1.2 Structure and Function

What are the two main cell types in the nervous system?

Neurons (nerve cells) and Glia

Neurons

Basic unit of the nervous system; communicate across tiny gaps called synapses

Glia

Divided into four support functions; Input, Integration, Conduction, and Output

Input

Dendrites receive information from other neurons

Integration

Cell body (or soma) that integrates the information

Conduction

A single axon conducts information away from the cell body as an electrical signal

Output

Axon terminals at the end of the axon communicate activity to other cells

Structure of Dendrite

Continuous with cell body, Branched; may have dendritic spines

Functions of Dendrites

Receive chemical signals from other neurons; Convert chemical signal to electrical signal

Soma structure

The cell body

Soma function

Integrates/combines information that has been received at the dendrites; Sums together the electrical signals

Axon structure

Long extensions from soma; insulated with myelin; may branch into axon collaterals toward the end

Axon function

Carries the action potential (electric signal) away from the cell body and to the terminals

Where is the action potential generated at?

Axon hillock

Axon terminals structure

Swellings at the ends of the axon

Axon terminals function

make synaptic contact with other cell’s dendrites

What happes when an action potential reaches the axon terminal?

Neurotransmitter (chemical) is released into the synapse

Information signals through neurons are?

Chemical

Chemical information signals between neurons

Neurotransmitters released into the synapse and from axon terminals and received by dendrites.

Information signals within a neuron are?

Electrical

Electrical information signals within neurons

An action potential travels down the axon, dendrites convert chemical signal into an electrical potential

How many neuron types are there? Which one is the most common?

3, multipolar

Multipolar Neuron

One axon, many dendrites

Bipolar Neuron

One axon, one dendrite; common in sensory

Unipolar Neuron

One extension branching in two directions; common for touch information

Synapse

Synaptic cleft; junction between two neurons; where neurotransmitters travel across the synapse

Presynaptic membrane

Axon terminal of the presynaptic neuron

Postsynaptic Membrane

Dendrite or cell body of the postsynaptic neuron

What happens in the presynaptic side of synapse?

The axon terminal contains synaptic vesicles that contain neurotransmitter

What happens in the postsynaptic side of synapse?

Receptors respond to the neurotransmitters

How many classes of glia? What are there names?

4; Oligodendrocytes, Schwann cells, Astrocytes, Microglia

What two types of glia wrap around axons to provide a fatty insulation layer called myelin?

Oligodendrocytes & Schwann Cells

Myelin

Fatty insulation layer

Oligodendrocytes

In the central nervous system

Schwann Cells

Outside the brain and spinal cord of the peripheral nervous system

Nodes of Ranvier

Gaps between sections of myelin where the axon is exposed

Astrocytes

Star shaped cell that stretch around neurons, synapses, and sometimes blood vessels

Microglia

Remove debris from injury

Central Nervous System

Brain and spinal cord

Peripheral Nervous System

All other parts outside of brain and spinal cord

What is the peripheral nervous system consist of?

Nerves, or bundle of axons

Motor nerves

Transmit information from CNS to muscle and glands

Sensory Nerves

Convey information from the body to the CNS

How is the peripheral nervous system divided?

Into 2; Somatic and Autonomic nervous system

Somatic Nervous Sysstem

Nerves that interconnect the brain and the major muscles and sensory systems of the body (soma)

Autonomic Nervous System

Nerves that connect to the internal organs (autonomic - autonomous)

What does the Somatic Nervous System include?

Cranial Nerves and Spinal Nerves

Cranial Nerves

12 pairs; connect brain to head, neck, visceral organs; have sensory and motor components

Spinal Nerves

(31 pairs) connect spinal cord to muscles and organs; has motor and sensory fibers

Motor fibers

In spinal nerves, project from the spinal cord

Sensory fibers

In spinal nerves, enter the spinal cord

How is the Autonomic Nervous System divided?

Sympathetic and Parasympathetic Nervous System

Sympathetic Nervous System

fight or flight

Parasympathetic Nervous System

rest-and-digest