Central Nervous System (CNS): brain and spinal cord. CNS contains tracts Peripheral Nervous System (PNS): nerves of the body PNS contains nerves                      -- Includes 31 pairs of spinal nerves                    -- And  12 pairs of cranial nerves

Basic Divisions of the Nervous System Figure 12.2

THREE BASIC FUNCTIONS OF THE NERVOUS SYSTEM Sensory -  gathers info Integrative - information is brought together Motor - responds to signals, homeostasis

Peripheral Nervous System Afferent  -  transmits action potentials from sensory organs to the CNS Efferent - transmits action potentials from the CNS to effector organs such as muscles - glands

Peripheral Nervous System Efferent divided further SOMATIC NERVOUS SYSTEM  -  skeletal muscles, under voluntary control AUTONOMIC NERVOUS SYSTEM - smooth muscles, glands, involuntary

Peripheral Nervous System Autonomic divided further Sympathetic – Fight or Flight Parasympathetic – Rest and Digest

Common Neurotransmitters Epinephrine/Adrenaline NorEpinephrine/Noradrenaline Acetylcholine

Neurons

Factors Affecting Nerve Impulse Velocity Diameter of the neuron Temperature Myelinated or Unmyelinated

Neuroglial Cells - support cells for the neurons   1.  Microglial : scattered throughout, digest debris or bacteria 2.  Oligodendrocytes:  provide insulation around the axons 3. Astrocytes:  connect blood vessels to neurons 4.  Ependymal Cells:  form a membrane that covers brain-like parts

5.  Schwann cells:  form the insulating sheath around the neurons within the PERIPHERAL nervous system Neurilemma = thin, membranous covering over Schwann cells that allows cells to slowly repair/regenerate themselves if injured *Myelin Sheaths - necessary for insulation of neurons

Supporting Cells in the CNS Microglial cells respond to immunological alarms

Supporting Cells in the CNS Creates the myelin sheath that insulates axons

Supporting Cells in the CNS Astrocytes connect neurons to blood vessels

Supporting Cells in the CNS Figure 12.12a

Supporting Cells in the CNS

Supporting Cells in the CNS

Supporting Cells

Neuron Structure Neurofibril -  fibers Chromatophilic substance (rough ER) - transport system Myelin -insulation surrounding axons Nodes of Ranvier - gaps in the insulation

White vs Grey Matter Myelinated (white matter) – myelinated axons Unmyelinated (grey matter) - unmyelinated

Label

NEURON (main cell of the nervous system) All neurons do three things: Receive a signal. Can be any type of stimulus (change in environment, signal from another neuron, etc). Transmit a signal to another location. E.g. finger touching something • signal to spinal cord or brain. Stimulate another cell Another neuron • transmit signal Muscle • contraction Gland • secretion

Other special characteristics The Neuron Other special characteristics Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose

Types of Neurons Functional: Sensory, Motor, Interneurons Structural: (A) Bipolar (B) Unipolar (C) Multipolar

Nerve Impulses

Nerve Impulses At rest, the inside of a neuron's membrane has a negative charge. As the figure shows, a Na+ / K+ pump in the cell membrane pumps sodium out of the cell and potassium into it. However, because the cell membrane is a bit leakier to potassium than it is to sodium, more potassium ions leak out of the cell. As a result, the inside of the membrane builds up a net negative charge relative to the outside.

Animations of Nerve Impulses http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html http://outreach.mcb.harvard.edu/animations/actionpotential.swf

The Synapse Synapse - junction between two communicating neurons Nerve pathway - nerve impulse travels from neuron to neuron Synaptic Transmission Dendrite ' cell body ' along axon ' synapse (gap) To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the next neuron

Structure of a Synapses Figure 12.8a, b

Neurotransmitters Excitatory - increase membrane permeability, increases chance for threshold to be achieved Inhibitory - decrease membrane permeability, decrease chance for threshold to be achieved

Types of Neurotransmitters Acetylcholine - stimulates muscle contraction Monoamines - Norepinephrine & Dopamine (sense of feeling good, low levels = depression) Serotonin (sleepiness) Endorphins (reduce pain, inhibit receptors)

Drugs that Affect Synapses and Neurotransmitters Curare Strychnine Cocaine, morphine, alcohol, ether and chloroform Mescaline and LSD Ecstasy

Antidepressants Zoloft is part of a class of drugs called selective serotonin reuptake inhibitors, or  SSRIs for short. SSRIs act on a specific chemical within the brain known as serotonin. This is one of several chemicals used to send messages from one nerve cell to another.

Impulse Processing Neuronal pool - groups of neurons that make hundreds of synaptic connections and work together to perform a common function

Types of Nerves Dorsal Root/Sensory Nerves - conduct impulses into the brain or spinal cord Ventral Root/Motor Nerves - carry impulses to muscles of glands Mixed Nerves - contain both sensory and motor nerves

Problem If Mary has a spinal cord injury to just her ventral portion of the spinal cord what would happen to her? HINT** Will she lose feeling, movement or both?

Neurons Classified by Function: Sensory vs. Motor Neurons Figure 12.11

Nerve Pathways Reflex arc - only includes a few neurons Reflex Behavior - automatic, subconscious responses Knee-jerk reflex - maintains uprightedness Withdrawal reflex - avoidance of painful stimuli