A&P Chp. 12:The Central Nervous System Flashcards
Gray Matter
mostly unmyelinated processes and neuron cell bodies
White Matter
myelinated fiber tracts (axons)
Major Subdivisions of the Brain
Cerebral Hemispheres
Diencephalon: thalamus, hypothalamus, epithalamus
Brain Stem: midbrain, pons, medulla oblongata
Cerebellum “little brain”
Does size represent intelligence?
No. Size and number of neurons is irrelevant to intelligence. Complexity, or interactions of neurons and how they work together, dictate processing power.
Brain Ventricles
Made of epidymal cells
Fluid filled spaces in the brain
2 Lateral Ventricles: C-shaped chambers deep in the brain where most of the cerebrospinal fluid is made and connected to a 3rd ventricle
3rd ventricle: slit between the right and left halves of the thalamus; connects to 4th
4th ventricle: lies between brain stem and cerebellum; connects to central canal of spinal cord; CSF then exits and goes around entire brain and spinal cord
Gyrus
elevated ridges of brain
Precentral gyrus: controls skeletal muscle
Postcentral gyrus: locates where senses are coming from
Sulcus (sulci)
Shallow grooves of brain
Central Sulcus: separates frontal from parietal lobe; in between precentral and postcentral gyrus
Lateral Sulcus: separates from from temporal lobe; very deep but not a fissure
Parieto-occipital Sulcus: separates parietal from occipital lobe
Fissure(s)
Deep grooves that separate major regions
Longitudinal Fissure: Separates R and L hemispheres
Transverse Fissure: Separates cortex from cerebellum
Cerebral Lobes/5 Hemispheres
- Frontal
- Parietal
- Temporal
- Occipital
- Insula
Insula
Cerebral Lobe/Hemisphere hidden deep to portions of the temporal, parietal, and frontal lobes
Cerebral Cortex
Center of consciousness (knowledge, memories, everything)
Contains neuron cell bodies, dendrites, unmylinated axons, and glial cells (nuclei)
A rich capillary blood supply is near for high metabolic rate
Folds greatly increase surface area possibly meaning greater intelligence
Three types of activity areas: motor, sensory, association
Consciousness involves all areas of the brain
Primary Motor Cortex
Motor Area of the Cerebral Cortex
Precentral gyrus of frontal lobe
Primarily involved in voluntary motor control area devoted to skilled muscles (controls fingers, face, etc)
Controls skeletal muscles
Map of the Primary Motor Cortex
Motor Homunculus: shows the locations on the precentral gyrus which control the skeletal muscles of each body region.
More precise movements require more neurons which is why fingers and face take up more room than arms and legs which have broad movements.
Control is contralateral: affecting the opposite side
Premotor Cortex
Motor Area of the Cerebral Cortex Anterior to the primary motor cortex Involved in learned repetitious or patterned movements such as learning the piano Does not control skeletal muscles If damaged, you can learn again Trained brain to do these actions
Damage to Primary Motor Cortex
Contralateral: affecting opposite side of the body
Only voluntary control of skeletal muscle is lost and it can never be regained. It is impossible to relearn.
Reflexes remain because they are controlled by the spinal cord.
Damage to Premotor Cortex
Loss of programmed motor skills
Can be relearned if brain is trained again
Muslce strength and the ability to perform tasks remain (not automatic tasks)
Language Areas
Motor Area of the Cerebal Cortex
A motor center fro speech, controlling muscles of the tongue, throat, and lips
involved in planning some voluntary motor activities
Only found in one hemisphere….left?
Frontal Eye Field
Motor Area of the Cerebral Cortex
Controls voluntary movements of the eye
Primary Somatosensory Cortex
Sensory area of the cerebral cortex
Pencil Poking demonstration: can’t read braille with your shoulder becasue receptive field of neurons is bigger
Receives inputs directly from peripheral somatic sensory receptors
Localizes points of the body where sensations originate
Distribution of input areas for cutaneous sensations
Spaital Discrimination: identifies the areas of the body being stimulated
Somatosensory Association Area
Sensory Area of the Cerebral Cortex
Identify key in your hand by senses associated with what a key looks like.
Posterior to the primary somatosensory area
Integrates and analyzes information relative to size, texture for identification
Gets input from primary somatosensory association area
Visual Cortex
Sensory Area of the Cerebral Cortex
Medial surface of occipital lobe
Impulses from teh eyes are routed through the thalamus
Optical Illusions
Sensory fibers cross over to the opopsite side at the optic chiasm; matters what you are looking at and where it is located
Lateral geniculate nucleus (visual area) of the thalamus
Auditory Cortex
Sensory Area of the Cerebral Cortex
Superior part of the temporal lobe
Primary auditory cortex: pitch rhythm and loudness
Auditory association area: identifies/ perceives sounds using memories as references
Olfactory Cortex
Sensory Area of the Cerebral Cortex
Located above the orbits in the medial portion of the temporal lobes
Conscious awareness of different smells
Anterior Association Area
Multimodal Association Area
Prefrontal cortex
matures slowly (doesn’t finish til 20s) and influenced by environment
anterior frontal lobe
intellect, complex learning, recall and personality
Judgment and planning
Posterior Association Area
Multimodal Association Area
temporal, parietal, and occipital lobes
pattern recognition, localizing position
receives input from motor and other sensory association areas and interprets it
Ex: dropping an acid bottle, many sensory inputs together give the dominant feeling of danger
Frontal Lobotomy
Sever the frontal lobe from the rest of the brain
Stops all strong emotional reaction
“Shutter Island”
Limbic Association Area
Multimodal Association Area
Cingulate and parahippocampal gyri, and hippocampus
Provides emotional impact and sense of danger
Brain Lateralization
Both hemispheres participate in every activity, but one hemisphere is dominant for most activites
Left Hemisphere: language skills, math and logic
Right Hemisphere: creative skills, intuition, emotion, appreciateion of art and music, visual-spatial skills
Most right dominant are left handed and male
Most left dominant are right handed
Equal function may result in ambidexterity and/or dyslexia
Commissural Fibers
Myelinated fibers providing type of connection within the CNS
connects the R and L hemispheres
Ex: corpus callosum “body collosal”
Association Fibers
Myelinated fibers providing type of connection within the CNS
connect neurons within one hemisphere
Projection Fibers
Myelinated fibers providing type of connection within the CNS
connect cerebral hemispheres to other parts of the CNS
Ex: Internal capsule
Cerebral White Matter
Myelinated fibers providing the 3 types of connection within the CNS
Deep Cerebral Gray Matter (Basal Nuclei)
Diffuses masses of gray matter deep within the cerebral hemispheres
Involved in regulating slow, sustained motor movements such as arm swinging
Also inhibit unnecessary movements (stabalize and smooth primary movements)
This area is affected in Parkinson’s Disease causing tremors and slow, unsteady movements
Diencephalon
Brain region composed of thalamus, hypothalamus, and epithalamus
Surrounded by the cerebral hemispheres
Encloses the third ventricle
Thalamus
“Gateway to the Cortex”
Egg shaped collection of nuclei found in the Diencephalon
Serves as a major switching station as impulses transfer from one neuron to the next
Forms the lateral walls of the third ventricle
Receives input from all ascending pathways and afferent impulses from all senses except smell
Processes sensory information: crude recognition of sensation (cerebral processing required for precise localization and conscious awareness)
Hypothalamus
Found below Thalamus in the Diencephalon
Forms the bottom of the third ventricle.
Contains many nuclei and infundibulum
Has 7 major functions
Infundibulum
the stalk connecting the hypothalamus and the pituitary gland
Pituitary Gland
Endocrine gland
releases several hormones in response to chemical regulation factors from the hypothalamus
Functions of the Hypothalamus
- Autonomic Nervous System (visceral) control center: important for homeostasis
- A center for emotional responses and behaviors
- Body temperature regulation
- Regulation of food intake
- Regulation of water balance and thirst
- Regulation of sleep-wake cycles
- Controls many endocrine system functions: neuroendocrine feedback control
Epithalamus
Found upon the Thalamus in the dorsal portion of the Diencephalon
Contains the pineal gland: melatonin/sleep-wake cycles
Location of one of the choroid plexus sites for production of cerebrospinal fluid (CSF)
Brain Stem
Brain region composed of the midbrain, pons, and medulla Involved in automatic, unconscious behaviors needed for survival Provides pathways (fiber tracts) for neurons which are communicating up or down
Midbrain
Part of the brain stem
Pons to the lower portion of the diencephalon with the cerebral aquaduct passing through it
Main connecting routes for all parts of the brain and spinal cord
Connections between the cerebellum and the brainstem (cerebellar peduncles)
Pons
Part of the brain stem
Found above the medulla and anterior to the cerebellum
Contains both gray matter nuclei and white fiber tracts
Primarily conduction pathways
Site of origin for several cranial nerves
Cerebral peduncles
Medulla Oblongata
Part of the brain stem
Most inferior part of the brain that merges into the spinal cord inferiorly
Involved in maintaining internal homeostasis
Contains: cardiovascular center, respiratory center, and other centers for vomiting, hiccupping, swallowing, coughing and sneezing
Cerebellum
Second-largest brain region
“small brain”
Separated from the cerebrum by the transverse fissure
Its surface is the cerebellar cortex (gray matter) with folds (folia); its white matter fiber tracts are located in the interior
arbor vitae: “tree of life”
Cerebellar Structure and Function
Shaped like a butterfly
Central vermis “worm”
cerebellar hemispheres
Functions compare an intended movement (directed from the cortex) with what movement is actually happening
Constantly receiving sensory input from muscle, tendon, and joint proprioceptors, and visual and equilibrium receptors
Purkinje neurons play a major role in control over the refinement of motor activities inititiated by the frontal motor cortex
Homunculi
maps of the functional area
The Limbic System
Encircles the brain stem
Emotional center
Different regions of gray matter, including part of the hypothalamus and the olfactory bulbs
Funcions in emotional aspects of behavior related to survival
“fight or flight”
Memory impairment results from damage to the limbic system
Also associated with pleasure and pain: electrical stimulation elicits different responses; includes defensive posturing (rage); others inspire timidity
Also functions with the cerebrum in memory: olfactory centers are near the limbic system; and experiences which initiate strong emotional responses are associated with smells are committed to memory more easily
Reticular Formation
Gray matter (nuclei) distributed within the medulla, pons, and midbrain Axonal connections to many other areas of the brain Structural and functional areas: sensory, integrative and motor functions; receives input from higher centers for skeletal muscle actions
Reticular Activating System (RAS)
- Functions to alert the cerebral cortex to important incoming signals
- Filters signal “noise” = repetitive stimuli (LSD interferes with this: constantly “your shirt is on” “this person is chewing gum”)
- Maintenance of consciousness and waking from sleep (sudden stimuli): sends a constant stream of information to the cortex, maintaining arousal
- The RAS is inhibited by sleep centers in the hypothalamus
- The RAS is depressed by alcohol, sleep-inducing drugs (hypnotics) and anti-anxiety drugs.
Protection of the brain
- bones: skull
- meninges: three connective tissue wrappings the CNS
- cerebrospinal fluid (CSF): a fluid “shock absorber” which cusions and nourishes the brain
- blood-brain barrier: the physical and physiological separation of the CNS from the bloodstream
(scalp hair to prevent sunstroke?)
Functions of the Meninges
- Covers and protects brain and spinal cord
- Protect blood vessels and enclose venous sinuses
- Confine the cerebrospinal fluid in the subarachnoid space
- Form major connective tissue partitions for brain regions within skull: falx cerebri (in longitudinal fissure), falx cerebelli, tentorium cerebelli (transverse fissure)
Dura Mater
Outermost layer of the meninges
“tough mother”
Dense, irregular fibrous connective tissue
Strong, protective wall around the brain and spinal cord
Pool of venous (deoxygenated) blood
Arachnoid Membrane
Middle layer of the meninges
Loose connective tissue
Subdural space (gap): separates the arachnoid from the dura; contains interstitial fluid
Arachnoid vili: extend into the subdural space creating larger surface area for reabsorption of CSF back into the blood
Subarachnoid Space: separates arachnoid from the pia mater; contains CSF
Pia Mater
Deepest layer of the meninges
“little mother”
Extends into the sulci and follows the large blood vessels into the brain
Thin/light transparent fibrous connective tissue supporting a network of many tiny blood vessels
Cerebrospinal Fluid
Protects against chemical and physical injury serving as secondary circulatory system nourishing the CNS
Found in the four ventricles and the subarachnoid space
Composition: H20, clucose, proteins, lactic acid, urea, cations (Na+, K+, Ca2+, Mg2+), anions (Cl-, HCO3-), some lymphocytes (WBCs)
80-150ml of CSF is normal for an adult
Formed by the choroid plexus; reabsorbed by the arachnoid villi and returned to the plasma
Functions of Cerebrospinal Fluid
- Mechanical Protection: shock absorbing fluid; the brain “floats” in this fluid
- Chemical Protection: provides a constant chemical environment; the pH of the CSF is important in the control of breathing; CSF composition is important for regulating cerebral blood flow
- Circulation for the exchange of nutrients and waste products between the blood and nervous tissue
Choroid Plexus
Where the CSF is formed
Special capillary networks in certain palces in the ventricular walls
Ependymal cells (glial cells of the CNS:barriers between brain tissue of fluid sacs (CSF))
Fluid from plasma passes through the ependymal cells
Cells have ion pumps that modify CSF and regulate and maintain the blood-brain barrier
Protect the brain from harmful substances in the blood
Blood-brain barrier
Penetration of molecules from the blood is regulated by:
1. Tight junctions between capillary cells. They prevent molecules from going in between the gaps and cells
2. Thick basal lamina (connective tissue layer)
3. Astrocytes (glial cells of the CNS that help anchor neurons to nearby blood capillaries) pressed against capillaries
The barrier is a selective membrane
1. Most charged ions do not pass easily
2. Proteins and most antibiotics do not pass at all
3. Some substances, particularly if lipid-soluable, pass easily from blood to the brain (water, glucose, O2, CO2, alcohol, caffeine, nicotine, heroin, most anesthetics)
Blood Brain Barrier Cont.
Permeability is variable depneding on the site
- choroid plexus: CSF production
- vomiting center in the brain: monitors the blood for toxic molecules and poison
- Hypothalamus: has no blood brain barrier; monitors blood compositition for water balance, temperature, pH, osmolarity and many other homeostatic metabolic functions
Parts of the brain with no effective blood-brain barrier
Hypothalamus
Choroid Plexus
Vomiting Center (on medulla oblongata)
Concussion
A blow to the head
The skull stops but the brain keeps moving
Brain bounces off the inside of the skull
Possibly, there is no visible external damage
A variety of cognitive problems follow
Contusion
Breaks in small vessels, some bleeding, visible bruising
Effect depends on the location
Laceration
Tearing of the brain
Major traumas such as knife and gunshot wounds
Epidural or subdural or subarachnoid hemorrhage
bleeding from ruptured vessels into that space
person is normal immediately after the injury, but deteriorates as the bleeding continues
hemorrhage increases intracranial pressure
effects vary with the location of the hematoma
Surgical intervention: drill holes (Izzy on Grey’s Anatomy during ferry accident), remove clots, install drainaige tubes
Stroke
Cerebrovascula Accident (CVA)
Ischemia anemia caused by reduced or blocked blood flow
hemorrhages nad blood clots increase intracranial pressure
brain tissue dies (infart)
risk factors: high bp, high cholesterol, heart disease, narrowed carotoid arteries, diabetes, smoking, obesity, excessive alcohol intake
third leading cause of death in the US (wonder why….hello)
Transient Ischemic Attack (TIA/ministroke)
type of cerebrovascular accident
may last minutes
flow is reduced and brain tissue suffers temporarily
blood flow is re-established
Alzheimer’s disease
Degenerative brain disease
Widespread cognitive deficits: (short term) memory loss, shortened attention span and disorientation, loss of language skills
Death from secondary causes; difficulty responding to difficult events. Ex: fire in your house
Diagnosis is difficult since there is no definitive test except during autopsy
Significant loss of neurons in specific regions
Abnormal proteins are deposited in the brain tissue
Tangled nerve masses
Generally, the damage is limited to the cerebral cortex
Brain is aware of what is going on, but doesn’t know how to deal with it
Parkinson’s Disease
Degenerative brain disease
progressive disorder of the CNS which typically affects victims at age 60 or so
characterized by degeneration of dopamine-releasing neurons, tremor (shaking), and rigidity (continues contractions)
Motor performance impaired by bradykinesia (slow motion) and hypokinesia (reduced range of motion)
Treatments try to increase dopamine and decrease ACh with theraputic drugs or by experimental implantation of fetal brain cells
Cerebral Palsy
Degenerative Brain Disease
Damage to the motor areas of brain during fetal life, at brith, or during infancy, and usually transient 02 deprivation
Poor control and coordination of voluntary muscle activities but usually little impact on intellect
Irreversible, but not progressive
Thinking is fine, but communication is limited to victims often seem mentally retarded
Anatomy and Protection of the Spinal Cord
Located within the vertebral column
Passes through the vertebral foramina
Spinal meninges (dura mater, arachnoid, pia mater) cover spinal cord and nerves
Epidural space between the dura mater and wall of the verterbral column (where epidural is administered during childbirth)
Nerves exit through interverterbal foramina
CSF is protection mechanism
External Spinal Cord Anatomy
From formen magnum to second lumbar vertebra (L2)
About 2cm wide and 42-45 cm long
Ends in the conus medullaris between L1 and L2
Cervical enlargement and lumbar enlargement
Cervical enlargement
enlarged area of the spinal cord for nerves for upper extremities to control arms
Lumbar enlargement
enlarged area of spinal cord for nerves for lower extremities to control legs
Filum terminale
pia mater
extends from the conus to attach the spinal cord to the coccyx
cauda equina
“horse’s tail” at the end of the cord are the last few pairs of spinal nerves that exit the vertebral column below the level of their exit from the spinal cord
Cross_sectional anatomy of the Spinal Cord
H shaped gray matter surrounded by butterfly white matter
Anterior median fissure
Posterior medial sulcus
Gray commisure
Central Canal: small space in the middle of gray commissure; extends length of spinal cord; at superior end continues with the 4th ventricle; contains CSF
Gray Commissure
forms the cross bar of the ‘H’
Link where info goes from one side of CNS to the other
Ex: corpus callosum
Anterior white commissure
Anterior to the gray commissure
Link where info goes from one side of the CNS to the other
Anterior (ventral) gray horns
In gray matter
visceral and somatic motor neurons
neurons, cell bodies, soma
Posterior (dorsal) gray horns
gray matter
fibers from somatic and visceral sensory neurons (cell bodies = soma)
Lateral Gray Horns
gray matter
between anterior and posterior horns
present only in thoracic, upper lumbar, and sacral segments
Ventral Root
gray matter
Efferent (motor) nerves(cell axons) to skeletal muscles and to the visceral organs (effectors)
Dorsal Root
gray matter
Afferent (sensory) nerves (cell axons) from skin, skeletal muscles, connecive tissues, visceral organs
Unipolar (1 process)
Visceral Motor (VM)
organs
smooth and cardiac muscle
involuntary movement
peristalsis (digestions)
Somatic Motor Neurons (SM)
control skeletal muscle
voluntary movement
White Matter of the Spinal Cord
Conduction Tracts (collections of myelinated axons going from one place to another) in the spinal cord
Named by where each is coming from and where each is going
More superficial areas
Fasciculi cuneatus and gracilis: fine touch and pressure
Lateral and anterior spinothalamic tracts: pain, temperature, deep pressure, and coarse touch
Two paths for similar functions
