16 lower

sensory in dorsal spinal cord, motor in ventral
- farther out neurons control farther out body parts (medial=trunk, lateral=arms,legs)
one motor neuron (MN) innervates multiple fibers
- the more fibers/neuron, the less precise
- MN pool - group of MNs=motor units
muscle tone = all your muscles are a little on, kind of like turning on the car engine and when you want to, you can move forward
- more firing = more contraction
MN types
1. fast fatiguable - white muscle
2. fast fatigue-resistant
3. slow - red muscles, make atp
  - muscles are innervated by a proportion of these MNs
reflex
- whenever you get positive signal on one side, also get negative on other
- flexor - curl in (bicep)
- extensor - extend (tricep) 1. proprioceptors (+) - measure length - more you stretch, more firing of alpha MN to contract
- intrafusal muscle=spindle - stretches the proprioceptor so that it can measure even when muscle is already stretched
  - $\gamma$ motor neuron - adjusts intrafusal muscles until they are just right
    - keeps muscles tight so you know how much muscle is streteched
    - if alpha fires a lot, gamma will increase as well
      - high gamma allows for fast responsiveness - brainstem modulators (serotonin) also do this
  - opposes muscle stretch to keep it fixed
  - spindle -> activates muscles -> contracts -> turns off
  - sensory neurons / gamma MNs innervate muscle spindle
- homonymous MNs go into same muscle, antagonistic muscle pushes other way 2. golgi tendon (-) measures pressure not stretch
- safety switch
- inhibits homonymous neuron so you don’t rip muscle off
ALS = Lou Gehrig’s disease
- MNs are degenerating - reflexes don’t work
- progressive loss of $\alpha$ MNs
- last neuron to go is superior rectus muscle -> people use eyes to talk with tracker
CPG = central pattern generator
- ex. step on pin, lift up leg
- walking works even if you cut cat’s spinal cord
- collection of interneurons

17 upper

cAMP is used by GPCR
lift and hold circuit
1. ctx->lateral white matter->lateral ventral horn->limb muscles
  - lateral white matter - most sensitive to injury
2. brainstem->medial white matter->medial horn->trunk
  - medial white matter -> goes into trunk
bulbarspinal tracts
1. lateral and medial vestibulospinal tracts - feedback
  - automated system - not much thinking
  - posture - reflex
  - too slow for learning surfing
2. reticular - feedforward = anticipate things before they happen
  - command / control system for trunk muscles (posture)
  - feedforward - not a reflex, lean back before opening drawer
  - caudal pontine - feeds into spinal cord
3. colliculospinal tract
  - has superior colliculus - eye muscles, neck-looking
  - see ch. 20 - reflex
corticular bulbar tract (premotor->primary motor->brainstem)
- motor cortexes - this info is descending
- can override reticular reflexes in reticular formation
- premotor cortex (P2) - contains all actions you can do
  - has mirror neurons that fire ahead of primary neurons
    - fire if you think about it or if you do it
- primary motor cortex (P1)
  - layer 1 ascending
  - layer 4 input
  - layer 5 - Betz cells - behave like 6 (output)
  - layer 6 - descending output
  - has map like S1 does
    - Jacksonian march get seizure that goes from feet to face (usually one side)
      - epileptic seizure - neurons fire too much and fire neurons near them
        
        insular - flashes of moods
        
        pyriform - flashes of smells
- Betz cells - if they fire, you will do something
  - dictate a goal, not single neuron to fire
  - axons to ventral horn of spinal cord
lesions
1. upper
  - spasticity - unorganized leg motions
  - increased tone - tight muscles
  - hyperactive deep reflexes
  - ex. babinski’s sign
  - curl foot down a lot because you don’t know how much to curl
  - curling foot down = normal plantar
  - more serotonin can cause this
2. lower
  - hypoactive deep reflexes
  - decreased tone
  - severe muscle atrophy
pathways
- Betz cell
  - 90% cross midline in brainstem - control limbs
  - 10% don’t cross - trunk muscles

18 basal ganglia (choose what you want to do)

“who you are”
outputs
1. brainstem
2. motor cortex
4 loops (last 2 aren’t really covered)
- motor loops
  1. body movement loop
    - SnC -> S (CP) -> (-) Gp -> (-) VA/VL -> motor cortex
  2. oculomotor loop
    - cortex -> caudate -> substantia nigra pars reticulata -> superior colliculus
- non-motor loops
  1. prefrontal loop - daydreaming (higher-order function)
    - spiny neurons corresponding to a silly idea (alien coming after you) filtered out because not fired enough
    - schizophrenia - can’t filter that out
  2. limbic loop - mood
    - has nucleus accumbens
    - can make mood better with dopamine
substantia nigra
1. pars compacta - dopaminergic neurons (input to striatum)
  - more dopamine = more strength between cortical pyramidal neurons and spiny neurons (turns up the gain)
  - dopamine helps activate a spiny neuron
  - may be the ones that learn (positive outcome is saved, will result in more dopamine later)
  - Parkinson’s - specific loss of dopaminergic neurons
  - dopaminergic neurons form melanin = dark color
  - when you get down to 20% what you were born with
  - know what they need to do - don’t have enough dopamine to act
  - treat with L Dopa -> something like dopamine -> take out globus pallidus - cocaine, amphetamine - too much dopamine - Huntington’s - death of specific class of spiny neurons
  - have uncontrolled actions - Tourette’s - too much dopamine
  - also alcohol - MPPP (synthetic heroin)
  - MPTP looks like dopamine but turns into MPP and kills dopaminergic neurons
  - treated with L Dopa to reactivate spiny neurons
2. pars reticulata
  - doesn’t have dopamine (output from striatum)
  1. striatum contains spiny neurons
3. caudate (for vision) - output to globus pallidus and substantia nigra (pars reticulata)
4. putamen - output only to globus pallidus
  - each spiny neuron gets input from ~1000 cortical pyramidal cells
  1. globus pallidus
    - each spiny neuron connects to one globus pallidus neuron
    - deja vu - spiny neuron you haven’t fired in a while
  2. VA/VL (thalamus)
    - all motor actions must go through here before cortex
    - has series of commands of all actions you can do
    - has parallel set of betz cells that will illicit those actions
    - VA/VL is always firing, globus pallidus inhibits it (tonic connection)

19 cerebellum (fine tuning all your motion)

redundant system - cortex could do all of this, but would be slow
repeated circuit - interesting for neuroscientists
all info comes in, gets processed and goes back out
- cerebellum gets motor efferant copy
- all structures on your brain that do processing send out efferent
- cerebellum sends efferant copy back to itself with time delay (through inferior olive) 1. cerebrocerebellum
- deals with premotor cortex (mostly motor cortex)
  1. spinocerebellum = clarke’s nucleus, knows stretch of every muscle, many proprioceptors go straight into here
- motor cortex
- has a map of muscles 3. vestibular cerebellum - vestibular->cerebellum->vestibular
- vestibular system leans you back but if wind blows, have to adjust to that
input
- pontine nuclei (from cortex)
- vestibular nuclei (balance)
- cuneate nucleus (somatosensory from spinal upper body)
- clarke (proprio from spinal lower body)
processing
- cerebellar deep nuclei
output
- deep cerebellar nuclei
  - go to superior colliculus, reticular formation
- VA/VL (thalamus) - back to cortex
- red nucleus
circuit 1 - fine-tuning
circuit 2 - detects differences, adjusts
- cerebellum -> red nucleus (is an efferant copy) -> inferior olive -> cerebellum
- compare new copy to old copy
cells
- purkinje cells - huge number of dendrite branches - dead planar allows good imaging
  - GABAergic
- (input) mossy fibers -(+)> granule cells (send parallel fibers) -(+)> purkinje cell -(-)> deep cerebellar nuclei (output)
  1. mossy->granule->parallel fibers connect to ~100,000 parallel fibers
  2. climbing fiber - comes from inferior olive and goes back to purkinje cell (this is the efferent copy) = training signal
- loops
  - deep excitatory loop (climbing/mossy) -(+)-> deep cerebellar nuclei
  - cortical inhibitory loop (climbing/granule) -(+)-> purkinje
    - the negative is from purkinje to deep cerebellar nuclei
alcohol
- can create gaps = folia
- long-term use causes degeneration = ataxia (lack of coordination)

20 eye movements/integration

Broca’s view - look at people with problems
Ramon y Cajal - look at circuits
5 kinds of eye movements
1. saccades
  - use cortex, superior colliculus (visual info -> LGN -> cortex, 10% goes to brainstem)
  - constantly moving eyes around (fovea)
  - ~scan at 30 Hz
  - 5 Hz=200 ms for cortex to process so pause eyes (get 5-6 images)
  - there is a little bit of drift - can’t control this - humans are better than other animals at seeing things that aren’t moving
2. VOR - vestibular ocular reflex - keeps eyes still
  - use vestibular system, occurs in comatose
  - fast
  - works better if you move your head fast
3. optokinetic system - tracks with eyes
  - ex. stick head out window of car and track objects as they go by
  - slower than VOR (takes 200 ms)
  - works better if slower
  - reflex
  - in cortex (textbooks) but probs brainstem (new)
4. smooth pursuit - can track things moving very fast
  - suppress saccades and track smoothly
  - only in higher apes
  - area MT is highest area of motion coding and goes up and comes down multiple ways
  - high speed processing isn’t understood
  - could be retina processing
5. vergence - crossing your eyes
  - suppresses conjugate eye movements
  - we can control this
  - only humans - bring objects up very close
  - reading uses this
eye muscles
- rectus
  - vertical
    - superior
    - inferior
    - use complicated vertical gaze center
      - last to degenerate in ALS
      - locked-in syndrome - can only move eyes vertically
      - controls oculomotor nucleus
  - lateral
    - medial
    - lateral (controlled by abducens)
    - use horizontal gaze center=PPRF which talk to abducens -MLF connects abducents to opposite medial lateral rectus muscle
  - oblique - more circular motions
    - superior (controlled by trochlear nucleus)
    - inferior
- everything else controlled by oculomotor nucleus
superior colliculus has visual map
- controls saccades, connects to gaze centers
- takes input from basal ganglia (oculomotor loop)
- also gets audio input from inferior colliculus (hear someone behind you and turn)
- gets strokes
- redundant with frontal eye field in secondary motor cortex
  - connects to superior colliculus, gaze center, and comes back
  - if you lose one of these, the other will replace it
  - if you lose both, can’t saccade to that side

21 visceral (how you control organs, stress levels, etc.)

parasympathetic works against sympathetic
divisions
1. sympathetic - fight-or-flight (adrenaline)
  - functions
  - neurons to smooth muscle
  - pupils dilate
  - increases heart rate
  - turn off digestive system
  - 2 things with no parasympathetic counterpart
    - increase BP
    - sweat glands - location
  - neurons in spinal cord lateral horn
    - send out neurons to sympathetic trunk (along the spinal cord)
    - all outgoing connections are adrenergic - beta-adrenergic drugs block adrenaline
  - beta agonist - activates adrenaline receptors (do this before EKG)
2. parasympathetic - relaxing (ACh)
  - location
  1. brainstem
  2. edinger westphal nucleus - pupil-constriction
  3. salivatory nucleus
  4. vagus nucleus - digestive system, sexual function
  5. nucleus ambiguous - heart
  6. nucleus of the solitary tract - all input/output goes through this 1. rostral part (front) - taste neurons 2. caudal part (back) contains all sensory information of viscera (ex. BP, heart rate, sexual
  7. sacral spinal cord (bottom) - gut/bladder/genitals
    - not parallel to sympathetic – poor design - may cause stress-associated diseases
      - hard to make drugs with ACh
3. enteric nervous system - in your gut
  - takes input through vagus nerve from vagus nucleus
  - also has sensory neurons and sends afferents back to brainstem
pathway
- insular cortex - what you care about
- amygdala - contains emotional memories
- hypothalamus - controls a lot
  - mostly peptinergin neurons
  - aging, digestion, mood, straight to bloodstream & CNS
  - releases hormones
  - ex. leptin - stops you eating when you eat calories
- reticular formation - feedforward, prepares digestion before we eat
three examples
1. heart rate
  - starts at nucleus ambiguous
  - also takes input from chemoreceptors (ex. pH)
  - SA node at heart generates heartbeat - balances Ach and adrenaline
  - sympathetic sends info from thoracic spinal cord - heart sends back baroreceptor afferents
2. bladder function
3. parasympathetic in sacral lateral horn make you pee (contracts bladder)
4. turn off sympathetic NS
5. open sphincter muscle (voluntary)
  - can also control this via skeletal nervous system
  - circuit
    - amygdala (can’t pee when nervous)
    - pontine micturation center -> parasympathetic preganglionic neurons -> parasympathetic ganglionic neurons
    - inhibitory local circuit neurons -> somatic MNs
6. sexual function
  - Viagra turns on parasympathetic NS
  - also gives temporal color blindness - sympathetic involved in ejaculation
  - temporal correlation (“Point and Shoot”)