Physiology Exam Study guide #2 (ch 9, 10, 12)

Ch 10 

Sensory Physiology 

Sensory Receptors

• Cells (neurons or modified epithelial cells)

• That receive sensory information , a stimulus, from the environment

• Transduce different energy forms (pressure, temperature, chemical, light, ect.) into graded potentials that initiate action potentials

  • Afferent sensory input to CNS

Classification of Sensory Receptors

Mechanoreceptors

• Respond to mechanical stimuli, like touch or pressure

Thermoreceptors

• Respond to cold/warmth

Photoreceptors

• Respond to light 

Chemoreceptors

• Respond to binding of particular chemicals

Nociceptors

• Respond to painful stimuli 

Receptor potential 

Receptor potential

• Graded potential in sensory receptor in response to environmental stimulus 

  • Transduction involves opening of ion channels

  • If depolarization at initial segment of axon reaches threshold, then gated ion channels open and AP is generated

Sensory Adaptation 

Sensory adaptation 

• Decrease in receptor sensitivity (responsiveness) during maintained stimulation 

Phasic or fast-adapting receptors:

• Respond with a burst of activity when stimulus is first applied but quickly adapt to the stimulus by decreasing response 

• Respond briefly before adapting to constant stimulus

  • Ex: pressure when seated on a chair, odor, temperature, taste

Tonic or slow-adapting receptors:

• Maintain a high firing rate as long as the stimulation is applied 

• Have persistent action potentials 

  • Ex: receptors in joint & muscle that maintain posture; pain 

Somatic Sensation 

• Touch, pressure, pain, temperature, and senses of picture and movement (proprioception)

Chemosensation 

• Chemoreceptors: respond to chemical stimuli 

• Gustation

  • Taste

• Olfaction

  • Smell

Gustation 

• A taste bud is comprised of 50-100 specialized epithelial cells called taste cells that undergo APs and synapse with sensory neurons 

• Taste cells transduce chemicals

• Salty taste 

  • Na+ through ion channel 

• Sour taste 

  • H+ through ion channel (and other effects)

• Sweet and Umami taste 

  • Bonds to membrane receptors for sweet or umami

• Bitter taste 

  • Binds back to membrane receptors 

Olfaction 

• Odorants (odorous substances) stimulate olfactory sensory neurons (bipolar neurons), by binding to membrane receptors, which are proteins in the cilia of these neurons

• Axons of these neurons synapse onto olfactory bulb of brain 

• Olfactory tract (grouping of axons) carries afferent information from bulb to other brain areas (e.g., primary olfactory cortex for perception to occur

Vestibular System 

• Structures are in inner ear

• Sensation of:

  • Head position 

  • Head movement (Angular acceleration in 3 dimensions)

  • Linear acceleration 

Labyrinth of Inner ear 

• The vestibular system detects changes in the motion and position of the head. Bending of hair cells (modified epithelial cells that are sensory receptors) in otolith organs and semicircular canals results in afferent activity 

Vestibular Sensors: Otolith Organs

2 otolith organs, or maculae(singular; macula)

• Saccule and utricle

• Sense linear acceleration with respect to gravity (e.g., jumping moving side to side)

• Each sensor has a mass of otoliths (otoconia) (calcium carbonate crystals) on top of gelatinous substance

Otolith Organ: Linear Acceleration

Otoliths  

• (tiny stones) in the gelatinous substance that covers the hair cells in the utricle and saccule make gelatinous substance heavier

• When the head tilts forward, gravitational force causes the hair cells to bend, stimulating the sensory neurons that they synapse with 

Vestibular Sensors: Semicircular Canals

3 semicircular canals (FLuid-filled, endolymph)

• Sense angular acceleration of the head in the three dimensions of space (X-Y-Z) (e.g., head rotation, nodding), to maintain balance 

• Each canal has a crista (sensory organ, in ampulla)

• Each crista has a gelatinous mass, a cupula, on top, which is pushed by endolymph movement

Cupula in Semicircular Canals: Angular Acceleration

During head rotation 

• Movement of endolymph bends cupula

The position of the cupula in the semicircular canal is such that fluid movement causes the cupula to bend, stimulating the hair cells

Auditory System 

•  Sound results from vibration of gas, liquid, or solid molecules

• Sound waves are zones of atmospheric refraction (low pressure) and compression (high pressure)

  • Sound waves that reach the ear cause movement of auditory structure, which is eventually transduced into action potential 

• Intensity:

  • Amplitude of sound wave, determines loudness

• Frequency:

  • Number of cycles per second of the sound wave, determines pitch ( higher frequency = higher pitch)

The Ear

•  The pinna and external auditory meatus (canal) focus sound waves on the tympanic membrane (eardrum), which rocks the malleus, incus, and stapes. The stapes is attached to the oval window of the cochlea

The Middle Ear

• The vibrations in the stapes are transmitted to the oval window, causing ripples in the cochlear fluid

Audition 

• Tympanic membrane -> ossicles -> oval window -> movement of fluid in cochlea -> vibrations in basilar membrane (tonotopic map)

• Movement of fluid in cochlea -> shearing between basilar membrane & tectorial membrane (both in organ of Corti, in cochlea), bending hair cells in organ of Corti to depolarize them 

  • Organ of Corti = basilar membrane + hair cells + tectorial membrane 

• Depolarization -> APs in sensory neurons (afferent signals)

Organ of Corti 

Audition 

• The organ of Corti is where auditory transduction occurs in the cochlea

• Ripples in the cochlear fluid mice and bond the hair cells to bend them, causing depolarization (due to opening of ion channels))

• This causes NT release and afferent signals to CNS

Sound Analysis

• Low frequency components causing large vibrations in the apical(“at the top”) cochlea 

  • Low pitched sounds (500Hz)

• High frequency components of complex sounds cause large vibrations in the basal (“at the bottom”) cochlea 

  • High pitched sounds (20,000 Hz)

• Pattern is called tonotopic = arranged by frequency

Visual System 

Light 

• Light is reflected from objects in the environment 

• Light has wave-like property

  • Wavelength, the distance between two peaks, is measured in nanometer(nm)

  • Wavelength corresponds to color

  • The visible spectrum is appx. 400-700 nm in humans 

The Electromagnetic Spectrum 

• These wavelengths constitute the stimuli transduced by the human visual system 400 to 700 nm is the visible spectrum 

• Visible light 

Three Layers (Tunics) of the Eye 

• Fibrous Tunic (outer connective tissue layer)

  • Slera: 

    • White;

      • attachment of muscles that move eyeballs

  • Cornea: 

    • anterior region of sclera; 

      • clear transmission of light 

• Choroid (beneath sclera)

  • Pupul:

    • Anterior opening for light entry into the eye

  • Iris 

    • Pigmented muscle around pupil

      • For pupillary dilation (expansion) and construction (narrowing) 

  • Uvea 

    • Blood vessels

  • Ciliary muscle 

    • Lens accommodation (changes lens shape to focus image of brain)

• Retina (posterior of eye; extension of brain 

  • Photoreceptors

    • Rods and cones for phototransduction

      • Other neurons

• Fovea

  • Small region in retina w/highest concentration of cones

  • Greatest visual acuity (resolution)

• Optic Nerve

  • Myelinated axons of ganglion cells in retina 

  • Afferent signals from eye to brain 

• Blind spot 

  • Exit point for optic nerve 

  • No photoreceptors

• Accommodation 

  •  Changing of lens shape to focus on retina 

  • Far vision: flattened lens

  • Near vision rounded lens

Eye Anatomy 

• Visual transduction occurs in the retina and is based in the image focused there by the camera and the lens

• Due to the optics of the lens images formed on the retina are upside down and are only a small fraction of the objects actually size

Accomodation & Ciliary Muscle 

Accommodation 

• Processes associated with the eye’s ability to change its focus. This involves a change in the shape of the lens to focus the light on the retina

• Results from 

  • Results from the contraction or relaxation 

• For distance objects, relaxation of ciliary muscle places tension on suspensory ligament

• At sida=tand contract, reduce rt

• Corrective Glasses 

  • And contact lenses alter the location of image focus to correct problems for eyeball length (and lost elasticity in the lens of the eye)

• Corrective glass contact lenses alter the location of image focus to correct the problem of eyeball length

Retinal Layers

• Light penetration past ganglion, bipolar, and other cells in the retina occurs to tranduction by the rods and cones

  • Fibers of optic nerve, ganglion cells, Amacrine cells, Bipolar cells, Horizontal cells, Photoreceptor cells, pigment epithelium 

  • Choroid layer

  • Sclera

Photoreceptor Cells of Retina 

• Activated when light produces chemical change in photopigment molecules

• Rods

  • Most sensitive photoreceptors

  • Black and white vision 

  • Vision in dim light

• Cones

  • Color vision (red, gree, & blue sensitivity)

  • High resolution vision (fine detail, fovea)

Color Vision 

• Each of the three types of cones has a photopigment that absorbs light in a specific range of wavelengths. 

  • In dim light, only rods respond

Visual Pathways

• This is the neuroanatomical pathway responsible for processing visual information. Signals from the eyes are eventually processed in the visual cortex of the brain 

Ch 12

Muscle

Muscle Cell types

• Skeletal (attached to bones)

  • Stiated, voluntary (somatic)

  • Striations (“Stripes”)are based on the ordered attunement of myofilaments in the cell cytoplasm (sarcoplasm)

• Smooth (in organs and skin)

  • Not striated , involuntary (autonomic)

• Cardiac (in heart) 

  • Striated, involuntary (Autonomic)

Skeletal Muscle

Muscle Fibers

• Due to its long shape, a skeletal muscles cell is called a muscle fiber

• Can be up to 10-100 um diameter 

• Multiple nuclei go into a muscle fiber (resulting from fusion of multiple cells during development)

Muscle

• Multiple skeletal muscle fibers bound together with connective tissue

• Muscle is attached to bones by tendons, bundles of muscle is attached to bones by consisting of collagen fibers

  • Muscle contraction is tension on the tendon, which moves the bone at a joint

• Skeletal muscles typically contain many muscles fibers (single muscle cells grouped into fascicles(

• Each muscle fiber may contain myofibrils, which contain myofilaments

• Not fully striped but has blue bands under a microscope

Neuromuscular Junction 

• Motor neurons innervate sekelate music=kes 

• AP in motor neuron causes APO in muscle fibers

• AP in motor neuron causes acetylcholine (ACh) release into the neuromuscular junction 

• ACh binds to nicotinic ACh receptors (NAchR) in the music video and in the muscle fiber membrane and an AP occurs in the muscle fiber, resulting in contraction of the fiber 

• One motor neuron may innervate many muscle fibers

  • Called a motor unit 

Neuromuscular junction 

• The point of synaptic contact between the axon terminal of a motor neuron and the muscle fibers it controls 

  • Contractions follows the delivery of ACh to the muscle fiber

Motor Unit

• A single motor unit consists of a motor neuron and all of the muscle fibers it controls

• Each muscle contains hundreds of motor units, each of which has many muscle fibers

• Smaller motor units allow finer muscle control (fewer fibers per neuron)

Recruitment

• Process of increasing the number of motor units that are active in a muscle at any given time, as needed, to increase muscle tension 

  • Activation of more motor neurons (and motor units) leads to increased muscle tension 

  • Brain recruits more motor units until desired movement is accomplished in a smooth fashion 

  • More and larger motor units are activated to produce greater strength 

  • In the lab, we saw recruitment when we increased the stimulus strength 

Myofilaments in a Skeletal Muscle Fiber 

• Each skeletal muscle fiber is packed with myofibrils, extending the length of the fiber 

  • Myofibrils are packed with the myofilaments actin and myosin, which produce the striated appearance 

    • The interaction of the myofilaments causes muscle fiber contraction

Myofilaments

• Myofibril: cylindrical bundle of myofilaments, 1-2 um in diameter 

  • Its sections are called sarcomeres

• Striations in myofibril are due to the arrangement of thick and thin protein filaments (filament = “thread”

• Think filament (dark)

  • Myosin

  • Has two globular heads that form cross-bridges with actin during muscle contraction 

• Thin filaments (light)

  • Actin 

  • Troponin C (binds Calcium), T (binds Tropomyosin), I (binds Actin)

  • Tropomyosin (blocks myosin binding site on actin )

Sarcomere

Sarcomere

• (“flesh part”) is the basic contractile unit in striated muscle structure

  • It is a section of the myofibril 

  • Pattern of thick and thin filaments

  • Z discs are at each end.

  • Actin is anchored to Z discs

  • Myosin is anchored to Z lines by titin 

  • Notice the A bands and I bands

• The sarcomere is composed of thick filaments called myosin, anchored in place by titin fibers, and thin filaments are called actin, anchored bu z discs

• Cross-bridges form between myosin and actin during muscle contraction 

Muscle Contraction 

For contraction to occur, myosin must bind to actin to form cross-bridges 

• In a relaxed muscle, binding site in actin is blocked by tropomyosin(thin)

• Troponin (thin) holds tropomyosin in blocking position 

  • Troponin is a heterotrimer CTI

  • C binds Ca2+, T binds Tropomyosin, I binds Actin 

• Contraction: Muscle fiber depolarized. AP travels down the transverse tubules in fiber, resulting increase of  Ca2+ from sarcoplasmic reticulum in fiber

  •  Ca2+ binds to troponin C, then troponin T undergoes a conformational change which moves tropomyosin out of its blocking position, thereby allowing the myosin cross-bridge to bind to actin

  • During contraction, filaments slide past each other

• Contraction: activation of the force-generating sites in muscle fibers (i.e., the cross-bridges in myosin) to generate tension

• Sliding filament mechanism: when overlapping thick and thin filaments in a sarcomere move past each other to contract a muscle fiber

• Myosin (thick) binds to actin (thin), and slides it, pulling the Z-lines closer together, and reducing the width of the I-bands and H-bands

• Calcium is from the Sarcoplasmic reticulum

The Cross-Bridge Cycle

1. Resting fiber; cross bridge is not attached to actin

2. Cross bridge binds to actin

3. Pi is released from myosin head cousin conformational change in myosin 

4. Power stroke causes filaments to slide; ADP is released

5. A new ATP binds to myosin head, allowing it to release form actin

6. ATP is hydrolyzed and phosphate binds to myosin, causing cross bridge to return to its original orientation 

Excitation-Contraction Coupling 

Coupling of AP (excitation) with muscle contraction

• Transverse tubules (T-tubules) bring APs into muscle fiber

• This causes sarcoplasmic reticulum (SR) to release  Ca2+ into Sarcoplasm

•  Ca2+binds to troponin C, stimulating contraction 

• Latent period

• Period between AP and contraction (delay) 

• AP in fiber lasts 1-2 ms, and ends before contraction. (contractions can last 100+ ms.)

Muscle Relaxation 

• Following contraction, force-generating mechanisms cease, tension reduces and muscle relaxation occurs

  • Muscle cell membrane repolarizes, and calcium moves back into the SR

  • With calcium gone, tropomyosin covers the binding site, and the actin and myosin cease to interact which relaxes the myofibrils and thus the muscle fiber

Mechanics of Contraction 

• Tension 

  • Force exerted on an object by contracting muscle

• Load:

  • Force exerted on a muscle by an object 

    • Tension and load are opposing forces

• Twitch:

  • Mechanical response (contraction) of muscle fiber to single AP

• Summation:

  • Increase in muscle tension in a fiber, due to successive APs (or stimuli) occurring during contraction

• Recruitment

  • Increase in muscle tension in a fiber due to activation of more motor units or due to increase stimulation (increase voltage)

• Tetanus/Tetany: 

  • Sustained maximal contraction due to repetitive stimulation 

    • Ex: Crouching, Maintaining posture, holding up a heavy box 

Twitch & Stummation 

Twitch: a single stimulus to a muscle stimulates a muscle twitch 

• The latent period between excitation and development of tension in a skeletal muscle includes the time needed to release Ca++ from SR, move tropomyosin, and cycle the cross-bridges 

Summation: When successive APs occur during a contraction, there is an increase in muscle tension 

• The second stimulus occurs prior to the dissipation of elastic tension from the first stimulus (Ca++ hasn’t returned to SR), so there is summation 

Types of Contraction 

• Isotonic Contraction “Same tension”

  • Tension is constant while muscle length changes

  • Ex: lifting (shorten) or lowering (lengthen) a weight (bicep curls) 

  • Ex: pedaling a bike on flat surface, running up a hill, swimming freestyle

• Isometric Contraction “Same size”

  • Muscle develops tension but doesn’t change length 

  • Ex: holding a weight steady

  • Ex: Balancing on tiptoes, planking, holding bench press bar in same position, pushing constantly against concrete wall

Length-Tension Relationship

• Short sarcomere:

  • Actin filaments lack room to slide, so little tension can be developed

• Optimal-length sarcomere

  • Lots of actin-myosin overlap and planty of room to slide. Maximum tension 

• Long sarcomere (due to stretching)

  • Actin and myosin do not overlap much, so little tension can be developed 

Skeletal Muscle Fiber Types 

Slow-twitch fibers: Type I fibers

• Slower contraction (slower to reach maximum tension) 

• SLow to fatigue

• Rich blood suppply and more mitochondira

• Respond well to repetitive stimulation without becoming fatigued

• Found in postural muscles

Fast twitch fibers: Type IIx fibers

• Faster contraction (reach maximum tension quickly) 

• Fatigue quickly 

• Less blood supply and fewer mitochondria

• Found in stronger, heavily utilized muscles to jump or rn a short sprint (quick burst of strong activation)

Intermediate: Type IIA fibers

• Like fast twitch but wth more mitochondria

• Intermediate time to contract and to fatigue

• Respond quickly and repetitive stimulation, like muscles used in walking

Muscle Fatigue

Decrease in muscle tension due to previous contrctile activity (repedtad stimulation)

Some Proposed Causes:

• Conduction failure as a result of increased extracellular (k+) after many APs

• LActic acid buildip results in acidification of muscle tissue, denturing contractile proteins 

• Reduced ability of SR to release  Ca2+ prevents excitation-contraction coupling

• Depletion of muscle glycogen during low-intesnity, long duration muscle activity 

Cardiac Muscle

• Found only in heart

• Involuntary, regulated by autonomic nervous system

• Contracts spontaneously due to pacemaker cells

• Striated due to sarcomeres

• Troponin and tropomyosisn have similar function as skeletal muscle

• Contraction via sliding filament mechanism 

• Small cells, single nucleus

• Cardiace muscle cells connect bia gap junctions (electrical synapses) called intercalated disks

Cardiac Muscle Contraction 

• Ap propagated through T-tubules

• Depolarization is due to Na+ and Ca2+ influx through voltage gated channels

• Entering  Ca2+depolarized membrane and increases ( Ca2+)

  • Triggers release of more  Ca2+ from SE

  • This is positive feedback!

• Then, thin filament activation, cross bridge activation, and force generation occur like in skeletal muscle

Excitation-Contraction Coupling in Cardiac Muscle

1. Stimulation causes NA+ and Ca2+ channels to open 

2. Stimulated the terlease of CA2+ from the SR

3. This Ca2+ binds to troponin C to stimulate contraction 

Smooth muscle

• Lacks striaction (“smooth’), myofibrils, and sarcomeres

• Small like cardiac muscle cells, single nucleus

• Found in blood vessel walls, bronchioles, digestive organs, urinary and reproductive tracts

• Cells are arranged in layers

• Involuntary; nerves are part of autonomic nervous system

• Cross-bridge movements between actin and myosin generate force

• Calcium ions control cross-bridge activity 

• Organizaiton of filimaents and excitation-contraction coupling are different than skeletal/cardiac muscle

Smooth Muscle Structure

• Thick and thin filaments interact to cause smooth muscle contraction 

Cross-Bridge Activation in Smooth Muscle

•  Ca2+ -mediated changes in thick filimates activate cross-bridges

  • There is no troponin C, so tropomyosin dosn’e block cross-bridge access to actin

•  Ca2+ comes from internal (SR) and external sources (ECF) 

  • Binds to calmodulin, which is similar to troponin

• Cross-bridges form between myosin and actin