Nervous System

Textbook page 351-353

 Structure of neurons

- has cell membrane, cytoplasm, mitochondria, nucleus

- transmits nerve impulses

- different neurons = different shapes and sizes

                4 common features = dendrites, cell body, axon, branching ends

Dendrites - receive nerve impulses from neurons/sensory receptors and passes the impulse to cell body

Cell Body - contains nucleus; site of metabolic reactions; processes input of dendrites (if large enough, passes to axon)

Axon - conducts impulse away from body

                Myelin sheath = insulating layer around axon of some neurons

                                        protects neurons and speeds rate of nerve impulse transmission

                Schwann cells = type of glial cell, form myelin by wrapping around axon

Classifying Neurons

1.  Structure - 3 types: multipolar, bipolar, unipolar neurons

2.  Function -3 types: sensory neurons, interneurons, motor neurons

The Reflect Arc

Reflexes - involuntary responses to certain stimuli

Reflex arcs -  connections of neurons explaining reflexive behaviour

- 3 neurons to transmit messages = fast reflexes

(from brain to spinal cord)                                                                                       

1. stimulus (cactus needle) - receptors in skin sense pressure

2. initiates impulse in sensory neuron

3. activates interneuron in spinal cord

4. signals motor neuron to withdraw hand