Unit #1: Wellness And Homeostasis Controlling Homeostasis (2) … · 2020. 2. 9. · Unit #1: Wellness And Homeostasis Controlling Homeostasis (2) ... 1. Resting Potential A signal

Unit #1: Wellness And HomeostasisControlling Homeostasis (2)

“Neurons and Nerve Impulses”

What is Nervous Tissue?

Why is Nervous Tissue important to Controlling and Maintaining Homeostasis?

How does a Nerve Cell Work?

Neuron Structure:

(A) Cell Body

(C) Dendrites

(D) Axon

• main portion of the cell

• contains a nucleus (B) and other

organelles

• extensions at one end of the neuron

• nerve impulses enter the cell body

through the dendrites

• A long extension that extends away from

the cell body

• carries the nerve impulse AWAY from the

cell body

(E) Axon Terminal

(F) SchwaanCells

(H) Nodes of Ranvier

• Thousands of microscopic branches

located at the end of the axon

• release Neurotransmitters that carry

nerve impulses to neighbouring neurons

and target muscles and glands

• these cells are wrapped around the axons

of the cells and form Myelin Sheaths (G)

• Myelin Sheaths insulate the axon which

speeds up nerve impulses

• Gaps between Schwaan cells

• found in longer Myelinated Axons

• allows the nerve impulse to “jump” from

node to node (moves further faster)

What is a Nerve?

Sensory Neurons

Motor Neurons

Interneurons

• A Nerve is a series of connected neurons that

form a pathway that an impulse can travel

through

• Neurons that build Sensory Nerve pathways

• carry impulses from the body to the CNS

• Dendrites are connected to body surfaces or

organs and axons lead to the CNS

• Neurons that build Motor Nerve pathways

• carry impulse from CNS to the body

• Dendrites are connected to the CNS and

axons lead to target areas of the body

• Neurons that connect Sensory and Motor

Neurons

• usually are found in reflex arcs in the spinal

cord

What is a Nerve Impulse?

How it works:

1. Resting Potential

A signal that is carried along a nerve

• The neuron is at “rest” - no impulse is

being transmitted

• Sodium Ions (I) are being actively

pumped out of the nerve cell while

Potassium Ions are equally concentrated

inside and outside of the cell

• cell membrane is “polarized” (inside is - ,

outside is + )

2. Action Potential

• the neuron is “firing”

• an electrical chemical, chemical or

mechanical stimulus alters the structure

of the cell membrane of the neuron

• Sodium Ions rush into the cell and the

membrane depolarizes

• the Action Potential (Impulse) is passed

down the axon and depolarizes the areas

in front of it)

• After the action potential passes the

neuron “re-polarizes” and returns to its

resting potential

• the entire process takes less than a

millisecond