Nervous System 1, 2, & 3 (WS 7, 8, & 9)

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1

Organization/Structure of Nervous System

Electrical signals in neurons
Cell-to-cell communication
Integration of neural information transfer

2

Central Nervous System

CNS

Afferent- Things moving toward
Efferent- Things moving away
Nerves that are firing towards (afferent) or away (efferent) from the CNS

Includes the brain and spinal cord
FUNCTIONS: Receives, processes, and transfers information

3

Efferent Neurons

PNS

Includes:
Autonomic neurons
Automatic
Sympathetic and parasympathetic
Somatic motor neurons
Control of skeletal muscles

4

Nervous System Components and Functions

1. Central Nervous System
2. Peripheral Nervous System

Functions:
Rapid communication for homeostatic balance
Properties of intelligence, consciousness & emotion, and memory

5

Peripheral Nervous System

PNS

The nerves and Ganglia outside of CNS

Includes:
Sensory neurons- carry info toward CNS
Motor neurons- carry info away from CNS
Nerves- Bundles of axons
Ganglia- Collections of nerve cell bodies; create swelling in nerves

6

Neurons

Basic functional unit of nervous system
Cell body site of energy generation and synthesis
For communication in the NS
Includes a:
Cell body
Dendrites
Axon
Terminal
Myelin Sheath

7

Cell Types

Neurons- Transmit communication signals
Communication
Glial Cells- Support neurons
Support, protection, myelin formation
* the cells that become TUMORS

8

Glial Cells

Found in CNS and PNS
Support neuron bodies, form myelin sheaths
Involved in cleaning up dead cells and fixing cell connections
barriers between compartments
Scavenger/defense and metabolic assistance
FIG 8.5 IN BOOK

9

Node of Ranvier

A section of unmyelinated axon membrane between two schwann cells

10

Glial Cells (continued)

Outnumber neurons 10-50X
do NOT conduct signals
provide physical support for neurons (direct growth and repair)
Form myelin sheaths
Acts as insulator
Increases speed

11

Glial cells in PNS

1. Schwan cells- Myelin production
Areas of non-insulated Nodes of Ranvier
2. satellite cells- Supporting cells around ganglia
no myelin

12

Glial cells in CNS

1. Oligodendrocytes- wrap around neurons, support, and insulate with myelin
2. Astrocytes- Contact neurons and blood vessels, transfer nutrients
3. Microglia- Specialized macrophages remove damaged cells

13

Electric Signals in Neurons

Ionic concentrations and potentials

For an ion to move it needs incentive and opportunity

EX: I want to leave and go to lunch during class (incentive), but I can't leave in the middle of class (no opportunity)

14

Information Transfer in Neurons

1. Gated Channels
2. Graded Potentials
3. Action Potentials

15

Gated Channels

Channel opens in response to stimuli
Keeps things that aren't lipophillic away from fats
Controls permeability
Types:
1. Mechanically Gated- Physical factors stimulate opening, pressure, and stretch
2. Chemically Gated- Ligand stimulates (neurotransmitters, neuromodulators)
3. Voltage Gated- Membrane potential changes stimulate opening

16

Graded Potentials

Localized, variable in size, dissipates
Dissipates due to:
1. Positive charge leakage
2. Cytoplasmic resistance

Incoming (input) signals
vary in strength
decreased strength over distance
slower moving than action potentials (AP)
travel to trigger zone and integration occurs

Sub-threshold: too weak, no AP
Supra-threshold: Generation of AP

17

Action Potentials

All or none
Spontaneous or graded potential initiates
START at trigger zone
Signal does NOT diminish with distance

18

Action Potential Components

Initiation
Depolarization
Signal Peak
Repolarization
Hyperpolarization

19

Refractory Period

Compromised ability to stimulate AP's
Two Types:
1. Absolute Refractory Period
1/1000th of a second you are in this period
2. Relative RP
this period is larger

20

Regulating RP

Na+ inactivation channel limits Na+ entry, K+ channel returns polarity to normal

21

Coding information in AP's

Control of Speed
Can change the frequency with which we see the AP's
Firing rate- "wave of AP's"
Proportional neurotransmitter (NT) release
Stronger Graded Potential (GP)
aka stimulus= more AP's and more NT

22

Speed of AP Conduction

Change the speed by diameter of the axon
larger is faster
axon myelination increases speed(creates saltatory conduction)
Voltage gated channels only in nodes of Ranvier