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.
*Purpose of Eye Movements?
Maintain a clear image/bring points of interest on the fovea.
Avoid visual blur and track objects effectively.
*Types of Eye Movements?
Fast movements:
Saccades: Quick jumps to reposition focus (up to 900°/s, ~3 per second).
Resetting movements: During Vestibulo-Ocular Reflex (VOR) and Optokinetic Reflex (OKR).
Slow movements:
VOR: Stabilizes vision during head movement.
OKR: Visual stabilization during prolonged motion.
Smooth pursuit: Tracks moving objects using predictive mechanisms.
Vergence: Aligns both eyes for depth perception
*Methods of Measurement of eye movements?
Electrooculography (EOG): Tracks electric potential changes.
Infrared reflectance: Monitors eye position using IR beams.
Scleral coil: Accurate but invasive.
Video-oculography (VOG): Tracks pupil and gaze with software
*What are the applications and observations of eye movements?
Saccades show motor prediction in activities like walking or sports (e.g., cricket).
Predictive gaze in tasks like tea-making or walking anticipates upcoming actions.
Action observation involves predictive gaze, aligning observed actions with motor representations.
*What does a locomotor pattern involve?
A locomotor pattern involves rhythmic muscle activity and characteristic ground reaction forces, enabling efficient propulsion, stability, and balance during movement
*Where does the basic locomotor pattern come from?
It comes from the spinal cord, where central pattern generators (CPGs) produce rhythmic muscle activity for movements like walking, even without brain input.
*What role do supraspinal areas play in locomotion?
Supraspinal areas:
initiate
stop
and fine-tune locomotion by modulating spinal cord activity for adaptive and goal-directed movements.
*How does sensory feedback influence locomotor patterns?
Sensory feedback adjusts locomotor patterns to:
maintain stability
adapt to changes
enhance movement efficiency
*How do saccades contribute to motor control?
Saccades provide predictive information, aiding in anticipation and adaptation during movements like locomotion.
*Components of the vestibular system?
Otoliths: Structures in the vestibular system that detect linear acceleration (e.g., moving forward in a car) and head tilt relative to gravity.
Semicircular canals: Fluid-filled structures that sense rotational movements of the head (e.g., turning or nodding).
Vestibular-ocular reflex (VOR): A reflex that stabilizes vision by moving the eyes in the opposite direction of head movement, ensuring a steady visual field.
*Vestibular ocular reflex?
The Vestibular-Ocular Reflex (VOR) stabilizes vision during head movements by moving the eyes in the opposite direction of the head. It uses vestibular system signals to ensure a steady gaze, preventing visual blur during motion
*Ways to test Vestibular function?
Real rotation: Assessing responses during head or body rotation.
Caloric stimulation: Introducing warm or cold water/air into the ear to stimulate the vestibular system.
Galvanic Vestibular Stimulation (GVS): Using electrical currents to activate vestibular nerves.
*What does the vestibular system measure?
The vestibular system measures linear acceleration, tilt, and rotation, playing a crucial role in balance, orientation, and eye movements
*What is phototransduction?
Bleaching: Light changes rhodopsin, separating retinal and opsin.
Hyperpolarization: Activated opsin reduces cGMP via PDE, closing Na+ channels.
Signal Transmission: Decreased neurotransmitter release alters bipolar and ganglion cell activity, transmitting signals to the brain.
*What is the role of the pupil in light adaptation?
The pupil adjusts from 2 to 8 mm, controlling light intake by up to 16 times. While it is the primary response to changing light, it plays a small part in overall light adaptation, with retinal adaptation providing significant contribution.
*Benefits of smaller pupil size?
Less light reaching retina
Greater depth of field (more focus)
Reduced spherical abberation
Reduced glare (scattering of light)
Infinite depth of field
Compensates for myopia
*Retina cell types?
Photoreceptors, horizontal,
amacrine, bipolar and ganglion cells
*Structure of Retina?
Consists of layers: photoreceptors (rods and cones), bipolar cells, and ganglion cells
Rods and cones?
Rods - Responsible for vision in low light (scotopic vision) and are highly sensitive to light but do not detect color.
Rods are most densely packed in the periphery of the retina, with the highest concentration around the fovea’s outer region, but they are absent in the central fovea
Cones - Cones are responsible for color vision and detailed vision (photopic vision) in bright light.
Cones are concentrated in the fovea, the central part of the retina, providing high visual acuity. The fovea contains almost exclusively cones, with the density decreasing in the periphery.
What is rhodopsin and its role in vision?
Rhodopsin is a light-sensitive pigment in rod cells, crucial for low-light vision. It consists of opsin and retinal.
Light changes retinal’s shape, activating opsin and sending signals to the brain. Rhodopsin must regenerate after each use for continued vision in dim light.
*Visible range of luminance?
Human vision functions across ~ 10^15 units of luminance
*Scotopic versus Photopic vision?
Scotopic
low light vision
Rods only
High sensitivity/low acuity
Non-foveal
Photopic
Suited for high luminance
Cones only
Lows sensitivity/high acuity
Foveal & peripheral
Mesopic
Intermediate luminance (e.g. Dusk)
Rods & cones
Intermediate sensitivity/acuity
Foveal & peripheral
*Adaptation of eye?
Pupil Size: Adjusts to control light intake; smaller pupils enhance depth of field and reduce scatter, larger pupils improve low-light vision.
Rod/Cone Switch:
Low light: Rods dominate for high sensitivity (scotopic vision) but low acuity.
Bright light: Cones dominate for high acuity and color vision (photopic vision) and high acuity.
Intermediate light: Both rods and cones work together (mesopic vision).
Photopigment Regeneration: Photopigments are bleached(broken down) by light and regenerate in darkness, essential for maintaining vision.
*Color Vision?
Human vision relies on three types of cones, each sensitive to different wavelengths:
S-Cones: Short wavelengths (blue).
M-Cones: Medium wavelengths (green).
L-Cones: Long wavelengths (red).
These cones work together to perceive a wide range of colors.
Colors are processed in opposing pairs:
Red-Green, Blue-Yellow, and Black-White.
Color blindness results from cone defects or absence
*Visual Pathways?
Retina: Light is detected and converted into neural signals.
Optic Nerve: Carries visual information from the eye.
Optic Chiasm: Some fibers cross to the opposite hemisphere.
Optic Tract: Transmits information to the thalamus.
Lateral Geniculate Nucleus (LGN): Processes and relays signals.
Primary Visual Cortex (V1): Interprets visual data in the occipital lobe.
Higher Visual Areas: Dorsal stream for motion, ventral stream for object recognition.
*Definition of Proprioception?
Proprioception is the sense of body position and movement, involving muscle spindles and Golgi tendon organs. It is highly sensitive for balance and integrates with vision and vestibular input.
