Nervous System

Nervous System

• The entire nervous system is composed of nerves.

Nerves

While variable in size and shape, all neurons have three parts.

- Dendrites receive information from another cell and transmit the message to the cell body.

- The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells.

- The axon conducts messages away from the cell body.

How do nerves work?• Neurons send messages electrochemically. This means that chemicals

cause an electrical signal.

• Neurons must reach the threshold before a full action potential is fired. This is an “all or none” principal. (The neuron either responds or it doesn’t).

How do nerves work?

• For communication between neurons to occur, an electrical impulse must travel down an axon to the synaptic terminal.

• Communication of information between neurons is accomplished by movement of chemicals across a small gap called the synapse. Chemicals, called neurotransmitters, are released from one neuron at the presynaptic nerve terminal. Neurotransmitters then cross the synapse where they may be accepted by the next neuron at a specialized site called a receptor.

Nervous System

Two major Systems

- Central Nervous(brain and spinal cord)

- Peripheral Nervous(all else not included in CNS, mainly nerves)

Central Nervous System (CNS)

• Brain– composed of five parts:

• cerebrum • cerebellum• brain stem • pituitary gland• hypothalamus

• Spinal Cord– The spinal cord runs along the dorsal side of the

body and links the brain to the rest of the body. Vertebrates have their spinal cords encased in a series of (usually) bony vertebrae that comprise the vertebral column.

Cerebrum

• The cerebrum makes up 85% of the brain's weight.

• The cerebrum is the thinking part of the brain and it controls your voluntary muscles.

Cerebellum

• Controls balance, movement, and coordination (how your muscles work together)

Brain stem

• In charge of all the functions your body needs to stay alive, like breathing air, digesting food, and circulating blood.

• Also, control your involuntary muscles (work automatically) such as the heart and stomach.

Pituitary gland

• Produce and release hormones into your body.

• Regulates metabolism - breathing, digesting food, and moving your blood around.

Hypothalamus

• Regulates body temperature.

(about 98.6° Fahrenheit or 37° Celsius).

Spinal Cord

• The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.

• The human spinal cord is protected by the bony spinal column shown to the left. The spinal column is made up of bones called vertebrae. Although the spinal column is somewhat flexible, some of the vertebrae in the lower parts of the spinal column become fused.

Peripheral Nervous System (stuff outside of the brain and spinal cord)• Somatic NS

– You control most of this.

• Autonomic NS– Controls organs

Somatic NS

• Responsible for coordinating the body movements, and also for receiving external stimuli.

• Regulates activities that are under conscious control.

Autonomic Nervous System

• Sympathetic (Fight or flight)

• Parasympathetic (Rest and digest)

Sympathetic Nervous System

It is a nice, sunny day...you are taking a nice walk in the park. Suddenly, an angry bear appears in your path. Do you stay and fight OR do you turn and run away? These are "Fight or Flight" responses. In these types of situations, your sympathetic nervous system is called into action - it uses energy - your blood pressure increases, your heart beats faster, and digestion slows down.

ParasympatheticIt is a nice, sunny day...you are taking a nice walk in the park. This time, however, you decide to relax in comfortable chair that you have brought along. This calls for "Rest and Digest" responses. Now is the time for the parasympathetic nervous to work to save energy - your blood pressure decreases, your heart beats slower, and digestion can start.

The Autonomic Nervous System

Structure Sympathetic Stimulation Parasympathetic Stimulation

Iris (eye muscle) Pupil dilation Pupil constriction

Salivary Glands Saliva production reduced Saliva production increased

Oral/Nasal Mucosa

Mucus production reduced Mucus production increased

HeartHeart rate and force increased

Heart rate and force decreased

Lung Bronchial muscle relaxed Bronchial muscle contracted

Stomach Peristalsis reducedGastric juice secreted; motility increased

Small Intestine Motility reduced Digestion increased

Large Intestine Motility reduced Secretions and motility increased

LiverIncreased conversion ofglycogen to glucose

Kidney Decreased urine secretion Increased urine secretion

Adrenal medullaNorepinephrine andepinephrine secreted

BladderWall relaxedSphincter closed

Wall contractedSphincter relaxed

Jamie McMullen can’t read thiss!

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• Weird, isn’t it?