Organization of the Nervous System Anatomy & Physiology Mrs. Halkuff

The nervous system is the master controlling and communicating system of the body. The nervous system has 3 main functions: –Uses sensory receptors to monitor changes inside and outside of the body. (Sensory Neurons) –Intergration: Processes and interprets sensory input and makes decision. –Motor output: Responds by muscles or glands. (Motor Neurons)

Organization of the Nervous System 1. Central Nervous System (CNS): –Brain and spinal cord –Command center –Interprets incoming sensory information –Make decisions based on past experiences

Organization of the Nervous System 2. Peripheral Nervous System (PNS): –Nerves that extend from the brain and spinal cord. 1. Sensory (Afferent) Division: Deliver impulses to the CNS from various parts of the body. 2. Motor (Efferent) Division: Carries impulses from the CNS to muscles and glands.

Neuron Dendrites: Increase the surface area for receiving incoming information. Axon: Carries information from the cell body to a neighboring neuron. Myelin Sheath: Insulating fat cells that increase the rate of signal transmissions. Node of Ranvier: Bare axon; allows action potential to jump from node to node. Axon Terminals: Release chemicals called neurotransmitters.

Supporting Cells: CNS 6 Cell Types Total: 4 CNS; 2 PNS Microglia: Destroy invading microorganisms that could be harmful to the CNS. A type of macrophage. Astrocytes: Most abundant; Anchors the neurons in place by attaching to capillaries. Also serve as a nutrient (blood supply) to neurons. Ependymal Cell: Line the brain & spinal cord cavities (dorsal). Have cilia that help to circulate the cerebro-spinal fluid. Oligodendrocytes: Wrap around axons of neurons to form myelin sheaths.

Supporting Cells: PNS Schwann Cells: Help form myelin sheath; also engulf deteriorating cell debris & aid in regeneration. Satellite Cells: Surround the cell bodies and regulate chemical environment.

Resting Potential A neuron sends messages electrochemically. Ions are Na & K (positive) A neuron is at rest when it is not sending a signal and is in a negatively charged state. Even at rest, the neuron allows K to pass. Neuron pumps 3 Na ions out for every 2 K ions it pumps in. At rest, there are more Na ions outside and more K ions inside Resting & Action Potential

Action Potential Occurs when a neuron sends information down the axon. Electrical activity created by a depolarizing current. A stimulus must make the neuron reach its threshold in order to fire an action potential. Stimulus causes Na channels to open and Na+ rushes into the neuron, depolarizing it. K rushes out of the cell, reversing the depolarization.

Autonomic Nervous System Part of the PNS. Has 2 divisions: Sympathetic & Parasympathetic Controls heart rate, digestion, respiration rate, salivation, & perspiration.

Sympathetic Neurons begin in the Thoracic & Lumbar region of the spinal cord Functions in actions that require a quick response. “Fight or Flight” response.

Parasympathetic Neurons begin in the cervical & sacral regions of the spinal cord. Functions in actions that do not require an immediate response. “Rest & Digest” Constant opposition to Sympathetic N.S. Sympathetic & Parasympathetic Clip Sympathetic & Parasympathetic Clip

Reflexes Involuntary, rapid actions; usually for survival. Most reflexes don’t have to travel to the brain, as they need to happen quickly. –Reflex Arc: 1.Receptors are excited. 2.Signal travels along sensory neuron to spinal cord 3.Signal is passed onto a motor neuron 4.Muscle/Gland is stimulated.