Lecture 11: Excitable Cells: Neurons & Glia

Question 0

The central nervous system (CNS)

Answer 0

Brain and spinal cord

Sensory receptors of sense organs (I.e. Eyes ears nose)

Nerves to connect nervous system with other systems

Peripheral nervous system: everything else

Question 1

The nervous system

Answer 1

Process and coordinates:

Sensory data from inside and outside body

Higher brain functions like intelligence memory, learning, emotion

Motor functions to control the activity and skeletal muscles

Question 2

Gray matter vs. white matter

Answer 2

White matter: regions of CNS tissue containing myelinated axons

Gray matter: cell bodies

Question 3

Cytology if the nervous system

Answer 3

Two primary cell types:
-neurons: send and receive electrical and chemical signs; excitable

Neuroglia (glial cells): support and protect neurons. May also play a role in signal transduction

Question 4

Neurons

Answer 4

Basic unit of the nervous system
-transmit impulses (APs) throughout the body

Characteristic of Neurons:

• high metabolic rate
• extreme longevity
• nonmitotic

Question 5

Axons and associated structures

Answer 5

1. Axon collaterals: side branches of the main axon

2. Synaptic knob: expanded regions at the tip of telodendria

Question 6

Structural classification

Answer 6

Based on the number of processes coming off of the soma

1. Unipolar: a single process usually T shaped
2. Bipolar: two processes (axon+dendrite)
3. Multipolar: many processes

Question 7

Synapses

Answer 7

The location of communication between neurons or between neurons and muscles

Early classifications/distinctions:

Morphologically:
- cell vs syncytium theory (mid to late 1800s)
Functionally:
- electrical vs chemical synapses

Question 8

Synaptic transmission

Answer 8

1. An action potential depolarizes the axon terminal
2. The depolarization opens voltage gated Ca2+ channels and Ca2+ enters the cell
3. Calcium entry triggers exocytosis of synaptic vesicle contents
4. Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the post synaptic cell
5. Neurotransmitter binding initiates a response in the post synaptic cell

Question 9

Unipolar axons

Answer 9

Very long axon, fused to dendrites

Not common in humans

Question 10

Bipolar neurons

Answer 10

Relatively small, one dendrite one axon

Bipolar cells are very common in the retina. This is thought to be because vision is a very complex process and you have lots of inputs and signal processing is happening.

Question 11

Multipolar neurons

Answer 11

Most abundant single long axon multiple dendrites

The most common type of neuron is a multipolar neuron. Again the major distinction is that the soma has multiple connections

Question 12

Classification of neurons

Answer 12

Functionally, neurons are classified according to the direction of the nerve impulse is traveling relative to the CNS:

1. Sensory (afferent): transmit impulses from sensory receptors to the CNS
2. Motor (efferent): transmit impulses from CNS to muscles or glands
3. Interneuron: facilitate communication between sensory and motor neurons

Interneurons are neurons that are inhibitory principle cells that propane information from

Question 13

Afferent to Efferent

Answer 13

Stimulus –> afferent (input) transmission–> cell body of sensory neuron –> posterior root ganglion –> CNS (spinal cord)

–> interneuron–> down motor neuron –> efferent (output) transmission–> motor unit –> response

Question 14

Neuroglia

Answer 14

Located in CNS and PNS

Half the volume of the nervous system

Smaller than neuron

Mitotic

Physically protect and nourish neuron

More abundant than neuron (10:1)

Brain tumors

Diverse but not as diverse as neurons. Neurons don’t make contact with capillaries, glia cells do. So nutrients pass through glial cells in order to reach the neuron

Question 15

Cells of the CNS

Answer 15

There are four types of cells found in the CNS:

1. Astrocytes
2. Ependymal cells
3. Micro glial cells
4. Oligodendrocyte

Question 16

Astrocytes

Answer 16

Protective: maintain blood brain barrier
Scaffold: create 3 dimensional framework for CNS
Repair: damaged neural tissue
Development: glial cells develop first
Regulation: control interstitial environment

Astrocytes maintain the blood brain barrier. It also has a scaffolding function as well. astrocytes appear first during development and so it’s thought they help to guide the development of neurons. Astrocytes also control the interstitial environment, for example astrocytes are very good at clearing potassium from the extra cellular space surrounding neurons

Question 17

Ependymal cells

Answer 17

Ciliated cuboidal epithelial cells that line the ventricles of the brain and the central canal of the spinal cord

In conjunction with other glial cells, the ependymal cells produce cerebral spinal fluid and form the choroid plexus and have stem cell like properties

Question 18

Microglial cells

Answer 18

Small, motile
Remove cell debris via phagocytosis

Micro glial cells are very important for the immune system so they have to be small and they have to be motile so that they can travel around to find these pathogens and cellular debris

Question 19

Oligodendrocytes

Answer 19

CNS only!
Wrap themselves around the axons like electrical tape wrapped around a wire

Produce myelin

Only glial cells that can form synapses with neurons as progenitor cells

Oligodendrocytes are important because they are the cells that provide that myelin sheath.

Question 20

Glial cells of the PNS

Answer 20

Two types of cells found in the PNS:

1. Satellite cells
2. Schwann cells (neurolemmocytes)

Question 21

Satellite cells

Answer 21

Also called amphicytes

Surrounding ganglia

Regulate environment around neuron

Question 22

Neurolemmocytes

Answer 22

Aka Schwann cells

PNS only!

Wrap themselves around the axons like electrical tape wrapped around a wire

Produce myelin

Comparable to oligodendrocytes except more cells are required

Unlike oligodendrocytes a Schwann cell only makes contact with a single cell not only that but it only makes a single myelin segment. This is also the reason why all of the motor neurons appear white because when you look at them what you are actually seeing is marking

Increases speed of action potentials

Myelin insulated myelinated axons

Makes nerves appear white