ap chap 50 sensory perception and motor action
TRANSCRIPT
Sensory and Motor Mechanisms
AP Chapter 50
The brain’s processing of sensory input and motor output is cyclical rather than linear
• The way it ISN’T: sensing brain analysis action.
• The way it is: sensing, analysis, and action are ongoing and overlapping processes.
• Sensations begin as different forms of energy that are detected by sensory receptors.– This energy is converted to action potentials
that travel to appropriate regions of the brain.• The limbic region plays a major role in determining
the importance of a particular sensory input.
Sensory receptors transduce stimulus energy and transmit signals to the nervous system
4 Functions common to all sensory pathways
1. Sensory Reception
2. Sensory transduction
3. Transmission
4. Perception
Sensory receptors are categorized by the type of energy they transduce.
Categories of sensory receptors
1. Mechanoreceptors – pressure, touch, motion, sound, hair cells
2. Chemoreceptors general – solute conc specific – molecules; gustatory (taste), olfactory (smell)3. Electromagnetic4. Thermoreceptors5. Photoreceptors6. Pain receptors – in humans, nociceptors in
epidermis, located in skin and other areas, aspirin/ibuprofen blocks prostaglandins
Mechanoreceptors for hearing and equilibrium
• Utilize moving fluid and settling particles• Mammals – pressure waves picked up by
ears and converted into nerve impulses• Fish – lateral line systems• Invertebrates – statocysts with ciliated
receptor cells with sand granules• Insects – body hairs that vibrate, some have
ears
Our Hearing and Balance
• Energy of fluid into energy of action potentials
• Uses sensitive hair cells
• True organ of hearing – the organ of Corti located in the cochlea
• Balance – semicircular canals
Hearing animation
Hearing
http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0019-swf_effect_of_soun.swf
The three small bones transmit vibrationsTo the inner ear which contains fluid-filled canals.
Air pressure vibrates fluid in canals which vibrate the basilar membrane, bending the hairs of its receptor cells against the tectorial membrane which opens ion channels and allows K+ to enter the cells and cause a depolarization and releases neurotransmitters to continue to the auditory nerve to the brain.
Frequency (pitch) determined by areas of basilar membrane that vibrate at different frequencies; areas are thick and thin
Volume is controlled by amplitude of wave – stronger bends hair cells more and more action potentials
• Balance in the semicircular canals is also a response to hair cells; different head angles stimulate different.
• Hair cells; lateral line systems in fish and some amphibians work like this too.
The inner ear also contains the organs of equilibrium
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Statocysts are mechanoreceptors that function in an invertebrates sense of equilibrium.– Statocyst function
is similar to that of the mammalian utricle and saccule.
– Use ciliated (hair-
like cells)
Many invertebrates have gravity sensors and are sound-sensitive
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 49.21
A diversity of photoreceptors has evolved among invertebrates.
Planaria – eyecup for light and direction Insects/crustaceans- compound eyes (ommatidia) Jellyfish, spider,
mollusks – single lens eye
Taste and Smell
• Odor/taste molecules bind to ciliated receptor cells and trigger a signal-transduction pathway that involves a G-protein and, often, adenylyl cyclase and cyclic AMP’s.
• cAMP to open Na+ channels, depolarizing the membrane and sending action potentials to the brain.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 49.24
Vertebrate eyes
• Rods and cones are photoreceptors located in the retina of the eye.
• Rods are more light sensitive and are concentrated toward the edge of the retina.
• Cones are more color sensitive and are concentrated in the center of the visual field called the
Vertebrates have single-lens eyes• Is structurally analogous to the invertebrate
single-lens eye.
How does this work?
• Rods and cones synapse with bipolar cells in the retina, which synapse with ganglion cells, whose axons form the optic nerve.
• R/C BP Ganglion Cells
Light hits the retinaand then comes backthrough the cells to theoptic nerve.
Photoreceptors
Rods and cones have visual pigments embedded in a stack of folded membranes or
disks in each cell.
Retinal is the light-absorbing pigment and is bonded to a membraneprotein – opsin. Combo – rhodopsin.
When retinal absorbs light, it changes shape and separates from opsin. In the dark, the retinal is
converted back to its original shape.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Opsin activates a G protein and opens/closes Na channels to continue/discontinue the nerve impulse.
Fig. 49.13
Notice in thelight, the Na+
channels areclosed.
Taste and Smell
• Odor/taste molecules bind to ciliated receptor cells and trigger a signal-transduction pathway that involves a G-protein and, often, adenylyl cyclase and cyclic AMP’s.
• cAMP to open Na+ channels, depolarizing the membrane and sending action potentials to the brain.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 49.24
remember…
The ultimate perception of the stimulus depends on the area of the brain that is stimulated!
Locomotion and muscle action
How the muscle cell is organized
Animations
This is ONEmuscle cell,called a muscle fiber.
for energy
The muscle fiber (cell) is made up of many myofibrilswhich in turn are made up of sarcomeres, the units ofcontraction.
• The sarcoplasmic reticulum (SR) is a special type of smooth ER found in smooth and striated muscle.
• The SR contains large stores of calcium ions, which it releases when the cell is depolarized.
Action potentialIs spread in theT tubules
Fig. 50-25b
TEM
Thickfilaments(myosin)
M line
Z line Z line
Thinfilaments(actin)
Sarcomere
0.5 µm
The contracting unit is the sarcomere.
When thesarcomerecontracts, the filaments slide over each other.
The sliding filament model
They do not change length.
How does this happen? a closer look: Myosin
Myosin is made of polypeptides twisted to form a fiber helix with a globular end, which has ATPase activity & an affinity to bind to actin.
a closer look: Actin
Actin is a globular protein;each globular actin unit contains a myosin binding site.
Remember – Actin – Ac”thin”
Mechanism of action
1. The Neuromuscular Junction – neuron to muscle
• Signal travels from motor neuron by acetycholine (excitatory) to the skeletal muscle cell and depolarizes it.
• An action potential is spread in the T tubules and changes the permeability of the sarcoplasmic reticulum which releases Ca+.
2. Actin involvement
Myosin-binding sites
are blocked by a strand
of tropomyosin whose
position is controlled by
Troponin complex molecules.
Ca+ ions bind to the complex
and move the tropomyosin and
expose the binding sites for
myosin.
3. Myosin Involvement- The globular heads of the myosin are
energized by ATP and bind to actin forming a cross-bridge
- When relaxing to its low-energy state, the myosin head bends and pulls the attached actin toward the center of the sarcomere
4. Completion
When its’s over, Ca+ returns to the sarcoplasmic reticulum and tropomyosin recovers binding sites on actin.
Mechanism of Filament Slidingat the Neuromuscular Junction
Mechanism of Filament Sliding
• The sliding-filament model of muscle contraction.
Interactions between myosin and actin generate force during uscle contractions
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 49.33
Protein models of muscle action
Contraction
• Of single muscle fiber – all or none• Twitch: slow – less SE, Ca in longer,
fibers must have many mitochondria, a good blood supply (myoglobin better which picks up O2 better and stores it)
• Fast – rapid and powerful contraction• Tetanus – smooth, sustained
contraction; action potentials arrive rapidly
Muscle Fatigue
• Depletion of ATP, loss of ion gradient, accumulation of lactic acid
• Hydrostatic skeleton: consists of fluid held under pressure in a closed body compartment.– Form and movement is controlled by
changing the shape of this compartment.– Advantageous in aquatic environments and
can support crawling and burrowing.– Does not allow for running or
walking.
Skeletons support and protect the animal body and are essential to movement
• Exoskeletons – supportive, protective but do not grow (molted)
• Endoskeletons – supportive, grow with the organism, less protective