Brain Anatomy Review lecture 22

Lecture 21 Quiz Review

• Epineurium is not a layer of the meninges.
• Cerebrospinal fluid (CSF) circulates around the arachnoid layer of the meninges.
• Old/used CSF is transported into the venous circulation through arachnoid granulations.
• The third ventricle is located within the diencephalon brain region.

Learning Objectives

• Describe the external anatomy of the brain from lateral (surface) and medial views.
• Identify and describe the lobes of the cerebral cortex (cerebrum).
• Identify and describe major sulci and gyri that divide the brain, and their basic functions.
• Name the regions of the brainstem from medial, ventral, and dorsolateral views.
• Identify selected internal structures of the brain from a coronal view.
• List the different types of white matter tracts in the brain.
• Understand the anatomy of the main motor pathway for voluntary movement (corticospinal tract).
• Understand the anatomy of a representative somatosensory pathway (dorsal/posterior column pathway).

Brain Anatomy: Lateral View

• SULCUS is a "furrow/valley," with the plural form being SULCI ("furrows/valleys").
• GYRUS is a “hill”, with the plural form being GYRI ("hills”).
• The brain's anatomy as seen from the side includes the frontal, parietal, occipital, and temporal lobes.

Brain Anatomy: Sulci, Gyri, and Fissures

• The central sulcus divides the frontal and parietal lobes.
• The lateral sulcus separates the temporal lobe from the frontal and parietal lobes.
• The parieto-occipital sulcus separates the parietal and occipital lobes.
• The transverse fissure separates the cerebrum from the cerebellum.

Functions of Cerebral Lobes (Cerebral Cortex)

• The frontal lobe is associated with motor control, language, and personality.
• The parietal lobe is associated with somatosensory processing.
• The temporal lobe is associated with memory and hearing.
• The occipital lobe is associated with vision.

Brain Divisions: Medial View

• The cerebral cortex (aka cerebrum) is a major brain division.
• The corpus callosum (white matter) is a major brain division.
• The diencephalon, including the thalamus and hypothalamus is a major brain division.
• The brainstem, including the midbrain, pons, and medulla oblongata is a major brain division.
• The cerebellum is a major brain division.

Brainstem Anatomy: Lateral Aspect

• The thalamus is part of the diencephalon and not the brainstem.
• The brainstem includes the midbrain, pons, and medulla oblongata

Brainstem Anatomy: Ventral Aspect

• The thalamus, part of the diencephalon, is not part of the brainstem.
• The brainstem consists of the midbrain, pons, and medulla oblongata.
• The spinal cord is not part of the brainstem.
• The level of the foramen magnum is shown.

Brain Internal Structures: Coronal View

• The cerebral cortex (gray matter) is a key component.
• White matter (3 types) constitute a significant portion.
• Deep nuclei are present.

White Matter: Commissural Tracts (#1)

• Axons cross from side to side in both directions.
• The corpus callosum is an example.

White Matter: Projection Tracts (#2)

• Axons extend between the cortex and other CNS areas outside the cerebrum.
• The corticospinal tract (somatic motor pathway) is an example.

White Matter: Association Tracts (#3)

• Axons are located on the same side within the cerebral cortex.
• Communication occurs between brain areas over short or long distances.

Cortical Areas for Motor Control / Somatosensory Perception

• The central sulcus separates the frontal lobe and parietal lobe.
• The pre-central gyrus is the primary motor cortex.
• The post-central gyrus is the primary somatosensory cortex.

Somatic Efferent (Motor) Division

• Voluntary movement is controlled by this division.
• Information flows AWAY from the CNS (efferent).
• The pathway includes two neurons between the brain and effector: an upper motor neuron and a lower motor neuron.
• Axons are myelinated.
• Acetylcholine (ACh) serves as the neurotransmitter.
• The effector is a skeletal muscle.
• The upper motor neuron cell body is in the primary motor cortex (precentral gyrus).

Motor Cortex Organization

• The precentral gyrus functions as the primary motor cortex.
• Specific regions of the motor cortex control specific body regions.
• More cortical area is devoted to sensitive and/or precision areas like hands and mouth/tongue.
• Relatively little area is devoted to regions like the trunk/abdomen.

Corticospinal Pathway

• It is a somatic efferent pathway.
• Involves two neurons: upper and lower motor neurons.
• The upper motor neuron's cell body is in the primary motor cortex (precentral gyrus).
• The upper motor neuron axon extends from the motor cortex to the spinal cord on the opposite side and makes a synapse on the lower motor neuron.
• The lower motor neuron's cell body is in the ventral horn (grey matter) of the spinal cord.
• The lower motor neuron axon extends out of the spinal cord (ventral root) into the body and makes a synapse on skeletal muscle.

Motor Cortex Damage

• Damage to the motor cortex results in muscle weakness and paralysis.
• These symptoms occur in the body region corresponding to the location of damage, but on the opposite side.

Somatosensory Cortex

• The postcentral gyrus functions as the primary somatosensory cortex.
• Specific regions of the somatosensory cortex receive sensory information from specific body regions.

Dorsal/Posterior Column Pathway

• It mediates fine touch, vibration, pressure, and proprioception.
• This pathway involves three neurons between the sensory receptor (in the body) and the somatosensory neuron in the postcentral gyrus.
• Neuron #1: cell body in the dorsal root ganglion; the peripheral fiber is from a sensory receptor in the skin; the central fiber ascends toward the brain in the dorsal columns; it makes a synapse on neuron #2 in the medulla oblongata.
• Neuron #2: cell body in the medulla oblongata; the axon crosses to the opposite side and ascends; it makes a synapse on neuron #3 in the thalamus.
• Neuron #3: cell body in the thalamus; the axon ascends to the somatosensory cortex and makes a synapse on the cell body of a somatosensory cortex neuron resulting in the perception of light touch.

Spinothalamic Tract

• It mediates pain and temperature senses.
• Involves three neurons between the sensory receptor (in the body) and the somatosensory neuron in the postcentral gyrus.
• Neuron #1: cell body in dorsal root ganglion; makes synapse on neuron #2 in the spinal cord.
• Neuron #2: cell body in the spinal cord, axon crosses to the opposite side via the anterior white commissure and the cell is called a tract cell; makes a synapse on neuron #3 in the thalamus.
• Neuron #3: cell body in the thalamus; its axon ascends to the somatosensory cortex, making a synapse on the cell body of a somatosensory cortex neuron.

Damage to Primary Somatosensory Cortex

• Occurs when a cell in the somatosensory cortex that receives information from the dorsal column pathway dies.
• This means ascending information has no place to go.
• This lack of processing leads to a lack of perception of touch in that body area on the opposite side.

Cortex Damage: Agnosias and Aphasias

• Agnosia: Damage to a region involved with sensory perception, causes changes in perception.
• Aphasia: Damage to regions governing language, causes changes in speech perception or production.

Agnosias

• Prosopagnosia: "Face blindness," is a type of agnosia with two kinds:
  • Apperceptive: inability to recognize facial expressions/cues.
  • Associative: inability to recognize an individual from their facial features.

Aphasias

• Wernicke's aphasia: individuals can produce words and even whole sentences, but the meaning is lost, resulting in a "word salad."
• Broca's aphasia: individuals can understand words, but cannot form the motor patterns to produce whole speech.

Blindsight

• Blindsight Damage to V1, where the brain recieves primary visual information.
• Individuals experience no conscious perception of "sight” but will still react to visual stimuli.

Blindsight Visual Pathway

• Retina → LGN → PN/SC → Posterior Parietal
• Vision is processed in the Posterior Parietal Cortex . Pulvinar Nucleus (PN) and Superior Colliculus (SC).