Here is the completed reflex arc: When you stand on a pin, the pain sensor sends an electrical impulse along the sensory neuron. This is passed across a synapse as a chemical and processed in the CNS in a relay neuron. It is passed across another synapse and through the motor neuron as an electrical impulse. This causes the muscle to move away from the pin. It is an involuntary response. CNS motor synapse electrical involuntary sensor

1. +
The Nervous System
Chapter 29.1 and 29.2

2. +
Learning Objectives:
To be able to:
 Explain the composition of the nervous system and how organ
systems communicate
 To identify the main features of a neuron
 Stimulus, Central nervous system, Peripheral nervous system,
Neuron, Dendrite, Axon
Keywords:

3. +The nervous system is a physically connected
network of cells, tissues and organs that controls
thoughts, movements and simpler life processes
such as swallowing.
For example, when you walk outside on a sunny day
without sunglasses, your nervous system senses the
bright light and sends messages that tell your pupils
to shrink.
The endocrine system is a collection physically
disconnected organs that helps to control growth,
development and responses to your environment.
- Can you give me an example?

4. + What is the nervous system?

5. +
What is the nervous system?
The Nervous System is split into the Central
Nervous System (CNS) and the Peripheral
Nervous System (PNS).
The CNS is the brain and spinal cord.
The PNS transmits electrical impulses to and from
the CNS.

6. +
In your books…
Use page 820 to answer the following questions:
 What is a neuron?
 What is the FUNCTION of a neuron?
 How many types of neurons are there and what are their
functions?

7. +
Check your answers!
 What is a neuron?
A neuron is a highly specialized cell
 What is the FUNCTION of a neuron?
A neuron receives and transmits signals. It stores information and carries
messages within the nervous system and between other body systems
 How many types of neurons are there and what are their functions?
- Sensory: detect stimuli & transmit signals to CNS
- interneuron (relay): receive signals from sensory neurons & relay them
within CNS
- motor: pass messages from nervous system to other tissues in body

9. What are the functions of:
 The cell body?
 Dendrites?
 Axons?
Use page 820 to help you

10. The Stimulus-Response Model
The basic pathway for a nerve impulse is described by the stimulus-response
model
A receptor converts a stimulus into a nerve impulse, which is transmitted by a
sensory neuron to the CNS (spinal cord)
Relay neurons within the CNS will transmit this signal to a control centre (usually
the brain), where the information is processed
Motor neurons will transmit a resultant nerve impulse from the CNS to an effector
organ (a muscle or gland), eliciting an appropriate response

11. +
Voluntary and Involuntary Responses
Voluntary responses are things that you can
control, for example picking up a pen, kicking
a ball.
Your brain sends an impulse down the spinal
cord which then passes an impulse to your
motor neurones to complete the action.

12. +
Voluntary and Involuntary Responses
Involuntary responses are things you can’t
control.
These are how you react to pain, your eyes
dilating and contracting, your heart beating
etc.

13. +
Reflex
A reflex is a rapid and involuntary response to a
stimulus and results from an even simpler pathway
called a 'reflex arc'
Reflex actions do not involve the brain in the
decision making process - instead sensory
information is relayed directly to motor pathways
within the spine
This results in a reaction without conscious thought,
which may be important in survival situations when
quick reactions are necessary to avoid permanent
damage or pain

14. + The Reflex Arc
PNS
CNS

15. +
The Reflex Arc
Copy and complete:
When you stand on a pin, the pain sensor sends an electrical
impulse along the sensory neuron. This is passed across a
synapse as a chemical and processed in the CNS in a relay
neuron. It is passed across another synapse and through the
motor neuron as an electrical impulse. This causes the
muscle to move. It is an involuntary response.
CNS motor synapse
electrical involuntary sensor

16. +
The Reflex Arc
Copy and complete:
When you stand on a pin, the pain sensor sends and
electrical impulse along the sensory neuron. This is passed
across a synapse as a chemical and processed in the CNS
in a relay neuron. It is passed across another synapse and
through the motor neuron as an electrical impulse. This
causes the muscle to move. It is an involuntary response.
CNS motor synapse
electrical involuntary sensor