Lecture 16

BIO 203 Fall 2024 Purdue

Grey Matter

• Contains cell bodies, dendrites, and synapses; primarily found on the outer layer of the brain and inner section of the spinal cord (shaped like a butterfly).

• communication between nerve cells

White Matter

• Composed of axon bundles covered in myelin; found in the inner part of the brain and outer part of the spinal cord.

• information transmission between brain areas

Accounts for 40% of brain volume

grey matter

Accounts for 60% of brain volume

white matter

Meninges

Three membranes surrounding the brain and spinal cord that provide protection, CSF circulation and structural framework.

Dura matter

outermost, tough layer

Arachnoid matter

middle layer with web-like extensions; has subarachnoid space filled with CSF

Pia matter

innermost, thinnest layer; follows brain contours; supplies nutrients/oxygen to brain tissues

Ganglion

Cluster of neuron cell bodies located outside the CNS

Nucleus

Cluster of neuron cell bodies located within the CNS

Tract

Bundle of axons that travel together within the CNS, often serving a specific function

Spinal nerves

Part of the PNS, emerge from the spinal cord, carry sensory and motor information

cranial nerves

belong to the PNS but emerge from brainstem

Funiculus

A region of white matter in the spinal cord that contains multiple tracts or fasiculi

CNS structures

• Group of neuron Cell Bodies: Nucleus/Nuclei

• Bundle of Axons: Tract

PNS structures

• Group of neuron Cell Bodies: Ganglion/ganglia

• Bundle of Axons: nerve

ventricles

Interconnected cavities within the brain filled with cerebrospinal fluid (CSF).

Choroid plexus

• A structure in each ventricle of the brain that produces cerebrospinal fluid (CSF) from blood plasma.

• Spongy mass of blood capillaries on the floor or wall of each ventricle

Function of CSF: Cushioning and protection

CSF acts as a buffer, protecting the Brian and spinal cord from injury caused by sudden movements, impacts or trauma

Function of CSF: Buoyancy

The Brian is heavy, but CSF buoyancy prevents the brain from compressing under its own weight.

Function of CSF: nutrient delivery and waste removal

Delivers nutrients and takes away metabolic waste produced by the CNS

Function of CSF: Homeostasis

Helps maintain a stable extracellular environment for neurons/glial cells by regulating ion concentrations and pH levels in the CNS

Function of CSF: Immunological protection

Contains immune cells and antibodies that provide immune surveillance

Function of CSF: regulation of intracranial pressure

helps regulate intracranial pressure, ensuring the pressure within the skull remains balanced despite changes in blood volume, brain tissue or CSF volume

Cerebrospinal Fluid (CSF)

A clear, colorless liquid found in the ventricles of the brain, produced by the choroid plexus, which protects, nourishes, and maintains the optimal environment for the CNS.

Dural (venous) sinuses

• Collects and drains pools of venous blood

• Retunes deoxygenated blood from the head to the heart

Blood-Brain Barrier (BBB)

• A selective barrier that regulates what substances can pass from the bloodstream into the brain's extracellular fluid.

• Lipophilic molecule with low molecular weight and positive charge can pass

• Non-fenestrated cells

Circumventricular organs (CVOs)

Places in the 3rd and 4th ventricle where the BBB is absent and the blood has direct access to brain neurons

Blood-CSF barrier

• Tight junctions between the ependymal cells

• Has fenestrated capillaries (direct exchange occurs)

Brainstem

• Connects the brain to the spinal cord

• maintains life and regulates body functions

Midbrain

Plays a role in motor functions, sensory processing and arousal (being awake/alert)

Pons

• Relay station for information passing between the forebrain and cerebellum

• Involved in motor control, sensory processing and respiration

Medulla Oblongata

• Conduit for sensory and motor information passing between the brain and spinal cord

• Houses vital centers that control autonomic functions like respiration, HR, BP, vomiting and swallowing

Forebrain

• Prosencephalon

• Split into the Cerebrum and Diencephalaon

• On limbic system

Midbrain

• Mesencephalon

• Surrounds cerebral aqueduct

• motor control, visual ad auditory processing, regulating certain reflexes

Hindbrain

Rhombencephalon

Cerebral aqueduct

connects 3rd and 4th ventricles

Tectum

Houses superior and inferior colliculi

Cerebral peduncles

• contain descending motor tracts

• Connect cerebellum to the brainstem

• Split into three parts: tegmentum, substantia nigra, crus cerebri

Corpora quadrigemina

makes up superior and inferior colliculi

superior colliculi

visual reflex center

inferior colliculi

auditory reflex center

Tegmentum

• contains the reticular formation, cranial nerve nuclei and various tracts

• most posterior part

substantia nigra

region rich in dopamine-producing neurons, crucial for motor control

crus cerebri

• contains the corticospinal tracts

corticospinal tract

involved in motor control of the body (voluntary control)

corticobulbar tract

controls the muscles of the face, head and neck

Red nucleus

• small structure located in the tegmentum

• Composed of grey matter and is involved in motor coordination

reticular formation

A net-like structure of neurons in the brainstem that regulates wakefulness and sleep-wake transitions.

Cerebral Cortex

The outer layer of the cerebrum responsible for complex functions, including perception, cognition, and motor control.

Cerebellum

A brain region that coordinates voluntary movements, balance, and posture; includes the cerebellar vermis and arbor vitae.

Reticular Activating System (RAS)

A component of the reticular formation involved in regulating alertness and the sleep-wake cycle.

Neural Tube

An embryonic structure that develops into the central nervous system, including the brain and spinal cord.

Synapses

The junctions between neurons where signaling occurs.

Dendrites

Branch-like structures of a neuron that receive signals from other neurons

Axons

Long, slender projections of a neuron that transmit electrical impulses away from the neuron’s cell body

Relay station

Place where information is received, processed, and then transmitted onward

Functions of the Reticular Formation

• arousal and consciousness

• attention and sensory processing

• motor controls

• autonomic functions

• pain modulation

• sleep regulation

Cerebellar vermis

Connects the two hemispheres of the cerebellum

Proprioception

adjusts motor output, ensuring coordination and balance

Arbor vitae

• tree like structure

• white matter

• found in cerebellum

Cerebellum layer: Molecular

• outermost layer

• consists of a dense network of neuronal processes

• create a complex structure where most of the synaptic activity occurs

Cerebellum layer: Purkinje

Comprised of a monolayer of purkinje cell somas (neuron’s cell bodies)

Cerebellum layer: Granular

Contains the cell bodies of granular cells (neurons)

Folia

cortex of grey matter with folds

Corpus callosum

Thick bundle of nerves connecting the brain’s left and right hemispheres