lab 04: sensory systems

what is resting membrane potential in a human cell a function of

leak channels and Na+/K+ pump

how did we demonstrate membrane potential as a function of K+ flow

we used KCl

the potential difference is the result of the diffusion of only K+ across a selectively permeable membrane

concentrations of KCl

inside: 0.1 M KCl

outside: 0.01 M KCl

what is nernest equation used for

to calculate equilibrium potential, the voltage where an ion is at equilibrium

Eion = (61/z)log(Co/Ci)

what was the result for K+ at the end of the experiment

negative potential inside of cell

due to K+ ions moving from inside of the cell to the outside, through the semi-permeable membrane, leaving the inside of the cell more negative compared to the outside of the cell

why was the membrane potential was closer to the equilibrium potential for K+ (-61 mV) than it was to the equilibrium potential for Cl- (+61 mV)

the membrane was permeable to K+ and not Cl-

In the membrane potential experiment, was the inside of cell or the outside of thecell more negative? What does this tell you about membrane permeability?

The inside was more negative. Because K+ has a negative equilibrium potential (-61 mV), this tells us that the membrane was permeable to K+ and not Cl-.

reflex

involuntary movement which occurs almost immediately after a stimulus, and does not require conscious thought or higher brain input

reflex arc

neural pathway through spinal cord through which reflexes are elicited

monosynaptic arc

(simple reflex): 1 sensory neuron + 1 motor neuron

polysynaptic arc

1 sensory neuron + ≥ 1 interneuron + 1 motor neuron

knee-jerk reflex

a classic monosynaptic stretch reflex

sensory neuron synapses directly with a motor neuron, which causes contraction of the quadriceps

why is the knee-jerk reflex enhanced by the jendrassik maneuver

because it causes excitation of the spinal cord by decreasing inhibitory input

less inhibition = stronger reflex

accommodation reflex

causes changes in lens and pupil that allow light rays to properly focus on the retina, allowing us to view objects at different distances:

distant object

near object

mediated by parasympathetic NS

distant object

pupils dilate and lens flatten

near object

pupils constrict and lens rounds

describe the phenomenon of accommodation

Accommodation is the ability of the eye to change the shape of the lens depending upon the distance of a visual target

Flat lens for far vision (& pupils dilate = more light enters)

Round lens for near vision (& pupils constrict = less light enters)

how did we study accommodation

with Ingersoll eye model and astigmatism chart

emmetropia

normal vision

rays focus on retina

no correction necessary

hyperopia

farsightedness

rays focus behind retina

convex lens corrects farsightedness

myopia

nearsightedness

rays focus in front of retina

concave lends corrects nearsightedness

astigmatism

rays do not focus

uneven lens corrects astigmatism

how do corrective glasses and contact lenses work

by altering the location of image focus to correct for problems of eyeball length and lost elasticity in the lens of the eye

pupillary light reflex

constriction or dilation of pupil in response to light intensity changes

two-point discrimination

ability to detect two separate points

depends on the density of the cutaneous receptors in a speecific area of the body

do different areas of the body have different densities of cutaneous receptors

yes

where is two-point discrimination best at

fingertips where density of cutaneous receptors is greatest (greatest sensitivity)

referred pain

involves the confusion of sensory information entering the CNS at the same level of the spinal cord as another region of the body

how was referred pain experimented

ulnar nerve was stimulated with ice, but felt it in our fingers

how is cold stimulation of the ulnar nerve interpreted

it is interpreted by the CNS as coming from the peripheral areas innervated by that nerve i.e., the ring and little fingers

auditory system

we used an audiometer to measure hearing in each ear

for each ear, we measured the lowest decibel level (dB, loudness) at which we could hear each frequency (500 Hz, 1000 Hz, 2000 Hz)

vestibular system (balance)

detects changes in the motion and position of the head by use of fluid-filled tubes:

semicircular canals and otolith organs

semicircular canals

filled with fluid (endolymph)

each ampulla contains a crista (sensory epithelium)

detect angular acceleration of the head

otolith organs

saccule and utricle

each has a macula (sensory epithelium)

detect linear acceleration of the head

nystagmus

rapid movement of the eyes, back and forth, as a result of vestibular simulation (rotation of the head) of the semicircular canals

example of nystagmus in lab

rapidly spun around in a barany chair for 10 rotations, abruptly stopped, and the eye movements observes are nystagmus

What are the sensory cells for vision called? For hearing? For balance?

vision: rods and cones

hearing: hair cells

balance: hair cells

visual system

anatomical eye model

visual acuity and astigmatism studied using vision test charts on wall

ingersoll eye model used to study visual optics and function of lends

negative afterimage

colorblindness

blind spot

gustatory system

tested whether students could taste the PTC paper

chemosensation

activated by chemicals

taste buds

comprised of 50-100 specialized epithelial cells called taste cells

where are taste buds located in

lingual papillae (bumps on the tongue)

olfactory system

tested adaptation to various odors

a chemosensation

Why are gustation and olfaction considered chemical senses?

The stimuli that cause sensation of taste and smell are chemicals or molecules.

Many sensory systems have topographic maps. Vision & hearing are good examples. What is a topographic map?

A topographic map is an organization ofneurons in the brain that corresponds to asensory surface. Types of topographic maps: Retinotopic (corresponds to locations on retina) Somatotopic (corresponds to somatosensation in body)

Tonotopic (corresponds to frequencies of sound)