NEUROANATOMY- Neurons

What is a neuron?

smallest and most basic unit of the nervous system

identify

Unipolar

identify

Bipolar

identify

Multipolar

Parts of a Neuron

receive signals

Dendrites

Parts of a Neuron

Process information (grey matter)

Cell Body

Parts of a Neuron

Transmits information to next neuron/muscle fibers

Axon (single)

1

dendrites

2

cell body

3

Axon Hillock

4

axon

5

Presynaptic terminal

Contains:

 Nucleus

 Endoplasmic reticulum

 Golgi apparatus

 Mitochondria

 Ribosomes

 Secretory vesicles

Cell Body – AKA Soma

1

Soma (cell body)

Dendrites → Cell Body → Axon → Next neuron/muscle

Receive → Process → Send

What is the typical number of axons in a neuron?

one

the main job of the axon is»»
Transmits the electrical signal _____from the cell body

away

Where does the electrical signal travel from and to?
From the ______ → _______

axon hillock; presynaptic terminal

fatty substance that increases the speed of conduction

myelin

How does myelin increase conduction speed?

The action potential jumps from one node to the next

Breaks (gaps) in the myelin sheet

myelin sheet

How long can an axon be?

It can exceed 1 meter (such as in the sciatic nerve)

How fast can a nerve signal travel?

Up to 150 m/s (335.5 mph)

sends signal away

Axon

fatty + faster

Myelin

gaps in myelin

Nodes of Ranvier

Axon length

>1 meter

Speed

up to 150 m/s

1

axon hillock

2

myelin

3

nodes of ranvier

4

axon

Glia =

glue

the components/cells (glue) that hold nervous tissue together

neuroglia

What are astrocytes?

The largest and most abundant glial cells in the CNS

What are the largest and most abundant glial cells in the CNS?

Astrocytes (CNS)

What structures do astrocytes connect?

CNSP

Capillaries, neurons, synaptic endings, and the pia mater

Astrocytes provide ________ support.

Structural

Astrocytes help form the ________

blood-brain barrier

Astrocytes recycle excess ________ and ________.

ions; neurotransmitters

Astrocytes exchange nutrients between ________ and ________.

capillary blood; neurons

Astrocytes secrete chemicals that aid ________, ________, and ________.

migration; growth; synapse formation

Astrocytes repair damaged ________

nervous tissue

What are the 6 main functions of astrocytes?

1. Structural support
2. Blood-brain barrier
3. Recycle excess ions & neurotransmitters
4. Exchange of nutrients between capillary blood & neurons
5. Secrete chemicals that aid migration, growth, and synapse formation
6. Repair damaged nervous tissue

basically form myelin sheath

Oligodendrocytes (CNS)

protection by removing cellular debris, micro-organisms, and damaged tissue

Microglial cells (CNS)

secretion & circulation of cerebrospinal fluid

Ependymal cells (CNS)

What do Schwann cells do?

Form the myelin sheath around axons in the PNS.

What are Schwann cells compared to in the CNS?

They are basically the oligodendrocytes of the PNS

What do satellite cells do?

Provide structural support and a barrier and regulate exchange between neuron cell bodies and interstitial fluid

What is the main function of satellite cells?

Structural support and forming a barrier around neuron cell bodies

What do satellite cells regulate?

The exchange of substances between neuron cell bodies and interstitial fluid.

Satellite cells regulate exchange between what two things?

Neuron cell bodies and interstitial fluid.

1

axon

2

Perineurium

3

fascicle

4

epineurium

nerve

A collection of axons bundled

together and enclosed by

perineurium forms a nerve

fascicle. Fascicles, bundles

together and surrounded by

epineurium

1

Basal Nuclei

cluster of neuronal cell bodies in CNS

Nucleus

1

Trigeminal Ganglia

cluster of neuronal cell bodies in the PNS

Ganglion

most abundant; structural support & blood-brain barrier

Astrocytes

form myelin

Oligodendrocytes

protect by cleaning

Microglial cells

cerebrospinal fluid circulation

Ependymal cells

myelin for nerves in PNS

Schwann cells

structural support & barrier

Satellite cells

What is an action potential?

An electrical signal that travels along a neuron to transmit information

Where does an action potential begin?

At the trigger zone of the neuron.

What must happen for an action potential to begin?

A stimulus must be strong enough to reach the threshold

What is threshold?

The point at which the membrane has been depolarized enough to trigger an action potential.

What are the three phases of an action potential?

Depolarization → Repolarization → After-hyperpolarization

What happens during depolarization?

The inside of the neuron becomes more positive.

What causes depolarization?

Channels open, allowing positive ions to enter the neuron.

What happens during repolarization?

The membrane becomes less positive and moves back toward its resting state.

What causes repolarization?

Sodium entry stops and potassium leaves the cell.

What is after-hyperpolarization?

A brief period when the membrane becomes more negative than its normal resting state.

Why does after-hyperpolarization happen?

The channels involved in returning the membrane to its resting state do not close immediately, causing the membrane to temporarily become too negative.

What does propagation mean?

The movement of an action potential along the axon.

In what direction does an action potential normally propagate?

Toward the axon terminal.

Why does an action potential move forward instead of backward?

The part of the axon that just fired becomes refractory, so it temporarily cannot fire another action potential

What does refractory mean?

The recently activated part of the membrane is temporarily unable to fire another action potential.

Where does continuous conduction occur?

In unmyelinated axons.

How does continuous conduction work?

The action potential travels continuously along the entire axon membrane, activating one section after another.

Why is it called continuous conduction?

Because the signal travels along each section of the membrane instead of jumping over sections.

Is continuous conduction faster or slower?

Slower than saltatory conduction

Where does saltatory conduction occur?

In myelinated axons

What is myelin?

An insulating covering around parts of the axon

What are Nodes of Ranvier?

Gaps in the myelin sheath along the axon

How does saltatory conduction work?

The action potential appears to jump from one Node of Ranvier to the next.

Is saltatory conduction faster or slower?

Faster than continuous conduction.

Why is saltatory conduction faster?

Because the action potential jumps between nodes instead of traveling along every section of the axon membrane.This allows the impulse to propagate more quickly, as the insulated sections of the axon do not require depolarization.

What is the main difference between continuous and saltatory conduction?

Continuous conduction occurs in unmyelinated axons and travels along the entire membrane. Saltatory conduction occurs in myelinated axons and appears to jump from node to node.

Which type of conduction is faster?

Saltatory conduction

Why is continuous conduction slower?

The action potential must activate each section of the axon membrane one after another

Why is saltatory conduction faster?

The action potential jumps between Nodes of Ranvier, so it does not need to travel across every section of the membrane

What do continuous and saltatory conduction have in common?

Both propagate an action potential along the axon toward the axon terminal

What is the goal of both types of conduction?

To carry the electrical signal from the trigger zone toward the axon terminal.