S&F Exam 3

Neurons

• Electrical cells

• How the body communicates

Ways that neurons communicate

• Electrical signals

• Chemical signals

Electrical signals name

Action potentials

• Cause the release of neurotransmitters

Chemical signals name

Neurotransmitters

Cranial nervous system

CNS

• Brain and spinal cord

Peripheral nervous system

PNS

• Cranial nerves, spinal nerves, ganglia

• Comes in and out of CNS

Path of information and response

Sensory information (afferent pathways) → Interneurons → Motor neurons

Sensory information

Information that goes from the body to CNS

Interneurons

Neurons in the brain or spinal cord

Motor neurons

Information going out of CNS to the body

Nerves

Carry info to CNS and from CNS to the body

How many spinal nerves are there

31 pairs (each side)

Origination of spinal nerves

Spinal cord

Types of neurons in spinal nerves

Mixed neurons

Mixed neuron

Has sensory neurons going in and motor coming out within one nerve

Where do spinal nerves enter and exit from

Through intervertebral foramen

What does spinal nerves innervate to

• Trunk

• Limbs

• Some go to head

How many cranial nerves are there

12 pairs (each side)

• 24 total

Where do cranial nerves originate

Brain and brain stem

• CN 1 & 2 → cranium

• CN 3-12 → brainstem

Types of neurons in cranial nerves

• Only sensory

• Only motor

• Mixed

Where do cranial nerves exit

Through all foramen in the skull

What do cranial nerves innervate to

Structures of head and neck

Which cranial nerve is different from the rest

CN 10

• innervates with all the organs

What is CN 10 name

Vagus nerve

Types of sensory neurons that go to spinal nerves

• Somatic sensory neurons

• Visceral sensory neurons

Where do somatic sensory neurons come from

• Skeletal muscles

• Joints

• Skin

Where do visceral sensory neurons come from

• Smooth muscle

• Cardiac muscle

• Glands

Types of motor neurons that come out of CNS

• Somatic motor neurons

• Visceral motor neurons

Where do somatic motor neurons go

• Skeletal muscles

• Joints

• Skin

Where do visceral motor neurons go

• Smooth muscle

• Cardiac muscle

• Glands

What is visceral motor actually

Autonomic system

Sections of the autonomic nervous system

• Sympathetic nervous system

• Parasympathetic nervous system

Sympathetic nervous system nickname

Fight or Flight

Parasympathetic nervous system nickname

Rest and Digest

Characteristics of neurons

• Amitotic

• High longevity

• High metabolic rate

Amitotic definition

Cannot divide

How much ATP is used by neurons

Neurons in the brain use 20% of body’s ATP

• Brain is 2% of bodyweight

Types of neurons

• Nuclei

• Ganglia

Nuclei definition

In CNS

• groups of neurons that work together to perform a specific function

Ganglia definition

In PNS

• groups of neurons that work together to perform a specific function

What do dendrites do

Receive signals from other cells

What is a synapse

Junction at the end of axon where it stimulates another cell

Soma

Cell body

What are nerves

Bundles of axons

What do nerves do

Carries information to or from CNS

What surrounds nerves

Surrounded by connective tissue in PNS

What are tracts

Bundles of axons in CNS

• has no connective tissue wrapping

What do tracts do

Carries information within the CNS

Myelin sheath

Surrounds the axon

Types of neuroglial cells of PNS

• Schwann cell

• Satellite cell

Schwann cells

Myelinate certain axons in PNS

Satellite cells

Surround somas of ganglia

• surrounds and support cell bodies

• physical support

• nutrient/ waste exchange

• microenvironment regulation

What are myelinated axons made up of

• 20% protein

• 80% lipids

Types of neuroglial cells of CNS

• Astrocytes

• Microglial cells

• Ependymal cells

• Oligodendrocyte

Astrocytes

• Anchor neurons and blood vessels

• Regulate extracellular environment

• Facilitate formation of blood-brain barrier

• Repair damaged tissue/ form scar tissue

• Feed neurons

• Secrete nerve growth-factor

• Signal vasodilation/ vasoconstriction

How do astrocytes feed neurons

Through glucose

What happens if there is no nerve growth factor

Neurons will die

Microglial cells

Act as phagocytes

• Can wander

Ependymal cells

• Line cavities

• Cilla circulate fluid

• Around brain and spinal cord

• Produce cerebral spinal fluid

Oligodendrocyte

Myelinate certain axons in CNS

• has arms

Factors that determine the conduction velocity of action potential

1. Diameter

2. Myelinated/ unmyelinated

What does diameter have to do with conduction velocity of action potential

Larger diameter = nerves have a faster conduction velocity

What does being myelinated or unmyelinated have to do with conduction velocity of action potential

Myelinated have faster conduction velocity

Multiple sclerosis

In CNS

• Destruction of nerve covering/ myelin sheath

Ions defintion

Charged particles

What causes electrical signals of neurons

• Ion channels

• Light stimulation

• Thermal stimulation

Types of ion channels that cause electrical signals of neurons

• chemically-gated ion channels

• voltage-gated ion channels

• mechanically-gated ion channels

What do ion channels do

Movement of ions cause an action potential

Chemically-gated ion channels

Ligand gated

• Opens in response to binding of the appropriate neurotransmitter

Chemically-gated ion channels examples

• neurotransmitters

• drugs

• odor molecules

Voltage-gated ion channels

Open in response to electrical changes in membrane

• change in membrane voltage/ charge

Mechanically-gated ion channels

Open from physical force

Mechanically-gated ion channels examples

• pressure

• stretch

Light stimulation

Opens channels when light hits retina

Thermal stimulation

Opens channels from heat

Where are voltage-gated channels

In the axon

Where is mechanically-gated channels located

Soma

• stimulated by something

Where is chemically-gated channels located

Soma

• stimulated by something

Where is light stimulation channels located

Soma

• stimulated by something

Where is thermal stimulation channels located

Soma

• stimulated by something

Excitatory neurotransmitter

Increase a response

• stimulate

Inhibitory neurotransmitter

Decrease a response

• inhibit

What happens if a neuron can’t generate ATP

It can’t do its job

What does movement of ions across the membrane do

Creates an electrical signal (AP)

Why do ions move when the channel opens

Electrochemical gradient

Chemical gradient

Concentration gradient

Electrical gradient

Opposite charges attract

Potential

Difference in change on either side of membrane

Equal charge

There is no potential

Current

An electrical signal moves down membrane

Resting Membrane Potential

RMP

• Difference in charge on either side of the membrane in a resting neuron

Resting neuron

Neuron that is not actively being stimulated to generate an AP

Resting membrane potential number

-70 mV

Because proteins are negative & there is a lot of protein inside cells

Why are gradients needed

To generate an AP because neurons don’t work without a gradient

Polarized

• Not the same charge inside and outside the cell

Depolorized

ICF is becomes negative

• higher than -70

How does depolarization occur

Influx of positive ions

Repolarized

Return of negative ICF and positive ECF

How does repolarization occur

• Influx of negative ions

• Efflux of positive ions

Hyperpolarized

ICF becomes more negative than resting membrane potential

• <70