Download The Nervous System

The Nervous System
Section 3.5 p. 146-151
Learning outcomes
• I can describe how the role and function of the nervous system
• I can list and describe the individual organs that make up the nervous
system, and how they work together
• I can describe how the nervous system responds to changing
conditions
Remember what a stimulus is??
Responding to a stimulus
• Stimulus: is a change in your
environment
• Can occur in many forms
• pressure, heat, cold, light, sound, or body
chemistry.
• Can be external or internal
• External – outside of your body
• i.e. walking in from the cold outdoors to a warm
room
• Internal – Inside your body
• i.e. the arrival of food in your stomach
• It is the job of the nervous system to
monitor and respond to these stimuli
Nervous Tissue
• Remember the four types of tissues?
•.
•.
•.
•.
• The nervous system is made up
almost entirely of Nervous tissue
• The nervous tissue is made up
entirely of one type of specialized cell
called Neurons
• A neurons job is to send and receive
messages
The Neuron
• The neuron receives messages
from small branches of the cell
called dendrites
• Messages are passed from the
dendrites through the cell body to
the axon
• The axon is a long extension of the
cell that ends in small branches
• It carries impulses away from the cell
body to its branches.
• These branches transmit the
message to the dendrites of
neighboring cells
• Signals travel very fast
• Myelinated cells up to 100 M/s
• Unmyelinated around 2-3 M/s
Organization of Nervous System
• All though there are many divisions of the
Nervous system
• There are two main important
components
• Central Nervous system: is composed of the
brain and spinal cord
• This is where the info processing occurs
• Peripheral Nervous system: is composed of
the cranial and spinal nerves that travel to all
parts of the body
• So all other nervous tissue that is contained outside
of the brain and spinal cord
Peripheral Nervous system
• Each nerve of the peripheral
nervous system is composed of
two types of neurons.
• Sensory Neurons: carry
information from the body to the
central nervous system
• Motor Neurons: carry
information from the central
nervous system to the muscles
and organs
The Peripheral Nervous system can be
divided again
• Within the peripheral nervous system, there are two
types of smaller systems
• Somatic Nervous System: System that refers to
actions that you have conscious control over
• These are voluntary responses, you choose to perform them
• i.e. when you hear a noise you decide to turn and investigate what it
might be
• Automatic Nervous System: controls the actions that
you respond to unconsciously ( without thought)
• You don’t think about these reactions, they occur
automatically
• i.e. adjusts size of pupils to amount of light, heart rate,
breathing rate, peristalsis in your digestive tract
• If you had to think of all these things you wouldn’t be able to
think of much else
The Reflex Response
• Reflex: is an automatic response by the
nervous system to an external stimulus
• Reflex Response: is when sensory neurons
and motor neurons work together with out
the Brain (CNS)
• So lets say you touch a hot stove element
• Your sensory neurons still send a message to the
brain(CNS)
• But interneurons recognize the severity of the
stimulus, and relay the message directly to the
motor neurons in your arm
• This way by the time your brain tells you to
scream out in pain, you’ve already removed your
arm from the danger
• Reflex's protect you from injury by reducing
the time it takes to reduce harmful stimuli
The Central Nervous System (CNS)
• Protected by the bones of the skull and
spinal cord
• Made up of two types of tissue
• Grey matter
• White matter
• The brain receives stimuli information
from your sense organs
• i.e. eyes, nose, mouth, skin, ears
• It also receives internal stimuli from
your body
• i.e. greater need for oxygen in a certain
area of the body due to increase in activity
• It reacts to these stimuli, and sends
messages to the appropriate body parts
3 main Components of the Brain
• The brain is generally divided
into three main sections
• Cerebrum
• Conscious events including
thoughts
• Cerebellum
• Programs and fine-tunes voluntary
and involuntary movements
• Medulla
• Controls your cardiac,
respiratory, and balance system
• There are around a 100 billion
neurons in your brain
• It accounts for 2% of your body
weight
• Consumes about 25% of the
oxygen your body uses
CNS Cont’d
• The spinal cord connects the
brain to the peripheral
nervous system
• It acts like a highway for
messages between the brain the
body
• It contains Interneurons (these
connect one neuron to
another)
An uneven sense of touch
• Unlike other senses such as vision, hearing,
smell, and taste, the sense of touch is not found
in one specific place
• The sense of touch is found in all areas of your
skin, making it the largest sense organ
• Not all areas have the same amount of touch
receptors
• Which area’s do you think will have the most