Anatomy & Physiology: Nervous System and Muscle Physiology Study Guide

Muscle Physiology

Motor Unit

A motor unit consists of a single motor neuron and all the muscle fibers it innervates. It is the basic functional unit of muscle contraction.

• Definition: A motor neuron and the skeletal muscle fibers it controls.

• Importance: Allows for graded control of muscle force.

• Example: Small motor units in the eye muscles allow for precise movements.

ATP Regeneration in Skeletal Muscle

Muscle cells regenerate ATP through three primary mechanisms:

• Creatine Phosphate: Transfers a phosphate group to ADP to form ATP rapidly.

• Anaerobic Glycolysis: Breaks down glucose without oxygen, producing ATP and lactic acid.

• Aerobic Respiration: Uses oxygen to produce ATP from glucose, fatty acids, or amino acids.

Equation:

$\text{Creatine~Phosphate} + \text{ADP} \rightarrow \text{Creatine} + \text{ATP}$

Contraction Comparison: Skeletal vs. Smooth Muscle

• Skeletal Muscle: Voluntary, striated, rapid contractions.

• Smooth Muscle: Involuntary, non-striated, slow and sustained contractions.

• Example: Skeletal muscle moves limbs; smooth muscle controls blood vessel diameter.

Mechanism of Contraction

• Sliding Filament Theory: Actin and myosin filaments slide past each other, shortening the muscle fiber.

• Role of Calcium: Calcium ions bind to troponin, allowing myosin to bind to actin.

• ATP: Required for both contraction and relaxation.

Nervous System Overview

Functions of the Nervous System

The nervous system is responsible for sensory input, integration, and motor output.

• Sensory Input: Detects changes in the environment.

• Integration: Processes and interprets sensory information.

• Motor Output: Initiates responses by activating muscles or glands.

Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): All neural tissue outside the CNS.

• Subdivisions: Somatic (voluntary) and autonomic (involuntary) systems.

Neurons and Neuroglia

• Neurons: Excitable cells that transmit electrical signals.

• Neuroglia: Support, protect, and nourish neurons.

• Types of Neuroglia: Astrocytes, oligodendrocytes, microglia, ependymal cells (CNS); Schwann cells, satellite cells (PNS).

Neuron Structure and Function

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

• Dendrites: Receive signals from other neurons.

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

Types of Neurons

• Multipolar: Many dendrites, one axon (most common in CNS).

• Bipolar: One dendrite, one axon (retina, olfactory epithelium).

• Unipolar: Single process splits into two branches (sensory neurons).

Myelination

• Myelin Sheath: Insulating layer around axons, increases speed of impulse transmission.

• Nodes of Ranvier: Gaps in myelin sheath where action potentials are regenerated.

Neurophysiology

Membrane Potentials

• Resting Membrane Potential: Difference in charge across the membrane at rest, typically -70 mV.

• Graded Potentials: Local changes in membrane potential, decrease with distance.

• Action Potentials: Rapid, large changes in membrane potential that propagate along axons.

Equation:

$\text{Resting~Potential} = -70~\text{mV}$

Generation and Propagation of Action Potentials

• Depolarization: Sodium channels open, Na+ enters cell.

• Repolarization: Potassium channels open, K+ exits cell.

• Propagation: Action potential moves along axon via local currents.

Synaptic Transmission

• Synapse: Junction between two neurons.

• Neurotransmitters: Chemical messengers released into synaptic cleft.

• Excitatory vs. Inhibitory: Excitatory neurotransmitters increase likelihood of action potential; inhibitory decrease it.

Central Nervous System (CNS)

Major Regions of the Brain

• Brain Stem: Includes midbrain, pons, medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

• Cerebrum: Responsible for higher cognitive functions.

Functions of Brain Regions

Region	Main Function
Midbrain	Visual and auditory reflexes
Pons	Relays signals, regulates breathing
Medulla Oblongata	Controls heart rate, breathing, swallowing
Cerebellum	Coordinates voluntary movements, balance

Meninges of the Brain

• Dura Mater: Tough outer layer.

• Arachnoid Mater: Web-like middle layer.

• Pia Mater: Delicate inner layer, adheres to brain surface.

Additional Structures

• Basal Nuclei: Involved in movement regulation.

• Limbic System: Controls emotions and memory.

• Corpus Callosum: Connects left and right cerebral hemispheres.

Peripheral Nervous System (PNS)

Components

• Cranial Nerves: 12 pairs, serve head and neck.

• Spinal Nerves: 31 pairs, serve rest of body.

• Ganglia: Clusters of neuron cell bodies outside CNS.

Functional Divisions

• Somatic Nervous System: Controls voluntary movements.

• Autonomic Nervous System: Regulates involuntary functions (sympathetic and parasympathetic divisions).

Summary Table: CNS vs. PNS

Feature	CNS	PNS
Main Components	Brain, Spinal Cord	Cranial & Spinal Nerves, Ganglia
Function	Integration, Processing	Communication, Sensory & Motor Relay
Neuroglia Types	Astrocytes, Oligodendrocytes, Microglia, Ependymal	Schwann, Satellite

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum (e.g., details on neuron types, neuroglia, and CNS/PNS comparison).

• Reference to textbook Table 12.1 suggests further reading for brain region functions.