Chapter 50: Sensory and Motor Mechanisms Flashcards
Cochlear anatomy
Organ of Corti anatomy
Sensory reception by hair cells
Organs that detect gravity or linear movement
The utricle and saccule contain granules called otoliths composed of calcium carbonate that allow us to perceive position relative to gravity or linear movement
Retinal anatomy
Visual pigments
Sensory transduction in the eye
Light induces the conversion of cis-retinal to trans-retinal
Trans-retinal activates opsin, a GPCR, leading to hydrolysis of cyclic GMP
When cyclic GMP breaks down, Na+ channels closes, hyperpolarizing the cell
The signal transduction pathway shuts off as enzymes convert retinal back to the cis form
Lateral inhibition
Sharpens the edges and inhances contrast
Horizontal cells inhibit more distant photoreceptors that are not illuminated
Focusing
Visual information pathway
Optic nerve→optic chiasm→lateral geniculate nuclei (LGN)→primary visual cortex
Taste
Gustation is dependent on the detection of chemicals called tastants
Receptor cells are modified epithelial cells organized into taste buds
- Most taste buds are associated with projections called papillae
Smell
Olfaction is dependent on the detection of odorant molecules
Taste receptor types
Taste receptors are of three types:
- The sensations of sweet, umami, and bitter require specific G protein-coupled receptors (GPCRs)
- The receptor for sour is similar to the capsaicin and other thermoreceptor proteins
- The taste receptor for salt is a sodium channel
Muscle filaments
Thin filaments are composed mainly of actin
Thick filaments are staggered arrays of myosin
Muscle cell anatomy
Muscle cells consist of a bundle of long fibers running parallel to the length of the muscle
- Each is a single fused cell with multiple nuclei
Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally
Functional unit of muscle cells
Sarcomere
Muscular contraction mechanism
Regulation of muscle contraction
The regulatory protein tropomyosin and the troponin complex bind to actin strands on thin filaments when a muscle fiber is at rest
- This prevents actin and myosin from interacting by covering myosin-binding sites on the thin filament
- For a muscle fiber to contract myosin-binding sites must be uncovered
Motor neurons enable actin and myosin to interact by triggering the release of Ca2+ which binds to the troponin complex and exposes the myosin-binding sites
- Contraction occurs when the concentration of Ca2+ is HIGH
- Relaxation occurs when the concentration of Ca2+ is LOW
Neuronal-muscular integration
The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine which depolarizes the muscle via an action potential
Action potentials travel to the interior of the muscle fiber along transverse (T) tubules
The action potential along T tubules causes the sarcoplasmic reticulum (SR) to release Ca2+
The Ca2+ binds to the troponin complex on the thin filaments allowing the cross-bridge cycle to proceed
Control of muscle tension
Control of muscle tension is achieved via two mechanisms:
- Varying the number of fibers that contract via differential motor unit activation
- As more motor units are recruited tension increaes
- Varying the rate at which fibers are stimulated via summation of twitches
- When the rate is high enough it results in a smooth, sustained contraction called tetanus
Types of skeletal muscle fibers
Oxidative fibers- mostly rely on aerobic respiration and make use of a steady energy supply
- Have many mitochondria
- Rich blood supply
- Large amounts of myoglobin- brownish in color oxygen-storing molecule that binds to oxygen more tightly than hemoglobin
Glycolytic fibers- rely on glycolysis and therefore fatigue much more easily
- LOW in myoglobin content and are therefore mugh lighter in color; white meat
