The Nervous System

Chapter 11

Functions of the Nervous system I Sensory (input): Light Sound Touch Temperature Taste Smell Internal Chemical Pressure Stretch

External Chemical

Functions of the Nervous system II Integration: Integration means making sense of

sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope).

Motor (output): The response to the sensory input and

subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.

The Basic Scheme

Organization of the Nervous system

The CNS compared with thePNS

Support Cells of the Nervous system

the Central Nervous System Astrocytes Microglia Oligodendrocytes Ependymal Cells

the Peripheral Nervous System Schwann Cells

(a.k.a. Neurolemmocytes)

Satellite Cells

Astrocytes & microglia

Astrocytes & microglial cells protect the neurons of the CNS.

Astrocytes & microglia Functions of astrocytes:1. Connect neurons to capillaries. This makes up

the “blood-brain barrier”. 2. Maintain the the electrochemical environment• Capture and recycle neurotransmitters• Absorb and return K+ and other ions.• Connected to one another and capable of

communicating via gap junctions.Function of microglial cells:1. Dendritic macrophages that phagocytize

microbes and necrotic (dead) tissue.

Ependymal Cells & oligodendrocytes

Ependymal Cells & oligodendrocytes

Functions: Ependymal Cells - Line the ventricles of

the brain an central canal of the spinal cord. They aid in the circulation of cerebrospinal fluid (CSF).

Oligodendrocytes - These cells have processes that wrap around the axons of neurons. This creates an insulation coating called a myelin sheath.

Schwann Cells & satellite cells

•These are the support cells in the peripheral nervous system.•Schwann cells provide the myelin sheath for peripheral axons.•Satellite cells serve a slightly similar function to astrocytes, supporting the cell bodies of peripheral neurons.

Neurons - the “action cells”

Characteristics of neurons

Long-lived Generally last a life time with 90% are formed

by the time you are 6 years old. The rest are produced when as you go through puberty.

Amitotic Until recently it was thought that neurons

didn’t regenerate at all! Some may but generally what you have at adulthood is all you get.

High metabolic rate This means high oxygen demand and lots of

mitochondria. Neurons also require glucose.

MyelinMyelin is a lipid-rich component of the cell membranes of Schwann cells and oligodendrocytes.It acts kind of like the insulation on an electrical wire.

Chemically gated ion channels

Voltage gated ion channels

A Resting Membrane Potential

Because there is a higher concentration of Na+ outside than there is K+ inside.This leads to an electric charge or electric potential.

Relative ion concentrations

Ions have differential permeability. The RMP is maintained by the pumping action of a Na+/K+ pump, powered by ATP

Polarization (subthreshold) and hyperpolarization

A stimulus leads to a depolarization

A change in ion concentrations leads to a reversal of the charge separation.

Ion flow in a neuron

The depolarization spreads along the cell membrane by serial opening and closing of ion gates.

A graded potential

Graded potentials are not “all-or-none”, like action potentials

The cycle of an Action Potential

Propagation of an Action Potential

Propagation of an Action Potential

Propagation of an Action Potential

Temporal summation

Anatomy of an Action Potential

Salutatory conduction

Different types of synapses

A Chemical Synapse

EPSPs & IPSPs

Integration: summation of potentials

Synthesis of Neurotransmitters

Mechanisms of Neurotransmitter activity

A Basic Neural Circuit

Type of neurons

Three structural classes of neurons

Multipolar Most numerous Many dendrites Motor and association neurons

Unipolar Second most numerous Rounded body with one process Somatic & general sensory neurons

Bipolar Least common, found in special sensory organs

Comparison of neuron types

Functional categories of neurons

This is it for 231

Lecture Final at 10 am next Tuesday.

Lab Practicals: Tuesday, 6/8 @ 2 pm

Thursday, 6/10 @ 10 am

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