PERIPHERAL NERVOUS SYSTEM - Texas A&M University Peripheral... · Nervous tissue Distribution:...

Peripheral

Nervous System

Four Basic Types of Tissues in

the Body

-----------------------------------------------

Epithelium (90% of tumors) Connective Tissue

Muscular Tissue Nervous Tissue

Objectives

Overview of the central and characteristics of the peripheral nervous system

Characteristics of neurons and support cells

Organization of peripheral nerves

Nerve is

Epithelium

Origin of nerve is

ectoderm

like epidermis

(epithelium) of skin

Nervous Tissue

Functions: specialized for

the transmission, reception,

and integration of

electrical impulses

Distinguishing features: Neurons – very large excitable cells with long

processes called axons and dendrites. The axons make contact with other neurons or muscle cells at a specialization called a synapse where the impulses are either electrically or chemically transmitted to other neurons or various target cells (e.g., muscle). Others secrete hormones.

Glial cells – the supporting cells of nervous

tissue.

Nerves – collections of neuronal processes

bound together by connective tissue. Axons

may be coated by a myelin sheath

(“myelinated”) or simply protected by being

cradled in an indentation of a glial cell

(“unmyelinated”).

Nervous tissue

Distribution: comprise the

central nervous system.

Individual peripheral nerves

are found throughout the

body. Individual neurons

and clusters of neurons

(called ganglia) are found in

most organs.

Function of the Nervous System is

Communication

Dependent upon special signaling

properties of neurons

Long processes of neurons (e.g., 1 meter

motor neuraxon)

Function of the Nervous System is

Communication

Characteristics of neurons

Irritability - protoplasm capable to react to various physical and chemical agents

Conductivity - ability to transmit the resulting excitation from one locality to another

Types of Nerves

The Nervous System

Central nervous system (CNS)

– Brain and spinal cord

– Neurons and support neuroglia

The Nervous System Peripheral nervous system (PNS)

All nervous tissue (neurons, support cells, and axons)

outside the brain and spinal cord

Activity of the Nervous System

Information

• Receive: receptors afferent pathway

• Process: CNS (centralization is

paramount)

• Transmit: efferent pathways effect

Voluntary (conscious ) = somatic

Involuntary = autonomic

• Sympathetic - fight or flight

• Parasympathetic - vegetative

Cells and Functions of the

Nervous System

CNS PNS Function

astrocytes (BBB) satellite cells ion exchange

oligodendrocytes Schwann cells myelin

production

microglia --- phagocytosis

Astrocytes

Oligodendrocytes Microglia

Schwann cells - Myelin

Cells of the Nervous System

Neuronal Structure / Function

Structure

• Perikaryon (soma, cell body)

• Axon hillock - site of beginning of axon

• Dendrites - reception

• Axon (nerve) - transmission

Neuronal

Structure

/ Function

• http://www.youtube.com/watch?v=XgIaAs

NEURONAL STRUCTURE / FUNCTION

Axonal transport

Anterograde - toward terminal - kinesin

Retrograde - toward cell body - dynein

• Tetanus toxin

• Neurotropic viruses (herpes and rabies) use path to get to cell

body in CNS

Neuronal Structure/Function

Function of Myelin

Increase speed of condition

– 1 meter/sec TO 120 meters/sec

High-resistance low capacitance

– Insulator

Protection of axon

Possible nutritional role

Direct regenerating axons

Schwann Cell

Structure /

Function

Most peripheral nerves are

myelinated

1 Schwann cell/1 axon for

location

Formation of myelin sheath

• Nodes of Ranvier

• Schmidt-Lantermann clefts

• Neurokeratin network

Schwann Cell Structure / Function

Node of Ranvier

Myelination and

Schwann Cells

http://www.youtube.com/watch?v=ifD1YG07fB8&feature=related

Organization of Peripheral

Nerves

Ganglia - collections of nerve cell bodies

Smooth muscle Smooth muscle

Remember Connective Tissue

Layers of Skeletal Muscle

Epimysium, Perimysium, and Endomysium

Organization of Peripheral Nerves

Nerve fibers - axons invested by connective tissue

Epineurum - surrounding entire nerve

Perineurum - surrounding fascicles –

constitutes the PNS blood barrier via tight

junctions between fibroblasts

Endoneurum - between individual nerve axons

PERINEURUM

Autonomic Nervous System

Sympathetic

- Fight or Flight

Parasympathetic

- Vegetative

Nerve Endings – Synapses

(Efferent Pathways)

– Electrical: gap junctions, slow ion exchange

between cells, not common in mammals

– Chemical: rapid plus or negative response

Characteristics

– Synaptic vesicles (neurotransmitters)

– Synaptic cleft

Motor End Plate

Nerve Endings - Synapses

End Plate

Nerve Endings – Synapses (Efferent

Pathways)

Nerve Endings –

Synapses

Neuroactive Substance

Neurotransmitters - Acetylcholine

Neuromodulators - Receptor Coupled and Second Messenger

Neurohormone - Serotonin, GABA slow but widespread effect

Innervation of Muscle

Physiological Events at the

Synapse

Arrival of Action Potential

Opening of

Voltage-Gated ion channels for Ca++ to enter terminal

Influx of Ca++

Synapse

Influx of Ca++ triggers exocytosis of neurotransmitters from docked vesicles

Transmitter diffuses across synaptic cleft

Synapse

Transmitter binds to

receptors on post-

synaptic membrane

Receptor binding causes

ion channels to open to

Na+ and causes

depolarization

Synapse

Depolarization (equal Na+ inside and outside)

Depolarization – Stimulation

Hyperpolarization – Inhibition

Removal of transmitter

Summary of the Physiological Events at

the Synapse

• Arrival of action potential

at axon terminal

• Opening Ca++ channels

• Influx of Ca++ into axon

terminal

• Exocytosis of neurotransmitter

• Diffusion of neurotransmitter across synaptic cleft

• Binding of neurotransmitter to receptors on target cell

• Opening of Na+ channels causing depolarization of target

• Removal of neurotransmitter

Vesicle Membrane is Recycled

Cycling of the Membrane

Types of Synapses

Anodendritic Synapses

http://www.youtube.com/watch?v=70DyJwwFnkU&NR=1

Nerve Endings - Receptors

Receptors (Afferent Pathways)

• Neuromuscular Spindles

• Pacinian Corpuscles

• Meissner’s Corpuscles

Receptors (Afferent Pathways)

Neuromuscular Spindles

Pacinian Corpuscles

Nerve Endings - Receptors Meissner’s Corpuscles

and other important corpuscles

Inner Ear

OLFACTORY

(Efferent Pathways) Summary

Regeneration of Axons

PERIPHERAL NERVOUS SYSTEM - Texas A&M University Peripheral... · Nervous tissue Distribution:...

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