physio exam 2 - nervous system neurons and synapses

neurons

basic structural units of the nervous system that transmit electrical signals

• found in grey matter of CNS and ganglia

• have a cell body

• processes called neurites

neuroglial cells

support cells that are nonexcitable

• surround and wrap neurons

neurons characteristics

• conduct electrical impulses along the plasma membrane

• produce nerve impulse

• produce action potential

• can live and function for a lifetime

• dont divide → fetal neurons lose ability to undergo mitosis

• high metabolic rate → need lots of oxygen and glucose

sugar

what is the main source of energy for neurons

• cell body

• axon (long)

• dendrite (short)

structure of a neuron includes (3)

• varied size of 5-140

• normal cell organeles

• nissl bodies (rER)

• neurofibrils

cell body (perikaryon)

• transmits impulses away from neuron

• no protein synthesis in axon

• no nissl bodies in axoplasma

axon (long)

intitial segment of axon

• a4 axon hillock; most excitable site, origination of site of AP

dendrite (short)

increases neuron’s receptive area

• transmits impulses towards the neuron

supporting cells

• provide supportive functions for neurons

• cover nonsynaptic regions of the neurons

supporting cells of the PNS

• schwann cells - make myelin sheaths

• satellite cell/ganglionic gliocytes - support neuron cell bodies/synapses in the ganglia by surrounding them

supporting cells of the CNS (neuroglial cells)

• oligodendrocytes - make myelin sheaths

• microglia - migrate through CNS and phagocytose foreign/degenerated material

• astrocytes - help regulate external environment of neurons in the CNS

• ependymal cells - line the ventricles of the brain and central canal of spinal cord → accelerated CSF fluid circulation

oligodendrocytes (oligs)

• small cell bodies

• no filaments in cytoplasm

• one can myelinate many fibers

• not surrounded by a basement membrane unlike schwann cells

• function: myelination in CNS

  • stellite oligs (surround nerve cell bodies) can influence the biochemical environment of neurons

microglia

smallest among neuroglial cells

• migrate into nervous system in fetal life

• scattered in the CNS

• function: proliferate, are active and phagocytic in inflammation/degeneration of CNS

  • inactive (resting) in normal CNS

ependyma

form a single layer of cuboidal cells lining the central cavities of the brain and spinal cord

• have microvilli

astrocytes

small cell body

• numerous branching processes

  • many of the processes are interwoven at inner/outer surfaces of CNS → make outer and inner glial limiting membranes

functions of astrocytes

1. supporting framework for neurons and act as scaffolding for migrating neurons during development in the embryo

2. cover the synaptic contacts between neurons → insulate axon terminals to stop influence to other neurons

3. absorb glutamate (tranform it into glutamin), and GABA secreted by the nerve terminals → limit influence of glutamate and GABA

4. absorb excess K+ of extracellular fluid to maintain proper ionic environment for neurons

5. take up glucose from blood by surrounding capillaries and metabolize it into lactic acid and release it and use it as energy for neurons

6. phagocytosis of degenerated axon terminals

7. replacement gliosis: when neurons die bc of disease/injury, they proliferate and fill the spaces

8. induce formation of blood brain barrier

9. release trophic factors for neurons to help them grow

gliosis and glial scar (gliosis and oligodendrocytes action)

gliosis - hyperplasia/hypertrophy of astrocytes that happens in rxn to CNS injury

• oligodendrocytes respond to injury be expanding and vacuolation of their cytoplasm

tumors of neuroglia (glioma)

• 50% of itnrcranial tumors

• astrocytomas and glioblastomas are astrocyte tumors

• gliomas are very invasive and grow large w/ minimal effect on neighboring neurons

multiple sclerosis (demyelinating diseases of the CNS)

unknown neurodegenerative disease that happens between the ages of 20-40 that causes demyelination in CNS

• starts w/ optic nerve, spinal cord, and cerebellum

• result is axonal degeneration

• ultimately affects APand central motor centers

oligodendrocytes … postnatal

• extensions … several

  • tissue white …white matter

  • cell bodies … dendrites … lack myeline sheaths

myelin sheaths of CNS are made by ___ during ___.

• each oligodendrocyte has ___ and forms myelin sheats around ___ axons

  • myeline sheats around axons give ___ color to tissue → high concentrated tissues make ___

    • gray matter of CNS are made of high concentrations of ___ and ___ which ___

regeneration of a cut axon

when an axon in peropheral n. is cut, schwann cells phagocytose the distal degenerated part of the axon

• it makes a regeneration tubes to be part of the axon that is connected to the cell body begins to grow and exhibit amoeboid movement and also guide regerenation axon to its destination

• they secrete chemical that attract the growing axon tip

CNS regeneration

limited bc of absence of continuous neurilemma of oligodendrocytes which causes no regeneration tube

• oligodendrocytes also release molecules that actively block axon regrowth

• astrocytes release inhibitory chemicals and proliferate to make glial scars that block axon from growing

neurotrophins

chemicals that promote neuron growth in developing fetal brain

• nerve growth factor (NGF)

• brain deprived neurotrophic factor (BDNF)

• glial-derived neurotrophic factor (GDNF)

• neurotrophin-3 (which is important for development of sensory neurons and sympathetic ganglia)

blood brain barrier (BBB)

barrier between cerebral capillary blood and CSF(brain tissue)

• made of endothelial cells of cerebral capillaries and choroid plexus epithelium

made by the choroid plexus epithelium

• lipid soluble substance pass through easily (CO2, O2, and H2O) - equilibrate between blood and CSF

• ions and nutrients need carriers via choroid plexus epithelium and are subsquently secreted/excreted via blood

• proteins and cholesterol are excluded

• CSF = interstitial brain fluid but differs from blood

physiology of BBB: made by? what can be pass through and what cant

functions of the blood-brain barrier

• maintains a constant environment for neurons in the CNS

• protects brain from endogenous/exogenous toxins

• prevents escape of neurotransmitters from functional sites in the CNS into general circulation

• nonionized … ionized

• antibiotics, radiolabeled markers

drugs penetrate the blood-brain barrier to varying degrees:

• ___ (lipid-soluble) drugs cross more readily than ___ (water-soluble) drugs

• inflammation, irradiation, and tumors can destroy it and let usually excluded substances enter such as:

dopamine

• dopaminergic neuron biosynthesis

L-DOPA, the precursor of dopamine can cross the BBB but ___ can not bc of its large size:

• in parkinson’s disease where there is deficiency of ___ in substansia niagra, we give L-dopa

Na+, Cl-, HCO3-, osmolarity

CSF has equal amounts of what concentrations to blood?

K+, Ca2+, glucose, cholestrol, and protein

CSF has less concentration of what compared to blood

Mg2+ and creatinine

CSF has more concentrations of what compared to blood

synapses

how neurons form functional conducting pathways

• also implies to nerve-muscle contact

• axodendritic and axosomatic are most common forms

• chemical (most common) and electrical types

buoton de passage

axons can have a terminal expansion or a sereas of expansions called ____ which make several contacts as they pass through a dendritic tree

chemical synapses

neurotransmitters are released from a pre-synaptic neuron that becomes attached to a protein receptor at the post synaptic membrane

• unidirectional

• presynaptic cytoplasms has vesicles, mitochondria, and lysosomes

• postsynaptic cytoplams have paralle cysternae

• synaptic clef has polysaccharides

neurotransmitter substance … ATP

the presynaptic vesicles have ___ and the mitochondria give ___ for neurotransmitter synthesis regarding neurotransmitters at chemical synapses

neurotransmitters at chemical synapses

Ach, norepinephrine, epinephrine, dopamine, glycine, serotonin, gamma-aminobutyric acid (GABA), enkephalines, substance P, and glutamic acid

• majority of neurons only release one principal neurotransmitter

have no chemical transmitters and are gap junctions made w/ connexon channels

• each connexon has 6 parts called connexins from cytoplasms of presynaptic neuron to that of the postsynaptic neuron which allow flow ionic current between cells w/ minimal delay

• found in group of neurons w/ idential function

• bidirectional

electrical synapses, function, location, and direction

NMJ, autoomic ganglia, parasympathetic nerve

distribution of ach

sympathetic nerve endings of CNS, hypothalamus

distribution of norepinephrine

basal ganglia and hypothalamus

distribution of dopamine

synapses of spinal cord

distribution of glycine

excitatory amino acid neurotransmitter in CNS neurons

distribution of glutamate

they’re released from nerve endings after action potential → influx of ca2+ into presynaptic part → synaptic vesicles fuse w/ presynaptic membrane briefly → postsynaptic membrane binds to the neurotransmitter → opening of ion channels → excitatory postsynaptic potential (EPSP)

• ach in nicotinic receptors

• IPSP in GABA

neurotransmitters action:

they’re released from nerve endings after___ → influx of ___ into the ____ part → synaptic vesicles fuse w/ ___ briefly → ____ binds to the neurotransmitter → opening of ____ → excitatory postsynaptic potential (____)

effect is short-lasting bc they either get destroyed in the cleft or reabsorbed by the presynaptic part

• effect of catecholamines is limited by their return to the presynaptic ending

fate of neurotransmitters:

effect is ___ bc they either get ___ in the cleft or ___ by the ____part

• effect of catecholamines is limited by their return to the presynaptic ending

neurotransmitter charactersitics

1. prescence of substance in terminals

2. release of substance w/ neuronal stimulation

3. exogenous substance application to postsynaptic membrane has the same effect of the normal stimulation of the presynaptic neuron

4. concentration - response curve of a substance applied to postsynaptic membrane is affected by drugs in a similiar way as normal postsynaptic repsonse

5. local mechanism exists for inactivation of substance (like enzymatic degradation or uptake into nerve terminal/glia)

• general anesthetic block synaptic transmission, preventing release or receptor activation

• local anesthetics block nerve conduction in local/specific areas by stopping the increase in permeability of Na+ and K+ to the axolemma

long chain neurons w/ multiple synapses are easier to block while small nerve fibers are more sensitive and slower to recover, what are the effects of general and local anesthetics?

phenothiazines

what blocks dopamine receptors postsynaptically

• epinephrine

• norepinephine

• dopamine

• serotonin

what are the 4 regulatory monoamine neurotransmitters?

serotonin

master neurotransmitter made via trptophan thats all over the body and plays a big role in regulation of stress hormones

it regulates anger, aggression, body temp, mood, sleep, vomiting, sexuality and appetite

what is the role of serotonin in the CNS

aggressive behaviors, depression, migraine, bipolar/anxiety disorders

what are the causes of low serotonin lvls in the CNS

there’s an increase in sudden infant death syndrom

• oral serotonin doesn’t pass into serotnergic pathways of CNS bc it cant cross the BBB

what happens if serotonergic neurons (brainstem neurons that make serotonin) are abnormal

dopamine

neurotransmitter that activates 5 types of receptors and their respective variants

• when given as a drug, has no affect on the CNS bc it cant cross the BBB

• can be supplied as meds that act on the sympa nervous system → increased heart rate and blood pressure

substansia nigra and hypothalamus

dopamine locations

inhibit the release of prolactin from the anterior lobe of the pituitary

what is the main function of dopamine neurohormone in the hypothalamus

• helps regulate attention via prefrontal cortex

• regulates prolactin secretion via arcuate nucleus of hypothalamus

• pleasure system via nucleus accumbens

• regulates to avoid schizo from excess

what are the overall functions of dopamine

norepinephrine

released from the adrenal medulla into the blood as a hormone but is also a neurotransmitter in the CNS and sympathetic nervous system released via noradrenergic receptors/neurons

affects parts of brain regarding attention and responding actions as a stress hormone

• underlies fight-or-flight by increases heart rate, triggering release of glucose, and increasing skeletal muscle readiness

norepinephrine function

excitatory postsynaptic potential (EPSP)

temporary depolarization of postsynaptic membrane potential caused by flow of positvely charges ions into the postsynaptic cell

• associated neurotransmitters: amino acid glutamate aka the main excitatory neurotransmitter in the CNS

• makes it easier for a neuron to fire an AP

inhibitor postsynaptic potentials (IPSPs)

change in membrane voltage of a postsynaptic neuron from inhibitory neurotransmitter receptors synaptic activation

• result of the negative ion flow into the cell

• most common: GABA and glycine

neuropeptide Y (NPY)

36 amino acid peptide neurotransmitter in the brain and ANS which augements/intensifies the vasoconstrictor effect of noradrenergic neurons

• regulation of appetite, energy balance, memory and learning, and epilepsy

• makes part of the lipostats system w/ leptin and corticotropin

function of NPY

gaseous signaling biological messenger molecule known as the endothelium-derived relaxing factor made from arginine and oxygen via nitric oxid synthase (NOS) enzymes and inorganic nitrate reduction

nitric oxide neurotransmitters

blood cell endothelium use it to signal the smooth muscle to relax and dilate the artery, increasing blood flow

• helps ppl avoid hypoxia in high-altitude places via elevation

• effects blood vasodilation w/ prostaglandins, neurotransmission, hair cycle, and penile erections

  • synthetic nitric oxide and prostaglandin can be used for erectile dysfunction treatment as they dilate the dorsal vein

nitric acid significance