Structure and Function of the Brain: Anatomy & Physiology Study Notes 14.0

Functional Organization of the Nervous System

Overview

The nervous system is divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS). It is responsible for integrating, processing, and coordinating sensory input and motor output, both voluntary and involuntary.

• CNS: Consists of the brain and spinal cord; serves as the integration center.

• PNS: Includes sensory (afferent) and motor (efferent) divisions, connecting the CNS to limbs and organs.

• Somatopleure: Relates to body wall structures (skin, skeletal muscle).

• Splanchnopleure: Relates to internal organs (viscera).

Example: Sensory input from the skin travels via the PNS to the CNS, which processes the information and sends motor output to muscles.

Anatomy of the Nervous System

Central Nervous System (CNS)

The CNS is composed of the brain and spinal cord, located within the cranial and vertebral cavities, respectively.

• Embryonic origin: CNS structures develop from the neural tube.

• Specific tissue: Neuroectoderm forms the brain and spinal cord.

Overview of the Brain

Major Functions

The brain integrates, processes, and coordinates sensory input and motor output. It is also responsible for higher functions such as intelligence, memory, learning, and emotion.

Brain Division	Function
Cerebrum	Performs higher mental functions, interprets sensory stimuli, initiates motor output
Diencephalon	Processes, integrates, and relays information; regulates biological rhythms
Cerebellum	Monitors and coordinates movement
Brainstem	Maintains homeostasis, controls reflexes, monitors movement
Ventricles	Hollow cavities that hold fluid

The Meninges

Protective Layers

The brain is protected by three layers of connective tissue (CT) called meninges, which prevent injury and provide structural support.

• Dura mater: Thick, superficial layer with abundant collagen; holds dural venous sinuses.

• Arachnoid mater: Web-like middle layer; subarachnoid space contains cerebrospinal fluid (CSF).

• Pia mater: Thin, vascularized layer adhered to the brain and spinal cord.

Additional info: The falx cerebri and tentorium cerebelli are extensions of the dura mater that help compartmentalize the brain and support venous sinuses.

The Cerebrum

Structure and Hemispheres

The cerebrum consists of two large hemispheres divided by the longitudinal fissure. Each hemisphere controls the opposite side of the body (contralateral control).

• Right hemisphere: Controls left side of the body.

• Left hemisphere: Controls right side of the body.

Internal Composition

• Cerebral cortex: Outer layer of gray matter; contains neuron cell bodies, dendrites, and synapses.

• Cerebral white matter: Interior myelinated axons; responsible for communication between regions.

• Basal nuclei: Deep gray matter islands; involved in motor control.

Cerebral Cortex Areas

Frontal Lobes

Located anterior to the central sulcus and lateral to the longitudinal fissure.

• Prefrontal cortex: Processes intellect, cognition, recall, personality, and working memory.

• Premotor cortex: Plans voluntary motor output.

• Motor cortex: Sends voluntary motor output to effectors.

Parietal Lobes

Located posterior to the central sulcus.

• Somatosensory cortex: Receives sensory information from the body.

• Remaining area: Interprets somatic sensory input.

Occipital Lobes

Located posterior and medial to the parietal lobes.

• Receives sensory input from the retina: Right eye to left occipital lobe, left eye to right occipital lobe.

• Visual interpretation: Remaining area interprets visual input.

Temporal Lobes

Located inferior to the lateral sulcus, frontal, and parietal lobes.

• Receives auditory information: Pitch, loudness, location.

• Receives olfactory information: Sense of smell.

• Interpretation: Remaining area interprets sensory input.

Insula Lobes

Deep to the temporal, parietal, and frontal lobes.

• Receives gustatory (taste) information.

• Receives visceral sensory input.

• Receives vestibular (equilibrium) information.

• Interpretation: Remaining area interprets sensory input.

Cerebral White Matter and Basal Nuclei

Communication and Motor Regulation

• White matter: Connects cerebral areas and links cortex to lower CNS.

• Corpus callosum: Major tract connecting right and left hemispheres.

• Basal nuclei: Regulate motor output to skeletal muscles.

The Diencephalon

Thalamus

• Central, egg-shaped structure.

• Sorts, edits, and relays sensory and motor messages to/from the cerebral cortex.

• Does not receive olfactory input.

Hypothalamus

• Located inferior to the thalamus; connected to the pituitary gland via the infundibulum.

• Makes endocrine hormones.

• Controls autonomic reflexes: body temperature, food/water intake, wake-sleep cycle.

Epithalamus

• Dorsal region forming the roof of the third ventricle.

• Includes the pineal gland, which secretes melatonin to regulate sleep.

The Brainstem

Midbrain

• Located between diencephalon and pons.

• Contains visual and auditory reflex centers (corpora quadrigemina).

• Divided by cerebral aqueduct, moving CSF toward the fourth ventricle.

Pons

• Enlarged region between midbrain and medulla oblongata.

• Assists medulla with breathing depth and rate.

• Relays motor information between cerebrum and cerebellum.

Medulla Oblongata

• Conical, inferior portion of the brainstem; continuous with spinal cord.

• Controls autonomic reflexes: heart rate, blood pressure, breathing, vomiting, hiccupping, swallowing, coughing, sneezing.

The Cerebellum

Structure and Function

• Dorsal to pons and medulla, inferior to cerebrum.

• Outer cortex of gray matter, internal white matter (arbor vitae).

• Evaluates body position and posture.

• Coordinates force, direction, and extent of skeletal muscle contraction.

Movement of CSF in the Ventricles

Ventricular System

• Lateral ventricles: Horns/horseshoe-shaped pockets in cerebral hemispheres.

• Third ventricle: Space between right/left thalamus.

• Cerebral aqueduct: Connects third and fourth ventricles.

• Fourth ventricle: Between pons, medulla, and cerebellum; continuous with central canal of spinal cord.

Additional info: CSF cushions the brain, removes waste, and provides nutrients.

Arterial Supply of the Brain

Major Arteries

• Internal carotid arteries: Supply most blood to the brain via the carotid canal.

• Vertebral arteries: Enter through transverse foramen of cervical vertebrae, fuse to form basilar artery.

• Basilar artery: Passes through foramen magnum to base of brain.

Circulosus Arteriosus Cerebri (Cerebral Arterial Circle)

Circle of Willis

• Formed by internal carotids and basilar artery.

• Provides alternative pathways for blood flow if one part is blocked.

Artery	Supplied Brain Region
Anterior cerebral artery	Anterior cerebrum
Middle cerebral artery	Lateral cerebrum
Posterior cerebral artery	Posterior cerebrum
Communicating arteries	Connect major arteries

Clinical Implications

Cerebrovascular Accident (CVA, Stroke)

• Definition: Damage to the brain due to disruption of blood flow.

• Causes: Blockage (clot) or hemorrhage (ruptured artery).

• Symptoms: Sudden paralysis, loss of vision, speech difficulties, headache; often affects one side of the body.

Venous Drainage of the Brain

Pathways

• Carbon dioxide and waste enter blood from brain capillaries.

• Drain into cerebral veins, then into dural venous sinuses (superior/inferior sagittal, straight, transverse, sigmoid).

• Sigmoid sinuses drain into internal jugular vein via jugular foramen.

Sinus	Location
Superior sagittal	Longitudinal fissure
Inferior sagittal	Longitudinal fissure
Straight	Intersection of falx cerebri and tentorium cerebelli
Transverse	Margin of occipital bone
Sigmoid	S-shaped, anteriorly

Check Your Understanding

Sample Questions

• List the three meninges of the brain in order from superficial to deep.

• Where in the brain is cerebrospinal fluid (CSF) located?

• What are the ventricles? Where is each of the four ventricles located?

• What are the main functions associated with the cerebrum?

• Where is the corpus callosum located? What is its function?

• Where are the motor and somatosensory cortices located? What is the function of each?

• Describe the parts associated with the diencephalon and brainstem, their locations, and functions.

• Explain how the cerebellum is connected to the brainstem and its functions.

• Why are the cerebral and cerebellar cortices folded? What is the advantage?

• What problems might you observe with a stroke in the anterior, middle, or posterior cerebral artery?

• What would occur if a patient had damage to the left primary motor cortex or frontal lobe?

• Would damage to the frontal lobe or medulla oblongata be more likely to lead to death? Why?

• Draw and label the arteries of the circulosus arteriosus cerebri and the dural sinuses.

• What areas of the brain function to move skeletal, cardiac, and smooth muscles?

• What areas of the brain receive sensory input from the body?

• What parts of the brain perform autonomic functions?

• After a severe blow to the head, a patient does not sense hunger or thirst. What region is likely damaged?

Additional info: Folding of the cortices increases surface area, allowing for more neurons and greater processing capacity.