Chapter 12 - 12.2 Part 1

Front 1

Nervous tissue comprises 2 types of cells─neurons and neuroglia. These cells combine in a variety of ways in different regions of the nervous system.

Back 1

- In addition to forming the complex processing networks w/in the brain and spinal cord, neurons also connect all regions of the body to the brain and spinal cord

- Neurons provide most of the unique functions of the nervous system (sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions)

Front 2

Neuroglia are smaller cells but they greatly outnumber neurons, perhaps by as much as 25 times.

Back 2

- Neuroglia support, nourish, and protect neurons, and maintain the interstitial fluid that bathes them

- Unlike neurons, neuroglia continue to divide throughout an individual's lifetime

Front 3

Neurons 1

Back 3

- Like muscle cells, neurons (nerve cells) possess electrical excitability, the ability to respond to a stimulus and convert it into an action potential

- A stimulus is any change in the environment that is strong enough to initiate an action potential

Front 4

Neurons 2

Back 4

- An action potential (nerve impulse) is an electrical signal that travels along the surface of the membrane of a neuron

- It begins and travels due to the movement of ions between int. fluid and the inside of a neuron through specific ion channels in its plasma membrane

Front 5

Most neurons have three parts :

Back 5

1. Cell Body

2. Dendrites

3. Axon

Front 6

Parts of a Neuron - Cell Body

Back 6

- Also called perikaryon or soma; Contains a nucleus surrounded by cytoplasm that includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex

- Neuronal cell bodies also contain free ribosomes and prominent clusters of rough ER, termed Nissl bodies

Front 7

The ribosomes are the sites of protein synthesis. Newly synthesized proteins produced by Nissl bodies are used to replace cellular components, as material for growth of neurons, and to regenerate damaged axons in the PNS.

Back 7

- The cytoskeleton includes both neurofibrils, composed of bundles of intermediate filaments that provide the cell shape and support, and microtubules, which assist in moving materials between the cell body and axon

- Aging neurons also contain lipofuscin, a pigment that occurs as clumps of yellowish brown granules in the cytoplasm

Front 8

Lipofuscin is a product of neuronal lysosomes that accumulates as the neuron ages, but does not seem to harm the neuron as it ages.

Back 8

- A nerve fiber is a general term for any neuronal process (extension) that emerges from the cell body of a neuron

- Most neurons contain 2 kinds of processes : multiple dendrites and a single axon

Front 9

Parts of a Neuron - Dendrites

Back 9

- The receiving or input portions of a neuron;Usually short, tapering, and highly branched

- The plasma membranes contain numerous receptor sites for binding chemical messengers from other cells

- The cytoplasm contains Nissl bodies, mitochondria, and other organelles

Front 10

Parts of a Neuron - Axon

Back 10

- Propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell

- A long, thin, cylindrical projection that often joins to the cell body at a cone-shaped elevation called the axon hillock

- The part closest to the axon hillock is the initial segment

Front 11

In most neurons, nerve impulses arise at the junction of the axon hillock and the initial segment, an area called the ________

Back 11

- Trigger zone, from which they travel along the axon to their destination

- An axon contains mitochondria, microtubules, and neurofibrils. B/c rough ER is not present, protein synthesis does not occur in the axon

Front 12

The cytoplasm of an axon, called ______

Back 12

- Axoplasm, is surrounded by a plasma membrane known as the axolemma

- Along the length of an axon, side branches called axon collaterals may branch off

- The axon and its collaterals end by dividing into many fine processes called axon terminals (telodendria)

Front 13

The site of communication between 2 neurons or between a neuron and an effector cell is called ___________

Back 13

- A synapse

- The tips of some axon terminals swell into bulb-shaped structures called synaptic end bulbs; other exhibit a string of swollen bumps called varicosities

- Both syn. end bulbs and varicosities contain many tiny membrane-enclosed sacs (synaptic vesicles) that store a chemical called a neurotransmitter

Front 14

Because some substances synthesized or recycled in the neuron cell body are needed in the axon or at the axon terminals, 2 types of transport systems carry materials from the cell body to the axon terminals and back.

Back 14

- The slower system, which moves materials about 1-5mm/day, is called slow axonal transport

- It conveys axoplasm in one direction only─from the cell body toward the axon terminals. It supplies new axoplasm to developing or regenerating axons and replenishes axoplasm in growing and mature axons

Front 15

Fast Axonal Transport

Back 15

- Capable of moving materials 200-400mm/day; uses proteins that function as "motors" to move materials along the surfaces of microtubules of the neuron's cytoskeleton

- Moves materials in both directions─away from and toward the cell body

Front 16

Fast axonal transport that occurs in an _______

Back 16

- Anterograde (forward) direction moves organelles and synaptic vesicles from the cell body to axon terminals

- Retrograde (backward) direction moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled

Front 17

Substances that enter the neuron at the axon terminals are also moved to the cell body by fast retrograde transport.

Back 17

- These substances include :

• Trophic Chemicals - nerve growth factor

• Harmful Agents - tetanus toxin and the viruses that cause rabies, herpes simplex, and polio