NERVOUS SYSTEMNERVOUS SYSTEM

Three Basic Functions Performed by Three Basic Functions Performed by Nervous Systems:Nervous Systems:

1. Receive sensory input from internal and external environments :pressure, taste, sound, light, blood pH, or hormone levels, that are converted to a signal and sent to the brain or spinal cord.

2. Integrate the input: input (feels hot) is integrated and a response (hormones, enzymes) is generated

3. Respond to stimuli: Response (pull hand away)

Nervous SystemNervous System• WHAT IS IT?• Vast network of cells specialized to carry information

(in the form of nerve impulses) to and from all parts of the body in order to bring about bodily activity.

• HOW DOES IT WORK?• Brain and spinal cord together form the central central

nervous system; nervous system; • the remaining nervous tissue is known as the

peripheral nervous systemperipheral nervous system and includes the autonomic nervous system, which is itself divided into the sympatheticsympathetic and parasympathetic nervous systems. The basic functional unit of the nervous system is the neuron (nerve cell).

2 Divisions of the Nervous 2 Divisions of the Nervous SystemSystem

• 1. CNS (Central Nervous System): consists of the spinal cord and brain– Responsible for integrating, processing, and

coordinating sensory data and motor commands.

• Ex) When you stumble, the CNS integrates information regarding balance and limb position and then coordinates your recovery by sending motor commands to appropriate skeletal muscles- all in a split second!!

2 Divisions of the Nervous 2 Divisions of the Nervous SystemSystem

• 2. PNS (Peripheral Nervous System): includes all neural tissue outside the CNS– Delivers sensory information to the CNS & carries

motor commands to peripheral tissues

2 Main Components of the PNS:2 Main Components of the PNS:

1. sensory pathways that provide input from the body into the CNS.

2. motor pathways that carry signals to muscles and glands (effectors).

• Most sensory input carried in the PNS remains below the level of conscious awareness. Input that does reach the conscious level contributes to perception of our external environment.

2 Divisions of Motor Commands2 Divisions of Motor Commands

1. Somatic Nervous System (SNS): includes all nerves controlling the muscular system and external sensory receptors. External sense organs (including skin) are receptors. Muscle fibers and gland cells are effectors.

2. Autonomic Nervous System: consists of motor neurons that control internal organs (heart, the smooth muscle in internal organs such as the intestine, bladder, and uterus)

1. The Sympathetic Nervous System is involved in the fight or flight response.

2. The Parasympathetic Nervous System is involved in relaxation.

The ANS is Most Important in The ANS is Most Important in Two Situations:Two Situations:

1. SYMPATHETIC: In emergencies that cause stress and require us to"fight" or take "flight" (run away)                       

and

2. PARASYMPATHETIC: In nonemergencies that allow us to "rest" and "digest"           .

Sympathetic Nervous System & Sympathetic Nervous System &

Parasympathetic Nervous SystemParasympathetic Nervous System

• Each of these subsystems operates in the reverse of the other (antagonistic effects).

• Both systems innervate the same organs and act in opposition to maintain homeostasis.

• For example: when you are scared the sympathetic system causes your heart to beat faster; the parasympathetic system reverses this effect.

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 medulla

Norepinephrine andepinephrine secreted

BladderWall relaxedSphincter closed

Wall contractedSphincter relaxed

Draw a Flow Diagram of the Nervous Draw a Flow Diagram of the Nervous SystemSystem

Central Nervous System

Sensory System

Nervous System

Peripheral Nervous System

Motor System

Somatic Nervous System

Autonomic Nervous System

SympatheticParasympathetic

Spinal cord

Brain

NEURONSNEURONS

• Cells of the nervous system, called nerve cells or neurons, are specialized to carry "messages" through an electrochemical process. The human brain has about 100 billion neurons.

Neurons in the hippocampus

NeuronsNeurons

• Neurons can be quite large - in some neurons, such as corticospinal neurons (from motor cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the spinal cord and up to the brain stem), can be several feet long!

Neurons are Neurons are Similar Similar to Other to Other Cells in the Body Because:Cells in the Body Because:

1. Neurons are surrounded by a cell membrane.

2. Neurons have a nucleus that contains genes.

3. Neurons contain cytoplasm (Perkaryon), mitochondria and other "organelles".

4. Neurons carry out basic cellular processes such as protein synthesis and energy production.

Neurons Neurons Differ Differ from Other Cells from Other Cells in the Body Because:in the Body Because:

• Neurons have specialized extensions called dendrites and axons. – Dendrites bring information to the cell body and

axons take information away from the cell body.

• Neurons communicate with each other through an electrochemical process.

• Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters).

NeuronsNeurons

• Neurons send messages electrochemically.

• This means that chemicals cause an electrical signal

• When a neuron is not sending a signal, it is "at rest."

• When a neuron is at rest, the inside of the neuron is negative relative to the outside.

Neuron at Rest:Neuron at Rest:

• Potassium ions (K+) can cross through the membrane easily.

• Chloride ions (Cl-)and sodium ions (Na+) have a more difficult time crossing.

• The negatively charged protein molecules (A-) inside the neuron cannot cross the membrane.

Na/K PumpsNa/K Pumps

• In addition to these selective ion channels, there is a pump that uses energy to move three sodium ions out of the neuron for every two potassium ions it puts in.

Resting PotentialResting Potential• Finally, when all these forces balance out, and

the difference in the voltage between the inside and outside of the neuron is measured, you have the resting potential.

• The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside.

• At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.

Action PotentialAction Potential

• An action potential occurs when a neuron sends information down an axon, away from the cell body.

• The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event (a stimulus) causes the resting potential to move toward 0 mV.

Action PotentialAction Potential

• For any given neuron, the size of the action potential is always the same.

• There are no big or small action potentials in one nerve cell - all action potentials are the same size.

• Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.

Action PotentialAction Potential• Action potentials are caused by an exchange

of ions across the neuron membrane.

1. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron.

2.Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized. It takes longer for potassium channels to open.

Action PotentialAction Potential3. When they do open, potassium rushes out of

the cell, reversing the depolarization. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization).

4. The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long.

5. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.

Transmission of an Impulse Transmission of an Impulse Across a SynapseAcross a Synapse

• This may be electrical or chemical:

– Electrical= the action potential travels along the membranes of a gap junction

– Chemical= action potential are transferred across the synapse by the diffusion of chemicals

CHEMICAL SYNAPSESCHEMICAL SYNAPSES

• Synapse= the location where one neuron communicates with another neuron; a narrow gap between a synaptic terminal of an axon and a signal receiving portion of a dendrite

Transmitting a SignalTransmitting a Signal

• Information from one neuron flows to another neuron across a synapse. The synapse is a small gap separating neurons. The synapse consists of:

1. a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles,2. a postsynaptic ending that contains receptor sites for neurotransmitters 3. a synaptic cleft or space between the presynaptic and postsynaptic endings.

NeurotransmittersNeurotransmitters• 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. Receptor

NeurotransmittersNeurotransmitters

• Neurotransmitters then cross the synapse where they may be accepted by the next neuron at a specialized site called a receptor.

• When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."

Common NeurotransmittersCommon Neurotransmitters

• Acetylcholine (Ach) is commonly secreted at neuromuscular junctions, where it stimulates muscles to contract

Synaptic vesicle fusion and Synaptic vesicle fusion and neurotransmitter release at the neurotransmitter release at the

neuromuscular junction. neuromuscular junction.

• http://www.blackwellscience.com/matthews/nmj.html

• Many psychoactive drugs and neurotoxins can change the properties of neurotransmitter release, neurotransmitter reuptake and the availability of receptor binding sites.

Controlling MessagesControlling Messages

• The brain keeps tight control of this message delivery system to avoid communication chaos.

• A single receiving neuron has thousands of receptor sites and may receive many different messages and passwords at once.

• Each neuron adds up the incoming signals and determines whether of not to pass the information along to other cells.

• Neuron communication is under intense investigation by researchers because when it goes out of balance ailments ranging from epilepsy to memory disorders can occur

THE BRAINTHE BRAIN

BRAINBRAIN FACTSFACTS

• The fastest impulses move along the nerves at rates of up to 250 m.p.h.

• Male brains are 10% larger than female brains, but this is in proportion to men's greater body size. The size of the brain does not correlate with intelligence.

• Although packed with nerve cells, the brain itself cannot detect touch, heat or even the surgeon's knife.

• Despite its relatively small size, the brain receives 20 percent of the body's oxygen and blood supply.

   

http://faculty.washington.edu/chudler/jigp3.html

FRONTAL FRONTAL LOBELOBE

• Concerned with reasoning

• Planning • Parts of speech

and movement (motor cortex)

• Emotions• Problem-solving

• Perception and recognition of auditory stimuli (hearing)

• and memory (hippocampus).

TEMPORAL LOBE

OCCIPITAL OCCIPITAL LOBELOBE

• Touch• Pressure• Temperature • Pain

• Vision

PARIENTAL LOBE

Cerebral Cerebral Cortex Cortex

• Functions:– Thought – Voluntary

movement – Language – Reasoning – Perception

• Is a sheet of tissue that makes up the outer layer of the brain = gray matter

• The thickness of the cerebral cortex varies from 2 to 6 mm.

• Note that the cerebral cortex is highly wrinkled.

• This makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it

Cerebellum Cerebellum

• Two peach-size mounds of folded tissue at the base of the brain form the cerebellum. Damage to this area leads to motor or movement difficulties.

• Controls coordinated movement and possibly even some forms of cognitive learning. 

• Functions:

– Movement – Balance – Posture

Corpus CallosumCorpus Callosum

• A flat, sheet-like nerve tract connecting the right and left cerebral hemispheres.

• Made up of mostly axons. So this is considered part of the white matter of the brain. Because:– The Myelinated Sheaths protecting the axons

Corpus Callosum

BrainBrain stemstem

• Is a general term for the area of the brain between the thalamus and spinal cord.

• Functions:

– Heart Rate – Blood

Pressure

– Breathing

Brain Stem

HypothalamusHypothalamus

• It is only the size of a pea

• Regulates the pituitary gland.

– Functions:

– Emotions – Hunger – Thirst – Circadian Rhythms– Body Temperature

Hypothalamus

ThalamusThalamus

• Receives sensory information and relays this information to the cerebral cortex.

• The cerebral cortex also sends information to the thalamus which then transmits this information to other areas of the brain and spinal cord.

• Functions:

– Sensory Integration

– Motor Integration

PonsPons

• Functions as a relay station between the sensory and motor pathways

Pons