Ch. 7: The Nervous System

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Chapter Overview

THE NERVOUS SYSTEM

OVERVIEW:
The nervous system maintains body homeostasis with electrical signals; provides for sensation, higher mental functioning, and emotional response; and activates muscles and glands

What is The nervous system?

This is the master controlling and communicating system of the body. Every though, action, and emotion reflects its activity

What are the nervous system's three overlapping functions?

1. Monitor changes
2. Processes and interprets
3. Effects, or causes, a response

What is sensory input?

This is the gathered information occurring both inside and outside the body

What is stimuli?

This is another word for change

What is Integration?

To process and interpret sensory input and decide if action is needed

What is motor output?

This is a response to integrated stimuli. The response activates muscles or glands

ORGANIZATION OF THE NERVOUS SYSTEM

OVERVIEW:
List the general functions of the nervous system
Explain the structural and functional classifications of the nervous system
Define central nervous system and peripheral nervous sytem, and list the major parts of each

What are the two structural subdivisions of the nervous system?

1. The central nervous system
2. The peripheral nervous system

What is the central nervous system (CNS)?

This consists of the brain and the spinal cord which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system.

What is the peripheral nervous system (PNS)?

This is the part of the nervous system outside the CNS. These are the nerves that extend from the brain and spinal cord

Ex: Spinal nerves - carry impulses to and from the spinal cord
Ex: Cranial nerves - carry impulses to and from the brain

What are the two functional subdivisions of the nervous system?

1. The sensory (afferent) division
2. The motor (efferent) division

What is the sensory, or afferent, division?

These are nerve fibers that carry information to the central nervous system

What is the motor, or efferent, division?

These are nerve fibers that carry impulses away from the central nervous systems.

What are the two motor subdivisions?

1. The somatic nervous system
2. The autonomic nervous system

What is the somatic nervous system?

This allows us to consciously, or voluntarily, control our skeletal muscles. This is often referred to as the voluntary nervous system.

What is the autonomic nervous system?

This regulates events that are automatic, or involuntary, such as the activity of the smooth and cardiac muscles and glands. This is often referred to as the involuntary nervous system.

NERVOUS TISSUE: STRUCTURE AND FUNCTION

OVERVIEW:
State the functions of neurons and neuroglia

What are the two principal types of cells in the nervous tissue?

1. Supporting cells
2. Neurons

What are supporting cells?

These cells in the CNS are "lumped together" as neuroglia, literally, nerve glue. These generally support, insulate, and protect delicate neurons.

Name the CNS glia

Astrocytes, microglia, ependymal cells, oligodendrocytes

What are astrocytes?

These are abundant, star-shaped cells that account for nearly half of the neural tissue. These brace neurons and form barrier between capillaries and neurons. These also help control the chemical environment of the brain.

What are microglia?

These are spiderlike phagocytes that monitor the health of nearby neurons, and dispose of debris, including dead brain cells and bacteria

What are ependymal cells?

These are glial cells that line the central cavities of the brain and the spinal cord. These have cilia that helps to circulate cerebrospinal fluid that fillds cavities and protects the CNS

What are oligodendrocytes?

These produce insulating coverings called myelin sheath around nerve fibers in the central nervous system

What are myelin sheath?

These are fatty insulating coverings that is produced by oligodendrocytes wrapping its cilia around the nerve fibers

Name the PNS glia

Satellite cells, schwann cells

What are satellite cells?

These cells act as protective, cushioning cells

What are schwann cells?

These cells form the myelin sheaths around nerve fibers that are found in the PNS

NEURON ANATOMY

OVERVIEW:
Describe the general structure of a neuron, and name its important anatomical regions
Describe the composition of gray matter and white matter

Neurons

These are nerve cells that are specialized to transmit messages (nerve impulses) from one part of the body to another

What are the major regions of neurons?

All have a cell body and processes

What is the cell body of neurons?

These are nucleus and metabolic center of the cell

What is the organelle that is lacking within the cytoplasm of the neuron's cell body?

This organelle is called centrioles

What are called Nissl bodies?

These are the specialized rough endoplasmic reticulum

What are the neurofibrils?

These are intermediate filaments that are important in maintaining cell shape

What are the processes of neurons?

These are fibers that extend from the cell body. These vary in length from microscopic to 3 to 4 feet.

Ex: The longest ones in humans reach from the lumbar region of the spine to the great toe

Name to extensions outside the cell body

Dendrites and Axons

What are dentdrites?

These are neuron processes that convey incoming messages (electrical signals) toward the cell body

What are axons?

These are neuron processes that generate nerve impulses and typically conduct them away from the cell body

What is an axon hillock?

This is the conelike region of the cell body

What are axon terminals?

This is where axons end
These contain vesicles with neurotransmitters
They are also separated from the next neuron by a gap

What are neurotransmitters?

These are chemicals that is contained in the terminals' tiny vesicles

What is the synaptic cleft?

This is the gap between adjacent neurons

What is a synapse?

Theses are the functioning junctions between the nerves

What is myelin?

This is the whitish, fatty material (which has a waxy appearance) covering most long nerve fibers. This protects and insulates the fibers and increases the transmission rate of nerve impulses.

What are schwann cells?

These produce myelin sheaths in jelly-roll like fashion

What are myelin sheaths?

This is a tight coil of wrapped membranes enclosing the axon.

What are Nodes of Ranvier?

These are the gaps, or indentations, in the myelin sheath along the axon

What is a nuclei?

These are clusters of cell bodies within the white matter of the central nervous system (CNS)

What is a ganglia?

These are collections of cell bodies outside the central nervous system (CNS)

What is the white matter?

This consists of dense collections of myelinated fiber tracts in of the CNS

What is the gray matter?

This consists of mostly unmyelinated fibers and cell bodies

CLASSIFICATION

OVERVIEW:
Classify neurons according to structure and function
List the types of general sensory receptors and describe their functions

How are neurons classified?

These are classified either according to how they function or according to their structure

What is functional classification of neurons?

This groups neurons according to the direction the nerve impulse is traveling relative to the CNS

What are sensory, or afferent, neurons?

These are neurons carrying impulses from sensory receptors to the CNS

These keep us informed about what is happening to both inside and outside the body

What are cutaneous sense organs?

These are sensory receptores in the skin

What are proprioceptors?

These are in the muscles and tendons that detect stretch or tensions.

What are motor, or efferent, neurons?

These are neurons carrying impulses from the CNS to the viscera and/or muscles and glands

These are always located in the CNS

What is the interneurons, or association neurons?

These are found in neural pathways in the central nervous system. These connect sensory and motor neurons

What is structural classification of neurons?

This is based on the number of processes extending from the cell body

What is multipolar neurons?

These are many processes extending from the cell body

What is called bipolar neurons?

These are neurons with two processes: an axon and a dendrite. These are rare in adults and are found only in some special sense organs (eye, nose) where they act in sensory processing as receptor cells

What is a unipolar neurons?

These are neurons that have a short single process leaving the cell body

PHYSIOLOGY: NERVE IMPULSES

OVERVIEW:
Describe the events that lead to the generation of a nerve impulse and its conduction from one neuron to another
Define reflex arc, and list its elements

What are the two major functional properties of neurons?

Irritability and Conductivity

What is irritability function of neurons?

This is the ability to respond to a stimulus and convert it into a nerve impulses

What is conductivity function of neurons?

This is the ability to transmit the impulse to other neurons, muscles, or glands

Describe the events that lead to the generation of a nerve impulse

1. The resting membrane is polarized
2. Stimulus initiates local depolarization
3. Depolarization and generation of an action potential
4. Propagation of the action potential
5. Repolarization
6. Initial ionic conditions restored

What does it mean when a neuron is polarized or at rest (irritability aspect)?

This means that there are fewer positive ions sitting on the inner face of the neuron's plasma membrane than there are on its outer face

What does it mean when the stimulus initiates local depolarization (irritability aspect)?

A stimulus changes the permeability of a local "patch" of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane (the inside becomes more positive; the outside becomes more negative) at that site

This exchange of ions initiates an action potential in the neuron

What is depolarization?

This is the inward rush of sodium (NA+) ions that changes the polarity of the neuron's membrane at that site.

What does it mean when depolarization and generation of an action potential happens (irritability aspect)?

If the stimulus is strong enough, depolarization causes membrane polarity to be completely reversed and an action potential is initiated

What does it mean when propagation of the action potential or nerve impulse happens (irritability aspect)?

The depolarization of the first membrane path causes permeability changes in the adjacent membrane, and the cycle repeats

What does it mean when repolarization happens (irritability aspect)?

Potassium (K+) ions diffuse out of the cell as the membrane permeability changes again, restoring the negative charge on the inside of the membrane and the positive charge on the outside surface.

This action requires ATP

What does it mean when initial ionic conditions are restored (irritability aspect)?

The ionic conditions of the resting state are restored later by the activity of the sodium-potassium pump. Three sodium ions are ejected for every two potassium ions carried back into the cell

Describe the continuation of the nerve impulse between neurons

Impulses are able to cross the synapse to another nerve. Neurotransmitter is released from a nerve's axon terminal. The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter. An action potential is started in the dendrite

What are reflexes?

These are rapid, predictable, and involuntary responses to stimuli

What is reflex arc?

This is a direct route from a sensory neuron, to an interneuron, to an effector

What are the types of reflexes that occur in the body?

Autonomic reflexes and Somatic reflexes

What is autonomic reflexes?

This regulate the activity of smooth muscles, the heart, and glands. This regulates digestion, elimination, blood pressure, and sweating.

What is somatic reflexes?

This include all reflexes that stimulate the skeletal muscle

CENTRAL NERVOUS SYSTEM

OVERVIEW:
During the embryonic development, the CNS first appears as a simple tube, the neural tube, which extends down the dorsal median plane of the developing embryo's body. By the fourth week, the anterior end of the neural tube begins to expand, and brain formation begins. The rest of the neural tube posterior to the forming brain becomes the spinal cord. The central canal of the neural tube, which is continuous between the brain and spinal cord, becomes enlarged in four regions of the brain to form chambers called ventricles

Give an overview of how CNS develops

(same as previous slide but shorter)
CNS develops from the embryonic neural tube
The neural tube becomes the brain and spinal cord
The opening of the neural tube becomes the ventricles
There are Four chambers within the brain
These are filled with cerebrospinal fluid

FUNCTIONAL ANATOMY OF THE BRAIN

OVERVIEW:
Identify and indicate the functions of the major regions of the cerebral hemispheres, diencephalon, brain stem, and cerebellum on a human brain model or diagram.

Name the four major regions of the brain?

1. Cerebral hemispheres
2. Diencephalon
3. Brain stem
4. Cerebellum

What are paired cerebral hemispheres?

Collectively these are called cerebrum, are the most superior part of the brain and together are a good deal larger than the other three brain regions combined

What is the cerebrum made of?

It is made of ridges (gyri) and grooves (sulci)

What is a gyri?

These are elevated ridges of tissue on the cerebral hemispheres

What is a sulci?

These are grooves that separate the gyri

What are fissures?

These are deep grooves that divide the cerebrum into lobes

Name the surface lobes that is divided by the fissure

1. Frontal lobe
2. Parietal lobe
3. Occipital lobe
4. Temporal lobe

Name specialized areas of the cerebrum

1. Somatic sensory area
2. Primary motor area
3. Broca's area
4. Cerebral areas involved in special senses
5. Interpretation areas of the cerebrum

What is the somatic sensory area?

This is the area that receives impulses from the body's sensory receptors

What is the primary motor area?

This area sends impulses to skeletal muscles

What is the broca's area?

This area is involved in our ability to speak

Name cerebral areas involved in special senses

1. Gustatory area (taste)
2. Visual Area
3. Auditory area
4. Olfactory area

Name interpretation areas of the cerebrum

1. Speech/language region
2. Language comprehension region
3. General interpretation area

What are the layers of the cerebrum?

1. Gray matter
2. White matter

What is the gray matter of the cerebrum?

This is the outer layer. This is composed of mostly of neuron cell bodies

What is basal nuclei?

These are several internal islands of gray matter buried deep within the white matter of the cerebral hemispheres

What is the white matter of the cerebrum?

These are fiber tracts inside the gray matter

Ex: corpus collosum connects hemispheres

What is diencephalon, or interbrain?

This sits atop the brain stem and is enclosed by the cereberal hemisphere

Name the three parts that make up the diencephalon.

1. Thalamus
2. Hypothalamus
3. Epithalamus

What is the thalamus?

This encloses the third ventricle. This is the relay station for sensory impulses for sensory impulses passing upward to the sensory cortex.

This also transfers impulses to the correct part of the cortex for localization and interpretation.

What is the hypothalamus?

This is under the thalamus. It is an important autonomic nervous system center because it helps regulate body temperature, controls water balance, and regulates metabolism.

This is an important part of the limbic system. The pituitary gland is attached to this.

What is the limbic system?

This is the "emotional-visceral-part" of the brain.

What is the pituitary gland?

This is the an endocrine gland that is attached to the hypothalamus.

What is the epithalamus?

This forms the roof of the third ventricle. This houses the pineal body (an endocrine gland). This also includes the choroid plexus.

What is the pineal glands?

This is an endocrine gland that is also an important part of the epithalamus.

What is the choroid plexus?

This are the knots of capillaries within each ventricle that form the cerebrospinal fluid.

What is the brain stem?

This attaches to the spinal cord. There are three parts of the brain stem.

What are the parts of the brain stem?

1. Midbrain
2. Pons
3. Medulla oblangata

What is the midbrain?

This is mostly composed of tracts of nerve fibers and has two bulging fiber tracts - cerebral peduncles. This also has four rounded protrusions - corpora quadrigemina - which are reflex centers for vision and hearing.

What is the cerebral peduncles?

These are the feet of the cerebrum which are two bulging fiber tracts.

What is the corpora quadrigemina?

These are four rounded protrusions are reflex centers involved with vision and hearing.

What are pons?

These are bulging center part of the brain stem. Mostly composed of fiber tracts. These includes nuclei involved in the control of breathing.

What is the medulla oblangata?

This the lowest part of the brain stem. Merges to the spinal cord. These important fiber tracts. It also contains important control centers.

Name examples of what control center control, or visceral activities.

Heart rate control, blood pressure regulation, breathing, swallowing, vomiting

What is the reticular formations?

These are two hemispheres with convoluted surfaces? They are involved in motor control of visceral organ.

What is the reticular activating systems?

These are a special group of reticular formation neurons, or reticular activating system, that play a role in awake/sleep cycles and consciousness.

What is the cerebellum?

This is the two hemisphere with convoluted surfaces. It provides involuntary coordination of body movements.

PROTECTION OF THE CENTRAL NERVOUS SYSTEM

OVERVIEW:
Name the three meningeal layers, and state their functions
Discuss the formation and function of cerebrospinal fluid and the blood-brain barrier.

Name some enclosures that protect the CNS

Scalp and skin. Skull and vertebral column

What is meninges?

These are three connective tissue membranes covering and protecting the CNS structures.

Name the three connective tissue membranes (or meninges)

1. Dura mater
2. Arachnoid mater
3. Pia mater

What is Dura mater?

This is the outermost leathery layer meaning "tough or hard mothe.". This is a double -layered external covering. This folds inward in several areas

What is periosteum?

One of the layers of the dura mater that is attached to the inner surface of the skull

What is the meningeal layer?

This is one of the layers of the dura mater that forms the outermost covering of the brain and continues as the dura mater of the spinal cord.

What is the arachnoid mater?

This is the web-like middle layer

What is the pia mater?

This is the internal layer that clings to the surface of the brain

What are the arachnoid villi?

These are specialized projections that protrude through the dura mater. The cerebrospinal fluid is absorbed into the venous dural sinuses through this special projections

What is cerebrospinal fluid?

This is similar to blood plasma. It contains less protein and more vitamin C. This is formed by the choroid plexus. It forms a watery cushion to protect the brain. It is circulated in arachnoid space, ventricles, and central canal of the spinal cord.

What are the choroid plexuses?

These are clusters of capillaries hanging from the "roof" of each of the brain's ventricles

What is the blood brain barrier?

These are the least permeable capillaries of the body. These excludes many potential harmful substances. They are useless against some substances

Name some substances that the blood brain barrier is useless against

1. Fats and fat-soluble substances
2. Respiratory gases
3. Alcohol
4. Nicotine
5. Anesthesia

BRAIN DYSFUNCTIONS

OVERVIEW:
Compare the signs of CVA with those of Alzheimer's disease; of a contusion with those of a concussion
Define EEG, and explain how it evaluates neural

Name some traumatic brain injuries and cerebrovascular accidents

1. Traumatic brain injuries
2. Cerebrovascular accident
3. Alzheimer's disease

Name the effect of the ricocheting brain hitting the opposite end of the skull

1. Concussion
2. Contusion
3. Cerebral edema

What is a concussion?

This is a slight brain injury where no permanent brain damage occurs. The victim may feel dizze or "see stars"

What is a contusion?

The nervous tissue destruction occurs. The nervous tissue does not regenerate.

May remain conscious but severe brain stem always result in a coma laying to an hour to a lifetime because of injury to the reticular activating system

What is cerebral edema or intracranial hemorrhage?

This is the swelling from inflammatory response. May compress and kill brain tissue

What is cerebrovascular accident (CVA)?

This is commonly called a stroke. This is the result of a ruptured blood vessel supplying a region of the brain. The brain tissue supplied with oxygen from that blood source dies. Loss of some functions or death may result

What is Alzheimer's disease?

This is a progressive degenerative brain disease.
Mostly seen in the elderly, but may begin in middle age.
Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons.
Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death

SPINAL CORD

OVERVIEW:
List two important functions of the spinal cord
Describe spinal cord structure

What is the spinal cord?

This extends from the medulla oblangata to the region of T12. Below the T12 is the cauda equine. Enlargement occurs in the cervical and lumbar regions

What is the cauda equine?

This is a collection of spinal nerves

How long is the spinal cord?

This cylindrical continuation of the brain stem is about 17 inches long

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