Anatomy & Physiology Study Guide: Muscular, Nervous, and Sensory Systems

Chapter 7: The Muscular System

General Functions and Characteristics of Muscle Tissue

The muscular system is responsible for movement, posture, and heat production in the body. Muscle tissue is classified into three types: skeletal, cardiac, and smooth.

• Skeletal muscle: Voluntary, striated, attached to bones for movement.

• Cardiac muscle: Involuntary, striated, found only in the heart.

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

• Key functions: Movement, stability, control of body openings, heat production.

Example: Skeletal muscles contract to move limbs; cardiac muscle pumps blood; smooth muscle moves food through the digestive tract.

Muscle Structure and Connective Tissue Components

Muscles are organized into bundles surrounded by connective tissue layers.

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds bundles (fascicles) of muscle fibers.

• Epimysium: Surrounds the entire muscle.

• Tendon: Connects muscle to bone, composed of dense regular connective tissue.

Additional info: These connective tissues provide support, transmit force, and allow for muscle elasticity.

Microscopic Structure of Skeletal Muscle

Skeletal muscle fibers are multinucleated, striated cells containing myofibrils made of actin and myosin filaments.

• Myofibrils: Contractile elements within muscle fibers.

• Actin and myosin: Proteins responsible for muscle contraction.

• Sarcomere: Functional unit of contraction, defined by Z-lines.

Neuromuscular Junction and Muscle Contraction

The neuromuscular junction is the site where a motor neuron stimulates a muscle fiber to contract.

• Motor neuron releases acetylcholine (ACh) into the synaptic cleft.

• ACh binds to receptors on the muscle cell membrane, initiating an action potential.

• Action potential triggers release of calcium ions, leading to contraction.

Types of Muscle Contractions

Muscle contractions can be classified based on their characteristics and effects.

• Graded responses: Variation in muscle contraction strength.

• Twitch: Single, brief contraction.

• Tetanus: Sustained contraction from rapid stimuli.

• Isometric contraction: Muscle tension without length change.

• Isotonic contraction: Muscle changes length while tension remains constant.

Formula:

$\text{Force} = \text{Mass} \times \text{Acceleration}$

Muscle Fatigue and Oxygen Debt

Muscle fatigue occurs when muscles can no longer contract efficiently, often due to depletion of energy reserves.

• Oxygen debt: Extra oxygen required after exercise to restore metabolic conditions.

• Fatigue causes: Lack of ATP, accumulation of lactic acid, ionic imbalances.

Exercise and Muscle Health

Regular exercise strengthens muscles and improves endurance.

• Strengthening: Increases muscle size and force.

• Conditioning: Improves efficiency and resistance to fatigue.

Isotonic vs. Isometric Contractions

Type	Muscle Length Change	Example
Isotonic	Yes	Lifting a weight
Isometric	No	Holding a plank position

Chapters 8 & 9: The Nervous System

General Functions and Organization

The nervous system coordinates body activities through electrical and chemical signals.

• Central nervous system (CNS): Brain and spinal cord.

• Peripheral nervous system (PNS): Nerves outside the CNS.

• Functions: Sensory input, integration, motor output.

Structure of Neurons and Nerves

Neurons are the functional units of the nervous system, transmitting impulses.

• Neuron parts: Cell body, dendrites, axon.

• Nerve: Bundle of axons in the PNS.

• Gray matter: Contains neuron cell bodies.

• White matter: Contains myelinated axons.

Major Regions of the Brain

The brain is divided into several regions, each with specific functions.

• Cerebral hemispheres: Higher functions, sensory and motor processing.

• Diencephalon: Thalamus and hypothalamus, relay and control centers.

• Brain stem: Basic life functions, connects brain and spinal cord.

• Cerebellum: Coordination and balance.

Spinal Cord and Reflexes

The spinal cord transmits signals between the brain and body and mediates reflex actions.

• Spinal cord structure: Central canal, gray and white matter.

• Reflex arc: Pathway for automatic responses.

Autonomic Nervous System

The autonomic nervous system regulates involuntary functions.

• Sympathetic division: Prepares body for 'fight or flight'.

• Parasympathetic division: Promotes 'rest and digest'.

Division	Main Effects
Sympathetic	Increases heart rate, dilates pupils
Parasympathetic	Decreases heart rate, stimulates digestion

Development and Disorders

Brain development is influenced by genetic and environmental factors. Disorders can affect structure and function.

• Congenital disorders: Spina bifida, anencephaly, cerebral palsy.

• Age-related changes: Decline in brain size and weight.

Chapter 10: The Sense Organs

General Structure and Function

Sensory organs detect changes in the environment and transmit information to the brain.

• Eye: Vision

• Ear: Hearing and equilibrium

• Olfactory organs: Smell

• Taste receptors: Taste

Eye Structure and Function

The eye consists of several layers and structures that focus light and convert it to neural signals.

• Layers: Sclera, choroid, retina

• Retina: Contains rods (dim light) and cones (color vision)

• Pathway of light: Cornea → lens → retina

Formula:

$\text{Refraction Index} = \frac{\text{Speed of light in vacuum}}{\text{Speed of light in medium}}$

Visual Pathway

Visual information travels from the retina to the brain via the optic nerve.

• Retinal photoreceptors → optic nerve → visual cortex

Ear Structure and Hearing

The ear is divided into outer, middle, and inner regions, each with specific roles in hearing and balance.

• Outer ear: Collects sound waves

• Middle ear: Transmits vibrations via ossicles

• Inner ear: Contains cochlea (hearing) and vestibular apparatus (balance)

Equilibrium and Balance

Equilibrium organs in the inner ear help maintain balance.

• Static equilibrium: Sensed by vestibule, detects head position.

• Dynamic equilibrium: Sensed by semicircular canals, detects rotational movement.

Hearing Loss and Deafness

Type	Description	Possible Causes
Sensorineural	Damage to inner ear or nerve pathways	Noise exposure, aging
Conductive	Obstruction or damage to outer/middle ear	Earwax, infection

Olfactory and Taste Receptors

Smell and taste are detected by specialized receptors in the nasal cavity and tongue.

• Olfactory receptors: Detect airborne chemicals

• Taste receptors: Detect five basic tastes: sweet, sour, salty, bitter, umami

Age-Related Changes in Sensory Organs

Sensory function may decline with age due to changes in receptor cells and neural pathways.

• Decreased sensitivity to light, sound, and taste

• Slower neural processing