Study Guide: Nervous System, Sensory Physiology, and Muscle Physiology

Chapter 7 – The Nervous System

Overview of the Nervous System

The nervous system is a complex network responsible for coordinating body activities and transmitting signals between different parts of the body. It consists of the central nervous system (CNS) and peripheral nervous system (PNS), which are further divided into somatic, autonomic, and enteric branches.

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

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; subdivided into somatic (voluntary control), autonomic (involuntary control), and enteric (digestive tract regulation).

• Autonomic Nervous System: Further divided into sympathetic ("fight or flight") and parasympathetic ("rest and digest") branches.

Anatomy of the Neuron

Neurons are the basic functional units of the nervous system, specialized for communication.

• Cell Body (Soma): Contains the nucleus and organelles.

• Dendrites: Receive incoming signals.

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

• Synapse: Junction between two neurons or a neuron and an effector cell.

Classification of Neurons and Effectors

Neurons can be classified by structure and function, and effectors are cells that respond to neural signals.

• Structural Classification: Multipolar, bipolar, and unipolar neurons.

• Functional Classification: Sensory (afferent), motor (efferent), and interneurons.

• Effectors: Muscles and glands that respond to neural input.

Glial Cells and Their Functions

Glial cells support and protect neurons. Major types include:

• Astrocytes: Maintain the blood-brain barrier and provide structural support.

• Oligodendrocytes (CNS) and Schwann Cells (PNS): Form myelin sheaths around axons.

• Microglia: Act as immune cells in the CNS.

Membrane Potential and Action Potentials

Neurons communicate via changes in membrane potential, leading to action potentials.

• Resting Membrane Potential: The voltage difference across the membrane at rest, typically around -70 mV.

• Action Potential: A rapid change in membrane potential that propagates along the axon.

• Hyperpolarization: Membrane potential becomes more negative than resting.

• Depolarization: Membrane potential becomes less negative (more positive).

• Repolarization: Return to resting membrane potential after depolarization.

Key Equation:

$V_m = V_{inside} - V_{outside}$

Voltage-Gated Channels and Synaptic Transmission

Voltage-gated channels are essential for action potential generation and propagation.

• Na+, K+, and Ca2+ Channels: Open and close in response to changes in membrane potential.

• Neurotransmitters: Chemical messengers released at synapses to transmit signals between neurons.

• Synaptic Inhibition: Inhibitory neurotransmitters decrease the likelihood of action potential generation.

Summary Table: Types of Neurons and Their Functions

Type	Structure	Function
Sensory (Afferent)	Unipolar/Bipolar	Transmit impulses from receptors to CNS
Motor (Efferent)	Multipolar	Transmit impulses from CNS to effectors
Interneurons	Multipolar	Connect sensory and motor neurons within CNS

Chapter 10 – Sensory Physiology

Overview of Sensory Physiology

Sensory physiology studies how sensory receptors detect stimuli and transmit information to the brain for interpretation.

• Sensory Receptors: Specialized cells that detect environmental changes (stimuli).

• Types of Receptors: Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors.

• Receptor Specificity: Each receptor type responds to a specific kind of stimulus.

Pathways and Processing

• Labelled Line Principle: Each sensory pathway transmits a specific type of information.

• Lateral Inhibition: Enhances contrast and sharpens sensory perception by inhibiting neighboring neurons.

• Neurotransmitter Release: Stimulus intensity affects the amount of neurotransmitter released.

Special Senses: Vision and Taste

• Photoreceptors: Rods (low light, black and white vision) and cones (color vision, high acuity).

• Pathway of Information in the Eye: Light → photoreceptors → bipolar cells → ganglion cells → optic nerve → brain.

• Taste Receptors: Detect different flavors via chemoreceptors on the tongue.

Chapter 12 – Muscle Physiology

Autonomic vs. Somatic Systems

The autonomic nervous system regulates involuntary functions, while the somatic system controls voluntary muscle movements.

• Parasympathetic (Rest and Digest): Promotes relaxation and digestion.

• Sympathetic (Fight or Flight): Prepares the body for stress or emergency.

• Neurotransmitters: Acetylcholine (parasympathetic), norepinephrine (sympathetic).

Muscle Contraction Mechanisms

Muscle contraction involves a series of steps from neural stimulation to actin-myosin interaction.

• Excitation-Contraction Coupling: Sequence from neural signal to muscle fiber contraction.

• Role of Calcium: Ca2+ ions trigger the interaction between actin and myosin filaments.

• Neuromuscular Junction: Synapse between a motor neuron and muscle fiber; acetylcholine is the main neurotransmitter.

• Curare: A toxin that blocks acetylcholine receptors, leading to muscle paralysis.

Key Equation:

$\text{Force} = \text{Number of cross-bridges} \times \text{Force per cross-bridge}$

Summary Table: Comparison of Somatic and Autonomic Systems

Feature	Somatic	Autonomic
Control	Voluntary	Involuntary
Effector	Skeletal muscle	Cardiac muscle, smooth muscle, glands
Neurotransmitter	Acetylcholine	Acetylcholine, norepinephrine
Number of Neurons	One	Two (pre- and post-ganglionic)

Example: Curare Poisoning

Curare blocks acetylcholine receptors at the neuromuscular junction, preventing muscle contraction and causing paralysis. This is clinically significant in anesthesia and toxicology.

Additional info: Some details, such as the specific steps of excitation-contraction coupling and the labelled line principle, were inferred for completeness and academic context.