Anatomy and Physiology of the Nervous System

3 Functions of the Nervous System

Sensory Input

Integration

Motor Output

Two Divisions of the Nervous System

Central Nervous System

Peripheral Nervous System

Two Divisions of the PNS

Sensory (Afferent)

Motor (Efferent)

Two Divisions of the Motor Division of the PNS

Somatic Nervous System

Autonomic Nervous System

Two Divisions of the ANS

Sympathetic Division

Parasympathetic Division

Primary Neurotransmitter of the SNS

Norepinephrine/Epinephrine

Primary Neurotransmitter of the PNS

Acetylcholine

What composes the central nervous system?

Brain

Spinal Cord

What composes the peripheral nervous system?

Cranial Nerves

Spinal Nerves

Ganglia

Which division of the nervous system innervates smooth muscle?

Autonomic Nervous System

Which division of the nervous system innervates skeletal muscle?

Somatic

Four Primary Neuoglia of the CNS

Astrocytes

Microglia

Ependymal Cells

Oligodendrocytes

Which glial cell forms the Blood Brain Barrier (BBB)?

Astrocytes

What are the 4 functions of astrocytes?

1. Cover capillaries to form the BBB

2. Synaptic formation

3. Regulate the chemical environment through removal of neurotransmitters from the synaptic cleft

4. Signaling/releasing chemical messengers to increase neuronal communication

What is the main function of microglia?

Immune-like cells that act as macrophages in the CNS detecting damage

Where are ependymal cells located?

Ventricles (Cavities in the CNS)

What is the main function of ependymal cells?

Move cerebrospinal fluid through the ventricles

How do ependymal cells move CSF?

Cilia

Oligodendrocytes form _______ around axons to insulate and increase the speed of nerve impulses.

Myelin Sheaths

What is the most abundant CNS neuroglia?

Astrocytes

What are the two primary neuroglia in the PNS?

Satellite cells

Schwann cells

Where are satelite cells located?

Surrounding neuronal cell bodies in the PNS

What function do satellite cells perform?

Protect and support the neuronal cell bodies and provide nutrients

What function do Schwann cells perform?

Forming myelin sheaths around axons of nerve fibers in the PNS to increase speed of action potentials

Which neuroglia participate in regeneration of damaged peripheral nerve fibers?

Schwann cells

What are the three parts of a neuron?

Cell body (Soma)

Dendrites

Axon

Neuron Cell Body in the CNS

Nuclei

Neuron Cell Body in the PNS

Ganglion

What is the function of dendrites?

Receive signals

Nerve Fibers

Long axons

Tract

Bundle of axons in the CNS

Nerve

Bundle of axons in the PNS

What part of the axon releases neurotransmitters?

Synaptic terminals

Action Potential

Impulse conducted down the axon

Myelin

Whitish, protein-lipid substance

Two functions of myelin

Protect/electrically insulate axon

Increase speed of nerve impulse

Myelinated Fibers

Segmented sheath surrounds most long or large-diameter axons to conduct impulses rapidly

Nonmyelinated Fibers

Contains no sheaths (or only lightly myelinated) resulting in slower impulse conduction

Which part of the neuron generates the action potential?

Axon hillock

What are the main types of membrane ion channels in neurophysiology?

Leak channels

Ligand-gated ion channels

Voltage-gated ion channels

Other gated ion channels

RMP

Resting Membrane Potential

RMP Value

Approx. -70 mV

What channels primarily produce and maintain the RMP?

K+ leak channels

NA+ leak channels

Na+-K+ ATPase Pump

Is the inside or outside of a cell negatively charged?

Inside

Polarized

Difference in charge across the cell membrane

Do K+ leak channels allow K+ into or out of the cell?

Out of the cell

Do Na+ leak channels allow Na+ into or out of the cell?

Into the cell

Do potassium leak channels or sodium leak channels create a greater negative charge inside of the cell?

Potassium leak channels

Depolarization

Decrease in the membrane potential

Does the cell become more positive or negative when depolarized?

More positive

Hyperpolarization

Increase in membrane potential

Does the cell become more positive or negative when hyperpolarized?

More negative

Changes in membrane potential are called...

Graded potentials

What are two examples of graded potentials?

Depolarization

Hyperpolarization

Graded potentials are _________ to stimulus strength.

Proportional

Graded potentials decay with distance as they are _________.

Localized

During an action potential, the membrane potential is reversed from -70 mV to _____.

+20 to 30 mV

When the membrane potential is reversed during an action potential, this is caused by local currents, also called ____________.

Graded potentials

The depolarizing current must reach _____ to initiate an action potential.

Threshold

Threshold value

-50 to -55 mV

T/F: Action pontentials decrease in strength along the distance of the axon.

False

What channels are primarily responsible for action pontentials?

Voltage-gated K+ channel

Voltage-gated Na+ channel

4 Steps of an Action Potential

1. Resting State

2. Depolarization

3. Repolarization

4. Hyperpolarization

State of Channels during the Resting State of an Action Potential

Closed activation gates on Na+ and K+ voltage-gated channels

Open Inactivation gate on Na+ channel

State of Channels during the Depolarization of an Action Potential

Open activation gate and inactivation gate on Na+ voltage-gated channel

Closed activation gate on K+ voltage-gated channel

State of Channels during the Repolarization of an Action Potential

Open activation gates on Na+ and K+ voltage-gated channels

Closed inactivation gate on Na+ voltage-gated channel

State of Channels during the Hyperpolarization of an Action Potential

Closed activation gates on Na+ voltage-gated channels

Open activation gates on K+ voltage-gated channels

Open Inactivation gate on Na+ channel

During what stages of an action potential is the cell membrane most permeable to Na+?

Depolarization

During what stages of an action potential is the cell membrane most permeable to K+?

Repolarization, with decreasing affinity through hyperpolarization

Refractory Period

Period where another action potential cannot be generated

Which channels are open causing the refractory period?

Voltage-gated Na+ Channels

What are the two subdivisions of the refractory period?

Absolute Refractory Period

Relative Refractory Period

Absolute Refractory Period

Cell is unresponsive to stimuli stopping another AP from being generated due to open Na+ channels

The absolute refractory period enforces __________ transmission of nerve impulses.

One-way

Relative Refractory Period

Cell can be responsive to stimuli as most Na+ channels are in resting state, but it requires a stronger stimulus

When is the relative refractory period?

During the end of repolarization and hyperpolarization

Propagation

The generation of an action potential along the length of an axon

Is propagation faster for myelinated or nonmyelinated axons?

Myelinated

Saltatory Conduction

Action potentials are generated at the gaps in myelination allowing for faster conduction than continuous conduction in nonmyelinated axons

Synapse

Site of communication between two neurons transmitting signals

Presynaptic neuron

Sends signal (transmits impulse towards synapse)

Postsynaptic neuron

Receives signal (transmits signal away from synapse)

Two Types of Synapses

Electrical

Chemical

What type of junction is present in electrical synapses?

Gap junctions and Connexons (Protein pores)

How do ions travel between electrical synapses?

Ions flow between adjacent cells using channels that are formed by pores to share ions quickly

How is communication between cells performed with chemical synapses?

Presynaptic neurons release neurotransmitters into the synaptic cleft to bind to receptors on the postsynaptic neuron's membrane

Which type of synapse is most common?

Chemical

When an AP arrives at the presynaptic axon terminal, depolarization of the membrane opens which channels?

Voltage-Gated Ca2+ Channels

When Ca2+ interacts with intracellular proteins, the vesicles of neurotransmitters go through this process.

Exocytosis

Neurotransmitters diffuse across this space to bind to specific receptors on the postsynaptic membrane?

Synaptic cleft

When neurotransmitters bind to the receptors, conformational changes happen to allow the ion channels to open and create ____________.

Graded potentials

Graded potentials can be either _________ (depolarization) or __________ (hyperpolarization), depending on the type of receptor.

Excitatory, Inhibitory

After causing graded potentials, the neurotransmitter is _________ through various methods.

Terminated

EPSP

Excitatory Postsynaptic Potential

Excitatory Postsynaptic Potential

Local depolarization of the postsynaptic membrane helps to produce an AP in the axon hillock, increasing the membrane Na+ permeability

IPSP

Inhibitory Postsynaptic Potential

Inhibitory Postsynaptic Potential

Local hyperpolarization of the postsynaptic membrane helps to prevent an AP by driving the neuron away from the threshold, increasing the membrane K+ or Cl- permeability

IPSPs cause K+ to be brought into or out of the cell?

Out of the cell

IPSPs cause Cl- to be brought into or out of the cell?

Into the cell

Neurotransmitter

Chemical messenger that facilitates communication between cells in the nervous system