Fundamentals of the Fundamentals of the Nervous SystemNervous System

Three functions of the nervous Three functions of the nervous systemsystem

1- sensory (afferent) input: sensory 1- sensory (afferent) input: sensory receptors that work with the NS.receptors that work with the NS.

2- integration: processing and 2- integration: processing and interpreting of data from the sensory interpreting of data from the sensory inputinput

3. motor (efferent) output: a response 3. motor (efferent) output: a response initiated by integration.initiated by integration.

Organization:Organization: CNS: (central nervous system)CNS: (central nervous system)

- brain- brain

- spinal cord- spinal cord (PNS) Peripheral Nervous System(PNS) Peripheral Nervous System

- cranial nerves (12 pairs)- cranial nerves (12 pairs)

- spinal nerves (31 pairs)- spinal nerves (31 pairs)

Communication lines between CNS and Communication lines between CNS and the rest of body the rest of body

Divisions: Divisions:

- - Sensory (afferent) division Sensory (afferent) division Somatic (skin, muscle, joints) and Somatic (skin, muscle, joints) and

visceral (organs) sensory neurons visceral (organs) sensory neurons Conducts impulses from receptors to the Conducts impulses from receptors to the

CNSCNS

- Motor (efferent) division - Motor (efferent) division Motor neurons Motor neurons Conducts impulses from the CNS to Conducts impulses from the CNS to

effectors (muscles and glands) effectors (muscles and glands)

Motor Divisions: Motor Divisions: Somatic Nervous System Somatic Nervous System

- Voluntary - Voluntary

- Conducts impulses from CNS to - Conducts impulses from CNS to skeletal skeletal muscles muscles

Autonomic Nervous System Autonomic Nervous System - Involuntary - Involuntary

- Conducts impulses from CNS to cardiac - Conducts impulses from CNS to cardiac muscles, smooth muscles, and glands. muscles, smooth muscles, and glands.

- Divisions: - Divisions: - Sympathetic- Sympathetic

- Parasympathetic- Parasympathetic

Two types of cells in the nervous system.Two types of cells in the nervous system.1- Neurons (nerve cells)1- Neurons (nerve cells)2- Glia: support, nourish and protect2- Glia: support, nourish and protect

neurons. “glue”neurons. “glue”

Glia: (neuroglia)Glia: (neuroglia)PNS:PNS:1- 1- Schwann cellsSchwann cells: cells produce a white fatty : cells produce a white fatty

substance called myelin around the large substance called myelin around the large nerve fibers of the PNS. Also called nerve fibers of the PNS. Also called neurolemmocytes.neurolemmocytes.

2- 2- Satellite cellsSatellite cells: surround neuron cell bodies : surround neuron cell bodies and may help regulate chemical and may help regulate chemical environment.environment.

Myelin Sheath and Myelin Sheath and NeurilemmaNeurilemma

CNS:CNS:

Astrocytes:Astrocytes:- connecting neurons to blood supplyconnecting neurons to blood supply- projections with bulbous ends that cling to projections with bulbous ends that cling to

neurons and capillaries neurons and capillaries - ½ of neural volume½ of neural volume- BBBBBB

Microglia:Microglia:

- small and remain stationary. When disease - small and remain stationary. When disease or inflammation is present they become or inflammation is present they become mobile and phagocytize microbes. mobile and phagocytize microbes. (macrophages) (macrophages)

Oligodendrocytes:Oligodendrocytes:

- Line up along the thicker neuron fibers- Line up along the thicker neuron fibers

- Produce myelin sheath around axons- Produce myelin sheath around axons

Ependymal cells:Ependymal cells:

- line central cavities of brain and spinal - line central cavities of brain and spinal cord, creating a barrier between CNS cord, creating a barrier between CNS cavities and tissues surrounding cavities and tissues surrounding cavities cavities

- cilia circulates the cerebrospinal fluid - cilia circulates the cerebrospinal fluid

Neurons (nerve cells):Neurons (nerve cells):

- Conducts messages in form of nerve - Conducts messages in form of nerve impulses impulses

- Has longevity - Has longevity

- Amitotic - Amitotic - Have a high metabolic rate Have a high metabolic rate Functionally composed of: Functionally composed of:

- A receptive (input) region - A receptive (input) region

- A conducting component (generates and - A conducting component (generates and propagates an action potential) propagates an action potential)

- A secretory (output) component - A secretory (output) component

- neurotransmitter- neurotransmitter

Neurons are composed ofNeurons are composed of- Cell bodyCell body- ProcessesProcesses

Cell body: (perikaryon or soma)Cell body: (perikaryon or soma)

- Most neuron cell bodies located within - Most neuron cell bodies located within CNS CNS

- Clusters of cell bodies in CNS are called - Clusters of cell bodies in CNS are called nuclei nuclei

- Few/clusters of cell bodies in PNS are Few/clusters of cell bodies in PNS are called called gangliaganglia

- Rough ER called Nissl bodies. Rough ER called Nissl bodies.

Processes Processes - Cellular processes are called either tracts- Cellular processes are called either tracts (in (in

CNS) or nervesCNS) or nerves (in PNS) (in PNS) - Dendrites - have large surface area to receive - Dendrites - have large surface area to receive

chemical signals as well as conduct electrical chemical signals as well as conduct electrical signals (graded potentials) signals (graded potentials)

- Axons - single in each neuron, transmit Axons - single in each neuron, transmit graded potential away from cell body to graded potential away from cell body to axonal terminal (generates action potential)axonal terminal (generates action potential)

- Axon hillock arises from the cell body into the Axon hillock arises from the cell body into the axon (graded potential)axon (graded potential)

- Profuse branching at end of axon called Profuse branching at end of axon called terminal branches or telodendria. At the tips terminal branches or telodendria. At the tips there are bulbous structures storing there are bulbous structures storing neurotransmitters. neurotransmitters.

Substances travel continuously up and Substances travel continuously up and down the axon.down the axon.

Anterograde: substances move from Anterograde: substances move from cell body to terminal axoncell body to terminal axon

Retrograde: substances move from Retrograde: substances move from terminal axon to cell body.terminal axon to cell body.

Plasma membrane of axon is Plasma membrane of axon is axolemma. axolemma.

- Electrochemical signals transmitted - Electrochemical signals transmitted with the aid by myelin sheath with the aid by myelin sheath (protein-lipoid) which insulates nerve (protein-lipoid) which insulates nerve fibers (long axons) and increases the fibers (long axons) and increases the transmission transmission

- - Nodes of Ranvier also aid in the Nodes of Ranvier also aid in the transmission of nerve impulses.transmission of nerve impulses.

- saltitory conduction - saltitory conduction - Myelinated processes form the white - Myelinated processes form the white

mattermatter of nervous tissue and of nervous tissue and unmyelinated processes form the unmyelinated processes form the gray mattergray matter of nervous tissue. of nervous tissue.

In the spinal cord, gray matter forms In the spinal cord, gray matter forms the H- shape in the center while the H- shape in the center while white matter surrounds it.white matter surrounds it.

In the brain, gray matter forms the In the brain, gray matter forms the thin outer cortex with white matter thin outer cortex with white matter filling the insidefilling the inside

Classification of neurons:Classification of neurons:

Structural Structural

FunctionalFunctional

Structural:Structural:

Neurons are classified as to how many Neurons are classified as to how many processes extend from their cell bodyprocesses extend from their cell body

Multipolar: three or more processes extend Multipolar: three or more processes extend from cell bodyfrom cell body

- posses single axon- posses single axon

- most common type of neuron in the CNS- most common type of neuron in the CNS

Bipolar: two processes (axon and dendrite) Bipolar: two processes (axon and dendrite) extend from opposite sides of neuron.extend from opposite sides of neuron.

- rare in adult but may be found in retina and rare in adult but may be found in retina and olfactory mucosa (special senses).olfactory mucosa (special senses).

Unipolar: one process extending from cell body Unipolar: one process extending from cell body and forms central and peripheral processes and forms central and peripheral processes

- Central process associated with secretory - Central process associated with secretory region region

- Peripheral process associated with sensory Peripheral process associated with sensory region (receptor).region (receptor).

- Found in ganglia of PNS where they function Found in ganglia of PNS where they function as sensory neuronsas sensory neurons

Functional Functional ClassificationClassificationof Neuronsof Neurons

Functional:Functional:

Sensory (afferent) neuronsSensory (afferent) neurons - transmit - transmit impulses from sensory receptors impulses from sensory receptors toward CNS toward CNS

Unipolar neurons - skin or internal Unipolar neurons - skin or internal organs to CNS for interpretation organs to CNS for interpretation

Bipolar neurons - special sense organs, Bipolar neurons - special sense organs, retina retina

Motor (efferent) neuronsMotor (efferent) neurons - carry - carry impulses away from CNS to organs impulses away from CNS to organs

Multipolar neurons - cell body located Multipolar neurons - cell body located within CNS and neurons form within CNS and neurons form neuromuscular junctions with neuromuscular junctions with effector (muscle or gland) cells effector (muscle or gland) cells

Association neurons (interneuronsAssociation neurons (interneurons) - ) - transmit impulses within CNS transmit impulses within CNS (usually sensory to motor); found in (usually sensory to motor); found in CNS only; mostly multipolar and 99% CNS only; mostly multipolar and 99% of neurons in body. Also called of neurons in body. Also called connecting neurons.connecting neurons.

Neurophysiology/Electrophysiology:Neurophysiology/Electrophysiology:

Resting Membrane Potential (RMP)Resting Membrane Potential (RMP)

Positive charge on the outsidePositive charge on the outside

Negative charge on the insideNegative charge on the inside

These electrical charges are in the form of These electrical charges are in the form of potential energy which is measured in potential energy which is measured in millivolts (-70mV in the plasma millivolts (-70mV in the plasma membrane)membrane)

The (-) in -70 mV refers to the inside of the The (-) in -70 mV refers to the inside of the membrane being more negative than the membrane being more negative than the outsideoutside

This membrane is said to be polarizedThis membrane is said to be polarized

The energy in the resting membrane is The energy in the resting membrane is likened to energy stored in a battery. likened to energy stored in a battery.

Flow of electrical charge is called Flow of electrical charge is called current.current.

In the membrane it flows by way of In the membrane it flows by way of ions instead of electrons (electricity)ions instead of electrons (electricity)

In a resting membrane (-70 mV) three In a resting membrane (-70 mV) three Na+ ions are pumped out for every Na+ ions are pumped out for every two K+ pumped in. This creates a two K+ pumped in. This creates a more negative situation on the inside:more negative situation on the inside:

Sodium/Potassium PumpSodium/Potassium Pump

Ion channels:Ion channels:

Leakage Leakage

GatedGated

Leakage channels are always open.Leakage channels are always open.

Gated channels open and close in response Gated channels open and close in response to a stimulus.to a stimulus.

Stimulus:Stimulus:

VoltageVoltage

ChemicalChemical

Mechanical pressureMechanical pressure

Light Light

Gated ChannelsGated Channels

Voltage gated ion channels will respond to Voltage gated ion channels will respond to the change in membrane potential the change in membrane potential (voltage). Excitability.(voltage). Excitability.

Chemically gated ion channels respond to Chemically gated ion channels respond to the presence of a specific chemical stimulus the presence of a specific chemical stimulus such as hormone, neurotransmitter, Ca+such as hormone, neurotransmitter, Ca+

The stimulus will result in a graded The stimulus will result in a graded potential that will either cause the neuron potential that will either cause the neuron to fire (depolarization) or not to fire (depolarization) or not (hyperpolarization).(hyperpolarization).

Impulse traveling over a long distance (axon) Impulse traveling over a long distance (axon) is called an action potentialis called an action potential

Depolarization: Reduction in membrane Depolarization: Reduction in membrane potential. When the membranes becomes potential. When the membranes becomes less negative on the inside (moves closer to less negative on the inside (moves closer to 0). Increases the probability the nerve will 0). Increases the probability the nerve will fire.fire.

i.e.: -70 to -65 mVi.e.: -70 to -65 mV-70 to +30 mV-70 to +30 mV

Hyperpolarization: Increase in membrane Hyperpolarization: Increase in membrane potential. When the membrane becomes potential. When the membrane becomes more negative on the inside. Decreases the more negative on the inside. Decreases the probabilityprobability

the nerve will fire.the nerve will fire.i.e.: -70 to -90 mV. i.e.: -70 to -90 mV.

Depolarization:Depolarization:

Voltage gated Na+ channels open and Na+ Voltage gated Na+ channels open and Na+ rushes in. -70 mV to 0mV to +30 mV.rushes in. -70 mV to 0mV to +30 mV.

Action Potential initiated. (all or none)Action Potential initiated. (all or none)

Repolarization:Repolarization:

Na+ channels close, K+ channels open and Na+ channels close, K+ channels open and K+ is pumped out. Restores electrical K+ is pumped out. Restores electrical conditions not original ionic distribution of conditions not original ionic distribution of resting state. It is the activation of the resting state. It is the activation of the sodium-potassium pump that sodium-potassium pump that reestablishes ionic distribution reestablishes ionic distribution

+30mV to -70m.+30mV to -70m.

Synapse:Synapse:

Junction between nerve cells and effector Junction between nerve cells and effector cells.cells.

Axodendritic:Axodendritic:

Presynaptic neuron: impulse firing Presynaptic neuron: impulse firing away from cell body towards the away from cell body towards the synapse (sender)synapse (sender)

Postsynaptic neuron: impulse away Postsynaptic neuron: impulse away from synapse. (receiver)from synapse. (receiver)

Chemical synapses uses a substance Chemical synapses uses a substance called a neurotransmitter to get called a neurotransmitter to get information across the synaptic cleft.information across the synaptic cleft.

The SynapseThe Synapse

1- Calcium channels open in the presynaptic 1- Calcium channels open in the presynaptic axonal terminal.axonal terminal.

Impulse reached axonal terminal causing a Impulse reached axonal terminal causing a rush of Ca+ in from the extracellular fluidrush of Ca+ in from the extracellular fluid

2- Ca+ causes the synaptic vesicles filled 2- Ca+ causes the synaptic vesicles filled with neurotransmitter to migrate and fuse with neurotransmitter to migrate and fuse with axonal membrane (exocytosis)with axonal membrane (exocytosis)

3- Ca+ is pumped out of terminal end3- Ca+ is pumped out of terminal end4- Neurotransmitter binds to postsynaptic 4- Neurotransmitter binds to postsynaptic

receptors.receptors.5- Ion channels open in postsynaptic 5- Ion channels open in postsynaptic

membrane causing changes in membrane membrane causing changes in membrane potential (action potential ?)potential (action potential ?)

Classes of Neurotransmitters:Classes of Neurotransmitters: Acetylcholine: excitatory (skeletal muscle) Acetylcholine: excitatory (skeletal muscle) Biogenic amines Biogenic amines

Dopamine, Norepinephrine, and epinephrine Dopamine, Norepinephrine, and epinephrine (feel good catecholamines)(feel good catecholamines)

Serotonin: mood, sleep, appetite & anger Serotonin: mood, sleep, appetite & anger (inhibitory)(inhibitory)

Histamine Histamine Amino acids Amino acids

GABA (gamma-aminobutyric acid) (inhibitory)GABA (gamma-aminobutyric acid) (inhibitory) Glutamate: excitatoryGlutamate: excitatory

Peptides Peptides Endorphins and enkephalins: inhibitory (opioids)Endorphins and enkephalins: inhibitory (opioids)