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Neurons - cells that are specialized for the reception, conduction, and transmission of electrochemical signals. an incredible variety of shapes and sizes.

multipolar neuron - more than two processes extending from its cell body, most neurons are multipolar. Around 99% of all neurons.

unipolar neuron -with one process extending from its cell body.

bipolar neuron - with two processes extending from its cell body.

interneurons - with a short axon or no axon at all, the ones in between their function is to integrate neural activity within a single brain structure, not to conduct signals from one structure to another. They Connect two brain regions.

The neuron cell membrane is composed of a lipid bilayer(two layers of fat molecules).

Some membrane proteins are:

Channel proteins -certain molecules can pass.

Signal proteins - transfer a signal to the inside of the neuron.

Gray matter - neurons

white matter-glial cells

Oligodendrocytes and Schwann cells:

• Myelin

• CNS and PNS.

Microglia:

• Immune system responsibilities

• Role in cell death, synapse formation, and synapse elimination.

Astroglia:

• Support and provide nourishment

• Form blood-brain barrier

• Send signals

• Establish and maintain connections.

Action potential - an electrical charge that travels along the membrane of a neuron. can be generated when a neuron’s membrane potential is changed by chemical signals from a nearby cell.

Sodium channels open  - Na+ ions rush in - membrane potential −70 to +50 mV. - influx of Na+ ions open potassium channels - K+ ions are driven out through these channels by the positive internal charge. - 1 millisecond, the sodium channels close - the end of the rising phase - the beginning of repolarization by the continued efflux of K+ ions - repolarization has been achieved - the potassium channels close - K+ ions flow out of the neuron - hyperpolarized.

they are all-or-none responses; either occur to their full extent or do not occur at all.

whether a neuron fires depends on the balance between the excitatory and inhibitory signals reaching its axon.

Synapses- contact between neurons where information is passed from one neuron to the next. form between axons and dendrites, consist of a presynaptic neuron, synaptic cleft, and a postsynaptic neuron.

Communication among neurons occurs across synapses.

axodendritic synapses—synapses of axon terminal buttons on dendrites.

axosomatic synapses— synapses of axon terminal buttons on somas (cell bodies).

axoaxonic synapses - can mediate presynaptic facilitation and inhibition. 

Dendrodendritic- connections between the dendrites of two different neurons.

Dendroaxonic- a dendrite communicates with axon (rare).

Presynaptic Inhibition-inhibitory neuron provides synaptic input to the axon of another neuron (axo-axonal synapse).

Postsynaptic Inhibition-postsynaptic receptors are attached to neurons. As a result, the postsynaptic neuronal membrane’s sensitivity to certain ions will be altered.

directed synapses—synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity.

Nondirected synapses - synapses at which the site of release is at some distance from the site of reception. \n \n The vertebrate nervous system includes the brain, brainstem, spinal cord, cranial and peripheral nerves, and ganglia.

The central nervous system is composed of two divisions: the brain and the spinal cord.

Peripheral nervous system (PNS) is the division located outside the skull and spine. The peripheral nervous system is located outside the skull and spine.

The somatic nervous system (SNS) is the part of the PNS that interacts with the external environment. It is composed of afferent nerves that carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and so on, to the central nervous system and efferent nerves that carry motor signals from the central nervous system to the skeletal muscles. 

The autonomic nervous system (ANS) is the part of the peripheral nervous system that regulates the body’s internal environment. It is composed of afferent nerves that carry sensory signals from internal organs to the CNS and efferent nerves that carry motor signals from the CNS to internal organs. 

The sympathetic nerves are autonomic motor nerves that project from the CNS in the lumbar (small of the back) and thoracic (chest area) regions of the spinal cord.

The parasympathetic nerves are those autonomic motor nerves that project from the brain and sacral(lower back) region of the spinal cord.

The cranial nerves include purely sensory nerves such as the olfactory nerves (I) and the optic nerves (II), but most contain both sensory and motor fibers. The longest cranial nerves are the vagus nerves (X), which contain motor and sensory fibers traveling to and from the gut. 

Ganglia - clusters of cell bodies in the peripheral nervous system.

EEG signal reflects the sum of electrical events throughout the head. These events include action potentials and postsynaptic potentials as well as electrical signals from the skin, muscles, blood, and eyes.

Magnetic resonance imaging (MRI) is a structural brain-imaging procedure in which high-resolution images are constructed from the measurement of radio-frequency waves that hydrogen atoms emit as they align with a powerful magnetic field.

Functional MRI (fMRI) produces images representing the increase in oxygen flow in the blood to active areas of the brain.  \n Intracranial Recording used for decades in patients with epilepsy to localize the seizure onset zone, prior to brain tissue resection. \n

Antagonist – drug that blocks a neurotransmitter (inhibits), decreases activity at a synapse (low affinity, low efficacy).

Agonist – drug that increases effects (facilitates), increases activity at a synapse (high affinity, high efficacy).

Mixed agonist-antagonist – agonist for some effects or doses and antagonist for others.

Affinity – tendency of a drug to bind to a receptor (varies from strong to weak).

Efficacy – drug’s tendency to activate/ stimulate the receptor.

Parental alcohol use correlates with that of biological (stronger) and adopted children.

Unstable environment – increased if having a gene affecting serotonin synapses.

Prenatal environment: Pregnant drinking alcohol = child likely to develop alcoholism, same in rats.

Careful parental supervision – child less likely to have impulse problems, even if have genes or antisocial behavior.

People with early-onset alcoholism – usually family history of alcoholism, genetic predisposition, rapid onset of the problem.

Late-onset – life difficulties, usually no history of alcoholism in family, respond better to treatment.

Drugs affect synapses differently at diff. stages – when its in the brain, during withdrawal and effects responsible for cravings

Cocaine, amphetamine, sexual excitement – increase or prolong the release of dopamine in nucleus accumbens 

Alcohol, marijuana, nicotine – non-stimulants increase dopamine release but not much. The amount of produced dopamine doesn’t correlate with pleasure or probability of addiction. 

Cravings -   insistent search for the activity/ substance. Even after a long period of abstinence cues can trigger a craving.

Tolerance – decrease in effect of the drug; its learned and can be weakened through extinction procedures

Withdrawal – body’s reaction to the absence of drugs. Addictive behavior might be a way to avoid withdrawal symptoms or to cope with stress. \n Medications to combat alcohol use

·         Antabuse (disulfiram) – antagonizes the enzyme that metabolizes acetaldehyde = sickness after drinking; nausea-inducing drug to associate the two-learned aversion. 

·         Naloxone and naltrexone – block opiate receptors and decrease pleasure from alcohol

Methadone – similar to heroin and morphine, activates the same brain receptors and produces the same effects; it can be taken orally and it gradually enters the blood and brain avoiding the ‘rush’ which disrupts behavior 

Buprenorphine and levomethadyl acetate (LAAM) – long-lasting effects so people don’t have to go to the clinic daily but 3 times a week. People using them live longer and healthier that heroin/morphine users and can hold a job.

 \n Major Depressive Disorder

–         extremely low mood for weeks, .

–         nucleus accumbens less responsive to reward 

–       Feelings of worthlessness, sadness, suicidal thoughts, trouble sleeping. Low motivation, problems with attention, memory and impaired sense of smell 

–         Depression more common in women during reproductive era 

–         Report less number of pleasant experiences, reacted normally to sad/ frightening images but rarely smiled at comedies/ pleasant pictures

Twin studies & adopted children show moderate heritability for depression \n Depression could be an evolutionary adaptation – conserving energy after defeat of some sort or valid purpose for ancestors after physical injury

Early onset depression (before 30 yo):

·         likely to have relatives with depression, anxiety disorders, neuroticism, attention-deficit disorder, alcohol or marijuana abuse, obsessive-compulsive disorder, bulimia, migraine and irritable bowel syndrome.

·         More severe, long-lasting and more associated with suicidal tendencies

Late onset depression (especially after 45-50) – likely to have relatives with circulatory problems.

 \n Simply inheriting the gene was not enough to lead to depression, but the genes' interaction with stressful life events increased one's likelihood of developing depression. 

Serotonin transporter gene – a protein that regulates the ability of axons to reabsorb serotonin after its release.

People without depression – happy mood = increased activity in the left prefrontal cortex.

Depressed people – higher activity in the right prefrontal cortex; the imbalance is stable over years despite changes in symptoms of depression (probably a predisposition not a reaction).

Iproniazid – first antidepressant drug, it was firstly used to treat tuberculosis then they found out it works for depression.

Chlorpromazine – used for different purposes then noticed to treat schizophrenia.

Tricyclics – block the transporter protein that reabsorb serotonin, dopamine and norepinephrine into the presynaptic neuron. 

Tricyclics also block histamine and acetylcholine receptors, and certain sodium channels.

Blocking histamine = drowsiness 

blocking acetylcholine = dry mouth, trouble urinating      

Serotonin reuptake into presynaptic neuron – serotonin transporter protein open to the outside of the neuron. Then it picks the molecule and flips position to the inside (tricyclics and SSRI lock the protein in position on the left):

SSRI – selective serotonin reuptake inhibitors; similar to tricyclics but specific to neurotransmitter serotonin. 

1.       Fluoxetine (Prozac)

2.       Sertraline (Zoloft)

3.       Fluvoxamine (Luvox)

4.       Citalopram (Celexa)

5.       Paroxetine (Paxil/ Seroxat)

SNRI – serotonin norepinephrine reuptake inhibitors; block serotonin and norepinephrine reuptake. Improve memory, many patients take two or more drugs with different mode of action.

1.       Duloxetine (Cymbalta)

2.       Venlafaxine (Effexor)

MAOIs – monoamine oxidase inhibitors; they block the enzyme monoamine oxidase.

(MAO): presynaptic enzyme that metabolizes catecholamines (dopamine, norepinephrine) and serotonin into inactive chemicals . 

 \n Atypical antidepressants – other types f. ex. Bupropion which reuptake of dopamine and norepinephrine but not serotonin. 

Possible antidepressants:

Ketamine – antagonizes NMDA type glutamate receptors; forms new synapses, rapid effects in patients who don’t respond to other medications. 

Cons: produces hallucinations, delusions and effects are not long-lasting. One of ketamine metabolites could be a great antidepressant

St. John’s wort herb – nutritional supplement, purity varies from a bottle. Less expensive than antidepressants, without prescription, effectiveness similar to antidepressants. 

Cons: people take too big doses; it increases effectiveness of a liver enzyme that breaks down toxins and most medicines!

How are antidepressants effective?

People with depression have normal levels of neurotransmitters.

Drugs affect neurotransmitters in synapses quickly (minutes to hours) 

People with depression have lower brain-derived neurotrophic factor (BDNF) - important for synaptic plasticity, 

People with depression show:

  Smaller hippocampus, impaired learning, reduced production of hippocampal neurons

  Prolonged use of antidepressants increases BDNF production

Alternatives to antidepressant drugs:

Cognitive-behavioral therapy – equal effects for all levels of depression; increased metabolism in the same brain areas as antidepressants; reduces relapse into depression which is more likely after antidepressants

Exercise has modest antidepressant benefits – best as a supplement to other treatments

Supplements – omega-3 fatty acids and B vitamins 

Ectroconvulsive Therapy (ECT) - electrically induced seizure used for treatment of severe depression:

·         For patients who don’t react to antidepressants

·         Side effect: memory impairment 

·         High risk of relapse without  continued treatment

Dissociative identity disorder – multiple personality disorder.

Schizophrenia – emotional expression unconnected with current experiences; deterioration in everyday functioning for at least 6 months, delusions (illogical beliefs), hallucinations (false sensory experience), disorganized speech (rambling / incoherent), grossly disorganized behavior, weak emotional expression, speech and socialization.

Positive symptoms – behaviors that are present that should be absent: delusions, hallucinations, disorganized speech and behavior.

Negative symptoms – behaviors that are absent that should be present f. ex. Weak emotional expression, speech, socialization; stable over time and difficult to treat.

Causes of schizophrenia:Genetics, Prenatal and Neonatal Environment, Mild Brain Abnormalities,

Genetics-schizophrenia does not depend on any single gene.

Probability of schizophrenia increases with how closely related u are with someone suffering from it.

Monozygotic twins - have higher concordance (probability that a trait in one person will be shared by another) for schizophrenia than dizygotic twins.

Microdeletion – deletion of a small part of a chromosome, more common among ppl with schizophrenia.

For adopted children the disorder is more common in biological relatives than the adopting ones. 

prenatal influence – women with schizophrenia often abuse drugs, alcohol, eat a poor diet and have complications during pregnancy and delivery.

environmental influences – higher probability for schizophrenia if a mother has the disease and the child is in a dysfunctional adopting family.

Prenatal or neonatal influences – genetic, environmental or both – produce abnormalities in the developing brain; vulnerability to disturbances at critical periods in childhood and adolescence such 

Treatments

Chlorpromazine – relieves positive symptoms for most patients.

Later discovered other antipsychotic and neuroleptic drugs in two chemical families:

-          Phenothiazines – include chlorpromazine

-          Butyrophenones – include haloperidol

 \n Temporal lobe - learning, advanced visual processing), 

Occipital lobe -vision

Parietal lobe -body sensations

Postcentral gyrus -primary somatosensory cortex 

Parietal lobe -body sensation

Visual Pathways: Retina —> Optic Nerve —> Optic Chiasm —> Optic Tract. 

▪ The thalamus sends information about vision to the amygdala and to the primary visual cortex in the occipital lobe.

▪ The amygdala uses visual information to make quick emotional judgments, particularly about harmful stimuli.

▪ The primary visual cortex responds to object, shape, location, movement, and color.

Sound - waves

Amplitude

Frequency

Complexity

Outer ear - gather the sound; tympanic membrane vibrates when sound reaches it, then triggers ossicles

Middle ear - ossicles, the vibration then trigger vibration of the oval window

Inner ear - oval window transfers the vibrations to the fluid of the snail-shaped cochlea

Two Streams of Auditory Cortex:

Anterior auditory pathway−identifies the sound

Posterior auditory pathway−identifies where the sound is

Parallel processing (info flows between structures, simultaneously along multiple pathways), can switch and focus on different stimuli, attention - perception 

Somatosensory system: touch and pain

Exteroceptive cutaneous system: outside body

   Mechanical stimulation - touch 

   Thermal stimulation - temperature 

   Nociceptive stimuli - sturface pain

Proprioceptive system -body position

Interoceptive system -within body

Stereognosis - identification of objects by hands, use both fast and slow-adapting receptors. 

Tactile sensations are produced by multiple receptor mechanisms 

Vestibular system carries information about the direction and intensity of head movements, which helps us maintain our balance.

Chemical senses evaluate potential foods

Olfaction- the sense of smell, is the response to chemicals that contact the membranes inside the nose. For most mammals, olfaction is critical for finding food and mates and for avoiding dangers.

The receptors for taste are not true neurons but modified skin cells. Like neurons, taste receptors have excitable membranes and release neurotransmitters to excite neighboring neurons,which in turn transmit information to the brain.

The eyes, the organs of balance, and the receptors in skin, muscles, and joints monitor the body’s responses, and they feed their information back into sensorimotor circuits. 

ballistic movements—brief, all­or­none, high­speed movements, such as swatting a fly,not influenced by sensory feedback

Association cortex is at the top of the sensorimotor hierarchy. 

Two major areas of sensorimotor association cortex: 

the posterior parietal association cortex

the dorsolateral prefrontal association cortex. 

The posterior parietal association cortex directs behavior by providing spatial information, and in directing attention.

It receives information from the three sensory systems: 

the visual system, 

the auditory system

the somatosensory system

The dorsolateral prefrontal association cortex receives projections from the posterior parietal cortex - sends projections to areas of secondary motor cortex -to primary motor cortex - to the frontal eye field.

Areas of secondary motor cortex - receive much of their input from association cortex and send much of their output to primary motor cortex.

Areas of the secondary motor cortex are thought to be involved in the programming of specific patterns of movements after taking general instructions from the dorsolateral prefrontal cortex.

Mirror neurons - neurons that fire when an individual performs a particular goal-directed hand movement or when they observe the same goal-directed movement performed by another.

The primary motor cortex - is dedicated to controlling parts of the body that are capable of intricate movements, such as t__he hands and mouth__.

The neurons of the primary motor cortex play a major role in initiating body movements. 

The cerebellum and the basal ganglia interact with different levels of the sensorimotor hierarchy and, in so doing, coordinate and modulate its activities

Cerebellum-motor learning, particularly in the learning of sequences of movements.

basal ganglia - habit learning.

Neural signals are conducted from the primary motor cortex to the motor neurons of the spinal cord over four different pathways. 

Two pathways descend in the dorsolateral region of the spinal cord(dorsolateral motor pathways) and two descend in the ventromedial region of the spinal cord(ventromedial motor pathways)

The motor neurons activated by the two ventromedial tracts project to proximal muscles of the trunk and limbs (e.g., shoulder muscles), whereas the motor neurons activated by the two dorsolateral tracts project to distal muscles (e.g., finger muscles).

Motor units - the smallest units of motor activity.

A skeletal muscle comprises threadlike muscle fibers bound together in a tough membrane and attached to a bone by a tendon. 

Golgi tendon organs and muscle spindles-monitor the activity of skeletal muscles.

Acetylcholine - activates the motor end-plate on each muscle fiber and causes the fiber to contract. Released by motor neurons at neuromuscular junctions.

Contraction - a method that muscles have for generating force, muscle can generate force in only one direction. All of the motor neurons that innervate the fibers of a single muscle are called its motor pool.

Fast muscle fibers - contract and relax quickly. quick movements such as jumping.

Slow muscle fibers - slower and weaker, capable of more sustained contraction. gradual movements such as walking.

Each muscle has both fast and slow fibers.

Flexors act to bend or flex a joint, and extensors act to straighten or extend it.

Cocontraction - the simultaneous activation of muscles on opposite sides of a joint

Movements produced by cocontraction are smooth, and they can be stopped with precision by a slight increase in the contraction of the antagonistic muscles. 

Motor equivalence-same basic movement can be carried out in different ways involving different muscles. 

Sensorimotor system - fundamentally plastic. General commands to act are issued by cortical circuits, but exactly how an act is actually completed depends on the current situation (e.g., body position). The sensorimotor system maintains the ability to change itself in response to practice.

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