The Nervous System

Nervous System• Three basic functions– Sensation

• gather information

– Integration• process information• use of multiple sources

of information.

– Response• coordinated action

appropriate to environment

EK3E2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and

produce responses.a. The neuron is the basic structure of the nervous system that reflects function.

1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator.2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information.3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

The neuron is the basic structure of the nervous system that reflects function.

1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator.

2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information.

3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

Rat Cortical NeuronHippocampal Neuron

Primary rat hippocampal neurons

Neurons are similar to other cells in the body because: 1. Neurons are surrounded by a cell membrane. 2. Neurons have a nucleus that contains genes. 3. Neurons contain cytoplasm with organelles4. Neurons carry out basic cellular processes such as protein synthesis and energy production.

However, neurons differ from other cells in the body because: 1. Neurons have specialized extensions called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. 2. Neurons communicate with each other through an electrochemical process. 3. Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters).

Neurons are the oldest and longest cells in the body! You have many of the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. In fact, you have fewer neurons when you are old compared to when you are young. On the other hand, data published in November 1998 show that in one area of the brain (the hippocampus), new neurons CAN grow in adult humans.

Neurons can be quite large - in some neurons, such as corticospinal neurons (from motor cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the spinal cord and up to the brain stem), can be several feet long!

Neuron Trivia

• Soma/Cell Body: is the metabolic center of the neuron, contains the Nucleus and Mitochondrion.

• Dendrites: convey incoming messages to the cell body.

• Axon: generates nerve impulses and topically conduct them away from the cell body myelinated by either oligodendroglia in CNS or Schwann cells in PNS. Each neuron has only one axon.

• Axon Hillock: a cone like region from where an axon arises.

• Presynaptic terminals: The swollen, distal end of an axon; contains a neurotransmitter substance within synaptic vesicles. Also called synaptic ending or synaptic bouton.

• Synapse: Specialized junctions with other cells that are along the length or at end of an axon.

Neuron Anatomy

Axons• Take information away

from the cell body • Smooth Surface • Generally only 1 axon per

cell • No ribosomes • Can have myelin • Branch further from the cell

body

DendritesDendrites Bring information to the Bring information to the

cell body cell body Rough Surface (dendritic Rough Surface (dendritic

spines) spines) Usually many dendrites Usually many dendrites

per cell per cell Have ribosomes Have ribosomes No myelin insulation No myelin insulation Branch near the cell Branch near the cell

bodybody

Neuron Anatomy

Neurons can also be classified by the direction that they send information:

• Sensory (or afferent) neurons: send information from sensory receptors (e.g., in skin, eyes, nose, tongue, ears) TOWARD the central nervous system.

• Motor (or efferent) neurons: send information AWAY from the central nervous system to muscles or glands.

• Interneurons: send information between sensory neurons and motor neurons. Most interneurons are located in the central nervous system.

b. Action potentials propagate impulses along neurons.

1. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes.2. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized.3. Na+/K+ pumps, powered by ATP, work to maintain membrane potential.

EK3E2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and

produce responses.

How neurons conduct

impulses:• Membrane potential (as seen in muscle cells)

• K+ diffuses out of neurons faster than Na+ diffuses in,

• Na-K pump moves 3Na+ back out for 2K+ back in

• Cl-, phosphate, protein anions balance cations

• “Resting potential” ~ -70mV

• Nerve Impulse

http://www.google.com/url?sa=i&source=images&cd=&cad=rja&docid=qfbWp0Wy-BjD-M&tbnid=B-dXZ81zn9ADIM:&ved=0CAgQjRwwAA&url=http%3A%2F%2Fbthsbioteacher.wikispaces.com%2FNervous%2BSystem%2BVocab&ei=QwBTUce6M8W0PLPigJgH&psig=AFQjCNF_2UwtFtW5efxXaTlMYh67irvqOQ&ust=1364480451891389

Rate of conduction• Unmyelinated axon

s– Action potential

propagates at 2-3 meters per second (m/sec)

• Saltatory Conduction• Action Potential occurs only

in nodes, – "leaps" from node to node– Ion attraction and diffusion

stimulate new A.P. in each node

– Saltatory conduction much faster than continuous conduction in unmyelinated fibers.• up to 100 m/sec

EK3E2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and

produce responses.c. Transmission of information between neurons occurs across synapses. 1. In most animals, transmission across synapses involves chemical messengers called neurotransmitters.

– Acetylcholine– Epinephrine– Norepinephrine– Dopamine– Serotonin– GABA

2. Transmission of information along neurons and synapses results in a response.

3. The response can be stimulatory or inhibitory.

How does impulse get from cell to cell?Electrical synapses

– “Gap junctions,” tiny holes connect cytoplasm of adjacent cells

– A.P. continuous from cell to cell

Chemical synapses, 2•Axon (& A.P.) ends short of next cell, •Synaptic knob (axon end) releases chemical transmitter

Neurotransmission

• When Action Potential reaches synaptic knob,– Synaptic vesicles unite with

membrane,– Release neurotransmitter,– Neurotransmitter diffuses

across synaptic cleft,– Neurotransmitter binds to

receptors in postsynaptic membrane,

– Chemically gated channels open

• Chemical Signals• Mouse Party

Synapse• Neurotransmitter can't remain in cleft (would continue

to stimulate uncontrollably)– ACh removed by acetylcholinesterase (AChE)– Acetate & choline reabsorbed by axon end, resynthesized to

ACh – Other neurotransmitters taken back by axon or diffuse away

Neurotransmitters may be …

• Excitatory– depolarize postsynaptic

membrane– Excitatory Postsynaptic

Potential (EPSP)

• Inhibitory– hyperpolarize

postsynaptic membrane– Inhibitory Postsynaptic

Potential (IPSP)

• Reward Pathway• Reflex Arc

d. Different regions of the vertebrate brain have different functions.

EK3E2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and

produce responses.

LO 3.43 The student is able to construct an explanation, based on scientific theoriesand models, about how nervous systems detect external and internal signals,transmit and integrate information, and produce responses. LO 3.44 The student is able to describe how nervous systems detect external andinternal signals. LO 3.45 The student is able to describe how nervous systems transmit information.LO 3.46 The student is able to describe how the vertebrate brain integratesinformation to produce a response. LO 3.47 The student is able to create a visual representation of complex nervoussystems to describe/explain how these systems detect external and internalsignals, transmit and integrate information, and produce responses. LO 3.48 The student is able to create a visual representation to describe hownervous systems detect external and internal signals. LO 3.49 The student is able to create a visual representation to describe hownervous systems transmit information. LO 3.50 The student is able to create a visual representation to describe how thevertebrate brain integrates information to produce a response.

Resources• Action Potential Tutorial• A&P Text, 2• Essential Study partner Links• Parts of a Neuron Review • Anatomy Drill • Body Smart Nervous System • Campbell’s Activity Quiz• Human A&P Lessons • Cerebral Commando • Synaptic Transmission Tutorial• Drugs, Brains & Behavior • Parts of the Brain, 2• Video Quiz - Making Brain Cells• Video Quiz - ALS Lost Nerve Power• Video Quiz - Wild Young Brains• Video Quiz - Vanishing Brain• Video Quiz - Meth and the Brain• Video Quiz - Paralysis Push