PNB 2774 Module 5 CNS

central nervous system (CNS)

• consists of the brain and spinal cord

• separated from the peripheral nervous system by the blood-brain barrier

• made up of neurons and supportive glial cells

afferent connections

“inward”, carrying information from the outside world to the CNS

efferent connections

“outward”, carrying processed information from the CNS to other structures (e.g. muscles and organs)

white matter

made up of neuronal axons that are myelinated

gray matter

made up of unmyelinated axons

functions of neuroglia

• myelinate

• keep neurons in place

• support neurons with nutrients and O₂

• remove pathogens and dead cells

• assist in development

• facilitate synaptic transmission

astrocytes

• most abundant in neuroglia

• regulate the environment surrounding neurons

microglia

remove debris and damaged cells

multipolar neurons

common in the CNS, distinguished by a single axon and short dendrites

pyramidal neurons

the longest CNS neurons with longer axons and dendrites

interneuron

a neuron entirely within the CNS

meninges

• three layers of membrane that separate the skull bone from CNS tissue

• dura mater

• arachnoid mater

• pia mater

dura mater

• thickest later of the meninges

• responsible for draining blood and cerebrospinal fluid (CSF) from the brain into the bloodstream

• two layers with blood vessels, ECF, and lymphatic vessels in between

arachnoid mater

• middle layer of the meninges

• creates the sub-arachnoid space between the dura and pia mater

• facilitates the movement of fluid out of the sub-arachnoid space

pia mater

• layer of the meninges directly on the surface of the brain

• protects the CNS tissues as well as the arteries that supply blood to the brain

• contains CSF

cerebrospinal fluid

• produced by ependymal cells that line the ventricles

• provides another layer of “padding”for the brain from physical injury

• closely regulates the extracellular environments of neurons

• facilitates waste removal

• provides solutes and water to interstitial fluid (ISF)

• flows from the choroid plexus into the ventricles

ventricles

fluid-filled spaces in the brain

blood-brain barrier 

• consists primarily of endothelial cells that form tight junctions with each other, preventing solute movement

• capillary endothelium responsible for moving nutrients from blood into the brain

  • water-soluble molecules not specifically transported can’t cross

• hydrophobic compounds (O₂, CO₂, free fatty acids) are diffusion limited

• things like ethanol, THC, nicotine, propofol can diffuse within 10 seconds

carrier-mediated transport (BBB)

amino acids, glucose, nucleotides, small peptides

receptor-mediated transport (BBB)

hormones, growth factors, enzymes, small proteins

important differences between ISF and blood plasma

• lower pH due to elevated CO₂

• less protein

• less glucose

• lower potassium

subdural hematoma

physical damage causes bleeding onto the surface of the brain, causing pressure and damage to neurons

simple circuits

everything is feed forward

complex circuit

• has feedback

• the activity of the second neuron projects back and affects the activity of the first

• promotes additional information processing, but the activity can be very difficult to predict and understand

divergent circuit

• one neuron projecting onto many others

• the singular neuron’s activity influences and coordinates the activity of many others

convergent circuit

• multiple neurons project onto a single neuron, which integrates all of this input into a singular output

• gives you more sensitivity

rhythm circuit

• some can be as generated as little as two cells that communicate with each other 

• rhythms in larger populations of neurons are associated with important brain functions

chemotaxis

process where axons are “guided” to the right targets

electroencephalogram

measures brain activity with scalp electrodes; used for diagnosing epilepsy, sleep disorders, behavioral disorders

functional MRI (fMRI)

a more modern that still detects functional activity in particular brain regions

structural MRI (sMRI)

same foundational technology as fMRI, but detects the brain’s structure

diffusional tensor imaging (DTI)

• detects how water travels along the axonal projections of the brain

• most useful for macro-scale connectivity

  • typically can’t tell you about the micro-scale connections defining a neuronal circuit

longitudinal fissure

divides the brain into left and right lobes

lateral fissure

divides into top and bottom sections

cerebrum

largest part of the brain, the top/outermost region

cerebral cortex

• outer layer of gray matter

• split into multiple lobes

• responsible for higher level processing and cognition

cerebral control

right side of the cerebral cortex controls left side of the body and vice versa

cerebral dominance

different sides of the brain are associated with different types of tasks

left side of the brain

language, mathematical reasoning, logical reasoning

right side of the brain

spatial awareness facial recognition, visual imagery, music

frontal lobe

• motor, speech, memory formation, personality, emotion

• divided into prefrontal cortex, motor cortex, and broca’s area

broca’s area

plays a key role in the generation of articulate speech

primary motor cortex

• functionally and anatomically stratified

• different regions are directly associated with controlling muscles in different regions of the body

• the larger the volume of the brain, the stronger the level of control of that area of the body

parietal lobe

• somatosensory cortex (touch, proprioception)

• integration of sensory information

• collects information from multiple sources

• manages taste (gustation), sight, touch, and smell

proprioception

awareness of your body in 3D space relative to other structures and itself

somatosensory cortex

• processes sensory input from contralateral cord and thalamus

• temp, touch (mechanoreception), proprioception, pain (nociception)

• integrates these inputs in order to perform skilled movements (sensory and motor signals)