Week 10

Question 1

*Definition of Reflex?

Answer 1

Automatic, involuntary motor response to a stimulus, modifiable by supraspinal inputs

Question 2

*Types of Reflexes?

Answer 2

Stretch Reflex:

Activated by muscle spindles sensing muscle length changes.

Uses a monosynaptic loop for rapid contraction of agonist muscles and inhibition of antagonists (reciprocal inhibition).

Serves as a feedback mechanism to maintain muscle length and correct small deviations.

Hoffman Reflex (H-Reflex):
Laboratory test for reflex pathways using electrical stimulation of sensory nerves.

Demonstrates plasticity in motor learning through conditioning.

Flexion Withdrawal Reflex:
Polysynaptic reflex triggered by painful stimuli.

Activates ipsilateral flexors and contralateral extensors for protective withdrawal.

Golgi Tendon Organ Reflex:
At rest, inhibits muscle contraction (negative feedback).
During locomotion, enhances extensor activity (positive feedback) based on gait phase.

Question 3

Adaptability of Reflexes?

Answer 3

Reflexes are modulated by descending motor commands and can adapt based on movement phase (e.g., stance vs. swing in gait).

Question 4

Key Functions of spinal reflexes?

Answer 4

Reflexes maintain stability, adapt to unexpected perturbations, and enhance movement precision through servo-assistance

Question 5

*Neural Components/Pathways of Stretch reflex?

Answer 5

Stimulus:
Triggered by a stretch or tendon tap, detected by
muscle spindles.

Afferent Pathway:
Group Ia afferent fibers: Carry stretch signals to the spinal dorsal horn.

Central Integration:
Monosynaptic loop:
Afferent neurons synapse directly with α-motor neurons in the spinal ventral horn.

Reciprocal inhibition:
Group Ia inhibitory interneurons inhibit antagonist muscles.

Efferent Pathway:
α-motor neurons: Signal the contraction of agonist/homonymous and synergist muscles.

Function:
Maintains muscle length via a negative feedback loop.
Compensates for deviations in muscle length due to unexpected loads (servo-assistance).

Hoffman Reflex (H-Reflex):
Elicited by electrical stimulation of Ia sensory fibers.
Evokes a similar pathway to the stretch reflex, with observable muscle contractions recorded via EMG
Higher stimulation intensity activates motor fibers, abolishing the H-reflex due to antidromic signals

Question 6

*Neural Components/Pathways of Flexion Withdrawal Reflex?

Answer 6

Stimulus:
Painful stimulus detected by free nerve endings (nociceptors) in the periphery.

Afferent Pathway:
Group III fibers: Thinly myelinated sensory neurons transmit signals to the spinal cord.

Central Integration:
Polysynaptic pathway:
Afferent neurons synapse with interneurons in the spinal cord.
Coordinates ipsilateral flexion and contralateral extension.

Efferent Pathway:
Ipsilateral side:
Flexor muscles are activated, and extensors are inhibited for withdrawal.
Contralateral side:
Extensor muscles are activated to stabilize the body.

Function:
Protective reflex for rapid withdrawal from harmful stimuli.
Operates independently of supraspinal inputs and persists even after spinal cord transection.

Question 7

*Flexion Withdrawal Reflex?

Answer 7

Polysynaptic reflex activating ipsilateral flexors and contralateral extensors in response to painful stimuli

Question 8

*Golgi Tendon Organ (GTO) Reflex?

Answer 8

At rest: Negative feedback inhibits muscle activity.

During locomotion: Positive feedback enhances extensor activity, modulated by descending motor commands

Question 9

*Respiratory control functions?

Answer 9

The respiratory control system must
be able to regulate:
1. Blood-gas tensions and acid-base
balance (alveolar ventilation)
2. Speech and breath-holding
3. Airway defence (cough, swallow)

Question 10

*Basic elements of the respiratory control system?

Answer 10

Central Controller (=pons,medulla, other parts of brain)
> Effectors (= resp muscles) > Sensors (= Chemoreceptors, lungs and other receptors)

CC > Eff = Output
S > CC = Input

Question 11

*PaCO2 regulation: feedforward and feedback control/adaptive control?

Answer 11

Feedforward Control:
Regulates PaCO₂ through goal-oriented commands that account for targets and disturbances, independent of chemoreception.

Feedback Control:
Uses closed-loop negative chemofeedback to adjust PaCO₂ based on detected changes.

Adaptive Control:
Involves long-term modifications (e.g., neuroplasticity) to the respiratory control system for sustained regulation.

Operates across multiple levels of respiratory control.

Question 12

Ventral respiratory group (VRG)?

Answer 12

The VRG is split into rostral (rVRG) and caudal (cVRG) aspects

rVRG = inspiratory (diaphragm and external interocostals)

cVRG = expiratory (abdominal and internal intercostals)

Question 13

Dorsal respiratory group (DRG)?

Answer 13

The DRG is a small collection of inspiratory (predominantly diaphragm) premotor neurons located in the caudal NTS

Question 14

Pontine respiratory group (PRG)?

Answer 14

The PRG contains the Kölliker-Fuse (KF) nucleus and parabrachial (PB) nucleus

These neurons inhibit inspiration and prolong expiration

Responsible for the Hering-Breuer lung inflation reflex

Question 15

Inspiratory and expiratory pump muscles?

Answer 15

Expiratory:
Internal
Intercostals
External Obliques
Internal Obliques
Transverse Abdominis
Rectus Abdominis

Inspiratory:
Sternocleidomastoids
Scalenes
External
Intercostals
Diaphragm

Question 16

Innervation of spinal respiratory motor neurons?

Answer 16

Insp -
Diaphragm - C3-C5
Scalenes - C2-C7

Exp -
Sterno - Accessory and C2-3
Intercostals - T1-T11
Abs especially Transversus abdominus - T7-L1

Question 17

Is breathing autonomic?

Answer 17

Breathing is often considered “autonomic,” but it is more similar to somatic processes, as it involves both voluntary and automatic control.

Phrenic motor neurons receive input from both the primary motor cortex for voluntary control and the brainstem for automatic control.

The cortex can override automatic breathing via corticobulbar tracts, allowing for voluntary control, such as during speech.

Question 18

How is breathing controlled?

Answer 18

Breathing is controlled both automatically and voluntarily.

The cortex can override automatic breathing processes, allowing voluntary actions like speech, singing, sniffing, coughing, spirometry tests, and breath-holding.

Deep-sea divers hyperventilate before breath-holding to lower PaCO2, which induces alkalosis. The urge to breathe during a breath-hold typically occurs at a PaCO2 of around 50 mmHg

Question 19

Central chemoreceptors (PCO2 sensors)?

Answer 19

Central chemoreceptors, located in the retrotrapezoid nucleus on the ventral surface of the medulla, sense CO2 levels.

CO2 crosses the blood-brain barrier and reacts with water in the cerebrospinal fluid (CSF) to form carbonic acid, which dissociates into bicarbonate and hydrogen ions (H+).

Changes in CSF CO2 or pH activate these chemoreceptors

Question 20

Peripheral chemoreceptors (PO2 sensors)?

Answer 20

Peripheral chemoreceptors, located in type I cells of the carotid bodies, detect low PaO2 (< 60 Torr).

This causes K+ channels to close, depolarizing the cell and opening Ca2+ channels.

Ca2+ influx triggers the release of ATP and acetylcholine (ACh), activating the afferent neuron (carotid sinus nerve).

This signals respiratory control centers to increase breathing.

Question 21

Central and peripheral chemoreceptor interdependence?

Answer 21

The central and peripheral chemoreceptors do not work independently

Isolating the carotid body from the systemic and cerebral circulation

CB stimulation (hypoxia and hypercapnia) = increased controller gain

CB inhibition (hyperoxia and hypocapnia) = decreased controller gain

Question 22

*What is the primary regulated variable in the respiratory system?

Answer 22

PaCO2 (arterial carbon dioxide pressure), which is key for maintaining acid-base balance and proper gas exchange

Question 23

*Where is the respiratory rhythm generated?

Answer 23

In the medulla of the brainstem, which produces the rhythmic breathing cycle

Question 24

*What is the primary muscle of inspiration?

Answer 24

The diaphragm, which contracts to expand the thoracic cavity and draw air into the lungs.