Part 1 Biology 12

 An integral part of your body’s communication system.  It plays an important role in the smooth functioning of the body.  The nervous system is a complex network of cells which are specialized in function.

 The Nervous System allows the body to respond to changes in the internal and external environments.  Communication comes in the form of electrochemical messages relayed to and from the brain, or a series of chemical messengers carried in the blood.  Through a series of adjustments, all systems of the body are regulated to maintain the internal environment within safe limits (homeostasis).

 The nervous system has two main divisions:  Central Nervous System (CNS)  Peripheral Nervous System (PNS)

 Consists of the nerves of the brain and spinal cord.  Brain is known as the “cerebrum”  Acts as a coordinating centre for incoming and outgoing information.

 The brain consists of millions of nerve cells that cluster together and interact with each other through the process of neurotransmission.  It controls most of the bodily functions like movements, thoughts, speech, sensations and memory.

 The spinal cord is a continuation of the brain and is surrounded by the vertebral bodies that form the spinal column.  The spinal cord is divided into four main segments; reach transferring signals to different parts of the body.

 ScM&NR=1 ScM&NR=1

 Consists of nerves that carry information between the organs of the body and the central nervous system.  It can be further divided into:  Somatic nervous system  Autonomic nervous system

 Information about your body is continuously relayed to your brain for processing and storage.  The cells that transfer these messages to the brain and around the body are nerve cells.

 Nerve cells gather & transmits electro- chemical signals. DID YOU KNOW????  Neurons cannot be repaired  Some last a life time  Approximately 1000 die each day!!!

 A nerve is a bundle of neurons attached by connective tissue

 Average number of neurons in the human brain = 100 billion  Nerve “highway” in the human body contains 100 billion neurons  1000 impluses/sec

 SENSORY  Carries signals FROM periphery (outside) TO central nervous system for processing  Information FROM environment  NOTE: detect external stimuli (light, sound, touch, heat, smell, & taste) or internal conditions (blood pressure, CO 2 level & muscle tension)

 MOTOR  Carries signals FROM central nervous system TO body part (e.g. muscles, skin, glands)  Respond to sensory neurons  Responsible for movement

 INTERNEURONS  Connects sensory or motor neurons to central nervous system  Carries messages in-between neurons  Majority of neurons in the brain are interneurons

 Cell Body  Contains all organelles, including a nucleus  Dendrites  Projections off cell bodies  Make connections with other cells

Figure 27.3 Dendrites Cell body Nucleus Cell body

 Axon  Long cable like projection off cell body  Sends messages (nerve impulses)  Myelin Sheath  Fatty protein that covers/insulates most nerves  Increases speed of transmission  Formed by Schwann cells  Nodes of Ranvier  Exposed axon between myelin sheath

Figure 27.3 Dendrites Cell body Nucleus Axon Myelin sheath Nodes of Ranvier Cell body

 Synaptic knob  End of axon branches  Comes near dendrites of adjacent neurons  Passes messages across synapse (the space between neurons)

Figure 27.3 Signal direction Dendrites Cell body Nucleus Axon Supporting cell Myelin sheath Signal pathway Nodes of Ranvier Synaptic knobs Cell body

 Moves in only one direction  From dendrite to cell body, axon, then synaptic knob

Figure 27.3 Signal direction Dendrites Cell body Nucleus Axon Supporting cell Myelin sheath Signal pathway Nodes of Ranvier Synaptic knobs Cell body

 The three interconnected functions of the nervous system are carried out by the three types of neurons Sensory input Sensory receptor Sensory neuron Integration Interneuron Brain and spinal cord Central nervous system (CNS) Motor neuron Motor output Peripheral nervous system (PNS) Effector Figure 27.2

 Nervous System explained Nervous System explained  Nervous System Rap Nervous System Rap  How Neurons Work How Neurons Work

 Draw a large motor neuron on a white piece of paper.  Label  Cell body  Nucleus  Dendrites  axon  Myelin sheath  Schwann cells  Node of Ranvier  Synaptic knob  Then draw arrows to show the message direction  Identify the motor neuron functions

Synaptic knob