Nervous System

Divisions of the Nervous System

• Central Nervous System (CNS)• Made up of the Brain and Spinal Cord

• Peripheral Nervous System (PNS)• All neural tissue outside of CNS

Functional Division of the Nervous System• CNS• Integrates and coordinates information • Involved in higher functioning

• PNS • Transmits information to and from the CNS• Sends information to the CNS (Sensory) • Gets information from the CNS (Motor)

Types of Neural Tissue• Neuron• Responsible for information transfer and processing

• Neuroglial Cells• Provide the framework for neurons• Phagocytic• Different types for each division

CNS• Astrocytes • Oligodendrocytes • Microglial

PNS• Schwann Cell

Neuron Structure

Neuron Structure Part 1• Cell Body • Nucleus • Axon: Carries the nerve impulse away from the cell body • Dendrite: Carries the nerve impulse towards the cell body •Myelin: Fatty substance that encases some of the axon • Allows nerve impulse to travel faster by jumping from node-to-

node• Nodes of Ranvier: Gaps between myelin • Schwann Cells: Produce the myelin

Neuron Structure Part 2

•White Matter: areas of neural tissue with myelin • LOTS of axons

•Gray Matter: areas of neural tissue without myelin • LOTS of cell bodies

Question

• What do you think are some of the consequences if Schwann Cells over time start to deteriorating?

Synapse

•Where the communication between cells takes place• How?• Through the release of

neurotransmitters • Very similar to NMJ, but

reuptake happens

Steps at Synapse

1. Nerve impulse travels down presynaptic neuron 2. Presynaptic neuron releases NTs from synaptic vesicles into synaptic

cleft 3. NTs land on receptors of postsynaptic neuron 4. Postsynaptic neuron responds 5. NTs return to presynaptic neuron in a process called ‘reuptake’

Action Potential (Nerve Impulse)

• Action Potential • The electrochemical changes that move along a cell to transmit information

• In neurons, action potentials involve sodium (Na) and potassium (K) and their movement across the cell membrane

• Propagation of an action potential down a nerve fiber is called a nerve impulse

Action Potential Graph

• X-Axis: Time

• Y-Axis: Membrane Potential (mV) • Way to measure electrical charge of the cell

Steps we will write out DO NOT match the numbers on your graph

1. Resting Potential

• Resting neuron’s cell membrane is polarized/charged because there is an uneven distribution of ions on both sides of the cell membrane

• Inside cell (-): K, PO, SO

• Outside cell (+): Na

• Membrane Potential: -70 mV

2. Depolarization

• STIMULUS • Na channels open and Na moves into cell • Membrane depolarizes from -70 mV to -55 mV• -55 mV is called THRESHOLD (minimum charge needed from impulse

to move on) • Amount of change in potential (charge) is directly proportional to

intensity of stimulus • Occurs at portion of cell membrane being stimulated and moves to

next part of cell membrane once threshold is reached

3. Action Potential

• At threshold, ALL Na channels suddenly open and Na rushes into cell

• Membrane depolarizes from -55 mV to +30 mV

4. Repolarization

• At +30 mV, Na channels close, K channels open and K rushes out

• Causes repolarization back to resting potential (-70 mV)

• At -70 mV, sodium-potassium pump exchanges Na and K to resets • 3 Na for 2 K

Look at Graph…

Poll Everywhere Question

• https://www.polleverywhere.com/free_text_polls/hkG1O5zmTmSVxZh

Meninges

• Connective tissue that covers the brain and spinal cord

• Made of 3 basic layers • Dura Mater• Arachnoid Mater• Pia Mater

Meningeal Layers

• Dura Mater • “Tough Mother” • Outermost Layer • Made of dense connective

tissue, super thick! • Supports and protects

Meningeal Layers

• Arachnoid Mater • “Spider Mother” • Middle Layer • Web-like • Holds Fluid

Meningeal Layers

• Pia Mater • “Delicate Mother” • Innermost Layer• Made of collagen and

elastin, very thin! • Contains blood vessels

that supply the brain

Cerebrospinal Fluid (CSF)

• Found within the Arachnoid Layer • Filtered by blood brain barrier • Very protective: chemically and

physically • Clear and colorless

Spinal Cord

• Structure • Adult length: 16-18 inches • Extends from foramen magnum to L2

• Portion of nerves after L2 is often referred to as a “Horsetail” (Cauda equina)

• Functions • Conducts nerve impulses • Center for spinal reflexes

Spinal Cord

• What is the significance of the gray matter? • Unmyelinated • More neuron cell bodies in

gray matter than white matter, so more “work” can be done…