The Nervous System rev 12-12

1Nervous System HANDOUT 1

The Nervous System rev 12-12

• Receives information and produces a meaningful, quick output.

• To do this, the nervous system– quickly sorts through our memory bank– decides the probable meaning of the input– integrates the information– Provides a quick response

• So, the nervous system controls and integrates all other body systems and functions


What are the characteristics of the nervous system that allow us to do this?

1. It must receive information from our senses.

2. It integrates information.

-Integration is the process of taking different pieces of information from different sources, making sense of all of it at the same time, and coming up with an action plan.

3. The nervous system is fast; it can do this within tenths of a second.


The CNS-Central Nervous System (the brain and spinal cord)– is the integrating and command center of the

nervous system– It receives and interprets incoming sensory

information and produces motor responses

The PNS-peripheral nervous system is the part of the nervous system outside the CNS. – it contains the communication lines that link all

parts of the body to the CNS


The Periph NS consists of• 12 pairs of cranial nerves: carry impulses

between brain and body• 31 pairs of spinal nerves: connect to spinal

cord via dorsal and ventral roots– Dorsal root has sensory neurons and

transmit information TO the cord– Ventral root has motor neurons that

transmit information FROM the cord to the body


• the Peripheral NS has 2 functional subdivisions– the sensory or afferent division carries

impulses TO the CNS • keeps the CNS informed of events going on

inside and outside of the body– The motor or efferent division carries

impulses FROM the CNS• this division enables us to respond to stimuli


The Motor Division can be further subdivided into 2 parts:

• the Somatic nervous system – Voluntary: controls voluntary and involuntary

skeletal muscle movements• Motor neurons are activated either by

conscious control from the brain or by an involuntary response called a reflex


Reflex Division:

– Spinal reflexes

• Spinal reflexes are involuntary, automatic responses handled primarily by the spinal cord and spinal nerves

And, the other part or division of the Periph NS, the Autonomic nervous system (ANS)•this division regulates involuntary activities; the activity of smooth muscles, cardiac muscles, and glands •Functions below the level of awareness•(regulates anything that occurs automatically in the body)


• Requires 2 neurons to transmit information from the CNS to a “target” cell– Preganglionic neurons: cell bodies of the first

neurons lie within the CNS• Sympathetic preganglionic fibers short• Parasympathetic preganglionic fibers long

– The axons of these go to postganglionic neurons which lie outside the CNS

• Postganglionic axons extend to wherever in our body the target glands or organs are located


The ANS is further sub-divided into the• SYMPATHETIC NERVOUS SYSTEM which

mobilizes body systems during emergency situations.

• Origin: thoracic or lumbar regions of the spinal cord

• Function: releases neurotransmitter norepinephrine for fight-or-flight reaction; opposes parasympathetic division

• reduces blood flow to organs that do not help with an immediate disaster


AND the PARASYMPATHETIC NERVOUS SYSTEM (PSNS) which conserves our energy and predominates during relaxing – Origin: brain and sacral area of spinal cord

(craniosacral)– Function: releases acetylcholine to relax the

body; opposes sympathetic division

• In most organs, the actions of the sympathetic and parasympathetic divisions have opposite effects.

• The two divisions counterbalance each other’s activities to maintain homeostasis.


Composition of the Nervous SystemNerves, Neurons, Neuroglia

The Nervous System is composed of Nerves which consists of the axons of many neurons

wrapped together in a sheath of connective tissueNeurons are cells which are specialized for

communication.• Classification of neurons

– Sensory or Afferent neurons carry (sensory) information from receptors TO the CNS

– Motor (Efferent) Neurons carry messages AWAY FROM the CNS to the muscles and the glands


– Interneurons or Association Neurons are located in the CNS and conduct impulses within the CNS. They receive information from sensory neurons, integrate the input, and then deliver the information to other neurons.• are multipolar neurons

• Neuroglia (or Glia) are the supporting and protecting cells of the nervous system. We will speak more of these later.


Neurons

• All neurons have

• a cell body (contains the nucleus)

• an axon (long slender tube of cell membrane; specialized to carry electrical impulses)

– Axons of sensory neurons originate from a dendrite

– Axons of interneurons and motor neurons originate from a cone shaped area of the cell body called the axon hillock

– At its other end, the axon branches into slender extensions called axon terminals and the end of this is called an axon bulb

• dendrites (typically slender extensions of the cell body; receive stimuli)


Types of Neurons

Unipolar Neurons have a single process which emerges from the cell body

• this process divides into a proximal and distal branch– One branch behaves as an afferent branch and

the other behaves as an efferent branch• All unipolar neurons are sensory

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Bipolar Neurons• have 2 processes emerging from a round cell body• processes extend from opposite sides of the cell

body• found only in some of the special sense organs

where they act as receptor cells


Multipolar Neurons• have 3 or more processes • are the most common neuron type in humans and

major neuron type in the CNS


Interneurons or Association Neurons• are a multipolar neuron• located in the CNS• conduct impulses within the CNS• are the connecting link between sensory and motor

neurons


Some neurons have a myelin sheath• the myelin sheath

– is a fatty wrapping around the axon which provides insulation to the axon and thus saves it energy

• The process of myelination continues during childhood and is the primary reason for the increase in a child's brain size

– it speeds impulse transmission by allowing a leaping pattern of transmission called saltatory conduction

– The impulse jumps from one Node of Ranvier to another


Between neighboring Schwann cells are short, uninsulated gaps called Nodes of Ranvier

Figure 11.7a

Myelin sheath


PNS: Schwann Cell

CNS: Oligodendrocyte


Myelin

• in the peripheral nervous system is formed from Schwann Cells which wrap around the axon

It helps damaged or severed axons of peripheral nerves regenerate

•in the CNS is formed by oligodendrocytes•The oligodendrocyte sheath degenerates once the axon it protects is damaged or destroyed


Neuroglial cells • Provide physical support to neurons• Protection to neurons• Help maintain concentrations of chemicals in the

fluid surrounding them• Neuroglial cells DO NOT generate or transmit

impulses

Examples of Neuroglial Cells:– Oligodendrocytes form the myelin sheath in the

CNS

– Schwann cells form the myelin sheath in the PNS

– Astrocytes anchor the neurons to nearby capillaries

– Ependymal cells are ciliated cells that move cerebrospinal fluid around the brain and spinal cord

– Microglia are phagocytic cells for the nervous system. They destroy microorganisms and damaged tissues near the neurons.



Impulse Transmission-SummaryThe function of a neuron is to transmit information from one

part of the body to another.• This is done in the form of electrical impulses.• An impulse arrives at the dendrite• When the impulse is strong enough, it depolarizes the

membrane and the impulse is transmitted along the axon• When the impulse reaches the axon terminals, the

information needs to be converted to another form of energy in order for the information to be transmitted to its target (i.e. a muscle, a gland, or another neuron)

• A chemical, called a neurotransmitter, is released which allows the impulse to jump the synapse, or space, between the 2 cells

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Impulse Transmission- Definitions

• Resting or Membrane Potential: a small difference in voltage across the cell membrane; the cell is normally negatively charged. – This allows the neuron to be ready to respond more quickly than it

could if it were electrically neutral.– Think about a car battery. It retains a charge so that the

car will start as soon as the key is turned – Unlike most body cells, neurons can alter the electrical

charge across the neurolemma. The membrane potential alternates between -70 and +30 millivolts. Charge differences are controlled by the movement of sodium and potassium ions entering and leaving the neuron

• Action Potential: changes in the electrical activity of the nerve of sufficient intensity to reach the threshold necessary to move an electrical impulse down the axon

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• Threshold: the level of stimulus a neuron needs in order to fire

• All or nothing phenomenon: once the threshold level is reached, the nerve transmits an impulse

• Depolarization: moving the negative charge within the axon closer to zero

• Na+ (sodium) moves into the cell via sodium channels which open

• Na channels act as molecular amplifiers and turn small electrical signals into action potentials that can conduct for long distances

Nervous System HANDOUT

• Repolarization: K+ (potassium) moves out of the cell;

Na+ channels close and the reversal of the membrane polarity triggers opening of the K+ channels so the K+ moves out of the cell. Loss of K+ means that the interior of the axon becomes negative again and the resting potential is restored

• Refractory period: The part of the axon that has already fired is unable to fire again so the impulse must move forward (This prevents the impulse from moving backwards.)


Nerve impulse transmission, explanation 2

•All cells demonstrate an unequal distribution of ions or a voltage difference across the cell membrane. This is called a MEMBRANE POTENTIAL OR A RESTING MEMBRANE POTENTIAL. It occurs when the membrane is not being stimulated.

• Nerve cells and muscle cells (and some cells of glands) can produce electrochemical impulses and transmit them along their membrane when the cell is stimulated or “excited”.

•When a nerve cell is stimulated sufficiently, the voltage across the membrane is changed.


• If the stimulus is strong enough, the impulse reaches the THRESHOLD. Once the impulse starts moving down the axon, it is called an ACTION POTENTIAL and follows an ALL OR NOTHING law.

• Two ions are responsible for this:


• The sodium and potassium ion permeabilities of the cell membrane changes.

• First, Na+ diffuses into the cell. This makes the inside of the axon more positively charged. As the cell becomes more positive, the THRESHOLD stimulus level is reached. Na+ DEPOLARIZES the membrane.

• As the action potential reaches its peak, sodium channels (or gates) close and the potassium channels (or gates) open so K+ diffuses to the outside of the cell. This allowing the cell to return to its original -70 mV charge or its resting potential. The Na+--K+ pump helps to maintain this ‘normal’ charge across the cell membrane.


• The change of electrical current occurs in a small portion of the cell membrane at any one time. This allows the charge to move forward in a step-like progression.

• Once activation of a cell has begun, the membrane is generally insensitive to any further stimulation. This is called the REFRACTORY PERIOD. Near the end of the activation impulse, the cell can be activated but only if a stimulus is much stronger than normal.



PART IIThe Brain and the Spinal Cord rev 12-12

The CNS controls and processes all information received by the body.

• Protection of the CNS– Bone protects it from physical injury

– the brain is covered by the skull – the spinal cord is surrounded by the

vertebrae


The Brain

• The brain is the central command center of the body– Receives information in the form of action

potentials from various nerves and the spinal cord, integrates it and generates the appropriate response.

• 3 major anatomical and functional divisions of the brain have been identified:


Brain: Major Divisions

• Hindbrain: coordinates basic, automatic, and vital functions

• Midbrain: helps coordinate muscle groups and responses to sight and sound

• Forebrain: receives and integrates sensory input from the external and internal environment and determines most of our complex behavior


Hindbrain: movement and automatic functionsMedulla, Pons, Cerebellum

• Connected to the spinal cord

• Is the oldest, most primitive brain division

Medulla Oblongata: controls automatic functions of internal organs

– cardiovascular center- regulates heart rate and blood pressure

– respiratory center-controls rate and depth of breathing

– other centers which coordinates reflexes such as coughing, vomiting, swallowing, and sneezing


– All information passing between the spinal cord and the higher areas of the brain must pass through the medulla

– Motor nerves from one side of the forebrain cross over to the other side of the body in the medulla

• Left side of brain controls right side of body

• Right side of brain controls left side of body


• Pons– Aids information flow

• connects the higher brain centers and the spinal cord

• its respiratory nuclei work with the respiratory centers of the medulla in regulating respiration

• coordinates the information flow between the cerebellum and higher brain centers


Cerebellum• Coordinates basic movements below the level

of conscious control– Stores and produces whole sequences of skilled

movements i.e. driving– Receives sensory input from many sources—joints,

muscles, balance and position receptors in the ear, and visual receptors

– excessive alcohol disrupts normal functioning of the cerebellum; this is why drunk people lose the ability to coordinate their movements including walking a straight line


• The Midbrain—functions relate to vision and hearing– Visual and auditory sensory inputs pass through the

midbrain before being relayed to higher brain centers– Coordinates movements of the head in response to

vision and hearing – controls movement of the eyes and pupil size– monitors the unconscious movement of skeletal

muscles so their actions are smooth and coordinated• The reticular formation extends through the

medulla, the pons, and the midbrain. – works with the cerebellum to coordinate muscle

activity to maintain posture, balance and muscle tone– The Reticular Activating System, within the reticular

formation, is responsible for maintaining our level of wakefulness


The forebrain and diencephalon: emotions and conscious thought

Important areas are the cerebrum, thalamus, hypothalamus, and limbic system– Also includes 2 glands: the pineal gland and the pituitary gland

• Determines our most complex behavior including emotions and conscious thought.

Hypothalamus and Thalamus maintain homeostasis and process information

• Hypothalamus is a small region at the base of the forebrain that coordinates some automatic functions including regulating homeostasis due to monitoring of sensory signals– Has a hunger center and a thirst center– Also controls the pituitary gland


• Thalamus: located just above the hypothalamus– Is primarily a receiving, processing and transfer

center; it sends signals to the cerebrum to be interpreted. (We become conscious of information when it arrives at the thalamus, but only after information arrives at the cerebrum are we aware of which part of the body is experiencing the information.

• Limbic System is a group of neuronal pathways which connect parts of the thalamus, hypothalamus and cerebrum.

– involved in emotions and memory.


• Cerebrum deals with higher functions and is most highly developed– is divided into left and right “cerebral

hemispheres” by the longitudinal fissure– each hemisphere controls the opposite side of

the body• the left hemisphere controls the right side of the body

• the right hemisphere controls the left side of the body


– In the middle of the hemispheres is the corpus callosum which joins the 2 hemispheres and enables them to communicate and share information

• Below the corpus callosum in each hemisphere are the lateral ventricles which secrete CSF

– The outer layer of the cerebrum is called the cerebral cortex and is primarily gray matter

– The inner portion of the cerebrum is primarily white matter


– surface tissue of the cerebrum is covered with sulci (grooves) and gyri (ridges) which increase the surface area for information exchange


– Each hemisphere is further divided into 4 lobes: the frontal, parietal, temporal, and occipital lobes

– all 4 lobes are involved in memory storage


• The frontal lobes initiate motor activity and are responsible for speech, conscious thought, and personality.

• these lobes may be further divided into the prefontal lobes or cortex (the most forward area of these lobes) which are the intellectual center

– intelligence, motivation, personality, abstract reasoning, judgment, planning, love, concern for others

• the premotor cortex – skilled repetitive activities (keyboarding/typing)

and conditioned reflexes (Pavlov’s dog)


• the primary motor cortex which initiates voluntary motor activity of the arms, legs, trunk and face

• In the dominant hemisphere only is our primary speech center


– The parietal lobes house the somatosensory cortex

• interpret sensory information from the skin and from proprioceptors in the muscles and joints.

– This allows us to identify the region of our body being stimulated without looking

• Stereognosis: integrate different sensory inputs to allow us to interpret sensory information i.e. reaching into your pocket and being able to interpret the coins in it without using visual cues.


– The occipital lobes house the primary visual cortex and the visual association area • association areas allow us to

interpret/understand information– The temporal lobes interprets auditory

information and is responsible for perceptual judgment


Cranial Nerves

• Twelve pairs of cranial nerves arise from the brain • They have sensory, motor, or both sensory and

motor functions• Each nerve is identified by a number (I through

XII) and a name


Memory: Storing and Retrieving Information

Memory has 2 stages: short term and long term• Short term: working memory, information from previous

few hours• Long term: information from previous days to yearsThe brain manages the 2 types of memory differently.STM goes into the limbic system and triggers a burst of action

potentials so we can remember information for a few minutes.

LTM: if information important, it is transmitted to your cerebral cortex for storage as LTM. Neurons undergo a permanent change and create additional synapses so we can remember and retrieve information.


Sleep

• Reticular activating system (RAS) controls levels of alertness and sleep– The neurotransmitter serotonin makes us sleepy by

inhibiting the neurons that arouse the brain

• Electroencephalograms (EEGs) allow us to study brain function during sleep

• Stages of sleep:– Stage 1: transitional stage between wakefulness

and sleep– Stage 2: skeletal muscles relax, little eye or

body movement


– Stage 3: sleep deepens, heart and respiration slower

– Stage 4: difficult to awaken, heart and respiration slowest, body temperature decreased

• REM (rapid eye movement) sleep: when we dream; EEG shows level of brain activity comparable to wakefulness

• People deprived of REM sleep become moody, irritable and depressed and if deprived long enough may suffer hallucinations


Psychoactive Drugs

• Action: affects higher brain functions (consciousness, emotions, or behavior); drugs alters the actions of brain neurotransmitters so that neurons in the brain release an excess of signaling molecules thus putting the brain cells into overstimulation feelings of energy and euphoria.

• can cross the blood brain barrier

– Methamphetamine (crystal meth), cocaine, crack, alcohol, nicotine, heroin

– When the body releases neurotransmitters, their effects are typically short because the neurotransmitter remains in the synapse for a brief period of time

– These drugs block the reabsorption of the neurotransmitters so they remain in the synapse and stimulate the body again and again

• Dopamine is one of the most important neurotransmitters in areas of the brain associated with pleasure

– But, as the neurotransmitter reuptake is blocked, the body releases less and less and the “good feeling” disappears

• Psychological dependence: user craves the feeling associated with the drug

• Tolerance: takes more of the substance to achieve the same affect

• Addiction: the need to continue obtaining and using a substance; no free choice

• Withdrawal: physical symptoms that occur upon stopping the drug



Autoimmune Disorders:Multiple Sclerosis (MS):

• An autoimmune disease that mainly affects young adults– The sheaths of myelinated neurons in the brain and

spinal cord degenerate and form hardened (sclerotic) scar tissue. These areas can’t effectively insulate the neurons and so impulse transmission is slowed and disrupted and the nerves are also damaged.

– People with MS experience a variety of symptoms depending on which areas of the CNS are damaged.

• Symptoms include visual disturbances, headaches, dizziness, weakness, loss of muscular control and sensation, and urinary incontinence

• In advanced MS, cognitive deficits, depression

Disorders of the Nervous System


• Cause: unknown. Thought to be disorder of the immune system or genetic tendency

– Thought that a virus attacks immune system so it perceives myelin as a threat

• Course: can be mild to severe. Onset typically between ages 20-40; affects more women than men

• Diagnosed: MRI, Evoked Potential nerve test to determine the speed of impulses traveling through nerves; examine CSF to see if any cell abnormalities

• Medications: Interferons, high doses of IV corticosteroids or Copaxone to reduce frequency of relapses, Avonex or Betaseran to help decrease disability

Multiple Sclerosis


Amyotrophic Lateral Sclerosis (ALS) - Lou Gehrig’s Disease

• Similar to MS; progressive neurodegenerative disease affecting motor nerve cells in the brain and spinal cord which control skeletal muscles. People do not lose their ability to think—are cognitively aware

• Average age of onset: 55 years; more common in males

• Primary symptom is progressive weakening and paralysis of skeletal muscles, especially those of the arms, legs, speech, swallowing and breathing

ALS

•Most common cause of death is respiratory failure; people typically die within 3 years of onset

•No cure or treatment– Only 1 FDA approved drug, Rilutek (brand name is

Riluzole); this minimally slows the disease progressiono New medication on the market: Nuedexta



Trauma

• Concussion: caused by a violent blow to the head or neck

– Usually see a short loss of consciousness due to a disruption of the electrical activity of brain neurons.

– After regaining consciousness, person may have blurred vision, confusion, nausea and vomiting

– New thinking—confusion may remain for period of time because of trauma/ “shaking of brain”


– Generally concussions don’t have permanent damage unless there is a subdural hematoma (bleeding into the space between the meninges)• Bleeding increases pressure within head

(cerebral edema)squashes brain tissue and disrupts function of brain

– Symptoms: drowsiness, headache and weakness of 1 side of body

• Treatment: surgery for immediate relief of pressure and repair of bleeding blood vessels

• Signs and Symptoms– Vary with artery affected, severity of damage

– Severe headache

– May see weakness on one side of the body, slurring of speech, trouble speaking or trouble understanding

– Sudden confusion

– Trouble seeing or walking

– Loss of balance or coordination

• Treatment– Endarterectomy (removal of atherosclerotic plaques)

– Anticlotting drugs or aspirin

– tPa (tissue plasminogen activator) to dissolve clot; must be administered within 3 hours of the onset of symptoms

– Steroids to try to decrease any brain swelling



• Spinal cord injuries: will impair sensation and function below the level of injury– Paraplegia or quadriplegia; can be fatal; will always

cause problems with bladder and bowel control– May cause respiratory difficulties

Infections: Brain and spinal cord typically do not get infected due to the blood-brain barrierMost body capillaries are leaky because materials diffuse into and out of the capillaries. The cells which produce CSF are fused more tightly and substances must pass through, not in between, the cells to get from the blood CSF. So, microorganisms generally can’t get into CSF.

• Encephalitis: inflammation of the brain; typically caused by a virus– Causes: breathing in respiratory droplets,

contaminated food, insect bite, skin contact– Symptoms: inflammation of brain tissuecerebral

edema, headache, fever, fatigue, hallucinations, confusion, disturbances in speech, memory or behavior, epileptic seizures



• Treatment: Hospitalization with intravenous medications –antiviral or antibiotics, anti-seizure to prevent seizures, steroids to reduce brain swelling

• Acute phase usually lasts for 1-2 weeks; fever and symptoms may gradually or suddenly disappear; some people may take several months to recover although in severe cases there may be residual disabilities

• Meningitis: Inflammation of the meninges; can be viral or bacterial

– Symptoms: headache, fever, nausea and vomiting, light sensitivity, stiff neck

– Treatment: hospitalization. If viral, mild symptoms and will improve in few weeks

– If bacterial, can be fatal; IV antibiotics needed ASAP


• Rabies: infectious viral brain disease – Transmitted to humans by direct contact, either bite or lick

over broken skin• Virus attacks the sensory neurons in the bite region then travels to

the spinal cord, then to the brain where it multiplies and kills cells

– Symptoms: swollen lymph glands, painful swallowing, vomiting, choking, spasms of throat and chest muscles, fever, becomes irrational. Death within 2-20 days

– Treatment:

• wash wound thoroughly ASAP, go to emergency room or doctor, have animal tested, receive rabies immunization ASAP

• a regimen of one dose of rabies immune globulin and five doses of the rabies vaccine over a 28-day period. – administer the rabies immune globulin and the first

dose of the vaccine as soon as possible after exposure. Normally, additional doses of rabies vaccine follow on days 3, 7, 14, and 28 after the first vaccination.

– Rabies immune globulin contains antibodies from blood donors who were given rabies vaccine. The antibodies provide interim protection until an exposed person's own antibodies develop in response to the vaccine.


• injecting rabies immune globulin at the site of injury reduces the amount of virus that is able to enter the nerve cells and potentially initiate an active infection.

• The vaccine works by stimulating the immune system to produce antibodies that neutralize the virus. The person develops a protective immune response before the virus reaches the brain and begins to actively replicate.

• Older rabies vaccines required painful, daily injections in the abdomen (stomach) for up to three weeks, and they could produce severe side effects. Current vaccines are relatively painless and are given in your arm.



Neural and synaptic transmission disorders: action potentials can’t be properly sent. Symptoms depend on which area of the brain/nerves are affected

• Epilepsy: recurring episodes of abnormal electrical activity in brain– Seizure triggers: fatigue, stress, flashing lights – Seizures vary widely due to which part of brain is

affected– Diagnosis: EEG– Treatment: medications

Things to do for person having seizure•Cushion head•Don’t try to restrain arms or legs•Loosen anything tight around neck (necktie or scarf)•Turn on side•Nothing in mouth•Time seizure•Make note of where seizure begins and how progresses



• Parkinson’s disease: progressive degenerative illness; loss of dopamine releasing neurons in the area of the midbrain that coordinates muscle movements; can’t perform smooth, coordinated movement– Symptoms: stiff joints, muscle tremors (resting) in

hand, loss of mobility, depression and other mental and cognitive (executive functioning) impairments

– Treatment: L-dopa (levodopa), a drug which the body converts to dopamine. Will become ineffective eventually

– Deep brain stimulation-implant an electrode deep in the parts of the brain that control movement

– Age of onset—typically middle or late in life

Dementia: Is not a disease itself but is a group of symptoms

caused by various diseases or conditions• Diagnosis made when people have 2 or more

major life functions impaired or lost • Loss of mental functions is severe enough to

interfere with a person’s daily life

General characteristics – decline in functioning over time; first symptom is

typically forgetfulnessmemory loss


• Begin to see many deficit areas: – language problem-difficulty communicating– Difficulty with: recognizing objects

--planning, reasoning, perception

--decision making, judgment

--cognitive deficits including an inability to manage finances, to find the way home

--loss of behavioral and emotional control

--Poor coordination

--Change in social skills


Alzheimer’s disease is most common cause of dementia•Other causes-stroke, alcohol abuse, excessive drug use, nutritional deficiencies (vit B12 deficiency), head injury, brain tumors•Some dementias are treatable if we can correct the cause i.e. stop abusing alcohol, remove tumors, correct nutritional deficiencies•Most dementias are not reversible•Risk factors: age, family history, smoking, atherosclerosis, diabetes



Alzheimer’s disease:

•disorder of mental impairment, especially memory, due to a shortage of the neurotransmitter acetylcholine.

– Primarily affects neurons in the limbic system and frontal lobe. See plaques (beta amyloid) in brain tissue and abnormal, tangled neurons. Possibly prion infection causing misfolded proteins which then infect healthy proteins

– Symptoms: Primarily affected are memory, thinking and behavior. Gets worse with time. Progresses from memory lapses to severe memory loss, especially of STM. LTM affected more slowly.

– See disorientation, behavior and personality changes, loss of ability to function independently

• Treatment: medications which increase the brain’s production of acetylcholine



Brain tumors: abnormal growth in or on the brain• Can be cancerous or benign

– Problems due to increased pressure within the brain

– Symptoms: headache, vomiting, visual impairment, confusion, muscle weakness, difficulty speaking, seizures

– Treatment: Radiation and chemotherapy to try to shrink the tumor. Surgical removal.

The Nervous System rev 12-12

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