Intro to Nervous System

HS 1300 Dr. McWatt UWO Objectives: Describe the basic cells of the central and peripheral nervous system, Differentiate between a typical motor versus sensory neuron, Explain the role of myelin and define white matter versus gray matter, Describe the structural and functional differences between the central versus peripheral nervous systems, as well as the somatic versus autonomic nervous systems

What are the two components of the nervous system?

Central Nervous System: Brain and spinal cord

Peripheral Nervous System: Nerves

What are neurons and what do they do?

• the basic unit of the CNS

• transmit electrical impulses to one another to communicate info

What are the 2 types of neurons?

Multipolar motor neuron

Pseudounipolar sensory neuron

Name the 2 neuroglia talked about in this course and how many myelin sheaths they form around however many axons:

Oligodendrocyte in the CNS: forms SEVERAL myelin sheaths around MULTIPLE axons

Schwann cells in the PNS: forms ONE myelin sheath around ONE section of axon

What is neuroglia?

Non- neuronal, non-excitable cells

5x as abundant as neurons

Support for neurons

What is myelin sheath?

Insulates axon to increase speed of signal

Label the multipolar motor neuron and explain what each part does:

Motor neurons send signals from the —- to ——-

from CNS

to Target organs

Label the pseudounipolar sensory neuron and explain what each part does:

What is multiple sclerosis and where does it occur?

• Degradation of oligodendrocytes

• Occurs in CNS

What is Gullian-Barre Syndrome and where does it occur?

• degradation of schwann cells

• Occurs in peripheral nervous system

White vs Gray Matter

White matter has myelinated axons for communication

Gray matter has unmyelinated neuron cell bodies that process info

Where is white matter located?

Tracts, axons, fascicles

Where is grey matter located?

Nerves, cortex, nucleus (ex. ganglia)

The pathway of a signal in an unmyelinated neuron

• Multiple action potentials need to be summated to overcome threshold 

• Depolarization of neuron occurs which sends action potential down the neuron 

• The speed is very slow (0.5-2ms) 

The pathway of a signal in a myelinated neuron:

• Depolarization only occurs at nodes of ranvier (between each myelin sheath) 

• Causes a very quick impulse as it is only depolarizing at the ranvier (3-120m/s)

The 4 steps of neuronal synapse (As action potentials are sent down; these will send the impulse to the next neuron 

• The very end of the axon terminal will synapse with dendrite on the next neuron 

• This is done by neurotransmitters as it is not a physical action)

Steps 

1. Nerve impulse arrives at axon terminal end bulb of presynaptic neuron 

2. Impulse causes calcium channels to open and calcium ions rush in 

3. This changes polarization which causes neurotransmitter to release and crosses the synaptic cleft to trigger opening of sodium channels on postsynaptic neuron 

4. This initiates a new nerve impulse; sodium flows into dendrite of postsynaptic neuron to initiate new nerve impulse 

2 components of Peripheral nervous system:

Autonomic and Somatic

Characteristics of autonomic ns

 Peripheral innervation to visceral organs and glands 

- can’t control 

- heart beat, digestion, glands, etc

Characteristics of Somatic nervous system

 Peripheral innervation to all other tissues -

• Voluntary motor control

- conscious thought 

- muscle, skin, etc

What are the 2 parts of the autonomic nervous system

Parasympathetic NS and Sympathetic NS

Where do the parasympathetic signals come from

Cranial nerves and sacral spinal levels

Where do sympathetic nerve signals come from

T1-L2 via the sympathetic chain/trunk

What is a dermatome?

Area of skin supplied by a single spinal nerves SENSORY fibers.

What is a myotome?

A group of muscles innervated by a single spinal nerves MOTOR fibers.

Functional Overview

CNS receives SENSORY info from PNS (thru external and internal environments) which processes info and produces a responses via MOTOR system.

Afferent vs Efferent

Sensory: Afferent

Motor: Efferent