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

Nervous System

Introduction to the Nervous System

The nervous system is a complex network responsible for coordinating the body's responses to internal and external stimuli. It works closely with the endocrine system to maintain homeostasis, but differs in speed and mechanism of action.

• Nervous vs. Endocrine Systems:

  • Nervous system uses electrical impulses and neurotransmitters for rapid, short-term responses.

  • Endocrine system uses hormones released into the bloodstream for slower, longer-lasting effects.

  • Example: Withdrawal reflex (nervous) vs. blood sugar regulation (endocrine).

• Organization:

  • Central Nervous System (CNS): Brain and spinal cord; processes and integrates information.

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

• Cells: Neurons (transmit signals) and neuroglia (support cells).

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

Neuron Structure and Synapse

• Basic Neuron Structure: Cell body (soma), dendrites (receive input), axon (transmits output), axon terminals.

• Synapse: Junction between neurons; includes presynaptic terminal, synaptic cleft, and postsynaptic membrane.

• Information Transmission: Electrical impulse (action potential) travels along axon, triggers neurotransmitter release at synapse.

Reflex Arcs

• Withdrawal Reflex Arc: Involuntary response to painful stimulus; involves five parts:

  1. Receptor (detects stimulus)

  2. Sensory neuron (transmits signal to CNS)

  3. Integration center (interneuron in spinal cord)

  4. Motor neuron (carries response signal)

  5. Effector (muscle or gland responds)

• Knee Jerk Reflex: Example of a monosynaptic reflex; used to assess nervous system function.

• Latent Period: Time between stimulus and response; shorter in reflexes than conscious responses.

Anatomy of the Nervous System

• Meninges: Three protective membranes (dura mater, arachnoid mater, pia mater) surrounding CNS; spaces include epidural, subdural, and subarachnoid.

• Spinal Cord: Transmits information between brain and body; contains gray matter (cell bodies) and white matter (myelinated axons).

• Blood-Brain Barrier: Selective barrier protecting brain from harmful substances.

• Major Brain Parts: Cerebrum, cerebellum, brainstem, diencephalon; each with specific functions.

• Cranial vs. Spinal Nerves: Cranial nerves (12 pairs) arise from brain; spinal nerves (31 pairs) from spinal cord.

• Motor vs. Sensory Innervation: Motor nerves control muscles; sensory nerves transmit sensory information. Damage can cause paralysis (motor) or loss of sensation (sensory).

• Sympathetic vs. Parasympathetic: Divisions of autonomic nervous system; sympathetic prepares for 'fight or flight,' parasympathetic for 'rest and digest.'

Clinical Applications

• Hemorrhage: Bleeding in or around the brain/spinal cord can cause neurological deficits.

• Meningitis: Inflammation of meninges; diagnosed via lumbar puncture.

• Encephalitis: Inflammation of brain tissue.

• Seizure: Abnormal electrical activity in the brain.

• CVA/Stroke: Disruption of blood flow to brain, causing tissue damage.

Senses

General and Special Senses

The body detects environmental changes through sensory receptors, which are classified as general (touch, pain, temperature) or special (vision, hearing, taste, smell, equilibrium).

• General Senses: Widely distributed; include touch, pressure, pain, temperature, proprioception.

• Special Senses: Localized in specific organs; include vision (eye), hearing and equilibrium (ear), taste (tongue), smell (nose).

Sensory Receptors and Pathways

• Receptors: Mechanoreceptors (touch), thermoreceptors (temperature), nociceptors (pain), photoreceptors (light), chemoreceptors (chemicals).

• Pathways: Sensory information travels from receptors to CNS via specific neural pathways.

Anatomy and Physiology of the Eye

• Structures: Cornea, lens, retina, iris, optic nerve, etc.

• Function: Focuses light on retina; photoreceptors convert light to neural signals.

• Vision Tests: Near point (accommodation), blind spot (optic disc), color vision (cones).

Anatomy and Physiology of the Ear

• Structures: Outer ear (auricle, canal), middle ear (ossicles), inner ear (cochlea, vestibular apparatus).

• Function: Hearing (cochlea), balance (vestibular system).

• Deafness: Conduction (mechanical problem) vs. nerve (neural problem).

• Hearing Tests: Weber and Rinne tests distinguish types of hearing loss.

Pain and Referred Pain

• Pain: Detected by nociceptors; can be acute or chronic.

• Referred Pain: Perceived at a location other than the site of stimulus due to shared neural pathways.

Endocrine System

Hormone Secretion and Action

The endocrine system regulates body functions through hormones, which are chemical messengers secreted by glands and transported in the blood to target organs.

• Secretion: Hormones released by endocrine glands (e.g., pituitary, thyroid).

• Circulation: Hormones travel in bloodstream to distant targets.

• Reception: Target cells have specific receptors for hormones.

Major Endocrine Glands and Hormones

• Hypothalamus: Regulates pituitary; produces releasing/inhibiting hormones.

• Pituitary Gland: Master gland; secretes growth hormone, prolactin, gonadotropins, TSH, ADH, oxytocin.

• Thyroid: Produces thyroid hormone (metabolism), calcitonin (lowers blood calcium).

• Parathyroids: Secrete parathyroid hormone (raises blood calcium).

• Adrenals: Cortex (cortisol, aldosterone), medulla (adrenaline/epinephrine, noradrenaline/norepinephrine).

• Pancreas: Insulin (lowers blood glucose), glucagon (raises blood glucose).

Hormonal Disorders

• Hyperthyroidism: Excess thyroid hormone; symptoms include weight loss, increased metabolism.

• Hypothyroidism: Deficient thyroid hormone; symptoms include weight gain, fatigue.

• Diabetes Mellitus: Type I (insulin deficiency), Type II (insulin resistance).

Muscular System

Types of Muscle Tissue

• Skeletal Muscle: Voluntary, striated, attached to bones; responsible for movement.

• Cardiac Muscle: Involuntary, striated, found in heart.

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

Hierarchy of Skeletal Muscle Structure

• Muscle → Fascicle → Muscle fiber (cell) → Myofibril → Sarcomere (contractile unit)

Functions of the Muscular System

• Movement, posture, heat production, joint stabilization.

Sliding Filament Theory

• Muscle contraction occurs as actin and myosin filaments slide past each other within the sarcomere.

• At rest, sarcomere is elongated; during contraction, sarcomere shortens.

Control of Muscle Contraction

• Neuromuscular Junction: Synapse between motor neuron and muscle fiber; acetylcholine triggers contraction.

• Motor Units: One motor neuron and all muscle fibers it innervates.

• Fiber Types: Slow-twitch (endurance) vs. fast-twitch (power).

Muscle Contraction Mechanics

• Twitch: Single, brief contraction.

• Summation: Increased force by repeated stimulation.

• Complete Tetanus: Sustained contraction with no relaxation.

Muscle Naming and Actions

• Named by location, shape, size, direction of fibers, number of origins, action.

• Origin: Fixed attachment; Insertion: Movable attachment.

• Tendon: Connects muscle to bone; Ligament: Connects bone to bone.

• Agonist: Prime mover; Antagonist: Opposes movement; Synergist: Assists agonist.

Role of ATP in Muscle Contraction

• ATP provides energy for cross-bridge cycling and detachment of myosin from actin.

• Threshold Voltage: Minimum stimulus needed to elicit a muscle contraction.

Key Tables

System	Main Function	Key Structures
Nervous	Rapid communication, coordination	Brain, spinal cord, nerves
Endocrine	Long-term regulation via hormones	Pituitary, thyroid, adrenals, pancreas
Muscular	Movement, posture, heat	Skeletal muscles, tendons

Muscle Type	Location	Control	Striations
Skeletal	Attached to bones	Voluntary	Yes
Cardiac	Heart	Involuntary	Yes
Smooth	Walls of organs	Involuntary	No

Key Equations

• Resting Membrane Potential: $V_m = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$ Additional info: This is the Nernst equation for potassium ions, a major determinant of neuron resting potential.

• ATP Hydrolysis (energy for muscle contraction): $\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P_i} + \text{energy}$