Chapter 13 Nervous System: Brain and Cranial Nerves

Structures that Protect and Support the Brain

• Identify the four structures that protect and support the brain:

  • Cranial Bones: The skull provides a rigid, bony framework that encases the brain, protecting it from mechanical damage.

  • Meninges: These are three layers of protective tissue that surround the brain and spinal cord, providing additional cushioning and support.

  • Cerebrospinal Fluid (CSF): This fluid circulates around the brain and spinal cord, providing a liquid cushion to absorb shocks and transport nutrients and waste products.

  • Blood-Brain Barrier (BBB): A specialized barrier formed by tightly packed endothelial cells lining the brain's blood vessels, which restricts the entry of harmful substances from the bloodstream into the brain tissue.

Meninges

• Arrange the meninges from most superficial to most deep:

  • Dura Mater: The outermost, tough, and fibrous layer of the meninges. It is composed of two layers in the skull, the periosteal layer (outermost) and the meningeal layer (innermost).

  • Arachnoid Mater: The middle layer of the meninges, characterized by its web-like appearance. It is separated from the dura mater by the subdural space.

  • Pia Mater: The innermost layer of the meninges, which is a thin, delicate membrane that adheres directly to the surface of the brain and spinal cord.

• Compare and contrast the three spaces found within the meninges:

  • Epidural Space: Located between the dura mater and the skull (or vertebral column in the spinal cord). Contains fat and blood vessels.

  • Subdural Space: Located between the dura mater and the arachnoid mater. Contains a thin layer of fluid.

  • Subarachnoid Space: Located between the arachnoid mater and the pia mater. Filled with cerebrospinal fluid (CSF) and contains blood vessels and nerves.

Cerebrospinal Fluid (CSF)

• Describe the functions, formation, and reabsorption of cerebrospinal fluid (CSF):

  • Functions:

  • Cushioning and Protection: CSF acts as a liquid cushion, protecting the brain and spinal cord from mechanical trauma.

  • Nutrient Delivery and Waste Removal: CSF transports nutrients and removes metabolic waste products from the brain tissue.

  • Regulation of Intracranial Pressure: CSF helps maintain stable intracranial pressure by adjusting its volume.

  • Formation: CSF is primarily produced by the choroid plexuses, which are networks of specialized ependymal cells and capillaries located within the ventricles of the brain.

  • Reabsorption: CSF is reabsorbed into the bloodstream through the arachnoid granulations (villi), which are small protrusions of the arachnoid mater into the dural sinuses.

• Trace the flow of CSF through the nervous system starting with the lateral ventricles:

  1. Lateral Ventricles

  2. Interventricular Foramen (Foramen of Monro)

  3. Third Ventricle

  4. Cerebral Aqueduct (Aqueduct of Sylvius)

  5. Fourth Ventricle

  6. Lateral Apertures (Foramina of Luschka) and Median Aperture (Foramen of Magendie)

  7. Subarachnoid Space

  8. Arachnoid Granulations (Villi)

  9. Dural Venous Sinuses

  10. Venous Circulation

Blood-Brain Barrier

• Identify the components of and the importance of the blood-brain barrier:

  • Components:

  • Tight Junctions: Specialized connections between endothelial cells lining the brain capillaries that prevent the passage of substances between cells.

  • Astrocytes: Star-shaped glial cells that surround brain capillaries and help regulate the permeability of the BBB.

  • Pericytes: Cells embedded in the capillary walls that provide structural support and regulate blood flow.

  • Importance:

  • Protection: The BBB protects the brain from harmful substances, toxins, and pathogens that may be present in the bloodstream.

  • Regulation: The BBB regulates the passage of essential nutrients and molecules, ensuring optimal brain function.

  • Stability: By maintaining a stable chemical environment, the BBB helps prevent fluctuations in ion concentrations and neurotransmitter levels that could disrupt neuronal activity.

Functional Areas of the Brain

• Create a table that describes the location and function of the five functional areas discussed in class:

Major Brain Regions

• List the four major regions of the brain and the structures that make up the cerebrum, diencephalon, and brainstem:

  • Cerebrum:

  • Cerebral Cortex

  • Basal Ganglia

  • Hippocampus

  • Amygdala

  • Diencephalon:

  • Thalamus

  • Hypothalamus

  • Epithalamus

  • Subthalamus

  • Brainstem:

  • Midbrain

  • Pons

  • Medulla Oblongata

  • Cerebellum

Gyri, Sulci, and Fissures

• Compare and contrast the following terms: gyrus, sulcus, and fissure.

  • Gyrus: A ridge or fold on the surface of the cerebral cortex.

  • Sulcus: A groove or depression on the surface of the cerebral cortex.

  • Fissure: A deep, prominent groove on the surface of the cerebral cortex.

Cerebral Hemispheres

• Define lateralization and describe the primary functions of the left and right cerebral hemispheres.

  • Lateralization: The specialization of function between the two cerebral hemispheres.

  • Left Cerebral Hemisphere:

  • Language processing (speech, grammar, vocabulary)

  • Analytical and logical reasoning

  • Mathematical abilities

  • Right Cerebral Hemisphere:

  • Spatial perception and orientation

  • Facial recognition

  • Musical and artistic abilities

  • Emotional processing

• Describe the importance of the corpus callosum in relation to the cerebral hemispheres.

  • The corpus callosum is a large bundle of nerve fibers that connects the left and right cerebral hemispheres, allowing them to communicate and coordinate their activities. It enables the transfer of information between the hemispheres, facilitating integrated brain function.

Cerebrum

• Describe the general function of the cerebrum as well as the functions of each lobe:

  • General Function: The cerebrum is responsible for higher-level cognitive functions such as perception, thought, memory, and voluntary movement.

  • Frontal Lobe:

  • Executive functions (planning, decision-making, problem-solving)

  • Voluntary motor control

  • Speech production (Broca’s area)

  • Personality and emotional regulation

  • Parietal Lobe:

  • Sensory perception (touch, temperature, pain, pressure)

  • Spatial awareness and navigation

  • Integration of sensory information

  • Occipital Lobe:

  • Visual processing

  • Object recognition

  • Color perception

  • Temporal Lobe:

  • Auditory processing

  • Memory formation

  • Language comprehension (Wernicke’s area)

  • Insular Lobe:

  • Taste perception

  • Visceral sensation

  • Autonomic control

  • Which lobe is not visible? The insular lobe is not visible from the surface of the brain because it is located deep within the lateral sulcus.

Cerebellum

• Describe the general functions of the cerebellum.

  • Motor Coordination: The cerebellum plays a critical role in coordinating voluntary movements, ensuring they are smooth and accurate.

  • Balance and Posture: The cerebellum helps maintain balance and posture by integrating sensory information from the inner ear, muscles, and joints.

  • Motor Learning: The cerebellum is involved in the learning and adaptation of motor skills, allowing us to improve our performance over time.

Diencephalon

• Describe the general functions of the diencephalon:

  • Epithalamus:

  • Contains the pineal gland, which secretes melatonin and regulates sleep-wake cycles.

  • Thalamus:

  • Acts as a relay station for sensory information, transmitting signals from the body to the cerebral cortex.

  • Involved in motor control, emotion, and memory.

  • Hypothalamus:

  • Regulates homeostasis by controlling body temperature, hunger, thirst, and sleep-wake cycles.

  • Controls the autonomic nervous system and endocrine system.

Brainstem

• Describe the general functions of the brainstem:

  • Midbrain:

  • Controls eye movements, auditory and visual processing, and motor control.

  • Pons:

  • Relays sensory information between the cerebrum and the cerebellum.

  • Involved in breathing, sleep, and arousal.

  • Medulla Oblongata:

  • Controls vital functions such as heart rate, blood pressure, and respiration.

  • Involved in reflexes such as coughing, sneezing, and swallowing.

Cranial Nerves

• Describe the function of each cranial nerve as well as what happens when each cranial nerve is damaged and how to assess cranial nerve damage.

  • I. Olfactory Nerve:

  • Function: Sense of smell.

  • Damage: Anosmia (loss of smell).

  • Assessment: Use familiar scents such as coffee or vanilla to assess the patient’s ability to smell.

  • II. Optic Nerve:

  • Function: Vision.

  • Damage: Visual defects, blindness.

  • Assessment: Use a Snellen chart to assess visual acuity and test visual fields.

  • III. Oculomotor Nerve:

  • Function: Eye movement, pupil constriction, and upper eyelid elevation.

  • Damage: Ptosis (drooping eyelid), pupil dilation, and inability to move the eye in certain directions.

  • Assessment: Assess pupil size and reactivity to light, and test the patient’s ability to follow a moving object with their eyes.

  • IV. Trochlear Nerve:

  • Function: Eye movement (specifically, downward and lateral movement).

  • Damage: Difficulty moving the eye downward and outward, double vision.

  • Assessment: Test the patient’s ability to follow a moving object with their eyes, particularly in the downward and lateral directions.

  • V. Trigeminal Nerve:

  • Function: Sensory innervation to the face, motor innervation to the muscles of mastication.

  • Damage: Loss of sensation in the face, weakness of the muscles of mastication.

  • Assessment: Assess sensation in the face using a cotton swab, and test the patient’s ability to clench their jaw and move it from side to side.

  • VI. Abducens Nerve:

  • Function: Eye movement (specifically, lateral movement).

  • Damage: Inability to move the eye laterally, double vision.

  • Assessment: Test the patient’s ability to move their eyes laterally.

  • VII. Facial Nerve:

  • Function: Motor innervation to the muscles of facial expression, taste sensation from the anterior two-thirds of the tongue, and autonomic innervation to the lacrimal and salivary glands.

  • Damage: Facial paralysis (Bell’s palsy), loss of taste sensation, and dry eyes.

  • Assessment: Assess the patient’s ability to smile, frown, and raise their eyebrows, and test their taste sensation.

  • VIII. Vestibulocochlear Nerve:

  • Function: Hearing and balance.

  • Damage: Hearing loss, tinnitus, vertigo, and loss of balance.

  • Assessment: Perform hearing tests and assess the patient’s balance and coordination.

  • IX. Glossopharyngeal Nerve:

  • Function: Taste sensation from the posterior one-third of the tongue, swallowing, and salivation.

  • Damage: Loss of taste sensation, difficulty swallowing, and dry mouth.

  • Assessment: Assess the patient’s ability to taste and swallow, and check for excessive dryness in the mouth.

  • X. Vagus Nerve:

  • Function: Autonomic innervation to the heart, lungs, and digestive system, as well as motor innervation to the muscles of the larynx and pharynx.

  • Damage: Hoarseness, difficulty swallowing, and impaired autonomic function.

  • Assessment: Assess the patient’s voice and swallowing ability, and monitor their heart rate and blood pressure.

  • XI. Accessory Nerve:

  • Function: Motor innervation to the sternocleidomastoid and trapezius muscles.

  • Damage: Weakness of the sternocleidomastoid and trapezius muscles, difficulty shrugging the shoulders and turning the head.

  • Assessment: Assess the patient’s ability to shrug their shoulders and turn their head against resistance.

  • XII. Hypoglossal Nerve:

  • Function: Motor innervation to the muscles of the tongue.

  • Damage: Weakness of the tongue muscles, difficulty speaking and swallowing.

  • Assessment: Assess the patient’s ability to stick out their tongue and move it from side to side.