Unit 3 Flashcards
why are tracers into the brain
- most tracers are not trans-synaptic
- for tracers that are trans-synaptic injected in different part of body- jumps and spreads to many other neurons b/c more than one neuron is connected to mechanoreceptor (really confusing)
why study invertebrates
- ) similar neural network and behavioral responses
- ) simplicity of nervous systems
- ) ideal for genetic manipulations
desert ant finds its way home
- ant integrates info about movements, keeping track of angles and distances
- pattern of polarized light defines position of the sun (angle), providing the ant with a “compass”
- summation of proprioceptive info associated w/ leg movements gives distance
ommatidia
- ant eye photoreceptors
- each has own nerve tract, so has own perspective
- arrangement helps ant detect polarized light
ant compensate for sun shifting
- becomes familiar with rate of sun movement
- accomplished in a day
- as if learning patterns of polarized light at different times of day
insect eye and landmark detection
- irregularities of microvilli arrangement in ommatidia outside the dorsal rim of the eye
- only dorsal is responsive to polarized light- restricts color detection
- twisted receptors outside dorsal- don’t sense polarized light, but can detect landmarks and color
- bee eye
bees and magnetic compass for orientation
- faced south before landing and taking off
- view visual cue and attractant from constant direction
- innate sense of N, S, E, W
segmented
-various tissues and organ systems are organized along anterior-posterior axis into repeating segments that are similar throughout the animal
bee vision
- bees can see UV
- see polarized light shifted into UV frequency
interganglionic connectives
- set of axon bundles where leech ganglion communicates with neighboring and distant parts of nervous system
- links ganglion of each segment together
N cells leech ganglion
- leech sensory neuron sensitive to noxious stimuli cause response
- require strong stimuli (pinch w/ forceps)
- respond to acid, heat, and capsaicin
- fire more slowly
- synapse to L and AE neurons
- activate AE; inhibit L
segmented leech CNS
- chain of 21 ganglia + head and tail ganglia
- each segment innervated by ganglion (400 nerve cells w/ distinct shapes, sizes, position, etc)
- longitudinal and angular muscles (stretch and constrict)
What does AE do
- causes segments to bunch together
- segments cause ridging- defensive strategy)
N cell transmission to L-motor
-chemical synapses
T cell transmission to L-motor
-electrical synapses
roots
- paired axon bundles where leech ganglion receives sensory info
- innervate leech body
P cell transmission to L-motor
-combo of chemical and electrical synapse
T cells in leech ganglion
- leech sensory receptor selective to touch
- adapt (cease firing) rapidly
- synapse onto L motor neuron
- smallest AP
P cells leech ganglion
- leech sensory neuron sensitive to marked pressure or deformation of skin
- slow adapting
- bigger AP
- synapse to L and AE neurons
motor cells in leech
- ) annulus erector
2. ) longitudinal
habituation
- reflexive withdrawal from a mild tactile stimulus becomes weaker if it is repeated enough times
- stimuli must become stronger and in different region in order to see response again
sever axon of S cell
- grows back to precisely re-form electrical connections with neighbor
- sensitization reappears
head direction cell
- entorhinal cortex
- fires when head is in particular direction
- keep track of which way head is pointing
- firing rates change in response to head movement
place cell
- fires when animal is in particular place
- each place cell has a different receptive field
- keep track of where rat is in arena
entorhinal cortex
-in or around hippocampus
deletion of annulus erector motor cell
- region of skin innervated by that cell fails to become erect in response to stimuli
- branches of other AE cells eventually supply territory (not permanent)
S cell
- leech inter neuron responsible to exciting motor neurons
- crucial for sensitization
- all connected via electrical synapses, so destroy one and all sensitization is lost
command neuron
- single neuron of simple nervous system that plays coordinating role in behavior of animal
- can initiate or orchestrate behavioral response
- modulate output behavior
sensitization
- strong stimulus produces increase in sensitivity
- occurs if no previous habituation
dishabituation
- recovery from habituation
- S cells responsible
- following habituation stimuli must become stronger and in different region in order to see response again
how to increase memory
- ) sleep enough
- ) use chunking techniques
- ) visualize an association
- ) localize and use cues
dorsal root ganglion
-nodule that contains cell bodies of nerve cells that carry signals from sensory organs to integration center
place field
- each place cell likes a different area of entorhinal cortex
- reverse of receptive field
- neuron responds to location in space
- each neuron has favorite space
grid cells
- establish coordinate system for you in space
- pay attention to landmarks
- lay out array when encounter room for first time
- reason why you can navigate in the dark
somatosensation
- what perceiving through skin
- touch
- pain
- temperature
- can adapt and desensitize
touch
- depends upon specific receptors in skin
- each touch receptor is sensitive to particular features of mechanical energy and insensitive to other features
- hairy and glabrous (hairless)
- fibers often myelinated and conduction is slower than pain
multiple layers of skin
- dermis
- epidermis
skin functions
- protects
- barrier
- keeps inside wet, outside dry
- boundary of self
mechanoreceptor
- flexing causes Na+ channels opening
- if depolarized enough, cell fires action potential
- indicates something is on skin
distinction between somatosensation and other senses
- ) somato receptors all over body (skin)
- ) many different types of somato receptors
- ) immediate sense (requires contact)- local sense
hearing
- actually somatosensation b/c response to hair cells bending and Na+ channels opening
- but only one type of auditory receptors (hair)
somatosensation and local sense
- parallels w/ boundary of self
- tells you something is touching you
main mechanoreceptors
- ) meissner’s corpuscle
- ) pacinian corpuscle
- ) merkel’s disk
- ) Ruffini’s ending
receptive field size
- Meissner’s and Merkel’s disk have small receptive fields
- Pacinian and ruffini’s ending have large receptive fields
large receptive field
- due to structure of receptors
- Pacinian corpuscle and Reffini’s ending
- poor for identifying localization
thalamus
-sensory relay switchboard
cortical magnification
- cortex overly represents certain portions of body
- Ex: mouth, tongue, etc
temporal cues
-determined by rate of vibration as skin is moved across finely textured surfaces
Pacinian receptors
- respond to high frequency vibrations
- rapid adapting
lower threshold
-higher sensitivity
naked mole rats
- blind
- have big teeth
- teeth, lips, and tissue around over represented in somatosensory cortex b/c it’s what they use to navigate world
- also have whiskers on front
star nosed mole
- nose densely innervated with receptors
- each ray of star represented on cortex
- example of neuroanotomical division that corresponds to function
- ray 11 has largest representation
what creates cortical magnification
- ) high receptor density
- ) receptive fields are small (higher resolution pic)
- ) maintain topographic map along pathway
- ) greater # of neurons along pathway- lots of connections that go to cortex
rat cortex
- whisker barrel pattern corresponds to # whiskers on face
- each whisker has certain spot in cortex
- whiskers that are used a lot have larger representation
rostral
-toward front
caudal
-toward back
posterior parietal cortex location
- association cortex
- behind S1, which is behind M1
association areas
-niether somato or motor
what does posterior parietal do
-integrates somatosensation and vision
dorsal column medial lemniscal pathway
- touch
- vibration
- two-point discrimination
- proprioception
- cell bodies in dorsal root ganglion
- one branch to reflex
- major branch axon continues up spinal cord ipsalaterally to dorsal columns
- cross at medulla
- to thalamus (VP nucleus)
- output to somatosensory cortex
spinothalamic pathway
- pain
- temperature
- some touch
- synapse immediately in dorsal root ganglion (cross immediately)
- ride up contralateral to sensation
- output up to thalamus (VP nucleus)
- output to somatosensory cortex
-contralateral
-on opposite side
where does touch info cross
-medulla
ventral posterior nucleus
- touch neuron
- somatosensory relay nucleus of thalamus
differences between pain and touch
- ) different pathway
- ) different crossing time
- ) different travel up (ipsalateral vs. contra)
parallel processing
- somatosensory areas next to each other that are processing different info
- each processing different info simultaneously
- Ex: one processing cutaneous, the other processing proprioception
shark sensory system
- use olfaction the most
- lots of receptors in olfactory bulb
- link of structure and function
armadillo
- lots of nervous system devoted to olfaction
- folds in brain- surface area
medial
-down midline
lateral
-out from midline
dorsal
-toward top
ventral
-toward bottom
dorsal side of spinal cord
- back side
- carries sensory info
dorsal side of brain
-top of brain
intra-hemispheric fissure
-fissure between the 2 hemispheres
lateral sulcus
-big sulcus on the side of brain
ventral portion of spinal cord
-carries motor output
cranial nerve 1
- olfactory nerve
- smell
cranial nerve 2
-optic nerve
adaptation
- Meissner’s and Pacinian are rapid adapting
- Merkel’s disk and Ruffin’s ending are slow adapting
microneurography
- stick electrodes into nerve in arm that contains fibers traveling from had to spinal cord
- shows that a single fiber is sensitive to one or a few distinct skin spots
- most fibers have no spontaneous activity and fire ONLY upon stimulation
ipsolateral
-same side as mechanoreceptor
topography
- order is the same
- body is represented in brain
- structures dense in receptors is over represented in cortex
merkel’s disc and ruffini’s complex
- Merkel- small epithelial cell under fingerprint ridges
- Ruffini- deeper in skin and around joints
- both respond to pressure or compression
- slow adapting
Meissner’s corpuscle
- in skin of lips, palm, fingers
- sensitive to initial contact and motion
free nerve ending
- not connected to specialized capsule or structure
- generate sensations of pain, temp, itch, tickle
- activated by strong mechanical, thermal, or chemical (painful) stimuli
feeling of pain
- nociceptor impulses are required from many fibers arising from free nerve endings (spatio-temporal summation)
- above threshold pain intensity correlated to # APs
- pain fibers are faster than touch
- fast velocity => reflex
distinct pathways
- neurons with different functions take distinct pathways to thalamus and cerebral cortex
- touch and pressure: dorsal column pathway
- pain and temp: spinothalamic tract
primary somatosensory cortex
- anterior to parietal cortex, behind central sulcus
- damage results in loss of touch sensation on opposite side of body
- most complete representation
- secondary are not as clear or specific
endogenous opioid receptors in brain
- modulate processing of nociceptor signals
- endogenous system releases endorphines in CNS, which inhibit neuronal activity in pain pathway
morphine
-endorphine agonist
whiskers
- mice and rats have poor vision, so rely on touch
- uses sweeping motion to collect sensory motions
- whisker contact with objects activate mechanoreceptors in whisker follicles, giving rise to neural signals
- cortical representation is high
- motion distinct for each texture
- whisker touch and cortical processing are contralateral
cortical representation in lips
- high
- crucial in sensory aspects of eating, speaking, and kissing
columnar organization
- regions of cortex on top of one another respond to the same receptor class and share overlapping receptive fields in skin
- go down column, same receptive field
- across column- different receptive field
map plasticity
- cortical topographic maps show remarkable capacity throughout life to make fine adjustments in their representation of external world
- cortical representation expands with sensory training
- plasticity also arises from rearrangement of adjacent neurons in cortical map
- Ex: blind people have expanded cortical representations of finger used to read braille
spatial cues
-determined by size, shape, and distribution of surface elements
plasticity and rewiring
- when hand is removed, touch face and think touching hand b/c face representations next to hand in cortical map
- face representations rewire into hand areas
posterior parietal cortex
-somatosensory and visual areas of cortex (visuospatial and somato)
-damage results in hemi-spatial neglect
-ignore side opposite to lesion
Ex: only draw half of pic (if damage to right, ignore left side of drawing)
same general areas of all ancestral mammals
- ) vision
- ) hearing
- ) touch
* suggests that ancestor of all mammals has similar arrangement
non-invasive brain imaging
- ) MRI
- ) fMRI
- ) PET scan
MRI
- just shows neuro-anatomy
- structure of brain
- protons are aligning with magnetic field
fMRI
- shows oxygenated blood vs. unoxygenated
- area used more = more oxygen
CT
- uses x-rays
- x-ray rotates so gives 3-D image
PET scan
- positron emission
- looking at radio activity in brain
- looking for what parts of brain will pick up radio-active material attached to sugar molecule (most active or tissue super active cell division)
disadvantage to PET and CT scan
-radiation
advantage CT
-can get high resolution images
advantage PET
-shows regions of activity
MRI advantage
-good spatial resolution
fMRI advantage
-can lay down areas of activation on top of anatomy
disadvantage fMRI
- poor temporal resolution
- can see area of activity, but there is a lag, so can’t see rapid activation
MEG
- allows you to see activity with excellent temporal resolution
- spatial resolution not great
proprioceptive fibers
- big, fat, and myelinated
- allows motor system to know quickly what is status of limbs and muscle
- crucial for movement
where are motor neurons located
-ventral portion of spinal cord
ventral horn
- where all motor neurons live
- cell bodies from MANY motor neurons
descending spinal tracts
- axons from brain descend along two major pathways
1. ) lateral pathways
2. ) medial pathways
lateral pathways
- ) corticospinal tract
- ) rubrospinal tract
* info about voluntary movement
* fine movement
* focus on distal muscles
corticospinal tract
- originates from primary motor cortex
- upper motor neurons descend to lower motor neurons in ventral horn
rubrospinal tract
- originates in red nucleus
- descend to lower motor neurons in ventral horn
medial pathways
- ) vestibular spinal tract
- ) tectospinal tract
- ) Pontine Reticulospinal tract
- ) Medullary Reticulospinal tract
- provide input to extensor motoneurons that are concerned with sustained activities like posture and stance
- axons originate in brainstem
vestibulospinal tract
- from vestibular nuclei
- important for head/eye movements
- important for posture
- descends ipsilaterally in spinal cord
- excites extensors; inhibits flexors
tectospinal tract
- originates in superior colliculus
- helps with orienting stimuli
- Ex: chasing a ball
pontine recticulospinal tract
- antigravity reflexes
- reflexes that keep you upright
medullary recticulospinal tract
- voluntary antigravity
- decision to be upright
final common path
- spinal motoneuron in ventral horn
- where ALL neural influences that concern movement or posture converge
lower motor neuron
- aka: alpha motor neuron
- directly commands muscle- talks to muscle
- cell bodies in ventral horn in spinal cord (sensory in dorsal root ganglia)
- releases ACh
- gets input from upper motor neurons
motor unit
- single motor neuron and all of the muscle fibers it contracts
- each muscle has multiple motor units
how to generate larger muscle output
- ) increase firing frequency
2. ) recruit more motor units
motor system recruiting
- recruit little neurons first b/c it is first to respond
- doesn’t require as much to depolarize
- bigger motor units need more umph from muscle spindle
- size principle
temporal summation
- synaptic potentials ride on falling phase of previous one
- build up to larger depolarization
- multiple AP in rapid succession from SINGLE presynaptic fiber
spatial summation
- MULTIPLE presynaptic fibers diverge to contact a motoneuron
- results in greater depolarization
muscle spindle
- proprioceptor sensor in muscle
- sends output (afferent) fibers to alpha motor neurons
- stretch gauge- tells length of muscle
- basis of myotatic reflex
- in parallel w/ muscle
muscle length increase
- spindle stretches
- output sent
- motor neuron fires
intrafusal fibers
- parallel with muscle
- controlled by gamma motor neuron
- muscle spindles within
- proprioceptors that play a role in length
shorten muscle
- spindles go slack
- would have no output if not for gamma motor neurons
gamma motor neurons
- as main muscle shortens, intrafusal muscle shortens
- spindle shortens
- gamma keeps muscle spindle taut allowing for continuous excitation of alpha motor neurons
myotatic reflex
- stretch of muscle (tapping patellar tendon) generates impulses that travel to the spinal cord
- produces monosynaptic excitation of motoneurons the that muscle (extensor)
- impulses also excite interneurons, which inhibit motoneurons supplying the antagonistic muscle (flexor)
- AKA: knee jerk- activate thigh; inhibit hamstring
golgi tendon organ
- another proprioceptor
- muscle tension gauge
- in series with muscles
- for fine grip
- send output to alpha motor neurons
motor neurons inputs from
- ) muscle spindles
- ) interneurons
- ) descending tracts
flexor reflex
- limb withdrawal reflex
- activated when banging leg, touching stove, etc
- movement of affected limb is primarily flexion and directed away from offending stimulus
- weight transferred to contralateral limb
- flexor neurons excited
- extensor neurons inhibited
- synapse at interneurons in spinal cord allows for excitation and inhibition
flexor muscles
- close or flex joints
- pull limb toward body
- -activation accompanied by simultaneous inhibition of antagonistic extensor muscles by spinal interneurons
extensor muscles
- open or extend joints
- oppose gravity
- activation accompanied by simultaneous inhibition of antagonistic flexor muscles by spinal interneurons
central pattern generators (CPG)
-neural networks that produce rhythmic patterned outputs without sensory feedback
-excite one side; inhibit the other
Ex: breathing and locomotion
reciprocal innervation
-one group of muscles excited, while their antagonists are inhibited
agonist
- groups of muscles that work together
- results in coordinated contractions that make limbs move
antagonist
-opposing muscles
local anesthetics
- inhibit gamma neurons
- when intrafusal fibers contracted (expiration), nothing keeping spindle afferent fibers to alpha motor neurons taut
- no info sent from muscle spindle to alpha motor neurons of diaphragm
plasticity of motor cortex
-changes in response to peripheral lesions or practicing new skill
trans-cranial magnetic stimulation (TMS)
- across the skull
- put coil on someones head
- delivers pulses of intense magnetic field (localized)
- magnetic field strong enough to stimulate neurons underneath
- allows us to disrupt proper functioning
- experimental technique to see what areas using
problems with TMS
- ) possible to stimulate temporalis muscle- clench teeth
2. ) difficult to localize b/c big spring
Utah array
- implant put into motor cortex
- using thoughts can move mouse to direct computer what to do
- Ex: turn on lights, etc
- way to interact with world when spinal cord is damaged
cerebellum and basal ganglia
- coordinate movement of body
- essential for accuracy & preventing tremor and spasticity
- contribute to motor learning
basal ganglia
-regulates motor control in regards to posture, counteract tremor, joint stabilization, and steady muscular contractions
Parkinson’s
- disease of basal ganglia caused by degeneration of dopaminergic neurons in substantia nigra
- continuous tremor at rest
- increased tone due to simultaneous activation of antagonist muscles
- difficulty initiating/finishing movements
- slowness of movements
cranial nerve 3
- ocular-motor nerve
- constricts pupils
cranial nerves that play role in eye movement
- ) trochlear
2. ) abducens
cranial nerve 8
-auditory
cranial nerve 10
- vagus nerve
- gagging, swallowing
- heart rate
hypoglossal nerve
- tries to control tongue movement
- controls which way tongue goes
meninges
- 3 layers covering nervous system to protect brain
1. ) dura mater
2. ) arachnoid membrane
3. ) pia mater
pia mater
- thin along cortex
- wraps around blood vessels and in groves
arachnoid membrane
- looks like spider web
- on top of pia
- space filled with CSF
dura mater
- hard
- thicker for bigger species
ventricular system
- spaces within the brain through which CSF flows
- CSF flows out and over top of brain
choroid plexus
-in ventricles where CSF originates
CSF
-flows through ventricles and down spinal cord
hydrocephalus
- common in infants
- pressure builds in brain due to CSF circulation block
- skull and brain get huge
retina
- part of the CNS
- back of eye connected to thalamus
thalamic nuclei
- all sensory input goes through
- touch and pain go through ventral posterior (VPN)
- vision goes through lateral geniculate (LGN)
- hearing goes through medial geniculate (MGN)
- sensory relay stations that send info to cortex
frontal cortex
-decision making
-impulse control
executive function
-planning
Korbinian Brodmann
- made # maps of brain
- used cresyl violet stain to look at cytoarchitecture in different species
- observed distinctions in laminar thicknesses
cytoarchitecture
architecture of cells
how to define area of brain
- ) architecture
- ) connections
- ) functions
central sulcus
- separates parietal and frontal lobes
- doesn’t quite reach temporal lobes
motor cortex
-rostral to central sulcus
somatosensory cortex
-caudal to central sulcus
area 8 frontal cortex
-helps generate eye movements
saggital plane
- passes from ventral to dorsal
- cuts into right and left
transverse plane
- divides into superior and inferior parts
- horizontal section
- can see inferior colliculus, superior colliculus, and red nucleus
frontal (coronal) plane
- separates into dorsal and ventral
- vertical section
- belly and back sections
corpus colosseum
-tract that connects fibers from one hemisphere to the other
inferior colliculus
-processes auditory info
superior colliculus
- processes visual and some auditory info
- important for orienting to new visual stimuli
red nucleus
- motor output
- part of rubro-spinal pathway
- sends info to spinal cord
Phineas Gage
-behavior change after rod through frontal cortex
layer 4 of of somatosensory cortex
- thalamic projections from VP nucleus go there
- thicker than other layers
motor cortex layers
- output layers are the thickest
- layers 5 and 6 thickest
- where pyramidal neurons originate
pyramidal neurons
- motor control
- part of corticospinal tract
how many layers mammalian cortex
- 6
- different thicknesses
