Ch1 - the nervous system + Ch2 - how neurons work + Ch11 - Reward, Reinforcement, and Addiction + Ch12 - stress, fear, and anxiety

What are the two main types of cells in the nervous system?

Neurons and glia

What are neurons?

Neurons are the fundamental units by which information moves through the nervous system. Sights, sounds, thoughts, memories - all depend upon communication between neurons.

What are the four major components of a neuron?

Cell body, dendrites, axon, terminal

What is the function of neurotransmitters?

They cross a synaptic cleft to communicate with receiving neurons; neurons release them

What role do astrocytes play in the nervous system?

They store substances (e.g., nutrients) for future use by nearby neurons.

What is the function of oligodendrocytes?

They form the myelin sheath around axons in the central nervous system.

What do Schwann cells do?

They produce myelin in the peripheral nervous system.

What is the role of microglia?

They remove debris left by damaged or dead neurons and are #tiny

What is the function of radial glia?

They guide newly born neurons to their final destinations in the brain.

What distinguishes gray matter from white matter in the brain?

Gray matter contains cell bodies and dendrites, while white matter consists of myelinated axons.

What are the three types of brain slices?

1) coronal/frontal (both hemispheres seen at once; like looking at someone's face)

2) sagittal (one hemisphere = side profile)

3) horizontal (both hemispheres seen but from the top)

What does the central nervous system (CNS) consist of?

The brain and spinal cord.

What is the function of the peripheral nervous system (PNS)?

It allows communication between the CNS and the rest of the body.

What does the somatic nervous system do?

Carries sensory information to the CNS and controls body movements.

What does the autonomic nervous system do?

It allows the CNS to communicate with the organs of the body

What are the two divisions of the autonomic nervous system?

Sympathetic division and parasympathetic division

What is the function of the sympathetic division?

Prepares the body for emergency situations (fight or flight).

What does the parasympathetic division do?

Restores resting state and stores energy (rest and digest).

CRANIAL NERVE I: olfactory nerve

Sense of smell

CRANIAL NERVE II: optic nerve

Vision

CRANIAL NERVE V: trigeminal nerve

It carries touch and pain sensations

CRANIAL NERVE VI: abducens nerve

eye movements

CRANIAL NERVE VII: facial nerve

Face muscles and taste.

CRANIAL NERVE VIII: auditory nerve

Hearing and balance.

CRANIAL NERVE IX: glossopharyngeal

muscles of throat and larynx, taste

CRANIAL NERVE X: vagus nerve

Internal organs, particularly in the parasympathetic system.

CRANIAL NERVE XI: spinal accessory

neck muscles

CRANIAL NERVE XII: hypoglossal

tongue movements

Brain imaging techniques such as CT scan or MRI…

…require the individual to place the head in a doughnut-shaped scanner while multiple brain images are collected

What is the role of the spinal cord?

• It carries tactile info from the skin up to the brain and sends signals down from the brain to control body movements.

• The central portion of the spinal cord is shaped like a butterfly and contains the cell bodies of neurons whose axons can cause muscles to contract

What is the central canal in the spinal cord?

It runs through the length of the spinal cord and connects to the brain's ventricles.

What is the primary role of cerebrospinal fluid?

• Helps keep the brain buoyant

• Acts as a cushion from mechanical damage

• Assists in maintaining chemical stability

• Carries nutrients to the brain

  • Lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle, central canal

What structures make up the brainstem?

Medulla, pons, cerebellum, and midbrain.

What are the functions of the medulla and pons

They contribute to processes critical for maintaining life, sleep and arousal, and basic sensory and motor responses

What is the primary function of the cerebellum?

It coordinates body movements and maintains balance.

What is the function of the midbrain?

• Connects the cell bodies of the DA neurons that play a key role in reinforcement, addiction, and the energizing effects of natural rewards

• Also contains inferior colliculi that direct attention to new auditory stimuli, and superior colliculi that direct attention to new visual stimuli

What is the role of the thalamus?

It acts as a relay for sensory information to the cerebral cortex.

What does the hypothalamus regulate?

Motivated behaviors such as sex, eating, and thirst.

Gateway to the cortex and a center for motivation: the diencephalon

• tiny gland, tucked in a groove between the left and right thalamus.

• the two key structures of the diencephalon are the thalamus and hypothalamus

THALAMIC NUCLEI TO KNOW: dorsomedial nucleus

memory

THALAMIC NUCLEI TO KNOW: medial geniculate nucleus

audition

THALAMIC NUCLEI TO KNOW: lateral geniculate nucleus

vision

THALAMIC NUCLEI TO KNOW: ventral posterior nucleus

touch, pain

THALAMIC NUCLEI TO KNOW: ventral anterior nucleus

bodily movement

HYPOTHALAMIC NUCLEI TO KNOW: paraventricular nucleus

release of stress hormones

HYPOTHALAMIC NUCLEI TO KNOW: preoptic nucleus

sleep/wake cycle

HYPOTHALAMIC NUCLEI TO KNOW: anterior hypothalamic area

sexual behavior

HYPOTHALAMIC NUCLEI TO KNOW: lateral hypothalamic area

eating/arousal

HYPOTHALAMIC NUCLEI TO KNOW: posterior hypothalamic area

maintains body temperature

Voluntary movement: the basal ganglia

Collection of brain regions critical for voluntary behaviors such as opening a door or reaching for a cup. Also involved in forming automized habits over the course of repeated practice

• striatum + globus pallidus

  • striatum comprised of the caudate and putamen

Memory and emotion: the limbic system

Two key components of the limbic system are the amygdala, which learns to recognize signs of imminent threat, and the hippocamous, which is critical for storing and recalling memories of our experiences

Senosry, motor, and higher cognitive processes: the cerebral cortex

• The cerebral cortex is where we see, hear, and sense touch, and generate instructions to move our body parts. It also carries out the complex cognitive processes, such as language, that define human species

• the human cortex contains gyri (hills) and sulci (valleys) that allow an enormous amount of brain tissue to fit within the skull

What are the four lobes of the cerebral cortex?

Frontal, parietal, occipital, and temporal lobes.

Lateral sulcus

Divides frontal from parietal and temporal lobe

Central sulcus

Divides frontal from parietal lobe

Longitudinal fissure

Divides both hemispheres

Cortex organization

6 distinct neuronal layers, each with different cell types and functions. Different stains reveal different aspects of cortical organization: structure vs. cell density

What is the function of the prefrontal cortex?

It is important for cognitive functions such as attention and working memory.

What distinguishes gray matter in the spinal cord from that in the brain?

In the spinal cord, gray matter is on the inside, while in the brain, it is on the outside.

What is the role of a sensory neuron in neurotransmission?

A sensory neuron carries information about environmental stimuli.

What does a motor neuron do?

A motor neuron causes muscles to contract.

What happens when a sensory neuron responds to heat?

• It sends a signal that excites the spinal cord neuron.

• Signals travel from one neuron to another

How does the brain influence the spinal cord neuron when holding an expensive cup?

• The sensory neuron responds to the heat of cup

• It sends a signal that excites the spinal cord neuron

• The brain recognizes that the cup is expensive and sends a signal that inhibits the spinal cord neuron

• The inhibitory signal from the brain cancels out the heat signal from the sensory neuron

What is the order of signal movement in a neuron?

Dendrites → Cell body → Axon → Axon terminal.

What happens when a signal reaches the axon terminal?

A neurotransmitter is released and crosses a synaptic cleft.

What are the steps involved in a chemical synapse?

1. NTs are synthesized and stored in vesicles

2. Action potential arrives at the presynaptic terminal

3. VGCCs open, allowing calcium influx

4. Calcium allows vesicle docking and neurotransmitter release.

5. NT binds to receptors, causing channel opening or closing

6. Excitatory or inhibitory postsynaptic potential is generated

7. NT is removed

8. The vesicular membrane is retrieved from the plasma membrane

What are the five outcomes for neurotransmitter removal?

1. Glial uptake.

2. Enzymatic degradation.

3. Astrocytes.

4. Reuptake.

5. Vesicular membrane retrieval.

What is the significance of sodium ions in neuronal activation?

Sodium ions entering the neuron are critical for thoughts, emotions, and behavior.

What does the neuron consist of?

• A thin cell membrane separates the inside from the outside of a neuron

• High concentrations of sodium and chloride ions are found OUTSIDE the neuron in the extracellular fluid; INSIDE the neuron are large, negatively charged proteins and potassium ions

What is the typical membrane potential of a resting neuron?

About -70mV (70mV more negative inside compared to outside).

What is required for a neuron to fire an action potential?

• The membrane potential must reach a critical level of depolarization known as the firing threshold.

• Sodium channels are located within the membrane that surrounds the neuron.

• When the channels open, sodium ions can move from the extracellular fluid to the inside of the neuron (intracellular fluid)

types of VGCCs

1) High voltage-activated

• Open ~20-40mV

• Cavα1 + ancillary subunits

• Result in L, P/Q, N, R-type currents

2) Low voltage-activated

• Open ~30-60mV

• No ancillary subunits

• Result in T-type current

Subunit composition of Cavα1 subunit

• 4 transmembrane domains --> Each with 6 membrane helices

• S4 segment - voltage sensor

• S5-S6 - pore loop

• Cytoplasmic loops --> Variation among Cav channels

  • Regulation:

    • For eg. 3 = synaptic protein interaction site

• Places VGCC close to Syntaxin-1, SNAP25

Calcium-triggered vesicle fusion and exocytosis of NTs

SNARE proteins: V (vesicle) and T (target)

• SNARE: soluble N-ethylmaleimide sensitive factor attachment protein receptors

• SNAP25: synaptosome-associated protein of 25kD

Neurotransmitters are released

The arrival of the action potential at the axon terminal causes exocytosis, the merging of NT vesicles with the membrane and release of NT into the synaptic cleft

Neurotransmitters bind to receptors

A neurotransmitter is released from the presynaptic neuron, crosses the synaptic cleft, and binds to a receptor in the postsynaptic neuron

Neurotransmitters are cleared from the synapse

Neurotransmitters are cleared from the synapse by reuptake and/or degradation by enzymes

Ionotropic receptors

• When a neurotransmitter binds to the ionotropic receptor, an ion channel opens within the receptor itself

  • = directly allows for ions to pass through; very fast and direct

Metabotropic receptors

• The metabotropic receptor takes its name from the fact that neurotransmitter binding initiates several metabolic steps (usually involving G-proteins and enzymes) that may lead to opening of ion channels within the membrane, not within the receptor itself

Membrane potential

• By placing an electrode on the interior side of the neuron's membrane and another on the exterior side, a voltmeter calculates the difference in charge across the membrane, i.e. the membrane potential

• At rest, most neurons have a membrane potential of about -70mV (= 70mV more negative inside compared to outside the neuron)

Reaching the firing threshold

• The membrane potential must reach a critical level of depolarization for the neuron to fire. This is the neuron's firing threshold

• When the firing threshold is reached at the axon hillock, the neuron fires an action potential, which sweeps along the axon until reaching the terminal

Myelinated axons permit saltatory conduction

• Some neurons have bands of myelin surrounding the axon. - Between each band of myelin are spaces called nodes of Ranvier

• In myelinated axons, the action potential "jumps" from one node to the next. This is called saltatory conduction

• Saltatory conduction greatly increases the speed of the action potential as it sweeps across the axon

What is saltatory conduction?

It is the process where the action potential 'jumps' from one node of Ranvier to the next in myelinated axons, increasing the speed of conduction.

What are the two most abundant neurotransmitters in the brain?

Glutamate (GLU) and GABA.

How does glutamate function as a neurotransmitter?

GLU is almost always excitatory; it depolarizes neurons to which it binds.

What is the effect of GABA on neurons?

GABA is almost always inhibitory; it hyperpolarizes the neuron to which it binds.

What is an excitatory postsynaptic potential (EPSP)?

An EPSP is a depolarization that increases the neuron's likelihood of firing.

• A neurotransmitter is excitatory at a synapse if it causes the opening of channels that allow the entry of positively charged ions, such as sodium

What is an inhibitory postsynaptic potential (IPSP)?

An IPSP is a hyperpolarization that decreases the neuron's likelihood of firing

• A neurotransmitter is inhibitory at a synapse if it interacts with a receptor to produce an IPSP, or hyperpolarization, and decreases the neuron's likelihood of firing (Inhibitory Postsynaptic Potential)

What is the role of VGCCs in neurotransmission?

Voltage-gated calcium channels (VGCCs) open to allow calcium influx, which triggers neurotransmitter release.

What is the significance of the action potential sweeping across the axon?

It allows for rapid transmission of signals along the neuron.

How do sodium channels contribute to action potential propagation?

Sodium channels open sequentially along the axon, causing depolarization that propagates the action potential.

What happens during exocytosis at the axon terminal?

Neurotransmitter vesicles merge with the membrane, releasing NT into the synaptic cleft.

What is shaping by successive approximations?

A method where a target behavior is gradually molded by rewarding increasingly accurate approximations of the behavior.

• As scientists, they are creating a pattern of behavior to show their response to XX

What is positive reinforcement?

A process in operant conditioning where a behavior is followed by a reinforcer, increasing its frequency.

What is operant conditioning?

A behavior that is followed by a reinforcer is acquired (increases in frequency), and if an acquired behavior is no longer followed by a reinforcer, the behavior extinguishes (decreases in frequency)

What is operant learning? (aka instrumental learning)

a subject learns a relationship between a behavior (pressing a lever, injecting a drug) and a particular outcome (receiving food into the mouth or heroin into the bloodstream). If the outcome is rewarding, the behavior is repeated.

What are primary reinforcers?

Innate stimuli that reinforce behavior by innate mechanisms, such as food when hungry, water when thirsty, and sex when aroused.

What are conditioned reinforcers?

Stimuli that acquire their reinforcing properties through association with primary reinforcers, like money.

What is Pavlovian conditioning?

A learning process where a conditioned stimulus (CS) becomes associated with an unconditioned stimulus (US) that is rewarding.

• For instance, a street corner (CS) may be associated with heroin (US), or a tone (CS) may be associated with food (CS)

• Pavlonian conditioning can also lead to an association between a CS and an aversive outcome (US) such as a robbery or physical pain

What is the medial forebrain bundle (MFB)?

A brain region where stimulation can improve mood and is associated with reward processing.

• Stimulation of the MFB improves mood in depressed patients --> Humans with treatment-resistant depression who have opted for brain stimulation to the MFB report positive effects on their mood