Nervous System II: Divisions and Functions of the Nervous System

General Characteristics of the Central Nervous System

Central Nervous System (CNS)

The central nervous system (CNS) is composed of the brain and spinal cord, serving as the primary control center for sensation, perception, movement, and higher mental functions. The brain is the largest and most complex part of the nervous system, consisting of two cerebral hemispheres, the diencephalon, brainstem, and cerebellum. The brainstem connects the brain to the spinal cord, and both structures communicate with the peripheral nervous system (PNS) via peripheral nerves.

• Meninges: Protective membranes that lie between the bone and soft tissues of the CNS.

Meninges

Types and Functions of Meninges

The meninges are three layers of membranes that protect the brain and spinal cord:

• Dura mater: Outer layer; tough, dense connective tissue. Contains dural sinuses and an epidural space.

• Arachnoid mater: Middle layer; web-like structure. The subarachnoid space contains cerebrospinal fluid (CSF).

• Pia mater: Inner layer; attached to the surface of the brain and spinal cord. Contains blood vessels and nerves, nourishing the CNS.

Example: The dura mater forms a protective barrier against physical impacts, while the pia mater supplies nutrients to neural tissue.

Ventricles and Cerebrospinal Fluid (CSF)

Formation and Function of CSF

Cerebrospinal fluid (CSF) is produced in four interconnected ventricles within the cerebral hemispheres and brainstem. These ventricles are continuous with the central canal of the spinal cord:

• 2 Lateral ventricles (first and second)

• Third ventricle

• Fourth ventricle

• Interventricular foramina: Connect third to lateral ventricles

• Cerebral aqueduct: Connects third and fourth ventricles

CSF is secreted by choroid plexuses (special capillaries of pia mater covered by ependymal cells) and serves nutritive and protective roles for CNS neurons. It helps maintain stable ionic concentrations and circulates through the ventricles, central canal, and subarachnoid space. CSF is absorbed by arachnoid granulations and its volume is about 140 mL at any time.

Example: CSF cushions the brain against trauma and removes metabolic waste.

Structure and Functions of Major Parts of the Brain, Brainstem, and Spinal Cord

Brain Functions

The brain contains centers for sensory function, motor commands, higher mental functions (memory, reasoning), coordination of movement, regulation of visceral activities, and personality.

Brain Development

The brain develops from three embryonic vesicles:

• Forebrain (prosencephalon): Divides into telencephalon and diencephalon

• Midbrain (mesencephalon): Remains as midbrain

• Hindbrain (rhombencephalon): Divides into metencephalon and myelencephalon

These regions form the major adult brain structures: cerebrum, basal nuclei, diencephalon, midbrain, cerebellum, pons, and medulla oblongata.

Table: Structural Development of the Brain

Embryonic Vesicle	Spaces Produced	Regions of the Brain Produced
Forebrain (prosencephalon)	Lateral ventricles	Cerebrum, Basal nuclei
Anterior portion (telencephalon)	Lateral ventricles	Cerebrum
Posterior portion (diencephalon)	Third ventricle	Thalamus, Hypothalamus, Posterior pituitary gland, Pineal gland
Midbrain (mesencephalon)	Cerebral aqueduct	Midbrain
Hindbrain (rhombencephalon)	Fourth ventricle	Cerebellum, Pons
Posterior portion (myelencephalon)	Fourth ventricle	Medulla oblongata

Major Portions of the Adult Brain

• Cerebrum

• Diencephalon

• Cerebellum

• Brainstem

Structure of the Cerebrum

• Cerebral hemispheres: Two halves separated by the falx cerebri

• Corpus callosum: Connects the hemispheres

• Gyri: Ridges or convolutions

• Sulci: Shallow grooves (e.g., central sulcus)

• Fissures: Deep grooves (longitudinal and transverse)

The cerebrum has five lobes: frontal, parietal, temporal, occipital, and insula (deep within the lateral sulcus).

Cerebral Cortex and White Matter

• Cerebral cortex: Thin layer of gray matter, outermost layer, contains ~75% of neuron cell bodies

• White matter: Lies beneath cortex, contains myelinated axons connecting cortex to other CNS regions

Functions of the Cerebral Cortex

• Interpreting sensory impulses

• Initiating voluntary movements

• Storing and retrieving information (memory)

• Reasoning, intelligence, personality

The cortex is divided into sensory, association, and motor areas, with some overlap.

Sensory Areas of the Cortex

• Cutaneous sensory area: Parietal lobe; interprets skin sensations

• Visual area: Occipital lobe; interprets vision

• Auditory area: Temporal lobe; interprets hearing

• Gustatory area: Near base of central sulcus; interprets taste

• Olfactory area: Deep within temporal lobes; interprets smell

• Wernicke's area: Temporal/parietal lobe; language comprehension

Association Areas of the Cortex

• Analyze and interpret sensory experiences

• Provide memory, reasoning, judgment, emotions

• Frontal lobe: Planning, problem solving, emotional behavior

• Parietal lobe: Understanding speech, expressing thoughts

• Temporal lobe: Understanding speech, reading, storing complex memories

• Occipital lobe: Combining visual images with other sensory experiences

• Insula: Translating sensory information into emotional responses

Motor Areas of the Cortex

• Primary motor cortex: Frontal lobes; controls voluntary muscles

• Broca's area: Controls muscles for speech

• Frontal eye field: Controls voluntary eye movements

Table: Functions of the Cerebral Lobes

Lobe	Functions
Frontal	Higher intellectual processes, voluntary skeletal muscle movements
Parietal	Sensations of temperature, touch, pressure, pain; speech and expression
Temporal	Hearing, interpreting sensory experiences, memory
Occipital	Vision, combining visual images with other sensory experiences

Hemisphere Dominance

Dominant vs. Nondominant Hemisphere

In most people, the left hemisphere is dominant, controlling language skills (speech, writing, reading), verbal, analytical, and computational skills. The nondominant hemisphere controls nonverbal tasks, spatial orientation, musical and visual pattern interpretation, and emotional/intuitive thought processes.

Stages in Memory Storage

Types of Memory

• Short-term (working) memory: Neurons connected in a circuit; memory persists only while impulses flow. Memory consolidation transfers information to long-term memory.

• Long-term memory: Lasts a lifetime; involves changes in neuron structure/function and increased synaptic connections. Long-term potentiation increases neurotransmitter release and synaptic effectiveness after repeated stimulation.

Basal Nuclei

Structure and Function

• Masses of gray matter deep within cerebral hemispheres

• Consist of caudate nucleus, putamen, globus pallidus

• Produce dopamine

• Help control voluntary movement

Diencephalon

Structure and Function

• Located between cerebral hemispheres and above brainstem

• Surrounds the third ventricle

• Composed of gray matter

• Includes thalamus, hypothalamus, optic tracts/chiasma, infundibulum, posterior pituitary, mammillary bodies, pineal gland

• Thalamus: Gateway for sensory impulses to cerebral cortex; channels impulses for interpretation

• Hypothalamus: Maintains homeostasis by regulating visceral activities (heart rate, blood pressure, temperature, hunger, etc.); links nervous and endocrine systems

• Limbic system: Controls emotional responses, survival behaviors, and reactions to stress

Additional info: These notes are based on textbook-style lecture slides and are suitable for introductory neuroscience or anatomy courses, not statistics.