Ch 7 - The Nervous System Part 1

central nervous system and peripheral nervous system

what 2 parts is the nervous system divided into

brain and spinal cord

what makes up the central nervous system

cranial and spinal nerves

what makes up the peripheral nervous system

neurons and neuroglia

what 2 types of cells is the nervous tissue composed of

1) neurons can conduct impulses but generally cannot divide

2) neuroglia support the neurons and can’t conduct impulses, but can divide

main differences between neurons and neuroglia in terms of impulses and dividing

1) respond to chemical and physical stimuli

2) conduct electrochemical impulses

3) release chemical regulators

4) enable perception of sensory stimuli, learning, memory, and control of muscles and glands

what are the 4 general functions of the neurons

1) cell body → contains the nucleus, Nissl bodies, and other organelles (most proteins are translated here)

2) dendrites → receive impulses and conducts a graded impulse toward the cell body (conduct chemical stimuli into electrical stimuli)

3) axon → conducts action potentials away from the cell body

3 parts of the structure of a neuron and its function

the secondary metabolic center (some proteins translated here)

what are the axon terminals considered

CNS → nuclei

PNS → ganglia

what is a cluster of cell bodies in the CNS vs in the PNS called

collateral axon → allows single neuron to have contact with many cells

what is a branched axon called and what does it allow

some need to make shorter or longer connections

why do axons vary in length

the axon hillock where action potentials are generated at the initial segment of the axon (also where synthesis from dendrites occurs)

what is the axon connected to the cell body by AND what occurs here

myelin sheath → open spots are nodes of Ranvier

what are axons covered in and what are the open, uncovered spots called

an active process needed to move organelles and proteins from the cell body to axon terminals

what is axonal transport

1) fast components move membranous vesicles

2) slow components move microfilaments, microtubules, and proteins

with axonal transport, what do fast vs slow components move

1) from cell body to dendrites and axon

2) uses kinesin molecular motors

3) carries neurotransmitters and ions

which way is anterograde transport, what does it use to transport, and what does it carry

1) from dendrites and axon to the cell body

2) uses dynein molecular motos with its activator dynactin

3) carries lysosomes, autophagosomes, endosomes, and other molecules AND certain viruses and tetanus toxin

which way is retrograde transport, what does it use to transport, and what does it carry

conduct impulses exclusively in the CNS and integrate functions of the NS

where do association/interneurons conduct impulses and what does it do

from sensory receptors to the CNS (afferent)

which way do sensory neurons conduct impulses

from the CNS to target organs (muscles or glands; efferent)

which way do motor neurons conduct impulses

for reflexes and voluntary control of skeletal muscles

what are somatic motor neurons responsible for

they innervate involuntary targets such as smooth muscle, cardiac muscle, and glands

what are autonomic motor neurons responsible for

1) parasympathetic → normal functions; “rest and digest”

2) sympathetic → emergency situations; “fight or flight”

both involve autonomic motor neurons

parasympathetic vs sympathetic nervous system AND what neurons involved

pseudounipolar, bipolar neurons, and multipolar neurons → based on the number of processes that extend from the cell body

what are the 3 structural classifications of neurons and what are they based on

1) pseudounipolar → single short process that branches like a T to form 2 longer processes (sensory neurons)

2) bipolar neuron → have 2 processes, one on either end (found in retina of eye)

3) multipolar neuron → several dendrites and one axon; most common (motor neurons)

pseudounipolar vs bipolar vs multipolar

pseudounipolar

what type of neuron is this

bipolar neuron

what type of neuron is this

multipolar neuron

what type of neuron is this

bundles of axons located outside the CNS

what are nerves

both sensory and motor neurons (mixed nerves)

what are most nerves composed of

sensory fibers

what do some of the cranial nerves only have

a tract

what is a bundle of axons in the CNS called

Schwann cells and satellite cells

what are the 2 types of neuroglia (glial cells) found in the PNS

they form myelin sheaths around peripheral axons

what do Schwann cells in the PNS do

they support cell bodies within the ganglia of the PNS (can migrate short distances also)

what do satellite cells do in the PNS

1) oligodendrocytes

2) microglia

3) astrocytes

4) ependymal cells

what are the 4 types of neuroglial cells found in the CNS

they form myelin sheaths around the axons of the CNS neurons

what do oligodendrocytes in the CNS do

they migrate around CNS tissue and phagocytize foreign and degenerated material

what do microglia in the CNS do

they regulate the external environment of the neurons

what do astrocytes in the CNS do

they line the ventricles central canal of the spinal cord and secrete cerebrospinal fluid

what do ependymal cells of the CNS do

they were produced in the embryonic yolk sac and migrated to the developing neural tube

what is unique about the microglia compared to other cells in the CNS

related to macrophages however when they die, they are replaced by cell division of existing microglia instead of monocytes of the blood like macrophages

what are microglial embryonically related to, and how do they differ from them also

they have a small cell body with many fine processes (helps maintain healthy neuronal synaptic function)

brief description of structure of microglia

infection or trauma → they become phagocytotic, mobile cells and sense ATP released from damaged cells and migrate towards them

what can lead to microglial activation and what does it lead to

they kill endogenous pathogens and remove damaged dendrites, myelin, and other debris

what do microglial cells kill and what do they remove in the CNS

pruning synapses

what can microglial cells do to axons to eliminate inappropriate synaptic connections

neurilemma (extends its plasma membrane and wraps it around axon)

sheath of Schwann cells that surrounds all axons in the PNS

myelin sheath

all axons in the PNS are surrounded by Schwann cells that have neurilemma, but not all of those cells have what

layers upon layers of plasma membrane (lipids)

what is the myelin sheath composed of

usually unmyelinated

in the PNS are small axons usually myelinated or unmyelinated

conduct impulses

what can myelinated axons do quicker than unmyelinated axons

1 Schwann cell : 1 axon

1 oligodendrocyte : multiple axons

ratio of Schwann cell to axon vs oligodendrocyte to axon

it sends extensions to several axons and each wraps around a section of an axon giving myelin sheath

how do oligodendrocytes produce myelin sheath for axons in CNS

myelin sheaths give white color while those without myelin sheath are gray

what color are tissues with myelination vs without it

those in which the immune system attacks the myelin sheaths that protect nerve fibers

what are demyelinating diseases

the T cells of the immune system attack the myelin sheaths of the PNS which produces rapid onset of symptoms that includes muscle weakness

what occurs in Guillain-Barre syndrome

autoimmune attack by T lymphocytes causing lymphocytes and monocyte-derived macrophages to enter the brain (CNS) and target the myelin sheaths leading to range of neurological symptoms

what occurs in multiple sclerosis (MS)

1) portion of neve fiber is cut, the severed part degenerates and Schwann cells form a regeneration tube

2) growth factors are released, stimulating the growth of axon spurts within this tube

3) new axon connects to the undamaged axon or the effector

(no-go inhibitor protein produced by Schwann cells are removed by phagocytosis to allow this to happen)

explain process of PNS regeneration

CNS axons have a limited ability to regenerate, unlike PNS axons

how does the ability of CNS axons to regenerate compare to PNS axons?

axon collaterals, but central axons have a much more limited ability to regenerate than peripheral axons

what does injury in the CNS stimulate growth of

1) oligodendrocyte apoptosis due to death receptors forming

2) inhibitory proteins in myelin like Nogo produce by oligodendrocytes

3) glial scar formation by astrocytes

what are the 3 major factors that make CNS regeneration difficult

1) promote neuronal growth in the fetal brain (nerve growth factor, etc.)

2) in adults, they aid in the maintenance of sympathetic ganglia and the regeneration of sensory neurons

what are the 2 main roles of neurotrophins through life

astrocytes

what is the most abundant glial cell in the brain

astrocyte end-feet

what is considered the 3rd metabolic center of the neuron

end-feet; they cover the entire surface of blood capillaries and associate with axon terminals

what are astrocytes processes known as and what do they cover

interactions between neurons and also between neurons and blood; helps regulate blood flow, maintain the blood-brain barrier, and support neuronal function

what do astrocytes influence interactions between and what do those interactions help regulate

1) K+ ions from extracellular environment, maintaining the ionic balance necessary for neurons

2) glutamate from CNS axon terminal (excitatory neurotransmitter) which can be converted to glutamine and then GABA (inhibitory neurotransmitter)

what 2 things can the astrocytes (not around the capillaries) take up and what does it do

glucose from blood and convert it to lactic acid for neurons to use in ATP production OR store it as glycogen and produce lactate for neurons when needed

what can astrocytes’ end-feet around capillaries absorb and do with it

the hippocampus and subventricular zone

where do astrocytes regulate neurogenesis in the adult brain

synapses

astrocytes create crucial environment for what to form in the CNS

glial-derives neurotrophic factor (GDNF)

what do astrocytes produce that is needed for survival of spinal cord neurons and dopamine-releasing neurons

the blood-brain barrier

what do astrocytes form that protects the brain from harmful substances

gliotransmitters, such as glutamate, ATP, adenosine, and D-serine

what do astrocytes release that can stimulate or inhibit neurons by responding to calcium signals

changes in intracellular Ca2+ concentration

astrocytes don’t produce action potentials, but they are excited by what

1) when some neurons are active, they release ATP; which increases Ca2+ of adjacent astrocytes; creates a Ca2+ wave

2) a rise in Ca2+ can also cause the astrocyte release prostaglandin E₂ from the end-feet on a blood capillary, increasing blood flow

explain intracellular Ca+ concentration changes exciting astrocytes

it’s a critical structure in the brain’s capillaries, where cells are joined by tight junctions, preventing pores between adjacent cells

where is the blood-brain barrier and how are cells joined

that substances can only move through very selective processes such as diffusion endothelial cells, ion channels, transport proteins, and active transport

what does the blood-brain barrier ensure

transcellular

what type of movement is it across the blood-brain barrier

they influence the production of ion channels, carrier proteins, and enzymes that can destroy toxin substances through the secretion of glial-derives neurotrophic factor

how do astrocytes play a significant role in the BBB

they surround the endothelium of CNS capillaries and produce transporters that facilitate two-way communication between endothelial cells and astrocytes

where are pericytes in the BBB and what do they produce

challenges in treating brain cancers, diseases, and infections because many drugs cannot penetrate this barrier

what challenges does the BBB create