Week 3 Flashcards
Sensory Cells
- Gather info about environment and internal state
- ionotropic: receptor molecule is an ion channel
- Metabotropic: acts via GPCR
- Respond to specific stimuli
Interoreceptors
Internal body fluids, pH, osmotic concentration or blood (homeostasis)
Prorprioreceptors
Body movement and position
Exteroreceptors
External stimuli
- somesthetic surfaces: body surfaces
- special senses - highly localized and specific
Mechanoreceptors
Touch, pressure, proprioreception (ionotropic)
Chemoreceptors
specific chemicals (ionotropic and metabotropic)
Thermoreceptors
heat and cold (ionotropic)
Photoreceptors
photic energy (metabotropic)
Electroreceptors
Electric fields (ionotropic)
Magnetoreceptors
Position or change or magnetic fields (unknown)
Nociceptors
Pain receptors (ionotropic)
Receptor potential in specialized afferent ending sequence
- Sensory receptor (modified ending of an afferent neuron)
- generator potential
1. Stimulus enters the sensory receptor which triggers the opening of the stimulus-sensitive nonspecific cation channel (causes sodium influx)
2. This triggers the voltage-gated Na+ channel a little further down the receptor
3. This causes an action potential to travel down the afferent neuron fiber
Receptor potential in separate receptor cell
- receptor potential
1. Stimulus enters separate receptor cell which triggers the opening of the stimulus sensitive nonspecific cation channels, causing an influx of Na+, leading to the opening of voltage-gated Ca2+ channels which cause Ca2+ to rush in
2. The neurotransmitter in this receptor cell is released
3. The neurotransmitter binds the chemically gated receptor- channel on the neuron which causes an influx of sodium
4. voltage gated Na+ channels further down are triggered to open which leads to an action potential down the afferent neuron fiber
Sensory signals pathways
- Carried by the PNS to the spinal cord or medulla
- Secondary synapses in thalamus
- signal is related to sensory cortex
- brain decodes type, location, and intensity of stimulus
Receptive fields
Each sensory neuron responds to stimuli in a specific area – receptive field
Size of receptive field
The smaller the receptive fields, the greater the density of receptors – smaller receptive fields produce greater acuity or discriminative ability (fingertips)
Receptor density
- greater density with smaller receptive fields
- amount of cortical representation on the sensory homunculus corresponds with receptor density
Lateral inhibition
Strong signal in center of receptive field inhibits pathways in fringe areas
- Inhibitory interneurons stop transmission to second-order neurons so that the frequency of action potentials is lessened in fringe areas
Pain corpuscle – Mechanoreceptor
Deep pressure – located in dermis (middle layer)
Touch sensors – Mechanoreceptors
Highly sensitive, closer to skin surface; has cell receptors near the dorsal root ganglion – located throughout dermis and epidermis
Touch mechanoreceptors – Mechanoreceptors
Base of hairs – in dermis
Layers of skin
Epidermis (top), dermis, hypodermis (bottom)
Stretch receptors – Proprioceptors
Muscle spindles, golgi tendon organs
-largely in ear
Statocysts – Proprioceptors
Gravity receptors
-statoliths move in direction of body movement, bending sensory hairs
- simplest organs of equilibrium
- this opens gated channels, generating action potentials
-fluid in ear and sensory hair in ear
Depolarization of receptor hair cell
- Tip links stretch and open mechanically gated cation channel when stereocillia bend towards tallest member
- K+ enters; cell depolarizes
- Depolarization opens voltage gated Ca2+ channels
- Ca2+ entry causes greater than basal release of neurotransmitter
- More neurotransmitter going to afferent fiber leads to higher rate of action potential
Hyperpolarization of receptor hair cell
- Tip links stretch and open mechanically gated cation channel when stereocillia bend towards shortest member
- No K+ enters; cell hyperpolarizes
- Hyperpolarization closes voltage gated Ca2+ channels
- No neurotransmitter is released
- No action potential
Vestibular apparatus of inner ears
- Serve as sensory functions of acceleration and balance
- Semicircular canals
- Otolith organs
- Signals from vestibular apparatus are carried through vestibulocochlear nerve to cerebellum and vestibular nuclei
Semicircular canals
-Detect rotation or angular acceleration or deceleration of the head
- Receptive hair cell in ampulla (each ear contains 3 semicircular canals arranged in 3D planes at right angles to each other and provide information to the CNS)
Otolith organs
Head position; provide information to CNS about position of head relative to gravity and changes in rate of linear motion (utricle and saccule are the otolith organs)
Direction of fluid movement in semicircular canals when head turns
Opposite the direction of head turning
Direction of fluid movement in semicircular canals when head angles down/up
Same direction of where the head moves (head forward- fluid moves forward)
Direction of fluid movement in otoliths when head moves forward/backwards
Opposite the direction of head movement
Vestibular nuclei (in brain stem)
Gets sensory input directly from receptors in eyes, skin, joints and muscles. Gets sensory input both directly and indirectly from receptors in semicircular canals and otolith organs. Coordinates with the cerebellum
What receptor type detects sound waves
mechanoreceptors
External ear
- Tympanic membrane (eardrum): vibrates as sound hits
- Pinna (external ear - what you see)
- External auditory meatus
Middle Ear
- Transfer vibration of tympanic membrane to the fluid of the inner ear
- Moveable chain of three small bone (ossicles)
- Reflex response tightens tympanic membrane during loud sound for protection
Ossicles
Malleus, Incus, Stapes
amplify sound
Malleus
Small bone attached to tympanic membrane
Incus
Bone between malleus and stapes
Stapes
Attached to oval window
Organ of Corti
Structure in inner ear with hairs of hair cells displayed on surface
Sense organ for hearing
15,000 hair cells
Transform cochlear fluid vibration into action potential
Hair bends trigger receptor cells to trigger release of neurotransmitter which will trigger action potential
Stereocilia (hair cells)
Movement of fluid that opens mechanically gated channels
Cochlea
Coiled tubular system with 3 longitudinal fluid filled compartments
-Scala vestibuli: perilymph (outer top)
-Scala media/cochlear duct: endolymph (middle)
-Scala tympani: perilymph (outer bottom)
Fluid movement in the perilymph
- 2 pathways
- set up by vibration of the oval window (top)
- can go through the perilymph (through oval window through scala vestibuli and down through scala tympani through round window)
- through endolymph
Mechanism for Organ of Corti
-Fluid movements in the cochlea cause deflection of the basilar membrane
- the hairs from the hair cells of the basilar membrane contact overlying tectorial membrane. There hairs bend and thus open mechanically gated channels leading to ions movements that result in receptor potential
Steps of hearing
- Sound waves enter ear
- Tympanic membrane vibrates
- vibrations amplified across ossicles
- vibrations against oval window set up standing wave in fluid of vestibuili/cochlea
- pressure bends the membrane of the cochlear duct at a given point of max. frequency, causing hair cells in the basilar membrane to vibrate
- Graded potential changes in receptor cells and changes in rate of action potentials generated in auditory nerve
- Propagation of action potentials to auditory corext
Vibration of round window causes
Dissipation of energy (no sound perception)
Chemicals must be in what state to evoke taste
solution
Taste
- Microvilli contain chemoreceptors
- Binding of tastants produces a depolarizing receptor potential
Tastes
Salty, sour, bitter, sweet, umami
Salty
sodium: direct entry of sodium ions through channels in cell membrane
Sour
Acid: H+ blocks K+ efflux from cell
Sweet
Sugar: GPCR stimulates cAMP or IP3
Bitter
Plant alkaloids: GPCRs
Umami
Savory: glutamate binds to GPCR
Olfactory
- Olfactory mucosa in nasal fossae contain receptors
- Olfactory afferent neurons are only mammalian neurons that undergo cell division
- Each cell responds to a single discrete component of an odor (GPCR)
Ciliary photoreceptors
Rods and cones
Visible light
400-700 nm
Light sensing organs
Eyespots
pinhole eye
camera eye
compound eye (arthropods)
Vertebrate eye
Fluid filled sphere enclosed by 3 layers
- sclera
- Choroid
- Retina
Sclera
White, cornea: transparent (outermost)
Choroid
Middle layer, highly pigmented, many blood vessels, ciliary body, iris
Retina
Photoreceptors
Anterior cavity
Between cornea and lens and contains aqueous humor
Posterior cavity
Between lens and retina and contains vitreous humor
Iris
- Controls the amount of light entering eye
- Pigmented ring of smooth muscle (circular and radial)
- Controlled by autonomic nervous system
Circular muscle
-Constricts pupil in response to light (parasympathetic)
Radial muscle
Increases pupil size in dim light (sympathetic)
Direction of visual processing
Back of retina towards front of retina (opposite of direction of light)
Rhodopsin
- Found on the outer segment of the rods
- Protein called scotopsin and a pigment called retinal (derivative of vitamin A) – only the cis form of retinal can bind with scotopsin to make rhodopsin
Rods and cones contain what
The chemical that changes in response to light that excites nerve fibers
Cone
Color
Lone with thin outer segment and has no capillaries; pigments are lodopsin; responds to specific wavelenght of light; comparatively low sensitivity
Rods
Light/Dark
Contain rhodopsin
Erythrolable in cones
Max sensitivty for red
Cholorable
maximum sensitivity for green
Cyanolable
maximum sensitivity for blue
Phototopic vision-daylight vision
due to cones, mainly color
Scotopic vision
Dim light vision due to rods
Mesopic vision
full moonlight vision, rods and cones
Serial processing of image in retina
First image
- Action of light on photoreceptors
-Breakup image into small pots of light and dark
Second image
-Bipolar cells
-Spatial summation by lateral inhibition by horizontal cells
Third image
- By ganglion cells
- Temporal summation by lateral inhibition by amacrine cells
Muscle classifications
smooth, cardiac, skeletal
How do muscles move a body part
By contracting/shortening
Visceral structures controlled by which muscle
smooth/cardiac muscles that have intimate association with that body part
skeletal muscle classifications
Flexors
Extensors
Adductors
Abductors
Sphincters
Tendons
Attach muscle to bone
Antagonistic pairs
Muscles have pairs that work against each other. Flexors bend limbs and extensors straighten limbs
Muscle structure
-Single action potential produces all or none contraction
-Tendons
-Antagonistic pairs
- each muscle fiber supplied by one motor neuron
-each motor neuron branches and innervates many muscle fibers and these fibers will contract simultaneously forming a motor unit
Skeletal muscle
-Voluntary movement
-Large fibers, elongated and cylindrical
-Multiple nuclei
- Lie parallel to each other and are bundled with connective tissue
-Myofibrils
Myofibrils
-contractile elements
-90% of muscle volume
-more fibers=greater force that can be generated
Layering of skeletal muscle
Epimysium around outside
Perimysium just underneath
Fascicle wraps around bundles
Bundles of fibers next to blood vessels
Endomysium wraps around fibers
Muscle fibers
Thick filaments
-Myosin
-Two heads
-Actin binding site on head
- Myosin ATPase site on head
Thin filament
-Actin molecules
- binding site for attachment with myosin cross bridge
- Binds with troponin and tropomyosin
Relaxed muscle fiber
- No excitation
- No cross-bridge binding because cross-bridge site on actin is physically covered by troponin-tropomyosin complex
Excited muscle fiber
- Muscle fiber is excited and Ca2+ is released
- Released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site
- cross bridge occurs
- Binding of actin and myosin cross bridge triggers power stroke that pulls thin filament inward during contraction
Single cross-bridge cycle
- Binding: myosin cross bridge binds to actin molecule
- Power stroke: cross bridge bends, pulling thin myofilament inward
- Detachment: Cross bridge detaches at end of power stroke and returns to original conformation
- Binding: Cross bridge binds to more distal actin molecule; cycle repeats
Calcium in Muscles
- Stored in lateral sacs of sarcoplasmic reticulum
- Action potential triggers release of calcium from SR in cytosol
- Increased cytosolic calcium increases binding of calcium to troponin initiating contraction
- During relaxation, calcium is pumped back into SR by calcium ATPase pumps, decreasing cytosolic calcium
- Ryanodine receptors are responsible for releasing calcium from SR
ATP: Cross bridge cycling
- Cross bridge cycling is turned on using excitation-contraction coupling
- Myosin ATPase on thick filaments split ATP to ADP and Pi
- ADP and Pi remain on myosin, providing energy during binding
- During and after power stroke, ADP and Pi are released
- Myosin ATPase site attaches new ATP
- Then detachment of cross bridge can occur, setting up another power stroke
Contractile activity
-Action potential lasts 1-2 msec
- Produces contraction (twitch) after a short latent period
- Contraction time averages 50 msec (occurs until Ca is released)
- Relaxation time is a little longer (occurs as Ca is pumped back into SR)
-Twitch time: 100 msec
Sequence of contraction
- Action potential during latent period
- Tension increases during contraction time
- Tension decreases during relaxation time
- This tension creates a muscle twitch
Motor unit
- Recruitment of multiple muscle fibers per nerve fiber to produce stronger contraction
- Precise movement has only a few fibers per unit
- Powerful movement has many muscle fibers per unit
- Occurs asynchronously to prevent fatigue
2 main factors control gradation of contraction of a given muscle
- Number of motor units stimulated
- Frequency of stimulation
Single twitch
If a muscle fiber is restimulated after it has completely relaxed, the second twitch is the same magnitude as the first twitch
Twitch summation
If a muscle fiber is restimulated before it has completely relaxed, the second twitch is added onto the first twitch, resulting in summation
Tetanus
If a muscle fiber is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction known as tetanus occurs
3 Steps Require ATP in Contraction-Relaxation
-Splitting of ATP by myosin ATPase (indirectly), the energy for the power stroke of the cross bridge
- Binding of a fresh ATP molecule to myosin permits detachment of bridge from actin filament at the end of power stroke to repeat cycle (provides energy for the next stroke)
- Active transport of Ca2+ back into SR during relaxation depends on ATP breakdown
Creatine phosphate
The first energy storehouse tapped at the onset of contraction (vertebrates use this)
- ATP is required for muscle contraction but storage is limited which is why this is needed
- Contains high energy phosphate group that can be donated to ADP
-Creatine phosphate + ADP = creatine +ATP
-Muscle contains 5x more creatine phosphate than ATP
Arginine Phosphate
Also used to store ATP for muscle contraction
- Contains high energy phosphate group that can be donated to ADP
Oxidative phosphorylation
-Takes place in mitochondria
- Requires oxygen
- Fueled by fatty acids/glucose
- Get 30 ATP per glucose molecule
-Multistep pathway (requires more time to get ATP)
- Light to moderate aerobic activity is supported by this process
Myoglobin
Stores oxygen in muscle fibers
Glycolysis
-Occurs in cytoplasm
-Can form ATP without oxygen
- Occurs quickly
- Operates anaerobically
- Fueled by glucose
- 2 ATP per every glucose molecule
-Produces lactate (acidosis) from pyruvic acid (end product of glycolysis)
SKM Fiber Types
- Slow oxidative fibers (Type I)
- Fast oxidative fibers (Type IIa)
- Fast-glycolytic fibers (Type IIb, IId, or IIx)
Slow oxidative fibers
- Lower myosin ATPase activity
-Slow speed of contraction - High resistance to fatigue
- High oxidative phosphorylation capacity
-Low amounts of enzymes for anaerobic glycolysis
-Many mitochondria and capillaries, and myoglobin
-Low glycogen content
-Red
Fast oxidative fibers
- Higher myosin ATPase activity
- Fast speed of contraction
- Intermediate resistance
- High oxidative phosphorylation capacity
- Intermediate enzymes for anaerobic glycolysis
- Many mitochondria, capillaries and myoglobin
-Red
-Intermediate glycogen content
Fast-glycolytic fibers
- High myosin ATPase activity
- Fast speed of contraction
- Low resistance to fatigue
- Low oxidative phosphorylation
-High enzymes for anaerobic glycolysis - Few mitochondira, capillaries and myoglobin
-White - High glycogen content
Control of Motor Movement
-Afferent Neurons
- Primary motor corex
- Brain stem
Afferent Neurons
- Spinal reflexes for posture and basic movements
Primary motor cortex
- Fine, discrete movements of hands and fingers
- Pyramidal cells within the primary motor cortex
Brain stem
-Overall body posture involving involuntary movements of trunk and limbs
