Neuro Exam 2

What does the somatosensory system control?

touch, pressure, vibration, temperature, position of body in space

What are the main receptors of the somatosensory system?

mechanoreceptors

• require mechanical stimulation to produce receptor potentials

What is the order of the vertebrae?

cervical, thoracic, lumbar, sacral

Do we relay sense of touch or pain faster?

touch; touch coal in fire we pull hand back first before we sense the pain due to touch response

What is the afferent axon type order from most myelinated to least?

Ia, II, AB, Ao, C

What are the two most important afferent characteristics of the somatosensory system?

1. axon diameter

2. receptor fields

What happens when the viscinian corpuscle is pushed?

• Before its pushed the ion channels are closed and sodium ions are high outside of afferent

• After pushing, the channels open and the membrane becomes stretched. Ions move through channels

What is a receptor field?

area that a mechanoreceptor is responsible for

What is two point discimmination?

• interstimulus distance required to perceive two simultaneously applied stimulus as distant

• dictated by the number of afferents, more afferents means smaller two point discimmination

What do mechanoreceptors need to produce receptor potentials?

• they require mechanical stimulation

• need to be physically displaced

• only exception is pain; pain= free nerve endings

• all receptors controlling body position in space are governed by mechanoreceptors

What characteristics are the same between axon diameter and conduction velocity?

diameter and CV

What is adaptation?

how long before a receptor stops responding to the presence of a stimulus

What are alpha motor neurons responsible for?

bulk muscle movements

What do gamma motor neurons do?

tweaking tension in muscle spindle to interpret level of stretch

What do proprioceptors do?

relay stretch information and receive motor signals

What does ipsilateral, contralateral, and decussation mean?

ipsilateral means same side, contralateral means other side, and decussation means crossing midline

What is the main mechanosensory pathway?

first order neuron rises up spinal cord on ipsilateral side, innervates 2nd order neuron in medulla

• gracilenuclus- lower body

• cuneutenucleus- upper body

2nd order neuron crosses over midline of body, travels up to thalamus in medial lemniscus to innervate 3rd order neuron

• ventral posterior lateral lobe of thalamus (VPL) is where it travels up to thalamus

3rd order neurons take to primary somatosensory cortex

What Brodmanns area is SI?

1, 2, 3a, B

What Brodmanns area is the posterior parietal cortex?

5 and 7

What Brodmans area is SII?

40

Who was Penfield?

• Canadian American neurosurgeon

• 1930’s: mapping SI

• exposed brain during surgery and apply stimulus to map where stimulus reached which part of the cortex

homunculus

• little man

• represents the relative proportion of the somatosensory cortex dedicated to the information of the human body

What is the responsibility of the amygdala?

emotions and fear

What is the responsibility of the hippocampus?

learning and memory

What is the pain receptor?

nocireceptor

• percieve a stimulus as harmful

three components of pain and temperature

1. discrimmitive- type? sharp, dull, achey, etc.

2. affective- emotion? level of fear, anxiety, etc.

3. motivational- avoid or go for it? athletes

What are thermoreceptors?

percieve temp changes, quick and sustained

What are nocireceptos?

percieve pain, delayed and exponential

Are thermoreceptors and nocireceptors myelinated?

no, they are free nerve endings that are lightly myelinated or not myelinated at all

Can you explain the responses to a paper cut?

First pain response at the Ao fiber

• myelinated and pretty big, low Tau and high conduction velocity

Second pain response at the C fiber

• unmyelinated, slower

If Ao is removed, no pain response

What is transcient receptor potential?

Family of thermoreceptors

• TRP family

• TRP1: capsaicin (makes chili peppers hot), stimulates the receptors

• V stands for vanillinoid

• TRP desensitizes very easily

TRPM8 receptor

• senses cold pain

• menthol- stimulates receptor

• menthol desensitizes the pain pathways

Thermal receptors can overlap with the function of nocireceptors

Can you describe pain pathways?

1. afferents send signals to dorsal lateral neurons (1st order) in grey matter of spinal cord

2. 2nd order neurons- wide range dynamic neurons- recieve nociception and non-nociceptive afferents. “referred pain” (result of y neurons doing their job but not in a specific way

Angina

caused by lack of oxygen to the heart (pain in neck, upper back, and left arm)

Anterolateral system

ascending tract to relay pain to brain

Do you look at two point discrimination and temp on one side of body or both sides?

two point discrimination on one side and temp/pain on the other

Second pain response pathway

Second pain

• affective, motivational

• brain areas- reticular formation, reticular activating system (RAS)

• consciousness- arousal, attention, and vigilance

• allows us to be alert and awake

• life saving aspects in the medulla

• if you lose RAS you are done

cingulate cortex

limbic system

• tells pain and then says do not do it again

• organizes our behavior

What is the responsibility of the limbic system?

emotion, fear, expression

What are the two parts of the anterolateral system?

1. sensory-discriminative (first pain); ventral posterior lateral nucleus up to SI

2. affective-motivational (second pain); parabrachial to hypothalamus to amygdala to cingulate cortex

Pain Sensitization

Chemical and/or inflammatory mediators that increase sensitivity to pain

• bradykinin: mucus formation, coughing

• prostaglandin: inflammation

• histamine: inflammation, pain

• calcitonin gene related peptide (CGRP): migrain, CGRP antagonists- ubrevly

Allodynia

clinical condition where nonpainful stimuli cause painful sensations

• shingles- experience pain even when no pain

• phantom limb- lose limb but still perceive pain and sensations in this limb even when no limb

Gate theory of pain

gateway between sense of touch and sense of pain

• all enter through dorsal root of spinal cord

• aside from the gate theory, there are so many ways we can reduce pain to the CNS

Inhibitory local circuit neurons

Gate

• inhibit 2nd order neurons

• rubbing injuries alleviates some pain because you are desensitizing the 2nd order neuron

What current does pain go through?

descending

Retina

ganglion cells- axons exit the eye by way of the optic disk

uveal tract

choroid= increase melanin

sclera

outermost part of wall of the eye, continuous with cornea

ciliary body

muscles that control the shape of the lens- produces aqueous and vitreous humor

Iris

colored part- muscles that constrict or dilate the pupil; sphincter muscles (miosis); pupils constrict; radial muscles (medriosis) pupils dilate

Emmetropia

refraction sits directly on the retina

Myopia

refraction is in front of the retina (near sighted)

Hyperopia

refraction is behind the retina (far sighted)

Presbyopia

loss of accommodation (loss if focus from far to near)

• happens with age to all of us

Retina

• optic nerve- produces visual field deficit= scotoma

• no rods and cones found in the optic disk

• macula lutea- associated with the highest visual acuity

• fovea- cones only, foviola

Where is the highest concentration of cones?

Macula lutea

What part of the eye is all cones?

fovea

Five classes of cells of the retina

• photoreceptors- rods and cones, photo pigments, rods (rhodopsin), cones (coneopsin; red, green, blue), rods and cones make photo conduction=conversion of light wavelengths to receptor potentials

• bipolar cells- connect rods and cones to ganglion cells, inhibitory

• ganglion cells- form optic nerve, relay information

• horizontal cells

• amacrine cells

horizontal and amacrine cells communicate laterally to several ganglion cells, give luminance

Luminance

vision under a number of different contrasts

Are rods or cones more sensitive?

cones; sensitive to light in different wavelengths

Phototransduction

hyperpolarization is the form, decrease bipolar cell activity (inhibitory)= disinhibition

• net result- excitation of granglion cells

• hyperpolarization is caused by glutamate release (increase potassium ions)

What NT is inhibitory in the eye?

glutamate

scotopic

only involves rods in low light, rods are in the sides of eye

mesopic

both rods and cones contribute

photopic

just cones in indoor lighting, rods go away

Why does it get harder to see bright light?

you saturate cones through bleaching

Which part of the eye are cones and rods?

rods are on the side and cones are in the middle

Stephen Kuffler

“Father of modern neuroscience”

• vision expertise

• function if ganglion cells and their receptive field

• ganglion cells have receptive fields on retina, can respond to different light exposure

How does ganglion response differ in the eye?

the outside is the basline response and middle is the best response

Retinogeniculostriate pathway

optic chiasma- info from retinas crosses to other side (60%)

Where does the path from optic nerve lead to in retinal ganglion cells?

optic tract→ lateral geniculate nucelus (DLG)(thalamus)→ optic radiation (circuits)→ striate cortex (primary visual cortex, VI, Brodmans 17)

• thalamus sense info where it needs to go

What lobe is the primary somatosensory cortex and primary visual cortex?

primary somatosensory is in the parietal and primary visual is in the occipital

hypothalamus

suprachiasmatic mucleus (SCN)- circadian rhythms

Pretectum

midbrain (just anterior to pons) occulomotor nerve 3

• tectum- head movements

Oculomotor nerve

allows us to blink, causes pupils to constrict

• cranial nerve 3

What happens to images before we see them?

they get inverted and turned to a mirror image

Binocular visual field

• using two eyes, inverted tear shape

• section of retina on nose side (nasal)- decusses (crosses over optic chiasma)

• temporal sends axons on same side

What type of information includes VI

binocular

Macular sporing

retinal info from macula lutea still make it to VI

What happens when some gets hit with an axe and they lose an eye?

One side of the visual field is completely black and vision lost

• left eye- temporal, nasal

• right eye- nasal, temporal

anopsias

large visual field deficits

scotomas

small visual field deficits

What did David Hubel and Torsten Wiesel do?

“visual kings”

• saw that neurons recognize lines not dots

• tied cats down and made them look at dots and lines on the ceiling

• like lines more than dots, but motion more than lines

Organization of VI

• 6 layers- all layers communicate with one another up and down column

• primary cell type: pyramidal neurons- all except 4C

• 4C contains spiny stellate neurons, no pyramidal

• 4C receives info from thalamus

• second/third layer send info to what and where pathways

• 4A and 4B send info to what and where pathways

• 5 does eye control

• 6 sends info back to thalamus

How does info move out of VI

• transfer of visual info from VI to the what and where pathways

• V4- color info

• MT=V5- where, medial temporal (sends info to parietal lobe)

• V3- area where you add what and where together, interface between two pathways

Stereopsis

• depth

• visual info gets summed in V1 because two points on retina are providing visual info

diplopia

double vision

autostereogram

• everything built into picture

• take one picture and slightly offset it

The auditory system

• interpret sound

• amplitude (decibals, dB)

• frequency (Hertz, Hz)- humans 20 Hz

Tympanic membrane

• detects sounds, vibrations

• vibrations transmitted to middle ear bones (malleus, incus, stapes)

• cochlea (oval window)

Two skeletal muscles of the auditory system

1. tensor tymperi- cranial nerve IV (trigeminal)

2. stapedius- cranial nerve VII (facial nerve), smallest skeletal muscle

Nerves say to constrict muscles when there is sound

Bells palsy

inflame facial nerve to when it does not work anymore, droppy on one isde, cant regulate stapedius, any sound is harmful to them, protective ear gear

What frequency do humans hear well at?

2-5 Hz

Cochlea

• stapes interfaces with the cochlear base

• fluid filled tube with three compartments- transmit what stapes is delivering

• scala media and scala tympani contain the organ of corti (tectorial and basilar membrane)

• inner and outer hair cells (inner- 95% of afferents to auditory nerve; outer- receive significant efferent signals from auditory nerve)

What do outer hair cells do?

fine tune what inner hair cells hear

tinnitis

ringing in the ears; outer hair cells vibrating on their own

What part of the ear sends info to hear sounds?

stereocilia of inner hair cells

Where is high frequency and low frequency in the cochlea?

high is at the cochlear base and low is at the cochlear apex

What does the round window of the cochlea do?

ability to absorb fluid waves (off beat drum)

Inner hair cells

• mechanical transduction of fluid waves in cochlea to receptor potentials

• glutamate is the NT of inner hair cells

• depolarization caused by K+

• scala media and scala tympani are filled with potassium

• EPSP when K+ rushes in

• calcium channels detect depolarization and allows NT release

Auditory nerve (Cranial nerve 8)

• medulla

• pons- decussation point; superior olive (nucelus, medial and lateral)

• medial geniculate nucleus- activates both sides

• primary auditory cortex (AI, Brodmans 41)