Brain, Mind, & Behavior: Exam 1

Boston College, Fall 2024

Axon Hillock

A specific place inside the soma, or cell body, that decides whether information is interesting enough to send to other neurons. It essentially combines input received and decides whether or not to send a signal.

Axonal Terminals

The output center of the neuron (also called synaptic boutons / buttons)

Dendrites

Cellular extensions off of the soma where neurons receive information via synapses from other neurons. This is where information comes into the neuron.

Myelin Sheath / Myelination:

The process in which glial cells wrap axons w/ a fatty sheath called myelin to insulate and speed conduction. White matter = cells that are coated in myelin, gray matter = different parts of cells that are not coated in myelin.

Nodes of Ranvier

The gaps between sections of myelin where the axon is exposed. Allows for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon. 

Presynaptic / postsynaptic neurons

Presynaptic: On the axon terminal of the presynaptic neuron, sends signals to the postsynaptic neuron across the synapse. Postsynaptic: On the dendrite / cell body of the postsynaptic neuron, receives signals from a presynaptic neuron through the synapse. 

Synaptic vesicles

A small secretory vesicle that is found inside an axon near the presynaptic membrane, and contains neurotransmitters which are released into the synaptic cleft after fusing with the membrane.

Synaptic cleft

The gap that separates the membranes (space between pre and postsynaptic membranes)

Synapse

Point where information is transmitted from neurons to other neurons (or other muscles /glands). Almost a contact point between two neurons. 

Multipolar neuron

One axon, many dendrites

Bipolar neuron

one axon, one dendrite

Monopolar neuron

a single body extension, branching in two directions: dendrites and axon

Ganglion

A collection of neurons in the PNS (pink)

Nerve

A collection of axons in the the PNS (pink)

Nuclei

A collection of neurons in the CNS 

Nerve fibers

A threadlike extension of a neuron, and consists of an axon and myelin sheath. 

Fiber tracts

A collection of axons in the CNS

Astrocytes

Star-shaped cells with many processes that stretch around and between neurons, clean up waste, mediate the brain / blood barrier, secrete chemicals, and help for the outer membrane of the brain

Oligodendrocytes

Form the myelin sheaths in the brain and spinal cord

Schwann cells

provide myelin to neurons outside the brain and spinal cord

Microglia

Tiny, mobile cells that remove debris from injured or dead cells; the brain’s resident immune cells; synaptic remodeling, shaping circuits in the brain

CNS

Central nervous system, brain and spinal cord

PNS

Peripheral nervous system, everything else

Somatic nervous system

 Nerves that interconnect CNS and the major muscles and sensory systems of the body

Autonomic nervous system

Nerves that connect to the viscera (other organs)

Cranial nerves

1. Olfactory; smell (sensory)

2. Optic; vision / sight (sensory)

3. Oculomotor; muscle that moves the eyes (motor) 

4. Trochlear; muscles that moves the eyes (motor) 

5. Trigeminal; face, sinuses, teeth (sensory) and jaw muscles (motor)

6. Abducens; muscle that moves the eyes (motor)

7. Facial; tongue, soft palette (sensory) and facial muscles, salivary glands, tear glands (motor)

8. Vestibulocochlear; Inner ear– hearing and balance (sensory)

9. Glossopharyngeal; Taste + other mouth sensations (sensory) and throat muscles (motor)

10. Vagus; information from internal organs (sensory) and internal organs (motor)

11. Spinal accessory; neck muscles (motor)

12. Hypoglossal; tongue muscles (motor)

Spinal nerves

Connected to the spinal cord; 31 pairs 

Sympathetic nervous system

“Fight or flight”, exits the middle of the spinal cord, ganglia in spinal column, norepinephrine (adrenaline)

parasympathetic nervous system

“Rest and digest”, exits the brainstem or the base of the spinal cord, ganglia are peripheral, acetylcholine 

Standard conventions for describing the brain

• Medial: Towards the middle

• Lateral: Towards the sides

• Ipsilateral: Same side

• Contralateral: opposite side

• Superior: above

• Inferior: below 

• Basal: towards the bottom

• Anterior / rostral: Head end (front)

• Posterior or caudal: Tail end (back)

• Proximal: near the center, close

• Distal: towards the periphery, far

• Dorsal: towards the back, top

• Ventral: towards the belly, bottom

• Afferent: carries information into a region of interest

• Efferent: carries information away from a region of interest 

Forebrain —> Telencephalon —> Cerebral Cortex

1. Cerebral cortex^: Made up of the frontal lobe (in the front), which includes the motor cortex and allows us to move the different parts of our body, the parietal lobe (upper back), which includes somatosensory cortex where out body sensations of touch, temperature, limb position, and pain are processed, the occipital lobe (at the very back), which helps with visual processing, distance and depth perception, memory, object / face recognition, and the temporal lobe (by the temples), which manages emotions, processes information from senses, stores and receives memory, and understands language.

 

• Layer 1: Almost no cells (maybe a few axons)

• Layers 2 + 3: Mostly local circuit neurons (communication is projecting in those layers)

• Layer 4: Mostly neurons that receives thalamic input (sensory information)

• Layers 5+6: Mostly output and projection neurons.

• There are axons and myelin below layer 6, these sometimes have pyramidal cells

Forebrain —> Telencephalon —> Basal Ganglia

1. *Basal Ganglia: Essentially regulates motor control, motivation / reward, and habit learning 

–Dorsal striatum: Regulates motor control, vocabulary motor control, and different types of learning. Made up of the caudate nucleus and putamen.

–Ventral striatum: Nucleus accumbens (reward center, where dopamine gets dumped)

–Pallidum: Made up of globus pallidum (dorsal pallidum) and ventral pallidum (connected to striatum)

Forebrain —> Telencephalon —> Limbic System

1. *Limbic System:  Includes structures important for emotion and learning / memory

–Amygdala: Emotional regulation, perception of odor in the temporal lobe, emotional processing

–Hippocampus: Learning / memory, spatial awareness (lies mostly in temporal lobe)

–Cingulate gyrus: Attention

–Olfactory bulb: sense of smell

Forebrain —> Diencephalon

a. Thalamus: The body’s information - relay system. All information from the senses, except smell, must be sent to the thalamus to be processed before being sent to the cerebral cortex. 

b. Hypothalamus: Involved in many vital functions including homeostasis, temperature regulation, thirst, hunger, sex, aggression

Midbrain —> Mesencephalon

Tectum: Superior colliculi (visual processing) and inferior colliculi (auditory processing) 

Tegmentum (SN, VTA, PAG):

1. Substantia nigra: Major input to the motor components of the basal ganglia 

2. Ventral tegmental area: Major input to the motivation / reward components of the basal ganglia (makes dopamine)

3.  Periaqueductal gray: Pain + threat (has pain receptors)

4. Reticular formation: Found throughout brainstem, sleep + arousal

Hindbrain —> Metencephalon

1. Cerebellum: Crucial for motor coordination and control, balance (alcohol affects these motor receptors)

2. Pons: Contains a variety of sensory and motor related nuclei important for relaying those types of messages to or from the brain ( some of these are also in the midbrain)

Hindbrain —> Myelincephalon

Medulla: Drives essential bodily functions like respiration, heart rate, and blood pressure (also contains reticular zone)

The meningeal layers

1. Dura mater: Tough outermost layer

2. Arachnoid membrane: Lies between the other two; filled with cerebrospinal fluid (CSF)

3. Pia mater: Delicate innermost layer

Where is the reticular formation and what is its main function?

The reticular formation is located in the tegmentum of the midbrain and is vital in sleep and arousal.

Permeability

The cell membrane of neurons has selective permeability, which is the property of a membrane that allows some substances to pass through but not others

Diffusion

Causes ions to spread towards a uniform concentration along a concentration gradient. Moves from high to low concentration. Ex: Na channels at beginning of action potential.

Electrostatic pressure

Causes ions to flow towards oppositely charged areas, and away from similarly charged areas. Like charges repel, opposites attract.

undated ion channel

An ion channel that stays open all the time and allows all ions to pass through

Active transport pump

The energy - requiring process of pumping molecules and ions across membranes against a concentration gradient. 

voltage gated channel

An ion channel that opens and closes in response to voltage changes in the membrane. Activated by changes in a cell’s electrical membrane potential near the channel.

Describe what is meant when we say action potentials are “all or none”

–The sum of the inputs (EPSP and IPSP) must reach a threshold, only when this is reached does the action potential occur.

Phases of the Action Potential

- Resting potential phase: The stable electrical charge across a neuron's membrane when it is not actively sending signals, typically ranging from -50 to -80 mV. Both Na and K are closed. 

- Local graded potential phase(EPSP vs IPSP) – inputs that the dendrites receive, can either be inhibitory or excitatory: Applying a stimulating response to a neuron that either hyperpolarizes (inhibitory) or depolarizes (excitatory). These cause a graded potential. -65 to -40 mV. Both Na and K are closed.

- Depolarization or Rising phase: The cell becomes depolarized, or gradually less and less negative. This is when the Na channels are open because they allow positive ions to flow into the cell, making it more positive. K channels closed, -40 to 30 mV.

- Repolarization or Falling phase: The cell begins to get more negative on the inside again, meaning that the positive K+ channels are open and ions are rushing out, but Na+ channels are closed. 0 to about -65 mV

- Hyperpolarization or Afterpotential phase: The inside of the cell becomes more negative, or hyperpolarized, because K+ channels open and positive ions rush out of the cell while the Na+ channels are closed. -65 mV and below.

Refractory period

Occurs at the top of the action potential, at the most positive point. Na channels are closed, K channels are open. About 40 mV.

Relative refractory phase

Subsequent stimulation is less able to trigger an action potential

Absolute refractory phase

Subsequent stimulation is unable to trigger an action potential.

The process of neuronal communication

- What happens when Neuron 1 receives input?

-When neuron 1 receives input, there will be a change in the membrane potential (Either EPSP or IPSP) 

- How does Neuron 1 make the “decision” to initiate an action potential

–When the sum of EPSPs and IPSPs reaches a threshold, the action potential will fire.

- How does Neuron 1 propagate the action potential?

–Travels in one direction down the axon  (also saltatory conduction – jumping from one node to the next)

- What happens when the action potential reaches the terminal?

-Neurotransmitters are released from the end of the presynaptic terminal. Voltage gated calcium channels open, Ca ions enter into the presynaptic terminal .

 - How is the message transmitted to Neuron 2?

–The neurotransmitters travel across the synapse and bind to the receptors of the postsynaptic neuron.
- What happens when Neuron 2 receives the message?

–The ion channels of the postsynaptic neuron will open and the flow of ions will cause a membrane potential. 

- How is synaptic transmission terminated?

–Degradation or reuptake 

Neurotransmitters may also activate presynaptic receptors, or autoreceptors, that decrease neurotransmitter release. These receptors regulate themselves on the presynaptic terminal. 

Endogenous ligand

Neurotransmitters and hormones are endogenous ligands, meaning they are made by our body.

exogenous ligand

 Drugs and toxins from outside the body are exogenous ligands. 

Ionotropic receptors

 Ligand gated ion channels that quickly change shape to open or close the channel (pore) when a transmitter molecule binds. It needs a ligand to bind to the receptor for it to open. Faster acting, their primary function is to transmit the signal from the presynaptic neuron.

Metabotropic receptor

(aka G protein coupled receptor, GPCR) cell membrane spanning proteins attached to an intracellular protein complex. Slower acting, effects are often more modulator and / or long lasting: changing cell excitability, changing cell structure and / or function, changing protein / enzyme / neurotransmitter making 

–The attached intracellular protein is released when the ligand attaches to the receptor binding site. 

–Sometimes opens channels or may activate another chemical known as a second messenger to affect ion channels … or produce other intracellular effects.

Excitatory

Depolarizing (less negative)

Inhibitory

Hyperpolarizing (more positive)

Neurotransmitter requirements

-Is synthesized in presynaptic neurons and shared in axon terminals.

–Is released when action potentials reach axon terminals

–Is recognized by receptors on the postsynaptic membrane

–Causes changes in a postsynaptic cell 

–Blocking its release w/ a presynaptic cell’s ability to affect a postsynaptic cell.

Amino acid neurotransmitters

• Glutamate (glutamic acid) – most widespread excitatory neurotransmitter 

• Ionotropic receptors: AMPA (Na+), NMDA (Na+ and Ca2+ - learning and memory!), Kainite, these depolarize cell and increase possibility of AP 

• Metabotropic receptors: mGLUR1-8, 

• GABA (most widespread inhibitory neurotransmitter) 

• Ionotropic receptors: GABAa + GABAc, Cl-, hyperpolarize and decrease AP chance 

• Metabotropic receptors: GABAb

Quaternary amines

• Acetylcholine: many cholinergic cell bodies are found in the basal forebrain (up front, down bottom of brain) and send projections throughout the forebrain. Basal forebrain to cortex, amygdala, and hippocampus. Another population of cholinergic cell bodies in the midbrain projects to the hindbrain. Involved in arousal, attention, learning / memory, muscle contraction. 

• Norepinephrine: (NE, aka noradrenaline): Noradrenergic cell bodies are found in the reticular formation. Locus coeruleus sends projections throughout the forebrain. Lateral tegmental area sense projections to the brainstem and spinal cord. Important for alertness and mood.
  

• Dopamine (DA): Most dopamine cell bodies are found in the midbrain, specifically within the tegmentum. Sends projections throughout the brain to nucleus accumbens and cortex. Involved in motor function, reward, aversion, motivation, learning. Binds to D2, inhibitory and metabotropic 

• Serotonin: Serotonergic cell bodies originate along the midline of the brainstem in the raphe nuclei. Sends projections throughout CNS. Involved in mood, vision, anxiety, sexual behavior, sleep. 

Neuropeptides

•  Endogenous opioids: Enkephalins, endorphins, and dynorphins.

• Synthesized throughout the brain, and send projections throughout the CNS

• Involved in pain, pleasure, mood

Other peptide hormones, such as oxytocin and vasopressin, contribute to memory and pair-bonding.

Gas transmitters (nitric oxide)

Are produced mainly in dendrites, are not stored in synaptic vesicles, diffuse out of the neuron as soon as they are produces, no receptors are involved, they diffuse into the target cell and activate second messengers, can function as retrograde transmitters (can work backwards) by diffusion from the postsynaptic neuron back to the presynaptic neuron. Can essentially ooze in and out of the cell as they please

Endocannabinoids (lipids)

Anandamide, 2-arachidonoyl glycerol. Act as retrograde transmitters and are made in the brain, involved in synaptic plasticity, mood, appetite, pain, sleep, can work backwards and have effects on presynaptic. Found in the brain, muscle, fatty tissue, and immune cells. 

3 layers that form in developing embryo

Ectoderm: Outside packaging (skin), but also CNS and PNS nervous system

Mesoderm: Structural components (bones, great muscle masses, structure of internal organs)

Endoderm: Cell systems that line the organs and vessels 

Define neuroectoderm: The region that gives rise to the entire nervous system (Both PNS and CNS)

Neurulation

The crests of the neural plate join, forming the neural tube. The edges buckle up.

Neural plate

serves as the basis for the nervous system

Neural groove

The depressed mid-region from the formation of neural folds

Neural folds

Extend towards the dorsal midline where they meet and fuse. In the neural crest, cells migrate to become the peripheral nervous system, or the folds.

Neural tube

Formed during neurulation, the neural tube will give rise to the nervous system in vertebrates. 

Central canal

Forms the ventricular system and the central canal of the spinal cord

When does a neural tube defect occur?

Occurs when crests fail to close properly

Anencephaly

Failure of the neural tube to close at the rostral (head on) end

Spinal Bifida

Failure of the neural tube to close at the caudal (tail) end

Folic acid

can prevent neural tube defects

3 primary brain vesicles and 5 secondary brain vesicles

Prosencephalon (forebrain) → telencephalon and diencephalon

Mesencephalon (midbrain) → stays the same

Rhombencephalon (hindbrain) → metencephalon, myelencephalon

6 stages of brain development

1. Neurogenesis: Mitosis produces neurons from non - neuronal stem cells, forming the ventricular zone. Proliferation of cells occurs quickly after the neural tube forms. Neural progenitors, or stem cells in the ventricular zone divide to produce neurons – this is neurogenesis.

2. Cell migration: Cells move out of the ventricular zone toward their destination, where they form distinct populations of neurons – when they find their resting location. These cells move over relatively long distances to fill out the brain. Special cells called radial glia assist many cells in migration. They radiate out the width of the neural tube. New neurons use the radial glia as guides to help them move.

3. Cell differentiation: Cells express particular genes and become distinctive types of neurons through cell-cell interaction. Factors can help neurons to grow the right things. This enables cells to acquire the distinctive appearances and functions of neurons characteristic of their particular region. 
   

4. Synaptogenesis: Establishment of synaptic connections. Synaptic formation occurs through signals from presynaptic and postsynaptic cells. Cells send chemical signals to one another, and these cell - cell interactions are important in the location and formation of synapses (starts very slow and sluggish) 

5. Cell death: Selective death of many neurons. Particularly in early development, many neurons die. Some may die due to a lack of synaptic contacts, some die of neurosis / inflammation, some die due to a process called apoptosis - a programmed cell death, or self destruct.

6. Synaptic rearrangement: Loss or development of synapses, fine-tuning (synapses adapt and change). Neurons form synapses onto many post-synaptic neurons. During synaptic rearrangement, the synaptic contacts of each axon become focused on a smaller number of cells (they only go to one).

2 types of migration

Radial: Follow poles by radial glia

Tangential: Swing from one glia to the next

Factors that contribute to significant brain growth following birth

Factors: Growth of neurons, dendritic branching, synaptogenesis, myelination, new glia 

Where does adult neurogenesis occur?

In the hippocampus

Pups of high cars moms vs low care moms

-Pups of high-caring dams receive more tactile stimulation

-Lower care = higher stress response as adults

-Low licking = lower levels of stress receptors

-High licking = higher levels of stress receptors

Main commissures

• Cerebral commissures connect two halves of the brain

• Ex: Anterior (front) commissure

• Posterior (further back) commissure 

• Corpus callosum: Largest cerebral commissure, which transfers learned information from one hemisphere to the other

Contralateral

• Information from one side of the body is processed on the opposite side of the brain. Left brain → information on the right, right brain → information on the left.

Method used to study split-brain individuals

• Scientists presented pictures and words to the different visual sides to test activity in each hemisphere (a commissurotomy) 

The results of these split-brain experiments

• The two hemispheres do something completely different – usually the stimulus presented to the left side gets stuck in the right side of the brain, while the information from the right visual side is processed normally. 

• Split-brain participant: Info gets stuck in right side of the brain – the two hemispheres are doing something different 

• Present picture in right visual field (left brain): Left hemisphere can tell you what it was; right hand can show you, left hand can’t 

• Present picture in left visual field (right brain): Subject will report that he does not know what it was, left hand can show you what it was, right hand can’t. 

• Left hemisphere can tell + show what it has seen, the right hemisphere can only show it (cannot be repeated verbally).

What does this tell us about lateralization?

• The right brain struggles with processing information while the left brain does not. 

Right ear advantage during dichotic presentations and why does it occur

• Dichotic presentations: Delivers different sounds to each ear at the same time. Eg, a participant will hear a speech sound in the right ear, and a different word in the left ear.

• Right handed people identify verbal stimuli delivered to the right ear more easily – a right ear “advantage”. 

• Up to 50% of left-handed people show a reduced or reversed pattern: no difference between ears, or left ear advantage. 

• When conflicting info goes to both ears, the information to the right ear reaches the left hemisphere speech system first (right ear advantage). So, the subject repeats only the right-ear information.

Asymmetry in the planum temporale

• The planum temporale is an area of the temporal cortex that is larger in the left hemisphere of 65% of people. Size of this area differs from infancy (before the development of language).

• People (and chimps) tend to show a strong preference for using their right hand when this occurs.

• The left hemisphere is more activated in monkeys when they hear other monkey vocalizations rather than human speech.

Left and right hemisphere specializations (music)

• Right hemisphere specializations: Perception of music. Musical perception is impaired by damage to the right hemisphere. Music activates the right hemisphere more than the left.

• Prosody: The perception of emotional tone aspects of language, yet is a right hemisphere specialization.

• Left hemisphere specializations: Recognizing rhythms of notes is a left-hemisphere specialization. Perfect pitch relies on left-hemisphere mechanisms.

Right hemisphere specialization

• Right hemisphere is more adept at comprehending spatial relationships:

–Geometric shapes

–Direction sense and navigation

–Face processing 

–Mental rotation of 3D objects

Damage to the right hemisphere can cause visuospatial impairments such as astereognosis, which is the inability to recognize objects by touch.

Prosopagnosia

• Prosopagnosia: (face blindness) is the inability to recognize faces, including one’s own

• The fusiform gyrus in inferotemporal cortex is usually damaged in cases of prosopagnosia

• Prosopagnosia can also be present at birth – developmental (congenital) prosopagnosia.

Aphasia + conditions that usually co-occur with it

Aphasia: Impairment in language ability, to varying degrees, caused by brain injury, especially to the left hemisphere.

• Agraphia: Impairment in writing

• Alexia: Impairment in reading

• Apraxia: Motor impairment: difficulty in making sequences of movements

What are Broca and Wernicke’s area important for?

Broca: Speech production

Wernicke: Comprehension

What happens if Broca / Wernicke area is damaged?

Broca: Produce nonfluent or Broca’s aphasia – difficulty with producing speech, but not with comprehension. Automatic speech is often preserved. Many people with nonfluent aphasia also have hemiplegia, paralysis of one side of the body, usually the right side.

Wernicke: Fluent (or Wernicke’s) aphasia: fluent, meaningless speech but lots of verbal output. Can speak but not comprehend. Accompanied by many paraphasias (sound or word substitutions). 

Minimal language comprehension; impaired ability to repeat words or phrases; and may also include anomia (difficulty naming persons or objects)