Neuroscience - Key Terms

Sagittal Plane

Divides into right and left

Mid-sagittal plane

Divides into right and left halves, and a parallel cut produces parasagittal sections

Horizontal plane

Cuts across at right angles to the long axis of a structure, creating horizontal section, or a cross section

Coronal plane

Divides a structure into anterior and posterior portions

White matter

Composed of axons, projections of nerve cells that usually convey info away from the cell body, and myelin, an insulating layer of cells that wraps around the axons

Internal capsule

Composed of axons connecting the cerebral cortex with other areas of the CNS

Ganglia

Groups of cell bodies in the PNS

Afferent axons

Carry info from peripheral receptors toward the CNS

Spinal Cord function

Convey info between neurons innervating peripheral structures and the brain

Process info

Brainstem function

Contains important groups of neurons that control equilibrium (sensations of head movement, orienting to vertical, postural adjustments), cardiovascular activity, respiration, eye movements, and other functions

Cerebellum function

Coordinate movements

Largest part of the CNS

Compromises diencephalon and the cerebral hemispheres

Diencephalon

Consists of 4 structures: Thalamus, Hypothalamus, Epithalamus, Subthalamus

Hypothalamus function

Maintains homeostasis and regulates growth, the reproductive organs and many behaviors

Internal carotid arteries

Provide blood to most of the cerebrum

Vertebral arteries

Provide blood to the occipital and inferior temporal lobes and to the brainstem/cerebellar region

Basilar Artery

Supply the pons and most of the cerebellum

Circle of Willis

Anastomotic ring of 9 arteries, which supply all of the blood to the cerebral hemispheres

Neurologic disorders

Events that may affect the nervous system include the following:

• Trauma • Vascular disorders • Inflammation • Degenerative disorders • Developmental disorders • Tumors • Immunologic disorders • Toxic or metabolic disorders

Speed of onset

Acute, indicating minutes or hours to maximal signs and symptoms (indicates vascular issue)

Subacute, progressing to maximal signs and symptoms over a few days (indicates inflammatory process)

Chronic, gradual worsening of signs and symptoms continuing for weeks or years (indicates a tumor or degenerative disease)

Episodic Memory

The collection of specific personal events, including who was present and where, why and when each took place

Semantic Memory

Comprises acquired common knowledge; not based on personal experience

Types of Memory

Working: Temporary storage and manipulation of info

Declarative: Facts, events, concepts and locations

Procedural: Knowledge of how to do actions and skills

Declarative Memory

Refers to recollections that can be easily verbalized; are also called conscious or explicit memory

Requires attention during recall; 3 stages - Encoding: Processes info into a memory representation. Consolidation: Stabilizes memories. Retrieval: Retrieves memories.

Encoded in: Medial temporal lobe, including the hippocampus, part of the fornix and the surrounding cerebral cortex

Procedural Memory

Refers to the recall of skills and habits

Is also called skill, habit or non-conscious memory

Includes perceptual and cognitive skill learning such as object, pattern and face recognition

Practice is required to store procedural memories

3 learning stages: Cognitive, Associative and Automatic

Learned movements are represented in: Supplementary motor cortex, Putamen and Globus pallidus

Consciousness

Responsible for waking and sleeping, paying attention and the initiation of action

Aspects include: Generalized arousal level, Attention, Selection of object of attention, based on goals, Motivation and initiation for motor activity and cognition

Structures required: Brainstem, Neurotransmitters that act as neuromodulators, intralaminar thalamic nuclei and cerebral cortex

Divided Attention

Ability to attend to 2 or more things simultaneously

Selective Attention

Ability to attend to important info and ignore distractions

Sustained Attention

Ability to continue an activity over time

Switching Attention

Ability to change from one task to another

Intellect

Ability to form concepts and to reason

Essential structures: Lateral prefrontal cortex, posterior parietal lobes and their white matter connections

Amnesia

The loss of declarative memory

Retrograde Amnesia

The loss of memories that occurred before the trauma or disease that caused the condition

Anterograde Amnesia

The loss of the memory for the events following the event that caused the amnesia

Dementia (Neurodegenerative Cognitive Disorder)

Typically occurs later in life

Generalized mental deterioration, characterized by disorientation and impaired memory, judgment and intellect

Causes: ALzheimers, Dementia with lewy bodies, Parkinsons dementia, Chronic traumatic encephalopathy and multiple infarcts

Alzheimers Disease

Causes progressive mental deterioration consisting of memory loss, confusion and disorientation

Typically symptoms become apparent after age 60; death following by 5-10 years

People with Alzheimers become lost easily due to motion blindness

Emotional liability, noted in 40 percent of people with Alzheimers disease

Frontotemporal Dementia

Atrophy of frontal and temporal cortices causes this type of dementia

2 Subtypes: Primary progressive aphasia and behavioral frontotemporal dementia

Parkinsons Dementia

Primarily effects goal-directed behavior

Causes hallucinations and delusions

Dementia with Lewy Bodies

Progressive cognitive decline

Memory impairments

Deficits in attention, goal-directed behavior and visuospatial ability

Chronic Traumatic Encephalopathy

Occurs following repeated head trauma; an acquired frontotemporal lobe degenerative disease

Causes behavioral and personality changes, memory impairment, parkinsonism, and speech and gait abnormalities

Hemispheric Specialization

Left hemisphere: Specializes in understanding and producing language, including speech and writing

Right hemisphere: Understanding space, organizing movements relative to spatial organization, navigating and understanding and producing nonverbal communication

Communication

Temporoparietal Association are is specialized in understanding communication, directing attention and comprehending space

Language

Occurs in Wernike’s area - includes understanding spoken, written and signed language

Symbols are words or signs that represent an object or concept

Broca’s area provides instructions for language output

How we process information

1. Primary auditory cortex - auditory discrimination

2. Secondary auditory cortex - Classification of sounds (language versus other sounds)

3. Wernicke’s area - Auditory comprehension vocabulary

4. Subcortical connections - Link Wernicke’s and Broca’s areas

5. Broca’s area - Instructions for language output

6. Oral and throat region of sensorimotor cortex - Cortical output to speech muscles

Perception of Language

Language comprehension occurs in Wernicke’s area

• Includes understanding spoken, written and signed language

Symbols are words or signs that represent an object or concept

Broca’s area provides instructions for language output

Language Disorders

Aphasia - Disorder affecting spoken language

Alexia - Disorder affecting comprehension of written language

Agraphia - Disorder affecting the ability to write

Wernicke’s Aphasia

Language comprehension is impaired

People with Wernicke’s aphasia easily produce spoken sounds, but the output is meaningless

People with Wernicke’s aphasia have alexia, inability to write meaningful words and paraphasia

• Paraphasia - Use of unintended words or phrases

Broca’s Aphasia

Difficulty expressing oneself using language

People with Broca’s aphasia may not produce any language output, or they may be able to generate habitual phrases

People with Broca’s aphasia usually are aware of their language difficulties and are frustrated

Conduction Aphasia

Results from damage to the neurons that connect Wernicke’s and Broca’s areas

In most severe form - speech and writing of people with conduction aphasia are meaningless

Global Aphasia

The most severe form of aphasia

An inability to use language in any form

People with global aphasia cannot produce understandable speech, comprehend spoken language, speak fluently, read or write

Usually secondary to a large lesion damaging most of the lateral left cerebrum

Non-Verbal Communication

Gestures, facial expressions, tone of voice, and posture convey meanings in addition to a verbal message

R hemisphere inferior frontal gyrus provides instructions for producing nonverbal communication, including emotional gestures and intonation of speech

Disorders of Non-Verbal Communication

Lesions of the right temporoparietal junction cause difficulty understanding non-verbal communication

Damage to the right inferior frontal gyrus may cause the person to speak in a monotone, to be unable to effectively communicate non-verbally, and to lack emotional facial expressions and gestures

Perception

The interpretation of sensation into meaningful forms

An active process, requiring interaction among the brain, body and environment

Involves memory of past experiences, motivation, expectations, selection of sensory info, and active search for pertinent sensory info

Many areas of the cerebrum are involved in perception, including the secondary sensory areas and the cortical association areas

Classification of Perception

Visual perceptual

Body schema perception

Language perception (expressive and receptive)

Motor planning perception (or praxis)

Tactile perception

Auditory perception

Perceptual Impairment

Dysfunction to the right hemisphere (R posterior multimodal association areas)

Disorders in the R hemisphere involve an impairment in the recognition of physical reality

Ones relationship to the environment and to one’s body becomes distorted

Perceptual Dysfunctions

Body Schema - unilateral neglect, finger agnosia, anosognosia, double simultaneous extinction

Visual Perceptual - visual agnosia, prosopagnosia, simultanagnosia, metamorphosia, color agnosia, color anomia, cerebral achromatopsia

Visual Spatial - right and left discrimination, figure ground, form constancy, position in space, topographical disorientation, depth perception

Language Perception - receptive and expressive aphasia

Perceptual Motor - ideational apraxia, ideomotor apraxia and dressing apraxia

Tactile Perceptual - cortical sensation agnosia and tactile agnosia

Auditory Perceptual - auditory agnosia

Directing Attention

The R temporoparietal association area determines the behavioral importance of stimuli and decides focus of attention

Spatial Perception

The R parietal lobe spatial coordinate system is essential for constructing an image of one’s own body and for planning movements

The R hemisphere parietal association cortex comprehends spatial relationships, providing schemas of the following: body, body in relation to its surroundings and the external world

Neglect

The tendency to behave as if one side of the body and/or one side of space does not exist

Usually affects L side of the body and the L side of space

May be misinterpreted by others as confusion or lack of cooperation

Personal Neglect

Aspect of personal neglect include:

• unilateral lack of awareness of sensory stimuli

• unilateral lack of personal hygiene and grooming

• unilateral lack of movement of the limbs

Results from failure to direct attention

Also called “hemi-inattention”

Anosognosia: a form of denial that occurs in some people with severe hemiparesis and personal neglect

Spatial Neglect

Characterized by a lack of understanding of spatial relationships; results in a deranged internal representation of space

Manifestations of spatial neglect include:

• Navigation

• Construction

• Dressing

People with spatial neglect may have difficulty finding their way even within a single room

Decreased comprehension of spatial relationships also causes 2 types of apraxia:

• Dressing apraxia - Difficulty with dressing due to an inability to correctly orient clothing to the body

• Construction apraxia - Difficulty with drawing, building and assembling objects

Visual System

Provides: sight, processing of visual info, recognition and location of objects, control of eye movement, info used in postural and limb movement control

Sight: Info Conveyed From the Retina to the Cortex

Visual pathway begins with cells in the retina that convert light into neural signals

Signals are processed within the retina and are conveyed to the retinal output cells

Retinal output is conveyed by the axons that travel in the optic nerve, optic chiasm and optic tract

Synapses in the lateral geniculate nucleus of the thalamus

Vision: 2 Neuron Pathway

• 1st Neuron in visual pathway:

  • Optic nerve (CN 2) is the bundle of axons that pass from the retina to the optic chiasm

  • Right and left optic nerves merge at the optic chiasm where some axons cross the midline

  • Optic tract conveys visual info from chiasm to the lateral geniculate

• 2nd Neuron in visual pathway: Optic radiations

  • From lateral geniculate to the primary visual cortex

Cortical Destination of Visual Input

Info from the nasal ½ of each retina

• Crosses midline in the optic chiasm

• Projects to the contralateral visual cortex

Info from the temporal ½ of each retina

• Remains ipsilateral in the optic chiasm

• Projects to ipsilateral visual cortex

Info from the right or left visual field

• Delivered to contralateral visual cortex

Processing Visual Information

Info reaching the primary visual cortex stimulates neurons that discriminate the shape, size or texture of objects

Info conveyed to the visual association cortex is analyzed for colors and motion

• Action stream: Is a stream of visual info that flows dorsally and used to direct movement

• Perception stream: Is a stream of visual info that flows ventrally and used to recognize visual objects

Visual Signals to the Midbrain

Collateral branches of the optic nerve convey signals to the midbrain

These signals elicit:

• Reflexive control of the pupils

• Orientation of the eyes and head

Eye Movement System

Precise control of eye position is vital for vision

Achieved by:

• MLF

• Vestibulo-ocular reflexes (VOR’s)

• Cerebral centers

Superior colliculus coordinates reflexive orienting movements of the eyes and head vis the MLF

Types of Eye Movements

2 Objectives:

• Keeping position of the eyes stable during head movements

• Directing the gaze at visual targets

Gaze Stabilization (aka visual fixation) during head movements is achieved by:

• The VOR

• Optokinetic nystagmus

Direction of Gaze

Achieved by:

Saccades

Sooth pursuits

Vergence movements

Vestibulo-Ocular Reflexes (VOR’s)

Stabilize visual images during head movements

• Prevents the visual world from bouncing around during head movements

Vestibular receptors for the VOR are in 3 fluid-filled tubes inside each inner ear called semicircular canals

Stimulating a pair of semicircular canals indues eye movements in roughly the same plane as the canals

Action of Ciliary Muscle

Contracts when looking at near objects

• Increased the curvature of the lens

This action is called Accommodation

• Increases refraction of light rays so that the focal point will be maintained on the retina

The Pupillary Light Reflex

Elicited by shining a bright light into one eye

Shining light into one eye causes pupil constriction in the eye directly stimulated by the bright light

Pathway consists of neurons that sequentially connect

• The retina to the pretectal nucleus in the midbrain

• The pretectal nucleus to the parasympathetic nuclei of the oculomotor nerve

• Parasympathetic nuclei of the oculomotor nerve to the ciliary ganglion

• Ciliary ganglion to the pupillary sphincter muscle

The Near Triad

Consists of adjustments to view a near object: The pupils constrict, the eyes converge and the lens become more complex

The accommodation reflex requires activation of the visual cortex and an area in the frontal lobe of the cerebral cortex (frontal eye field)

CN’s 3, 4, and 6: Control of Eye Movement

Oculomotor, trochlear, and abducens nerves are the primary motor, containing motor neurons innervating the 6 extraocular muscles that move the eye

Extra-ocular Muscles

Extraocular muscles include 4 straight (rectus) muscles and 2 oblique muscles

• The 2 oblique muscles attach to the posterior half of the eyeball

  • When eye is adducted, the superior oblique muscle depresses and the inferior oblique muscle elevates the eye

Innervation of the Extra-Ocular Muscles

CN 3 Oculomotor Nerve - Controls contraction of the superior, inferior and medial rectus, the inferior oblique and levator palpebrae superioris muscles

CN 4 Trochlear Nerve - Controls the superior oblique muscle, which rotates the eye or if the eye is adducted, depresses the eye

CN 6 Abducens Nerve - Controls the lateral rectus muscle, which moves the eye laterally

Coordination of Eye Movements: Medial Longitudinal Fasciculus

Coordination of the 2 eyes is maintained via synergistic action of the extraocular muscles

Signals conveyed by the MLF coordinate hand and eye movements by providing bilateral connections among vestibular and ocular motor nuclei in the brainstem and spinal accessory nerve nuclei in the spinal cord

Optic Nerve Lesions

Complete interruption of the optic nerve results in:

• Ipsilateral blindness

• Loss of direct pupillary light reflex

  • This reflex may also be lost with a lesion of CN 3 because the oculomotor nerve is the efferent limb of the reflex

Optic nerve is entirely myelinated by oligodendroglia and is frequently affected by multiple sclerosis

Visual Field Deficits

Visual loss is described by referring to the visual field deficit

Complete lesion of the retina or optic nerve results in total loss of vision in ipsilateral eye

Bitemporal hemianopia: Loss of info in both temporal visual fields

• Lesion: Center of optic chiasm

Homonymous hemianopia: Loss of visual info from the same visual field, right or left, in both eyes

• Lesion: Complete lesion of visual pathway posterior to chiasm

Cortical Blindness and Blindsight

Cortically blind: The person has no awareness of any visual information due to a lesion in the brain

Blindsight: The ability of a cortically blind individual to orient to, point to, or detect movements of visual objects

• Requires intact function of the retina and pathways from the retina to the superior colliculus and lateral geniculate nucleus

CN 3 - Oculomotor Parasympathetic Efferents for the Pupillary Light Reflex and Near Triad

CN 3 - Has parasympathetic neurons that innervate the intrinsic muscles of the eye

Pathway:

• 1st Neuron - Parasympathetic nucleus of oculomotor nerve (in the midbrain) to the ciliary ganglion (behind the eyeball)

• 2nd Neurons - To the pupillary sphincter and the ciliary muscle

Disorders Affecting Cranial Nerves 3, 4, and 6

Lesions affecting the CN’s that innervate extra-ocular muscles or the MLF cause misalignment of the eyes

Acute disorders

• Double vision (diplopia)

Chronic disorders

• With suppression of vision from one eye, the person will lose depth perception

Oculomotor Nerve Lesion

Complete lesion of the oculomotor nerve causes:

• Severe ptosis (drooping of eyelid)

• Ipsilateral eye is aimed outward and down

• Diplopia

• Deficits in moving ipsilateral eye medially, down and up

• Loss of direct (ipsilateral) pupillary light reflex

• Loss of constriction of pupil in response to focusing on a near object

Trochlear Nerve Lesion

Lesion of trochlear nerve prevents activation of superior oblique muscle

• ipsilateral eye cannot look downward or inward

People with lesions of trochlear nerve complain of diplopia, difficulty reading, and visual problems when descending stairs

Abducens Nerve Lesion

Complete lesion of abducens nerve will cause eye to deviate inward

A person with this lesion will be unable to voluntarily abduct the eye and will have diplopia

Medial Longitudinal Fasciculus Lesion

A lesion affecting the MLF produces internuclear ophthalmoplegia by interrupting signals from abducens nucleus to the oculomotor nerve

When connection between the abducens nucleus and the oculomotor nucleus is interrupted, the eye contralateral to the lesion moves normally, but the eye ipsilateral to the lesion cannot adduct past midline when contralateral eye moves laterally

Optokinetic Nystagmus

Adjusts eye position during slow head movements

• Ex: when a person is walking, the head moves relative to objects in the environment

Is elicited by moving visual stimuli

Allows the eyes to follow large objects in the visual field

Physiologic Vs. Pathologic Nystagmus

Physiologic nystagmus: Normal response that can be elicited in an intact nervous system by optokinetic stimulation, rotation of the head, temperature stimulation of the semicircular canals or by moving eyes to extreme horizontal position

Pathologic nystagmus: Sign of nervous system abnormality

Direction of Gaze

Following may influence eye movements:

• Auditory info

• VOR

• Visual stimuli

• Sensory info from extra-ocular muscles

  • The emotion system

Direction of Gaze: Saccades

Saccades quickly switch vision from one object to another

Control of diagonal saccades

• Requires adjusting relative levels of activity of the pontine gaze center and midbrain

Saccades can be generated voluntarily or elicited by a variety of stimuli

Direction of Gaze: Smooth Pursuits

Smooth pursuits eye movements are used to follow a moving object

Moving visual stimulus is essential for the production of smooth pursuit movements

Direction of Gaze: Convergence Eye Movements

During reading and other activities in which the visual object is near eyes; eyes are aimed toward midline to allow image to fall on corresponding areas of retinas

Disorders of the Eye Movement System

Trophia - Deviation of one eye from forward gaze when both eyes are open

Phoria - Deviation from forward gaze apparent only when person is looking forward with one eye and other eye covered

Binocular fusion - Blending of the image from each eye to become a single image

Lesion Locations that Interfere with Eye Movements

CN’s that control extra-ocular muscles

Neuromuscular junction of extra-ocular muscles

MLF

Vestibular system

Cerebellum

Eye fields in the cerebral cortex

Motion Sickness

Is nausea, headache, anxiety and vomiting experienced in moving vehicles

May be caused by a conflict between different types of sensory info or by postural instability

• This triggers a stress reaction, eliciting an autonomic reaction

Seasickness may be caused by a conflict between visual and vestibular information

Pathways to the Brain

Individuals with somatosensory deficits are prone to pressure-induced skin lesions, burns, and joint damage bc they are unaware of the threat

People with congenital insensitivity to pain: tend to self-inflict injuries, have bone fractures, joint deformities, and amputations, often die young

Important distinction among the types of pathways: accuracy of the info conveyed

High-accuracy transmission provides accurate details regarding the location of the stimulation

Low accuracy pathways convey info that is not well-localized such as aching pain

When describing pathways in the NS, only the neurons with long axons that connect distant regions of the NS (projection neurons) are counted

A tract is the bundle of axons with the same origin and a common termination

Somatosensory pathways are often named for the origin and termination of the tract that contains the second neuron in the series

3 Types of Somatosensory Pathways

Conscious relay

Divergent

Non-conscious relay

Conscious Relay Pathways

Transmit info to the cerebral cortex

Info in conscious relay pathways is transmitted with high accuracy

Info in these pathways allows individuals to make fine distinctions about stimuli

Not all info conveyed by conscious relay pathways is perceived

• Attention must be directed specifically to the sensory info for perception

Divergent Pathways

Info is transmitted to many locations in the brainstem and cerebrum and use the pathways with varying numbers of neurons

Sensory info is used at both the conscious and unconscious levels

Aching pain is a form of sensation that is transmitted via divergent pathways in the CNS

Non-Conscious Relay Pathways

Nonconscious proprioceptive and other movement-related info is carried to the cerebellum

Info plays an essential role in automatic adjustments of our movements and posture