Neuroanatomy and Memory

Introduction to Basic Neuroanatomy/Nervous System

• nervous system is the chief controlling and coordinating system of the body.

• responsible for judgment, intelligence, and memory.

• controls voluntary and involuntary body activities.

Neuron

• Neurons (nerve cells) are the fundamental units of the brain and nervous system.

• They receive sensory input, send motor commands, and transform and relay electrical signals.

• Neurogenesis, the creation of new neurons (can occur even in adults.

Structure of a Neuron

• A neuron has three main parts:

  • Dendrites: Receive input from other cells. Dendrites receive synaptic inputs from axons.

  • Axon: The output structure, communicates through electrical messages called action potentials.the transmitting part of the neuron. Action potentials travel down axons to cause release of neurotransmitter.

  • Soma (cell body): Contains the nucleus, DNA, and produces proteins for the neuron.

  • Approximately 86 billion neurons in the brain.

Neuron Function

• transmits neural impulses or messages to:

  • Other neurons

  • Glands

  • Muscles

• It is the structural and functional unit of the nervous system.

Types of Neurons

• Sensory neurons:

  • Activated by sensory input from the environment.

  • Mostly pseudo-unipolar, with one axon split into two branches.

• Motor neurons:

  • central nervous system (CNS), connect to muscles, glands, and organs.

  • Transmit impulses from the spinal cord to skeletal and smooth muscles, controlling muscle movements.

  • Types:

    • Lower motor neurons: travel from the spinal cord to the muscle.

    • Upper motor neurons: travel between the brain and spinal cord.

  • Multipolar, with one axon and several dendrites.

• Interneurons:

  • Connect spinal motor and sensory neurons.

  • Transfer signals between sensory and motor neurons.

  • Communicate with each other, forming circuits of various complexity.

  • Multipolar

Concepts and Definitions

• Spine: Small protrusions found on dendrites that are the postsynaptic contact site.

• Action potential: A brief electrical event generated in the axon, signaling the neuron as 'active'. It travels the length of the axon and causes release of neurotransmitter into the synapse.

Synapse

• The junction point from one neuron to the next.

• Each synapse consists of:

  • Presynaptic membrane: membrane of the terminal button of the nerve fiber

  • Postsynaptic membrane: membrane of the target cell

  • Synaptic cleft: a gap between the presynaptic and postsynaptic membranes

Action Potential Characteristics

• Sudden

• Fast

• Transitory

• Propagating change of the resting membrane potential

• Only neurons and muscle cells are capable of generating an action potential; that property is called excitability.

  Glial Cells

• The nervous system consists of glia and neurons; they cooperate to carry out nervous system functions.

• Glia serve a variety of support functions for neurons; the name comes from the Greek word for glue.

Glial Cell Numbers

• Approximately 360 billion glial cells make up 80 to 90 percent of all cells found in the central nervous system.

• Additional glia are found in the peripheral nervous system.

Types of Glial Cells

• Categorized by size:

  • Macroglia (large varieties)

  • Microglia (relatively small)

• Four primary types of macroglia:

  • Astrocytes: Provide a variety of support functions to neurons.

  • Ependymal cells: Line the ventricles of the brain and the central canal of the spinal cord.

  • Oligodendrocytes: Supply the myelin covering that insulates nerve fibers (axons).

  • Schwann cells: Supply the myelin covering that insulates nerve fibers (axons).

Glial cells vs. Neurons

Major Divisions of the Brain

• Forebrain:

  • Processes sensory information

  • Helps with reasoning and problem-solving

  • Regulates autonomic, endocrine, and motor functions

• Midbrain:

  • Helps regulate movement

  • Processes auditory and visual information

• Hindbrain:

  • Helps regulate autonomic functions

  • Relays sensory information

  • Coordinates movement

  • Maintains balance and equilibrium

The Nervous System

• Central Nervous System (CNS):

  • Brain

  • Spinal cord: Connects the brain to the rest of the body

• Peripheral Nervous System:

  • Cranial nerves

  • Spinal nerves

  • Autonomic division:

    • Regulates internal environment

    • Carries information from the CNS to organs, blood vessels, and glands

    • Sympathetic (Arouses the body)

    • Parasympathetic (Calms after arousal)

  • Somatic division:

    • Carries information to the CNS from the senses and from the CNS to the skeletal muscles

Major Levels of Central Nervous System Function

• Spinal cord level

• Lower brain or subcortical level

  • Medulla oblongata

  • Pons

  • Midbrain - Together Brainstem

  • Hypothalamus

  • Thalamus

  • Cerebellum

  • Basal Ganglia

• Higher brain or cortical level

  • Cerebral cortex

  • Large memory storehouse

  • Thought processes

  • Works in association with the lower centers of the nervous system

Brain Structures and Their Functions

• Frontal Lobe

  • movement

  • reasoning

  • behavior

  • memory

  • decision making

  • personality

  • planning

  • judgment

  • initiative

  • inhibition

  • mood

• Temporal Lobe

  • language comprehension

  • behavior

  • memory

  • hearing

  • emotions

• Parietal Lobe

  • telling right from left

  • calculations

  • sensations

  • reading

  • writing

• Occipital Lobe

  • vision

• Brain Stem

  • breathing

  • blood pressure

  • heartbeat

  • swallowing

• Cerebellum

  • balance

  • coordination

  • fine muscle control

• Pituitary Gland

  • hormones

  • growth

  • fertility

Lobes of the Cerebral Cortex

• Frontal Lobe

• Parietal Lobe

• Occipital Lobe

• Temporal Lobe

Basic Terminology - Motor Functions

• Gross motor skills: Movement and coordination of the arms, legs, and other large body parts and movements; e.g., running, crawling, and swimming.

• Fine motor skills: Smaller movements that occur in the wrists, hands, fingers, feet, and toes.

Basic Terminology - Sensory Functions

• The extent to which an individual correctly senses skin stimulation, sounds, proprioception, taste and smell, and visual images.

Motor Areas

• Primary Motor Area

• Premotor Area

• Supplementary Motor Area

Motor/Sensory Functions

• primary sensory area

• primary motor area.

• anterior speech area (Broca's area).

• primary auditory area.

• secondary motor and sensory area

• posterior speech area (Wernicke's area)

• secondary visual area

• primary visual area

• secondary auditory area

Motor Area Functions

• Responsible for contraction of the skeletal musculature of the opposite side of the body.

• The right side of the cerebral cortex controls the left side of the body.

Clinical Pearl - Primary Motor Area

• Damage leads to Paralysis

Clinical Pearl - Premotor Cortex

• Involved in the planning of motor activities; damage here results in apraxia.

Apraxia

• A disruption of the patterning and execution of learned motor movements.

• Lack of understanding of how to organize the performance of a pattern of a movement.

Lesion in the Motor Cortex

• Stroke

  • Blockage

  • Rupture

  • Cerebral artery

Stroke and Language

• Language is much more than words.

• It involves our ability to recognize and use words and sentences.

• Much of this capability resides in the left hemisphere of the brain.

• When a person has a stroke or other injury that affects the left side of the brain, it typically disrupts their ability to use language.

Functions of Language

• Communicate our inner thoughts, desires, intentions, and motivations.

• Understand what others say to us.

• Ask questions.

• Give commands.

• Comment and interchange.

• Listen.

• Speak.

• Read.

• Write.

Aphasia: Language Impairment

• Language is probably the most remarkable and unique capacity humans have.

• In this capacity, humans differ from all other animals.

• Human linguistic capacity is represented in the left hemisphere of the human brain in both right- and left-handers, except in extremely rare cases.

Broca's Area (Motor Speech Area)

• Partly in the prefrontal cortex/premotor area

• Word formation area

Clinical Correlates - Broca's Area of Speech

• Cannot speak whole words

• Uncoordinated utterances

Loss of Broca's Area

• Results in Motor Aphasia

Wernicke's Area

• Location:

  • Left Temporal lobe

• Major function:

  • Important for the comprehension of speech sounds and is considered to be the language comprehension center.

Wernicke's Aphasia

• Some people are capable of understanding either the spoken word or the written word but are unable to interpret the thought that is expressed!

• Often say many words that don’t make sense.

• May fail to realize they are saying the wrong words

• May string together a series of meaningless words that sound like a sentence but don’t make sense.

• Have challenges because our dictionary of words is shelved in a similar region of the left hemisphere, near the area used for understanding words.

Clinical Correlates - Damage to Wernicke's Area

• A person can:

  • Hear perfectly well

  • Recognize different words

  • Cannot arrange words into coherent thoughts

  • Can read a book

  • Cannot understand meaning

Angular Gyrus

• We see a word, then we get meaning out of the visually perceived words via the angular gyrus.

• Comprehension occurs in Wernicke's area.

Area for Recognition of Faces

• Partly in the temporal lobes/occipital lobes

Cerebral Hemispheres

• Left hemisphere

• Right hemisphere

Corpus Callosum

• Connects the two cerebral hemispheres, allowing them to work together.

Human Memory

• Sensory Memory (

• Short-term Memory (Working Memory) ( 1 min)

• Long-term Memory (life-time)

  • Explicit Memory (conscious)

    • Declarative Memory (facts, events)

      • Episodic Memory (events, experiences)

      • Semantic Memory (facts, concepts)

  • Implicit Memory (unconscious)

    • Procedural Memory (skills, tasks)

Neuroanatomy of Memory

• Circuits or pathways.

• Hippocampus:

  • Crucial for the formation and consolidation of new memories.

  • Involved in spatial memory and navigation.

• Amygdala:

  • Involved in the formation and storage of emotional memories.

• Prefrontal cortex:

  • Involved in working memory, decision-making, and executive function.

• Basal ganglia:

  • Involved in motor control but also have a role in procedural memory.

• Cerebellum:

  • Involved in motor coordination but also has a role in certain types of learning and memory, such as motor skills.

• Thalamus:

  • Involved in sensory processing and also has a role in certain types of memory.

• damage or dysfunction in specific brain regions can lead to different types of memory deficits.

The Role of Memories

• Humans are shaped by:

  • emotions

  • thoughts

  • beliefs

  • values

  • relationships, among other factors

• Humans are ever-evolving.

Reasons to Forget

• Retrograde Amnesia

  • Brain damage to the hippocampus that results in the inability to remember events that happened before the event

• Anterograde Amnesia

  • Brain damage to the hippocampus that results in the inability to form new memories

Amnesia

• A condition where a person loses their ability to remember information, typically as a result of damage or injury to the brain.

• Possible causes:

  • Traumatic brain injury

  • Stroke

  • Brain infection

  • Alcohol or drug abuse

  • Degenerative brain diseases such as Alzheimer's disease

• Treatment options depend on the underlying cause and may include medication, therapy, or rehabilitation.

DSM 5

• The DSM-5 includes two main types of amnesia:

  • Dissociative amnesia: Involves the inability to recall important personal information, usually as a result of a traumatic or stressful event. Not due to other medical or neurological conditions.

  • Dissociative amnesia with fugue: Involves not only memory loss but also a loss of personal identity. Individuals may suddenly leave their home or workplace and may assume a new identity. Not due to other medical or neurological conditions.

• The DSM-5 also recognizes other types of dissociative disorders, including dissociative identity disorder (formerly known as multiple personality disorder) and depersonalization/derealization disorder.

Other Conditions Related to Memory

• Age-related memory decline: A natural decline in memory function that occurs with aging.

• Transient global amnesia: A sudden and temporary loss of memory that usually lasts for several hours.

• Mild cognitive impairment (MCI): A mild decline in memory and other cognitive functions that may be a precursor to dementia.

• Alzheimer's disease: A progressive brain disorder that slowly destroys memory and thinking skills. It is the most common cause of dementia in older adults.

• Dementia: A general term for a decline in cognitive function, including memory loss, that interferes with daily life.

• Traumatic brain injury (TBI): A blow or jolt to the head that disrupts normal brain function, including memory.

• Stroke: A condition where the blood supply to the brain is interrupted, leading to brain damage that can affect memory and other cognitive functions.

• Parkinson's disease: A neurodegenerative disorder that affects movement and can also lead to memory impairment.

• Huntington's disease: An inherited disorder that causes the progressive breakdown of nerve cells in the brain, leading to cognitive decline, including memory loss.

• Korsakoff's syndrome: A brain disorder caused by severe deficiency of thiamine (vitamin B1), often associated with alcoholism, that leads to memory loss, confusion, and other symptoms.

Etiology of Amnesia

• Psychological trauma: Traumatic events can lead to dissociative amnesia.

• Brain injury or damage: Can result from head trauma, stroke, or damage to the hippocampus.

• Neurodegenerative diseases: Conditions that cause damage or death to brain cells can lead to memory loss.

• Substance abuse: Can lead to memory loss, especially if used over a long period.

• Infections or diseases: Certain infections or diseases, such as encephalitis, meningitis, or HIV/AIDS, can cause memory loss.

• Electroconvulsive therapy (ECT): Can cause memory loss as a side effect.

• Medications: Certain medications can cause memory loss as a side effect.

Treatment of Amnesia

• Treatment options depend on the underlying cause and may include:

  • Medication

  • Therapy

  • Rehabilitation

Psychological Conditions Associated with Memory Difficulties

• Anxiety: Excessive worry or fear can impair attention and interfere with memory.

• Depression: Mood disturbances can interfere with cognitive function, including memory.

• Post-traumatic stress disorder (PTSD): Traumatic events can have a profound impact on memory.

• Attention-deficit/hyperactivity disorder (ADHD): Individuals with ADHD may have difficulty with attention and working memory.

• Dissociative disorders: Conditions where a person experiences a disconnection from reality can cause memory loss.

• Schizophrenia: Individuals may have difficulty with memory and cognitive function.

• Trauma-related disorders: Trauma-related disorders can cause memory loss or distortions.

• Sleep disorders: Sleep deprivation or disruptions in sleep patterns can interfere with memory.

• Substance abuse: Can cause memory loss, particularly in cases of long-term drug or alcohol abuse.