CH 10 – Nervous System

Basic Structure and Function

System Function

• Sensory (internal & external)• Integration• Motor

Major Organs

• Central Nervous System (CNS)– Brain– Spinal Cord

• Peripheral Nervous System (PNS)– Connect brain to the rest

of the body

Pieces and Parts

• Neural Tissue– Neurons– neuroglial cells

• Blood Vessels• Connective Tissue

Neural Tissue

• Neurons• Neuroglial Cells

Anatomy of a Neuron

Generalized Model of a myelinated neuron.

Tissue made of these kinds of cells appear white: “white matter” of brain and spinal cord.

(Nissl Bodies)

Some differences

• Nissl bodies (RER)• Axon hillock• Soma = body

Synapses

• Space between neurons

Electrochemical

• Chemicals (neurotransmitters) cause an electric charge (action potential) to travel through a nerve

• Calcium and sodium ions are essential to the process

• Lead (Pb) will replace calcium ions in the body and interfere with neurotransmitter release

An action potential arrives

Peripheral Nervous System

• Sensory = afferent • Motor = efferent– Somatic (voluntary)– Autonomic (involuntary)

Somatic Motor Functions

Somatic Reflex Arc

Autonomic Functions

• Parasympathetic– Rest and Digest

• Stimulates peristalsis• Lowers blood pressure• Slows breathing• Stimulates anal sphincter

• Sympathetic– Fight or Flight

• Blood vessels constrict• Heart beats faster• Breathing quickens• Peristalsis stops

Autonomic Motor Functions

Unmyelinated axons

• Gray matter in brain and spinal cord

White matter & Gray matter

Most neurons in the brain and spinal cord are multipolar.

Types of Neuroglial Cells

• Astrocyte Star-shaped cells that provide physical and nutritional support for neurons

• Microglia: digest parts of dead neurons.• Oligodendroglia: Provide the insulation (myelin)

to neurons in the central nervous system.• Ependymal: line the central canal• Schwann Cells: Provide the insulation (myelin)

to neurons in the peripheral nervous system.

Neuroglial Fun Facts

• Neuroglial cells account for half the brain’s volume

• Most brain tumors are from neuroglial cells that divide too often

• Researchers are trying to develop implants of neuroglial cells that secrete chemicals to treat Alzheimers, MS and Parkinson disease

Neuron Not-so-Fun Fact

• Mature neurons in CNS do not divide• What you got, is what you got– Unless neural stem cells are stimulated to

proliferate• Axons may regenerate

Axon Regeneration (PNS only)

Neuroma

• Tangled mass of sensory axons• Damaged neurons that don’t repair can do

this.

How do signals move through a neuron?

It all starts at the cell membrane

Neuron cell membranes are polarized

Resting potential: -70 mv

Stimuli disrupt homeostasis

• Light, temperature or pressure cause ion channels to open and the voltage changes

• If stimuli reaches a certain threshold, it generates an action potential

• Several sub-threshold potential stimuli can can generate an action potential via summation

1) Neuron stimulation causes sodium channels to open

2) Sodium flows in and makes the local area positive

3) Positive charge triggers same action further down the axon

4) Behind the action potential Potassium channels open to let K+ ions flow out and reestablish polarization

Low on Ca+ ?

• It takes calcium ions to close voltage gated channels

• If there aren’t enough Ca+, the gates may be stuck in the open position. (Tetany)

Axons piling on a single dendrite= action potential???

Neurotransmitters

• 30 different kinds!!• Synthesized in cytoplasm of synaptic knobs• Release is triggered by calcium ions diffusing

IN through voltage gated ion channels

Neurotransmitter SamplerNeurotransmitter What it does

Acetylcholine Triggers skeletal muscle action

Histamine Promotes alertness

Endorphins Reduce pain (our natural opiate)

Epinephrin Mood enhancer

Dopamine Mood enhancer

Drugs can alter neurotransmitter levels

• Tryptophan affects serotonin (makes you sleepy)• Nicotine tricks neurons into releasing dopamine• Curare blocks acetylcholine

Spent Neurotransmitters

• Some are decomposed by enzymes• Some are returned to the presynaptic neuron

by neuroglial cells