Nervous System

Nervous System Design 2 main section Central Nervous System Peripheral Nervous System

Central Nervous System (CNS) brain and spinal cord. encased in skull and vertebral column to protect them

Peripheral Nervous System (PNS) All of the nerves going to and from the central nervous system

Peripheral Nervous System (PNS) Sensory fibers info from the body to the central nervous system  General senses spread around the body  Special senses  special sensory organs.

motor fibers deliver information from the central nervous system to the body. somatic nervous system skeletal muscles motor neurons .

Autonomic Nervous System smooth muscle, cardiac muscle, and glands Autonomic Nervous System smooth muscle, cardiac muscle, and glands. Homeostasis sympathetic (alert, fight of flight) and parasympathetic (relaxed, rest and digest) nervous systems balance with each other

Neuron Neurons -the cells which can send electrical impulses Most of the neurons are found in the central nervous system.

Neuron Cell Body- contains the nucleus and most of the cell's organelles

Neuron The neuron lacks one organelle which other body cells have, the centriole.  The centriole allows the cell to reproduce.  As a result, neurons are unable to multiply to replace any neurons that are lost or damaged.

Neuron nerve fibers transmit electrical impulses. 2 types dendrites and axons.

Neuron Axon impulses away from the cell body. Message to the body for action only one axon associated with each neuron.  end of the axon may be split Each end enlarged terminal bulb. Terminal bulb releases neurotransmitters- chemicals that tell the other cell what to do.

Neuron Dendrites impulses towards the cell body of the neuron. Many per neuron Info sent from nerve receptors.  

Neurons 3 basic types Number of dentrites varies

Multipolar neurons- single axon and many dendrites Multipolar neurons- single axon and many dendrites. Most common type of neuron in the CNS.

Bipolar neurons have one axon and one dendrite, Generally opposite sides.  typically found in the special sense organs (e.g. the eye, ear, and nose).

Unipolar neurons have a single fiber which exits the cell body then splits into two parts.  One part serves as the axon while the other part serves as the dendrite.  The central stalk is used for impulses going in either direction (to or from the cell body).

Neuroglia Neuroglia support cells of the nervous system.

Microglia small, phagocytic . brain's microbial defense mechanism. consume bacteria and viruses that enter the brain tissue clean up damaged tissue too.    

Astrocytes blood/brain barrier. Materials moving from the blood to the neurons must first pass through the astrocyte.  Toxic material will not be passed to neurons Will die to protect neuron if need be

Ependymal cells form cerebrospinal fluid (fluid is shock absorber) fluid is formed within chambers in the interior of the brain tissue. 

Ependymal cells flows through several tunnels until it reaches the outside of the brain and spinal cord tissues.  Continuously made and reabsorbed

Schwann cells and the Oligodendroglia. form the myelin sheath around some of the nerve fibers (axons or dendrites). 

insulating wrapper that covers large areas of a nerve fiber. Myelin Sheath insulating wrapper that covers large areas of a nerve fiber.  wrap in a jelly-roll fashion around the nerve fiber.  Many line up end to end down a neuron fiber

Oligodendroglia form myelin in the CNS Schwann cell form myelin in the PNS myelinated fiber has myeline unmyelinated fiber no myeline

Nodes of Ranvier. small spaces between the cells

Myelinated fibers send impulses more rapidly

At birth, the myelin sheath is just beginning to form At birth, the myelin sheath is just beginning to form.  By age two, most of the myelin sheath is in place

Multiple Sclerosis (MS), the myelin sheath is slowly deteriorating. Devastating effect on body function Possibly autoimmune 

Sending an Electrical Signal Neuron At Rest Unequal ions on sides of membrane at rest Excessive sodium (Na) ions (+) outside of the nerve fiber Few Na+ inside membrane is not permeable to Na+.  Also excessive proteins on inside of membrane Membrane is very negative on inside Sending an Electrical Signal See hand out 

Types of Impulse Transmission Impulse can go towards nerve body or away dendrite or axon

Types of Impulse Transmission Continuous Conduction occurs in unmyelinated fibers. very slow because each segment of the nerve fiber must be depolarized.  Long fibers (like 3 ft) takes as long as ½ a second  

Types of Impulse Transmission  Saltatory Conduction Myelinated fiber transmission. extremely rapid about 1/60 the time for the same length of unmyelinated fiber

Types of Impulse Transmission  Saltatory Conduction only the exposed fiber at the nodes of Ranvier needs to be depolarized.  Signal skips from node to node. 

Synapse Synapse- a junction between a neuron and another cell. Cell could be another neuron or a body cell.  neuron does not actually come in contact with the other cell. 

Synapse Synaptic Gap or Cleft- between the two cells. Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Synaptic Gap or Cleft- between the two cells.  neurotransmitters- chemical messengers between the gaps released by the terminal bulb of the neuron bind to receptors located on the membrane of the other cell

Neurotransmitters Acetylcholine PNS / some CNS Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Vesicle fuses with plasma membrane Ion channels Transmitting neuron Acetylcholine  PNS / some CNS Used to stimulate skeletal muscles and visceral smooth muscle

Neurotransmitters Acetylcholine Inhibits cardiac muscle and multiunit smooth muscle Stimulates secretions from most glands and stimulates impulse transmission in other neurons.

Neurotransmitters Norepinephrine PNS / some CNS stimulates contraction of cardiac and multiunit smooth muscle

Neurotransmitters Norepinephrine Inhibits contraction of visceral smooth muscle.  No effect on skeletal muscle.  Inhibits secretion by most glands and inhibits impulse transmission in other neurons.

Neurotransmitters Dopamine and GABA (gamma amino butyric acid) CNS inhibit impulses to neurons controlling certain muscle movements.  

Neurotransmitters Endorphins and Enkephalins CNS block, or inhibit, transmission of pain impulses.  Hundreds of times more powerful than morphine

Neural Networks Neural networks - formed when several neurons link together to form a pathway.  critical to the functioning of the body.  different types of neural networks. examples: divergent circuit, a single neuron sends impulses to several other neurons.  This allows information to be disseminated to many areas simultaneously to allow a coordination of activities. convergent circuit, several neurons send information to a single neuron.  This type of circuit will allow information from a number of sources to be processed in one central location. reverberating circuit cycles the impulse back through the neural network.  This continues to restimulate the neurons near the beginning of the neural network and keeps the information cycling through the network.  This type of circuit is involved in short-term memory.