nervous system · brain and cranial nerves. central nervous system (cns) - consists of the brain...

Nervous SystemBrain and Cranial Nerves

Central Nervous System (CNS)- Consists of the brain and spinal cord

The Brain

- Protected by the cranium (skull)- Made of 100 billion neurons- Weighs ~ 3 pounds- Uses only glucose for energy- Different regions of the brain are specialized

for different functions

Overview of Functions- center for registering sensations- correlation of sensations- making decisions- taking actions- center for intellect, emotions, behaviour and

memory- directs our behaviour toward others

Coverings of the Brainbrain is surrounded by three layers of cranial meninges

1. dura mater - tough, outer layer (leather like)2. arachnoid - middle layer; has a spider-web

appearance3. pia mater - innermost layer that adheres to the

brain

Extensions of the Dura Mater- three extensions of the dura mater separate

the parts of the brain- falx cerebri - separates the 2 hemispheres

of the cerebrum- falx cerebelli - separates the 2 hemispheres

of the cerebellum- tentorium cerebelli - separates the

cerebrum from the cerebellum

Cerebrospinal fluid- circulates in subarachnoid space around the brain

and in four cavities called ventricles of the brain- function - mechanical protection (shock absorber),

chemical protection (carries electrical impulses), and circulation (exchange of nutrients and waste)

- choroid plexuses - networks of capillaries in the walls of the ventricles that produce CSF

- arachnoid villi - reabsorb CSF (as rapidly as it’s formed, so pressure remains constant)

Blood Supply to the Brain-brain is 2% of body mass but consumes 20% of oxygen and glucose at rest

-brain can’t store glucose, so if blood entering the brain has low levels of glucose, mental confusion, dizziness, convulsions, loss of consciousness may occur

-even a slight interruption of blood flow may cause unconsciousness (lack of O2 for 4 minutes = permanent brain damage)

Blood-brain barrier

-protects brain cells from harmful substances passing from blood into brain

-glucose, O2, CO2, anesthesia, alcohol all readily pass from blood into brain

-proteins and most antibiotics do not cross

Parts of the Brain

1. brain stem - continuous with the spinal cord; 3 main partsa. midbrain b. pons c. medulla oblongata

Midbrain- controls reflexes & eye movement- contains nuclei associated with cranial nerves III and IV

- III - oculomotor nerve - movement of eyeball, constriction of pupil, shape of lens

- IV - trochlear nerve - movement of the eyeball

Pons- “bridge” that relays sensory info from peripheral nerves

to cerebellum and cerebrum - also regulates rate & depth of breathing within the medulla- contains nuclei associated w/ cranial nerves V,VI,VII,VIII

- V-trigeminal -sensory head & face, motor-chewing- VI - abducans - eyeball movement- VII - facial -taste, secretion of saliva & tears, facial

muscles- VIII-vestibulocochlear- balance & equilibrium

Medulla oblongata- inferior part of brain stem- controls heart rate, breathing rate and smooth

muscle contractions- pyramids - formed by the largest motor tracts that

pass from cerebrum to spinal cord- decussation of pyramids - where most axons in the

left pyramid cross to the right side and vice versa (neurons in the left cerebral cortex control skeletal muscle movement on the right side of the body and vice versa

Medulla oblongata (cont)- contains nuclei associated with cranial nerves

VIII, IX, X, XI, XII- VIII- vestibulocochlear - hearing- IX - glossopharyngeal - taste, swallowing and

salivation- X - vagus - thoracic and abdominal viscera- XI - accessory (spinal) - swallowing- XII - hypoglossal - tongue movements during

speech

2. cerebellum - posterior part of the brain

- information about body position- coordination of complex skeletal movements- regulates posture and balance

3. diencephalon - extends from the brain stem to the cerebrum and has 3 parts

a. thalamus b. hypothalamusc. epithalamus, which contains the pineal gland

Thalamus

- relay station for all impulses to cerebrum- essential role in awareness and acquisition

of knowledge (cognition)

Hypothalamus

- control center of Autonomic Nervous System

- one of the major regulators of homeostasis- controls pituitary gland, regulate emotions

& behavioral patterns, eating & drinking, circadian rhythms & consciousness (daily sleep and wake cycles), and controls body temp

Epithalamus

- involved in emotional response to odors- contains the pineal gland- pineal gland - secretes the hormone

melatonin, which contributes to sleepiness and the setting of the body’s biological clock

4. cerebrum - forms the bulk of the brain

- The “seat of intelligence”...lets us read, write, speak, do math, remember, plan and imagine

- longitudinal fissure - splits cerebrum into right and left hemispheres which control opposite sides of the body

- corpus callosum - connects hemispheres internally; where nerves cross to opposite side

Cerebrum (continued)- cerebral cortex - consists of grey matter

- During embryonic development, grey matter develops faster than white matter, so it folds upon itself

- gyri - folds (gyrus - singular)- fissures - deep grooves between folds- sulci - shallower grooves (sulcus - singular)- Each hemisphere is divided into four lobes

Lobes of cerebrum

a. frontal lobe - responsible for concentration, problem-solving, planning & formation of speech - Contains pre-central gyrus - motor area

controlling voluntary muscles b. parietal lobe - sensory area for skin, interprets

sensory info, storage of memories of past sensory experiences- Contains post-central gyrus - sensory area

Lobes of cerebrum (cont)

c. occipital lobe - responsible for combining visual images and visual recognition

d. temporal lobe - olfactory (smell) and auditory (hearing) info

- Memory of visual and auditory patterns- Understanding speech (translating words to

thoughts), addition of emotion to speech

Functional Areas of the Cerebral Cortex-there are 3 general types of signals

1. Sensory areas receive & interpret sensory info

2. Motor areas initiate movements

3. Association areas deal with more complex integrative functions like memory, emotion, reasoning, will, judgement, personality, intelligence

Sensory Areasprimary somatosensory - localize exact point on the body where sensations originate

primary visual - shape, color and movement of visual stimuli

primary auditory - pitch and rhythm of sound

primary gustatory - taste

primary oflactory - smell

Motor Areas

primary motor area - voluntary contraction of specific muscles or muscle groups (electrical stimulation results in contraction on opposite side of the body)

Broca’s speech area - production of speech (occurs in left hemisphere in 97% of people)

Association Areassomatosensory association area -integrates and interprets sensations and stores memories of past sensory experiences

visual association area - relates present and past visual experiences and is essential for recognizing and evaluating what is seen

auditory association area - helps identify if a sound is speech, music or noise

Association Areas (cont)Wernicke’s area - interprets meaning of speech by recognizing spoken words; translates words into thoughts

common integrative area - allows one thought to be formed on the basis of a variety of sensory inputs

premotor area - controls learned,skilled movements & serves as a memory bank for them

Association Areas (cont)

frontal eye field area - controls voluntary scanning movements of the eyes (ex. reading)

language area - muscle contraction for speaking and control of breathing to regulate air flow past vocal cords

Hemispheric Lateralization- The functional asymmetry that exists within the

brain - hemispheric lateralization

left hemisphere - more important for spoken and written language, numerical and scientific skills, ability to use and understand sign language and reasoning

right hemisphere - more important for musical and artistic awareness, spatial and pattern perception, recognition, emotional content of language

- Because the left hemisphere receives sensory signals from and controls the right side of the body and vice versa, people with damage to their left hemisphere might lose the ability to speak whereas people with damage to their right hemisphere might lose inflection in their voice

Limbic System-encircles upper part of brainstem and corpus callosum, and the floor of the diencephalon

- referred to as the “emotional brain” because it plays a primary role in a range of emotions including pain, pleasure, docility, affection and anger

- a portion called the hippocampus functions in memory

Brain Waves

-electrical signals produced by the brain that can be detected by electrodes

electroencephalogram - record of brain waves

- useful to determine normal brain function, changes that occur during sleep, and to diagnose tumors, trauma, disease or epilepsy

Brain wavesalpha waves - appear when people are awake, disappear when sleeping

beta waves - appear when nervous system is active (sensory input and mental activity

theta waves - appear in kids and adults experiencing emotional stress, and in disorders of the brain

delta waves - occur during deep sleep in adults. Indicate brain damage if present in an awake adult. Normal in awake infants.

Brain waves

Cranial NervesI olfactory - sensory VII facial - both

II optic - sensory VIII vestibulocochlear-sensory

III oculomotor - motor IX glossopharyngeal-both

IV trochlear - motor X vagus - both

V trigeminal - both XI accessory - motor

VI abducens - motor XII hypoglossal -motor

Cranial NervesSome Say Marry Money, But My Brother Says Big Brains Matter Most

Aging and the Nervous System- Brain grows rapidly during the first few

years of life- By age 80, brain weighs 7% less than it did

in the prime of life- Ability to send nerve impulses decreases,

resulting in diminished processing of info, slower voluntary motor movements and an increase in reflex time

Disordershydrocephalus - accumulation of excess CSF in the ventricles (causes pressure to rise)

concussion - an abrupt, but temporary loss of consciousness (seconds to hours) following a blow to the head

contusion - bruising of the brain due to trauma; includes blood leakage from microscopic vessels

- Immediate loss of consciousness (no longer than 5 minutes), loss of reflexes, decreased BP

laceration - tear of the brain, usually from a skull fracture or gunshot

- Rupture of large blood vessels with bleeding into the brain and subarachnoid space

aphasia - an injury to association or motor speech areas resulting in the inability to use or comprehend words

- nonfluent aphasia - damage to Broca’s speech area results in the inability to properly articulate or form words (know what they want to say but can’t speak)

- fluent aphasia - damage to common integrative or auditory association area results in faulty understanding of spoken or written words

Cerebrovascular accident (CVA) - stroke

- Characterized by abrupt onset of persisting neurological symptoms like paralysis or loss of sensation from destruction of brain tissue

- Caused by intracerebral hemorrhage, blood clot, atherosclerosis

- Risk factors include high blood pressure, high cholesterol, heart disease, narrowed carotid arteries, TIA’s, obesity, diabetes, smoking

transient ischemic attack (TIA) - an episode of temporary cerebral dysfunction caused by impaired blood flow to the brain.

- Sudden onset of symptoms include dizziness, weakness, numbness, paralysis in a limb or on one side of body, drooping of one side of face, headache, slurred speech, partial loss of vision or double vision

- Usually only lasts 5-10 minutes and leaves no persistent neurological deficits

- Caused by blood clots, atherosclerosis, certain blood disorders

Alzheimer Disease - a disabling, senile dementia

- the loss of reasoning and ability to care for oneself- begins with trouble remembering recent events,

confusion, forgetfulness, repeating questions or getting lost traveling to familiar places

- episodes of paranoia, hallucination or violent changes in mood may occur

- eventually, will lose the ability to read, write, talk, eat and walk

Parkinson’s Disease - results from degeneration of specific neurons in the midbrain, which normally supply dopamine in order to regulate voluntary motor activity

- Symptoms include a persistent tremor at rest (head nodding and a “pill-rolling” movement of fingers), forward bent walking posture, shuffling gait and stiff facial expression, along with trouble initiating movement

- Promise has been shown from using fetal tissue transplanted into the brain to relieve the tremors (ethical issue)

Huntington’s Disease - genetic disease leading to massive degeneration of the cerebral cortex

- Symptoms include involuntary wild, jerky, and almost continuous flapping movements called chorea

- Later symptoms include marked mental deterioration, resulting in a lack of focus, fatigue and irritability.