Intro to Psychology basic processes - Chapter 3: Biological bases of behaviour

Neurons

Individual cells in the nervous system that receive, integrate, and transmit information from different parts of the brain to other areas of the brain and spinal cord.

Neurons (con’t)

We have about 86 billion neurons, and different neurons do different things (neurotransmitters)

Soma (nucleus)

The cell body of the neuron.

Dendrites

The arms (i.e tree branches) of the neuron that gather and receive communication from other neurons by

Dendrites (con’t)

Increases the surface area of the neuron so that chemicals (released from other cells) can influence the activity of the neuron that the dendrites belong to

Axon

A long structure that gives length to the neuron and carries information away from the cell body.

Axon Terminal

The end of the axon that communicates information to other postsynaptic neurons.

Axon Terminal (con’t)

Where chemicals are released by the neuron to influence the activity of other neurons

Myelin Sheath

A type of glial cell that insulates the axon to speed up communication and allow for faster reflexes.

Myelin Sheath (con’t)

The loss of muscle control resulting from multiple sclerosis is due to a degeneration of myelin sheaths

Synapse

The junctions where information is transmitted from one neuron to the next; there are approximately $100$ trillion of these connections in the human brain.

Synaptic connections

Are important for learning, and they change in number over time as life goes

Glial Cells (Glia)

Cells that support neurons by providing nutrients, structure, insulation, and protection of the axon

e.g. Forming the blood-brain barrier.

Glial Cells (Glia) [con’t]

They play a role in a variety of major disorders

e.g. Dysfunction in glial cells may contribute to the cognitive impairment seen in schizophrenic disorders and to some forms of depressive disorders

Cerebrospinal fluid (CSF)

A colourless fluid that surrounds the brain and spinal cord with several functions,

e.g. Serving to cushion the brain during an impact

Blood-brain Barrier

A filter formed by glial cells that prevents foreign materials from entering the brain or cerebral spinal fluid.

Resting Potential

The negative charge associated with a neuron at rest, approximately $-70\,mV$

Resting Potential (con’t)

Is caused by an unequal distribution of potassium ($K^+$), sodium ($Na^+$), and chloride ($Cl^-$) ions.

Sodium-Potassium Pump

A mechanism in the cell membrane that maintains resting potential by sending $3$ sodium ions out for every potassium ion allowed in.

Action Potential

A rapid, brief reversal of electrical charge across the membrane, shifting from $-70\,mV$ to $+30\,mV$, which creates depolarization along the entire axon.

Depolarization

A change in electrical charge that triggers a chain-like effect along the axon toward the axon terminal during an action potential.

Absolute Refractory Period

The minimum length of time after an action potential during which another action potential cannot begin, allowing the cell to restore itself.

Microglia

A specific type of glial cell mentioned for its role in producing toxins that can lead to disorders such as Parkinson's disease.

The different types of neural connections

1. Within the neuron

2. Between neurons

Sodium-potassium pump (con’t)

Is a large membrane-associated enzyme and protein pump that transports sodium ions out and potassium ions into the cell to stabilize the cell membrane potential

Adenosine triphosphate (ATP)

The energy source (cycle) used by the sodium-potassium pump to transport ions across the cell membrane.

Action potential (con’t)

The basis of electrical signaling in neurons, which requires the stabilization of the cell’s membrane potential by the sodium-potassium pump.

Phosphate group

A chemical group transferred from ATP to the pump that prompts a conformational change, causing sodium ions to be released into the extracellular fluid.

Conformational change

A change in the shape of the pump prompted by the transfer of a phosphate group or the binding of ions to move them across the membrane.

Ion movement ratio

The specific count in each cycle where the pump moves $3$ sodium ions out of the cell and $2$ potassium ions into the cell.

Resting membrane potential effect

The net loss of positive ions during the pump cycle that makes the electrical charge of the cell slightly more negative.

Extracellular fluid

The area outside the cell into which the pump releases sodium ions after a conformational change.

Action potential (III)

A momentary reversal of membrane potential that serves as the basis for electrical signaling within neurons.

Resting membrane potential effect (con’t)

The neuron’s charge is approximately $-70 mV$.

Depolarization (con’t)

An effect on the neuron that makes the membrane potential less polarized, moving it closer to $0$.

Threshold membrane potential

The specific level (generally around $-55 mV$) a neuron must reach to trigger an action potential.

Sodium channels

Channels that open when a threshold is reached, allowing positively charged sodium ions to flow into the cell.

Rising phase

The stage of an action potential characterized by massive depolarization as the membrane potential reaches $0$ and becomes positive.

Potassium channels

Channels that open when the action potential reaches its peak, allowing potassium to flow out of the cell.

Repolarization

The process promoted by the loss of positive potassium ions, returning the neuron toward its resting membrane potential.

Falling phase

The part of the action potential associated with repolarization as potassium ions exit the neuron.

Hyperpolarization

A state where the neuron's membrane potential overshoots its resting level and becomes more negative than $-70 mV$.

Refractory period

A phase following an action potential during which the cell is hyperpolarized and it is very difficult to cause the neuron to fire again.

Axon terminals

The structures where the action potential signal can cause the release of neurotransmitters to pass the signal to the next neuron.

Synaptic cleft

The gap or space between the presynaptic and postsynaptic neurons, where synaptic transmission occurs between two neurons

Presynaptic neuron

The neuron that releases neurotransmitters from its axon terminal into the synaptic gap.

Postsynaptic neuron

The neuron that picks up or binds to neurotransmitters at its receptor sites.

Synaptic vesicles

Storage sacs located within the axon terminal (terminal button) that house neurotransmitters.

Synaptic transmission

When post-synaptic neurons are stimulated if pre-synaptic neurons release via neurotransmitters

How synaptic transmission is stopped

Enzymes are released that destroy neurotransmitters; leftover neurotransmitters are reabsorbed by the presynaptic neurons

Resting potential (con’t)

The stable negative charge of a neuron when it is not active ( $-70\,mV$ )

Threshold

The specific level of depolarization, identified as $-55\,mV$, required to automatically trigger an action potential.

All-or-none response

The principle that if a neuron reaches the required threshold, an action potential will occur completely; if not, it will not fire at all.

Enzymes

Substances released by the presynaptic neuron that destroy neurotransmitters in the synaptic gap to stop transmission.

Re-uptake pump

A mechanism that stops transmission by re-absorbing leftover neurotransmitters back into the presynaptic neuron.

Graded potentials

When a neuron receives thousands of inhibitory or excitatory signals from other neurons.

Hyperpolarization (con’t)

A process where the cell becomes more negative, creating inhibitory signals that prevent an action potential from occurring.

Depolarization (III)

The cell becomes more positive, leading to excitatory postsynaptic potentials.

Spatial summation

The determination of whether a neuron fires based on the physical location or spacing of the presynaptic neurons feeding into it.

Temporal summation

The determination of whether a neuron fires based on the timing of the presynaptic neurons firing.

Pruning

A natural biological process of eliminating less active or old synaptic connections as we age.

Learning and neural connections

Learning and development are based on creating new synaptic connections and getting rid of older connections via pruning

Learning and neural connections (con’t)

Learning is easier with more synaptic connections

Long-term potentiation

A long-lasting increase in neural excitability in synapses along a specific neural pathway due to repeated synaptic activity.

Potentiated state

A strengthened connection between neurons characterized by increased neurotransmitter release and a higher number of receptor sites.

Neuroplasticity

The brain's ability to learn and change, which is higher in younger individuals and decreases as one ages.

Acetlycholine (ACh)

A neurotransmitter released by motor neurons controlling skeletal muscles and contributes to attention, arousal, and memory; is associated with alzheimers

Dopamine (DA)

A neurotransmitter contributing to the control of voluntary movement

Norenpinephrine (NE)

A neurotransmitter contributing to the modulation of mood and arousal

Serotonin

A neurotransmitter involved in the regulation of sleep, wakefulness, eating, and aggression

GABA [Gamma-aminobutyric acid]

A neurotransmitter which serves as a widely distributed inhibitory transmitter contributing to the regulation of anxiety, sleep, and arousal

Endorphins

A neurotransmitter which resembles opiate drugs in structure and effects, and also plays a role in pain relief, stress responses, and regulation of eating priority

Synapse

A specialized structure where two neurons come close enough to one another that they are able to pass chemical signals from one cell to another.

Synaptic cleft (con’t)

A microscopically small space (less than $40\,nm$ wide) that separates the presynaptic and postsynaptic neurons.

Presynaptic neuron

The neuron where the signal is initiated.

Postsynaptic neuron

The neuron that receives the signal from the presynaptic neuron.

Neurotransmitters

Chemical signals packaged into vesicles within the presynaptic neuron.

Vesicles

Small sacs in the presynaptic neuron that can contain thousands of neurotransmitter molecules.

Action potential (IV)

The presynaptic neuron becomes excited via an electrical signal, causing vesicles to fuse with the presynaptic membrane and release neurotransmitters.

Receptors

Structures on the postsynaptic membrane that neurotransmitters bind to, which can increase or decrease the likelihood of the postsynaptic cell firing an action potential.

Diffusion

The process by which neurotransmitter molecules eventually clear the synaptic cleft by simply drifting away.

Reuptake

A process where the neurotransmitter is taken back up into the presynaptic neuron to be recycled and reused.

Enzymes (con’t)

Molecules that break down neurotransmitters within the synaptic cleft so their component parts can be sent back into the presynaptic neuron.

Central Nervous System (CNS)

The core part of the nervous system consisting of the brain and the spinal cord.

Peripheral Nervous System (PNS)

All the nerves located outside of the brain and the spinal cord.

Somatic Nervous System

A part of the peripheral nervous system that connects nerves to sensory organs, voluntary skeletal muscles and sensory receptors; uses afferent and efferent nerve fibers.

Afferent Nerves

Nerve fibres that carry sensory information from the peripheral nervous system to the central nervous system.

Efferent Nerves

Nerve pathways that carry motor information from the central nervous system to the peripheral nervous system.

Reflex Arc

A rapid, involuntary response to a stimulus that minimally involves the central nervous system and often remains in the spinal cord.

Autonomic Nervous System (ANS)

The system that handles involuntary functions of the heart, blood vessels, smooth muscles, and glands without conscious awareness because of connected nerves

Sympathetic Division

The branch of the autonomic nervous system that triggers physiological arousal and the fight or flight response during stress.

Parasympathetic Division

The system associated with "rest and digest," which relaxes the body, slows the heartbeat, and stimulates stomach activity for digestion.

Hindbrain [rhombencephalon]

The evolutionary lowest part of the brain, which is composed of the cerebellum, medulla, and pons.

Cerebellum

A structure involved in:

• Movement coordination

• Balance

• Recall of emotions and language-processing tasks.

Medulla

A brain structure involved in unconscious functions like blood circulation, breathing, and reflexes such as coughing.

Pons

A bridge of fibers connecting the brain stem to the cerebellum that is involved in sleep and arousal.

Midbrain

The region located above the fore and mid-brains that integrates sensory processes like vision and hearing and contains dopamine-releasing neurons.

Reticular Formation

A structure running through the hindbrain to the midbrain that modulates muscle reflexes, breathing, pain perception, sleep, and arousal.

Forebrain

The largest and most complex region of the brain, encompassing a variety of structures

e.g. The thalamus, hypothalamus, limbic system, and cerebrum

Thalamus

A relay station in the forebrain through which all sensory information (except for smell) passes to the cerebral cortex.