What do you know & want to know about the Nervous

System?Collins type 1, ~10 lines, sentences related

to the question please

Nervous System

Pages 228-237

1. Sensory input—gathering info◦Monitor changes occurring inside & outside the body

2. Integration◦Make sense of information &decide if/what action is needed

3. Motor output◦The “response” ◦activates muscles or glands in response to the stimulus

Functions of the nervous system

Central nervous system (CNS)◦Brain◦Spinal cord

Peripheral nervous system (PNS)◦Nerves outside the brain and spinal cord

◦Spinal nerves◦Cranial nerves

Structural Classification of the NS

Sensory (afferent) division◦Nerve fibers that carry information to the

CNS◦“On ramp”

Motor (efferent) division◦Nerve fibers that carry impulses away

from the CNS◦Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

Functional Classification of the Peripheral NS

In the scenario identify the sensory input, motor effect, and integration (not specifically stated). Also identify the role of the efferent and afferent divisions of the nervous system and explain which specific efferent/motor division is being used.

Fritz was putting a tray of cookies into the oven. The top of his hand accidently grazed the side of the oven and he quickly retracted his hand out of the oven.

Practice… Do you have the gist?

Called neuroglia, glia, or glial cells◦Literally mean “nerve glue”

supporting cells of the CNS that help protect, support, and insulate

4 types to know1. Astrocytes

◦Star-shaped◦Make up ~½ of the neural tissue in body◦Anchor neurons to blood supply◦Form a living, protective barrier barrier

between capillaries and neurons

Supporting cells of the CNS

2. Microglia◦ Spider-like macrophages that destroy

debris bacteria and dead brain cells

3. Ependymal Cells◦ Line the cavities of the brain & spinal cord◦Have cilia that move and help circulate

cerebrospinal fluid

Neuroglia AKA Glial Cells

4. Oligodendrocytes◦Have flat extensions that wrap around

nerve fibers◦Make myelin sheaths fatty cover that

insulates nerve fibers

Glial cells VS. Neurons◦ Look similar BUT glial cells can’t transmit or

conduct nerve impulsesk◦ Glial cells can divide, neurons can’t (most

brain tunmors are gliomas formed by glial cells)

Neuroglia AKA Glial Cells

Schwann Cells◦ Form myelin sheaths around nerve fibers◦ MS attacks myelin sheaths, converts them to hard

covers that can’t conduct electrical impulses slurred speech, loss of balance, impaired vision, etc

Sattellite Cells◦ Serve as protective cushioning cells

Supporting Cells of the PNS

What is a Schwann cell?

What part of the NS does it support?

What structural part of the neuron can it form?

Something to think about…

Cell body/soma◦ Metabolic center

Dendrites◦ Can have a few or 60◦ Receive messages from other

neurons Axon

◦ Can only have ONE◦ Sends the message from the

body

Neuron Anatomy

Axon hillock (where AP is generated) and axon terminal (branches at the end of an axon)

Myelin sheath◦ Not present on every axon

Pain receptors don’t have myelin on their axons

◦ Help message travel faster◦ By schwann or oligodendrocytes

Neuron Anatomy

Synapse… where neurons meet

Neurons are selectively permeable◦ Contain ion channels

Voltage gated ion channels only open when there is a change in electrical charge necessary for transmission of an action potential!

At resting state the neurons is polarized (has a slightly negative charge compared to the outside of the neuron)◦ b/c inside of cell has proteins that have – charges◦ Has K+ but not enough to balance out the –

At resting state the area around a neuron is more positive

Neuron Physiology

A stimulus causes Na+ to flow into the neuron

If enough Na+ flows in, the neuron’s charge becomes more positive and becomes depolarized (not as negative) causing the nerve to send an electrical signal action potential AKA nerve impulse

Sodium voltage-gated ion channels open and Na+ rushes in make the inside very +

Making an Action Potential

Once one area is positive, the positive charge moves down the axon causing more Na+ channels to open

After Na+ enters, the ions channels for Na+ close but the inside is still very +

Sodium-potassium pumps then use ATP to move Na+ out of the neuron and K+ in to return the charges inside and outside of the neuron to “normal” repolarization

All or Nothing Response 1 action potential at a time while neuron is

recovering it is in a refractory period no nerve impulses an be generated

Making an Action Potential

Myelinated fibers carry messages faster◦ Use saltatory conduction (charge jumps from

node of Ranvier to node of Ranvier)

Non-myelinated fibers transmit messages slower b/c all of the ion channels must open and close to propagate the electrical signal

Action Potentials in Myelinated vs. Not fibers

http://184.171.162.94/images/prevjhy.php?u=Oi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9REplM18zWHNCT2c%3D&b=5

http://184.171.162.94/images/prevjhy.php?u=Oi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9aWZEMVlHMDdmQjg%3D&b=5

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Animations of AP Generation

In groups of 2-4 create an analogy that parallels the event that take place to create an action potential/nerve impulse

Consider ◦ the initial locations of Na+ and K+ ◦ the movement of Na+ while the action potential is

being created◦ The movement of K+ immediately after the AP has

been generated ◦ How the levels of Na+ and K+ inside and outside of

the cell is corrected after the AP has been transmitted

Practice

1. A neuron is more negative inside the cell relative to the outside (polarized)

Step By Step…

2. A stimulus makes causes the cell’s charge to reach the threshold

3. Na+ channels open and sodium floods into the cell in one section of the axon

4. The Na+ channels in that area close but the region down the axon gets positive enough to reach threshold Na+ channels open and sodium rushes in… this continues down the axon

5. The K+ channels open and potassium diffuses out6. The cell becomes repolarized BUT K+ is concentrated outside

and Na+ is concentrated inside… must swap!7. The sodium-potassium pumps move Na+ our of the neuron

and K+ into the neuron