SBI4U The Nervous System Central Nervous System (CNS): consists of the brain and spinal cord Acts as the coordinating centre for incoming and outgoing information Peripheral Nervous System (PNS): consists of the nerves that carry information between the organs of the body and the CNS. The PNS can be divided further: Somatic: controls the skeletal muscle, bones, and skin Autonomic: controls the internal organs of the body
Anatomy of a Nerve Cell Two different types of cells are found in the nervous system Glial cells (neuroglial cells): nonconducting cells important for structural support and metabolism of the nerve cells Important for structural support and metabolism of nerve cells Glia means glue in Greek Schwann cells are types of glial cells The blood brain barrier is made up of glia Neurons: nerve cells that conduct nerve impulses Functional units of the nervous system Sensory neurons (afferent neurons) Interneurons Motor neurons (efferent neurons)
Structure of the Neuron
Nerve Impulses Jump from one node to another Move faster along myelinated nerve fibers than nonmyelinated ones Smaller the diameter the faster the speed of the impulse
All neurons contain dendrites, cell bodies, and axons Dendrites: projections of cytoplasm that carry impulses toward the cell Receive information from sensory neurons Conduct nerve impulses toward the cell body Axon: extension of cytoplasm that carries nerve impulses away from the cell body Carries the nerve pulse impulse toward other neurons or to effectors Myelin sheath: insulated covering over the axon of a nerve cell White coat of a fatty protein Schwann 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 Neurilemma: delicate thin membrane that surrounds the axon of nerve fibers found within the PNS Made of Schwann cells Promotes the regeneration of damaged axons Nerves in the CNS do not have neurilemma, but they can still be myelinated
Sensory Neurons Sensory neurons (afferent neurons) carry impulses from sensory receptors to the CNS. Ganglia: clusters of sensory neurons located outside of the spinal cord
Receptive Field: Each sensory neuron has a specific sensory field where that one neuron will receive stimuli from. These receptive fields have the ability to overlap. These receptive fields are larger in our back and forearms, and much smaller in our lips, and finger pads.
Interneurons These neurons lie completely within the CNS. They process the incoming signals by the sensory neurons and signal the appropriate outgoing motor neurons. Link neurons within the body
Motor Neurons Motor neurons (efferent neurons) receive information from interneurons. These neurons carry impulses from the CNS to effectors. Muscles, organs, and glands are classified as effectors because they produce responses.
Neurons Travel in Bundles Neurons travel throughout our body in bundles referred to as nerves.
Reflexes Reflexes are specific, predictable, involuntary responses to types of stimulation Neuronal Circuits When we feel pain, we don't stop to think about how much that pain hurts. For example if we touch a hot stove, we pull our hand away quickly without thinking about it. Reflex arc: neural circuit through the spinal cord that provides a framework for a reflex action (no direct input from the brain) The reflex arc begins when a receptor picks up a painful stimulus. Sensory information is sent to the spinal cord, and interneurons relay this information directly to the motor neuron. The motor neuron activates the muscle, causing it to contract. This allows our bodies to react as quick as possible.