Unit IV Laboratory Practical Review: Nervous System, Special Senses, and Related Anatomy

Structure of a Neuron

Overview

The neuron is the fundamental unit of the nervous system, responsible for transmitting electrical and chemical signals throughout the body. Understanding its structure is essential for comprehending neural function.

• Dendrites: Branch-like extensions that receive signals from other neurons.

• Axon Hillock: The region where the axon originates; site of action potential initiation.

• Axon: Long, slender projection that conducts electrical impulses away from the soma.

• Myelin Sheath (Schwann Cells): Insulating layer around the axon, produced by Schwann cells in the PNS, which increases signal conduction speed.

• Nucleus of Schwann Cell: The control center of the Schwann cell, involved in myelin production.

• Nucleus of Neuron: Contains genetic material; located in the soma.

• Soma: The cell body; contains organelles and the nucleus.

• Nissl Bodies: Rough endoplasmic reticulum in neurons, involved in protein synthesis.

• Internode: The segment of axon covered by myelin between two nodes of Ranvier.

• Node of Ranvier: Gaps in the myelin sheath where ion channels are concentrated, facilitating saltatory conduction.

Example: The myelin sheath allows rapid transmission of action potentials via saltatory conduction, jumping from node to node.

Spinal Cord Anatomy

Key Structures

The spinal cord is a major pathway for information traveling between the brain and peripheral nervous system. Its anatomy is organized for both sensory and motor functions.

• Central Canal: A small channel in the center of the spinal cord containing cerebrospinal fluid (CSF).

• Dorsal Root Ganglion: Cluster of sensory neuron cell bodies located outside the spinal cord.

• Dorsal Root: Carries sensory information into the spinal cord.

• Ventral Root: Carries motor information out of the spinal cord.

• Gray Horn (anterior/posterior): Regions of gray matter; anterior horn contains motor neurons, posterior horn contains sensory neurons.

Example: The dorsal root ganglion is the site of sensory neuron cell bodies, while the ventral root transmits motor commands.

Layers of the Brain

Meninges and Spaces

The brain is protected by three connective tissue layers called meninges, which also surround the spinal cord.

• Pia Mater: Innermost, delicate layer directly covering the brain and spinal cord.

• Arachnoid Mater: Middle, web-like layer.

• Dura Mater: Outermost, tough layer.

• Subdural Space: Space between dura and arachnoid mater.

• Subarachnoid Space: Space between arachnoid and pia mater, filled with CSF.

Example: Cerebrospinal fluid circulates in the subarachnoid space, providing cushioning and nutrient transport.

The Brain & Spinal Cord

Major Regions and Functions

The brain and spinal cord form the central nervous system (CNS), responsible for processing and integrating information.

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic control.

• Pituitary: Master endocrine gland, controlled by the hypothalamus.

• Corpus Callosum: Large bundle of fibers connecting the two cerebral hemispheres.

• Pons: Part of the brainstem; involved in respiration and communication between brain regions.

• Cerebrum: Largest part of the brain; responsible for higher functions like reasoning, memory, and voluntary movement.

• Midbrain: Controls visual and auditory reflexes.

• Medulla Oblongata: Controls vital functions such as heart rate and breathing.

• Cerebellum: Coordinates movement and balance.

• Lobes: Occipital (vision), Frontal (reasoning, motor control), Parietal (sensory processing), Temporal (hearing, memory).

• Sulci/Gyri: Precentral gyrus (primary motor cortex), Postcentral gyrus (primary sensory cortex), Central sulcus (divides frontal and parietal lobes).

• Fissures: Longitudinal (divides hemispheres), Lateral (separates temporal lobe).

• Spinal Cord: Main pathway for information between brain and body.

Example: The cerebellum is essential for fine motor coordination, while the medulla oblongata regulates involuntary functions.

Cranial Nerves

Identification and Function

There are twelve pairs of cranial nerves, each with specific sensory, motor, or mixed functions. Students should be able to identify them and understand their roles.

• Olfactory (I): Smell

• Optic (II): Vision

• Oculomotor (III): Eye movement

• Trochlear (IV): Eye movement

• Trigeminal (V): Facial sensation, chewing

• Abducens (VI): Eye movement

• Facial (VII): Facial expression, taste

• Vestibulocochlear (VIII): Hearing, balance

• Glossopharyngeal (IX): Taste, swallowing

• Vagus (X): Parasympathetic control of heart, lungs, digestive tract

• Accessory (XI): Neck muscles

• Hypoglossal (XII): Tongue movement

Example: The facial nerve controls muscles of facial expression and conveys taste from the anterior tongue.

The Eye

Anatomy and Function

The eye is a complex organ responsible for vision, composed of several specialized structures.

• Retina: Contains photoreceptors (rods and cones) for detecting light.

• Sclera: Tough, white outer layer providing protection.

• Cornea: Transparent front part; refracts light.

• Lens: Focuses light onto the retina.

• Pupil: Opening in the iris controlling light entry.

• Optic Nerve: Transmits visual information to the brain.

• Optic Disc: Blind spot where optic nerve exits the eye.

• Lacrimal Gland/Duct: Produces and drains tears.

• Aqueous Humor: Fluid in anterior chamber; maintains intraocular pressure.

• Vitreous Humor: Gel-like substance in posterior chamber; maintains eye shape.

• Suspensory Ligament: Holds lens in place.

• Ciliary Body: Produces aqueous humor and controls lens shape.

Example: The cornea and lens work together to focus light onto the retina for clear vision.

The Ear

Anatomy and Function

The ear is responsible for hearing and balance, consisting of external, middle, and inner regions.

• Tympanic Membrane: Eardrum; vibrates in response to sound.

• Ossicles: Malleus, Incus, Stapes; transmit vibrations from tympanic membrane to inner ear.

• External Auditory Canal: Channel for sound waves to reach tympanic membrane.

• Cochlea: Spiral-shaped organ; converts sound vibrations into nerve impulses.

• Semicircular Canals: Detect rotational movement; involved in balance.

• Eustachian Tube: Equalizes pressure between middle ear and atmosphere.

• Pinna/Auricle: External part; collects sound waves.

• Vestibulocochlear Nerve: Transmits hearing and balance information to the brain.

Example: The stapes transmits vibrations to the oval window of the cochlea, initiating the process of hearing.

Additional info: Academic context and definitions were added to expand brief points into full explanations. The cranial nerves list was inferred for completeness. This review covers content relevant to chapters 11-15 (nervous system and special senses) of a typical ANP college course.