The Nervous System

I. The Nervous System • A. The Nervous system controls & coordinates

functions throughout the body and responds to internal & external stimuli.

Choreographing a dance, Writing a song, Practicing lines in a play….have one thing in common.

II. Neurons • A. Messages that are carried by the

nervous system are called impulses and travel along neurons.

• B. Neurons can either be a sensory, motor or interneurons; but all have the same structures including:– 1. Cell Body – contains nucleus, most

of cytoplasm & most metabolic activity takes place here.

– 2. Dendrites – branched extensions, receive signals

– 3. Axon – carries impulses across neuron to another (covered by myelin)

III. Nerve Impulse• A. An impulse begins when a neuron is stimulated

by another neuron or by the environment. • B. The flow of an impulse is similar to an electrical

current through a wire as charged ions move along ion pumps across the neuron membrane changing the energy potential.

IV. The Synapse

• A. The synapse is where one neuron transmits the impulse to another neuron. (synaptic terminal)– Ex. Motor neuron pass impulse to

muscle cell

• B. The synaptic cleft is the space between neurons where neurotransmitters (chemicals used by neurons) to transmit an impulse.

V. Ion Pumps & Membrane Potential• A. All neurons have a membrane potential. A

difference between the inside of the cell (negative) and extracellular fluid (positive). – 1. Polarized state resting potential (-70mV)

• B. Sodium-Potassium pump maintains the polarization by pumping ions that leak across the membrane– 1. In order for the nerve to fire a stimulus it must be

strong enough to overcome the resting potential (threshold)

V. Ion Pumps & Membrane Potential

• C. Neurons have gated-ion channels that open/close in response to a stimulus. – 1. Only allowing one kind of ion to flow through

• D. If a stimulus triggers a sodium-ion gated channel to open sodium flows into the cytoplasm resulting in a decrease in polarization, becoming somewhat depolarized (making it easier for the nerve to fire). The opposite occurs if potassium-ion channel is stimulated and membrane is hyperpolarized.

V. Ion Pumps & Membrane Potential

• E. An action potential, impulse, can only be generated in an axon of a neuron. – 1. When this occurs and the axon is stimulated the

sodium channels open and sodium ions flood in the cell, potassium channels open and flood potassium out as a response causing a wave of depolarization reversing the action potential which only lasts a short time.

• F. The sodium-potassium pump restores the membrane to the original polarized condition (repolarization) or refractory period

VI. Division of the Nervous System• A. The human nervous system can be divided into 2

parts:– 1. Central nervous system – relays messages, processes

& analyzes information– 2. Peripheral nervous system – transmits impulses from

sense organs to central nervous system & vice-versa

VII. Central Nervous System

• A. Central nervous system includes the brain & spinal cord.– 1. These are surrounded by meninges & cerebrospinal

fluid to not only act as a shock absorber but also allows exchange of nutrients and waste products

VII. Central Nervous System• B. The Brain (consists of over 100 bill neurons):– 1. Cerebrum – largest most prominent region of brain• a. Responsible for voluntary activities, site for

intelligence/learning & judgment• b. Divided into regions called lobes based off the skull bones

that surround the lobe (frontal, temporal, parietal, & occipital)

– 2. Cerebellum – second largest region of brain, located at the back of the skull. • a. coordinates & balances actions of the muscles

– 3. Brain stem – located below cerebellum connecting brain to spinal cord consists of the pons & medulla oblongata• a. control blood pressure, heart rate, breathing & swallowing

– 4. Thalamus – found between brain stem & cerebrum, • a. receives messages from sensory

receptors & relays message to cerebrum

– 5. Hypothalamus – control/analyze hunger, thirst, fatigue, anger & body temp. works with endocrine as well.

– 6. Spinal Cord – communication between brain & rest of body (31 pairs of nerve branches). Processes reflexes directly.

IIX. Peripheral Nervous System • A. Peripheral nervous system consist of all the

nerves, ganglia & associated cells that are not part of the brain & spinal cord.

• B. The peripheral is divided further into 2 systems:– 1. Somatic nervous system– 2. Autonomic nervous system

– 1. Somatic nervous system – regulates activities that are under conscious control• a. allow quick reflex movement due to reflex arcs; inborn,

automatic & protective. Only goes to spinal cord

– 2. Autonomic nervous system – regulates activities that are automatic, or involuntary movement• a. Divided into 2 parts farther

that oppose one another actions sympathetic & parasympathetic– Ex. Sympathetic speed up

heart rate during a run while the parasympathetic will decrease the heart rate when you finish