BIO 162: Skeletal, Muscular, Nervous, and Special Senses Study Guide

Skeletal and Muscular System

Types of Muscle Tissue

The human body contains three main types of muscle tissue, each with distinct structure and function:

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

• Cardiac Muscle: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs (e.g., intestines, blood vessels).

Example: Skeletal muscles contract to move limbs, while cardiac muscle contracts rhythmically to circulate blood.

Movement of Joints

Joints allow for movement between bones. Types of joint movements include:

• Flexion and Extension: Decreasing or increasing the angle between bones.

• Abduction and Adduction: Moving limbs away from or toward the body's midline.

• Rotation: Turning a bone around its axis.

Example: The elbow joint allows flexion and extension of the forearm.

Parts of a Long Bone

Long bones have several key structural components:

• Diaphysis: Shaft of the bone, composed of compact bone.

• Epiphyses: Ends of the bone, containing spongy bone and red marrow.

• Periosteum: Outer fibrous covering.

• Medullary Cavity: Central cavity containing yellow marrow (fat).

Bone Cells

Bone tissue contains several types of cells:

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteoclasts: Break down bone matrix for remodeling.

The Nervous System

Functions of the Nervous System

The nervous system has three main functions:

• Sensory Input: Detects changes inside and outside the body.

• Integration: Processes and interprets sensory input.

• Motor Output: Responds by activating muscles or glands.

Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; integration and command center.

• Peripheral Nervous System (PNS): Nerves outside the CNS; connects CNS to limbs and organs.

Functional Classification of Neurons

• Sensory (Afferent) Neurons: Carry impulses toward the CNS.

• Motor (Efferent) Neurons: Carry impulses away from the CNS to effectors.

• Interneurons: Connect sensory and motor neurons within the CNS.

Neuroglia and Neuron Structure

Neuroglia are supporting cells in the nervous system, including astrocytes, microglia, ependymal cells, and oligodendrocytes. Neurons have a cell body, dendrites (receive signals), and an axon (transmits signals).

Myelination and Nerve Impulse Transmission

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

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

Example: Saltatory conduction allows impulses to "jump" from node to node, speeding transmission.

Resting and Action Potentials

• Resting Potential: Difference in charge across the membrane of a resting neuron (typically -70 mV).

• Action Potential: Rapid change in membrane potential that travels along the axon.

Equation:

$V_{rest} \approx -70\ \text{mV}$

Synaptic Transmission

• Synapse: Junction between neurons; neurotransmitters cross the synaptic cleft to transmit signals.

• Neurotransmitters: Chemical messengers (e.g., acetylcholine, dopamine, serotonin).

Reflex Arcs

Reflexes are rapid, automatic responses to stimuli. A typical reflex arc includes:

• Receptor

• Sensory neuron

• Integration center

• Motor neuron

• Effector

Central Nervous System Structures

• Cerebrum: Largest part of the brain; responsible for higher functions.

• Cerebellum: Coordinates movement and balance.

• Brain Stem: Controls vital functions (e.g., breathing, heart rate).

• Spinal Cord: Conducts impulses to and from the brain; center for reflexes.

Major Brain Regions and Functions

Region	Main Function
Cerebrum	Conscious thought, memory, voluntary movement
Cerebellum	Coordination, balance
Brain Stem	Autonomic functions (breathing, heart rate)
Diencephalon	Thalamus (relay center), hypothalamus (homeostasis)

Spinal Cord Structure

• Gray Matter: Contains neuron cell bodies.

• White Matter: Contains myelinated axons.

• Dorsal Root: Sensory input to spinal cord.

• Ventral Root: Motor output from spinal cord.

Peripheral Nervous System

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

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

Autonomic Nervous System

• Sympathetic Division: Prepares body for "fight or flight".

• Parasympathetic Division: Promotes "rest and digest" activities.

Comparison Table:

Division	Main Effect
Sympathetic	Increases heart rate, dilates pupils, inhibits digestion
Parasympathetic	Decreases heart rate, constricts pupils, stimulates digestion

Special Senses

General Anatomy of the Eye

The eye is a complex organ responsible for vision. Key structures include:

• Sclera: Outer white layer providing protection.

• Cornea: Transparent front part; refracts light.

• Choroid: Middle layer; contains blood vessels.

• Retina: Inner layer; contains photoreceptors (rods and cones).

Photoreceptors

• Rods: Sensitive to low light; responsible for night vision.

• Cones: Detect color; responsible for sharp, detailed vision.

Visual Pathway

Light passes through the cornea, lens, and vitreous humor to reach the retina, where photoreceptors convert it to electrical signals sent to the brain via the optic nerve.

Ear Anatomy and Hearing

• Outer Ear: Collects sound waves.

• Middle Ear: Contains ossicles (malleus, incus, stapes) that transmit vibrations.

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

Equilibrium and Balance

• Static Equilibrium: Maintained by the vestibule; detects head position.

• Dynamic Equilibrium: Maintained by semicircular canals; detects rotational movement.

Other Special Senses

• Taste: Detected by taste buds on the tongue.

• Smell: Detected by olfactory receptors in the nasal cavity.

Additional info: The sense of vision is not fully functional at birth; it develops over time.