The Central Nervous System

Central Nervous System

Brain and spinal cord
Control center for: thoughts, emotions, creativity, wisdom, memories, activities, and behaviors

Brain

What contains the cerebrum, diencephalon, brain stem, and cerebellum?
Cerebrum and cerebellum mostly white matter surrounded by gray matter
Stem has gray matter nuclei scattered within white matter

Spinal cord

What contains the medulla oblongata to superior edge of L2?
Gray matter surrounded by white matter
Centrally located H shape to gray matter

Ventricles

____ of the brain
Filled with cerebrospinal fluid
1 and 2. The paired C Shaped lateral ____
- separated by membranous septum pellucidum
3. Found in diencephalon
4. Found posterior to the pons

Protection

What function of CNS?
Bone (skull and vertebral column)
Membranes (meninges)
Watery cushion (cerebrospinal fluid)
Blood brain barrier (brain)

Skeletal protection

Brain is located in cranial cavity of skull
Spinal cord is located within vertebral canal of vertebral column

Meninges

3 connective tissue coverings that encircle brain and spinal cord
Cranial
Spinal
Superficial to deep (dura mater, arachnoid mater, and pia mater)

Dura mater layers

___ ____ of brain
Two layers
- inner fibrous layer (meningeal layer)
- outer fibrous layer (periosteal layer) fused to periosteum
- venous sinuses between 2 layers
Strongest menix

Dural venous sinuses

Dura mater of brain
Spaces within dura mater
Sinuses act as collection points for interstitial fluid and blood leaving brain
Return interstitial fluid and blood to internal jugular veins of neck

Dura folds

Dura mater of brain
Folded inner layer of dura mater
Extend into cranial cavity
Stabilize and support brain
Contain collecting veins (dural sinuses)
3 largest dural folds (falex cerebri, tentorium cerebelli, and falex cerebelli)

Dura mater

___ ____ of spinal cord
Epidural space
- space between dura mater and wall of vertebral canal (cushion of fat)
Dura mater tissue: dense irregular connective tissue

Arachnoid mater

The middle meninx, found in both the brain and spinal cord
It is separated from the dura mater by the subdural space
Beneath the _____ is a wide subarachnoid space filled with CSF and large blood vessels

Pia mater

Deep meninx composed of delicate connective tissue that clings tightly to the brain and spinal cord

Cerebrospinal fluid

Watery solution similar in composition to blood plasma
Forms a liquid cushion that gives buoyancy to the CNS organs
-prevents the brain from crushing under its own weight
-reduces weight by 97%
Protects the CNS from blows and other trauma
Nourishes the brain and carries chemical signals throughout it

Choroid plexuses

Clusters of capillaries that form tissue fluid filters, which hang from the roof of each ventricle
CSF produced in choroid plexuses
-specialized ependymal cells and capillaries (secrete CSF into ventricles, remove waste products from CSF, adjust composition of CSF)
-produces about 450-500mL of CSF/day

Blood brain barrier

Protective mechanism that helps maintain a stable environment for the brain
Blood borne substances are separated from neurons by continuous endothelium of capillary walls, relatively thick basal lamina, bulbous feet of astrocytes
Isolates CNS neural tissue from general circulation
Formed by network of tight junctions
-between endothelial cells of CNS capillaries
Lipid-soluable compounds (O2,CO2), steroids, and prostaglandins
-diffuse into interstitial fluid of brain and spinal cord
Astrocytes control BBB by releasing chemicals that control permeability of endothelium

d

Why is the BBB ineffective against alcohol?
a. alcohol is water-soluable
b. the BBB prevents only blood cells from reaching the brain
c. it isn't: alcohol cannot reach the brain
d. alcohol is lipid-soluble

Selective barrier

A function of BBB
Allows nutrients to move by facilitated diffusion
Allows any fat soluble substances to pass, including alcohol, nicotine, and anesthetics
Metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids, K+ denied

BBB functions

Including selective barrier
Stress increases the ability of chemicals to pass through the BBB
Absent in some areas ex: vomiting center and hypothalamus, where necessary to monitor chemical composition of blood, areas where hormones are released

Brain stem

Consists of midbrain, pons, and medulla oblongata
Similar in structure to spinal cord but contains nuclei embedded in whiter matter
Controls automatic behaviors necessary for survival
Provides the pathway for tracts between higher and lower brain centers
Associated with 10 of 12 pairs of cranial nerves

Midbrain

Located between the diencephalon and the pons
Conducts nerve impulses from cerebrum to spinal cord, medulla, and pons
-processes sight, sound, and associated reflexes (ex: startle)
-maintains consciousness

Pons

Bulging brainstem region between the midbrain and the medulla oblongata
Connect higher brain centers and the spinal cord
Relay impulses between the motor cortex and the cerebellum
Helps maintain normal rhythm of breathing by fine tuning breathing rhythms generated in medulla oblongata

Medulla oblongata

Inferior part of brain stem
Contains all sensory and motor tracts connecting brain and spinal cord
-90% of axons in left pass to right & right to left
Cardiovascular and respiratory rhythmicity areas
-regulate heartbeat, blood pressure, breathing
Coordinates complex autonomic reflexes
-Vomiting, hiccupping, swallowing, coughing, and sneezing

Reticular activating system

Located in brain stem
Helps maintain homeostasis for many visceral functions
Sends impulses to cerebral cortex to keep it conscious and alert
Filters out repetitive, familiar, or weak stimuli (~99% of all stimuli)

Cerebellum

Located dorsal to the pons and medulla
Protrudes under the occipital lobes of the cerebrum
Makes up 11% of the brain's mass
Provides precise timing and appropriate patterns of skeletal muscle contraction
Cerebellar activity occurs subconsciously

Cerebellum functions

Receives impulses from the cerebral cortex of the intent of initiate voluntary muscle contraction
Signals from proprioceptors and visual and equilibrium pathways continuously "inform" the ____ of the body's position and momentum
____ 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
Recognizes and predicts sequences of events during complex movements
May compare actual with expected output and adjust accordingly
Adjust muscles for posture

Diencephalon

Central core of the forebrain
Consists of thalamus, hypothalamus, and epithalamus
Encloses the third ventricle

Thalamus

Paired, egg shaped masses that form the superolateral walls of the third ventricle
Main thalamic function is to act as relay station for information coming into cortex
Sorts, edits, and relays ascending input such as: impulses for sensory integration, impulses from hypothalamus for regulating emotion and visceral function, impulses from cerebellum and basal nuclei to help direct motor cortices
Mediates sensation, motor activities, cortical arousal, learning, and memory

Epithalamus

Most posterior portion of the diencephalon; forms roof of the third ventricle
Pineal gland- extends from the posterior border and secretes melatonin (a hormone involved with sleep regulation, sleep-awake cycles, and mood)
Regulation of motor pathways and emotions

Hypothalamus

Located inferior to the thalamus
Mammillary bodies
-small, paired nuclei bulging anteriorly from the ____
-relay station for olfactory pathways
-control reflex eating movements
Infundibulum- stalk of the ___; connects to the pituitary gland
Main visceral control center of the body

Hypothalamus functions

Provides subconscious control of skeletal muscle
Controls autonomic function
Coordinates activities of nervous and endocrine systems
Secrete hormones- Antidiuretic hormone (ADH) and Oxytocin
Produces emotions and behavioral drives (hunger and thirst)
Coordinates voluntary and autonomic functions
Regulates body temperature
Controls circadian rhythms (day-night cycles)

Limbic system

Emotional part of brain
Structures on medial aspects of cerebral hemispheres and diencephalon
Fornix: fiber tract that links limbic system regions
Includes parts of diencephalon and some cerebral structures that encircle brain stem
Amygdaloid body- recognizes angry or fearful facial expressions, assesses danger, and elicits fear response

LS emotion and cognition

Cingulate gyrus- role in expressing emotions vias gestures, and resolves mental conflict
Puts emotional responses to odors
Most output relayed via hypothalamus
Limbic system interacts with prefrontal lobes
Hippocampus and amygdaloid body- play a role in memory

Cerebrum

Form the superior part of the brain and make up 83% of its mass and divided into two hemispheres- right and left
Have 3 basic regions: cortex, white matter, and basal nuclei
Five lobes: frontal, parietal, temporal, occipital, insula
Contains ridges (gyri (plural) gyrus (singular)) and shallow grooves (sulci (plural) sulcus (singular))
-to increase surface area of gray matter
Contain deep grooves called fissures
Cerebral hemispheres are separated by the longitudinal fissure

Cerebral white matter

Consists of deep myelinated fibers and their tracts
It is responsible for communication between: the cerebral cortex and lower CNS center, and areas of cerebrum

Association fibers

What fiber?
Connections within one hemisphere
Cerebral white matter

Commissural fibers

What fiber?
Bands of fibers connecting two hemispheres
Cerebral white matter

Projection fibers

What fiber?
Connect cerebrum with lower areas
Cerebral white matter

Basal nuclei

Mass of cell bodies
Gray matter in the white matter
Functions: direct subconscious activities
-subconscious control of skeletal muscle tone
-coordination of learned movement patterns (walking, lifting)

Cerebral cortex

Thin (2-4mm) superficial layer of gray matter
Accounts for 40% of the mass in the brain
It enables sensation, communication, memory, understanding and voluntary movements
Each hemisphere acts contralaterally (controls opposite side of the body)
Hemispheres are not equal in function
No functional area acts alone; conscious behavior involves the entire cortex
3 types of functional areas: motor, sensory, and association

Motor areas

What area?
Control voluntary movement
Cerebral cortex

Sensory areas

What area?
Conscious awareness of sensation
Cerebral cortex

Association areas

What area?
Integrate diverse information
Largest area
Cerebral cortex

Primary motor cortex

Located in the precentral gyrus
Allows conscious control of precise, skilled, voluntary movements

Premotor cortex

Somatic motor association area
Located anterior to the precentral gyrus
Helps plan movements, staging area for skilled motor activities
Controls learned, repetitious, or patterned motor skills
Coordinates simultaneous or sequential actions

Broca's area

Located anterior to the inferior region of the premotor area
Present in one hemisphere (usually the left)
Regulates patterns of breathing and vocalization needed for normal speech
"My boca (mouth) is broken so I can't speak"

Frontal eye field

Located anterior to the premotor cortex and superior to Broca's area
Controls learned eye movements

Sensory areas

Areas of cortex concerned with conscious awareness of sensation
Occur in parietal, insular, temporal, and occipital lobes
8 main areas: primary somatosensory cortex, somatosensory association cortex, visual areas, auditory areas, vestibular cortex, olfactory cortex, gustatory cortex, and visceral sensory area

Primary somatosensory cortex

Located in the postcentral gyrus
Receives general sensory information from skin, and proprioceptors of skeletal muscle, joints, and tendons
-exhibits spatial discrimination identification of body region being stimulated

Somatosensory association cortex

Located posterior to the primary somatosensory cortex
Integrates sensory information from primary somatosensory cortex
Forms comprehensive understanding of the stimulus
Determines size, texture, and relationship of parts

Visual areas

Primary visual cortex
-on the posterior tip of the occipital lobe
-receives visual information from the retinas
Visual association area
-surrounds the primary visual cortex
-interprets visual stimuli (ex. color, form, and movement)

Auditory areas

Primary auditory cortex
-located in the temporal lobe
-receives information related to pitch, rhythm, and loudness
Auditory association area
-located posterior to the primary auditory cortex
-stores memories of sounds and permits perception of sounds
-part of General Interpretive or Wernicke's area

Olfactory cortex

Medial aspect of temporal lobes
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
ex: upset stomach or full bladder

Vestibular sensory area

Posterior part of the insula and adjacent parietal cortex
Responsible for conscious awareness of balance (position of the head in space)

Wernicke's area

AKA general interpretive area
Present in only one hemisphere (left)
Language comprehension
Receives information from all sensory association areas
Coordinates access to complex visual and auditory memories

Multimodal association areas

Receives 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 3 parts- anterior association area, posterior association area, and limbic association area

Prefrontal cortex

AKA anterior association area
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
Closely linked to the limbic system (emotional part of brain)

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)

Hemispheric lateralization

Each hemisphere has abilities not shared with its partner
Cerebral dominance- Designates the hemisphere dominant for language
Usually results in right-handedness
Left hemisphere- language, math, and logic
Right hemisphere- visual-spatial skills, emotion, and artistic skills, analysis of sensations
Controls voluntary actions that depend on sensory feedback

Language areas

Located in the area surrounding the left lateral sulcus
Major parts and functions
-Wernicke's area
-Broca's area
-Lateral prefrontal cortex- language comprehension and word analysis
-Lateral and ventral temporal lobe- coordinate auditory and visual aspects of language

Spinal cord

Runs through the vertebral column from the foramen magnum to superior L2
-about 18in (45cm) long
-1/2in (14mm) wide
-stops lengthening around age 4, but the vertebral column still grows
-4 regions (cervical, thoracic, lumbar, sacral)
-grooves divide spinal cord into left and right (posterior median sulcus- posterior side) (anterior median fissure- deeper, anterior groove)

Conus medullaris

Terminal portion of the spinal cord
Spinal cord

Filum terminale

Fibrous tissue that anchors the spinal cord to the coccyx
Spinal cord

Spinal nerves

31 pairs attach to the cord by paired roots
Spinal cord
Part of the PNS
Formed by fusion of posterior and anterior roots
Posterior roots- sensory input to cord
Posterior root ganglia- cell bodies of sensory neurons
Anterior roots- bundle of motor neuron axons that exit the spinal cord

Cauda equina

Collection of spinal nerves at the inferior end of the vertebral canal
Spinal cord

Gray matter

Consists of cell bodies, unmyelinated processes, and neuroglia
Gray commissure- connects masses of gray matter; encloses central canal
Posterior horns- sensory input
Anterior horns- somatic motor output
Lateral horns- (only in thoracic and superior lumbar regions) sympathetic motor neurons

White matter

Divided into 3 white columns (funiculi) on each side
-posterior white column
-lateral white column
-anterior white column
Each spinal tract is composed of axons with similar destinations and functions
Myelinated and nonmyelinated nerve fibers allow communicated between parts of spinal cord, and spinal cord and brain
Run in 3 directions
-ascending- up to higher centers (sensory inputs)
-descending- from brain to cord or lower cord levels (motor outputs)
-transverse- from one side to other (commissural fibers)

Concussion

Temporary alteration in function
Traumatic brain injuries

Contusion

Permanent damage
Traumatic brain injuries

Hemorrhage

Subdural or subarachnoid
May force brain stem through foramen magnum, resulting in death
Traumatic brain injuries

Cerebral dema

Swelling of brain associated with traumatic brain injury
Traumatic brain injuries

Ischemia

Tissue deprived of blood supply, leading to death of brain tissue
-can be caused by blockage of cerebral artery by blood clot
-glutamate acts as excitotoxin, worsening condition
Cerebrovascular accidents AKA strokes

Hemiplegia

Paralysis on one side or sensory and speech deficits may result
Cerebrovascular accidents AKA strokes

Transient ischemic attacks

Temporary episodes of reversible cerebral ischemia
Cerebrovascular accidents AKA strokes

Treatments

For Ischemic strokes focus on busting the clot
-tissue plasminogen activator (TPA), thrombectomy
For Hemorrhagic strokes is to stop bleeding

Alzheimer's disease

A progressive degenerative disease of brain that results in dementia
-memory loss, short attention span, disorientation, eventual language loss, irritable, moody, confused, hallucinations
-plaques of beta-amyloid peptide form in brain
-neurofibrillary tangles inside neurons kill them
-brain shrinks

Parkinson's disease

Degeneration of dopamine-releasing neurons of substantial nigra
Basal nuclei deprived of dopamine become overactive -> tremors at rest
Cause unknown, but theories include mitochondrial abnormalities or protein degradation pathways
-treatment includes L-dopa (dopamine precursor), deep brain stimulation, gene therapy
Research into stem cell transplants is promising

Huntington's disease

Fatal hereditary disorder
Caused by accumulation of protein huntingtin
-leads to degeneration of basal nuclei and cerebral cortex
Initial symptoms wild, jerky, flapping, movements
-later marked mental deterioration
Usually fatal within 15 years of onset

Poliomyelitis

Destruction of the anterior horn motor neurons by the poliovirus
Early symptoms- fever, headache, muscle pain, weakness, and loss of somatic reflexes
Vaccines are available and can prevent infection

Lou Gehrig's disease

AKA Amyotrophic lateral sclerosis (ALS)
Neuromuscular condition involving destruction of anterior horn motor neurons and fibers
Symptoms- loss of the ability to speak, swallow, and breathe
Death 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