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Physical Functions - Coggle Diagram
Physical Functions
Vision
Structures & function
- Iris: coloured
- Pupil: aperture in iris to let more/less light in
- Cornea: focuses light, not adjustable, 80% refractive power, in front of iris
- Lens: focuses - focuses light, accommodates (changes shape), 20% refractive power, behind iris
- Retina: lined with photoreceptors (image inverted)
- Fovea: tightly packed receptors, 70% input to brain, no blood vessels/ganglion cells -> acute, detail
- Blind spot: no receptors, where optic nerve & blood vessels exit at back of eye -> no vision
Retina
- Light -> R&C -> H&B -> A&G -> ganglion axons form optic nerve
- Rods & cones have photopigment - release energy when struck by light
- Cones: detail - 90% input
** Fovea, 1 cone -> 1B/G => detail; g
** Good in bright light
** High wavelength sensitive (low = blue, high = red) - good colour
- Rods: movement - more rods (20:1)
** Periphery, many rods -> 1B/G => poor detail
** Low wavelength sensitivity (500nm) - poor colour/spatial locaiton
** Good in dim light
- Horizontal: connects R&C, lateral inhibition
- Amacrine: connects G(/A/B), refine input to G, (some for colour vs light vs mvt vs shape)
- Ganglion cells: sends summary info from many rods to brain
Wavelength vs colour
- Blue = 350nm
- Green = 500nm
- Red = 700nm
Theories
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Opponent-process: more active in response to 1 wl, less in response to opposite; red/green, yellow/blue, black/white - afterimage
Retinex
- Retinex: retina + cortex - cortex compares input from diff parts of retina to determine brightness/colour
- Context changes colour perception -> colour constancy
Visual pathways to brain
Eye
-> nasal->contralateral, temporal-ipsilateral at optic chiasm
-> LGN in thalamus
-> primary visual cortex/V1/striate cortex
-> dorsal or ventral stream
- Magnocellular cells in LGN: large cell bodies & receptive fields (like rods)
- Dorsal pathway = why - through parietal cortex
- Action - visually guided movements, depth/movement/patterns;
damage = bump, can't reach, can't post letter - visuomotor
- Complex cells in cortex: bar/shape, moving in direction within large area (field), e.g. bar moving L to R
- Middle temporal cortex/M5: motion processing - direction & speed;
damage = motion blindness (can see object but no mvt)
- Posterior parietal cortex: movement perception
- Parvocellular cells in LGN/fovea: small cell bodies & receptive fields (like cones)
- Ventral pathway = what - through temporal cortex
- Perception - recognise objects/patterns/shape, colour, fine detail;
damage = can't ID objects, can't line up letter to post - perceptual orientation
- Simple cells in cortex: bar/shape, in one location (small receptive field)
=> feature detection (colour/orientation/width) - e.g. red vertical bar
=> spatial frequency detection
- Inferior temporal cortex: object ID/shape analysis, despite change in position/size;
damage = visual object agnosia
- Posterior inferior temporal cortex: mixed parvo/magno - colour & brightness
Receptive fields
Visual field: visual pattern that most excites neurons (for each neuron)
- Depends on location, wavelength, movement, orientation, size, colour
- Receptor (small) -> B cell -> ganglion cell (large)
Gratings
- Square-wave: blocked stripes
- Sine-wave: graded stripes
Spatial frequency: sine wave grating corresponding to width of simple cell
- Low frequency = wide = large objects = overall shape
- High frequency = narrow = small objects = detail
- -> simple cells respond to particular spatial frequency, not feature
Lateral inhibition: stimulation in retina suppresses neighbours' response -> enhance contrast of boundaries (e.g. for brightness contrast)
- Receptors stimulate B & H -> H inhibits B and B to the side
- Retina & LGN: doughnut shaped
- Cortex: edge/feature or motion detectors? spatial frequency
Disorders
Visual object agnosia
- Can't recognise objects
- Inferior temporal cortex damage
Prosopagnosia
- Can't recognise faces
- Damage to fusiform gyrus of temporal cortex
Movement
Muscles
Categories
- Skeletal/striated: body & limbs, involuntary & voluntary*
Smooth: internal organs, involuntary (pupils, blood vessels, intestines)
- Cardiac: heart, fibres fused so contract together
- Fast-twitch: contract fast, sprint, fatigue fast, don't use O2
- Slow-twitch: contract slow, long-distance running, don't fatigue, use O2
- Neuromuscular junction: synapse between alpha motor neuron & muscle fibre
- Motor unit: 1 motor neuron + >=1 muscle cells it innervates (more force - more motor units)
- Acetylcholine excites -> so muscles only contract (no message for relax or opp. direction)
- Antagonistic muscles: to move joints in 2 directions (one contracts, other relaxes)
- Flexor, e.g. hand to shoulder
- Extensor, e.g. straighten arm
Functions
- Movement
- Secrete fluid (salivary/sweat glands)
- Regulate body (blood pressure, digestion)
- Heart pumping
Proprioception
Muscle spindle organ: if stretch -> contraction
- Parallel (inside) muscle fibres
- Muscle stretches -> muscle spindle stretches & messages motor neuron -> messages muscle -> contracts (negative feedback)
- Before Golgi tendon
- e.g. walk on uneven ground, prevent too much stretch
Golgi tendon organ: if tension/contract -> inhibit contraction
- Inside tendon (between muscle & bone)
- Muscle contracts -> Golgi tendon stretches & messages motor interneuron -> inhibits motor neuron (stop further contraction)
- e.g. prevent injury to muscle
Reflexes
- Consistent, involuntary, single response to stimuli
- In spinal cord & brain stem (not brain)
- e.g. pupil, pain, postural, infant, muscle spindle/Golgi tendon
Central pattern generators
- Involuntary, repetitive, rhythmic sequence of behaviour
- In spinal cord & brain stem
- Stimulus starts it, but doesn't control frequency
- e.g. bird flapping wing, wet dog shake
Motor programs
- Fixed sequence of movements (not just repeated mvt)
- Innate: yawn, smile, frown, animal self-wash
- Learnt: riding a bike, speaking, playing an instrument
- In SMA
- Disrupted when think about it
- Proprioception: sense that tracks where body parts are in relation to each other
- Proprioceptors: receptor that detects position or mvt of body
e.g. touch receptors: respond to squeezing/stretching
Brain - cortex = complex actions
- Larger cortical area = higher precision
- Posterior parietal cortex: monitors body/object position - planning/intention to move -> premotor
- Premotor cortex: prepares mvt -> primary
- Prefrontal cortex: prepares mvt, store sensory info, consider outcomes
- Primary motor cortex: orders outcome (more neurons for hands/face/tongue/swallowing)
- Primary somatosensory cortex: feels body
- Supplementary motor cortex: prepares well-learned mvt (internally cued, prevents habitual errors)
Lateral premotor cortex: externally cued, habitual errors
Brain - subcortical = involuntary actions
- Coughing, laughing, crying
Brain - other
- Cerebellum: aim/timing, coordination, balance
** Sends corrections to motor cortex (compares expected/actual mvt)
** No. Purkinje cells stimulated (via parallel fibres) = passage of time
- Basal ganglia: well-learned, internally cued (cues SMA)
* Direct - enhances* mvt; SN on -> putamen on I -> GP off -> thalamus on -> SMA on
* Indirect - inhibits* competing mvt; SN off -> putamen off -> GP I -> thalamus off -> SMA off
** Increases vigour of mvt
** Stores sensory info
Disorders
Cerebellum
- Balance & coordination (like intoxication)
- Timing/aim/error correction
- Attention shifting
Parkinson's
- Symptoms: can't initiate voluntary mvt (rigidity), can't inhibit inappropriate mvt (tremor), slow/weak/inaccurate, cognitive deficit, depression
- Cause: death of dopamine-releasing neurons in SN (stuck in off); genetic + environmental (toxins)
- Treatment: L-dopa (precursor to dopamine) + electrically stimulate GP, cell transplant
Huntington's
- Symptoms: deterioration of motor control (jerk -> writhe)
- Cause: damage to CN, P, GP & cerebral cortex (less I of thalamus -> involuntary/jerky mvt); hereditary (gene alters structure of huntingtin protein)
- Treatment: tetrabenzine (reduces dopamine, serotonin, norepinephrine)
Brain - spinal cord
- Corticospinal tracts: from brain to spinal cord
- Lateral: precise, discrete, detailed - peripheral (hands/fingers/feet)
** Primary motor cortex & surrounding areas
** -> midbrain (red nucleus) - connects to cerebellum
** -> upper medulla (pyramids) - cross to contralateral
* -> contralateral side of spinal cord -> move sides independently
- Medial: postural, bilateral (standing/bending/walking/turning)
** Many areas
** -> midbrain (tectum, reticular formation)
** -> medulla & cerebellum (vestibular nucleus) - balance
* -> both sides of spinal cord
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Hearing
Dimensions
- Pitch = frequency = waves/sec
- Loudness = amplitude (in general) = height
(15-20k Hz; low = low sound)
- Location: arrives at ear at diff times
- Timbre: wave shape
- Prosody: conveying info by tone of voice
Structures & function
- Sound -> strike tympanic membrane
- -> vibrates bones in middle ear (hammer, anvil, stirrup) - amplifies vibrations
- -> stirrup vibrates oval window of cochlea
- -> moves fluid in cochlea
- -> vibration displaces hair cells between basilar membrane & tectorial membrane in organ of Corti (cochlear duct)
- -> opens K+ channels in hair cell membrane - mechanical
- -> stimulates auditory nerve cells
Auditory pathways to brain
Ear
-> cochlear nucleus: cross in midbrain to
-> superior olive: compare sounds to tell location
-> inferior colliculus: orienting (bring attention to sound)
-> medical geniculate nuclei: sensitive to complex sounds
-> cortex: tonotopic (higher at back, complex on outside)
Theories
Place
- 1 place in basilar membrane = 1 frequency
- But membrane wound too tightly, neurons can't respond quickly enough
Frequency
- Basilar membrane vibrates -> AP at same frequency
- Frequency = pitch, no. cells firing = loudness
- But limited by refractory period to 100Hz
Compatible theories
- Low frequency (0-100Hz) = frequency theory
- Intermediate (100-4kHz) = volley principle (staggered)
- Highest (>4kHz) = place theory
** High: vibrate cells near base - at oval window (stiff)
** Low: vibrate cells at apex (floppy)
Primary auditory cortex/A1
- In superior temporal cortex
** Respond best to particular frequency/complex tones
- Anterior temporal cortex: ID sounds
- Posterior temporal & parietal cortex: locate sound
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