PNB 2264 Exam 4

Protection of the brain

Skin (physical barrier), cranial bones (form cranium), cranial meninges (protect brain & spinal cord), & CSF (chemical and physical protection)

Cranial Meninges

3 layers, physically protect tissues of CNS: Dura Mater, Arachnoid Layer, Pia Mater

Dura Mater

outermost layer, made of 2 layers of fibrous connective tissue, blood vessels that supply the brain are in between layers

Arachnoid Layer

middle, made of epithelial tissue, CSF located beneath (subarachnoid space)

Pia Mater

innermost, thin layer of cells surrounded by thin layer of connective tissue, sits directly on top of brain like plastic wrap

CSF

ventricles produce, store, and circulate CSF (continuous between brain & spinal cord); median & lateral apertures deliver CSF into subarachnoid space where it is circulated to the rest of the brain

CSF Exchange

CSF facilitates exchange w/ tissues of brain & eventually drains out of subarachnoid space into veins (bulk flow) because the subarachnoid space is at a higher pressure gradient than veins (CSF follows pressure gradient)

CSF Production

about 75% of CSF is produced by ependymal cells in the choroid plexus (type of tissue) in ventricles and the other 25% is produced in regions of blood outside choroid plexus

CSF & Blood

have different solute compositions
CSF: lower protein, glucose, K+ & higher Na+
allows for flow of Na+ into cell during AP & efflux of K+ to maintain negative resting membrane potential

Blood Supply

Internal Carotid Artery (makes up anterior & medial portion of brain), Vertebral Artery (supplies posterior structures of brain), Circle of Willis (redundant/overlapping flow), blood returns through jugular vein

Circle of Willis

circular arrangement of vessels allows blood to reroute if there's blockages in brain

metabolic needs of the brain

normally 1/5 of the body's blood is going to the brain, glucose concentration in CSF is lower than in plasma because neurons are constantly consuming glucose (so CSF is flowing constantly)

blood brain barrier

forms primarily from endothelial cells (epithelial cells that form blood vessels); have a lot of tight junction proteins that limit paracellular transport & makes exchange between blood & CSF extremely selective

blood brain barrier selectivity

prevents leakage of ions & neurotransmitters, keeps out toxins & pathogens (protein is lower in CSF than blood because low amino acid concentration stops viruses from forming in the brain)

blood brain barrier regulation

tight junction proteins regulated by supporting cells called astrocytes (glial cells) & regulating blood flow by contractile cells (pericytes); all of the cells that regulate BBB are called a neuromuscular unity (NVU)

Tight Junction Proteins

regulated by astrocytes (glial cells) that signal to endothelial cells when they need to increase/decrease expression of tjp

Blood Flow

regulated by contractile cells (pericytes) the contract to reduce blood flow & limit exchange

Gray Matter

contains cell bodies & synapses of neurons; cerebral cortex & basal ganglia

White Matter

consists of myelinated axons in the brain (whiteness comes from myelin); axons in white matter in brain referred to as fibers that connect different structures

Commissural Fibers

connects left & right hemispheres

Projection Fibers

connects cortex w/ regions outside

Associated Fibers

connect different structures w/in same hemisphere

Cerebral Features

system of hills & valleys; raised portion/hill - gyrus groove/valley - sulcus
increase surface area for exchange for ions w/ CSF, efficiency, & fits more brain tissue in cranial vault

Fissure

a really deep sulcus (creates major separations)

Landmarks of the Cerebrum

Central Sulcus: separates frontal & parietal lobe, Longitudinal Fissure: separates left & right cerebral hemispheres, Transverse Fissure: separates cerebral cortex from cerebellum, Lateral Fissure: separates temporal lobe from other frontal & parietal lobes

Cerebral Cortex

largest & most superficial part, control of body structures is contralateral

Cerebrum Lobes (all have left & right)

Frontal: motor, speech, memory formation, personality, & emotion
Parietal: somatosensory cortex
Occipital: visual processing & storing visual memories
Temporal: hearing, smell, speech & language

Frontal Lobe

largest & most well developed; responsible for hypothesis generation, planning, organization, decision making, inhibitions, & perseverance

Frontal Lobe Specifics

Orbital Frontal Cortex- decision making/adaptive learning; Primary Motor Cortex (pre central gyrus): movement; Broca's area: speech; Olfactory Bulb: odor perception

Parietal Lobe

contains primary somatosensory cortex (postcentral gyrus) where sensory info is collected & sensory association areas; primary tells you that you're touching something, association areas tells you it's sharp

Motor & Sensory Homunculus

primary motor cortex & primary somatosensory cortex organized based on homunculus
more space in PMC= more controlled movements
more space in PSC= more sensitive

Temporal Lobe

involved in hearing, some sensation, learning, & memory; primary auditory complex (where sound info is collected); also contains Vernicke's area (language comprehension)

Occipital Lobe

contains primary visual cortex & visual association areas

Broca's area

speech production & language expression, located in left frontal lobe, commissural fibers connect it to structures on right hemisphere

Vernicke's Area

language comprehension, located in left temporal lobe, commissural fibers connect it to structures on right hemisphere

Arcuate Fascisulus

white matter track that connects Broca's to Vernicke's; signals sent through here let us produce coherent speech

Angular Gyrus

transforms visual representations into an auditory code; helps to comprehend written language; a collection of association fibers connecting visual cortex to Vernicke's

Language & Aphasia

aphasia (inability to communicate), word deafness, & conduction aphasia (caused by damage to arcuate fasciculus)

Language Dysfunction Examples

trouble forming words (can produce speech & can understand language)- damage to Broca's
inability to come up w/ name of everyday objects- anomia
incoherent speech- due to damage in Vernicke's area

Basal Nuclei (Ganglia)

gray matter area deep to cortex that contains a lot of different neurons; plays a role in sensory & motor functions; prevents unwanted movements & helps w/ patterned movements; also plays a role in unconscious sensory processing/visual stimuli

Amygdala

important role in mood, emotion, & emotional control over behavior, fear conditioning relayed through here; alcoholism/binge drinking causes damage

Diencephalon

located below corpus callosum; made up of epithalamus (posterior/superior), thalamus (superior), hypothalamus (inferior/anterior)

Corpus Callosum

white matter tract connecting left & right hemispheres

Epithalamus

contains pineal gland (which secretes melatonin- a hormone that regulates day/night cycles) & habenular nuclei (plays a role in emotional responses to odor)

Thalamus

all sensory info passes through here (switchboard); 90% of info is filtered here and never makes it to PSC; all sensory info converges here (except for olfactory), principal & final relay for all sensory info

Hypothalamus

produces a lot of chemical messengers that can regulate many chemical processes in the body

Brainstem

deepest & most inferior part, controls critical/basic autonomic functions in the body, contains midbrain (mesencephalon), pons, medulla, 2 colliculi structures

Midbrain (mesencephalon)

some cranial nerves originate here

Pons

important for respiration

Medulla

cardiovascular & respiratory regulation

2 Colliculi Structures

coordinate auditory & visual reflexes

Cerebellum

coordinates movements, controls body structures on the SAME side

The Case of Henry Molaison

hippocampus removed, his short & long term memories were fine, but he couldn't create new memories, passed the mirror drawing test

2 Categories of Memories

explicit/declarative (factual info stored in hippocampus
implicit/reflex (motor memory stored elsewhere)

Mechanisms to Convert Short to Long Term Memories

repetition, intensity (a strong emotional response or motivational component), exercise (promotes memory formation), age (formation decreases w/ age)

Memory: Long-term Potentiation

osteocalcin (hormone released from bone) travels to brain & increases ability to form new memories, brain derived neurotrophic factor (BDNF) also drives memory formation (both work on tissues in hippocampus & change it at the molecular level)

Long-term Potentiation

a memory is a stronger response to a repeated stimulus; if no learning happens an identical response occurs (producing EPSP at the same amplitude)
if memories occur there is a stronger response & EPSP has a bigger amplitude

Memory Formation Requires

protein synthesis (increase in neurotransmitters, ligand-gated channels. growth of new neurons or axon terminals), can be more synapses or more neurons

Spinal Cord Anatomy

CSF is continuous throughout brain & spinal cord, meninges surround SC, gray matter is deeper & white matter is closer to periphery, white matter axons are called tracks when traveling out in periphery

Flow in Spinal Cord

neurons continuously leave to tissues, neurons flow in to bring sensory info to CNS, all nerves myelinated in order to carry signals over long distances

Sensation

process of converting an external stimulus into an action potential that can be brought into the CNS, then spinal cord, & up to the brain

Perception

process inside the brain allowing us to assign meaning to a particular sensation

General (somatic) Senses

touch, pressure, temperature, & pain

Special Senses

vision, olfaction (smell), hearing, & gustation (taste)

Adequate Stimulus

specific type of stimulation that a receptor is able to respond to;

Receptors Classified by Adequate Stimulus

thermoreceptor (temperature), mechanoreceptors (touch/pressure), nociceptors (pain), photoreceptors (photon), chemoreceptors (chemical)

Thermoreceptors

a family of ion channels (trip) that are gated by hot, warm, & cold temperatures

Law of Specific Nerve Energies

activity by a particular nerve always conveys the same type of information to the brain however, receptors can respond to more than one type of stimulus

Sensory Receptors Location

exteroceptors, interoceptors, & proprioceptors

Exteroceptors

locates things outside the body such as thermoreceptors & temperatures in the environment

Interoceptors

collect sensory information from inside the body (ex: chemoreceptors sensing blood gases & mechanoreceptors monitoring blood pressure)

Proprioceptors

gives information about where limbs are located in space at any moment (ex: closing eyes & raising hand)

Sensory Receptors Structural

most sensory receptors located on dendrites;
free- naked/exposed (pain, temperature, & smell)
encapsulated- wrapped in layers of tissue (pressure/touch)

Epithelial Cell Receptors

very rarely epithelial cells are receptors instead of neuron (happens in visual/hearing systems); epithelium release neurotransmitter to neuron

Sensory Unit

a neuron & all of it's receptors (can be big or small)

Receptor Field

an area/region that can be sensed by a sensory unit, usually overlap

Receptor Potential

A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus; sensory receptors on dendrites produce this graded potential (RP) similar to EPSP, amplitude always proportional to stimulus intensity

Receptor Potential Amplitude

RP develops on dendrites, travels to axon hillock & initiates AP, neurotransmitter releases from axon terminal, & message is delivered to CNS

Action Potential Intensity

AP has a constant amplitude while traveling,

Strong Stimulus

creates more receptor potential & EPSP's which is what leads to more frequent AP's

Weak Stimulus

creates less receptor potential & lower amplitude EPSP's which means less frequent AP's

Receptor Field Distribution

receptor fields unevenly distributed throughout body, some have punctate (random) distribution; can be difficult to localize stimuli

Sensory Unit Examples

hands & face have a lot of sensory units whereas back, forearm, & legs have fewer; this is why face pain is easily identified but abdominal & back isn't

Receptor Field Sizes

larger RF's are worse for localization; smaller RF's allow us to localize to a much smaller area of skin

Overlap of Receptive Fields

more overlap leads to better localization; if both A & B are firing AP's, the stimulus can be localized to the area of overlap

Lateral Inhibition

process where the most strongly stimulated neurons shut down sensory transmission in weakly stimulated neurons; CNS receivers 1 intense signal as opposed to multiple weak signals; works through pre-synaptic inhibition; usually takes place in thalamus

Presynaptic Inhibition

synapse between second order neurons: axo-axonic synapse (between axon terminals of neurons)

Pathways Sensory Information

Dorsal/Posterior Column & Anterolateral Pathway, both ascending pathways describe sensory info coming into CNS & traveling up spinal cord into brain

3 Types of Neurons in Ascending Pathways

1st order (contains sensory receptors & collects info from periphery), 2nd order (carry signals from spinal cord to thalamus), & 3rd order (carry signal from thalamus to primary somatosensory cortex)

Sensory Adaptation

becoming desensitized to a repeated stimulus

Phasic Receptors

rapidly adapting, ex: pressure receptors (receptor potential & AP frequency decrease)

Tonic Receptors

slowly adapting, ex: getting a headache & not being able to focus

Sensation Process

has a lot of plasticity, very dynamic (they can change)

Intense Pain Stimulus

continual receptor potential from nociceptors & high frequency AP's delivered to primary somatosensory cortex through anterolateral pathway

Desensitizing Pain

don't want body to desensitize pain because then you won't know when something is wrong

Phototransduction

converting a photon of light into an AP

Retina

located posteriorly on the eye, contains photoreceptors (rods/cones), ganglion cells (optic nerve)

Overview of Visual Pathway

Begins in the photoreceptors of the retina, which synapse with bipolar and retinal ganglion cells. The axons of the retinal ganglion cells then send visual information to the rest of the brain by ascending through the optic nerves to the LGN in the thalamus. Neurons in the LGN send their axons to the primary visual cortex which then spreads to the association areas

Transport to Retina

light enters anteriorly, glial cells called mueller glia carry photons to photoreceptors in retina; once proton is transduced, cells really message back towards anterior part of retina (where optic nerve neurons are)

Distal Membrane of Rods & Cones

organized into stacks containing pigmented molecules (opsin)