Summaries Flashcards
*What is the primary muscle of inspiration?
The diaphragm, which contracts to expand the thoracic cavity and draw air into the lungs.
*Where is the respiratory rhythm generated?
In the medulla of the brainstem, which produces the rhythmic breathing cycle
*What is the primary regulated variable in the respiratory system?
PaCO2 (arterial carbon dioxide pressure), which is key for maintaining acid-base balance and proper gas exchange
How is breathing controlled?
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
Innervation of spinal respiratory motor neurons?
Insp -
Diaphragm - C3-C5
Scalenes - C2-C7
Exp -
Sterno - Accessory and C2-3
Intercostals - T1-T11
Abs especially Transversus abdominus - T7-L1
*PaCO2 regulation: feedforward and feedback control/adaptive control?
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.
*Basic elements of the respiratory control system?
Central Controller (=pons,medulla, other parts of brain)
> Effectors (= resp muscles) > Sensors (= Chemoreceptors, lungs and other receptors)
CC > Eff = Output
S > CC = Input
*Respiratory control functions?
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)
*Golgi Tendon Organ (GTO) Reflex?
At rest: Negative feedback inhibits muscle activity.
During locomotion: Positive feedback enhances extensor activity, modulated by descending motor commands
*Flexion Withdrawal Reflex?
Polysynaptic reflex activating ipsilateral flexors and contralateral extensors in response to painful stimuli
What is the neural pathway of the flexion withdrawal reflex?
Stimulus: Painful stimulus detected by free nerve endings (nociceptors).
Afferent Pathway: Group III fibers transmit signals to the spinal cord.
Central Integration: Polysynaptic pathway with interneurons; coordinates ipsilateral flexion and contralateral extension.
Efferent Pathway:
Ipsilateral: Flexors activated, extensors inhibited for withdrawal.
Contralateral: Extensors activated for stabilization.
Function: Protective reflex for rapid withdrawal, independent of supraspinal inputs.
*What is the neural pathway of the stretch reflex?
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.
Reciprocal inhibition: Group Ia interneurons inhibit antagonist muscles.
Efferent Pathway: α-motor neurons signal contraction of agonist/homonymous and synergist muscles.
Function: Maintains muscle length via negative feedback, compensating for unexpected load deviations.
H-Reflex: Elicited by electrical stimulation of Ia fibers, similar to stretch reflex with EMG-recorded muscle contractions.
*Types of Reflexes?
Stretch Reflex: Activated by muscle spindles, using a monosynaptic loop for rapid contraction and reciprocal inhibition to maintain muscle length.
Hoffman Reflex (H-Reflex): Laboratory test using electrical stimulation to assess reflex pathways and demonstrate plasticity in motor learning.
Flexion Withdrawal Reflex: Polysynaptic reflex triggered by painful stimuli, activating ipsilateral flexors and contralateral extensors for protective withdrawal.
Golgi Tendon Organ Reflex: Inhibits muscle contraction at rest (negative feedback) and enhances extensor activity during locomotion (positive feedback) based on gait phase.
*Definition of Reflex?
Automatic, involuntary motor response to a stimulus, modifiable by supraspinal inputs
*What is balance?
Quiet standing involves keeping the centre of
mass (COM) within the base of support (BOS)
*Centre of Mass & Pressure?
The Center of Pressure (COP) is the point where the ground reaction force acts on the body. It actively shifts forward and backward to help maintain the Center of Mass (COM) within the body’s limits of stability, ensuring balance. By adjusting the COP, the body compensates for any shifts in the COM to prevent falling
*What is sway? Why do we sway?
Sway is the natural oscillation of the body to maintain balance, typically occurring at the ankle joint.
Reasons for sway:
Imperfect sensory estimation due to sensor noise.
Imperfect motor output in executing movement.
External/internal perturbations like wind, breathing, or being pushed.
Lack of visual information, which increases sway by limiting sensory feedback.
*Active Modulation?
Passive ankle stiffness alone cannot maintain balance; active muscle control is required to adjust and stabilize the body during movement. Active modulation allows for dynamic adjustments to prevent falls and maintain posture.
*Perturbing visual input? What does it look like?
Perturbing visual input involves changing the visual scene, causing the brain to misinterpret motion.
Subjects sway in the direction of the visual scene movement, as the brain interprets forward scene motion as backward body motion, producing a compensatory forward response.
Response timeline:
Initial sway in the direction of visual motion (~1s).
Corrective sway after 2-3 seconds.
Best responses occur with slow, low-frequency motion (<0.1Hz, <5°/s).
Responses habituate quickly and are influenced by expectation and cognition.
The brain uses prior knowledge to distinguish between object motion and self-motion.
*Ground reaction forces - walking?
Large vertical force upon heel-strike
Accompanied by a decelerating (backward) shear force (dotted line)
Push-off includes an ACCelerating shear force, accompanied by a secondary vertical force
Swing-stance pattern?
Alternating pattern of swing-stance
Flexors active during swing (e.g. TA, hamstrings, Hip flexors)
Extensors active during stance (e.g. triceps surae, quadriceps, Gluteus)
*Muscle actions of locomotion?
Alternating eccentric and concentric contractions control locomotion.
Eccentric contraction (stance start) brakes motion, while concentric contraction (stance end) provides push-off
*How do central pattern generators (CPGs) contribute to locomotion?
Spinal networks: CPGs generate rhythmic locomotor patterns even without sensory input.
Half-center model: Flexor and extensor neurons alternate activity through mutual inhibition.
Sensory feedback: Modulates CPG activity, helping with phase transitions, such as initiating the swing phase of gait.
What parts of the brain contribute in locomotion?
Motor cortex: Adjusts for obstacles using visual inputs.
Mesencephalic locomotor region (MLR): Initiates and adjusts gait speed.
Cerebellum/brainstem: Fine-tunes patterns with real-time sensory input.