CM II - Neuro Study Guide

what is the structure of a typical neuron?

Dendrite → cell body (w/ nucleus) → axon (coated in myelin sheath) → axon terminal

what is gray matter made of?

dendrite and axon terminal

where do you find gray matter?

cerebral cortex, nuclei, ganglia, and horns of the cord

what is white matter made of?

axons

where do you find white matter?

tracts and columns of cord

what is the central nervous system? (CNS)

Contains neurons whose entire structure lies within the brain and/or spinal cord

what is the peripheral nervous system (PNS)?

Contains neurons whose structure lies either entirely or partly outside the brain and spinal cord

what is the somatic nervous system associated with?

conscious and voluntary control of body using skeletal muscles

what kinds of nerves does the somatic nervous system have?

• Consists of both afferent (sensory) and efferent (motor) nerves

• 12 pairs of cranial nerves and 31* pairs (bc of coccygeal plexus) of spinal nerves (C8, T12, L5, S5, C1)

what are spinal reflex arcs?

involve interneurons (very tiny axon nerves relaying directly from sensory to motor nerves) that perform reflexive (largely unconscious and involuntary) actions

what is the autonomic nervous system responsible for?

involuntary and without conscious effort

what are the 3 subdivisions of ANS?

contains afferent and efferent fibers

• Sympathetic nervous system:

  • Involves visceral reactions with “fight or flight”

• Parasympathetic nervous system:

  • Involves visceral reactions with “feeding and breeding”

• Enteric nervous system:

  • Extensive, web like structure that is capable of functioning independently of the remainder of nervous system (doesn’t require the brain to work)

  • Digestion and enteric endocrine function

what is preganglionic neuron?

• a higher order nerve - peripheral nerve

Cell body (but not entire structure) lies within the CNS

what is the postganglionic neuron?

• a lower order nerve - peripheral nerve

  • Cell body (and entire structure) lie outside the CNS (in ganglion beyond)

  • Innervates target tissues

what is a glia/glial cells?

non-neuronal cells in CNS and PNS that maintain homeostasis, form myelin, provide support for nerves and protect neurons. Don’t produce electrical impulses

what is a schwann cell?

glial cell that makes myelin in PNS

what is oligodendrocyte?

glial cell makes myelin in CNS

what is a ganglion?

collection of nerve cell bodies in PNS, gray matter (can be S or M)

what is a nucleus?

collection of nerve cell bodies in CNS, gray matter, M and S

what is horner’s syndrome?

damage to any of the cervical sympathetic chain ganglions (superior, middle, or inferior)

what is the relationship between superior, middle, and inferior cervical sympathetic chain with the spinal cord?

there is NO connection

what initiates input to the superior, middle, and inferior cervical sympathetic chain ganglia?

thoracic sympathetic ganglia (T1, T2, and T3)

what does the cervical sympathetic chain innervate?

head/face and neck

what does excitatory mean?

neuron/nt it releases, describing ability to stimulate the natural function of the cell upon which is synapses

what does inhibitory mean?

refer to neuron or the neurotransmitter it releases, describing ability to inhibit the natural function of the cell upon which is synapses

the result (excitatory or inhibitory) is what?

NOT a property of nt (no properties)

increase or decrease in the usual activity of that post-synaptic cell

what does cholinergic mean?

referring to NT acetylcholine and its receptors, both nicotinic and muscarinic

what does adrenergic mean?

referring to NT of catecholamine class, particularly norepinephrine and its receptors, both alpha and beta types

what are catecholamines?

• Epinephrine, norepinephrine, and dopamine 

• Epinephrine is a hormone (made in adrenal glands) NOT a NT

what are the major NT’s in the CNS?

• glutamate (E)

• acetycholine (E)

• norepinephrine (E)

• dopamine (E/I)

• serotonin (I)

• GABA (I)

what is glutamate associated with?

learning and memory

what is excess glutamate associated with?

alzheimer’s disease (1st sx: memory loss)

what is acetylcholine involved in?

Involved in wakefulness, attentiveness, memory, anger, aggression, sexuality, and thirst

what is norepinephrine important for?

attentiveness, emotions, sleeping, dreaming, and learning

what does a lack of norepinephrine cause?

mood disorders → depression

what is dopamine involved/regulate?

• Involved in modulating movement and posture 

• Regulates mood → plays role in depression and positive reinforcement (euphoria and dependency)

loss of DA in substantia nigra can cause what?

parkinson’s disease

activity of DA (dopamine) in nucleus accumbens can cause what?

addiction

what does serotonin contribute to?

regulation body temp, sleep, mood appetite, and pain

what would happen if there are imbalances of serotonin?

Depression, suicide, impulsive behavior, and aggressiveness

what does GABA contribute to?

• Contributes to motor control, vision, and other cortical functions

Regulates anxiety

what can a GABA deficiency cause?

huntington’s disease

what stimulates release of GABA?

alcohol and benzodiazepines

what drug increases GABA levels in the brain?

antiepileptics (treats epilepsy)

what type of receptors most common in brain?

glutaminergic (E) and GABAnergic (I)

what NT are associated with mood disorders?

norepinephrine, serotonin, and dopamine

what does acetylcholine do?

Triggers muscle contraction and stimulates the secretion of certain hormones

what does norepinephrine do?

important for cardiovascular tones

what blocks nicotinic receptors?

curare (paralytic drugs)

what blocks muscarinic receptors?

atropine

response of nicotinic receptors?

fast but brief

response of muscarinic receptors?

slow and prolonged

nicotinic receptor cells and location

excitatory

postsynaptic membranes, all autonomic ganglia, adrenal glands, CNS, and neuromuscular junction

muscarinic receptor cells and location

excitatory and inhibitory

pre- and post-synaptic membranes, myocardium, smooth muscle, CNS

sulcus definition

relatively short and shallow depression, surrounds a gyrus

fissure definition

relatively long and deep furrow, helps divide brain into lobes and into the two major hemispheres (medial longitudinal fissure)

gyrus definition

prominence in cerebral cortex, bordered by sulci and fissures

what is the circle of willis?

circle formed through the anastomoses of arteries in the area

what is homunculus?

• A grotesque proportion character used to represent the amount of cerebral cortex dedicated to the motor and sensory innervation of various human body parts

  • The larger the portion on the homunculus → the larger the area on the cerebral cortex → more of cerebral cortex dedicated to innervation

• Precentral gyrus → motor cortex

• Postcentral gyrus → somatosensory cortex

what are the ganglia in the sympathetic autonomic ganglia?

• Paravertebral ganglia (sympathetic chain ganglia)

• Prevertebral ganglia (celiac, superior mesenteric, and inferior mesenteric ganglion)

• Preganglionic sympathetic fibers that have exited the spinal cord synapse at either of these ganglia to release the NT by synapsing with a postganglionic neuron

• Both forms release NT acetylcholine (ACh) which binds to only nicotinic receptors 

• Activating the nicotinic receptors depolarizes the cell body of the long postganglionic neuron and generates action potentials that travel to the target organ to elicit a response

summary: preganglionic neuron: acetylcholine which binds to nicotinic receptor on postganglionic neuron, which releases NOREPINEPHRINE → adrenergic receptor (on effector neuron)

parasympathetic autonomic ganglia is found where?

• Found within the target organ itself (embedded in the tissue)

• Ex: in case of vagal nerves, exit the brainstem and their long preganglionic fibers enter the target organ (the heart) where they have a synapse with a very short postganglionic neurons with small ganglia to the target tissue (i.e. SA node)/organ 

what is the NT used in parasympathetic autonomic ganglia?

parasympathetic autonomic ganglia pathway

• preganglionic neuron = acetylcholine (binds to nicotinic)

• postganglionic neuron = Ach, binds to muscarinic on effector organ

where are the parasympathetic presynaptic cell bodies located?

brainstem (CN III, VII, IX, and X) and the lateral horns to sacral spinal cord (ventral primary rami S2-S4)

what is the manifestation of Horner’s Syndrome?

ipsilateral loss of sympathetic input to structures

• ptosis

• meiosis

• enophthalmos

• anhydrosis

what is ptosis?

drooping eyelid

what is meiosis?

constricted pupil, a parasympathetic effect whereas pupillary dilation is a sympathetic effect

what is enophthalmos?

eye that is recessed in orbit

what is anhydrosis?

inability to sweat on that side of face

ventral cortex is usually?

motor

dorsal cortex tends to be?

sensory

Within the SNS the only postganglionic neurons that release ACh as their primary NT are what?

innervating the sudoriferous (sweat) glands and some blood vessels of the non-apical skin (arrector pili muscles - make your hair stand up/on edge)

[parasympathetic]

what is the main excitatory NT in visceral smooth muscles → activates muscarinic receptors to cause contraction?

ach (specifically last step of parasympathetic pathway)

what are posterior (dorsal) columns responsible for [sensory pathway]?

• Discriminatory touch (fine distinction, like slightly different points on the hand)

• vibration sense

• proprioception (where you are in space)

• Pressure

what is the path of peripheral sensory neurons?

• enters spinal cord

• goes up to medulla on the SAME side as it entered

• in medulla, it synapses and crosses over to opposite side to continue through brain

what is the spinothalamic (anterolateral) tracts [sensory pathway] responsible for?

• Pain

• Temperature

• Crude touch (gross distinction, like front and back)

what is the path of the spinothalamic (anterolateral) tracts [sensory pathway]?

• synapses in posterior sensory horn of spinal cord

• crosses immediately at level of spinal cord they entered and synapse at

• ascends to brain

where does crossing over occur in the dorsal column?

in the medulla (second order neuron)

where does crossing over occur in the spinothalamic tract?

the spinal cord (second order neuron)

dorsal column vs. spinothalamic tract: which has the longest first order axon?

dorsal column

dorsal column vs. spinothalamic tract: which has the longer second-order neuron?

spinothalamic tract

the right side of the visual fields projects to the what side of the visual cortex?

left side (in general, the visual system projects to the opposite side in terms of top → bottom, lateral → anterior, medial → posterior)

once it hits the retina, it stays in that orientation going all the way to the brain

where do your optic nerves cross over?

optic chiasm (they don’t always cross though)

what’s read on the LEFT side of the right eye eyes to get to the left cerebral hemisphere so it crosses, and vice versa, whereas what’s read on the RIGHT side of the right eye doesn’t cross and goes straight to the right cerebral hemi

as you get more binocular in your vision (peripheral), what happens?

it gets more “superficial”/on the outside of the visual cortex/most posterior

what is anoopsia?

complete blindness of one eye

what is hemianopsia?

blindness of HALF the visual field of one eye

what is quadranopsia?

blindness of a quarter of the field of one eye

what is homonymous?

same side of the visual fields of both eyes (either L or R sides, so both LEFT sides of the L and R eye)

what is heteronymous?

opposite sides of the visual fields of each eye (so ie is if RIGHT side of L eye and LEFT side of R eye, or maybe LEFT side of left eye and RIGHT side of right eye)

(generally temporal → tunnel vision, more common than homonymous)

what happens if you cut the optic nerve on the right side? (lesion #1)

total blindness of right eye

what happens if a cut is made in the optic chiasm up and down (vertical)? (lesion #2)

bipolar hemianopia - tunnel vision (loses peripheral vision)

what happens if a cut was made in optic chiasm horizontally HALFWAY? (lesion #3)

• right nasal hemianopia

• AKA left eye is ok, but half of R eye is lost

what happens if you cut the right optic tract after crossing over on the right? (lesion #4)

• left homonymous hemianopia

• both sides of the left and right eye are blind (ie both left sides of L and R eye are blind)

what happens if you cut upper right of occipital lobe on the right side? (lesion #5)

• left homonymous inferior quadrantanopia

• lose same lower left field of visual field (quarter) in both eyes

what happens if you cut lower right of occipital lobe? (lesion #6)

• left homonymous superior quadrantopsia

• blind both sides top right of visual field (quarter)

what if i cut through the entire optic radiations/occipital lobe on the right side? (lesion #7)

• left homonymous hemianopia

• left 50% of L and R are blind

• presents same visual defect as #4

what is the lowest part of spinal cord?

conus medullaris (L2)

L3-Cox1 originate where?

filum terminale, very compressed in conus medullaris

plexus of very thick nerve roots

cauda equina

Parasympathetic NS (cranial-sacral) has roots that come from the conus medullaris and some that don’t. which ones originate from conus medullaris?

S2-S4

pre-ganglionic sympathetic nerves start/leave T1-L2/L3, but there are some nerves originating from where (anterior motor horn) that go lower than L2/L3?

conus medullaris