COGS 107B Week 2 Hyun Ji Friday 4:00-4:50pm
Lecture 3: Proprioception Principles: The Neuron Doctrine and The Law of Dynamic Polarization
Proprioception Joint-protecting reflexes (ex. Knee jerk reflex) Adjustment of muscle contraction/recruitment Recruitment: getting more muscles to work together in a more strenuous task Kinesthesia: detection of body position and movement Coordination of motor commands Sense of self?
The All-Axon Ganglion Cell Dorsal root ganglion (DRG) cell Bend unmyelinated tip -> depolarization (mechanoreceptors) -> generator potentials Four examples discussed so far: Pacinian, Meissner, Merkel, Hair Two more discussed: Muscle spindle afferent, Golgi tendon organ
Muscle Spindle Afferent Two types of muscle fibers: Extrafusal muscle What we typically think of when we say muscle Alpha motor neuron excites extrafusal muscles Intrafusal muscle Where DRG cell innervation happens (muscle spindle afferent) Sends messages to brain when the muscle elongates Contractile/non-contractile(DRG wraps around)/contractile Gamma motor neuron relaxes contractile part
Muscle Spindle Afferent (Cont.) Activated by elongation of muscle, carries transient information Contractile portions contract, stretching non-contractile portion Causes bending of DRG cell (muscle spindle afferent) Generator potential -> Action potential!
Golgi Tendon Organ DRG cell dendrites branch out through tendon GTO is connected to different muscle fibers, and links joints together Extrafusal muscle contraction -> GTO stretched -> flex of joint Physical disturbance of DRG cell dendrites -> Depolarization -> Generator potential -> Action potential Carries sustained information
Muscle Spindle Afferent vs. Golgi Tendon Organ Muscle Spindle Afferent Muscle stretch Transient (RA) DRG dendrites wrap non-contracting portion GTO Muscle contraction Sustained (SA) DRG dendrites branch throughout
Somatosensory Cortex Information (proprioceptive and tactile) is segregated until S1 Information crosses over in the Medulla Finally integrated in S1
Posterior Parietal Cortex (PPC) PPC is divided into multiple sub-regions Monkey must reach into a container without being able to see Sensors encode its arm movements and categorize them into important postures Thinking about holding and object and actually holding it both have firing in the PPC Lots of firing to both the cue of the object and the object itself
Pinocchio Effect Pt holds their nose Vibration sent to bicep muscle spindle afferent Tricks the MSA into thinking the bicep is being stretched Pt is touching their nose and can feel it Hand on nose + elongating biceps Feels like the nose is growing!
Lecture 4: The Vestibular System
Functions of the Vestibular System Postural reflexes Gaze adjustment Assessment of self-motion A reason not to drink too heavily!
The Hair Cell Receptor Transduction of head motion (vestibular system) and sound waves (auditory system) into neural signals Mechanical -> electrical = transduction! Cilia arranged from short to long Bump on end = kinocilium Cilia connected by tendrils When moved, ion channels physically pulled open Short -> Long = depolarization Long -> Short = hyperpolarization
The Hair Cell Receptor Cont. Different from neuron in that depolarization of hair cell is associated with INFLUX of potassium ions This means there is a higher concentration of K+ outside of the cell at rest Arrangement of stereocilia matters! Directions determines if the cell becomes depolarized or hyperpolarized Amount of movement matters! More bending = channel opens more = more depolarization Depolarization = release more glutamate Hyperpolarization = release less glutamate Very fragile mechanism, dies off with age, doesn t regenerate
The Inner Ear Vestibular organ Semicircular Canals Hair cells inside cupula, which exists within endolymph Radial motion Transient like water in a glass Otolith organ Comprised of utricle and saccule (bone compartments) Utricle: Horizontal movement Saccule: Vertical movement Linear motion Sustained like in a moving car
The Vestibulo-ocular Reflex Keep eyes fixated on something and rotate head Move head to right, your eyes must move left Hair cells on the right side are excited, left side is inhibited Movement of head -> inhibition/excitation of extraocular muscles -> eye movement
Integrating Vestibular Signals - Head Direction Neuron Neuron fires based on head position relative to surroundings (NOT body!) Incredibly fine tuned Responds to head direction in degrees horizontally (not side to side, not up and down) Can fire up to 150 spikes per second in preferred direction but have 0 spikes per second for non-preferred direction Exquisite tuning!! **Drosophila study Flies have head direction cells and they are organized topographically on a ring Networks of neurons found in multiple brain regions Medial vestibular nucleus -> Nucleus prepositus -> Dorsal tegmental nucleus (Where info from otolith organ and semicircular canals become integrated!!!!) The faster you move in one direction, the more the neurons fire (sensitive to velocity)