Unit 3: Chapter 9 How Nerve Signals Maintain Homeostasis Section 9.1 (pages )

Recap Endocrine system (location of endocrine glands) Hormones Pituitary Gland Proteins vs. Steroid Signaling Blood sugar levels (Insulin, Glucagon) Metabolism (T4, T3) Adrenal Glands (Short vs. Long term response)

The Importance of the Nervous System Communication system that contains 100 billion nerve cells in the brain alone Nerve cells detect air temperature, light intensity and odours

The Importance of the Nervous System Responds to internal/external environments through electrochemical message or a series of chemical messengers (hormones) Hormones require more time than nerves require Memories, learning and language  functions of the nervous system.

Vertebrate Nervous Systems The nervous system has 2 main divisions: 1.Central Nervous System (CNS) 2.Peripheral Nervous System (PNS)

Vertebrate Nervous Systems CNSPNS Consists of the nerves of the brain and spinal cord Coordinating Center for incoming/outgoing information Nerves that carry information between the organs of the body and the CNS Subdivided into: somatic and autonomic nerves Somatic nerves: skeletal muscle, bones and skin Autonomic nerves: special motor nerves that control internal organs of the body Autonomic nerves  sympathetic and parasympathetic nervous system

Figure 1. page 412

Anatomy of a Nerve Cell Two types of cells exist in the nervous system: 1.Glial cells 2.Neurons Glial cells: Non-conducting cells that are important for the structural support and metabolism of the nerve cells

The Types of Neurons Neurons: Are the functional units of the nervous system. These specialized nerve cells are categorized into three groups: 1.The sensory neurons 2.Interneurons 3.Motor Neurons

1. Sensory Neurons Sense and relay information (stimuli) from the environment to the CNS for processing Example: photoreceptors, chemoreceptors and thermoreceptors Sensory neurons are located in clusters  ganglia

2. Interneurons Link neurons within the body Predominantly located in the brain and spinal cord Integrate and interpret sensory information and connect neurons to outgoing motor neurons 3. Motor Neurons Relay information to the effectors Effectors include muscles, organs and glands  because they produce responses

Anatomy of the Neuron All neurons contain dendrites, cell bodies, and axons Dendrites Receive information from either sensory receptors (sensory neurons) or nerve cells (motor neurons) Conduct nerve impulses toward the cell body

Axon An extension of the cytoplasm that carries nerve impulses away from the cell body Carries nerve impulse toward other neurons or to effectors Myelin Sheath Insulted covering over the axon of a nerve cell Schwaan Cells Special type of glial cell that produces the myelin sheath

Nodes of Ranvier Regularly occurring gaps between sections of myelin sheath along the axon Nerve impulses jump from one node to another Neurilemma Within the PNS, some nerve cells have a delicate membrane that surrounds the axon Promotes the regeneration of damaged axons Speed of an impulse increases if: Nerve fiber is myelinated The axon has a small diameter

Figure 2. Page 413

Let’s suppose you touch a hot stove… 1.Heat is detected by temperature receptors in the skin 2.A nerve impulse is carried to your spinal cord 3.Sensory neuron  interneuron  motor neuron 4.Motor neuron causes the hand to contract and pull away from the stove 5.All this happens in less than 1 second, before information travels to your brain

Neural Circuits: Reflex Arc Reflexes are involuntary and often unconscious The simplest nerve pathway is the reflex arc Most reflexes occur without brain coordination Reflex arcs contain 5 essential components: 1.Receptor 2.Sensory Neuron 3.Interneuron in the spinal cord 4.The motor neuron 5.Effector

Figure 6. Page 416

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