CNS

Central Nervous System (CNS)

• Components of CNS:
  • Brain
  • Spinal Cord

Areas of Nervous Tissue

• Gray Matter:
  • Description: Continuous areas of neuron cell bodies, dendrites, synapses, unmyelinated neurons, and glia.
  • Discrete areas of gray matter are called nuclei, which are surrounded by white matter.
• White Matter:
  • Description: Areas containing axons. The vast majority of these axons are myelinated (myelin appears white). Includes glial cells.

The Brain

• Regions of the Brain:
  • Cerebrum
  • Diencephalon
  • Brainstem
  • Cerebellum

Cerebrum

• Cortical Gray Matter Characteristics:
  • Follows the patterns of sulci (grooves) and gyri (ridges).
  • Functions include the highest level of:
  • Sensory input processing
  • Somatic motor control, i.e., planning responses
  • Speech and articulation of thought
  • Memory, emotion, reasoning, motivation, personality, judgment, and intelligence.

Cerebral Hemispheres

• Major Lobes:
  • Frontal Lobe
  • Parietal Lobe
  • Occipital Lobe
  • Temporal Lobe

Gyri and Sulci Patterns

• Recognizable Patterns of Gyri and Sulci:
  • Central Sulcus: Divides precentral and postcentral gyri.
  • Lateral Fissure (Sylvian Fissure)
  • Longitudinal Cerebral Fissure
  • Transverse Cerebral Fissure

Somatosensory Cortex

• Homunculus:
  • Topographically organized representation of sensory receptors. Each area corresponds to a specific part of the body, indicating the density of sensory receptors.
  • Axonal endings are grouped based on the location of receptors that give rise to specific sensory pathways.

Cerebral Cortex and White Matter

• Components:
  • Cerebral White Matter
  • Insula: Cortex beneath the lateral sulcus.
  • Basal Nuclei (Basal Ganglia): Groups of nuclei involved in motor control, emotions.
  • Hypothalamus: Regulates homeostasis, links endocrine and nervous systems.
  • Notable structures:
  • Longitudinal Fissure: Separates the brain into left and right hemispheres.
  • Fornix: A C-shaped bundle of fibers in the brain.
  • Corpus Callosum: Connects the left and right cerebral hemispheres.
  • Caudate Nucleus and Putamen: Parts of basal ganglia involved in movement regulation.
  • Globus Pallidus: Involved in the regulation of voluntary movement.
  • Thalamus: Encloses the third ventricle.

Diencephalon

• Components:
  • Third Ventricle: Space filled with cerebrospinal fluid (CSF).
  • Septum Pellucidum: Membrane separating the lateral ventricles.
  • Interthalamic Adhesion (Intermediate Mass of Thalamus): Connects bilateral thalamic bodies.
  • Interventricular Foramen (Foramen of Monro): Connects lateral ventricles to the third ventricle.
  • Notable structures:
  • Anterior Commissure: Connects the two cerebral hemispheres.
  • Hypothalamus: Homeostasis, emotional response control.
  • Optic Chiasma: Crossing of optic nerves.
  • Pituitary Gland (Hypophysis Cerebri): Hormonal regulation.
  • Pineal Body: Part of the epithalamus; secretes melatonin.
  • Various lobes of cerebral hemispheres: Frontal, parietal, occipital, and temporal lobes.
  • Corpora Quadrigemina: Reflex centers for vision and hearing.

Brainstem

• Components:
  • Midbrain
  • Pons
  • Medulla Oblongata

Midbrain

• Functions in visual and auditory processing, motor control, alertness, and temperature regulation.
• Contains important structures such as:
  • Trochlear Nerve (IV): Responsible for vertical eye movement.
  • Oculomotor Nerve (III): Controls eye movements and pupil dilation.

Pons

• Connects the upper and lower parts of the brain, playing critical roles in managing sleep and arousal.
• Important components included:
  • Mammillary Bodies: Associated with memory.
  • Several cranial nerves (e.g., Facial Nerve VII, Trigeminal Nerve V).

Medulla Oblongata

• Controls involuntary functions such as heartbeat and respiration.
• Contains vital centers for regulating breathing, heart rate, and blood pressure.
  • Pyramids: Decussation of pyramids (where signals cross between hemispheres).

Cerebellum

• Function:
  • Coordinates somatic motor activity.
  • Regulates muscle tone, fine motor skills, and balance (maintains equilibrium).
• Fiber tracts connect the cerebellum with the cerebral hemispheres and spinal cord.

Ventricles of the Brain

• Characteristics:
  • Derived from the central canal of the neural tube.
  • Lined with ependymal cells.
  • Filled with cerebrospinal fluid (CSF).

Ventricular Structure:

• Lateral Ventricles:
  • Contains the anterior horn, posterior horn, and inferior horn.
• Third Ventricle:
  • Located between the lateral ventricles.
• Cerebral Aqueduct: Connects third and fourth ventricles.
• Fourth Ventricle: Connects to the central canal of the spinal cord.

Meninges

• Three Layers of Meninges Surrounding CNS:
  • Pia Mater: Highly vascularized connective tissue layer; adheres closely to the surface of the brain and follows gyri and sulci.
  • Functions: Vascular supply of the brain within, helps form the choroid plexus.
  • Arachnoid Mater: Web-like layer with elastic and collagen fibers; subarachnoid space filled with CSF.
  • Dura Mater:
  • Single layer in the vertebral canal.
  • Double layer in the cranium:
    • Periosteal Layer: Adheres to skull.
    • Meningeal Layer: Follows contours of the skull.

Dural Folds

• Folds of Dura Mater:
  1. Falx Cerebri: Sickle-shaped fold along the longitudinal fissure.
  2. Tentorium Cerebelli: Separates cerebellum from the cerebrum.
  3. Falx Cerebelli: Separates the two cerebellar hemispheres.

Cerebrospinal Fluid (CSF)

• Description: Watery, viscous fluid similar to lymph and plasma.
• Function:
  • Provides cushioning and buoyancy to the brain.
  • Produced by the choroid plexus in each ventricle and circulates through the ventricles, escaping into the subarachnoid space.

CSF Circulation:

• Circulated through ventricles and escapes to the subarachnoid space via three openings from the fourth ventricle.
• CSF escapes via arachnoid villi into the superior sagittal sinus.

Venous Sinuses

• Characteristics:
  • Travel between the two layers of the dura mater and are lined by endothelium.
  • Continuous with blood vessels and drain toward the jugular foramen and internal jugular vein.
  • Main sinuses include the superior sagittal sinus, inferior sagittal sinus, straight sinus, and the transverse sinuses.

Spinal Cord

• Structure:
  • Composed of cervical, thoracic, lumbar, sacral, and coccygeal spinal nerves.
  • Enclosed by spinal meninges and sections include:
  • Cervical Enlargement: Contains nerves servicing the upper limbs.
  • Lumbar Enlargement: Serves the lower limbs.
  • Conus Medullaris: The tapered end of the spinal cord.
  • Cauda Equina: A bundle of spinal nerves traversing downward.
  • Spinal Meninges: Surrounded by epidural, subdural, and subarachnoid spaces.
• Gray and White Matter Structures:
  • Gray Matter: Contains dorsal (sensory) and ventral (motor) horns plus lateral horns (ANS).
  • White Matter: Comprised of tracts known as funiculi, including posterior, lateral, and anterior funiculi.

Reflex Arc

• Definition: A neural pathway that controls a reflex action.
• Components:
  • Dendrites & Receptors: Detect sensory stimuli.
  • Sensory Neuron: Transmits afferent signals towards the CNS.
  • Interneuron(s): Processes information within the CNS.
  • Motor Neuron: Sends efferent signals to effectors (muscles and glands).
• Functionality: Ensures fast response to specific stimuli by bypassing higher brain centers, facilitating quick reflex actions.

Sensory Pathways

• Spinal Pathway (Rapid):
  • Example of a withdrawal reflex initiated by a painful stimulus, processing through sensory neurons and interneurons, and activating somatic motor neurons for rapid response.
• Cortical Pathway (Slower):
  • Involves integration within the gray matter of the cortex, localization of the stimulus, and planning more complex responses through multiple nerve pathways.