Cells of the Nervous System and Neurophysiology

What are the functions of neurons?

• send signals along thin fibers (axons)

• communicate with other cells by releasing NTs at synapses

What are the functions of neuroglial cells?

• provide support and nutrition in the nervous system

• maintain the electrochemical surroundings of neurons

How can neuroglial cells be describe?

metabolic; help neurons function well

What is grey matter?

dendrites, cell bodies, axon terminals and synapses

What can grey matter also be called?

nuclei

What is white matter?

bundles of myelinated axons

What the areas of White matter?

• Fasciculus

• funinculus

• lemniscus

• peduncle

• tract

Myelin is …

fatty.

What are the 3 structural types of neurons?

1. multipolar

2. bipolar

3. unipolar

What are multipolar neurons?

motor neurons; most numerous in the CNS

What are bipolar neurons?

sensory neurons of the retina of eye and nose

What are unipolar neurons?

single process that divides into two branches; one branch extends to the CNS, the other extends to the periphery.

Where are unipolar neurons mostly found?

in sensory ganglia neurons

What are the 3 functional classifications of of neurons?

1. sensory or afferent

2. motor or efferent

3. interneurons (association neurons)

What are Sensory/Afferent neurons?

action potentials are towards the CNS

What are motor/efferent neurons?

action potentials are away from the CNS

What are interneurons?

within CNS from one neuron to another (99%)

Interneurons make … connections in the brain?

local

Sensory neurons are … in info.

taking

Motor neurons are … out info.

sending

What are neurons?

electrically excitable cells in the nervous system that function to process and transmit information

What is the function of dendrites?

to receive signals

What is the function of the soma or cell body?

to integrate signals

The soma is the … neuron.

skeleton

What is axon of a neuron?

long extension sends signals (starts at axon hillock)

what are the components of a synapse?

• myelin sheath, nodes of ranvier

• presynaptic

• postsynaptic

structure of a neuron

What is the axon hillock?

the “trigger zone”; gathers incoming electrical signals and decides whether to fire an action potential.

Why is axonal transport necessary?

because axons can be 1,000-10,000x length of the cell body

What is antegrade transport?

transport away from the cell body, toward synapse

What is retrograde transport?

transport toward the cell body

What can retrograde transport be hijacked by and how?

• viruses

• taken up by axon terminals in peripheral nerves and transported back to cell bodies in CNS by rapid retrograde transport

• 
  

which viruses can hijack axonal transport?

herpes simplex, polio, rabies and toxins - tetanus toxin

What is the synapse?

facilitates transmission of impulses from one neuron to another neuron

chemical synapses =

neurotransmitters

electrical synapses =

gap junctions in mammals

What are the majority of synapses in the body?

chemical synapses

What are the 6 types of neuroglial cells?

1. astrocytes

2. microglia

3. oligodendrocytes

4. ependymal cells

5. schwann cells

6. satellite cells

Which neuroglial cells are in the CNS?

1. astrocytes

2. microglia

3. oligodendrocytes

4. ependymal cells

How can you describe the look of astrocytes?

star-like

What is the most numerous and diverse neurological cells?

astrocytes

What are the 2 types of astrocytes?

1. fibrous

2. protoplasmic

fibrous and protoplasmic astrocytes

What are the functions of astrocytes?

• maintain brain homeostasis by regulating extracellular K and glutamate

• Form the BBB; provides brain defense

• regulate blood flow in CNS

• Store and distribute energy substrates

• eliminate neurons that are not useful

What are astrocytomas?

primary brain tumors in children and adults

What diseases do astrocytes play a role in?

• neurodevelopment - rett syndrome, fragile X, mental retardation, Alexander disease

• inflammation in neurodegenerative disease (AD, PD)

what are microglia?

macrophages of the brain and spinal cord

True or false. Microglia are derived from the same lineage as neurons and astrocytes.

false

What are the origins of microglia?

macrophages and other hematopoietic cells

What do “resting” microglia continuously do?

scan their environment

phases of microglia from resting to active

What are the functions of microglia?

• main form of active immune defense in CNS

• phagocytosis

• promote repair following damage

What happens when microglia are chronically activated?

release of reactive oxygen species = BAD

What is the primary purpose of oligodendrocytes?

create myelin sheaths

What is the composition of myelin sheaths?

80% lipid and 20% protein

what is an example of a demyelinating disease?

multiple sclerosis

What happens cellularly during multiple sclerosis?

groups of oligodendrocytes and their myelin segments degenerate → replaced by astrocytic plaques

attack on myelin sheaths

In MS, the loss of myelin results in what?

interruption of the propagation of action potential down the axons.

What are ependymal cells?

cells that line the inner surfaces of the brain ventricles and the central canal of the spinal cord

What are functions of ependymal cells?

• control production/flow of CSF

• create barrier b/t brain tissue and CSF

• controls brain metabolism

• waste clearance

What structure produces CSF?

choroid plexus

What do satellite cells do?

surround cell bodies of neurons in sensory and autonomic ganglia

What do schwann cells do?

ensheath axons in PNS; wraps around the axons

What are schwannomas?

nerve sheath tumors that develop from schwann cells

what is the most common type of schwannoma?

vestibular schwannoma

What do the electrical properties of neurons result from?

• different concentrations of ions across plasma membrane

• permeability characteristics of plasma membrane

What is excitability?

cells stimulated by appropriate mechanical, thermal, chemical, and electric stimula

What principle applies to excitability?

all or none law

the size of an AP is …. of the stimulus

independent

What is conductivity?

impulse if conducted similar to cable conduction - in one direction

What kind of periods do neurons have?

refractory

action potential

What is a refractory period?

a brief time after an action potential when the cell cannot easily fire another signal.

true or false. An AP can regenerate itself.

true

AP propagation in unmyelinated axons

occurs as a continuous wave-like movement of electrical depolarization along the length of the axon.

What prevents retrograde movement in unmyelinated axons?

inactivated sodium channels behind the zone of depolarization

What direction do action potentials travel in?

one direction toward the synaptic terminals

How do AP travel down unmyelinated axons?

the electrical current depolarizes the neighboring regions of the axon - SLOWER

How does propagation work in myelinated axons?

by myelin preventing the movement of Na and K ions through the membrane; “turns off” certain Na/K pumps where myelin is at

What are nodes of Ranvier?

interruption of myelin where there are “active” Na channels and Na/K pumps

Where does the AP occur on myelinated axons?

• at nodes of Ranvier

• AP at one node depolarizes the membrane to reach threshold at the next node

What do myelinated axons participate in?

saltatory conduction

What is saltatory conduction?

“leaps” to other nodes of Ranvier; FAST

What makes myelinated axons even faster?

a larger diameter axon + more myelin = fast

What are the 2 types of synapses?

1. electric

2. chemical

What are majority of synapses in the body?

chemical synapses

What are electrical synapses?

passive flow of ionic current through gap junction b/t presynaptic and postsynaptic neuron

electrical synapse

gap junctions contain the ion-gated channels

What are chemical synapses?

signaling mediated by chemicals → neurotransmitters

utilize vesicles/exocytosis

chemical synapse

What is a synapse?

where communication between neurons takes place

What happens in the presynaptic cell?

1. AP arrives at axon terminal

2. Ca²⁺ channels open

3. Ca²⁺ enters the cell

4. Calcium signals to vesicles

5. vesicles move to synaptic membrane

6. docked vesicles release NTs via exocytosis

7. NT diffuses across synaptic cleft and binds to receptor

Presynaptic cell functions

What are the 2 types of synaptic transmission?

fast and slow

How quickly do fast synaptic transmission occur?

within 1 m/s

What channels do fast synaptic transmission use?

ligand-gated ion channels

Which NTs does fast synaptic transmission use?

glutamate and GABA

Which cells use fast synaptic transmission?

• motor neurons

• tract cell projecting to the thalamus

What is the speed of slow synaptic transmission occur?

over 100 m/s - 1 minute

What structures use slow synaptic transmission?

• metabotropic receptors

• linked to adjacent to guanine nucleotide-binding proteins (G proteins), second messenger system