PPT Notes Chapter 12 Flashcards
Central Nervous System (CNS)
CNS consists of the brain and spinal cord
Cephalization
Evolutionary development of the rostral (anterior) portion of the CNS
Increased number of neurons in the head
Highest level is reached in the human brain
Background: Embryonic Development
Neural groove fuses dorsally to form the neural tube
Neural tube gives rise to the brain and spinal cord
Anterior end of the neural tube gives rise to three primary brain vesicles
Prosencephalon—forebrain
Mesencephalon—midbrain
Rhombencephalon—hindbrain
Background: Effect of Space Restriction on Brain Development
Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem
Cerebral hemispheres grow posteriorly and laterally
Cerebral hemisphere surfaces crease and fold into convolutions
Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem
Cerebral hemispheres grow posteriorly and laterally
Cerebral hemisphere surfaces crease and fold into convolutions
Regions and Organization of the CNS
Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum Spinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tracts
REMEMBER! Gray matter interprets, white matter transmits!!
Brain
Similar pattern with additional areas of gray matter
Nuclei in cerebellum and cerebrum
Cortex of cerebellum and cerebrum
Ventricles of the Brain
Connected to one another and to the central canal of the spinal cord
Lined by ependymal cells
Contain cerebrospinal fluid
Two C-shaped lateral ventricles in the cerebral hemispheres
Third ventricle in the diencephalon
Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tube
Cerebral Hemispheres: Important!!
Surface markings Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) Five lobes Frontal Parietal Temporal Occipital Insula Surface markings Central sulcus Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe Longitudinal fissure Separates the two hemispheres Transverse cerebral fissure Separates the cerebrum and the cerebellum
Cerebral Cortex
Thin (2–4 mm) superficial layer of gray matter
40% of the mass of the brain
Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding
Each hemisphere connects to contralateral side of the body
There is lateralization of cortical function in the hemispheres [right brain/left brain]
Functional Areas of the Cerebral Cortex
The three types of functional areas are:
Motor areas—control voluntary movement
Sensory areas—conscious awareness of sensation
Association areas—integrate diverse information
Conscious behavior involves the entire cortex
Motor Areas
Primary (somatic) motor cortex
Premotor cortex
Broca’s area
Frontal eye field
Primary Motor Cortex
Large pyramidal cells of the precentral gyri
Long axons pyramidal (corticospinal) tracts
Allows conscious control of precise, skilled, voluntary movements
Motor homunculi: upside-down caricatures representing the motor innervation of body regions
Premotor Cortex
Anterior to the precentral gyrus
Controls learned, repetitious, or patterned motor skills
Coordinates simultaneous or sequential actions
Involved in the planning of movements that depend on sensory feedback
Broca’s Area
Anterior to the inferior region of the premotor area
Present in one hemisphere (usually the left)
A motor speech area that directs muscles of the tongue
Is active as one prepares to speak
Frontal Eye Field
Anterior to the premotor cortex and superior to Broca’s area
Controls voluntary eye movements
Sensory Areas
Primary somatosensory cortex
Somatosensory association cortex
Visual areas
Auditory areas
Primary Somatosensory Cortex
In the postcentral gyri
Receives sensory information from the skin, skeletal muscles, and joints
Capable of spatial discrimination: identification of body region being stimulated
Somatosensory Association Cortex
Posterior to the primary somatosensory cortex
Integrates sensory input from primary somatosensory cortex
Determines size, texture, and relationship of parts of objects being felt
Visual Areas
Primary visual (striate) cortex
Extreme posterior tip of the occipital lobe
Receives visual information from the retinas
Visual association area
Surrounds the primary visual cortex
Uses past visual experiences to interpret visual stimuli (e.g., color, form, and movement)
Complex processing involves entire posterior half of the hemispheres
Auditory Areas
Primary auditory cortex
Superior margin of the temporal lobes
Interprets information from inner ear as pitch, loudness, and location
Auditory association area
Located posterior to the primary auditory cortex
Stores memories of sounds and permits perception of sounds
OIfactory Cortex
Medial aspect of temporal lobes (in piriform lobes)
Part of the primitive rhinencephalon, along with the olfactory bulbs and tracts
(Remainder of the rhinencephalon in humans is part of the limbic system)
Region of conscious awareness of odors
Gustatory Cortex
In the insula
Involved in the perception of taste
Visceral Sensory Area
Posterior to gustatory cortex
Conscious perception of visceral sensations, e.g., upset stomach or full bladder
Vestibular Cortex
Posterior part of the insula and adjacent parietal cortex
Responsible for conscious awareness of balance (position of the head in space)
Multimodal Association Areas
Receive inputs from multiple sensory areas
Send outputs to multiple areas, including the premotor cortex
Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take
There are several multimodal association areas.
Limbic Association Area
Part of the limbic system
Provides emotional impact that helps establish memories
Lateralization of Cortical Function
Lateralization
Division of labor between hemispheres
Cerebral dominance
Designates the hemisphere dominant for language (left hemisphere in 90% of people)
Left hemisphere
Controls language, math, and logic
Right hemisphere
Insight, visual-spatial skills, intuition, and artistic skills
Left and right hemispheres communicate via fiber tracts in the cerebral white matter
Cerebral White Matter
Myelinated fibers and their tracts
Responsible for communication
Commissures (in corpus callosum)—connect gray matter of the two hemispheres
Association fibers—connect different parts of the same hemisphere
Projection fibers—(corona radiata) connect the hemispheres with lower brain or spinal cord
Basal Nuclei (Ganglia)
Subcortical nuclei [islands within white matter]
Consists of the corpus striatum
Caudate nucleus
Lentiform nucleus (putamen + globus pallidus)
Functionally associated with the subthalamic nuclei (diencephalon) and the substantia nigra (midbrain)
Functions of Basal Nuclei
Though somewhat elusive, the following are thought to be functions of basal nuclei
Influence muscular control
Help regulate attention and cognition
Regulate intensity of slow or stereotyped movements
Inhibit antagonistic and unnecessary movements
Diencephalon
Three paired structures Thalamus Hypothalamus Epithalamus Encloses the third ventricle
Thalamus
80% of diencephalon
Superolateral walls of the third ventricle
Connected by the interthalamic adhesion (intermediate mass)
Contains several nuclei, named for their location
Nuclei project and receive fibers from the cerebral cortex
Thalamic Function
Gateway to the cerebral cortex
Sorts, edits, and relays information
Afferent impulses from all senses and all parts of the body
Impulses from the hypothalamus for regulation of emotion and visceral function
Impulses from the cerebellum and basal nuclei to help direct the motor cortices
Mediates sensation, motor activities, cortical arousal, learning, and memory
Hypothalamus
Forms the inferolateral walls of the third ventricle
Contains many nuclei
Example: mammillary bodies
Paired anterior nuclei
Olfactory relay stations
Infundibulum—stalk that connects to the pituitary gland
Hypothalamic Function
Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility)
Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives
Regulates body temperature, food intake, water balance, and thirst
Regulates sleep and the sleep cycle
Controls release of hormones by the anterior pituitary
Produces posterior pituitary hormones
Epithalamus
Most dorsal portion of the diencephalon; forms roof of the third ventricle
Pineal gland—extends from the posterior border and secretes melatonin
Melatonin—helps regulate sleep-wake cycles
Brain Stem
Three regions
Midbrain
Pons
Medulla oblongata
Similar structure to spinal cord but contains embedded nuclei
Controls automatic behaviors necessary for survival
Contains fiber tracts connecting higher and lower neural centers
Associated with 10 of the 12 pairs of cranial nerves
Midbrain
Located between the diencephalon and the pons
Cerebral peduncles
Contain pyramidal motor tracts
Cerebral aqueduct
Channel between third and fourth ventricles
Pons
Forms part of the anterior wall of the fourth ventricle
Fibers of the pons
Connect higher brain centers and the spinal cord
Relay impulses between the motor cortex and the cerebellum
Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)
Some nuclei of the reticular formation
Nuclei that help maintain normal rhythm of breathing
Medulla Oblongata
Joins spinal cord at foramen magnum
Forms part of the ventral wall of the fourth ventricle
Contains a choroid plexus of the fourth ventricle
Pyramids—two ventral longitudinal ridges formed by pyramidal fiber tracts
Functions to relay sensory information from muscles and joints to cerebellum
Cranial nerves VIII, X, and XII are associated with the medulla
mediates responses that maintain equilibrium
Autonomic reflex centers
Cardiovascular center
Cardiac center adjusts force and rate of heart contraction
Vasomotor center adjusts blood vessel diameter for blood pressure regulation
Respiratory centers
Generate respiratory rhythm
Control rate and depth of breathing, with pontine centers
Additional centers regulate
Vomiting
Hiccuping
Swallowing
Coughing
Sneezing
The Cerebellum
11% of brain mass
Dorsal to the pons and medulla
Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction
Anatomy of the Cerebellum
Two hemispheres connected by vermis
Each hemisphere has three lobes
Anterior, posterior, and flocculonodular
Folia—transversely oriented gyri
Arbor vitae—distinctive treelike pattern of the cerebellar white matter
Cerebellar Peduncles
All fibers in the cerebellum are ipsilateral
Three paired fiber tracts connect the cerebellum to the brain stem
Superior peduncles connect the cerebellum to the midbrain
Middle peduncles connect the pons to the cerebellum
Inferior peduncles connect the medulla to the cerebellum
Cerebellar Processing for Motor Activity
Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction
Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum
Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction
A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei
Cognitive Function of the Cerebellum
Recognizes and predicts sequences of events during complex movements
Plays a role in nonmotor functions such as word association and puzzle solving
Protection of the Brain
Bone (skull)
Membranes (meninges)
Watery cushion (cerebrospinal fluid)
Blood-brain barrier
Meninges
Cover and protect the CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in the skull Three layers Dura mater Arachnoid mater Pia mater
Dura Mater
Strongest meninx
Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses
Arachnoid Mater
Middle layer with weblike extensions
Separated from the dura mater by the subdural space
Subarachnoid space contains CSF and blood vessels
Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption
Pia Mater
Layer of delicate vascularized connective tissue that clings tightly to the brain
Cerebrospinal Fluid (CSF)
Composition
Watery solution
Less protein and different ion concentrations than plasma
Constant volume
Functions
Gives buoyancy to the CNS organs
Protects the CNS from blows and other trauma
Nourishes the brain and carries chemical signals
Choroid Plexuses
Produce CSF at a constant rate
Hang from the roof of each ventricle
Clusters of capillaries enclosed by pia mater and a layer of ependymal cells
Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes
Blood-Brain Barrier
Helps maintain a stable environment for the brain
Separates neurons from some bloodborne substances
Composition
Continuous endothelium of capillary walls
Basal lamina
Feet of astrocytes
Provide signal to endothelium for the formation of tight junctions
Blood-Brain Barrier: Functions
Selective barrier
Allows nutrients to move by facilitated diffusion
Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics
Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood
Homeostatic Imbalances of the Brain
Traumatic brain injuries
Concussion—temporary alteration in function
Contusion—permanent damage
Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death
Cerebral edema—swelling of the brain associated with traumatic head injury
Cerebrovascular accidents (CVAs)(strokes)
Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot
Typically leads to hemiplegia, or sensory and speed deficits
Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia
Tissue plasminogen activator (TPA) is the only approved treatment for stroke
Degenerative brain disorders
Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia
Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra
Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex
Spinal Cord
Location Begins at the foramen magnum Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal
Spinal Cord: Protection
Bone, meninges, and CSF
Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater
CSF in subarachnoid space
Cross-Sectional Anatomy
Two lengthwise grooves divide cord into right and left halves
Ventral (anterior) median fissure
Dorsal (posterior) median sulcus
Gray commissure—connects masses of gray matter; encloses central canal
Gray Matter
Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons
White Matter
Consists mostly of ascending (sensory) and descending (motor) tracts Transverse tracts (commissural fibers) cross from one side to the other Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions
Pathway Generalizations
Pathways decussate (cross over)
Most consist of two or three neurons (a relay)
Pathways are paired symmetrically (one on each side of the spinal cord or brain)
Spinal Cord Trauma
Functional losses
Parasthesias
Sensory loss
Paralysis
Loss of motor function
Flaccid paralysis—severe damage to the ventral root or ventral horn cells
Impulses do not reach muscles; there is no voluntary or involuntary control of muscles
Muscles atrophy
Spastic paralysis—damage to upper motor neurons of the primary motor cortex
Spinal neurons remain intact; muscles are stimulated by reflex activity
No voluntary control of muscles
Transection
Cross sectioning of the spinal cord at any level
Results in total motor and sensory loss in regions inferior to the cut
Paraplegia—transection between T1 and L1
Quadriplegia—transection in the cervical region
Amyotrophic Lateral Sclerosis (ALS)
Also called Lou Gehrig’s disease
Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract
Symptoms—loss of the ability to speak, swallow, and breathe
Death typically occurs within five years
Linked to glutamate excitotoxicity, attack by the immune system, or both
