Module A1 - Cytology of neurons (Class Notes)

What is best to describe a reflex?

A reflex is a simple involuntary and instantaneous motor responses to a given stimulus

What is the local neural circuits made reflex possible?

Reflex arcs ( operate at spinal level - simple)

Do reflex depend on conscious thoughts or processing by the brain?

No

What is mono synaptic reflex?

• Simple reflex

• 2 Neurons and 1 synapse

For patellar reflex, what is the stimulus

Tap tendon below knee

For patellar reflex - what is the response

Contraction of quadriceps m.

What are the components of a reflex

• Receptor

• Sensory neuron

• Motor Neuron

• Effector

• Synapse

What do receptors do on a reflex?

-Communicate information back to CNS

-Generate action potential

What is Effector do on a reflex?

Muscle constraction

Why are reflexes being evaluated?

Provide information about the background tone of the Nervous system

General Rule:

Dysfunction in the PNS

Hyporeflexia (decrease in reflex)

General rule:

Dysfunction to CNS

Hypereflexia (increase in reflexes)

Best estimate: how many neurons are in human brain

100 billion

neurons can be classified as ____ types, they share _____features

10,000 (10 thousand)

Common

Why do neurons with similar properties can produce very different actions

Precise connection with each other ( sensory receptors and muscle)

What are the 2 distinct classes of cells do Nervous system have

-Neurons

-Glial cells

What are the components of Neurons

Excitable-communication

• have resting state

What are the components for Glial Cells

support system- help with communication (can’t communicate itself

Non-excitable

Myelinated Axons

What are the morphologically of a typical neuron

Cell body (soma)

Dendrites

Axon/Myelin

Terminal Site

describe cell body

-Soma

-Contain Nucleus (metabolic center)

-10% of neuron

describe Dendrites

-comes out of cell body

-Receive information from other neuron

Describe Axon/ Myelin

Action potential travel: Axon——>Terminal site

What are the range of Axon’s Diameter

2-20ųm micrometer

How long are Axon

40in (1m)

Components of Terminal site

-Communicate with other neuron

-Chemical message

Nature neurons do not undergo______

Proitferation

Damage to neuron

- irreversible damage

-Most disease process that affect neuron associated with neuronal degradation and loss

Neuron Doctrine

Neurons are the basic butting block of nervous system

Principle of dynamic polarization

Information always flows in a specific direction

• action potential: generate in cell body and travels down to the terminal site

Principle of connection specificity

1. Neuron make specific precise connection to certain neuron and not others

2. Sensory nerve and motor nerve connect to the same muscle

Nodes of Ranvier

Exposed internodal area between the nodes cover with myelin

Axon Hillock

• also known as trigger zone

• Start of Action potential

• Start of Axon

Synapse:

• Space between neuron

• Use chemical to commicate

Sensory nerve

• Ascending pathway

• Information into CNS

Motor Nerve

• Descending pathway

• Information leaves CNS to PNS to activate muscles

Reflex arc

• muscle stretch—>muscle contraction without using the brain

  • Eg. Patellar reflex

  • Monosynaptic reflex

Soma

• body of Neuron

• metabolic center

Neuron differentiation

Distinguish neuron by: shape, number of neuritis

Unipolar cells

• 1 neurites from cell body

• Not common in mammals

• Common in cold blood animals ( shellfish)

Bipolar Neurons

• 2 Neurites from cell body

• Common in mammals (sensory)

Multipolar cell

• more than two neurites from cell body

• MOTOR NERVE

Pseudounipolar cell

• one neurites comes from the cell body

• Starts off as bipolar; after maturation cell body goes into dorsal root ganglion

• SENSORY NERVE

Neurons can be further classified_______ into three major groups

Functional

3 groups neuron can be classified as:

1. Afferent

2. Efferent

3. Interneurons

Afferent neuron (Ascending)

• carry info into CNS

• Sensory n.

Efferent neuron ( Descending)

• carry info out CNS

• Motor n.

Interneurons

• Most common

• Carry info b/w Afferent and efferent

What are Somas and axons surrounded by?

Glial cells

Glia means ______ in Greek

Glue

How many more glial cells than neurons in CNS of vertebrates

10-50x more

Glial cells____

• are non-excitable

• Support cells

• Can replicate

Functions of Glial cells

1. Supporting Elements

2. Form myelin

3. Scavengers in CNS

4. Buffer ions and neurotransmitters

5. Guide neuron during development

Functions of Glial cells: Supporting elements

Provide firmness to the brain

Functions of Glial cells: Form myelin

• Oligodendrocytes: CNS

  • To multiple axons~15 different areas

• Schwann cells: PNS

  • To one nodal area

Multiple sclerosis

• demyelinating disorder in CNS

• Effect the Oligodendrocytes

Functions of Glial cells: Scavengers in CNS

Clean up and repair injury

-activate during an injury

Functions of Glial cells: Buffer ions and Neurotransmitters

When large # of neuron activity; stabilize it

Functions of Glial cells: Guide neurons during development

Guide neuron to their proper location

Functions of Glial cells: form Blood brain barrier/CSF

Prevent chemicals into the brain (Ependymal cells)

Functions of Glial cells: Nutritive Function

Depending on their _____, Glial cell are divide into ___ major classes

1. Size

2. 2

2 classes of Glial cells are:

1. Microglia

2. Macroglia

Function: Microglia

Immune system for nervous system

Function: macroglia

• Oligodendrocytes

• Schwann cells

• Astrocytes

Function: Astrocyte

• most abundant

• Do not produce myelin

• Perform all the rest functions

Brain cancer (Gliomas)

• most are associated with glial cells

• B/c they can replicate

How many ways which constituents move within the axon?

3 ways

What are the 3 ways constituents move within the axon?

1. Fast Anterograde

2. Slow Anterograde

3. Fast Retrograde

What is the lifespan of Axonal transport

70-100years

Function of fast Axonal transport

Energy dependent process

Uses micro tubules for transport

Soma to terminal site

What protein does fast anterograde uses

Kinesin

What protein does fast retrograde use

Dynein

Rate for Fast anterograde:

400-1000 mm/day

Rate for slow anterograde

3mm/day

Rate for fast retrograde is

150-400mm/day

Function of slow anterograde

• using fluid; not microtubules

• Soma to terminal site

Function of fast retrograde

• Energy dependent

• Active process by Microtubules

Neurotropic Viruses travels through axon

• Herpes simplex (cold sores)

• Polio

• Rabies

• Tentanus