Human Phys Exam 2

what does it mean for a stimulus to be the adequate stimulus for a sensory receptor? provide several examples, using stimuli and sensory receptors that were discussed in class.

it refers to the specific type of energy/signal that’s most effective in activating a particular sensory receptor. ex. photoreceptors in the retina, mechanoreceptors in the skin (pressure), thermoreceptors in the skin (heat/cold), olfactory receptors in the nose

define adaptation as that term is applied to sensory receptors and distinguish between phasic and tonic sensory receptors using the characteristic of receptor adaptation

when a sensory receptor responsiveness to a stimuli changes over time when a stimulus is constant

phasic sensory receptors

adapt rapidly to a constant stimulus, but response diminishes quickly if the response is constant (clothes on skin)

tonic sensory receptors

adapt slowly, if at all, to a constant stimulus, continuing to respond as long as stimulus is present and responsiveness does not decrease significantly over time (pain receptors)

phasic sensory receptor examples

Meissner’s corpuscles and Pacinian corpuscles

Meissner’s corpuscles

fingertips and lips, quickly respond to light touch with a burst of nerve impulses but rapidly adapt to pressure making them highly sensitive

Pacinian Corpuscles

deeper in skin responding to deep pressure, fond in connective tissue of feet and hands, generate a strong response but adapt quickly to sustained pressure, allowing them to detect transient mechanical events like rapid skin deformation

tonic sensory receptor examples

nociceptors and baroreceptors

nociceptors

detect pain (extreme heat, intense pressure, tissue damage), exhibit little to no adaptation, they continue to fire action potentials for the duration of the stimulus, providing a constant signal of pain to the brain, ensuring an immediate and sustained response to potential harm

baroreceptors

in walls of blood vessels and heart, monitor blood pressure, continuously providing feedback to the brain about blood pressure changes, helping the body regulate blood pressure by adjusting heart rate and blood vessel contraction/dilation as needed to maintain homeostasis

ionotropic receptors

ligand-gated ion channels, directly allowing ions to flow across th4e cell membrane upon binding to a ligand (neurotransmitter/sensory stimulus), resulting in a rapid response

ionotropic receptor examples

ionotropic gustatory receptors taste receptors - binding of taste molecules to ionotropic receptors triggers the flow of ions into the taste receptor cells, initiating an electric signal

ionotropic mechanoreceptors - in the hair cells of the inner ear, mechanical displacement of hair bundles in response to sound waves opens ion channels allowing for the influx of ions and generating electric signals

metabotropic receptors

G-protein coupled receptors, when activated by a sensory stimulus/ligand, they initiate a cascade of intracellular events through second messenger systems, leading to a slower, but more prolonged, cellular response

metabotropic receptor examples

olfactory receptors - metabotropic G-protein response receptors in olfactory receptor neurons; odorant binding to metabotropic receptors activates a signaling pathway through G-proteins, ultimately leading to changes in membrane potential and the transmission of olfactory signals to the brain

metabotropic photoreceptors - in rod cells, when exposed to light, metabotropic receptors (opsin) activate G-protein signaling cascade that results in changes in membrane potential, ultimately leading to the transmission of visual information to the brain

how is stimulus intensity encoded by sensory neurons and transmitted to the central nervous system?

stimulus intensity is encoded through population coding (brain using input from multiple receptors to calculate location/timing of a stimulus), frequency coding (the frequency of action potentials encodes the strength/intensity of a stimulus), receptor types, adaption, and different pathways

what is referred pain and how is this sensation generated?

when pain is felt in an area of the body that is different from where the actual source of pain is, due to the convergence of sensory nerve pathways from different regions in the body onto the same neurons in the spinal cord/brain

referred pain examples

kidney stones - pain is referred to the groin area/lower abdomen on the same side of the kidney stone because the kidney and groin share common pathways in the spinal cord

gallbladder/liver pains - pain is referred to the right shoulder/scapula because they share common pathways to the brain

pain

nociceptors, free nerve endings

fine touch/rapidly adapts

meissners corpuscles, complex receptor

fine touch/doesn’t rapidly adapt

merkel cells, complex receptors

deep pressure/rapidly adapts

pacinian corpuscles, complex receptors

deep pressure/doesn’t adapt

ruffini corpuscles, complex receptor

vision

photoreceptors (rods and cones), special senses

hearing

hair cells (cilia), special senses

balance and equilibrium

hair cells (in cochlea), special senses

taste

taste buds, special senses

position of body (proprioception)

muscle spindles (for muscle length) and golgi tendon organs (for muscle tension), complex receptors

sweet taste

metabotropic receptor

salty taste

ionotropic receptor

sour taste

ionotropic receptor

umami taste

metabotropic receptor

bitter taste

metabotropic receptor

hearing

sound waves enter the ear and cause vibrations of the tympanic membrane (ear drum), vibrations are transmitted through ossicles (ear bones) reaching the cochlea, hair cells with cilia are responsible for transduction - sound-induced vibrations cause cilia to bend, activating mechanically gated ion channels and generation of electrical signals which are transmitted to the auditory nerve and information is relayed to the brain

equilibrium

vestibular system in the inner ear contains hair cells within the semicircular canals and otolithic organs, movement changes in head position cause the displacement of hair cells and bending of cilia, mechanically gated ion channels open leading to generation of electrical signals, information about head movement and orientation is transmitted via vestibular nerve to the brain

taste

taste buds contain taste receptors, taste receptors have specialized receptors for different taste qualities, when tastings (taste molecules) interact with taste receptors, signal transduction pathways are initiated, activation of metabotropic receptors (besides salty) results in release of neurotransmitters, stimulating primary sensory neurons to transmit taste information to the brain

smell

olfactory receptors contain specialized receptors for various odor molecules, when odorant molecules bind to olfactory receptors, signaling cascade is initiated leading to a generation of electrical signals, which are transmitted along the olfactory nerve to the olfactory bulb, then to higher brain regions for odor perception

vision

photoreceptor cells (cones and rods) transduce light, when light enters the eye and strikes photoreceptor cells, it causes a change in the photopigments within these cells, resulting in the activation of photoreceptor cells and generation of electrical signals, signals are processed by other retina cells and information is sent via optic nerve to the visual cortex

name at least one clinical pathology that directly results from disruption of sensory transduction

conductive hearing loss - blockage of ear canal, damage to ossicles, tympanic membrane perforation

dorsal column-medial lemniscal pathway

sensory modalities: fine touch, proprioception, vibration

receptor type: mechanoreceptor

function: responsible for precise, coordinated movement and spatial orientation

anterior spinothalamic pathway (anterior tract)

sensory modalities: crude touch and pressure

receptor type: mechanoreceptor

function: responsible for general awareness of tactile stimulation

lateral spinothalamic pathway (lateral tract)

sensory modalities: pain and temperature

receptor type: nociceptors

function: alerting the body to potentially harmful stimuli and changes in temperature

spinocerebellar pathways (anterior and posterior)

sensory modalities: proprioception, muscle spindles, glogi tendon organs

receptor type: joint receptors

function: coordinate fine-tuning motor activities and maintaining balance and posture

primary somatosensory cortex

postcentral gyrus

visual cortex

in the occipital lobe

gustatory cortex

in the insula (cerebral cortex)

primary auditory cortex

superior temporal gyrus

simple monosynaptic reflex arc

stimulus —> receptor —> sensory neuron —> spinal cord (one synapse) —> efferent neurons —> target cell —> response

what is the muscle spindle and how does it work in deep tendon reflexes? what is gamma neuron co-activation used for?

its a specialized sensory receptor in skeletal muscles, plays a huge role in proprioception, keeping tension on the tonically active sensory receptor, exciting the intrafusal fiber; occurs when extrafusal fiber is stimulated via alpha motor neurons

monosynaptic neuron

one synapse, faster than polysynaptic (ex. knee jerk)

polysynaptic neuron

2+ synapses, involves groups of interneurons (ex. crossed-extensive reflex)

corticobulbar tracts

cranial nerve motor output, decussation in brain stem, synapse onto motor neurons in cranial nerve motor nuclei (lower motor neuron)

lateral corticospinal tracts

85% decussate in medulla oblongata, pyramids, synapse onto alpha motor neurons in anterior horn

anterior corticospinal tracts

15% of pyramidal cells descend on ipsilateral side, decussate in spinal cord, synapse onto alpha motor neurons in anterior horn

what does ‘extrapyramidal’ mean when it refers to origin and type of motor control

does not travel through the pyramids in the medulla oblongata, responsible for regulating muscle tone, postural control, coordination movement, and subconscious/conscious movement (overall motor function control, ensuring smooth movements)

what is the ‘general function’ of motor control centers (both pyramidal and extra-pyramidal)?

they contribute to motor control by allowing the body to move in a coordinated, balanced, and controlled matter (not twitching when moving)

what brain centers are used in directing conscious (or voluntary) activity? generally, what are the major steps in taking conscious action?

you have your idea (cerebellum, cortical association areas, basal ganglia), then initiating movement (motor cortex), then executing your movement (cerebellum and movement)

ALS

degeneration of upper and lower motor neurons and destruction of motor neurons causes atrophy of muscle

parkinsons disease

loss of cerebral nuclei inhibition (upper motor neurons), increase in muscle tone, opposing muscle groups don’t relax, jerky movements, conscious movement result

describe the anatomy of the neuromuscular junction including the motor end plate, transmitter involved, the receptor type involved, and the specific location of receptors and other ion channel elements in the postsynaptic cell membrane.

motor end plate- post-junctional folds, designed to transmit and receive neural signals

neurotransmitter - ACh released when action potential reaches the end of the neuron

receptor type - nicotinic ACh and voltage-gated Na+ channels

location - nAChR clustered close to the ACh release area at the TOP of post-junctional folds, Na+V channels at BASE of post-junctional folds

myathenia gravis

self recognition and destruction of nAChR autoimmune disease (droopy eyes, double vision, fatigue, weakness) treatment is using acetylcholinesterase inhibitors

sarcolemma

“muscle coding”, plasma membrane

sarcoplasmic reticulum

smooth endoplasmic reticulum

sarcoplasm

cytoplasm; contains mitochondria and glycogen granules

myofibril

bundles of contractile and elastic proteins (contract and relax)

contractile filaments

protein structures within muscle cells - actin (thin) and myosin (thick)

transverse tubules

contiguous with sarcolemma, enables action potential to propagate through the cell

terminal cisternae

longitudinal tubules with enlarged and regions (in sarcoplasmic reticulum)

triad

a t-tubule and its 2 flanking terminal cisternae

z-disks

define a “sarcomere”, where actin (thin) attach

I-band

lightest band, Z-disk running down center, made of actin

A-band

thick filaments (myosin)

H-zone

only thick filaments, bands change size when contracting

M-line

attachment point for thick filaments, made of accessory proteins

zone of overlap

overlapping of actin and myosin

actin

attaches at z-line, thin filaments

myosin

attaches at the M-line, structural tail region, head region is a catalytic function: ATPase, pivots, binds to actin

nebulin

structural support for actin, not elastic, “inside” sarcomere

tinin

large protein, provides elastic rebound from contraction, Z-M line attached (sping-like)

G-actin

subunits tropomyosin and troponin “on-off switch”

F-actin

G-actin molecules polymerize to form long chains of this

how do myosin subunits form myosin filaments

myosin heads interact with actin, forming cross-bridges and pulling the actin filaments toward the center of the sarcomere, this sliding of actin and myosin filaments leads to muscle shortening and contraction

what is the function of the actin binding site and the ATPase in cross bridge cycling and where are they located in the myosin molecule?

the actin binding site causes the sarcomere to shorten, ATPase activity of myosin hydrolyzes ATP, inducing myosin head pivoting (energy for movement from ATP hydrolysis)

describe what molecule binds to troponin and how tropomyosin is positioned on the thin filament at rest.

Ca2+ binds to troponin, leading to a conformational change in troponin, causing tropomyosin to move away from the binding sites on actin, allowing the myosin head to connect to actin

tinin

large protein, provides elastic rebound from contraction, Z-M line attached

nebulin

provides additional structural support for actin thin filaments, not elastic like titin

describe the sequence of events that occur during one complete cross-bridge cycle period

Ca2+ gets released into the sarcomere, binding to troponin, changing its shape and signaling tropomyosin to expose the binding sites, myosin heads attach to the binding sites so myosin heads can bind to actin, then ATP binds to the myosin heads, Pi dissociates turning ATP into ADP + Pi, then myosin head detaches from actin and initiates a power stroke, causing actin filament to move

describe the detailed sequence of events that occur during excitation-contraction coupling.

there is a generation of an action potential at the motor endplate, then it propagates through t-tubules, then the action potential couples between voltage-sensitive DHP Ca+ channels in the t-tubules and the ryanodine receptor in the sarcoplasmic reticulum causes Ca+ channels to release, then cross-bridge cycling can occur

isometric contraction

when a force of contraction is less than force applied to muscle, contraction force is maximal, muscle length doesn’t change

isotonic contraction

when a force of contraction is greater or less than force applied to the muscle

subthreshold

no contractile response

threshold

stimulus causing contractile response

submaximal

stimulus causing greater contraction strength than threshold, but not the greatest tension produced

maximal

stimulus causing greatest contraction strength

submaximal

stimulus causing greater contraction strength than threshold, but not the greatest tension produced

supramaximal

larger stimulus than maximal; contraction strength no larger than seen with maximal stimulus

summate

adding together

treppe

“steplike” rise in muscle tension (maximal tension)

incomplete tetanus

maximal tension not reached

complete tetnus

stimulation frequency is high enough, no relaxation between stimuli

describe the relationship between the length of a skeletal muscle fiber prior to stimulation and the amount of tension that it can develop after stimulation. what does optimal length mean?

it directly affects the amount of tensions it can develop. the optimal length is the resting length at which the muscle can generate the most force, allowing for the ideal between actin and myosin filaments, optimizing the formation of cross-bridges and force population