HAN 200 - Chapter 12 (CNS)

Regions and organization of CNS

• Spinal Cord

• Adult brain regions:

1. Cerebral hemispheres - cortex, cerebral white matter, basal ganglia)

2. Diencephalon - thalamus, hypothalamus, epithalamus

3. Brain stem - midbrain, pons, medulla

4. Cerebellum

Cerebral white matter

• Myelinated fibers and their tracts

• Responsible for communication:

  • Commissures

  • Association fibers

  • Projection fibers

Ventricles of brains

• Connected to one another and to central canal of spinal cord

• Lined by ependymal cells

• Contain cerebrospinal fluid

  • 2 C-shaped lateral ventricles

  • 3rd and 4th ventricle

Hydrocephalus

Cerebrospinal fluid builds up in ventricles deep in brain, causing head to expand.

Cerebral hemispheres

• Surface markings: ridges (gyri), shallow grooves (sulci), deep grooves (fissures)

• 5 lobes per hemisphere

  • Frontal

  • Parietal

  • Temporal

  • Occipital

  • Insula

Cerebral cortex

Site of conscious mind:

• Awareness

• Sensory perception

• Voluntary motor initiation

• Communication

• Memory storage

• Understanding

Function areas of cerebral cortex

• Motor areas - control voluntary movement

• Sensory areas - conscious awareness of sensation

• Association areas - integrate diverse information

Frontal lobe: motor areas

• Primary (somatic) motor cortex

  • control of skeletal muscles

  • pyramidal cells → pyramidal tracts

• Premotor cortex

  • plan and coordinate movements of several groups into complex tasks

• Broca’s area

  • motor speech area (left hemisphere)

Sensory areas

• Primary somatosensory cortex (parietal lobe) - touch

• Association areas - understanding of senses

• Visual areas

• Auditory areas

• Olfactory area - smell

• Visceral sensory area - bladder

• Vestibular cortex - equilibrium

Occipital lobe: visual areas

• Primary visual (striate) cortex: posterior tip of occipital lobe

• Visual association area​

Primary visual cortex

• Extreme posterior tip of occipital lobe

• Receives visual information from retinas

Visual association area

• Uses past visual experiences to interpret visual stimuli (color, form, movement)

• Recognizes faces and familiar objects

Temporal lobe: auditory areas

• Primary auditory cortex : temporal lobe

• Auditory association area

Primary auditory cortex

• Temporal lobes

• Interprets information from inner ear as pitch, loudness, location

Auditory association area

Stores memories of sounds and permits perception of sounds (car brakes, voices)

Prefrontal cortex

• Most complicated cortical region

• Involved with intellect, cognition, recall, personality

• Contains working memory needed for judgment, reasoning, persistence, conscience

• Develops slowly in children, depends on feedback from environment

• Lesions in this area can cause personality changes

Lateralization of cortical function

Division of labor between hemispheres, left and right hemispheres communicate via fiber tracts in cerebral white matter

Left hemisphere

Controls language, math, logic

Right hemisphere

Insight, visual-spatial skills, intuition, artistic skills

Commissures

Connect the two hemispheres (corpus callosum)

Association fibers

Connect different parts of the same hemisphere

Projection fibers

Connect the hemispheres with lower brain or spinal cord

Basal nuclei (ganglia)

Subcortical nuclei

Functions of basal nuclei

• Help regulate attention and cognition

• Regulate intensity of slow or stereotyped movements

• Inhibit unnecessary movements

Diencephalon

3 paired structures, these structures enclose 3rd ventricle:

• Thalamus - relay station

• Hypothalamus - homeostasis

• Epithalamus - melatonin

Thalamic function

Thalamus means “Inner room”

• Gateway to cerebral cortex

  • relay station

• Sorts, edits, relays information

  • afferent impulses from all sense

Hypothalamic function

• Connected to pituitary gland

• Autonomic control center

  • blood pressure, rate and force of heartbeat, digestive tract mobility

• Emotional response (limbic system)

  • involved in perception of pleasure, fear, rage, and in biological rhythms and drives

• Regulate body temp, food intake, water balance, thirst

What occurs in a fearful person?

Pounding heart, high blood pressure, sweating, dry mouth

Epithalamus

• Part of diencephalon

• Pineal gland - secretes melatonin

  • Melatonin - helps regulate sleep-wake cycles

3 regions of brain stem

• Midbrain - substantia nigra (Parkinson’s disease)

• Pons - “bridge”

• Medulla oblongata - connects to spinal cord

Substantia nigra

• Functionally linked to basal ganglia (nuclei)

• Produce neurotransmitter dopamine

• Degeneration of dopamine releasing neurons causes Parkinson’s disease

Medulla oblongata

• Autonomic reflex centers - unconscious activity

• Cardiovascular center

  • Cardiac center adjusts force and rate of heart contraction

  • Vasomotor center adjusts blood vessel diameter

• Respiratory centers

  • Generate respiratory rhythm

  • Control rate and depth of breathing

Damage to brain stem, especially medulla oblongata results in…

Death

Cerebellum

• Dorsal to brainstem, inferior to occipital lobe

• Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction

• Tests: balance, coordination, finger-nose

• Involved in learning motor tasks (sports, music)

Functional brain systems

Networks of neurons that work together and span wide areas of brain.

• Limbic system - emotional brain

• Reticular formation - wakefulness

Limbic system

Emotional or affective brain, limbic system and olfactory area related, odors recall memories

• Hippocampus (stress)

• Amygdala

• Cingulate gyrus

• Hypothalamus (diencephalon)

Amygdala

“Body’s alarm system”. Recognizes angry or fearful facial expressions, assesses danger, elicits fear response.

Cingulate gyrus

Plays role in expressing emotions via gestures, and resolves mental conflict

Limbic system: emotion and cognition

Limbic system (emotional brain) interacts with prefrontal lobes (thinking brain), therefore:

• Emotions sometimes override logic and conversely why reason can stop us from expressing emotions

• Hippocampus and amygdala play a role in memory

Reticular formation

Reticular activating system

• Sends impulses to cerebral cortex to keep it conscious and alert

• Filters out repetitive and weak stimuli (~99% all stimuli, ex: wrist watch), allows important sensations in

• RAS inhibited by sleep centers (depressed by EtOH and tranquilizers)

• Severe injury results in permanent unconsciousness (coma)

Sleep

• State of partial unconsciousness from which a person can be aroused by stimulation

• Environmental monitoring continues (can be aroused - baby cry; sleepwalkers avoid obstacles)

• Two major types of sleep:

  • Nonrapid eye movement (NREM)

  • Rapid eye movement (REM)

Importance of sleep

• Slow-wave sleep (NREM stages 3 and 4) presumed to be restorative stage

• Deprivation of REM sleep = moody and depressed

• Sleep deprivation linked to increase risk of heart disease, DM, kidney disease, stroke and HBP

• REM sleep may be reverse learning process where superfluous information is purged from brain

• Daily sleep requirements decline with age

Language

Language implementation system:

• Basal nuclei

• Broca’s area (frontal lobe): expressive speech

• Wernicke’s area (temporal lobe): understanding speech

• Corresponding areas on right side are involved with nonverbal language components