bme 202 final review (neuro branch)

can the spinal cord be modeled as a cable?

no

how many pairs of nerves are on the spinal cord

31

how does the spinal cord split?

into 2 roots in the vicinity of the spinal cord

what are the two roots that the spinal cord splits into?

the dorsal (sensory) root and the ventral (motor) root.

how is white matter shaped?

columns

how is grey matter shaped?

butterfly shaped pattern

what is composed of grey matter?

cell bodies, dendrites, synapses

what are the functions of the spinal cord?

• mediating various reflexes

• generating locomotor rhythms

• “user interface” to muscullature

where is the medulla?

widening of the spinal cord at the top

where does the spinal cord primarily extend relating nerves to?

trunk and limbs

where does the medulla primarily extend relating nerves to?

head and neck

how does the medulla relate to the head/neck/face?

sensory input and motor output

what is the muscular makeup of the medulla?

ascending and descending fiber tracts

what sensory nuclei are between the medulla’s fiber tracks?

somatosensory, auditory, vestibular

what functions does the medulla control?

rhythmic functions such as

• breathing

• heartbeat

• digestion

what is the cerebellum responsible for?

involved coordination/timing of complex learned skills

• skeletal movement

• posture

• eye movements

• cognitive skills

what are the pons responsible for?

contain nuclei providing major input to cerebellum & numerous other nuclei and fibers of passage

what is the midbrain responsible for?

orienting responses towards and away from things of interest

what is the responsibility of the inferior colliculus?

integrating auditory and visual information

what is the responsibility off the superior colliculus?

orienting eyes and head movements

other important structures in the midbrain?

• substantia nigra (part of basal ganglia)

• red nucleus (output nucleus of the cerebellum)

• raphe nucleus (contains serotoninergic neurons that project over the brain)

where is the diencephalon?

“between brain”

what is in the thalamus

sensory relay nuclei, higher order relay nuclei, gating input to cortex

responsibility of sensory relay nuclei?

receive input from peripheral sensory ganglion (ex: retina) and relay to primary sensory cortex

responsibility of higher order relay nuclei?

receive input from lower order cortical areas and project to higher order cortical areas

responsibility of the hypothalamus?

• management of basic drives (hunger, thirst, rage, sex, etc)

• head of autonomic nervous system

  • sympathetic (fight/flight, adrenaline, etc)

  • parasympathetic (rest and digestion)

• pituitary gland

responsibility of cerebral cortex?

• sensory processing (low to high level)

• motor processing (including premotor/movement planning and primary motor/generating movements)

• associations

• working and semantic memory

• executive function/deciding whaat to do

• limbing function/emotional responses

• language

composition of basal ganglia?

parallel loops from cortex to basal ganglia, to thalamus, to cortic areas including

• striatum

• gllobus pallidus

• substantia nigra

• subthalamic nucleus

responsibility of basal ganglia?

• picking up sensory cues for motor actions

• habit learning

responsibility of the hippocampus?

• episodic memory formation

• spatial navigation

four parts of the spinal cord

• cervical

• thoraic

• lumbar

• sacral

what is the dorsal root composed of?

sensory axons from the periphery into the dorsal horn

what is the ventral root composed of?

outbound axons of ventral horn motorneurons to the muscles

what is white matter composed of?

• descending axons from brainstem and higher brain ceneters that terminate on motor and other neurons

• ascending sensory axons carrying sensory information from skin, muscles, joints of trunks and limbs up to brainstem and higher brain centers

what is grey matter composed of?

• 9 layer structure

• sensory neurons in dorsol horn

• motor neurons in ventral horn

• excitatory and inhibitory interneurons in intermediate layers

how are the motor neurons in the grey matter mapped out

medially to laterally

how many muscle fibers are activated by one motor neuron in the ventral horn

100-1000

how many motor units in one muscle

~ 100

what is a motor nucleus and what does it contain

a cylindrical nucleus verticallly spanning multiple segments of the spinal cord grey matter; contains all the motor neurons for a muscle

in what ways can muscle force be graded

• varying the rate of AP’s generated in the motor neuron population

• varying the number of motor neurons activted in the motor nucleus

• ordered recruitment of slow then fast twitch muscle fibers

what’s the difference between slow and fast twitch muscle fibers?

slow twitch are smaller and more easily excited

what makes the muscles “springy”?

monosynaptic stretch

what do descending axons modulate?

• gain of reflexes

• direction of reflexes

• balance between antagonist muscles

• target of modular inputs

what are the main subdivisions of the motor cortex?

primary motor cortex (m1), premotor area (pma), supplementary motor cortex (sma)

is the mapping of the m1’s areas proportional and continuous to that of the body

no

are the neurons controlling movement in relating body parts segregated?

NO, they are often intermixed

what is associated with the neurons in m1?

direction of force

what are M1 neurons tuned towards (when will it fire the most)?

desired direction

how many neurons can be decoded in the direction of a simple movement?

100 or less

how do M1 neurons project?

through the pyramidal tract into the spinal cord grey matter to activate a single motorneuron pool OR to activate multiple flexor/extensor neuron pools

where do PMA neurons send their axons?

M1

how do PMA neurons differ from M1 neurons?

• firing is not directly tiied to movement

• can continue firing during a delay movement (representing preparation)

• neurons can be tuned to specific preparations

do PMA neurons fire the same way during delay periods

NO, they can ramp up or down, have constant firing, etc

some unique ways PMA neurons can act?

• can fire for the direction of movement rather than for a specific muscle’s movement

• can fire in relation to specific hand grip shapes

• can be mirrors to learn for the basis of imitation

when is the SMA activated?

actual or imagined execution of complex motor sequences (complex tapping of rhythm); can be tuned to particular sequences

where is the cerebellum?

mini brain at the bottom back of the brain

what inputs does the cerebellum receive?

feedback sensory information relating to the programming and execution of skilled action

to where does the cerebellum output?

motor systems (movement related nuclei, thalamus areas targeting motor, premotor, prefrontal, and parietal cortex)

what does the cerebellum focus on learning?

optimizing rapid “automatic” sensory guided actions requiring practice

what actions are associated with the cerebellum?

• coordination of several muscle groups

• complex timing of movements

• adaptation to varying loads

what diseases are associated with damage to the cerebellum?

• delayed movement

• lowered range of movement

• movement errors

• timing problems

what are the 3 main functional subdivisions of the cerebellum?

• vestibulo

• spino

• cerebro

what are deep nuclei, and what are some deep nuclei examples?

output nuclei of the cerebellum

includes: dentate nucleus, fastigial nucleus, interposed nuclei

include vestibular nuclei in medula, excite targets in the brainstem/spinal cord/thalamus

how does the cerebellum as a whole act on the neurons in the output nuclei?

• output neurons have high firing rate; get excited and inhibited by cerebellar system so they are activated and shut down when needed

• mossy fibers excite output neurons (site of learning)

• purkinje cells inhibit output neurons in the deep nuclei

• synapses from granule cell axons are also site of learning

• output neurons in deep nuclei can be excited and inhibited at certain times

how does learning happen in the cerebellar cortex?

• mossy fibers input on granule cells (billions!)

• granule cels fire when 4-7 mossy fibers are active

• each granule cell splits onto another parallel fiber that cuts through the trees of purkinje cells

how are parallel fiber synapses modifiable in strength?

• parallel fiber activated in close proximity to cell’s climbing fiber output → weakened synapse

• not paired → stronger synapse

• mossy fiber is opposite; pairing = stronger

• “electric car brake” metaphor

what is the somatosensory system?

how you feel things

where are somatosensory neurons located?

dorsal root ganglia (DRG)

what is the difference between rapid adapting and slowly adapting neurons?

rapid = rapidly gets used to the stimulus (sudden drop) even if the stimulus is still happening

slow = gradual drop of responses, slowly gets used to it

what is the path of the axons of the somatosensory neurons?

periphery → DRGs → spinal cord → direct contact with motoneurons and interneurons in grey matter

what are the two major ascending pathways carrying somatosensory information to the brain?

dorsal column medial lemniscus (DCML) and anterolateral

what is the difference between DCML and anterolateral?

DCML has lots of myelin, is rapid, and is for motor control. anterolateral is not myelinated

where does the DCML pathway project to?

dorsal column in brainstem → relay station in the thalamus → primary somatosensory cortex (s1)

where does the anterolateral pathway project to?

projects widely within the brainstem and reaches the cortex

how are rapid/slow adapting neurons in cortical area S1 segregated?

columns running from the cortical surface through the 6 layers of cortex

what are common features of neurons in different cortical columns?

neurons within a column usually have similar receptive fields

how are the S1 subareas (1,2,3a,3b) structured?

strips running from the top across the sides of the cortical areas. 4 copies of the somatosensory homunculus.

what is the hierarchy between the s1 subareas, area 5 and the secondary somatosensory cortex (s2)?

progression where receptive fields of neurons grow larger and more complex through a sequence of processing stages (example: neurons in area 3b have small receptive fields like a small area of one fingertip while area 5 neurons receptive fields could cover large areas over both hands)

how does sound travel to the ear?

pressure waves in air (aka sound) causes the eardrum to move back and forth

through what bones are the vibrations translated from the eardrum to the cochlea?

incus, maleus, stapes

what is the cochlea?

snail shaped bone cavity containing fluid compartments (scala vestibuli, scala tympani), organ of corti (basilar and tectorial membranes), primary transducing neurons (hair cells), and axon endings of the neurons that carry signals to the brainstem (spiral ganglion neurons)

how does sound get transmitted through the cochlea?

changes in fluid pressure from vibrations → back and forth movements of basilar membrane; area where it hits the membrane is based on frequency of sound

how does sound turn into brain signals?

motion of basilar and tectorial membranes → movement of cilia (hair cells), → open and closing of nonselective cation channels in cell membrane → hyper/depolarization → voltage signal!

what is a frequency phase code?

assignment of particular sound frequencies to neurons depeniding on their location

what is a timing code?

output neurons tend to fire at the frequency of the sound they represent

what is the path through which sound signals go through?

spiral ganglion → cochlear nucleus → medulla

how do cochlear implants help restore hearing?

loss of inner ear hair cells → loss of hearing → cochlear implants directly activate spiral ganglion neurons instead of going through hair translation

what is phototransduction?

the process whereby photos are converted into neural activity aat the first stage of retinal processing

what does the retina do?

converts light into neural signals, does early stage visual processing, and sends information up to the brain for further processing

what are the two types of retinal photoreceptors? what light levels can they see?

rods: light conditions from starllight to candlelight

cones: candelight to brightest daylight conditions

how many types of cones are there, and how are they distinguished?

3 types

distinguished by wavelength of light they are most sensitive to (red, blue, green)

where are cones heavily concentrated?

fovea (center of the visual field), highest resolution images

where are the photoreceptor cells?

back of the retina, furthest from light, against the pigment epithelium

what does the pigment epithelium do?

absorbs photons that make it through the retina and past the photoreceptors without getting caught. mirrored in cats and dogs

how is light transduced?

• photon is caused by a pigment molecule

• molecules are lodged iin disks (rods) or disk like folds (cones)

• rhodopsin molecule undergoes a conformational change

• g protein is activated → enzyme is activated → cGMP is turned into GMP → cGMP concentration goes down → hyperpolarization

• hyperpolarization of a retinal photoreceptor → reduction of the rate of synaptic release

what is a pedicle

supersynapse with up to 50 release zones and 500 synaptic contacts

what is the path electrical signals take from the photoreceptors?

photoreceptors → bipolar cells → ganglion cells → outside retina

how do cones interact with the bipolar cells?

cone releases glutamate → excites off bipolar cells → inhibits on bipolar cells

how do bipolar cells send electrical signals?

excite ganglion cellls

what lateral connections exist in the retina

• mutual inhibition between neighboring photoreceptors (center surround receptive field)

• amacrine cells → direction selectivity