Chapter 07: Nervous System and Neurons

Major Divisions of the Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integrating and processing information.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

Direction of Information Flow

• Sensory (afferent) neurons: Carry information from sensory receptors to the CNS.

• Motor (efferent) neurons: Transmit commands from the CNS to effectors (muscles/glands).

Basic Anatomy of a Neuron

• Dendrites: Receive incoming signals.

• Cell body (soma): Contains the nucleus and processes signals.

• Axon: Transmits electrical impulses away from the cell body.

• Axon terminals: Release neurotransmitters to communicate with other cells.

Types of Ion Channels

• Leak channels: Always open; contribute to resting membrane potential.

• Voltage-gated channels: Open or close in response to changes in membrane potential.

• Ligand-gated channels: Open in response to binding of a chemical messenger (ligand).

Active vs. Passive Transport

• Active transport: Requires energy (ATP), e.g., Na+/K+ pump.

• Passive transport: Movement of ions by diffusion through channels, no energy required.

Primary Ions in Resting Membrane Potential

• Sodium (Na+): Higher concentration outside the cell.

• Potassium (K+): Higher concentration inside the cell.

• Chloride (Cl-): Also contributes to membrane potential.

Electrochemical Gradient

• Na+: Wants to enter the cell (high outside, low inside).

• K+: Wants to exit the cell (high inside, low outside).

Ion Pumps and Channels

• Na+/K+ pump: 3 Na+ out, 2 K+ in; maintains resting potential.

• Leak channels: Allow passive movement of ions.

• Gated channels: Open in response to stimuli.

Structure and Function of Myelin

• Insulates axons, increasing the speed of signal transmission.

• Formed by Schwann cells (PNS) and oligodendrocytes (CNS).

Types of Neurons

• Sensory (afferent): Detect stimuli and send information to CNS.

• Interneurons: Process information within the CNS.

• Motor (efferent): Activate muscles and glands.

Glial Cells Functions

• CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells.

• PNS: Schwann cells, satellite cells.

Membrane Potential Terms

• Resting potential: Approximately -70 mV.

• Threshold: About -55 mV; minimum potential needed to trigger an action potential.

• Depolarization: Na+ enters the cell, making the inside more positive.

• Repolarization: K+ exits the cell, restoring negative potential.

• Hyperpolarization: K+ continues to exit, making the cell more negative than resting potential.

Graded vs. Action Potentials

• Graded potentials: Small, localized, variable strength; can summate.

• Action potentials: All-or-none, travel long distances without decrement.

EPSP vs. IPSP

• EPSP (Excitatory Postsynaptic Potential): Depolarizes membrane, increases likelihood of action potential.

• IPSP (Inhibitory Postsynaptic Potential): Hyperpolarizes membrane, decreases likelihood of action potential.

Summation of EPSPs/IPSPs

• Multiple EPSPs and IPSPs can combine to reach threshold and trigger an action potential.

Plotting Action Potential

• Shows depolarization, repolarization, hyperpolarization, and return to resting potential.

Factors Influencing Action Potential Speed

• Axon diameter: Larger diameter = faster conduction.

• Myelination: Myelinated axons conduct faster than unmyelinated.

Propagation of Action Potential

• Unmyelinated: Continuous conduction along the axon.

• Myelinated: Saltatory conduction (jumps between nodes of Ranvier).

Chapter 08: Synapses

Anatomy of a Synapse

• Presynaptic neuron: Sends the signal; contains synaptic vesicles filled with neurotransmitters.

• Synaptic cleft: Small gap between neurons.

• Postsynaptic neuron: Receives the signal; has receptors for neurotransmitters.

Types of Synapses

• Axaxoaxonic: Between axon terminals of two neurons; modulates neurotransmitter release.

• Axodendritic: Between an axon and a dendrite; most common type.

• Axosomatic: Between an axon and the soma (cell body); strong influence on action potential generation.

Events Leading to Neurotransmitter Release

1. Action potential reaches the axon terminal.

2. Voltage-gated calcium channels open.

3. Calcium enters the terminal.

4. Synaptic vesicles fuse with the membrane.

5. Neurotransmitters are released into the synaptic cleft via exocytosis.

Fates of Neurotransmitters After Binding

• Reuptake: Into the presynaptic neuron.

• Enzymatic degradation: In the synaptic cleft.

• Diffusion: Away from the synapse.

Types of Signal Transduction in Postsynaptic Neurons

• Ionotropic receptors: Directly open ion channels; fast response.

• Metabotropic receptors: Activate intracellular signaling cascades; slower, longer-lasting effects.

Postsynaptic Potential Changes

• Inhibitory stimulus: Causes hyperpolarization (IPSP), making the neuron less likely to fire.

• Excitatory stimulus: Causes depolarization (EPSP), increasing the likelihood of an action potential.

Key Ions in Postsynaptic Potentials

• IPSP: Chloride (Cl-) influx or potassium (K+) efflux.

• EPSP: Sodium (Na+) influx, sometimes calcium (Ca2+) influx.

Summation of Postsynaptic Potentials

• Temporal summation: Multiple signals from one neuron in quick succession.

• Spatial summation: Signals from multiple neurons at the same time.

Receptor Types for Hydrophilic Messengers

• Channel-linked receptors (ionotropic): Fast, direct ion flow.

• G-protein coupled receptors (metabotropic): Activate intracellular signaling; slower, more complex.

Cholinergic Receptors: Nicotinic vs. Muscarinic

• Nicotinic: Ionotropic; fast; found in neuromuscular junctions.

• Muscarinic: Metabotropic; slower; found in cardiac and smooth muscle.

Cholinergic vs. Adrenergic Receptor Signal Transduction

• Cholinergic: Uses acetylcholine; can be ionotropic or metabotropic.

• Adrenergic: Uses norepinephrine/epinephrine; always metabotropic via G-proteins.

Alpha vs. Beta Adrenergic Receptors

• Alpha receptors: Generally cause vasoconstriction and increased blood pressure.

• Beta receptors: Increase heart rate and cause bronchodilation.

Chapter 09: Central Nervous System Study Guide

Function of the Blood-Brain Barrier (BBB)

• Restricts entry of harmful substances.

• Allows selective transport of nutrients.

• Maintains a stable environment for neural function.

Capillary Structure: Brain vs. Body

• Brain capillaries: Tight junctions, no fenestrations, surrounded by astrocytes.

• Body capillaries: Looser junctions, fenestrated or sinusoidal for exchange.

Differences in CSF vs. Blood Plasma

Primary Energy Source for CNS

• Glucose is the main energy source; the brain relies on a constant supply.

Overall Spinal Cord Anatomy

• Extends from brainstem to lumbar region.

• Protected by vertebrae.

• Contains central canal, gray matter (internal), white matter (external).

Spinal Cord Cross-Section Anatomy

• Afferent nerves: Enter dorsally (sensory input).

• Interneurons: Located in gray matter.

• Efferent nerves: Exit ventrally (motor output).

• White matter: Surrounds gray matter; contains ascending and descending tracts.

• Gray matter: Butterfly-shaped center; contains neuron cell bodies.

• Ascending tracts: Carry sensory information up to the brain.

Reflexes

• Definition: An automatic, rapid response to a stimulus, bypassing conscious brain processing.

• Components: Sensory receptor, afferent nerve, interneuron, efferent nerve, effector.

Classes of Reflexes

• Somatic: Involve skeletal muscles.

• Autonomic: Involve smooth muscle, glands.

• Monosynaptic: One synapse (e.g., knee-jerk reflex).

• Polysynaptic: Multiple synapses (e.g., withdrawal reflex).

Overall Brain Anatomy

• Cerebrum: Higher functions (thinking, memory, voluntary movement).

• Cerebellum: Coordination and balance.

Cerebral Cortex Lobes

• Frontal: Decision-making, motor control.

• Parietal: Sensory processing.

• Occipital: Vision.

• Temporal: Hearing, memory.

Function of Basal Nuclei

• Regulate voluntary motor movements.

• Inhibit unnecessary movements.

• Involved in habit formation.

Functions of the Thalamus

• Relay station for sensory information.

• Filters and directs signals to cortex.

• Involved in consciousness and alertness.

Functions of the Hypothalamus

• Regulates homeostasis (temperature, hunger, thirst).

• Controls endocrine system via pituitary gland.

• Involved in emotional responses.

Broca's vs. Wernicke's Area

• Broca's area: Speech production.

• Wernicke's area: Language comprehension.