THE NERVOUS SYSTEM

9.1 Introduction

A. Neurons = masses of nerve cells that transmit information to other nerves, tissues or cells (nerve impulses)

1. ___________________ - contains the nucleus and two extensions
2. ___________________ - shorter, more numerous, receive information
3. _________ - single, long fiber which conducts impulses away from the cell

B. The nervous system is divided into two parts:

1. Central Nervous System (CNS) - brain and spinal cord
2. Peripheral Nervous System (PNS) - peripheral nerves through the body
        - includes 31 pairs of spinal nerves
        - includes 12 pairs of cranial nerves

9.2 Three Basic Functions

1. Sensory Function -

2. Integrative Function -

3. Motor Function -

                        - Homeostasis. Motor neurons.

- Somatic Nervous System (skeletal muscles)
- Autonomic Nervous System (smooth muscles, glands)

Neurons: Nerve cells. - cell body with many extensions or processes (nerve "fibers") which conduct impulses

1. Dendrites -

2. Axons -

9.3 Neuroglial Cells (neuroglia)

- supportive tissue of the nervous system (more numerous than neurons). Five types

1. Microglial Cells
2. Oligodendrocytes
3. Astrocytes
4. Ependymal Cells
5. Schwann cells

*Myelin Sheaths

neuroglia

neuron

9.4 Neurons

Axon

Dendrite

Neurofibril - fibers within the axon

Chromatophilic substance

Myelin

Nodes of Ranvier

 

Myelinated (white matter) vs Unmyelinated (grey matter)

 

Classification of Neurons

1. Functional (sensory neurons, motor neurons, interneurons)
2. Structural (multipolar, bipolar, unipolar)

 

 

9.5 Cell Membrane Potential

Resting Potential / Threshold Potential / Action Potential

1. Neuron membrane maintains _______________________________________
2. Threshold stimulus is received
3. _______________________________________channels open
4. Sodium ions diffuse inward, depolarizing the membrane
5. _______________________________________ channels open
6. Potassium ions diffuse outward, repolarizing the membrane
7. The resulting action potential causes a local ________________________ current that stimulates adjacent portions of the membrane.
synapse8. Wave of a______________________________ travel the length of the axon as a nerve impulse

9.6 Nerve Impulse

*Propagation of action potentials along a nerve axon

Impulse Conduction – speed of an impulse proportionate to ____________________of axon (greater diameter = faster impulse)

Myelinated axons conduct ________________________________than unmyelinated axons

9.7 The Synapse

Synapse =
Nerve pathway – nerve impulse travels from neuron to neuron

Dendrite >> cell body >> along axon >> synapse (gap)

To complete the signal, a _______________________________ is released at the gap to signal the next neuron

_________________________________ – increase membrane permeability, increases chance for threshold to be achieved
Inhibitory – decrease membrane permeability, decrease chance for threshold to be achieved

Types of Neurotransmitters

Acetylcholine – stimulates ______________________________________
Monoamines – Norepinephrine & Dopamine (sense of feeling good, low levels = depression)
Serotonin = ________________________________________________

Endorphins = ______________________________________________

Synapses are highly susceptible to drugs and fatigue

What is Curare?

Strychnine and some nerve gases inhibit or destroy acetylcholinesterase formation. Prolongs and enhances any stimulus, i.e. leads to convulsions, contraction of muscles upon the slightest stimulus.

Cocaine, morphine, alcohol, ether and chloroform anaesthetise nerve fibers. (inhibitory)

Mescaline and LSD produce their hallucinatory effect by interfering with nor-adrenaline & serotonin

9.8 Impulse Processing

Neuronal pool – groups of neurons that make hundreds of synaptic connections and work together to perform a common function

9.9 Types of Nerves

Sensory Nerves – conduct impulses into the brain or spinal cord
Motor Nerves – carry impulses to muscles of glands
Mixed Nerves - contain both sensory and motor nerve

9.10 Nerve Pathways

Reflex arc – simple pathway, includes only a few neurons (_____________________________)

Reflex Behavior – automatic, subconscious responses to stimulu

Knee-jerk reflex =

Withdrawal reflex =

reflex