Nervous System [humans] unit 4.5
The Nervous System The nervous system is divided into two main areas/parts. • The central nervous system [CNS] • The peripheral nervous system [PNS]
CNS • The central nervous system is made up of the brain [and all it components] and the spinal cord. • Acts as the control centre; • Receiving information from the receptors which are throughout the body. • Decides what to do with the information. • Coordinates the response by sending messages out to different parts [effectors] instructing them what to do.
PNS The peripheral nervous system is made up of the sensory receptors and nerves. The PNS forms the communication links between the receptors & effectors and the CNS
Neurons • Specialised cells that transmit and receive messages in the form of electrical impulses. • Neurons are grouped together in bundles called nerves.
Neuron structure • Dendrites: small thread like structures around the soma [cell body] • Axon: one long thread which carries information away from the cell body. • Myelin: the insulating coating over the axon.
Types of Neurons • Interneuron: transfer electrical messages within the CNS • Motor neurons: transfer electrical messages from the CNS to effectors. • Sensory neurons: transfer electrical messages from receptors in the PNS.
Synapse • The synapse is the connections between nerves. These are small gaps across which the messages are sent as chemical compounds. These compounds are called neurotransmitters. • When a message reaches the synapse the electrical message is converted into a chemical one and sent across the synapse, where it is converted back to an electrical message.
Neurotransmitters • There are approximately 50 known neurotransmitters in the human body. • Dopamine – associated with emotion • Serotonin – regulate intestinal movement and also includes the regulation of sleep, appetite, mood and muscle contraction. • Noradrenalin – associated with alertness.
The Brain • Weighs about 1.4 kg • About 25 billion neurons • Each neurons connected to as many 1000 neighbouring neurons. • Neurons connected in specific circuits and networks.
Parts of the brain • Cerebrum – The two large hemispheres of the brain [grey matter] responsible for complex thoughts, senses, muscle control, memory and thinking. • Cerebellum – base of the brain which controls complex muscular movement • Medulla – Brain stem, controls involuntary actions like heart beat and breathing.
Reflex action • Reflex actions are fast, occurring automatically and without thinking. They use the pathway known as the reflex arc. • Examples – blinking, coughing, sweating.
Activity • Draw and label a neuron • Homework – due next lesson. • U4.5 [page 135] questions 1, 3, 4, 5, 8, 10, 14, 16 & 17