Human Anatomy Unit 5a - Central Nervous System

General Purposes of the brain

General Purposes of the brain

• Basic survival (unconscious operations)

• Conscious decisions/responses

Meninges

• Membranes covering and protecting the CNS

3 layers of the meninges

1. Dura Mater

2. Arachnoid Mater

3. Pia Mater

Dura Mater

Attached to inner surface of the skull; protects the brain from displacement

Arachnoid Mater

Transports cerebrospinal fluid from brain ventricles back into blood vessels

Pia Mater

Attached tightly to brain

Cerebrospinal fluid

• Clear liquid produced within ventricles (spaces within brain) and surround CNS

  • Protects and cushions the brain and spine

3 main regions of the brain

1. Brain stem

2. Cerebellum

3. Cerebrum

Brain stem

• Basic life functions

• Contains:

  • Pons: Motor control, sensory analysis

  • Medulla Oblongata: Breathing and heart rate

Cerebellum

• Regulation and coordination of movement/balance/posture

Cerebrum

• Higher level functioning

  • Covered with gyri (ridges) and sulci (grooves)

• Contains: frontal, parietal, temporal, and occipital lobes

• Divided into 2 hemispheres

• Connected by corpus callosum

  • Allows communication between sides

Gyri

Ridges

Sulci

Grooves

Corpus Callosum

• Allows communication between sides

Cerebrum: Frontal Lobe

• Executive functioning skills (planning, problem, solving, decision making, memory, ect.)

• Long term memory

Cerebrum: Temporal Lobe

• Auditory, speech, and memory

• Contains:

  • Amygdala: “fight or fight”, memory, emotion, and fear

  • Hippocampus: learning and short term memory

Cerebrum: Parietal Lobe

• Movement, recognition, perception of stimuli (touch, pressure, temperature, and pain)

Cerebrum: Occipital Lobe

• Vision

Thalamus

• Sensory information travels through before going to the cerebral cortex

Hypothalamus

• Maintains homeostasis

• Controls automatic responses and pituitary gland

Functions of Nervous System

1. Gathers info (sensory input)

2. Interprets info & determines response (integration)

3. Causes response (motor output)

Subdivisions of Nervous System

• Central Nervous System (CNS): brain and spinal cord

• Peripheral Nervous System (PNS): all neurons lateral to CNS

Characteristics of neurons

1. Long life span

2. Amitotic (do not reproduce)

3. High metabolic rate (require constant energy and O₂)

Neurons

Nerve cells that communicate

Neuroglia

Nerve cells that do NOT communicate

Characteristics of neuroglia

• Nourish neurons to promote growth & health

  • Scaffolding for cells to climb

  • Remove debris from dead cells (after injury)

  • Role in neuron maturation (add myelin)

2 Types of Neuroglia

1. Astrocytes

2. Schwann Cells

Astrocytes

• Nourish neurons

• Maintain appropriate chemical environment for neurons (“mop up” toxins)

Schwann cells

• Form myelin sheaths around axons

Myelin sheath

• Made of lipids and proteins

• Surrounds axon of neuron

• Allows for quick nerve impulse transmission

• At age 9-18 months, myelin forms in motor neurons to leg muscles – can start walking!

Multiple Sclerosis

• Autoimmune disorder

  • WBC fight cells of myelin sheath —> causes scarring

  • Results in delayed or blocked signals that control muscle coordination, strength, sensation & vision

Types of neurons

1. Sensory

2. Interneuron

3. Motor neuron

Sensory Neurons

(afferent, PNS): receives info from outside and takes it to CNS

Interneuron Neurons

(CNS): coordinates info & determines response

Motor Neuron

(efferent, PNS): causes response

Micro Anatomy: Dendrites

• Receive neurotransmitters

Micro Anatomy: Axon

• Send neurotransmitters away to next neuron

Micro Anatomy: Nodes of Ranvier

• Periodic gaps along the axon (no myelin)

• Allows for rapid conduction of nerve impulses

Synapse

• Space in between neurons

• Allows for instantaneous communication throughout body

Olfactory Nerve

Smell

Oculomotor nerve

Eye movement

Trochlear Nerve

Eye movement

Abducens Nerve

Eye movement

Vestibulocochlear Nerve

Hearing and balance

Hypoglossal Nerve

Moves tongue

Accessory Nerve

Swallowing, controls superior torso muscles

Optic Nerve

Sight

Trigeminal Nerve

Facial sensation and chewing

Facial Nerve

Facial expression & taste

Glossopharyngeal Nerve

Taste, swallowing & secreting saliva

Vagus Nerve

Slows heart rate, stimulates digestion, taste

Functions of the Prefrontal Cortex (PFC)

• Executive functioning skills (analyze, prioritize, goal setting, risk evaluation, judgment, organization, adapting, flexibility in thought)

• Reflective - considers feelings & response

• Long term memory

• Emotional management

• Neural networks in the PFC mature last!

• If info does not go to PFC, it goes to remaining 80% of brain which is reactive (fight vs flight)

How Information is Transferred: In the PNS

Begins in PNS —> Amygdala —> PFC (forms long term memory & learning occurs)

Amygdala is Sensitive to Stress

• Stress greatly increases dopamine —> inhibits nerve impulses —> stops transfer of info to PFC

• Regulate dopamine levels to regulate stress!

Stress…

Shrinks neural networks

Amygdala & Stress

• Low stress —> low metabolic activity —> info goes to PFC (can learn)

• High Stress —> hyper-metabolic —> info goes to reactive part of brain (NOT PFC: cannot learn)

Regulate Dopamine to…

Regulate Stress

PET Scans

• Used to observe brain activity

• Radioactive glucose injected —> travels to brain —> ”working” part of brain lights up on scan

Mentalizing

Making connections between “old” information & new circumstances

Neural Networks

• Arrangement of neurons in a circuit; neurons pass electrical impulses on to the next neuron

• Strengthened through use (otherwise will be pruned)

• Maturation of network results in neuroplasticity

• Electricity from impulse leads to

  • more dendrites (à more networks)

  • more myelin formation (more maturation)

  • more intentional synapse connections (better communication)

• The more brain activity, the greater the neuroplasticity

Neuroplasticity

• Brain's ability to form new neural networks throughout life

• Allows one to learn & adjust to new situations

• Continual process of pruning & myelination

• Ex. In a blind person, the occipital lobe assists with hearing and reading Braille

Pruning

• “Weeding out” unused connections AND strengthening used connections based on experiences

• Provides room for most important connections to grow & expand – makes brain more efficient

If pruning does not occur…

Leads to overgrowth of connections —> inefficient communication

Fetal Brain Development

• Neurons generate at rate of 250,000/minute

• Neurons pruned away by apoptosis —> prevents “overcrowded” brain ~50% of all neurons pruned before birth

Brain in Childhood

By age 3: pruning based on early childhood experiences begins

Immature brains

• More densely packed cells & more synapses per cell than mature brains

• Possible developmental problems occur if pruning does not occur

Alzheimer’s

• Chronic and Progressive

• Symptoms: MEMORY LOSS, difficulty performing tasks, misusing words, problems with judgment & reasoning, confusing time & place, and personality & mood changes

• Degenerative

• Fatal

Alzheimer’s: Amyloid Plaques Form

• Healthy brain: beta amyloid is removed naturally

• In Alzheimer’s: beta amyloid accumulates and forms plaques

  • Smaller “clumps” of beta amyloid can block synapses —> prevents communication —> neuron death

Alzheimer’s: Neurofibrillary Tangles Form

• Healthy brain: tau protein forms microtubules to help transport nutrients between neurons

• In Alzheimer’s: the tau protein is abnormal —> tangles —> microtubule collapses —> no nutrients —> neuron dies

Alzheimer’s: Hippocampus degenerates

• Hippocampal cells lose connection to other cells & die

• Causes STM loss & confusion

Alzheimer’s: Cerebral cortex degenerates

• Neurons in cerebral cortex die

  • Causes: Language & judgment difficulties, complete loss of mental function, recognition & communication

Alzheimer’s: Changes in ACh

• In normal aging: ACh decreases in brain à sporadic STM loss

• In Alzheimer’s: ACh levels in brain decrease by 90%  (due to enzyme inactivating ACh at synapse)

Spina Bifida

• A neural tube defect (incomplete development of spine and/or meninges)

Causes of Spina Bifida

• Combination of genetics & lack of folic acid during EARLY embryonic development

• Results in incomplete fusion of spine during 1^st month of pregnancy

Spina Bifida: Diagnostics: Pre-Natal

Fetus can be evaluated during 1st trimester:

1. Measure protein in mother’s blood (high levels indicate neural tube defect)

2. Ultrasound

3 Forms of Spina Bifida

1. Occulta

2. Meningocele

3. Myelomeningocele

Occulta Spina Bifida

Vertebrae malformed

Meningocele Spina Bifida

Meninges and CSF form a sac that protrudes through vertebrae

Myelomeningocele Spina Bifida

Spinal cord, spinal nerves, meninges & CSF protrude through vertebrae

Symptoms of Spina Bifida

• Possible nerve damage leading to:

  • Paralysis

  • Bladder & bowel problems

  • Hydrocephalus (cerebrospinal fluid leakage causes brain to bulge)

    • Possible cognitive impairment

Spina Bifida Postnatal Treatment: (traditional)

• Surgery to correct spine 24-48 hrs after birth

• Shunt on brain to drain fluid & alleviate pressure from hydrocephalus

Spina Bifida Prenatal Surgery:

• Surgeons open the uterus and repair the fetus’ spine during pregnancy (before 26 wks gestation)

  • Pros: decreases need for shunts & decreases brain swelling

  • Risks: increases chances for uterine rupture (miscarriage) & premature birth

Brain in Fetal Development:

• Progesterone: helps neurons grow

• Oxytocin: protects neurons from dying; “cuddling hormone” – plays role in social attachment

Alcohol affects on brain

Discoloration and developmental affects

Dopamine in teenage vs adult brains

Dopamine is at a lower concentration in teenage brains —> more impulsive reactions

Dopamine increases in adulthood —> more reflective; impulses controlled

Natural dopamine “boosts”…

• Boost dopamine naturally through exercise, music, humor, social interactions, meditation, good sleeping habits, good eating habits

• Biggest dopamine booster is intrinsic satisfaction

Stress on Brain

• Stress greatly increases dopamine (too much inhibits nerve impulses)

• Dopamine is good, but TOO much becomes BAD

Exercise on Brain

1. More oxygen in blood —> more oxygen to brain —> improved capillary health —> greater plasticity of frontal lobe

2. Releases protein (IGF-1) that stimulates neuron growth

3. Causes neurogenesis in hippocampus (memory)

Sleep on Brain

• REM sleep (“dream sleep”) —> skills & habits are consolidated

• Non REM sleep (“deep sleep”) —> facts & concepts are consolidated

• Memory Consolidation occurs in Sleep

• As adenosine builds up in brain & bonds to receptors, you feel tired

• As you sleep, adenosine is recycled & ATP re-builds —> you wake up energized

Sleep and Pruning

• Pruning occurs in sleep

  • The brain is not distracted and can evaluate synapses

• During the day many temporary synapses form

  • Unused synapses are pruned away

• Used (unpruned) synapses are larger & more stable (due to protein synthesis)

  • These are your most important memories/learnings

Caffeine on Brain

• Caffeine inhibits receptors so adenosine cannot bond —> so you feel awake!

• BUT…adenosine does not disappear so when the caffeine “wears off”, the adenosine build-up makes you feel very tired (“crash”)