study guide + mine ch 14

Central Nervous System: Brain and Spinal Cord

Overview of CNS Structure and Function

• Central Nervous System (CNS) consists of the brain and spinal cord, serving as the main control center for the body’s activities, thoughts, and emotions.

• The brain is divided into several major regions: cerebrum, diencephalon, brainstem (midbrain, pons, medulla oblongata), and cerebellum.

• The spinal cord connects the brain to the peripheral nervous system and facilitates communication between the brain and body.

Major Brain Regions and Landmarks

Cerebrum

• The cerebrum is the largest and most anterior part of the brain, responsible for higher cognitive functions, voluntary movement, and sensory perception.

• Cerebral cortex: The outer layer of gray matter, involved in conscious thought and action.

• Basal nuclei: Clusters of gray matter deep within the cerebrum, involved in movement regulation.

• Lobes of the cerebrum:

  • Frontal lobe: Voluntary movement, planning, decision-making, and consciousness.

  • Parietal lobe: Sensation, temperature, pain, and touch.

  • Occipital lobe: Vision and visual association.

  • Temporal lobe: Hearing, smell, and long-term memory.

• Landmarks:

  • Gyrus: Elevated ridges on the brain surface.

  • Sulcus: Shallow grooves separating gyri.

  • Fissure: Deep grooves separating larger brain regions.

  • Central sulcus: Separates frontal and parietal lobes.

  • Lateral fissure: Separates temporal lobe from frontal and parietal lobes.

  • Longitudinal fissure: Divides left and right cerebral hemispheres.

Diencephalon

• Located centrally, includes the thalamus, hypothalamus, and epithalamus.

• Thalamus: Relay and processing center for sensory information (except olfaction).

• Hypothalamus: Regulates emotions, autonomic functions, hormone production, and links nervous and endocrine systems.

• Epithalamus: Contains the pineal gland, which secretes melatonin for circadian rhythm regulation.

Brainstem

• Connects the cerebrum to the spinal cord and consists of the midbrain, pons, and medulla oblongata.

• Midbrain (Mesencephalon): Processes visual and auditory data, maintains consciousness, and controls reflexive somatic motor responses.

• Pons: Relays sensory information to the cerebellum and thalamus; involved in subconscious somatic and visceral motor control.

• Medulla oblongata: Relays sensory information, regulates autonomic functions (cardiovascular, respiratory, digestive), and contains important reflex centers.

Cerebellum

• Located posteriorly, the cerebellum coordinates somatic motor activity, balance, and posture.

• Contains Purkinje cells (large neurons) and arbor vitae (tree-like arrangement of white matter).

Development of the Brain

Neural Tube and Brain Vesicles

• The neural tube is the embryonic structure that forms the CNS.

• Primary brain vesicles:

  • Prosencephalon (forebrain): Forms the cerebrum and diencephalon.

  • Mesencephalon (midbrain): Forms the midbrain.

  • Rhombencephalon (hindbrain): Forms the pons, cerebellum, and medulla oblongata.

• Secondary brain vesicles further differentiate into specific brain regions and ventricles.

White and Gray Matter Organization

Brain vs. Spinal Cord

• White matter: Myelinated axons; in the brain, found internally; in the spinal cord, found externally.

• Gray matter: Neuron cell bodies, dendrites, and unmyelinated axons; in the brain, forms the cortex and basal nuclei; in the spinal cord, forms the central core.

Ventricular System

Brain Ventricles and CSF Circulation

• The brain contains four ventricles: two lateral ventricles, third ventricle, and fourth ventricle, connected by passageways (interventricular foramen and cerebral aqueduct).

• Cerebrospinal fluid (CSF) is produced by the choroid plexus in all four ventricles, circulates through the ventricles, central canal, and subarachnoid space, and is reabsorbed into the venous system.

• Functions of CSF: supports and cushions the CNS, transports nutrients, chemical messengers, and waste products.

• CSF is produced at a rate of about 500 mL/day, with a total volume of about 150 mL, replaced every 8 hours.

Cranial Meninges

Protective Layers of the Brain

• Three layers: dura mater (outermost, tough), arachnoid mater (middle, web-like), and pia mater (innermost, delicate, adheres to brain surface).

• Dura mater in the brain has two layers: periosteal (fused with skull) and meningeal (closer to brain).

• Dural folds and dural venous sinuses stabilize the brain and drain venous blood.

• Spaces:

  • Subdural space: Between dura and arachnoid; can fill with blood after trauma (subdural hemorrhage).

  • Subarachnoid space: Between arachnoid and pia; contains CSF and blood vessels.

Blood-Brain Barrier (BBB)

Selective Permeability of the CNS

• The blood-brain barrier restricts passage of substances from the blood into the CNS, protecting neural tissue from toxins and pathogens.

• Formed by tight junctions between endothelial cells and astrocyte end-feet.

• Some regions (e.g., hypothalamus, choroid plexus) have a less restrictive barrier to allow hormone exchange.

Brainstem: Medulla Oblongata, Pons, and Midbrain

Medulla Oblongata

• Located at the inferior part of the brainstem, continuous with the spinal cord.

• Contains nuclei for autonomic functions (cardiovascular and respiratory centers), sensory and motor relay stations, and cranial nerve nuclei (VIII, IX, X, XI, XII).

• Decussation of pyramids: Crossing of motor fibers, resulting in contralateral control of the body.

• Reticular formation: Network of neurons involved in consciousness and alertness.

Pons

• Links cerebellum with the rest of the brain and spinal cord.

• Contains nuclei for cranial nerves V, VI, VII, and VIII, and centers for respiratory regulation.

• Transverse pontine fibers connect the pons to the cerebellum.

Midbrain (Mesencephalon)

• Contains sensory nuclei (corpora quadrigemina: superior and inferior colliculi) for visual and auditory reflexes.

• Substantia nigra: Produces dopamine; degeneration leads to Parkinson’s disease.

• Cerebral peduncles: Bundles of nerve fibers carrying motor commands.

Cerebellum

Structure and Function

• Coordinates voluntary movements, balance, and posture.

• Contains anterior and posterior lobes, vermis (midline structure), and arbor vitae (white matter).

• Purkinje cells: Large neurons that integrate sensory and motor information.

Cerebral Cortex and Functional Areas

Motor and Sensory Areas

• Primary motor cortex (precentral gyrus): Initiates voluntary movements.

• Primary somatosensory cortex (postcentral gyrus): Receives sensory input from skin, muscles, and joints.

• Homunculus: Map showing the proportional representation of body parts based on neural connections.

• Association areas: Integrate and interpret sensory and motor information.

• Broca’s area: Speech production (frontal lobe).

• Wernicke’s area: Language comprehension (temporal lobe).

White Matter Tracts

• Association fibers: Connect regions within the same hemisphere.

• Commissural fibers: Connect left and right hemispheres (e.g., corpus callosum).

• Projection fibers: Connect the cortex with lower brain regions and spinal cord.

Basal Nuclei

• Subcortical clusters of gray matter involved in movement regulation, initiation, and inhibition of unwanted movements.

• Includes structures such as the caudate nucleus, putamen, and globus pallidus.

Diencephalon: Thalamus, Hypothalamus, Epithalamus

Thalamus

• Major relay station for sensory information (except olfaction) to the cerebral cortex.

• Coordinates activity between basal nuclei and cortex.

Hypothalamus

• Regulates autonomic and endocrine functions, body temperature, circadian rhythms, emotions, and behaviors.

• Produces hormones: antidiuretic hormone (ADH) and oxytocin.

• Controls hunger, thirst, and satiety centers.

Epithalamus

• Contains the pineal gland, which secretes melatonin for sleep-wake regulation.

Limbic System

Emotion and Memory

• Involved in emotional responses, motivation, and memory formation.

• Includes the hippocampus (memory), amygdaloid body (emotion), and parts of the diencephalon and reticular formation.

Hemispheric Lateralization

Specialization of Brain Hemispheres

• Each hemisphere is specialized for certain functions (e.g., left: language and logic; right: spatial and artistic abilities).

• Contralateral control: Each hemisphere controls the opposite side of the body.

• Cerebral dominance: One hemisphere is dominant for specific functions (e.g., language).

Cranial Nerves

Overview and Functions

Number	Name	Function
I	Olfactory	Sensory: Smell
II	Optic	Sensory: Vision
III	Oculomotor	Motor: Eye movement
IV	Trochlear	Motor: Eye movement (superior oblique)
V	Trigeminal	Mixed: Sensation from face, chewing
VI	Abducens	Motor: Eye movement (lateral rectus)
VII	Facial	Mixed: Facial expression, taste
VIII	Vestibulocochlear	Sensory: Hearing, balance
IX	Glossopharyngeal	Mixed: Taste, swallowing
X	Vagus	Mixed: Autonomic control of thoracic and abdominal organs
XI	Accessory	Motor: Swallowing, head movement
XII	Hypoglossal	Motor: Tongue movement

Clinical Correlates and Disorders

Hemorrhages and Hydrocephalus

• Epidural hemorrhage: Bleeding between dura mater and skull, often due to trauma; can cause rapid increase in intracranial pressure.

• Subdural hemorrhage: Bleeding between dura mater and arachnoid mater, usually from ruptured veins; symptoms may develop gradually.

• Hydrocephalus: Accumulation of CSF due to impaired resorption or circulation; can cause enlarged skull in infants and brain damage in adults.

Cerebrovascular Diseases

• Cerebrovascular accident (CVA, stroke): Interruption of blood supply to the brain, leading to tissue damage and loss of function.

Disorders of the Nervous System

• Dyslexia: Difficulty in reading and writing due to problems processing visual or auditory information.

• Aphasia: Impairment of language abilities (speaking, reading, understanding) due to brain damage, often from stroke.

• Seizure disorders (epilepsies): Temporary disturbances in brain function, causing abnormal movements, sensations, or behaviors.

• Parkinson’s disease: Degeneration of substantia nigra neurons, leading to motor deficits due to decreased dopamine.

Key Terms and Concepts

• Tracts: Bundles of CNS axons.

• Nuclei: Collections of neuron cell bodies in the CNS (gray matter).

• Decussation: Crossing of nerve fibers from one side to the other (e.g., in the medulla oblongata).

• Reticular formation: Network of neurons involved in arousal and consciousness.

Summary Table: Brain Regions and Main Functions

Region	Main Functions
Cerebrum	Conscious thought, voluntary movement, sensory perception
Diencephalon	Sensory relay, autonomic and endocrine regulation, emotion
Brainstem	Autonomic functions, reflexes, cranial nerve nuclei
Cerebellum	Coordination of movement, balance, posture

Example Applications

• Example: Damage to the left primary motor cortex (precentral gyrus) results in paralysis of the right side of the body due to contralateral control.

• Example: A stroke affecting Broca’s area leads to expressive aphasia, where speech production is impaired but comprehension may remain intact.

• Example: Parkinson’s disease is characterized by tremors and rigidity due to loss of dopamine-producing neurons in the substantia nigra.

Additional info: Academic context and explanations have been expanded for clarity and completeness. Table entries and some clinical details are inferred from standard anatomy and physiology textbooks.