Chapter #12: Central Nervous System Flashcards
What is the Nervous System composed of?
the brain and spinal cord
What are the functions of the CNS?
- Integration/interpretation of incoming sensory information
- Sending out a motor response to effector organs
Gray Matter
Contains dendrites, cell bodies, & axon terminals (where integration takes place)
What is the function of gray matter?
All synapses are found in gray matter: motor controls, sensory perception, memory, personality, decision-making, etc. etc.
(all synapses are found between axon terminals and dendrites)
White matter
Contains myelinated axons, mostly in fiber tracts
What is the function of white matter?
passes ”messages” between different areas of gray matter (must pass trough white matter first)
Where is gray matter found in the brain?
-gray matter is peripheral
-closer to the outside
-outer layer of gray matter is called the cerebral cortex
Where is white matter found in the brain?
-white matter is more central, under gray matter
-gray matter is superficial and white matter is deep
Where in the brain stem is gray and white matter found?
-scattered brain matter found within the white matter
-white matter is superficial and gray matter is deep
Where in the spinal cord is the gray and white matter found?
-gray matter in a butterfly pattern surrounded externally by white matter
-Central canal found at the center of gray matter
What are ventricles?
hollow chambers found in the brain that are filled with cerebrospinal fluid (CSF) and lined with ependymal cells
Where are the 2 lateral ventricles found?
-one in each cerebral hemisphere
-one on the left, one on the right because 2 cerebral hemispheres
Where is the third ventricle found?
-found in diencephalon (completely enclosed)
Where is the fourth ventricle found?
-most inferior ventricle
-found in hindbrain
-connects to third ventricle via cerebral aqueduct
-continuous with central canal
What happens if ventricles are too large?
-pushes surrounding brain tissue
-prevents parts of the brain from developing correctly
-leads to brain function problems (ex. Schizophrenia)
Cerebral Hemispheres
-Form the most superior portion of the brain, make up most of brain by mass
-Hemispheres have characteristic ridges & valleys
-Gyri: ridges of cerebral hemispheres
-Sulci: shallow ggrooves
-Fissures separate larger regions of the brain (basically really deep sulci)
-Longitudinal fissure: separates the left & right hemispheres
-Transverse cerebral fissure: separates the cerebral hemispheres from the cerebellum
Three general regions of the cerebral hemispheres
Cerebral cortex (gray matter), white matter, and basal nuclei
Why is it important for the brain to have a wrinkled appearance?
-wrinkled appearance allows brain to have more surface area and more surface area means more neurons and more neurons means more brain activity
Lobes of the cerebral hemispheres
-Sulci divide the cerebral hemispheres into lobes
1. Central sulcus: separates frontal lobe and parietal lobe
2. Parieto-occipital sulcus: separates the occipital lobe from the parietal lobe
3. Lateral sulcus separates the temporal lobe from frontal & parietal lobes
-Insula is deep to lateral sulcus
***each lobe is named under the bone its underneath
What is the cerebral cortex?
The portion of the brain where the conscious mind is found
Functions of the cerebral cortex
provides self-awareness, sensation, communication, memory, understanding/learning, initiation of voluntary movement
Three functional areas of the cerebral cortex
1) Motor areas: control voluntary movement (muscle movement)
2) Sensory areas: conscious awareness of sensations (outside or inside the body)
3) Association areas: integrate diverse information (interpreting new and incoming info based on memories)
What does contralateral mean?
-right hemisphere is concerned with sensory & motor functions of the left side of the body (and vice versa)
-cerebral hemispheres are contralateral
-relating to or denoting the side of the body opposite to that on which a particular structure or condition occurs
Why are hemispheres not completely equal in function?
-One hemisphere may have structure/function that other side does not
-Ex: Broca’s area (speech) is usually found in left hemisphere but not right
-No functional area of the cortex works alone (conscious behavior involves entire cortex)
Motor areas of the cerebral cortex and function
-controls voluntary movement
1. Primary Motor cortex
2. Premotor cortex
3. Broca’s area
4. Frontal eye field
Primary Motor Cortex
-allows for conscious control of skilled/precise voluntary movements (initiate movement of skeletal muscle tissue)
-Pyramidal cells: large neurons found in primary motor cortex
-Axons of these neurons travel to spinal cord in corticospinal tracts (tracts carry movement-related information from the cortex to the spinal cord)
-Synapse with and stimulate motor neurons
-contains motor homunculus
What is the motor homunculus?
-the body is represented spatially in the primary motor cortex of each hemisphere
-Each region of the primary motor cortex is responsible for initiating movement in a part of the body
-The larger the body part, the more neurons are dedicated to that region of the body on the cortex (indicates that more neurons are dedicated to initiating movement to these parts of the body)
-larger the body part on motor homunculus = the more precise movements needed (ex. hands and face)
Premotor Cortex
1) Helps plan movements by selecting and sequencing basic motor movements into more complex tasks
-Must “communicate” with the primary motor cortex
2) Controls voluntary actions that depend on sensory feedback (causes your body to move away from negative stimulus and toward a positive one)
-damage to premotor cortex leads to apraxia
What is Broca’s area?
-Function: Specialized motor speech area that directs muscles involved in speech production (important to spoken language)
-Becomes active as we prepare to speak or as we plan other voluntary motor activities
-Is usually found on one side of the brain only (usually left)
What is the function of frontal eye field?
controls voluntary movement of the eyes
Function and sensory areas of cerebral cortex
-General function (of any area): Allows for conscious awareness of sensation
-Consists of:
1) Primary somatosensory cortex
2) Somatosensory association cortex
3) Visual areas (sight)
4) Auditory areas (hearing)
5) Vestibular cortex (balance/orientation)
6) Olfactory cortex (smell)
7) Gustatory cortex (taste)
8) Visceral sensory area (sensations of internal organs)
Primary Sensory Cortex
-Function: receive information from the general sensory receptors in skin
-The body is represented spatially according to site of stimulus input: forms a sensory homunculus
-The larger the body part, the more neurons are dedicated to that area of the body on the cortex
-Damage: difficulty with perceiving touch, fail to recognize an object by touching it, problems with recognizing their own body parts
What is meant by “general” senses?
-a sense in your body can be picked up anywhere (thermal perception and touch)
-special senses are vision, smell, taste, hearing, and equilibrium (collection of neurons only found in certain spots of the body)
Somatosensory Association Cortex
-Function: integrates sensory input relayed to it via primary somatosensory cortex
-Effect: produces understanding of what is being felt (size, texture, relationship of its parts)
-Ex: reaching into a bag and being able to identify phone vs. keys
-produces understanding of what is being touched
Visual Areas of the brain
1) Primary visual cortex: largest cortical sensory area!!
-Function: receives visual information that originates on the retina in the eye
-processes static and moving objects
2) Visual association area
-Function: uses past visual experiences to interpret visual stimuli: allows us to recognize things
-we rely on vision more than any other sense
Auditory Areas
1) Primary auditory cortex
-Function: Interpretation of sound from inner ear as pitch, loudness, and location
2) Auditory association area
-Function: Permits perception of sound stimulus & stores memories of sounds for reference
-ex. this is why you remember song lyrics
Vestibular Cortex
Function: allows for conscious awareness of balance/orientation
Olfactory Cortex
Primary olfactory cortex
-Function: conscious awareness of different odors
Gustatory Cortex
Function: perception of taste stimuli
Visceral Sensory Area
Function: allows conscious perception of visceral sensations
-Ex: you can feel a full stomach or bladder, you can feel your heart racing
Lateralization of Cortical Functioning
-A division of labor exists between the two hemispheres
-We call this division of labor lateralization
-Division of labor: means that the two sides do not do exactly the same thing
-Fiber tracts connect the left & right side of brain: can share information almost instantaneously and allows complete functional integration
Cerebral Dominance: the Lateralization of Cortical Functioning
-one hemisphere “dominates” a particular task
-This is usually in reference to language
-Left side of brain: language abilities, math, logic
-Ex: the left side of the brain is dominant while speaking publicly, memorize information
-Right side of brain: visual-spatial skills, insightful, creative
-Ex: right side of brain is dominant for new ideas, art, poetry, etc.
-explains why we are left handed or right handed
Cerebral White Matter
-Location: lies deep to cortical gray matter
-Function: communication in the CNS (see below for specifics)
-Classification of cerebral white matter:
1) Association fibers: connect different areas of the same hemisphere
2) Commissural fibers: connect corresponding areas of different hemispheres
-Benefit: Allows hemispheres to function as a coordinated “team”
3) Projection fibers: allows sensory information to reach cortex motor output to leave cortex (afferent or efferent messages)
Basal Nuclei of Cerebral Cortex
-Sometimes referred to as “basal ganglia”
-Location: deep to the white matter in each hemisphere
-Functions: Filters out incorrect or inappropriate responses relating to:
1) Muscle movement
2) Emotions and cognition
-Damage: tremors, involuntary muscle movement, poor posture, depression, anxiety, introversion, difficulty expressing emotions
Diencephalon
-completely encloses 3rd ventricle
-Made up of 3 paired structures:
1) Thalamus
2) Hypothalamus
3) Epithalamus
Thalamus
-Functions: relays sensory information coming into the cerebral cortex (like a mailman)
-Nuclei here have a certain function and therefore project information to a specific part of the cortex
-Information is “edited” here:impulses with similar functions are grouped together and relayed to appropriate part of cortex
-Motor activities
-Cortical arousal (sleep/wake cycles)
-Learning
-Memory
-damage: amnesia due to functions with sleep and memory. apathy: lack of interest in anything, loss of awareness, unexplained pain
Hypothalamus
Function: Main visceral control center in body
1) Controls autonomic nervous system: blood pressure, rate & force of heartbeat, digestive tract mobility, pupil size of eye, etc. etc. etc.
2) Initiates physical response to emotion: limbic system involvement
-Involved in perception of pleasure, fear, rage, sex drive, sleep
-Ex: pounding heartbeat, sweating, etc.
3) Regulates body temperature: the “body thermostat”
-Hypothalamus monitors blood temperature: initiates cooling or heat-generating processes
4) Regulates food intake
-Monitors blood nutrient levels (glucose and amino acids, some hormones)
5) Regulates water balance and thirst
-Monitors concentration of body fluids
When concentration is HIGH: thirst activated
6) Regulates sleep-wake cycles
-Uses daylight-darkness cues from visual pathways
7) Controls endocrine system function
-Controls secretion of hormones by other glands (i.e. anterior pituitary)
Epithalamus
-Pineal gland (pineal body)
-Secretes hormone melatonin
-Function of melatonin: helps regulate the sleep-wake cycle
Brain Stem
-Consists of 3 regions
1) Midbrain
2) Pons
3) Medulla Oblongata
-General functions of the brain stem:
1) Produces rigidly programmed, automatic behaviors necessary for survival
2) Provides pathway for fiber tracts running from higher brain centers to lower brain centers
3) Innervation of the head
-10 of the 12 pairs of cranial nerves are associated with the brain stem
The midbrain
-Functions:
1) Regulates motor movement
-ex: limb flexion, coordinates eye & head movement while following a moving object
2) Regulates hearing and vision
-Ex: auditory relay from ear to cortex, activate reflexive responses to sound (i.e. the startle reflex)
3) Alertness
4) Temperature control
The pons
-Functions:
1) Respiratory control
2) Bladder control (controls actual act of urination)
3) Swallowing (send fibers to esophagus)
4) Most functions associated with attached cranial nerves (4 cranial nerves attach to the pons; head and neck structures)
The medulla oblongata
-hypothalamus relays info through this structure
-Functions:
1) Cardiovascular center: regulates heart rate and blood pressure
2) Respiratory center: controls respiratory rhythm, depth of breath
3) Others: regulation of vomiting, swallowing, coughing, sneezing
Cerebellum
-General function: Coordinaton
1) Receptors in body relay information to cerebellum about body position, where the body is in space (relative to surrounding objects)
-Motor cortex sends information to cerebellum about intent to move
2) Cerebellar cortex “decides” best way to execute movement: force, direction, and extent of muscle contraction
-Effect: allows smooth, coordinated movement required for everyday life
-Other functions of the cerebellum:
-Cognitive functions
1) Thinking
2) Language
3) Emotion
-Underdeveloped cerebellum: cannot coordinate movements correctly; individuals have uncoordinated body movements, also very dizzy
Functional Brain Systems
-networks of neurons that span multiple regions of the brain that work together to accomplish one or more related tasks
-Includes 2 systems:
1) The Limbic System
2) The Reticular Formation
The Limbic System
-The “emotional brain”
-Regions:
1) Amygdaloid body
-Functions: response to perceived threats with fear or aggression (fight or flight response)
-damage: person not feeling fear, ex. bear scenario
2) Cingulate gyrus
-Functions: expressing emotions through gestures, resolving mental conflicts during times of frustration (more physical responses like punching a wall)
-Other functions: causes emotional responses to smell (survival mechanism like smelling gasoline or positive responses like perfume)
-Limbic system output is relayed through hypothalamus
-Remember: the hypothalamus is the main visceral control center in the body
-Emotional stress can cause visceral illnesses (strong emotions can have an effect on internal organs)
-Psychosomatic illness: illness with physical symptoms that results specifically from emotional causes
-Ex: being excited or nervous causes an increase in heart rate, blood pressure
Limbic System interactions with the prefrontal cortex
-Limbic system interacts with prefrontal cortex (who we are as a person is the prefrontal cortex)
-Intimate relationship between our feelings and our thoughts
-Results:
1) React emotionally to things we consciously understand to be happening
2) Are consciously aware of emotions
-Communication between limbic system and prefrontal cortex explains
1) Why emotions sometimes override logic or
2) Why reason can stop us from expressing emotion inappropriately
Reticular Activating System (RAS)
1) Sends continuous stream of impulses to the cerebral cortex
-Effect: cerebral cortex is kept alert, excitability is enhanced
-Severe injury to RAS results in a permanent coma
2) Filters out repetitive, familiar, or weak signals
-What happens to the information that is “filtered out” : nothing, the brain doesn’t receive them, your brain doesn’t care
-Effect: prevention of sensory overload
~99% of incoming information is filtered out
-RAS inhibited by sleep centers (decreases cortical arousal)& is depressed by alcohol, sleep-inducing drugs, and tranquilizers
-Autism: brain does not filter out as much info that it needs to (sensory overload)
Higher Mental Functions of the Brain
- Language
- Memory
Language
-Left side of brain is mostly responsible for a) understanding language and b) speaking
-Other regions of brain responsible for language
1) Broca’s area: production of spoken and written language, language processing & comprehension
2) Wernicke’s area: language comprehension, “speaking clearly”
-Right hemisphere understands and interprets nonverbal components of language and understands emotional components of language (ex. body language, facial expressions, tone of language)
Memory
-the storage and retrieval of information/past experiences (amygdala, prefrontal cortex, cerebellum, hippocampus) (only ~5% of info is stored as memory)
-Two stages of memory:
1) Short-term memory (STM/working memory): stores small amounts of information for short periods of time; forgotten in minutes, hours, days
2) Long-term memory (LTM): stores large amounts of information for longer periods of time; lasts weeks, years, maybe lifetime
Transfer from STM to LTM is possible, but depends on several factors:
-transfer from SLT to LTM is possible, but depends on:
1) Emotional state: heightened emotional state (alert, motivated, surprised, shocked, etc.) leads to almost instantaneous memory formation & storage
2) Rehearsal: repeating information enhances memory
3) Association: linking new information to old information that is already stored in LTM increases memory formation
4) Automatic memory: unconscious formation of memory in LTM (have no control over this, ex. remembering the names of characters in books)
Categories of memory
1) Declarative memory: learning explicit information (factual information)
-Involves ability to manipulate symbols & language
-Ex: names, dates
2) Nondeclarative memory:
-Memories acquired through repetition: difficult to “unlearn”
-Usually based on performance rather than recollection
-Ex: riding a bike, playing an instrument, etc.
Protection of the brain
-CNS tissue is delicate: neurons can be easily damaged (neurons cannot be replaced once damaged, amitotic)
-Forms of protection for the brain:
1) Skull
2) Meninges
3) Cerebrospinal Fluid (CSF)
4) Blood-brain barrier
Meninges
-membranes that surround and protect the brain
-Functions: covers and protect CNS, protect blood vessels around CNS, contains CSF, etc.
-Three layers of connective tissue membrane make up meninges:
1) Dura mater: most external layer
-Contains two sublayers
A) Periosteal layer attaches to inner surface of skull bones
B) Meningeal layer forms true external covering of the brain
2) Arachnoid mater: deep to dura mater
-Beneath membrane is subarachnoid spacecontains spiderweb-like projections to secure arachnoid mater to underlying pia mater
-Cerebrospinal fluid flows through subarachnoid space
3) Pia mater: innermost meningeal layer: clings to brain surface
-Highly vascularized layer
-Damage to meninges: Meningitis; become inflamed, cause nausea, vomiting, stiffness in neck
Cerebrospinal Fluid (CSF)
-liquid surrounding brain and spinal cord
-Produced by layer of cells in the ventricles called choroid plexus
-Functions:
1) Forms liquid cushion: protection from physical trauma
2) Gives buoyancy to CNS structures: reduces brain weight by ~97%
-Importance: without CSF, your brain would crush itself!
3) Nutrient & chemical-messenger carrier
Creation of Blood-Brain Barrier
Created by:
1) Tight junctions between cells making up capillary walls in CNS
-prevents any free flow
2) Astrocytes and pericytes surrounding the capillary
-form a wall around blood capillary, must pass through astrocyte
-Function: provides a constant environment for CNS tissue operation
Movement across the blood-brain barrier
1) Simple diffusion allows lipid-soluble substances to pass freely
-Ex: fatty acids, fats, oxygen, carbon dioxide, etc.
-Most drugs that affect the brain cross this was (alcohol, anesthetic, etc.)
2) Specific transport mechanisms move substances important to the brain
-Facilitated diffusion: glucose, amino acids, specific ions
-Transcytosis moves large substances into/out of CNS tissue
-Substances that are not allowed entry:
-Bloodborne metabolic waste, protein, certain toxins, most drugs, nonessential amino acids, potassium ions
Blood-brain barrier function
-The blood-brain barrier structure is variable in the brain (certain parts of the brain receive almost direct exposure to blood supply)
-Function: some parts of the brain need easy access to blood to measure variables in order to maintain homeostasis
-Ex: vomiting center of the brain in the pons: no barrier here allows monitoring of blood for poisonous chemicals/substances
-Ex: hypothalamus: monitors blood closely for temperature changes, water balance, various metabolic activities
Brain traumas
-Concussions: alteration in brain functions following a physical blow to the head
-This alteration is usually temporary, but multiple concussions will produce cumulative damage
-Victim may be dizzy or lose consciousness
-Contusions: permanent neurological damage resulting from bruising of the brain
-Victim usually loses consciousness, may enter coma
Degenerative Brain Disorders
Alzheimer’s disease and Parkinson’s disease
Alzheimer’s Disease
-Cause: senile plaques found throughout the brain: sit between neurons & eventually cause neuron death (prevents neuron communication)
-Effects:
-Early symptoms: memory loss (especially recent events & STM), shortened attention span, disorientation
-Long-term symptoms: language loss, dementia, changes in personality/mood
Parkinson’s Disease
-Cause: degeneration of dopamine-releasing cells in substantia nigra of midbrain
-Effect: basal nuclei become overactive without dopamine
-Symptoms: consistent tremors at rest, stiff facial expression, forward-bent walking posture; late stages = inability to chew and swallow food, need feeding tube, paralysis of diaphragm
Primary Functions of Spinal Cord
1) Conduction pathway: carries impulses to and from the brain
2) Major reflex center: spinal reflexes are initiated and completed at the spinal cord level
Protection of Spinal Cord
1) Bone: vertebrae
2) Meninges: single-layered dura mater, arachnoid mater, and pia mater (difference between the brain’s meninges is that the dura matter has 2 layers and 1 in spinal cord)
3) Cerebrospinal fluid
Anatomy of the Spinal Cord
-The spinal cord extends from the foramen magnum to L1 or L2
-Conus medullaris: tapered, cone-shaped structure where the spinal cord ends
-Filum terminale: fibrous extensions that extend from conus medullaris to coccyx
-Function: helps to hold the spinal cord in place
-Dural and arachnoid membranes continue past conus medullaris to the sacral vertebrae
-Importance: Allows site for spinal tap to withdraw CSF without risk to spinal cord injury
-Spinal tap: procedure to test for infection (meningitis)
-Width of spinal cord is consistent along length
-Exceptions: cervical and lumbar enlargements where nerves serving upper and lower limbs arise
-Spinal nerves of the PNS attach to spinal cord
-31 pairs (62 nerves total)
-Cauda equina: collection of nerve roots at the end of the vertebral canal
Cross-Sectional Anatomy of Spinal Cord
1) Central canal is located at the center
-Function: serves spinal cord with CSF
2) Gray matter is deep
3) White matter is superficial to grey matter
-white matter sends info, gray matter has neurons, cell bodies, axons, and dendrites to interpret and receive info
Gray Matter in Spinal Cord
-arranged in “horns”
-Dorsal horns: projections of gray matter on the dorsal side of the spinal cord
-Consist of interneurons
-Function: receive somatic (muscle tissue or skin) and visceral sensory input
-Ventral horns: projections of gray matter on the ventral side of the spinal cord
-Consist of interneurons and somatic motor neurons
-Function: motor output
-Lateral horn: projection of gray matter found only in thoracic and superior lumbar segments
-Function: contains sympathetic neurons that serve visceral organs (neurons are entirely motor in nature)
Roots of the Spinal Cord
-Axons enter or leave the spinal cord at “roots” (named after what horn they attach to)
-Ventral roots: where axons of ventral horn motor neurons (efferent fibers) exit the spinal cord
-Can be somatic or visceral
-Dorsal roots: where axons of sensory receptors (afferent fibers) enter the spinal cord
-Can be somatic or visceral
-Dorsal root ganglia: swelling of a portion of the dorsal root where cell bodies of sensory neurons are found
-Dorsal and ventral roots fuse to form spinal nerves (have both sensory & motor functions)
Homeostatic Imbalances of the Spinal Cord: Traumatic
-Damage to dorsal roots/sensory tracts: loss of sensation or paresthesia (abnormal sensation)
-Damage to ventral roots/motor tracts: paralysis (loss of motor function)
-Two types of paralysis:
1) Flaccid paralysis
2) Spastic paralysis
Flaccid paralysis
-injury to spinal cord or ventral roots prevents impulses from reaching skeletal muscle tissue
-Effect: muscle(s) innervated by damaged portion(s) cannot move (voluntarily or involuntarily)
Spastic paralysis
-upper motor neurons of primary motor cortex are damaged
-Spinal motor neurons are still intactspinal reflexes can still occur
-Effect: muscle can still move, but is completely involuntary
Spastic paralysis
-upper motor neurons of primary motor cortex are damaged
-Spinal motor neurons are still intact: spinal reflexes can still occur
-Effect: muscle can still move, but is completely involuntary
Transection of Spinal Cord
