SCB 204 quiz 1

Lec 1 - lec 4

Controls Perceptions

Manages sensory input from the environment, allowing us to interpret and interact with it.

Directs Voluntary Movement

Governs purposeful muscle movements.

Consciousness and Memory

Responsible for awareness, personality, learning, and memory.

Regulates Homeostasis

Works with the endocrine system to maintain equilibrium (e.g., respiratory rate, BP, body temperature).

Central Nervous System

Brain, spinal cord; processes, interprets information; decision-making center.

Peripheral Nervous System

Cranial nerves (12 pairs), spinal nerves (31 pairs); transmits signals to/from CNS.

Sensory

Gathers information from the body and environment for processing by CNS.

Integrative

Analyzes sensory data and formulates responses.

Motor

Executes responses via voluntary (skeletal) or involuntary (smooth, cardiac) muscles.

Cell Body (Soma)

Contains organelles; the metabolic hub of the neuron.

Dendrites

Short, branched structures; receive and transmit electrical impulses.

Axon

Long projection; conducts action potentials to target cells.

Receptive Region

Dendrites and cell body receive signals.

Conducting Region

Axon transmits action potentials.

Secretory Region

Axon terminals release neurotransmitters.

Astrocytes

Support blood-brain barrier, repair neurons.

Oligodendrocytes

Form myelin sheath for axons.

Microglia

Act as phagocytes to clear debris.

Ependymal cells

Produce, circulate cerebrospinal fluid (CSF).

Schwann cells

Myelinate axons, assist in repair.

Satellite cells

Support and protect neuron cell bodies.

Multipolar Neurons

One axon, multiple dendrites; motor neurons, interneurons.

Bipolar Neurons

One axon, one dendrite; sensory neurons in the retina.

Pseudounipolar Neurons

Single fused axon, no true dendrites; sensory neurons for touch, vibration.

Sensory Neurons

Transmit input to CNS; found in sensory organs (e.g., skin).

Motor Neurons

Transmit output from CNS; found in PNS controlling muscles and glands.

Interneurons

Relay signals within CNS; found in brain and spinal cord.

Wallerian Degeneration

Axon and myelin sheath degenerate distal to injury.

Growth Processes

Proximal end of the axon generates new processes.

Regeneration Tube Formation

Guides regeneration.

New Axon Formation

A growth process reconnects to the target cell.

Nerve

Bundle of axons in the PNS.

Tract

Bundle of axons in the CNS.

Ganglion

Cluster of neuron cell bodies in the PNS.

Nucleus

Cluster of neuron cell bodies in the CNS.

Node of Ranvier

Gaps between myelin sheath segments on an axon, aiding in action potential speed.

Ion Channels

Proteins that allow ions to flow across the membrane, crucial for neuronal signaling.

Leak Channels

Always open, maintain resting membrane potential.

Gated Channels

Open in response to specific stimuli (ligand, voltage, or mechanical).

Resting Membrane Potential (RMP)

Typically -70 mV, maintained by Na+/K+ pump and leak channels.

Local Potentials

Small, graded, reversible changes in membrane potential.

Action Potentials

All-or-none events, involve depolarization, repolarization, and hyperpolarization.

Refractory Periods

Absolute and relative, ensure unidirectional propagation.

Propagation of Action Potentials

Saltatory (myelinated) vs. Continuous (unmyelinated).

Depolarization

Membrane becomes less negative.

Hyperpolarization

Membrane becomes more negative.

Threshold

Minimum membrane potential (-55 mV) required to trigger an action potential.

All-or-None Principle

Action potentials either occur fully or not at all.

Absolute Refractory Period

No new action potential can be triggered, regardless of stimulus strength.

Relative Refractory Period

A stronger-than-usual stimulus can trigger a new action potential.

Saltatory Conduction

Action potentials jump between nodes of Ranvier, increasing speed.

Continuous Conduction

Every segment of the axon membrane depolarizes, slowing signal transmission.

Factors Affecting Speed

Axon diameter: Larger diameter = faster conduction; Myelination: Myelinated axons conduct signals faster.

Maintenance of Resting Membrane Potential

Na+/K+ pump actively transports 3 Na+ out and 2 K+ in.

Significance of Resting Membrane Potential

Provides the potential energy needed for neuronal signaling.

Characteristics of Local Potentials

Small and localized, graded, reversible, and decremental.

Importance of Refractory Periods

Ensures unidirectional flow of action potentials.

Synapse

A synapse is the site where a neuron meets its target cell (another neuron in the case of neuronal synapses).

Electrical Synapses

Involve direct electrical communication.

Chemical Synapses

Use neurotransmitters for communication.

Presynaptic Neuron

Sends messages from its axon terminals.

Postsynaptic Neuron

Receives messages at its cell body, axon, or dendrites.

Average Presynaptic Neuron

Forms about 1,000 synapses.

Postsynaptic Neurons

Can have up to 10,000 synaptic connections.

Events at a Chemical Synapse

1. Action potential arrives at the synaptic terminus. 2. Voltage-gated calcium channels open, allowing calcium influx. 3. Synaptic vesicles release neurotransmitters into the synaptic cleft. 4. Neurotransmitters bind to receptors on the postsynaptic membrane, causing local potentials.

Termination of Synaptic Transmission

1. Diffusion of neurotransmitters away from the cleft. 2. Enzymatic degradation (e.g., acetylcholinesterase). 3. Reuptake into the presynaptic neuron.

Characteristics of Neurotransmitters

Synthesized in the cell body or axon terminal and stored in vesicles. Released upon action potential arrival. Bind to specific receptors on the postsynaptic membrane. Effects are terminated rapidly via removal or degradation.

Ionotropic Receptors

Ligand-gated ion channels for rapid ion movement.

Metabotropic Receptors

Activate metabolic processes and are indirectly linked to ion channels.

Excitatory Post-Synaptic Potentials (EPSPs)

Depolarization, promoting action potential generation.

Inhibitory Post-Synaptic Potentials (IPSPs)

Hyperpolarization, reducing action potential likelihood.

Acetylcholine (ACh)

Found in cholinergic synapses, neuromuscular junctions, CNS, and PNS. Excitatory effects but can be inhibitory in certain PNS contexts. Degraded by acetylcholinesterase.

Biogenic Amines (Monoamines)

Synthesized from amino acids.

Norepinephrine

Regulates heart rate, digestion, and attention.

Epinephrine

Similar to norepinephrine.

Dopamine

Affects movement, emotion, and motivation.

Serotonin

Influences mood and daily rhythms.

Histamine

Regulates arousal and attention.

Glutamate

Primary excitatory neurotransmitter in the CNS.

Glycine and GABA

Major inhibitory neurotransmitters inducing IPSPs.

Substance P

Involved in pain and temperature regulation.

Opioids

Provide pain relief and are depressants.

Neuropeptide Y

Regulates feeding behaviors.

Correct Sequence of Events at a Chemical Synapse

Action potential arrival ➔ neurotransmitter release ➔ receptor binding ➔ local potential generation.

Trigger for Neurotransmitter Release

What triggers neurotransmitter release?

Neurotransmitter release trigger

Influx of calcium into the synaptic terminus.

Effect of neurotransmitter binding on postsynaptic neurons

Opens or closes ligand-gated sodium channels.

Termination methods for synaptic transmission

Diffusion, enzymatic degradation, and reuptake.

Excitatory Postsynaptic Potential (EPSP)

Caused by small depolarization; triggered by opening sodium (Na⁺) or calcium (Ca²⁺) channels; brings membrane potential closer to threshold, increasing the likelihood of an action potential.

Inhibitory Postsynaptic Potential (IPSP)

Caused by small hyperpolarization; triggered by opening potassium (K⁺) or chloride (Cl⁻) channels; moves membrane potential further from threshold, reducing the likelihood of an action potential.

Neural Integration

The process by which a postsynaptic neuron combines incoming excitatory and inhibitory signals into a single effect.

Summation

Determines whether the neuron will generate an action potential.

Temporal Summation

Neurotransmitter is released repeatedly from a single presynaptic neuron; each EPSP must be generated quickly to reach the threshold for an action potential.

Spatial Summation

Simultaneous neurotransmitter release from multiple presynaptic neurons; combines the effects of all inputs at the same time.

Net excitatory effect

Action potential generated.

Net inhibitory effect

No action potential, membrane hyperpolarizes.

Neuronal Pools

Groups of interneurons in the CNS with interconnected functions; synaptic connections define the type of information processed.

Diverging Circuits

Single input neuron communicates with multiple parts of the brain or body; example: sensory signals diverging to multiple processing areas.

Converging Circuits

Multiple input neurons converge onto a single postsynaptic neuron; example: coordination of skeletal muscle movement.

Inhibitory Circuits

Provide negative feedback to control neural activity.