriminative (first) pain and temperature.

What are the primary outputs from the spinothalamic tract?

To the VPL of thalamus.

What is the impact of pyramidal decussation on motor signals?

Most motor signals cross to the opposite side of the body.

What role does the primary motor cortex play in controlling movements?

It initiates voluntary skilled movements.

What are the structural characteristics of free nerve endings?

Morphologically unspecialized; terminate in skin.

What does the presence of muscle spindles indicate about the muscle?

It is sensitive to stretch and contributes to stretch reflex.

What happens to the projections from upper motor neurons following an injury?

They may become hyperactive, leading to spastic paralysis.

What can a person with congenital insensitivity to pain experience?

They cannot feel or properly respond to harmful stimuli.

What neurotransmitters do nociceptors release upon activation?

Substance P, CGRP, and ATP.

What signifies the start of motor control signals in the pyramidal system?

Activation of Betz cells in the primary motor cortex.

What principle governs muscle movement across joints?

Muscles act as antagonists to achieve coordinated movement.

How is sensory information from nociceptors processed in the spinal cord?

It synapses on second-order neurons in the dorsal horn.

Which brain area is primarily responsible for voluntary motor control?

The primary motor cortex.

What indicates a successful recovery from an upper motor neuron injury?

Recovery of function and unregulated muscle control.

What indicates the limitations in voluntary movements following a stroke?

Loss of fine motor control and spasticity.

What significant role does the cingulate premotor area play?

It is involved in regulating emotions in facial expression.

What phenomenon may occur due to corticobulbar tract damage?

Facial muscle paralysis on the contralateral side.

How are lower motor neurons characterized in terms of their connections?

They synapse directly on muscle fibers.

What is the main function of the primary somatosensory cortex?

To process sensory information from the body.

What term describes the pattern of muscle contractions opposing each other?

Reciprocal inhibition.

What does spastic paralysis indicate about muscle condition post upper motor neuron injury?

Muscles remain contracted and exhibit exaggerated reflexes.

What is the result of training in skilled tasks like playing piano on the motor cortex?

Expansion of the hand representation in the motor cortex.

What are the symptoms of injury to the anterior corticospinal tract?

Difficulty in maintaining posture and balance.

What implications does the pyramidal system have for rehab strategies?

Understanding of motor pathways can inform physical therapy techniques.

In what ways can the somatosensory homunculus differ from the motor homunculus?

Different body parts are represented in varying sizes based on sensitivity and motor control requirements.

How does the brain integrate sensory data from multiple modalities?

Convergence of pathways in higher cortical areas.

What condition might arise from an ineffective stretch reflex?

Inability to maintain posture correctly.