The Nervous System Chapter 11
Functions of the Nervous system I Sensory (input): Light Sound Touch Temperature Taste Smell Internal Chemical Pressure Stretch External Chemical
Functions of the Nervous system II Integration: Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope). Motor (output): The response to the sesnsory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.
The Basic Scheme
Organization of the Nervous system
The CNS compared with the PNS
Support Cells of the Nervous system the Central Nervous System Astrocytes Microglia Oligodendrocytes Ependymal Cells the Peripheral Nervous System Schwann Cells (a.k.a. Neurolemmocytes) Satellite Cells
Astrocytes & microglia Astrocytes & microglial cells protect the neurons of the CNS.
Astrocytes & microglia Functions of astrocytes: 1.Connect neurons to capillaries. This makes up the “blood-brain barrier”. 2.Maintain the the electrochemical environment Capture and recycle neurotransmitters Absorb and return K + and other ions. Connected to one another and capable of communicating via gap junctions. Function of microglial cells: 1.Dendritic macrophages that phagocytize microbes and necrotic (dead) tissue.
Ependymal Cells & oligodendrocytes
Functions: Ependymal Cells - Line the ventricles of the brain an central cnal of the spinal cord. They aid in the circulation of cerebrospinal fluid (CSF). Oligodendrocytes - These cells have processes that wrap around the axons of neurons. This creates an insulation coating called a myelin sheath.
Schwann Cells & satellite cells These are the suport cells in the peripheral nervous system. Schwann cells provide the myelin sheath for peripheral axons. Satellite cells serve a slightly similar function to astrocytes, supporting the cell bodies of peripheral neurons.
Neurons - the “action cells”
Characteristics of neurons Long-lived Generally last a life time with 90% are formed by the time you are 6 years old. The rest are produced when as you go through puberty. Amitotic Until recently it was thought that neurons didn’t regenerate at all! Some may but generally what you have at adulthood is all you get. High metabolic rate This means high oxygen demand and lots of mitochondria. Neurons also require glucose.
Myelin Myelin is a lipid- rich component of the cell membranes of Schwann cells and oligodendrocytes. It acts kind of like the insulation on an electrical wire.
The cycle of an Action Potential
Anatomy of an Action Potential
A Basic Neural Circuit
Type of neurons
Three structural classes of neurons Multipolar Most numerous Many dendrites Motor and association neurons Unipolar Second most numerous Rounded body with one process Somatic & general sensory neurons Bipolar Least common, found in special sensory organs
Comparison of neuron types
Functional categories of neurons