human phys exam 2

general scheme of CNS

• receive sensory inputs

• coordinate response of organs and functions of the body

surface area

• more connections between parts of cortex = greater x

  • also more wrinkly

• axons try to minimize distance btwn connected neurons

without gyrus

• local connections require long axons

within gyrus

• local connection use short axons

• long-distance still require long axons

frontal lobe

• voluntary motor control of skeletal muscles

• personality

• concentration, planning, decision making

• verbal communication

parietal lobe

• somatesthetic interpretation (cutaenous and muscular sensations)

• understanding speech & formulating words to express thoughts and emotions

• interpretation of textures and shapes

temporal lobe

• interpretation of auditory sensations

• storage/memory of auditory and visual experiences

occipital lobe

• integration of movements in focusing the eye

• correlation of visual images w prev visual experiences and other sensory stimuli

• conscious perception of vision

insula lobe

• memory

• sensory (mainly pain) and visceral integration

phineas gage

• personality changed after acident

• iron bar driven thru prefrontal cortex

somatosensory cortex

• located right behind central sulcus

• termination of sensory (touch) info coming from skin

• cortical neurons have receptive fields that correspond to receptive fields of somatosensory nerves that provide input

motor cortex

• located right in front of central sulcus

• cerebral neurons that initiate movement

• sending axons directly and indirectly to spinal motor neurons

homunculus

• little person

• topographic map of sensory input to somatosensory cortex and motor output of motor cortex

• parts of body w highest density of sensory receptors get a bigger share of the somatosensory cortex dedicated to processing

  • mouth big bc of tactile sensations for speech and lips and tongue as last line of defense

• parts of body w finest motor control (most muscles) get bigger share of motor cortex

brainstem

• monitors internal chem signals and controls autonomic function

  • breathing, heart rate, digestion

• carries out reflexive functions to respond to acute (immediate) changes in bodily function

  • postural changes in BP

hypothalamus

• integrator

• uses neural and endocrine signals to monitor peripheral variables

• controls long-term homeostasis by hormonal signals via pituitary gland or by neural outputs through the brainstem

• control center of autonomic ns along w brainstem

peripheral ns hierarchy

• sensory

  • sensing external environment

  • sensing internal environment

• motor

  • autonomic

    • parasympathetic

    • sympathetic

  • somatic

mechanoreceptors

• stimulus: mechanical force

• channels are pressure-gated and pop open when spindle/cytoskeleton is stretched

• ex: cutaneous touch and pressure receptors, vestibular apparatus, and cochlea

pain receptors

• stimulus: tissue damage

• ex: cutaneous pain receptors

chemoreceptors

• stimulus: dissolved chemicals

• smell and taste

phasic receptor

• fast-adapting

• respond well when stimulus first applied but then adapt

tonic receptor

• slow-adapting to stimuli

somatosensation

• mechanoreceptors that respond to touch/pressure on surface of the body

• sensory nerve responds proportional to pressure

• touch and proprioception cross over in brainstem

• temp and pain cross over right away at entry lvl in spinal cord

meissner corpuscles

• type of mechanoreceptor

• rapidly adapting (phasic response)

• cutaneous light touch w high rez

merkel discs

• type of mechanoreceptor

• slow adapting (tonic response)

• cutaneous light touch w high rez

ruffini endings

• type of mechanoreceptor

• slow adapting (tonic response)

• deep receptors responding to stronger force w less acuity

pacinian corpuscles

• type of mechanoreceptor

• rapidly adapting (phasic response)

• deep receptors responding to stronger force w less acuity

free nerve endings

• respond to temperature and painful stimuli

somatosensory receptive fields

• map to specific area on the body that dendrites of 1 neuron respond to

• density varies across body

  • fingers have highest = most sensitive

• small pt causes intense pressure over small area

• large pt spreads pressure over wider area

two touch discrimination

• maps out receptive field density

  • determines somatosensory acuity

• how far touch can be before detected as two points (2 diff neurons)

firing rate

• response to pressure

• more diffuse pressure, neuron doesn’t respond as well

monosynaptic stretch reflex

• stretch of patellar tendon > spindle stretch in quadriceps > firing of dynamic Ia afferent sensory nerves > x connection causes motor neurons to fire

  • afferent sensory input coming from spindle receptors

• reflex under control of brain

knee jerk steps

1. striking patellar ligament stretches tendon and quadriceps muscle

2. spindle fibers stretched, send impulses up sensory neuron into spinal cord on dorsal roots of spinal nerves

3. sensory neuron synapses onto alpha motor neuron in ventral horn that goes back down same nerve

4. alpha motor neuron releases ACh causing extrafusal muscle fibers to contract

5. contraction of muscle relieves stretch of its spindles, dec activity in spindle afferent fibers

descending corticospinal inhibition

• corticospinal input from cerebral cortex

• neuron from cortex synapses on interneuron that synapses on inhibitory neuron

• inhibitory neuron releases GABA onto presynaptic terminal of sensory neuron

  • even if impulses coming from sensory, IPSPs generated inhibit release of glutamate from AP

• spinal cord injury causes reflex to be stronger bc of lack of x

proprioception

• awareness of position of joints and limbs w/o looking based on stretching force

• crosses over in brainstem

cranial nerve

• sensory and motor nerves that come straight to and from the brain

spinal nerves

• 31 pairs that emerge from segments along spinal cord

• multiple somatosensory neurons gathered into single x

dermatome

• each spinal nerve innervates a single segment of the body

• damage to single spinal segment will affect corresponding x

• infections of peripheral nerves will affect specific x

• receptive fields of one dorsal root ganglia = x

  • ex: herpes zoster/chicken pox/shingles

  • ex: pain in heart transmitted as pain in left arm by DRG

somatotopy

• cortical neurons arranged in same topology as peripheral receptive fields on the skin

  • make up homunculus

feature extraction

• cortical somatosensory neurons have more complex receptive fields than just location

• neurons respond to orientation of pressure across multiple fields

• direction of movement of touch across multiple

• input of multiple peripheral neurons converge onto 1 cortical neuron

stereopsis

• ability to identify 3D shape of an object

• extracted by higher cortical areas

horizontal orientation neuron

• cortical extraction

  • gets raw input and takes out features from it

• stimulating x line of receptive fields

  • hardly responds to vertical despite overlap

• ex: is there smth pressing across palm in x direction

• neuron responding to multiple receptive fields that converge on

  • fires when all are stimulated; stationary stimulus

directional movement neuron

• feature extraction by cortical neurons

• responds to point of pressuring moving in certain direction

• neuron fires when specific order of receptive fields are stimulated

• ex: bug moving across

hair cells

• mechanoreceptor cells for audition and vestibular system

• not neurons, detect vibration and head acceleration

• contain kinocilia and stereocilia

utricle and saccule

• vestibular apparatus

• detect linear acceleration (gravity)

• using otoliths as inertial mass to detect gravity and starting/stopping linear motion

  • calcium carbonate crystals

  • mass bends hair cells and can sense head bending forward or back from acceleration

    • hair cells stimulate neurons

semicircular canals

• vestibular apparatus

• detect rotational acceleration in each of 3 planes

• sloshing of endolymph around canal

  • head spins & endo moves in opp direction

    • deforms cupula which bends hair cells

audition

• cochlea detects sound waves

endolymph

• fills ducts that connect inner ear

• high in K+ fluid, positive

outer ear

• composed of:

  • pinna/auricle

  • ear canal

• captures sound

middle ear

• transfer and amplify vibration to oval window

• consists of:

  • tympanic membrane

  • bones

    • malleus

    • incus

    • stapes

auditory system

• captures sound via outer ear

  • sends to middle ear where vibrations are amplified to oval window

• transmits to receptors

• transduction of sound frequency into spatial location to stimulate auditory nerve fibers

• receptive field tuned to characteristic freq

  • neuronal response reflects intensity of sound

• cranial nerve 8 projects to cochlear nucleus in brainstem

  • vestibulocochlear nerve

inner ear

• semicircular canals

• vestibular nerve

• cochlea

stereocilia

• tufted projections that stick to endolymph and gelatinous tectoral membrane and bend w vibration

• bending causes mem potential change and regulates release of NT onto afferent nerve

  • bending opens mechanically-gated K+ channels by tip link of neighboring x

    • K+ rushes into hair cell bc of high conc in endolymph

kinocilium

• one per hair cell located on apex

  • longer than surrounding stereocilia

• when stereocilia bend towards x, AP freq inc

• when x bends towards stereocilia, AP freq dec

vestibular system

• to maintain balance and maintenance of gaze/eye position and posture (skeletal position)

• requires 2/3

  • proprioception

  • inner ear

  • visual input

conflict hypothesis of motion sickness

• when inputs to vestibular system from 3 components don’t agree w each other

• causes dizziness and nausea

• ex: visual field steady but inner ear reports accelerations

sound frequency

• number of cycles per sec expressed in Hz

  • cycle: distance btwn successive compressed patches

nature of sound

• audible variation in air pressure

• range: 20-20k Hz

• pitch

  • high=high freq

• intensity

  • higher intensity louder than low

  • amp

vibration of basilar membrane

• vibration of oval window > vibration in perilymph > x

• response of x varies across its length

• low freq vibrates apex of cochlea

  • x is thicker

• high freq vibrates base of cochlea

  • x is thinner

• transduce sound frequency into spatial location

audition sequence

• tympanic mem vibrates ossicles

• amplify onto oval window

• vibration of oval window sends oscillations of fluid thru perilymph of scala vestibuli to apex of basilar

• vibration goes to perilymph of scala tympani back to base

• causes contraction of round window

• WHOLE PERILYMPH VIBRATING BUT ONLY BASE OF BASILAR MEM RESPONDS WHEN HIGH FREQ

• auditory input projects to mostly contralateral auditory cortex and some ipsilateral

basilar membrane

• apex responds to low freq

  • x is thicker

• base responds to high freq

  • x is thinner

• have hair cells that stick up into cochlear duct w endolymph and attach to tectorial mem

  • vibrated by sound

• as x pop up and down from vibration, stereocilia pops up and down opening or closing K+ channels depending on direction

frequency map

• depending on where hair cell is, responds best to diff sounds

  • no difference in them only location

• entire cochlea experiences every vibration

  • only hair cells that respond are those on basilar mem that respond to certain freq

tonotopic map

• on basilar membrane

  • 20-20k Hz range

  • position of hair cell maps freq they respond to

    • base responds to high

    • apex responds to low

• projected into brain

• 0.3% discrimination

  • can distinguish tens of Hz btwn sound; density of cells

receptive field in audition

• of neurons: is patch of basilar membrane it is sensitive to

  • position of hair cells in cochlea

• each auditory neuron responds best to characteristic frequency

cochlear implants

• reproduce function of basilar membrane and hair cells

• directly stimulate auditory nerve endings at appropriate point in cochlea to reproduce tonotopic mapping of missing hair cells

wernicke’s area

• higher level cortex that auditory cortex neurons send projections to

• extracts meaning from words

• integrate w vision

broca’s area

• higher level cortex that auditory cortex neurons send projections to

• generates speech via projections to motor cortex

• to move tongue, lips, and throat

mcgurk effect

• example of sound integration w visual information to change perception of syllable

fovea

• highest density of photoreceptors

• center of visual field w highest acuity

• one photoreceptor transmits to one ganglion cell, higher acuity

• unimpeding access to light, other receptors bend out of way

retina

• layer of photoreceptor cells (rods and cones), neurons, and ganglion cells at back of eye

• light passes through neural layers to reach photoreceptors

optic disk

• blind spot

• point where optic nerve (cranial 2) leaves eye and central artery & vein enter eye

• interrupts retina, no photoreceptor cells

pupil and lens

• constriction & dilation of pupil

• ciliary muscle contraction focuses lens on nearby objects

  • flips visual field projected onto retina

bipolar cells

• photoreceptors synapse onto x

• synapse onto ganglion cells

ganglion cells

• bipolar cells synapse onto x

  • input from bipolar modulated by horizontal cells

• axons project to brain via optic nerve (cranial 2)

photoreceptor cells

• rods and cones in back of eye in retina

  • detect photon

• synapse onto bipolar cells

peripheral vision

• less cones

• multiple photoreceptors transmit to one ganglion cell

  • lower acuity

touch pathway

1. stimulus & receptive field; pressure on cutaneous spot

2. mechanoreceptors at spinal nerve endings

3. dorsal root ganglion cell

4. spinal cord and brain via spinal nerves

auditory pathway

1. stimulus & receptive field; characteristic frequency of vibration

2. hair cell

3. spiral ganglion cell

4. brainstem via vestibulocochlear nerve 8

vision pathway

1. stimulus & receptive field

2. photoreceptor cell

3. retinal network; where visual processing begins

4. retinal ganglion cell

5. brain via optic nerve 2

rods

• contain light-sensitive photopigment ptn, rhodopsin

• grayscale, low-light level

• night vision

• peripheral vision

• have cGMP-gated Na+ channels on plasma membrane

cones

• contain photopigments, photopsins

  • S (short blue), M (medium green), or L (long red)

    • L & M pigment genes next to each other on X chromosome, X-linked red-green color blindness

• high-light level

• high density in fovea, detail vision

outer segment

• extension of photoreceptor cell body that contains phospholipid bilayer discs

  • photopigments float in membrane of discs

  • discs increase surface area that can intercept photons of light

• opposite to end w synaptic endings

rhodopsin

• G-protein coupled receptor, similar to NTs

• amplifies, 1 x → 100s of G-ptns → 100s phosphodiesterase → closing of 1000 Na+ channels/sec

  • 1 photon blocks 1 mil Na+ ions from entering, still nothing compared to outside conc

dark current

• in dark, cGMP levels high, Na+ channels are open

• in-rush of Na+ depolarizes photoreceptor cell, releases inhibitory NT to bipolar, ganglion cell not stimulated

• light activates rhodopsin in disc membranes by altering config of retinal (Vitamin A)

  • cis to trans

• Rhodopsin activated by light

  • G-ptn activate phosphodiesterase that breaks down cGMP

    • cGMP levels fall, cGMP-gated Na+ channels close

      • photoreceptor hyperpolarized, releases less inhibitory NT in light

        • bipolar cell activated and releases excitatory NT onto ganglion cell

receptive field of ganglion cell

• based on:

  • spatial location

    • specific spot in visual field as it is projected onto retina at back of eye

  • contrast

    • on-center or off-center

      • allows to respond well to contrast edges in visual field

• overlapping of on and off center allows for complete coverage

• alternating btwn on and off center to get info abt edges

  • diffuse illumination or total darkness results in low level firing of both/no detectable differences

on-center ganglion cell

• light on center stimulates

  • max firing rate when light only on center

• light on surround inhibits

  • max inhibition when only surround in light

• light across center and surround is less effective in stimulating

  • no detectable response when both illuminated

off-center ganglion cell

• light on center inhibits

  • max inhibition when light only on center

• light on surround stimulates

  • max firing rate when light only on surround

• light across center and surround is less effective in stimulating

  • no detectable response when both illuminated

optic projection

• optic nerves meet and enter brain

• cross at chiasm

• nerve fibers after are optic tract

visual field organization

• entire left visual field projected to right brain

  • most of left field captured by left eye and crosses to right

  • part of left captured by right eye and stays ipsilateral

• entire right visual field projected to left brain

  • most of right captured by right eye and crossed to left

  • some captured by left eye and stays ipsilateral

small lesion in one retina

• lesion in one part of retina results in blind spot in corresponding visual field

• ex: lesion in temporal left eye, blind spot in right visual field

transection of left optic nerve

• left eye sees nothing

• can’t see in left peripheral

• right eye accounts for rest

  • before crossing over

transection of left optic tract

• can’t see right visual field

• deficit in both eyes

loss of left visual cortex

• can’t see right visual field

• deficit in both eyes

• info has already crossed

small stroke in right visual cortex

• small blind spot in left visual field

• info alr crossed over

• deficit in both eyes

transection of optic chiasm

• lose peripheral vision

• lose whatever is getting crossed

simple cells

• in V1 for feature extraction

• respond to orientation of stimulus at specific spot in visual field

  • ex: only responds to vertical, not to horizontal despite overlap

    • fires for other but not as much as vertical

    • when vertical, all ganglion are activated for max firing

• built up from input of ganglion cells

complex cells

• in V1 for feature extraction

• respond to orientation and direction of specific movement anywhere in field

  • order of ganglions activated

• build up from input of simple cells

dorsal pathway

• where info

• extrastriate pathway

  • V1 → parietal cortex

• action or spatial tasks

• lesions

  • can’t pick up or orient objects

ventral pathway

• what info

• extastriate pathway

  • V1 → temporal lobe, speech centers

• lesions

  • can’t recognize or describe objects & orientations

  • visually guided motor responses okay

autonomic ns

two step projection:

1. spinal/brainstem pre-ganglionic neuron (cell body in CNS, axon in PNS) synapses onto post-ganglionic neuron (cell body & axon in PNS)

2. post-ganglionic neuron synapses onto target smooth muscle (ex: blood vessel, glands)

sympathetic ns

• nerves from spinal cord run to chain or collateral ganglia and then to glands and smooth muscle

• mobilize energy, divert blood to muscle, prepare to fight/flee

  • widen pupils to see better

• no fine tuning, preganglionic doesn’t just project to one ganglia

  • has spill over that can activate other actions