B1- Understanding organisms

LO – Describe the parts of the nervous system. Explain how reflex actions work and why they are important.

Keywords– axon CNS dendrites effector neurone peripheral receptor Lung structure clip reflex sheath synapse stimulus spinal cord transmitter substance voluntary response

Identification of the density of nerve endings – AIM: To investigate the sensitivity of different areas of the skin. Method: Working in pairs, one student looks in a different direction, while another student touches them on the back of the hand with either one or two pieces of blunt pencil about 1 cm apart. The blindfolded student has to say whether it was one point or two points that touched them. Place a cross on the hand for each point felt. Results: Map the density of sensory receptors by drawing it into your book. Conclusion: Are the receptors in groups? Or randomly placed? What can you say about the density of the receptors identified?

NERVE FIBRES Clip slide 04, last slide draw neurones Nerve fibres are bundles of nerve cells (neurones) that pass on electrical signals (impulses) to the brain. From the brain, nerve fibres send impulses to effectors (muscles/glands).

What is happening? Your body’s sense organs contain receptors. Receptors (sensory neurons) detect changes in the environment called stimuli and send messages (nerve impulses) along nerves to the brain and spinal cord (CNS).

Lets consider the reflex response! The Reflex Arc Reflexes are an involuntary response to a stimulus, they exist because throughout our evolution we have needed to respond to a variety of different situations quickly...otherwise we die!!! Lets consider the reflex response!

The Reflex Arc Response Clip slide 07,12, 14 Stimulus picked up by Receptor cells in finger (skin) Impulse passed on to sensory neurone Sensory neurone passes impulse to spinal cord Spinal cord sorts out (relays) a response and sends a message to motor neurone Motor neurone tells the muscle (effector) to contract The finger moves away from the stimulus

Put these is the correct order to annotate your diagram! Fruit Groups! Spinal cord or brain relays the message Impulse carried along nerve cell (Sensory neurone) to spinal cord Stimulus (change) picked up by receptor Effector organ brings about a response Impulse carried along nerve cell (motor neurone) to effector organ Put these is the correct order to annotate your diagram!

1.

Spinal cord cross section Main part of our nervous system is called the Central Nervous system Spinal cord cross section

Spinal Cord

Reflex in the finger Stimulus picked up by Receptor cells in finger (skin) Impulse passed on to sensory neurone Sensory neurone passes impulse to spinal cord Spinal cord sorts out response and send message to motor neurone Motor neurone tells the finger to pull away

Reflex in the leg Stimulus picked up by Receptor cells in leg (skin) Impulse passed on to sensory neurone Sensory neurone passes impulse to spinal cord Spinal cord sorts out response and send message to motor neurone Motor neurone tells the leg to move

EFFECTORS An effector is any part of the body that produces the response. Here are some examples of effectors: a muscle contracting to move the arm a muscle squeezing saliva from the salivary gland a gland releasing a hormone into the blood

What would happen if…. You were cooking and you put your hand on to a hot pan. You task as a group: -how would detect this? -what process would your nervous system go through? -how would you avoid it! Fill in the boxes below! Stimulus Receptor Effector Response

NEURONES There are three types of neurones Sensory neurone – carries impulses from the receptors to the spinal cord. Relay Neurone – carries impulses to and from the spinal cord and the brain Motor Neurone – carries impulses from the brain to the effector Relay neurone

2 TYPES OF OF NERVE PATHWAY… SENSORY NEURONE Takes impulses from the sense organ to the relay neurone. RELAY NEURONE Takes impulses to the brain and from the brain. MOTOR NEURONE Takes impulses from the relay neurone to the effector. BRAIN Receives impulses from the spinal cord and sends out new impulses. SENSE ORGAN/ RECEPTOR Senses stimuli from our surroundings. EFFECTOR The muscle that receives the impulse from motor neurone. SPINAL CORD Where the relay neurones are found. VOLUNTARY INVOLUNTARY

Reflex Arc Automatic responses to stimuli are called reflex actions. A reflex response is rapid and its function is protection The spinal cord mediates reflex responses to some sensory impulses directly ie. without going to the brain. This makes it much faster. The messages pass through a reflex arc:

What’s happening when we detect a stimulus which causes a reflex? Each reflex action takes the follows the pathway: stimulus  receptor  sensory neurone  relay neurone  motor neurone  synapses  effector  response

Synapses An electrical impulse travels along an axon. This triggers the nerve-ending of a neuron to release chemical messengers called neurotransmitters. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron. The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse.

Effectors Effectors are muscles or glands which carry out a response. A muscle responds by contracting. A gland responds by secreting chemical substances.

Effectors Fatty deposits which stop the electrical impulse from leaking away. The gaps between allow the impulse to “jump” which means it moves along the neuron rapidly. The end of the neuron is branched so that they can communicate with many other neurons (or effector cells!)

Copy the diagram below of a reflex arc into your book. Label: a sensory neurone a motor neurone an intermediate (relay) neurone an axon a synapse the spinal cord a sense organ/receptor and an effector muscle Put arrows on the neurones to show the direction of the impulses.

Answers Student Book Q8 Get smaller • Q9 To control the amount of light entering the eye • Q10 Knee jerk, dropping a hot plate • Q11 Electrical impulses • Q12 Because they are not delayed by the brain thinking about them • Q13 Axon • Q14 It can make decisions such as examining the fingers and using first aid • Q15 They are very long and thin to carry impulses directly to body parts. They have an insulatory sheath to stop electrical impulses spreading to other neurones. They have branching dendrites to make contact with other neurones or act as receptors • Q17 Description to include receptor, sensory neurone, central nervous system, relay neurone, motor neurone, effector. Fig 8 as electrical impulses • Fig 9 no • Fig 10 away from the cell body • Fig 12 allows impulses to pass along different pathways.

Answers Worksheet Q1a quick, does not involve thought • Q1b along (sensory) neurones • Q1c brain and spinal cord • Q2a dendron/ cytoplasm/axon/muscle/fatty sheath/nucleus • Q2b does not involve the brain and involves conscious thought. Also quicker • Q2c skin/sensory/relay/motor/muscle • Q3a insulates the neurone and speeds up the impulse • Q3b transmitter molecules are released when an impulse reaches the synapse/diffuse across the gap/bind with receptors on next neurone/cause an impulse to pass along this neurone.

Learning outcomes Name and locate the main parts of the nervous system. Describe the nerve impulse as an electrical signal. Describe the difference between reflex actions and voluntary actions. Describe a reflex arc. Name and locate the parts of a motor neurone and explain how neurones are adapted to their function. Describe a synapse and explain how it works.

Reflexes always involve the spinal cord. True or False? Reflexes always involve the spinal cord. Reflexes always involve the spinal cord.

Reflexes never involve the brain. Reflexes never involve the brain. True or False? Reflexes never involve the brain. Reflexes never involve the brain.

Reflexes allow us to respond quickly and they protect us from harm. True or False? Reflexes allow us to respond quickly and they protect us from harm. Reflexes allow us to respond quickly and they protect us from harm.

Reflexes have to be learnt. Reflexes have to be learnt. True or False? Reflexes have to be learnt. Reflexes have to be learnt.

Reflexes involve receptors, effectors, and neurons. True or False? Reflexes involve receptors, effectors, and neurons. Reflexes involve receptors, effectors, and neurons.

Reflexes are voluntary. True or False? Reflexes are voluntary.

Reflexes are voluntary. True or False? Reflexes are voluntary.

True or False? In a reflex pathway, relay neurones pass impulses from sensory neurones to motor neurones.

True or False? In a reflex pathway, relay neurones pass impulses from sensory neurones to motor neurones.

What did we do last lesson?? Reflex Arc What did we do last lesson?? Central Nervous System, electrical, organs, stimuli Sense ____ in the body are eye, tongue, ear, skin and nose Sense organs have receptor cells which respond to specific _______ Nerve cells relay information (messengers) as ____________ impulses CNS – ________________make the decisions!