Central Nervous System Vocabulary

Learning Objectives

• Identify and explain major anatomical structures and functions of the brain.
• Describe the ventricles and their openings.
• Explain the formation and circulation of cerebrospinal fluid.
• Explain the structure and arrangement of the meninges.
• Identify and explain the major anatomical structures and functions of the spinal cord.

Overview of the Nervous System

• The nervous system performs tasks in three steps:
  • Sense organs receive information about changes in the body and external environment, transmitting coded messages to the central nervous system (CNS).
  • The CNS processes this information, relates it to past experiences, and determines an appropriate response.
  • The CNS issues commands to muscles and gland cells to carry out the response.

Overview of the Brain

• Four major subdivisions:
  • Cerebrum
  • Diencephalon
  • Cerebellum
  • Brainstem

The Cerebrum

• Two hemispheres:
  • Left hemisphere.
  • Right hemisphere.
• The Longitudinal Fissure separates the two hemispheres.
• Fissure: a deep groove in the brain.
• Functions are equally distributed, with some exceptions.
  • Language is primarily processed in the left hemisphere, with right counterparts.
• Some specialization exists for types of mental activities.
• The Transverse Fissure separates the cerebrum from the cerebellum.

Surface of the Cerebrum

• The surface contains:
  • Gyri: Ridges of tissue.
  • Sulci: Shallow grooves separating gyri.
• These increase the surface area of the brain.

Brain Matter

• The brain consists of gray matter and white matter.
• Gray Matter:
  • Contains cell bodies and dendrites of motor neurons and interneurons.
  • The outer sheet of gray matter is called the Cortex.
  • The Cerebral Cortex is the wrinkled portion.

The Cerebral Cortex

• Involved in:
  • Awareness
  • Sensory perception
  • Voluntary motor initiation
  • Communication
  • Memory
  • Understanding

Cerebral Lobes

• Comprising 83% of the brain volume, they conceal other structures.
• Several sulci divide each hemisphere into five lobes:
  • Frontal
  • Parietal
  • Temporal
  • Occipital
  • Insula

Cerebral Cortex Considerations

• Four general considerations:
  • Contains three types of functional areas:
  • Motor areas: control voluntary movement.
  • Sensory areas: conscious awareness of sensation.
  • Association areas: integrate diverse information.
  • Each hemisphere is concerned with the contralateral (opposite) side of the body.
  • Lateralization (specialization) of cortical function can occur in only one hemisphere.
  • Conscious behavior involves the entire cortex in one way or another.

Functional MRIs

• Functional MRIs help determine functions of the cerebral cortex.

Cerebrum: Frontal Lobes

• Involved in:
  • Thinking, reasoning, planning, personality, and emotions (Prefrontal Cortex).
  • Initiating voluntary motion (pre-central gyrus).
  • Producing speech (Broca’s Area).

Frontal Lobe Areas

• Primary motor cortex (precentral gyrus):
  • Starts conscious control of precise, skilled skeletal movements.
• Premotor area:
  • Helps plan movements.
• Frontal eye field area:
  • Controls voluntary eye movement.
• Broca’s motor speech area:
  • Usually in left lobe only.
  • Receives impulses from sensory speech area and formulates spoken response.
  • Relays impulses to premotor area and finally motor cortex.
• Prefrontal cortex:
  • Primary association area (personality, intellect, cognition, etc.).
  • Motivation and regulation of emotional behavior and mood, goal setting.

Cerebrum: Parietal Lobes

• Involved in:
  • Primary somatosensory cortex: receives general sensory information from skin and proprioceptors (post-central gyrus).
  • Somatosensory association cortex: integrates sensory input from primary somatosensory cortex for understanding (size, texture, relationship of parts).
  • Understanding our physical environment and body part relations.
  • Processing some taste information.

Cerebrum: Temporal Lobes

• Involved in:
  • Processing hearing (primary auditory area).
  • Word recognition and comprehension (Wernicke’s area).
  • Contains auditory association area.
  • Sends impulses to Broca’s motor area for speech.
  • Processes taste.
  • Primary olfactory area.
  • Memory.

Cerebrum: Occipital Lobe

• Involved in:
  • Processing visual information.
  • Contains primary visual areas and visual association areas.

Cerebrum: Insula Lobe

• Insula Lobe (aka limbic lobe):
  • Involved in emotional responses and the behaviors & memories associated with them.

Strokes and the Motor Cortex

• Damage to areas of primary motor cortex, as seen in a stroke, paralyzes muscles controlled by those areas.
• Paralysis occurs on the opposite side of the body from the damage.
• Muscle strength or ability to perform discrete individual movements is not impaired; only control over movements is lost.
  • Example: damage to premotor area controlling movement of fingers would still allow fingers to move, but voluntary control needed to type would be lost.
• Other premotor neurons can be reprogrammed to take over skill of damaged neurons.
  • Would require practice, just as the initial learning process did.

Cerebral Cortex: General Association Areas

• Multimodal association areas:
  • Receive inputs from multiple sensory areas.
  • Send outputs to multiple areas.
  • Allows us to give meaning to information received, store in memory, tie to previous experience, and decide on actions.
  • Sensations, thoughts, emotions become conscious: makes us who we are.
  • Broadly divided into three parts:
  • Anterior association area - prefrontal cortex
  • Posterior association area
  • Limbic association area

Cerebral Cortex: Anterior Association Area

• Also called prefrontal cortex
• Most complicated cortical region
• Involved with intellect, cognition, recall, and personality
• Contains working memory needed for abstract ideas, judgment, reasoning, persistence, and planning
• Development depends on feedback from social environment

Cerebral Cortex: Posterior Association Area

• Large region in temporal, parietal, and occipital lobes
• Plays role in recognizing patterns and faces and localizing us in space
• Involved in understanding written and spoken language (Wernicke’s area)

Cerebral Cortex: Limbic Association Area

• Part of limbic system
• Involves cingulate gyrus, parahippocampal gyrus, and hippocampus
• Provides emotional impact that makes a scene important to us and helps establish memories

The Cerebral White Matter

• Contains myelinated axons and coverings = lighter colored tissue
• Found deep to gray matter of the brain
• Projections travel from grey matter to grey matter
  • To and from brainstem or spinal cord
  • Between different areas of the cortex

Cerebral White Matter: Association Tracts

• Association Tracts Connect grey matter in same hemisphere
  • Connect nearby gyri of same lobe
  • Connect gyri of different lobes

Cerebral White Matter: Commissural Tracts

• Commissural Tracts connect areas between hemispheres
  • Example: Corpus collosum

Cerebral White Matter: Projection Tracts

• Projection Tracts connect cerebrum to other portions of brain or spinal cord

Cerebrum: Basal Nuclei

• Functions of basal nuclei are thought to:
  • Influence muscle movements
  • Play role in cognition and emotion
  • Regulate intensity of slow or stereotyped movements
  • Filter out incorrect/inappropriate responses
  • Inhibit antagonistic/unnecessary movements
• Parkinson’s disease and Huntington’s disease are disorders of the basal nuclei

Diencephalon

• Most central region of brain, made of 3 portions:
  • Thalamus
  • Epithalamus
  • Hypothalamus & Pituitary Gland

Thalamus

• Main function is to act as relay station for information coming into cortex
• Two lateral portions connected by the intermediate mass
• Has nuclei that receive information from spinal cord, brainstem, and eyes, ears
• Is relay center for all sensations except for olfaction (i.e. smell)
  • Receives, sorts, and relays sensory information to appropriate area of cortex capable of interpreting the sensation
  • Impulses from hypothalamus for regulating emotion & visceral function
  • Impulses from cerebellum and basal nuclei to help direct motor cortices
  • Impulses for memory or sensory integration
• Overall, it acts to mediate sensation, motor activities, cortical arousal, learning, and memory

Hypothalamus

• Located below the thalamus
• Mammillary bodies: olfactory relay station
• Infundibulum: connects hypothalamus to pituitary glandà controls endocrine system
• The hypothalamus is the main visceral control and regulating center that is vital to homeostasis
  • Controls autonomic nervous system
  • Examples: blood pressure, rate and force of heartbeat, digestive tract motility, pupil size
  • Initiates physical responses to emotions
  • Part of limbic system: perceives pleasure, fear, rage, biological rhythms, and drives (sex drive)
  • Regulates body temp, hunger, thirst, sleep-wake cycles

Hypothalamus and Pituitary Gland

• Has important structural relationship with pituitary gland
• Pituitary gland releases hormones in response to hormones from the hypothalamus

Dysregulation of the Hypothalamus

• Hypothalamic disturbances cause a number of disorders such as:
  • Severe body wasting
  • Obesity
  • Sleep disturbances
  • Dehydration
  • Emotional imbalances
• Can be damaged by tumors, radiation, surgery or trauma

Epithalamus

• Most dorsal part of diencephalon
• Pineal gland- regulates biological clock, onset of puberty
  • Produces melatonin in response to darkness and helps regulate circadian rhythms
• Plays role in emotional and visceral responses to odors

Brainstem

• Consists of three regions: midbrain (1), pons (2), medulla oblongata (3)
• Similar in structure to spinal cord but contains nuclei embedded in white matter
• Controls automatic behaviors necessary for survival
• Contains fiber tracts connecting higher and lower neural centers
• Nuclei are associated with 10 of the 12 pairs of cranial nerves

Brainstem: Midbrain

• Superior most part of brainstem
• It is involved in:
  • Visual Reflexes
  • Auditory reflexes

Brainstem: Pons

• The pons is located between the midbrain and the medulla.
• Relays between cerebrum and cerebellum and brain and spinal cord; acts as bridge
• Sleep center, respiratory center (coordination with medulla)

Brainstem: Medulla Oblongata

• Inferior most part
• Continuous with spinal cord
• Discrete nuclei in gray matter
• Functions:
  • Autonomic reflex centers
  • Cardiovascular centers (cardiac and vasomotor)
  • Respiratory centers (rhythm, rate, depth)
  • Vomiting, Hiccupping, Swallowing, coughing, sneezing

The Cerebellum

• “Little Brain”
• Posterior to pons and medulla
• Processes input from cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles
• Also plays a major role in balance
• Gray (cortex) and white (arbor vitae) matter like cerebrum

Cerebellum Functions

• Fine-tunes the timing of motor function (coordination)
  • Receives info from cerebral cortex on intent to initiate movement
  • Receives signals from proprioceptors, visual, equilibrium to inform on body’s position
  • Cerebellar cortex calculations best muscle contraction
  • Sends blueprint of coordinated movement to motor cortex
• Roles in thinking, language, emotion

Functional Brain Systems

• Functional Brain Systems are Spread out but have a specific function

Limbic System

• Located in medial cerebrum and diencephalon
• Fornix- fiber tract that links limbic regions
• Amygdaloid body: recognizes angry or fearful facial expressions, assesses danger, and elicits fear response
• Cingulate gyrus: plays role in expressing emotions via gestures and resolves mental conflict
• Connects scents to emotions
• Interacts with prefrontal cortex- react to emotions
• Hippocampus and amygdaloid body also play a role in memory

Reticular Formation

• Nuclei throughout brainstem with axonal connections to hypothalamus, thalamus, cerebral cortex, cerebellum, spinal cord
• Filters out “background” stimuli
• Keeps you conscious, alert, and awake
  • Inhibited by sleep centers, alcohol, drugs
• Autonomic centers several visceral motor functions

Memory and Consciousness

• Memory: storage and retrieval of information
• Consciousness involves:
  • Perception of sensation
  • Voluntary initiation and control of movement
  • Capabilities associated with higher mental processing (memory, logic, judgment, etc.)

The Meninges

• Meninges: Connective tissue coverings around the brain and spinal cord
• Functions
  • Cover and protect CNS
  • Protect blood vessels and enclose venous sinuses
  • Contain cerebrospinal fluid (CSF)
  • Form partitions in skull
• Three Layers
  • Dura Mater- outermost layer
  • Arachnoid Mater- middle layer
  • Pia Mater- Bound tightly to the brain, innermost

Dura Mater

• Outermost layer
• Has two layers
  • Periosteal layer- attached to skull bones
  • Meningeal layer- loose covering surrounding brain and spinal cord
  • Two layers separate to form dural venous sinuses

Arachnoid Mater

• Middle layer with web-like extensions
• Delicate, loose brain covering
  • Separated from dura mater by subdural space
  • Subarachnoid space contains CSF and largest blood vessels of brain
  • Arachnoid granulations protrude through dura mater into superior sagittal sinus
  • Permit reabsorption of CSF back into venous blood

Pia Mater

• Innermost layer
• Delicate covering that clings tightly to brain
• Contains numerous tiny blood vessels

Meningitis

• Meningitis: inflammation of the meninges
• May spread to CNS, which would lead to inflammation of the brain, referred to as encephalitis
• Meningitis is usually diagnosed by observing microbes in a sample of CSF obtained via lumbar puncture

Cerebrospinal Fluid (CSF)

• Cerebrospinal fluid (CSF) forms a liquid cushion of constant volume around brain
• Functions
  • Gives buoyancy to CNS structures
  • Reduces weight of brain by 97% by floating it so it is not crushed under its own weight
  • Protects CNS from blows and other trauma
  • Nourishes brain and carries chemical signals
• Composed of watery solution formed from blood plasma, but with less protein and different ion concentrations from plasma

Cerebral Spinal Fluid

• Choroid plexus: cluster of capillaries that hangs from roof of each ventricle, enclosed by pia mater and surrounding layer of ependymal cells
  • CSF is filtered from plexus at constant rate
  • Ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes
  • Cilia of ependymal cells help to keep CSF in motion
• Normal adult CSF volume of ~150 ml is replaced every 8 hours

Choroid Plexus

• Cerebral Capillaries coated with ependymal cells
  • Blood Brain Barrier- filter blood to produce CSF
  • CSF has open access to brain barrier

Ventricles of the Brain

• Ventricles- fluid filled chambers continuous to one another and to central canal of spinal cord
  • Filled with cerebrospinal fluid (CSF)
  • Lined by ependymal cells (neuroglial cells)

Ventricles and CSF Flow

• Produces in the lateral ventricle
• Flows into third ventricle
• Flows into cerebral aqueduct
• Flows into fourth ventricle
• Either goes down central canal or out through holes in fourth ventricle to the subarachnoid space
• Eventually returns to jugular vein

Brain Barrier System

• Helps maintain stable environment for brain
  • Chemical variations could lead to uncontrollable neuron firings
• Substances from blood must first past through continuous endothelium of capillary walls before gaining entry into neurons
• Substances move through endothelial cells via:
  • Simple diffusion - allows lipid-soluble substances, as well as blood gases to pass freely through cell membrane
  • Specific transport mechanisms - facilitated diffusion moves substances important to the brain such as glucose, amino acids and specific ions
• Thick basement membrane surrounding capillaries is last part of barrier substances must pass through
  • Contains enzymes that destroy certain chemicals that would activate brain neurons
• Absent in some areas, such as vomiting center and hypothalamus
  • Necessary to monitor chemical composition and temperature of blood

Strokes

• Loss of blood flow to brain causes damage (starves and dies)
  • Bleeding of arteries supplying brain
  • Blockage of blood flow to brain (blood clot, fat embolism, air bubble)
• Transient ischemic attacks (TIAs)- mini strokes, temporary blockage
• FAST
  • Face muscles
  • Arms above head
  • Speech change
  • Time to call for help (if any of the above is problematic)
• Treatment: blood thinners of underlying causes

Caffeine Effects

• Most healthy adults can safely consume up to 400 milligrams of caffeine per day.
• An 8.4 oz can of Red Bull contains about 80 milligrams of caffeine.
• Caffeine can improve memory in some but seems to be most effective for people who are not hooked on it already.
• Caffeine can improve focus in moderate doses, but too much can give you the jitters, which reduces focus.
• Caffeine raises acid levels in your stomach and can lead to heartburn.
• Caffeine blocks the molecules in our brain, called adenosine, that make us sleepy, so we feel more awake.
• By blocking adenosine, caffeine promotes the brain’s production of two natural stimulants: dopamine and glutamine, which help boost our mood and even reduce the risk of depression.
• A moderate dose of caffeine can temporarily increase blood pressure, but it doesn't raise it high enough or long enough to cause harm in healthy adults.
• One side effect of caffeine’s effect on the brain is that it tells the adrenal glands (located above the kidneys) to flood the body with adrenaline, which makes us more irritable and emotionally charged.
• Some studies suggest that caffeine can temporarily reduce appetite.
• When ingested, caffeine is absorbed from the stomach; after about an hour or two, it enters the bloodstream.
• It takes about 5 or 6 hours before half of the caffeine you've ingested wears off.

Concussion

Concussion Signs

• Loss of consciousness
• Vomiting
• Balance problems
• Glazed look in the eyes

Concussion Symptoms

1. Physical Symptoms
   • Headaches
   • Dizziness
   • Nausea
   • Light-headedness
   • Sensitivity to light
   • Sensitivity to noise
   • Inappropriate crying
2. Cognitive Symptoms
   • Forgetting an assignment or play
   • Delayed response to questions
   • Amnesia
   • Confusion about location, date, or game score
   • Loss of focus
   • Attention difficulties
   • Difficulty completing mental tasks
   • Memory problems
   • Difficulty multitasking
3. Sleep Symptoms
   • Sleeping more than usual
   • Sleeping less than usual
   • Trouble falling asleep
4. Emotional Symptoms
   • Anxiety
   • Depression
   • Panic attacks

The Spinal Cord

• Spinal cord is enclosed in vertebral column
  • Begins at the foramen magnum
  • Ends at L1 or L2 vertebra
• Functions
  • Provides two-way communication to and from brain and body
  • Major reflex center: reflexes are initiated and completed at spinal cord

Spinal Cord Protection

• Protected by bone, meninges, and CSF
• Spinal dura mater is one layer thick
• Epidural space: Cushion of fat and network of veins in space between vertebrae and spinal dura mater
• CSF fills subarachnoid space between arachnoid and pia maters
• Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2
• Spinal cord terminates in cone-shaped structure called conus medullaris
• Filum terminale extends to coccyx- fibrous extensions of conus anchors spinal cord
• Spinal nerves- part of PNS coming off spinal cord
• Cervical and lumbosacral enlargements
  • Nerves serving upper and lower limbs emerge here
• Cauda equina
  • Collection of nerve roots at inferior end of vertebral canal

Spinal Cord Structure

• Contains gray and white matter
• Gray matter (central region)- butterfly shape
• Central Canal- space that runs down the spinal cord and contains CSF

Spinal Cord Gray Matter

• The gray matter is further divided into
  • Posterior/Dorsal Horn
  • Sensory neurons
  • Anterior/Ventral Horn
  • Motor Neurons
  • Lateral Horn
  • Only found in thoracic and lumbar regions
  • Contains sympathetic neurons

Spinal Cord White Matter

• The white matter contains myelinated axons arranged into tracts
• Ascending tracts carry afferent sensory information up to brain
• Descending tracts carry efferent motor neurons down to spinal cord
• Transverse- from one side to the other

Spinal Cord Trauma and Disorders

• Spinal cord trauma
  • Localized injury to spinal cord or its roots leads to functional losses
  • Paresthesias: caused by damage to dorsal roots or sensory tractsà loss of sensory function
  • Paralysis: caused by damage to ventral roots or ventral horn cellsà loss of motor functions
  • Transection (cross sectioning) of spinal cord at any level results in total motor and sensory loss in regions inferior to cut
  • Paraplegia: transection between T1 and L1
  • Quadriplegia: transection in cervical region

Spinal Cord Injury (SCI)

• Usually begins with blow that fractures or dislocates vertebrae.
• Most don't sever spinal cord, but cause damage when pieces of vertebrae tear or press down on nerves.
• In complete SCI, paralysis below level of injury.
• In incomplete SCI, some movement, sensation below injury.

Spinal Cord Injury Treatment

• Animal studies had suggested that signals from brain not needed to control details of standing, walking, but just to activate spinal cord.
• Stimulator implanted in lower back to send electrical signals to spinal cord.
• On his third day of electrical stimulation, Rob managed to stand on his own
• People with partial spinal cord injuries have experienced some improvement after electrical stimulation, but this is first time someone with motor or sensory function below injury has been able to stand.
• Can remain standing for up to four minutes; with help of a harness, he can walk.
• Dr. Harkema said, "This is a breakthrough. But we have a long road ahead”

Spinal Cord Injury: Future Study

• As reported in the initial study with the first four participants, epidural stimulation led to the recovery of critical functions like improved bladder and bowel control, sexual function, and temperature regulation. When stimulated, the participants can also voluntarily control their legs and bear weight. Most importantly, their lives have been transformed with improved health and quality of life.
• Not a cure yet. The next step is to fund a new study with 36 additional participants to prove that this therapy is viable. This will allow us to expedite epidural stimulation to the clinic.
• Efforts are underway to develop more sophisticated technology that may allow people living with SCI to maintain balance, continue to bear weight and work toward stepping in the presence of epidural stimulation.

Spinal Cord Trauma and Disorders

Poliomyelitis

• Destruction of ventral horn motor neurons by poliovirus
• Muscles atrophy
• Death may occur from paralysis of respiratory muscles or cardiac arrest
• Survivors often develop postpolio syndrome many years later from neuron loss

Amyotrophic lateral sclerosis (ALS)

• Also called Lou Gehrig’s disease
• Destruction of ventral horn motor neurons and fibers of pyramidal tract
• Symptoms: loss of ability to speak, swallow, and breathe
• Death typically occurs within 5 years
• Caused by environmental factors and genetic mutations involving RNA processing
  • Involves glutamate excitotoxicity
  • Drug riluzole interferes with glutamate signaling: only treatment

The Spinal Cord & Reflexes

• Sensory = enter cord through dorsal root, to dorsal horn and then travel up ascending tracts
• Motor – travel down from brain in descending tracts, then ventral horn, then out ventral root