Download The Nervous System: Neurons and The Reflex Arc

The Nervous System:
Chapter 35-2
Neurons and The Reflex Arc
Science Standards: 9b and 9e
Ms. Y. Martinez
LSHS
Science Standards you will learn:
9b: how the nervous system mediates
communication between different parts of the body
and the body’s interactions with the environment.
9e: the roles of sensory neurons, interneurons, and
motor neurons in sensation, thought, and response.
The Nervous System
In your body, the job of receiving and sending
messages is done by your nervous system.
The Nervous System allows us to run, write, see,
talk, breath, etc.
The basic cell of the Nervous System is the neuron.
The Nervous System controls and coordinates
functions throughout the body and responds to
internal and external stimuli.
Neurons
The nervous system is composed of nerve
cells, or neurons.
Neurons, the basic cells of the Nervous
System, are cells that transmit impulses.
Impulses are messages in the form of
electrical signals.
B. Nucleus
E. Axon
Terminal
F. Cell Body
D. Myelin
Sheath
A. Axon
C. Dendrites
Although neurons come in all shapes and
sizes, they have certain features in common.
The largest part of
a typical neuron is
the cell body.
The cell body
contains the
nucleus and much
of the cytoplasm.
Cytoplasm
Nucleus
Spreading out from the
cell body are short,
branched extensions
called dendrites.
Dendrites provide a
large surface area for
connecting with other
neurons, and carry
nerve impulses towards
the cell body.
The long fiber that carries
impulses away from the cell
body is called the axon.
A single long axon carries
the nerve impulse away
from the cell body.
The axon ends in a series of
small swellings called axon
terminals.
Most neurons have many
companion cells called
Schwann cells.
Schwann cells wrap their cell
membrane around the axon
many times in a spiral to form a
thick insulating lipid layer called
the myelin sheath.
As an impulse moves along the
axon, it jumps between each
Schwann cell, which increases
the speed at which the impulse
can travel.
A nerve is a discrete bundle of several
thousand neuron axons.
Neuron Types
Neurons can be classified into three types
according to the direction in which an
impulse travels.
There are three types of neurons:
–
–
–
Sensory Neuron
Motor Neuron
Interneuron
Sensory Neuron
Sensory Neuron:
–
carry impulses from the sense organs to the
spinal cord and brain.
Motor Neuron
Motor Neuron:
–
carry impulses from the brain and the spinal cord
to muscles and glands.
Interneuron
Interneuron:
–
–
Make up the brain and spinal cord
connect sensory and motor neurons and carry
impulses between them.
Name the Neuron:
A. Sensory Neuron
C. Interneuron
Spinal
Cord
B. Motor Neuron
Divisions of the Nervous System
The human nervous
system is separated into
two major divisions:
–
–
the central nervous system
(CNS) and
the peripheral nervous
system (PNS).
Central Nervous System
The CNS relays
messages, processes
information, and analyzes
information.
It is the control center of
the body.
It includes the brain and
spinal cord.
The Brain
The brain is composed of three
major parts:
–
–
–
Cerebrum - largest part; controls
senses, memory, intelligence
Cerebellum - coordinates
voluntary muscle movement
Brain Stem - controls the body's
involuntary actions
Peripheral Nervous System
The PNS lies outside of
the central nervous
system.
It receives information
from the environment
and relays commands
from the central nervous
system to organs and
glands.
The Reflex Arc
A reflex arc is the pathway along the central
nervous system where an impulse must
travel to bring about a reflex.
A reflex arc is how neurons work together.
It is how a stimulus elicits a response from
your body without thinking.
Examples include coughing and sneezing.
You need to keep the conditions inside your
body constant. Doing this is called
homeostasis.
You need to detect a change in the
environment (a stimulus) and react to the
change (a response) in a way that maintains
homeostasis.
When you do this without thinking, it is called
a reflex.
An example…
What is the stimulus?
-The hammer hits the tendon.
What is the response?
-The muscle contracts, causing
the foot to jerk upward.
Other Reflexes:
Stimulus
Response
The aroma of your favorite food
Salivation
A nasty odor
Nausea
A bright light shining in your eye
Pupils get smaller
An insect flying towards your eye Blinking
Consider the following situation:
How it works:
A reflex arc includes a
sensory receptor, sensory
neuron, an interneuron, motor
neuron, and effector.
An effector is a bodily organ
(as a gland or muscle) that
becomes active in response to
stimulation.
Salivary Gland
When you step on a tack,
sensory receptors stimulate
a sensory neuron.
The sensory neuron relays
the signal to an interneuron
within the spinal cord.
The signal is then sent to a
motor neuron
The motor neuron
stimulates a muscle in your
leg to lift your leg.
Reflex Arc Pathway:
C. Sensory Neuron
B. Receptor
A. Stimulus
D. Interneuron
G. Response
F. Effector
E. Motor Neuron