Anatomy of the Brain and Spinal Cord

Meninges

3 layers of tissue provide protection to the brain and spinal cord

Dura Mater (Meninges)

outermost layer, it’s tough and leathery (Meninges)

Arachnoid (Meninges)

middle layer, it is fairly delicate and impermeable (Meninges)

Subdural Space

separates the arachnoid mater from the dura

Subarachnoid Space

• separates the arachnoid mater from the pia mater

• filled with cerebrospinal fluid

Pia Mater (Meninges)

• the innermost layer, it adheres to the surface of the brain

• covers the gyri and descending into the sulci

• it appears glossy, it is so thin it’s almost invisible to the naked eye

Meningitis

infection/inflammation of the meninges (viral) (bacterial: more serious)

Ventricular System

a series of interconnected, fluid-filled spaces within the core of the CNS (brain and spinal cord)

Cerebrospinal Fluid (CSF)

• fluid in the ventricle

• derived from the choroid plexus

• can be collected for testing (i.e meningitis)

• drugs can be delivered into (epidural)

Choroid Plexus

• a specialized vascular tissue within walls of ventricles

• filters capillary blood and secretes the CSF product into the ventricles

Cerebrospinal Fluid (CSF) Neutral Buoyancy

the brain can be dense without being damaged by its own weight

Cerebrospinal Fluid (CSF) Protection

protects the brain tissue from injury by providing a fluid buffer that acts as a shock absorber

Blood-Brain-Barrier(BBB)

• protects the brain from substances in the blood

• formed by the tight junctions between capillary endothelial cells within the brain and spinal cord

• helps keep blood cells, proteins, toxins, hormones, bacteria, etc. out of brain tissue

• preserves “optimal balance of extracellular chemical composition within the brain

Astrocytes

maintain tight junctions via their “end feet”, which contact vascular endothelial cells

Brain capillaries

NON-FENESTRATED ( have tights junctions that form a barrier)

Capillaries in the rest of the body

FENESTRATED (no tight junction/no barriers)

What gets through the Blood Brain Barrier?

• anything that is both small and lipid-soluble, or for which specific transporters exist

• Oxygen, CO2, and other blood gases

• Glucose, insuline, amino acids
  Alcohol, nicotine, cocaine, other psychoactive drugs

Circumventricular Organs

• NOT protected by the Blood Brain Barrier

• on brain midline, adjacent to ventricles

• detect osmolarity of extracellular fluid

• lets us know when we are thirsty

• its receptors help us detect the presence of toxins in the blood

Axes and Directional Terminology

• Rostral

• Caudal

• Coronal

• Sagittal

• Horizontal

Axes and Directional Terminology: Anterior

in front of

Axes and Directional Terminology: Posterior

behind

Axes and Directional Terminology: Superior

above

Axes and Directional Terminology: Inferior

below

Axes and Directional Terminology: Rostral (BRAIN)

front of the brain

Axes and Directional Terminology: Caudal (BRAIN)

back of the brain

Axes and Directional Terminology: Dorsal (BRAIN)

top of the brain

Axes and Directional Terminology: Ventral (BRAIN)

bottom of the brain

Axes and Directional Terminology: Dorsal (Spinal Cord/Brain Stem)

back of the brain stem/spinal cord

Axes and Directional Terminology: Ventral (Spinal Cord/Brain Stem)

front of the brain stem/spinal cord

Axes and Directional Terminology: Caudal (Spinal Cord/Brain Stem)

bottom of the brain stem/spinal cord

Axes and Directional Terminology: Rostral (Spinal Cord/Brain Stem)

top of the brain stem/spinal cord

Axes and Directional Terminology: Coronal

slicing to have a front and back

Axes and Directional Terminology: Horizontal

slicing to have a top and bottom

Axes and Directional Terminology: Sagittal

slicing in half; having a left/right side

White Matter

myelinated (white) axons

Gray Matter

consists mostly of cell bodies and dendrites

Which of the following cells are found in the white matter of the spinal cord?

Oligodendrocytes

Spinal Cord

• located within the vertebral column

• transfer information between the CNS and PNS

• Pairs of spinal nerves are attached to the cord at 31 different levels

• Sensory information enters the dorsal (back) portion and motor commands exit on the ventral (stomach) side.

• Ganglion

• Root - axons entering and exiting the spinal cord

Ganglion

collection of somas

Ventral Root

conveys motor information from the spinal cord to the muscles

Cranial Nerves

• 12 pairs of nerves

• emerge from the brain, rather than from segments of the spinal cord

• send motor commands to and receive sensory information from the head and neck

• Some nerves are only sensory or motor, and some are both

Cranial Nerves can be identified by:

• Rostro-caudal position

• Information type (sensory v. motor)

• function

Divisions of the Brainstem: Medulla

• closest to the spinal cord

• includes neurons that maintain normal rhythmic breathing

Divisions of the Brainstem: Pons

• above the Medulla

• includes axons that allow the cerebellum to communicate with the brainstem and the cerebral cortex

• fourth ventricle is on the dorsal side of this region

Divisions of the Brainstem: Midbrain

• above the pons

• has a superior and inferior colliculi

• has a nucleus called the Ventral Tegmental Area and another called the Substantia Nigra

Superior and Inferior Colliculi

involved in localization of visual and auditory stimuli

Brainstem

all levels contain sensory and motor axons

Cerebellum

• motor planning

• motor learning

Motor planning

aids the motor cortices in planning complex movement

Motor learning

• error correction when learning movement: compares intended movement with actual movement and correct errors that might occur

• synapses change with experience

Diencephalon

• include the Thalamus and Hypothalamus

Thalamus

• located rostral to the midbrain

• “Relay” for information going to and coming from the neocortex

Hypothalamus

• located below the thalamus

• regulates the autonomic nervous system

• regulates hormone release

Cerebral Cortex (neocortex)

• Sulci (sulcus): grooves

• Fissures: deep sulci

• Gyri (gyrus): rounded regions between sulci

Cerebral Cortex (neocortex) Function

• processing of sensory input

• Initiation/planning of movements

• “Higher-order” functions including memory, cognition, language

Lobes of the Cerebral Cortex

• Occipital

• Parietal

• Temporal

• Frontal

Central sulcus (Cerebral Cortex)

separates parietal and frontal lobes

Lateral fissure (Cerebral Cortex)

separates the temporal lobe from the frontal and the parietal lobe

Longitudinal fissure (Cerebral Cortex)

separates the two hemispheres of the brain

Postcentral gyrus

• directly caudal to the central sulcus

• contains the primary somatosensory cortex, which process touch and pain information

Precentral gyrus

• directly rostral to the central sulcus

• contains the primary motor cortex, which helps plan movement and sends motor (movement) signal to the spinal cord

Occipital Lobe

• early-stage vision

• first place in the cortex (NOT THE BRAIN) where your visual information is processed after coming though the eye

Parietal Lobe

• somatosensory (touch and pain)

• late stage vision

Temporal Lobe

• memory

• hearing

• language comprehension

• has a region called Hornica’s Area

Lateralization of function

functions are either located on one side of the brain or the other (left/right hemisphere)

Hornica’s Area

located on the left side of the temporal lobe in most people

Frontal Lobe

• planning and signaling movements

• working memory

• inhibition of inappropriate behaviors

• planning

Where is the occipital lobe located with respect to the parietal? (The occipital lobe is ____ to the parietal lobe?)

Caudal

A 41-year old male presents to the ER with paralysis involving the left arm and hand. Imaging shows a small lesion in his cerebral cortex. The lesion is located in which lobe of the brain?

Frontal Lobe

Neocortex

• 6 layer cortex

• layer 1 is a molecular layer and consist mainly of Dendrites

• layers 2/3 are processing layers

• layer 4 is the main input layer; receives input from the thalamus

• layer 5 is the maini output layer; sends projections to other parts of neocortex and to other brain region

• layer 6 is a multiform layer; sends input to the thalamus

• white matter: were all axons are leaving the cortex

Thickness of the cortical layers

• dependent of where you are in the cortex

• layers can be different in thickness (thicker it is the more signal you get for it)

Why do cortical layers vary in size across different regions of the cortex?

Different cortical regions are specialized for distinct functions, requiring varying amounts of input, output, and processing capacity.

Limbic System

• a group of interconnected structures that are related to emotional behavior and emotional interpretation

• sexual behavior

• involved in the formation of memory, contains primary reward and punishment centers

• site of action of drugs which produce euphoria (direct and indirect)

Hypothalamus

• in the limbic system

• regulates many motivated functions (e.g eating and drinking), sleep/wake cycle

• controls activity of the pituitary gland

Pituitary gland

• master gland that interacts with the hypothalamus to regulate many functions via the release of hormones

Hippocampus

• involved in memory consolidation and provide the organism’s spacial awareness

• in limbic system

Amygdala

• coordinates autonomic responses in with emotional states

• in the limbic system

Cerebral Cortex

• interacts with subcortical structures to guide behavior (e.g sweat when scared)

• in the limbic system

Basal Ganglia

• A group of interconnected structures that control voluntary, smooth movement

• The action of stimulants (drugs) increases motor activity

Basal Ganglia structure includes

• striatum (caudate/putamen)

• globus pallidus

• Substantia nigra: sends dopamine to other regions on the basal ganglia to help control movement

Corpus Callosum

• Long-range neurons that connect the two halves of the brain

• axons going from one hemisphere of the brain to the other