Neuropsychology (Psyc 3311)

D. Erik Everhart, Ph.D.

everhartd@mail.ecu.edu

314 Rawl Building

Office Phone:  328-4138

Background

z    BA  (1992) University of Delaware

z    MS  (1995) Clinical Psych, Virginia Tech

z    PhD (1998) Clinical Psych, Virginia Tech

z    Neuropsych/Geropsych Internship (1998) Buffalo VAMC

z    Neuropsychology Fellowship (2000) Department of Neurology                     SUNY Buffalo School of Medicine

Neurons and Glial Cells

z     Cells range from .01 to .05 mm in diameter.

z     Brain tissue = Jello!

z     Fix in formaldehyde

z     Histology

z     Nissl (cresyl violet) stain.

z     Golgi stain (silver chromate).

z     Golgi, Cajal, and the Neuron Doctrine.

Prototypical Neuron

z     Soma organelles:

y    nucleus

y    rough ER

y    smooth ER

y    Golgi apparatus

y    mitochondria

z     Axon

y    axon hillock

y    terminal bouton

y    microtubules, microfilaments

y    synaptic cleft

Prototypical Neuron - con’t

z     Dendrites

y    dendritic tree

y    receptors

 

Classifying Neurons

z     Neurites

y    unipolar

y    bipolar

y    multipolar

 

z     Dendrites

y    pyramidal

y    stellate

Classifying neurons- con’t

z     Connections

y    sensory neurons

y    motor neurons

y    interneurons

z     Axon length

y    Golgi I

y    Golgi II

Classifying Neurons- con’t

z     Neurotransmitters

y    dopamine

y    acetylcholine

Glial Cells

z     Microglia

z     Astrocytes

 

z     Oligodendrocytes

z     Schwann cells

 

z     Radial Glia

 

 

 

Blood Brain Barrier

Neurons and Synapses

Sensory Neurons

z    INPUT  From sensory organs to the brain and spinal cord.

Motor Neurons

z    OUTPUT  From the brain and spinal cord To the muscles and glands.

 

Interneurons

z    Interneurons carry information between other neurons only found in the brain and spinal cord.

 

 

Structures of a neuron

The cell body

y    Round, centrally located structure

y    Contains DNA

y    Controls protein  manufacturing

y    Directs metabolism

y    No role in neural signaling

Dendrites

z    Information collectors

z    Receive inputs from neighboring neurons

z    Inputs may number in thousands

z    If enough inputs the cell’s AXON may generate an output

Dendritic Growth

z    Mature neurons generally can’t divide

z    But new dendrites can grow

z    Provides room for more connections to other neurons

z    New connections are basis for learning

Axon

z    The cell’s output structure

z    One axon per cell, 2 distinct parts

y   tubelike structure branches at end  that connect to dendrites of other cells

 

Myelin sheath

z    White  fatty casing on axon

z    Acts as an electrical insulator

z    Not present on all cells

z    When present increases the speed of neural signals down the axon.

How neurons communicate

z    Neurons communicate by means of an electrical signal called the Action Potential

z    Action Potentials are based on movements of ions between the outside and inside of the cell

z    When an Action Potential occurs a molecular message is sent to neighboring neurons

Ion concentrations

The Cell Membrane is Semi-Permeable

Resting Potential

z     At rest the inside of the cell is at -70 microvolts

z     With inputs to dendrites inside becomes more positive

z     if resting potential rises above threshold (-55) an action potential starts to travel from cell body down the axon

z     Figure shows resting axon being approached by an AP

 

Depolarization ahead of AP

z     AP opens cell membrane to allow sodium (NA+) in

z     inside of cell rapidly becomes more positive than outside

z     this depolarization travels down the axon as leading edge of the AP

Repolarization follows

z     After depolarization potassium (K+) moves out restoring the inside to a negative voltage

z     This is called repolarization

z     The  rapid depolarization and repolarization produce a pattern called a spike discharge

Finally, Hyperpolarization

z     Repolarization leads to a voltage below the resting potential, called hyperpolarization

z     Now neuron cannot produce a new action potential

z     This is the relative refractory period

 

 

Neuron to Neuron

z    Axons branch out and end near dendrites of neighboring cells

z    Axon terminals are the tips of the axon’s branches

z    A gap separates the axon terminals from dendrites

z    Gap is the Synapse

Synapse

z    axon terminals contain small storage sacs called synaptic vesicles

 

 

Neurotransmitter Release

z    Action Potential causes vesicle to open          

Locks and Keys

z     Neurotransmitter molecules have specific shapes

Some Drugs work on receptors

z    Some drugs are shaped like neurotransmitters

z    Antagonists : fit the receptor but poorly and block the NT

y    e.g. beta blockers

 

Summary

z    3 types of neurons

z    The cell membrane

z    Ion movements

z    Action potentials

z    Synapse

z    Neurotransmitters

z    Receptors and ions

z    Agonists and antagonists

 

Terms con’t

Basic terms - con’t

Other basic terms

z     Contralateral and ipsilateral

z     unilateral and bilateral

z     proximal and distal

z     Afferent and efferent

Meninges

 

Spinal cord and peripheral nerves

z     31 segments

y    8 cervical

y    12 thoracic

y    5 lumbar

y    5 sacral

y    1 coccygeal

 

 

 

Spinal cord cross section

z      White and gray matter

z      Anterior horn

z      Posterior horn

z      Peripheral nerves

y    anterior root (motor)

y    posterior root (sensory

x   also called dorsal root

Question…...

z     What happens if you cut the posterior root (dorsal root) on any given peripheral nerve?

Sensory Pathways

z    Three main sensory pathways enter the spinal cord.

z    In general, sensory fibers synapse just prior to crossing over.

Pain-temperature pathway

z    Enters spinal cord, crosses over to opposite half almost immediately (within one or two spinal cord segments.

z    Ascends to thalamus on the opposite side.

z    Moves on to cortex.

Pain-temperature con’t

z    Lesion:  results in loss of pain-temperature sensation contralaterally below the level of the lesion.

Proprioception/stereognosis
(conscious pathway)

z    Remains ipsilateral, crosses over at the junction between the spinal cord and brain stem.

z    After the crossover, forms medial lemniscus and travels to the thalamus and cortex.

z    Fasciculus gracilus and fasciculus cuneatus (or posterior columns).

Proprioception/stereognosis

z    Lesion:  results in loss of conscious proprioception and stereognosis ipsilaterally below the level of the lesion.

 

Proprioception (unconscious)

z    Also known as spinocerebellar pathway.

z    For walking/performing duties subconsciously.

z    Ipsilateral….goes to cerebellum.

z    Lesion:  Ipsilateral loss of unconscious proprioception.

Light touch

z    Part of this pathway remains uncrossed until it reaches the brain stem, and partially crosses over at lower levels of the thalamus.

z    Lesion:  light touch is typically               spared in unilateral spinal                          cord injuries!

Major Descending Spinal Tracts

Motor pathways

z    The spinal cord has two major descending motor pathways.

y   Lateral pathway - direct cortical control

y   Ventromedial pathway - brain stem control

 

The Lateral Pathway

z    Voluntary movement

z    There are two tracts within the lateral pathway that you should know:

z    Corticospinal tract

x about 1 million axons

z    Cortico-rubrospinal tract

y   facial muscles

y   cranial nerves ~

 

Corticospinal tract

z    Originates in the motor cortex, descends to brainstem, and crosses at the pyramidal decussation.

z    Synapses on anterior horn cells just prior to leaving the spinal cord.

z    Upper motor neuron versus lower motor neuron.

Spinal Cord: Lateral Pathway

Corticospinal tract

z    Also called Pyramidal tract

z    Motor cortex ---> spinal cord

y   uninterrupted axon

y   2/3 of axons from motor cortex

y   1/3 from somatosensory cortex

z    Decussates at medullary pyramids

z    Contralateral control movement ~

Upper and lower MN defects

z     Upper Motor Neuron

y    spastic paralysis

y    minimal atrophy

y    hyperreflexia

y    babinski reflex present

z     Lower Motor Neuron

y    flaccid paralysis

y    significant atrophy

y    fasciculations and fibrillations present

y    hyporeflexia

y    babinski not present

Major Descending Spinal Tracts

Rubrospinal tract

z     Begins in the red-nucleus of the midbrain.

z     Receives input from the cortex and cerebellum.

 

z     Assists with motor control of the lower arms, feet, and legs….but NOT fingers!

Lateral Pathway Damage

z    Lesion both tracts

y   no independent movement of distal limbs

z    Corticospinal only

y   same deficits

y   recovery over several months

y   compensation by rubrospinal tract ~

Major Descending Spinal Tracts

The Ventromedial Pathway

z    Neurons originate in brainstem

z    Vestibulospinal & tectospinal tracts

y   head & posture posture

y   orienting responses

z    Pontine & medullary reticulospinal tracts

y   originate in reticular formation

y   trunk & antigravity leg muscles

Ventromedial pathway

z    There are two ventromedial tracts that you should know at this point:

y   vestibulospinal

y   reticulospinal

Vestibulospinal tract

z    Originates in brainstem

z    Projects bilaterally down the spinal cord

z    Important for regulation of posture (within trunk and legs).

Major Descending Spinal Tracts

Spinal Cord: Ventromedial Pathway

Reticulospinal tract

z    Located within midbrain

y   important for control of muscle tone, respiration, and coughing.

Spinal Cord: Ventromedial Pathway

Major Descending Spinal Tracts

12 Cranial nerves

12 Cranial nerves

 

 

z     I.  Olfactory

z     II. Optic

z     III.  Oculomotor

z     IV.  Trochlear

z     V.  Trigeminal

z     VI.  Abducens

z     VII.  Facial

 

z     VIII. Statoacoustic

z     IX.  Glossopharyngeal

z     X.  Vagus

z     XI.  Acessory

z     XII. Hypoglossal

 

 

 

 

 

 

 

Ventricular system

z     Lateral Ventricles

z     Third ventricle

z     cerebral aqueduct

z     fourth ventricle

 

z     Purpose:  cushions brain and provides nutrients.

Ventricular system

Medulla

z      Directly superior to spinal cord.

z      Contains cell bodies of many cranial nerves.

z      Most motor fibers cross at this region (pontomedullary junction)

z      Control of many vital functions.

 

Medulla

z      Reticular activating system (which is important for arousal and sleep).

 

Pons

z      Superior to medulla and anterior to cerebellum.

z      Main connective bridge from rest of brain to cerebellum.

z      Point of synapse of some cranial nerves.

z      Important center for eye movements and balance.

Pons

z      All descending info goes through pons.

z      Ascending information from medulla.

z      Portions of the reticular formation.

Inferior Colliculi

z     Back of brainstem, superior to pons.

z     Inferior colliculus

y    auditory

y    tonotopic mapping of frequencies

 

Superior Colliculi

z     Superior to inferior colliculi

z     Visual

y    point to point mapping

y    orienting responses

y    depth vision

y    conjugate vision

y    attention shifts

Pineal Gland

z     Top of brainstem and superior to superior colliculus.

z     “Third eye.”

z     Regulates sleep/wake cycles.

z     Regulates temperature changes.

Hypothalamus

z      Below the thalamus.

z      “kingpin of the viscera”

z      Regulates homeostasis

z      Feeding/drinking.

 

Cerebellum

z      Posterior or caudal to brainstem.

z      “Real-time updating of where things are.”

z      Smooth, coordinated movement.

z      Procedural memory.

 

Thalamus

z     Gateway to the cortex.

z     Relay center

y    sensory information

y    motor information

 

 

Thalamus

z     Lateral geniculate nucleus and vision.

Thalamus

z    Magnocellular layer:  low levels of light, insensitive to color.

z    Parvocellular layer:  color sensitive, requires high levels of light.

Cerebral Cortex

z     Vocabulary

y    gyri (gyrus)

y    sulci (sulcus)

y    fissure

 

Cerebral Cortex

z    Cytoarchitecture

y   Brodman’s map

z    Function

y   Luria

Luria’s First Functional Unit

z    Regulation of cortical “tone”

z    Waking and sleeping

z    General arousal

z    Posture

 

Second Functional Unit

z    Obtaining, processing, and storing information arriving from the outside world.

z    (primarily sensory functions)

Third Functional Unit

z    Programming, regulating, and sequencing mental and motor activity.

z    (primarily motor output)

Within second and third functional units….

z    Primary cortex

z    Secondary cortex

z    Tertiary cortex

Third Unit - Frontal lobes

z     Primary motor cortex

z     Homunculus Man

z     Secondary motor cortex

z     tertiary - Prefrontal

 

Homunculus Man

Second Unit -Parietal Lobes

z      Primary somatosensory cortex

z      Secondary association

y    astereognosis

z      Tertiary areas

y    math, geography, construction

 

 

 

Homunculus Man

Second Unit -Occipital Lobes

z     Primary cortex

y    area 17 or V1

z     Secondary cortex

y    area 18 or V2

z     Tertiary cortex

y    area 19 or V3

 

Second Unit - Temporal Lobes

z      Primary auditory cortex (Heschyl’s Gyrus)

z      Secondary cortex

y    Wernicke’s area

z      Tertiary cortex

y    hippocampus