CENTRAL NERVOUS SYSTEM

http://www.youtube.com/watch?v=GTv2mRH1Wac&feature=related

CNS

• The study of functions reveals that the body consists of millions of small structures that perform a multitude of different activities that are coordinated and integrated in one harmonious whole.

Divisions of the Nervous System

• The nervous system can be divided into three divisions:– Central nervous system (brain and spinal

cord)– Peripheral nervous system (12 pair cranial

nerves extending out from brain and 31 pairs of spinal nerves from the spinal cord)

– Autonomic nervous system (peripheral nerves and ganglia)

Central and Peripheral Nervous Systems

• Where decision is called for and action must be taken, the central and peripheral nervous systems are involved.

• They carry information to the brain where it is interpreted, organized, and stored. An appropriate message is sent to organs or muscles.

http://www.youtube.com/watch?v=xRkPNwqm0mM&feature=related

Autonomic Nervous System

• This is part of the peripheral nervous system because it involves the peripheral nerves as well as ganglia, which are a group of cell bodies outside the central nervous system that carry impulses to involuntary muscles and glands.

• Supplies the heart muscle, smooth muscle, and secretory glands with nervous impulses as needed.

• It is usually involuntary. http://www.nda.ox.ac.uk/wfsa/html/u05/u05_010.htm

http://faculty.washington.edu/chudler/auto.html

Autonomic Nervous System

Central Nervous System

• Brain and Spinal Cord

Function of CNS

• It is the communication and coordination system in the body– It receives messages from stimuli all over the

body– The brain interprets the message– The brain responds to the message and

carries out an activity

• The brain is also the seat of intellect and reasoning

CNS

• Most highly organized system of the body

http://anatomy.med.umich.edu/modules/spinal_cord_module/spinalcord_01.html

Neuron• Is another name for a

nerve cell• Constructed to transmit a

message from one cell to the next

• It has a nucleus, cytoplasm, and cell membrane

• From the cell body, the neuron has extensions of cytoplasm from the cell body called dendrites and axons

More on the Neuron…

• A neuron may have many dendrites, but only one axon.

• The axon has a specialized covering called the myelin sheath which speeds up nerve impulse as it travels along the axon.

• The myelin sheath produces a fatty substance called myelin that protects the axon; it is also called white matter.

• Axons carry impulses away from the body; dendrites carry messages to the cell body.

Nervous Tissue

• There are two major types of nerve cells:

• Neuroglia – Known as “nerve glue”– These cells insulate,

support, and protect the neurons

• Neurons– Have the characteristics of

irritability and excitability– Dendrites receive the

impulse and transmit it to the cell body, and then to the axon.

Three Types of Neurons

• Sensory neurons or afferent neurons– Emerge from the skin or sense organs and carry

messages toward the spinal cord and brain

• Motor neurons or efferent neurons– Carry messages from the brain and spinal cord to the

muscles and glands

• Associative neurons or interneurons– Carry sensory impulses from the sensory neuron to

the motor neuron

Function of Nerve Cell• Nerves carry impulses by

creating electric charges in a process known as membrane excitability.

• Neurons have a membrane that separates the inside cytoplasm from the fluids outside the cell which creates two chemically different environments.

• The inside cells are more negatively charged.

• When a neuron is stimulated, ions move across the membrane creating a current.

Synapse• A synapse is where messages of from one cell to the next.

• Messages go from the axon of one cell to the dendrite of another…without actually touching.

• The “space” is called the synaptic cleft and the conduction is done by neurotransmitters at the end of each axon.

Synapse

The Brain• Weighs about 3 lbs• consists of 100 billion

neurons

• The brain is white and gray matter (the outer or cerebral cortex is gray)

More Brain…

• The outer part of the cerebral cortex is the highest center of reasoning and intellect, “you need to use your gray matter.”

• The deeper part of the cerebral cortex is the white matter and has the myelinated nerve tracts.

• Without oxygen, brain damage will occur within 4 to 8 minutes

• The brain is divided into four major parts…cerebrum, diencephalon, cerebellum, and brain stem.

Protection for the Brain…• Protected by the cranium and three membranes

called meninges and cerebrospinal fluid.• There are three layers of meninges…

– Dura mater – outer covering of the brain and spinal cord– Arachnoid – middle layer– Pia mater – inner covering of the brain and spinal cord

• The ventricles – four lined cavities within the brain that contain the choroid plexus, a rich network of blood vessels that help form the cerebrospinal fluid.

• Cerebrospinal fluid – acts as a shock absorber and a source of nutrients for the bain and spianl cord.

Memory• The brain stores “old”

information we have learned and packages and stores new information…memory!

• To create a memory, it is thought that nerve cells make a new connection.

• No one area of the brain stores all memories, because the storage site depends on the type of memory…swimming would be inn the motor area, visual would be stored in the visual area.

• Can be long or short term depending on how much attention we pay to that memory, and how many times we repeat an activity.

Effects of Aging• As an individual ages, there is

a general slowing of nerve conduction due to a decrease in the number of functioning neurons and a degeneration of the existing neurons.

• Changes in the nervous system are primarily due to diminished blood supply to the brain and loss of neurons.

• Slow progressive loss in brain size in the cerebral cortex leads to impairment in thinking, reasoning, and remembering.

• There is a slowing in reaction time due to decrease in motor and sensory nerve conduction

More on Aging…

• Sleep patterns change…they easily waken, take longer to fall asleep, and wake up more frequently during the night…napping is a normal pattern as people age.

• There is evidence that continued physical and mental activity keeps minds sharp. Disrupting the ‘Normal” routine can stimulate nerve cells, enhance blood flow, and increase chemicals called nerotrophins.

Parts of the Brain

• The cerebrum is the largest and highest part of the brain.– It is divided into two hemispheres

• Each hemisphere is divided into:– Frontal– Parietal– Occipital– And temporal lobes

Cerebral Lobe

• Functions:• Frontal – motor area; controls voluntary muscles

(lt controls rt – rt controls lt) speech is on the left• Parietal – sensory area pain, touch, heat, and

cold and helps with distance, size, and shape.• Occipital – visual• Temporal – auditory and olfactory• Limbic – survival behaviors

Diencephalon

• Located between the cerebrum and midbrain