1. Responses in the Human
Nervous System 1
Objectives – What you will need to know from this section
Outline the nervous system components: central nervous system (CNS) and the peripheral nervous system (PNS)
Receptor messages are carried through these systems by nerve cells or neurons.
Outline the structure & function of the neuron including: cell body, dendrites, axon, myelin sheath, schwann cell, and neurotransmitter vesicles & synaptic cleft
Outline impulse movement & synapse.
Explain activation & inactivation of neurotransmitter.

2. 2
The structure and function of a neuron: variation in size and shape.
Neuron -- Three part structure: > dendrite(s) receive information and carry it towards the cell body, > the axon conducts nerve impulses away from the cell body, > the cell body contains the nucleus and other organelles and produces neurotransmitter chemicals.
Explain the role & position of 3 types of neuron -- sensory/motor/inter

3. The Nervous System
Organisms must be aware of what is happening around them, as this affects their survival chances.
Co-ordination of an organism’s activities is carried out by the nervous system
A nervous system allows an organism to detect and respond to stimuli in its internal or external environment.
A stimulus is any change in your environment
e.g. a flash of light, a noise, a fly landing on your nose.

4. The nervous system relies on electrical signals, carried by specialised cells [neurons], and is involved in fast responses.
The central nervous system (CNS) is your brain and spinal cord.
The brain keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.
The peripheral nervous system (PNS) is the nerves branching from the CNS to all parts of the body.

5. LEARNING CHECK
Co-ordination of an organism’s activities is carried out by what body system?
Distinguish between the CNS and PNS.
What is a neuron?
What is an impulse?

6. NS ----- Co-ordination & Response
A stimulus is any change in your environment
A receptor is a nerve cell that detects the stimulus
A neuron is a specialised cell that carries electrical messages (impulses) around the body.
An impulse is an electrical message that is carried along a neuron.

7. Neuron structure
The cell body contains the nucleus and other organelles and produces neurotransmitter chemicals.
A dendron is a short fibre that receives information and carries it towards the cell body.
The axon is a very long fibre that conducts impulses away from the cell body.

8. A dendron is a short fibre that receives information and carry it towards the cell body.
Dendrites are small branches of a dendron.
Many Schwann cells wrap their fatty cell membranes around an axon, forming a myelin sheath.
The myelin sheath insulates the neuron from electrical impulses flowing in other neurons.

9. There are three types of Neuron :
Sensory neuron –carries messages from the sense organ to the central nervous system (CNS).
Interneuron –connects sensory and motor neurons and so carries messages within the CNS.
Motor neuron –carries impulses from the CNS to muscles and glands.

11. Synapse—region where two neurons come into close contact.
Synaptic cleft—the gap between two neurons, bridged by chemicals (neurotransmitters).
SYNAPSE
Neurotransmitter—chemical released across a synaptic cleft to carry a signal from one neuron to another.
The chemical is then destroyed or removed

12. LEARNING CHECK What is a stimulus? What is a receptor?
Name the main parts of a neuron and give one function of each.
Distinguish between a sensory and motor neuron.
Distinguish between synapse and synaptic cleft.
What are neurotransmitters?

13. The Brain
The brain is composed of over 100 billion neurons, each receiving messages simultaneously from thousands of other neurons.
The brain is protected by the skull bones, meninges (three membranes) and cerebrospinal fluid.

14. The cerebrum is our conscious brain, with different parts having different jobs to do.
hypothalamus
pituitary
The hypothalmus is the centre for the regulation of the internal organs.
The pituitary ‘[master] gland secretes hormones that stimulate other glands to release their hormones.

16. Conscious actions
A conscious action is one where the brain makes a considered response. Here’s what happens:
4) The brain decides to move away the hand
3) Here another sensory neuron carries the signal to the brain
5) This impulse is sent by MOTOR NEURONS to the hand muscles (the effectors) via the spinal chord…
2) The impulse is carried by SENSORY NEURONS to the spinal chord
1) Receptors in your skin detect a stimulus
6) Which then moves the hand away
Stimulus Receptor Sensory Neuron Coordinator
Motor Neuron Effector Response

17. The cerebellum co-ordinates processes that we have learned to do automatically, such as speaking.
Medulla oblongata
The medulla oblongata co-ordinates involuntary, automatic processes — such as breathing, heartbeat.

18. LEARNING CHECK
Name the 3 main parts of the brain and one function of each.
How is the brain protected?
What is meant by “conscious action”?
What does the term “involuntary” mean?
Distinguish between the cerebrum and the cerebellum.

19. SENSE ORGANS
Animals have specialised senses to provide them with information about their environment.
The five senses are sight, hearing, touch, taste and smell.
A receptor is a cell that can detect a stimulus
A stimulus is any change in your environment, e.g. light, sound.

20. Sense Organ Stimulus detected Sense Organ Sense
Smell
Taste
Touch
Hearing
Sight
Sense
Nose
Tongue
Skin
Ear
Eye
Organ
chemicals [receptors in the nasal cavity detect vapours]
chemicals [taste buds detect sweet, sour, salt and bitter].
touch, pressure, temperature and pain [receptors spread throughout body]
sound [receptors in cochlea]
light [by rods and cones in the retina]
Stimulus detected
Smell
Taste
Touch
Hearing
Sight
Sense
Nose
Tongue
Skin
Ear
Eye
Organ
Smell
Taste
Touch
Hearing
Sight
Sense