exer 4 report - sensory pathways

8/4/2019 Exer 4 Report - Sensory Pathways

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SENSORY PATHWAYS IN MAN


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Introduction

Sensory system

part of the nervous system

consists of: sensory receptors

Neural pathways

Parts of the brain thatprocess the information


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Introduction

Sensory system

processed information that may or may notlead to conscious awareness is called sensory

information

if it does reach consciousness it is called asensation


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Introduction

Sensory system

A persons understanding of the sensation iscalled perception

for example feeling pain sensation; awareness

that your tooth hurts perception


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Introduction

Information about the environment exists in

different forms of energy

Pressure

light

Temperature

sound waves


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Introduction

Sensory system

Different energy forms are then changed intograded potentials that initiate action potential

which travel to the central nervous system


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Introduction

Sensory system

Energy that activates sensory receptors isknown as stimulus

A term for stimulus type is stimulus modality(heat, cold, sound, pressure etc.)


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Introduction

Stimulus transduction

The process by which a stimulus is transformed to an

electrical response known as stimulus transduction.

Stimulus transduction involves the opening or closing ofion channels

Adaptation

decrease in receptor sensitivity, results to decreased in thefrequency of action potential


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Introduction

Neural Pathways

Bundles of parallel, three-neuron chains for a

sensory pathway

Chains parallel to each other

Carry information to cerebral cortex for processing

Also called ascending pathways because they go

up the brain


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Introduction

Ascending pathway

two types:

1. Specific ascending pathways

Carry information about single types of stimuli Pass to the brainstem and thalamus, and final neurons and

go to different areas of the cerebral cortex

Exception olfactory pathway

2. Nonspecific ascending pathways

activated by sensory units of several types

They indicate that something is happening

Not specifying what or where


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Olfactory sensations

Least understood of all the senses

Smell and taste classified as visceral senses

Both taste and smell receptors arechemoreceptors

Stimulated by molecules in solution in mucus in

nose and saliva in mouth


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(Ganong, 2003)

(Guyton and Hall, 2006)


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Signal transduction

Odorant substance came in contact with olfactorymembrane

Substance diffused into mucus membrane Substance bound to a portion of the receptor

proteins in cilium membrane

Receptor proteins threads thru the membrane several

times folding inward and outward Odorant binds to the receptor protein that folds

outward

G-protein found on the inside of the folding protein


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G-proteins were excited, dissociating the alpha

subunit

Alpha subunit activated adenylyl cyclase, attached

to the inside of the ciliary membrane

Adenylyl cyclase converted ATP to cAMP

cAMP activated nearby sodium channels, opening

them Action potential was transmitted into the CNS by

means of the olfactory nerve (smell pathway has

no relay in the thalamus


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(Mader, 2001)


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The distance of the odoriferous substance to the

receptors determines the strength of the perceived

odor.

Concentration of odorant substance was high, thusmore of the substance binds to the receptors

The substance must be slightly water soluble so it

can pass thru the mucus

The substance must be slightly lipid soluble,

because lipid constituents of cilium are weak

barrier to non-lipid-soluble odorants


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Gustatory Sensations

Taste is mainly a function of the taste buds in

the mouth



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Primary sensations

Sweet sugars, glycols and aldehydes

Sour evoked by H+, this is why all acidstaste sour

Bitter evoked by alkaloids

Salty evoked by anions (schaum)


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Area of

tongue

Sweet Salty Sour Bitter

Tip + _ _ _

Sides _ + + +

Back _ _ _ +

Table 4.1 areas of tongue in which different tastesare detected


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Schaum,


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Form of sugar Time tasted (second)

Crystals 13

solution 3

Table 4.2 Time it takes for sugar to be tasted

Molecules were already

dissipated, readily stimulating the

taste buds


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Taste threshold the minimum amount a

substance in order to perceive a stimulus

whether pleasant or unpleasant

Different values for different substances

According to Despopoulous and Silbernagl (2003)

the taste threshold for table sugar is 10-2 mol/L


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Table 4.2 the concentration of table sugar before it can

be perceived

Concentration of table sugar Perception to taste*

0.5 % -1.0 % -

5.0 % +

10.0 % +

25.0 % +

50.0 % +

* + reception of taste; - non reception of taste


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The sense of taste is influenced greatly bythe sense of smell.

The gustation and olfaction work together tolet the cerebral cortex interpret a certainstimulus.

Some particles of the odorants move to themouth region and excite the taste budspresent (Mader, 2004; Seeley, 2004).


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Food Placed on

tongue

Chewing (closed

nostrils)

Chewing (open

nostrils)

Carrot - - +

Banana - - +

Potato - - +

Onion - - +

Table 4.2 Sensations produced by four different foods

* + reception of taste; - non reception of taste


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Signal transduction

taste chemical binds to a protein receptor

molecule lying on the outer surface of thetaste receptor cell

Sodium ion channels opened

Na+

or H+

ion influx depolarization Transmission of action potential


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Pathway

Taste receptors from the anterior 2/3 of the tongue generateaction potential that pass thru the

1. lingual node,

2. chorda tympani3. facial nerve, CN VII

4. Tractus solitarius

Posterior 1/3 of the tongue, (circumvallate papillae). APtransmitted thru

1. Glossopharyngeal nerves, CN IX2. Tractus solitarius

Base of tongue

Vagus nerve, CN X

Tractus solitarius


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Pathway

Note that all taste fibers synapse at thenuclei of the tractus solitarius

Second order neurons were sent to ventralposterior medial nucleus of the thalamus

third order neurons were transmitted to thelower tip of the postcentral gyrus in pareital

cerebral cortex perception was formed, identification of the

taste (bitter, sweet, sour, or salty)


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Salivary reflex

Conditions Volume (ml) pH

Normal 7 7

With vinegar 6 8

After 10 minutes 6 7

Table 4.4 Amount and pH of salivary secretions are different

concentrations


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SALIVATION: SYMPATHETIC

from the superiorcervical ganglia

Towards the bloodvessel walls to the

salivary glands

Thicker saliva

(Guyton, 2006)


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SALIVATION: PARASYMPATHETIC

bodies of the secretomotorneurons lie in the salivatory nucleus

situated adjacent and medio-

ventral to the solitary nucleus

Efferent axons from the salivatoryneurons travel in the facial (VII) and

glossopharyngeal (IX) nerves

Salivatory neurons with axons inthe facial nerve are situated in the

superior salivatory nucleus,whereas salivatory neurons with

axons in the glossopharyngealnerve are situated in the inferior

salivatory nucleus

The axons from the salivatoryneurons (preganglionic) synapse ina peripheral ganglion, which givesrise to postganglionic fibers that

synapse on the salivary gland acinarcells

The inferior salivatory nucleusinnervates the parotid and vonEbners (lingual) salivary glands.The superior salivatory nucleus

controls the sublingual andsubmandibular salivary glands

Watery saliva (Bradley and Kim,2007 )


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Auditory Sensations

Sound

is an energy transmitted thru a medium

solid liquid or gas in a vacuum, there is no sound

Sound source

anything that can disturb molecules toproduce sound

vibrating instruments e.g tuning fork


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Auditory Sensations

When the tuning fork was struck air molecules were

disturbed forming:

zone of compression

molecules are close together, high pressure

;and zone of rarefraction

molecules are farther apart, pressure low

Molecules travelled thru air...


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Auditory Sensations

Sound transmission

Sound waves enter external auditory canal

Air molecules push against the tympanicmembrane, causing it to vibrate at the same

frequency

Inner ear (malleus, incus, stapes) multiplies the

pressure about 20 times

Oval window transfers pressure to cochlea


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Auditory Sensations

Signal transduction

Specialized cells in organ of corti called hair

cells(mechanoreceptors)

hair cells have stereocilia that transform

pressure into action potential

Once the stereocilia is bent, ion channels are

opened; there is influx of ions; propagation of

action potential


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Auditory Sensations

Signal transduction

The depolarization of the hair cell caused the

release of neurotransmitter glutamate

Glutamate binds to the afferent neurons that

form a synapse with the hair cell

Action potential propagated to the cochlear

nerve


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Auditory Sensations



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Auditory Sensations

Signal transduction

The depolarization of the hair cell caused the

release of neurotransmitter glutamate

Glutamate binds to the afferent neurons that

form a synapse with the hair cell

Action potential propagated to the cochlear

nerve


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Auditory Sensations

Sound localization

Determination of the direction from which a

sound emanates in the horizontal plane

depends upon detecting the difference in time

between the arrival of the stimulus in the two

ears


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Auditory Sensations

Pathways



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Auditory Sensations

Conduction of sound waves

1. Ossicular conduction

2. Air conduction

3. Bone conduction


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Auditory Sensations

Kinds of deafness


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Auditory Sensations

Table 9-1. Common tests with a tuning fork to distinguish between nerve and conduction deafness.Weber Rinne Schwabach

Method Base of vibrating tuning fork

placed on vertex of skull.

Base of vibrating tuning fork

placed on mastoid process until

subject no longer hears it, then

held in air next to ear.

Bone conduction of

patient compared with

that of normal subject.

Normal Hears equally on both sides. Hears vibration in air after bone

conduction is over.

Conduction

deafness

(one ear)

Sound louder in diseased ear

because masking effect of

environmental noise is absent

on diseased side.

Vibrations in air not heard after

bone conduction is over.

Bone conduction

better than normal

(conduction defect

excludes masking

noise).

Nerve

deafness

(one ear)

Sound louder in normal ear. Vibration heard in air after bone

conduction is over, as long as

nerve deafness is partial.

Bone conduction

worse than normal.


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VESTIBULO-COCHLEAR SYSTEM

proprioception and visual information

elements needed for equilibrium

pressure in the foot pad

determines whether weight is evenly distributed


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VESTIBULO-COCHLEAR SYSTEM

individuals with impaired balance system

maintain their equilibrium through visualsensation

any linear movement or rotation immediately

shifts the visual images of retina and such

information are relayed to equilibrium centers.

S O COC S S


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VESTIBULO-COCHLEAR SYSTEMSensory axons from the

vestibular ganglion pass through

the vestibular nerve to thevestibular nucleus, which also

receives input from several othersources, such as proprioception

from the legs.

Vestibular neurons send axons tothe cerebellum, which influences

postural muscles, and to themotor nuclei (oculomotor,

trochlear, and

abducens), which controlextrinsic eye muscles.

Vestibular neurons alsosend axons to theposterior ventral

nucleus of the

thalamus.

Thalamic neuronsproject to the vestibular

area of the cortex.


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Cutaneous sensations

Somatic sensation

skin, muscle, bones, tendons and joints

Distinct receptors for heat, cold, touch,pressure, limb position, movement and pain

Densely innervated parts: fingers, limbs, and

lips


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Touch

Mechanoreceptors

highly specialized nerve endings

encapsulated in elaborate cellular structures

Transmit mechanical tension in the capsule to ion

channels in nerve endings


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Skin mechanoreceptors (Vander, 2001)


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Pain p p p P Tactile t t x tp p x p t t x tp p p p t t t xx p p p x x x t

Hot h x x h Cold c x x ch h h h x x x ch h x x c x x xh h h h x x x c


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Pathways

dorsal column-medial leminiscal system

The dorsal columnmedial lemniscal system,carries

signals upward to the medulla of the brain the anterolateral system

Capable of transmitting broad spectrum of sensemodalities

In this exercise we were only concerned with thistype since it is the pathway for pain, thermalsensations and crude touch/tactile


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the anterolateral system



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Optical pathway

Photoreceptors:

Rods sensitive to dim light (scotopic

vision)

- photoreceptive pigment:

rhodopsin

Cones sensitive to bright light

(photopic vision) and color vision

- photoreceptive pigment: opsin


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Optical pathway

light cornea pupil lens

(light rays are refracted)

retina rods and cones (nerve cells)

optic nerve optic chiasma (2

optic nerves cross) optic tracts occipital lobe of the brain


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Optical pathway



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Signal Transduction

rod exposed to light

rhodopsin decomposes, decreases the rod

membrane conductance for sodium ions in

the outer segment of the rod

results to increased negativity of rod

membrane potential (hyperpolarization)

complete opposite of depolarization.


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Signal Transduction

Transmits signals to the plexiform layer where

it synapses with the bipolar and horizantal

cells

bipolar cells transmit signals to the inside of

the inner plexiform layer, where synapse with

the ganglion cells and amacrine cells

Ganglion cells transmit impulse from retina tothe optic nerve

Rhodopsin


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Rhodopsindecomposition



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influx of ions


dark condition (non

excited state)

slight influx of

sodium ions (slightdepolarization)

-40mv inside cell


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Optic Disk

axons of ganglion neurons extend posteriorly to a

small patch of the retina

devoid of any receptors

site where axons are formed into bundles and exitas the optic nerveBLIND SPOT

THIS REGION IS VOID OF PHOTORECEPTOR

NEURONS light cannot be perceived

no impulse conduction no image


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Refraction

when light travels through a transparent

medium of different density, like water

light bends

four refracting media of the eye

cornea

aqueous humor

lens

vitreous humor


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Refraction

bent light rays verge

forms an image at the retina VISION

lens adjust for distance in order to focus on

the retina

any adjustments of image in the retina

ACCOMODATION


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Near Point Accomodation

the closer an image to the eye the LENS

curve more light adjustments on the retina

there is such a distance between object andlight which is of the limits of the contraction of

the ciliary muscles bound to suspensory

ligaments to the lens IMAGE BEGINS TO BLUR


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Other ACCOMODATION mechanisms

sometimes, lens move toward the back of the

eye turning inside the nose

CONVERGENCE

dilation or constriction

FLASHING OF LIGHT CONSTRICTION

DARK ENVT. DILATION

PUPILLARY CONSTRICTION


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PUPILLARY CONSTRICTION

and DILATION

SYMPATHETIC and PARASYMPATHETIC NS

controls pupillary sphincter muscle

signals through them sent to the eye via THIRD

CRANIAL NERVE from THIRD NERVE NUCLEUS IN THE

BRAIN STEM


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light strikes retinaimpulses from optic

nervespre-tectal nuclei

secondary impulsespass thru Edinger-

Westphal nucleus

CONSTRICTION OFTHE IRIS


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VISUAL FIELD

entire vision that one sees out of each eye

bundles in certain regions of the eye can bedetermined by mapping the field of vision for

each eyePERIMETRY

assessed by Goldmann Perimeter


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Goldmann Perimeter

subject is allowed to stare at the center with

one eye closed

small object or light is moved slowly from

periphery to center of vision from many

directions

subject indicates whether light is seen or not

from the corner of the eye

blind spots can be assessed using the test


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Goldmann Perimeter

subject is allowed to stare at the center with

one eye closed

small object or light is moved slowly from

periphery to center of vision from many

directions

subject indicates whether light is seen or not

from the corner of the eye

blind spots can be assessed using the test

exer 4 report - sensory pathways

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