Neuro Block 1

reticular theory

nerves communicate through a continuous nerve net (protoplasmic links)

Golgi method

Silver solution that randomly stains about 1% of neurons in their entirety

Camillo Golgi

proponent of reticular theory

Santiago Ramon y Cajal

used Golgi method to provide evidence against reticular theory, no continuity between neurons

Neuron Doctrine

The hypothesis that the brain is composed of separate cells that are distinct structurally, metabolically, and functionally.

Ross Harrison

showed that neural processes (dendrites and axon) grow from the cell body when neurons are isolated in culture, axons can extend to target neurons or tissue

Brainbow

individual neurons stained using genetically encoded fluorescent proteins

neuron

basic unit of the nervous system; about 86 billion but only 1% work; specialized for reception, conduction, and transmission of electrochemical signals

dendrites

receive input from other neurons and carry messages towards cell (many per neuron)

soma

contains nucleus and machinery to maintain life

axon hillock

integration and initiation of new message; membrane potential here determines if an action potential will be fired

axon

carries new message away from cell body to another neuron (1 per neuron, but can branch to form axon collaterals)

terminal bouton

site of neurotransmitter release, "output"

principle of dynamic polarity

electrical signals within a neuron flow in one direction

potential

electrical impulse within neurons

chemical neurotransmitters

communication between a neuron and its target

sensory neurons

afferent; specialized at one end to be highly sensitive to a particular type of sensory stimulation; conducts impulses from periphery to CNS; may be bipolar or pseudo-unipolar; soma in ganglia

interneurons

primary neurons of CNS; serve as relay or integration units between afferent and efferent; multipolar

motor neurons

efferent; receive signals from other neurons and conduct impulses to a muscle; multipolar; soma in spinal cord

central nervous system

brain and spinal cord; protected inside bone (skull and vertebral column)

glia

cells that aid and modulate neurons' activities

ventricles

series of interconnected, fluid filled spaces within the core of the CNS; filled with cerebrospinal fluid (CSF) derived from ependymal cells in choroid plexus

choroid plexus

a network of blood vessels and cells in the ventricles of the brain; have cilia, which circulate CSF around the CNS

astrocytes

most abundant type of glia; structural support for neurons; synthesize and regulate NT levels; regulate Blood Brain Barrier (BBB); help maintain proper extracellular chemical environment for neural signaling; "endfeet" interact with capillary endothelial cells to maintain their tight junctions, which comprise BBB

Blood Brain Barrier (BBB)

limits what can get into brain; small, uncharged molecules pass with ease while big molecules have to be fat soluble or have a transporter

microglia

immune defense for CNS; change shape, proliferate, and move to site of problem; phagocytize debris, plaques, and pathogens; thought to be impacted in Alzheimer's, Parkinson's, Schizophrenia, + pain conditions

oligodendrocytes

myelinate axons in the CNS

myelin sheath

fatty tissue that covers the axon of some neurons and helps speed neural impulses

Schwann cells

myelinate axons in the PNS; facilitates repairs if PNS axons are damaged

nodes of Ranvier

unmyelinated sections between myelination on an axon

peripheral nervous system

extends beyond (or exists entirely outside of ) the bony skull and vertebral column, including cranial and spinal nerves

visceral stimuli

afferent, produced by internal organs

dorso-ventral axis

The axis in bilateral symmetry that defines the top of an organism from the bottom

rostro-caudal axis

(relative to forebrain) long head-tail axis; axis for brainstem is perpendicular to that of rest of brain, thus coordinates change accordingly

anterior-posterior axis

front to back axis

superior-inferior axis

up and down axis

proximal/medial

closer to body midline

distal/lateral

further from body midline

horizontal/axial

coronal

sagittal

gray matter

made up of cell bodies and dendrites, color comes from nuclei

white matter

made up of myelinated axons

nuclei

bundles of gray matter in the CNS

tracts

bundles of white matter in the CNS

ganglia

groups of neuron cell bodies in the PNS

nerves

groups of axons in the PNS

medulla

part of the brainstem that coordinates basic life functions and reflexes (breathing, heart rate, vomiting, salivation, coughing and sneezing)

pons

part of the brainstem that includes axons that allow the cerebellum to communicate with the brainstem and cerebral cortex

midbrain

part of the brain that contains structures involved in processing visual and auditory information

tectum

sensory region of midbrain; contains colliculi

superior colliculus

part of the midbrain that receives visual sensory input

inferior colliculus

part of the midbrain involved in auditory processing

tegmentum

motor region of the midbrain; contains dopaminergic neurons

ventral tegmental area (VTA)

part of the midbrain associated with reward pathway + dopamine

substantia nigra (SN)

part of midbrain that initiates movements; black substance

cerebellum

motor planning, motor learning, and balance

Diencephalon

thalamus and hypothalamus

thalamus

relay for information going to and coming from the neocortex

hypothalamus

regulates body temperature, hunger, thirst, and sexual behavior; regulates hormone release by coordinating with the pituitary

basal ganglia

group of interconnected structures that curve in a C shape around the thalamus that control planning and initiation of voluntary, smooth movement

limbic system

group of interconnected structures related to emotions, motivation, aggression, memory; the 4 Fs- fleeing, feeding, fighting, sexual behavior

amygdala

emotions (fear, reward, anger, etc)

hippocampus

memory formation and storage

cerebral cortex (cerebrum)

80% of brain volume; higher order functions; expanded most in evolution

frontal lobe

motor control and executive functions (planning, inhibition of inappropriate behaviors, working memory)

parietal lobe

somatosensory and tactile processing

temporal lobe

auditory processing, language and memory

occipital lobe

visual processing

central sulcus

separates parietal and frontal lobes

Sylvian fissure (lateral sulcus)

separates temporal lobe from frontal and parietal lobes

longitudinal fissure

separates cerebral hemispheres

gyrus

ridge/bump

sulcus

groove/crack

fissure

infolding of gyrus/sulcus

postcentral gyrus

directly caudal to central sulcus; contains primary somatosensory cortex, which processes touch and pain information

precentral gyrus

directly rostral to central sulcus; contains primary motor cortex, which helps plan movements and sends motor signals to spinal cord

corpus callosum

where axons cross between brain hemispheres

31

# of pairs of spinal nerves

cauda equina

collection of spinal nerves below the end of the spinal cord

dorsal horn

contains sensory axons (afferents) entering spinal cord

ventral horn

contains cell bodies of motor neurons (efferents)

cranial nerves

send motor commands to and receive sensory information from the head and neck; emerge from the brain; 12 pairs

olfactory (I)

sensory nerve; sense of smell

optic (II)

sensory nerve; vision

oculomotor (III)

motor nerve; eye movement (papillary constriction/accommodation, eyelid muscles)

trochlear (IV)

motor nerve; eye movement (intorsion, downward gaze)

trigeminal (V)

sensory/motor nerve; somatic sensation of face, mouth, and cornea; muscles of mastication

abducens (VI)

motor nerve; eye movement (abduction or lateral movement)

facial (VII)

sensory/motor nerve; facial expressions; taste from anterior tongue; lacrimal and salivary glands

vestibulocochlear (VIII)

sensory nerve; hearing and balance

glossopharyngeal (IX)

sensory/motor nerve; sensation and taste of posterior tongue; carotid baroreceptors and chemoreceptors

vagus (X)

sensory/motor nerve; autonomic gut functions; larynx and pharynx sensation; vocal cord muscles; swallowing

spinal accessory (XI)

motor nerve; shoulder and neck muscles

hypoglossal (XII)

motor nerve; tongue movements

Somatic Nervous System (SNS)

part of PNS that controls voluntary movements of skeletal muscles

autonomic nervous system (ANS)

part of PNS that controls involuntary bodily functions

sympathetic division

part of ANS that arouses the body to expend energy; fight or flight

parasympathetic division

part of ANS that calms body to conserve and maintain energy; rest and digest

preganglionic neurons

neurons involved in ANS that originate in CNS; cell bodies in lateral horn of spinal cord/brain stem; project to postganglionic neurons

postganglionic neurons

neurons involved in ANS that originate in peripheral ganglia; project to target tissue

meninges

membranes that protect brain and spinal cord

dura mater

tough outermost layer of meninges

arachnoid mater

middle layer of meninges

pia mater

glossy thin innermost layer of meninges

migraine

inflammation of meninges causing activation of painful meningeal afferents

aura

cortical spreading depression over cortex that precedes 20-30% of migraine attacks

foramina

openings in bones that allow nerves and blood vessels to enter or leave the bone

subarachnoid space

a space in the meninges beneath the arachnoid membrane and above the pia mater that contains the cerebrospinal fluid (CSF)

neutral buoyancy

CSF allows dense brain to not be damaged by its own weight

spinal tap/lumbar puncture

spinal needle inserted between L3-L4 to collect CSF; drugs can also be administered

hydrocephalus

abnormal accumulation of fluid (CSF) in the brain

shunt

tube that redirects excess CSF from brain to vein or stomach

nonfenestrated

capillaries with tight junctions to prevent openings

circumventricular organs

vascularized structures around the third and fourth ventricles with no blood brain barrier

membrane potential (Vm)

measure of the difference between the summed ionic charges inside and outside a neuron; separation of charges across the membrane

resting membrane potential

electrical potential of a neuron at rest; inside negative by -70mV relative to outside

ions

charged particles in solution; atoms with extra electrons or missing electrons, giving them a + or - charge

voltage-gated channels

open and close in response to changes in membrane potential

ligand-gated channels

open in response to binding of specific molecule to a specific receptor

Na+ and Cl-

concentration of these ions greater outside neuron

K+ and protein (A-)

concentration of these ions greater inside neuron

homogenizing forces

promote equal distribution of ions across the membrane through concentration gradients and voltage gradients

opposing forces

differential permeability and Na+/K+ pump (ATP dependent)

reversal potential

membrane potential where the current reverses its polarity (ions go from flowing out to in or from in to out); if cell permeable to only one ion, equilibrium potential = reversal potential

differential permeability

-K+ and Cl- pass readily through resting membrane -Na+ cannot pass through resting membrane

current

movement of ions across membrane through ion channels; causes Vm to become positive or negative

graded potentials

small fluctuations in ion concentrations that create small voltage fluctuations; proportional to intensity of stimulation; decremental; travel by passive spread of ions

postsynaptic potential (PSP)

type of graded potential where a cell is stimulated on dendrites/soma and membrane voltage changes as ions flow across the membrane

hyperpolarization

change in membrane potential that makes the inside of the cell more negative than the outside

inhibitory postsynaptic potential

IPSP; negative graded hyperpolarization of the postsynaptic membrane

depolarization

change in membrane potential that makes inside of the cell less negative than the outside

excitatory postsynaptic potential

EPSP; positive graded depolarization of the postsynaptic membrane

summation

multiple PSPs come in at the same time, pushing the membrane potential to threshold

EPSP-IPSP cancellation

excitatory and inhibitory graded potentials cancel each other out

spatial summation

excitatory potentials from many neurons trigger threshold point

temporal summation

many excitatory potentials from one neuron trigger threshold point

threshold potential

minimum membrane potential that must be reached in order for an action potential to be generated; -50 to -30mV

driving force

difference between membrane potential and equilibrium potential of ion; determines directions and strength of current (negative means inward and positive means outward)

action potential

electrical signal used for neuronal communication and due to functioning of voltage-gated ion channels; rapid (~1ms), transient change in membrane voltage from negative resting potential to positive voltages (>0mV); non-decremental

all or none

neuron either fires completely or not at all; always the same strength once threshold is reached

upstroke

N+ influx, voltage-gated channels opened, strong electrochemical driving force, not competing with K+ efflux