The Nervous System

consists of brain + spinal cord

Spinal Cord

serves as superhighway for action potentials traveling b/w brain + rest of body

White Matter

myelinated axons on outer portions of spinal cord

Grey Matter

non-myelinated structures near centre of spinal cord

sensory + motor neurons synapse w/ CNS

processes, receives, stores + transfers info

Oligodendrocytes

produces myelin sheaths

Multiple Sclerosis

myelin sheaths in CNS become damaged + form hard scar tissue that cannot allow neuron to transmit impulses

Amyotrophic Lateral Sclerosis

begins in spinal cord in areas involved in motor control of skeletal muscle

Autonomic Division

2 neurons transmit info to target cells

Preganglionic Cells

Ganglia

Postganglionic Neurons

axons extend far reaches of body to communicate w/ internal glads + organs

lie outside CNS

cell bodies of first neurons within CNS

Protection

protected by bone

brain enclosed by skull + spinal cord enclosed by hollow channel

Meninges

dura mater (outer)

pia mater (inner)

arachnoid (medium)

Cerebrospinal Fluid

fills space b/w arachnoid + pia mater

isolates nervous system from infections

DOES NOT exchange substances

Blood-Brain Barrier

prevents charged molecules + large objects (proteins, viruses + bacteria) from entering cerebrospinal fluid

Sensory Neurons

specialized to respond to stimulus

transmit info from PNS to CNS as electrical impulses

Interneurons

transmit impulses around CNS

receive info from sensory neurons

Motor Neurons

transmit impulses away from CNS

carry nervous systems output to tissues + organs as electrical impulses

Cell Body

contains nucleus, DNA, mitochondria + organelles of the neuron

Dendrites

slender extensions that receive info from receptors or incoming impulses from other neurons

motor + interneurons have numerous ones that are short + extend in many directions

axons originate from point of union with cell body

receive impulses here

sensory neurons connect directly to an axon

axon originates from a dendrite

Axon

slender tube of cell membrane containing a small amount of cytoplasm

specialized to conduct electrical impulses

Axon Terminals

ends in an axon bulb

Neuroglial Cells

provide physical support + protection to neurons + help maintain healthy chemical concentrations

DO NOT make impulses

main function is to transmit info from one part of the body to the other via electrical impulses

Convergence

neuron receives input from many neurons

Divergence

action potential from convergence goes to many other neurons

Excitatory

depolarize postsynaptic cell, causing threshold to be exceeded

Acetylcholine

released in neuromuscular junctions, autonomic nervous systems + brain

excitatory on skeletal muscles

can be either excitatory or inhibitory on other sites

Glutamate

released in areas of brain + spinal cord

major excitatory neurotransmitter in the brain

Inhibitory

hyperpolarize postsynaptic cell + makes it harder for threshold to be reached

makes interior more negative

Norepinephrine

released in areas of the brain, spinal cord + autonomic nervous system

depedning on receptors can be excitatory or inhibitory

plays role in emotions

Serotonin

released in areas of brain + spinal cord

involved in moods, sleep cycle + appetite

Dopamine

released in areas of brian + parts of PNS

excitatory or inhibitory depending on the receptors

plays role in emotions

Endorphins

released in many areas in brain + spinal cord

natural opiates that inhibit pain

Gamma-Aminobutyric Acid

released in areas of brain + spinal cord

principal inhibitory neurotransmitter in brain

Somatostatin

released in areas of brain + pancreas

inhibits pancreatic release of growth hormone

Removing Neurotransmitters

may be taken back up by presynaptic neuron, repackaged + reused

may be destroyed by enzymes

may diffuse away from synaptic cleft into general circulation + is destroyed

command center of body

receives info in form of action potentials from nerves + spinal cord, integrates info + generates appropriate response

Hindbrain

coordinates basic automatic + vital tasks

connected to the spinal cord

oldest, most primitive brain division

Medulla Oblongata

controls vital automatic functions of interval organs

Cardiovascular Center

regulates heart rate + blood pressure

Respiratory Center

integrates info about blood levels of oxygen + CO2 + adjusts respiration

controls coughing, sneezing, vomiting + swallowing

all info going b/w higher areas of brain must go through here

motor nerves from one side of forebrain crosses over to other side of body

left brain controls right body

right brain controls left body

Cerebellum

coordinates basic body movements that are below level of conscious control

stores + replicates sequences of skilled events

muscle memories

receives input from joint + muscle receptors, balance + position receptors in ear + visual receptors

excessive amounts of alcohol disrupts function

Pons

connects higher brain to spine

contains group of axons that extend from cerebellum to rest of CNS

important in coordinating flow of info b/w cerebellum + high brain

aids medulla oblongata in regulating respiration

Midbrain

visual + auditory sensory inputs from eyes + ears pass through here before being relayed to high brain

coordinates movements of head related to vision + hearing

monitors unconscious movement of skeletal muscles so actions are smooth + coordinated

controls sleep cycles + wakefulness

Sleep Center

group of neurons comprise it + release serotonin that induces sleep by inhibiting neurons that arouse the brain

Stages of Sleep

1. Wakefulness

steady stream of action potentials get transmitted to cerebrum

2. Deep Sleep

muscles relax, heart rate + respiration slow + body temperature falls

3. Rapid Eye Movement (REM)

when we dream, eyes move rapidly, heart rate, respiration + blood flow to brain increases, + most skeletal muscles go limp to prevent us from responding to our dreams

Forebrain

determines complex behaviour (emotions + conscious thought)

Hypothalamus

coordinates functions for pituitary gland

regulates homeostasis by monitoring sensory signals

lets us know when we are hungry or thirsty

Thalamus

receives, processes + transfers info

integrates + relays some outgoing motor activity

sends signals to the cerebrum

Limbic System

describes all neuronal structures that control emotional behaviour + motivational drives

when different areas are over stimulated we experience strong feelings + emotions

feelings + emotions influence behaviour

Cerebrum

most highly developed region of the brain

associated with language, decisions making + conscious thought

Cerebral Cortex

outer layer of the cerebrum

receives, integrates + interprets sensory info from all organs

responsible for memory storage, though, conscious awareness + conscious control of muscles

gray matter consisting of neurons w/ unmyelinated axons + their associated neuroglial cells

Parietal Lobe

receives sensory input from skin

sensitive body parts (lips + genitals)

involve more neurons + larger portions

less sensitive body parts (thigh)

involve fewer neurons + smaller portions

primary somatosensory area

primary motor areas initiates motor activity

Temporal Lobe

interprets info comprehends written + spoken language + responsible for judgement

Occipital Lobe

processes visual info

Frontal Lobe

most developed lobe

initiates motor activity, speech + thought

inner portion mostly white matter that connects to lower brain areas

left + right brains connected by corpus callosum

allows hemispheres to share sensory + motor info

any substance introduced into body for purpose of causing physiological change

Psychoactive Drugs

drugs that affect states of consciousness, emotions or behaviour (alcohol + nicotine)

able to cross blood-brain barrier

work by influencing concentrations or actions of neurotransmitters

either bind or affect their release action or reuptake in some way

cocaine blocks reuptake of dopamine

Psychological Dependence

users begin to crave feelings associated with drug or alter their behaviour to obtain it

includes components of nervous system outside CNS

Sensory Division (input)

carries info to CNS

signals from external environment

signals from skin, tendons + muscles

signals from internal organs

Motor Division (output)

carries info from CNS to other parts of the body

Somatic Division

controls voluntary + involuntary skeletal muscle movements

Spinal Reflexes

involuntary responses that are mediated by spinal cord + nerves

1. person steps on sharp objects + activates pain receptors

2. produces action potentials in sensory neurons travelling to spinal cord

3. sensory neurons stimulate interneurons within spinal cord + signals brain + then motor neurons in leg

4. causes flex of appropriate muscles + lift your foot

called flexor (withdrawal) reflex

Autonomic Division

controls smooth muscle, cardiac muscle + glands

Parasympathetic

originate in brain

becomes part of outflow of cranial nerves

releases acetylcholine

lets your body relax

function automatically

regulate body functions

innervate smooth + cardiac muscle, glands, epithelial cells of kidneys + every organ

Sympathetic

originate in thoracic + lumbar regions of spinal cord

provide unified responses

releases norepinephrine

prepares body for emergencies

contains motor neurons carrying info to smooth or cardiac muscle + all other tissue organs EXCEPT skeletal muscle

carries signals from CNS to PNS that control internal organs

Neurons

protected + enclosed by Schwann Cells

produce myelin sheaths around axons

saves neuron energy

prevents inward leak of Na + outward leak of K

speeds up transmission of impulses

causes action potentials to jump from node to node fast

saltatory conduction

helps regenerate damaged or severed axons in PNS

Nodes of Ranvier

uninsulated gaps b/w schwann cells (surface of the axon is exposed)

Myelinated Neurons

neurons that have axons wrapped in myelin sheaths

3 Na out, 2 K in

maintains resting potential

-70 mV

inside of neuron is (-) compared to outside

Na concentration higher in interstitial fluid than in cytoplasm

K concentration higher in cytoplasm than interstitial fluid

Na leaking in + K leaking out balance the rate of leakage

Na + K channels closed to match rate of leakage

Graded Potentials

Depolarization

threshold is exceeded

Na channels open

Na goes into axon

inside membrane becomes (+) inside

moves voltage closer to 0

Repolarization

triggered by influx of Na

Na channels close

K channels open

K moves out

makes interior of axon negative again

Reestablishing Resting Potential

potassium channels close

ready for another action potential

Summation

incoming signals from other neurons produce bigger change in membrane potential than one impulse alone

Action Potential

sudden temporary reversal of voltage difference across cell membrane

results when sum of all graded potentials is strong enough to reach certain triggering membrane voltage

causes the release of neurotransmitter across synapse

Factors Affecting Threshold

stimulus intensity

how many neurons form synapses

whether synaptic connections are excitatory or inhibitory

Synapse

specialized junction b/w 2 cells

Synaptic Cleft

fluid filled gap that separates post + presynaptic membranes

Postsynaptic membrane is the cell membrane of a neuron that receives info

muscle cells do not process + integrate info like postsynaptic neurons

muscle cells receive input from 1 neuron (no converging inputs)

too big

Presynaptic membrane is the cell membrane of a neuron that is sending info

1. action potential arrives at axon bulb, Ca channels in presynaptic membrane open + Ca diffuses into bulb

action potential caused by opening of chemically sensitive ion channels

2. Ca causes vesicles to fuse with presynaptic membrane + release neurotransmitter into synaptic cleft

enters by diffusion b/c synaptic cleft is too narrow

3. neurotransmitter molecules bind to receptors on post synaptic membrane + causes gated channels to open

4. Na ions diffuse in + depolarizes postsynaptic membrane in area of synapse

consists of axons of many neurons wrapped in tissue coming + going to the same place

Cranial Nerves

12 pairs in PNS

Olfactory

sense of smell

Optic

vision

Oculomotor

movement of eyelid, eyeball, lens, pupil constriction

Trochlear

movement of eyeball

Trigeminal

sensations in head, face + jaw, motor control of chewing

Abducens

movement of eyeball

Facial

taste, facial expressions, tears, salivation + facial sensations

Vestibulocochlear

equilibrium + hearing

Vagus

taste, sensations from pharynx, swallowing, coughing, voice, GI tract smooth muscle contraction, heart rate reduction, digestive secretion

Glossopharyngeal

taste, swallowing, speech + salivation

Accessory

swallowing + movement of head + shoulders

Hypoglossal

speech + swallowing (tongue muscles)

carry action potentials b/w brain + muscles, glands + receptors of head, neck + thoracic + abdominal cavities

Spinal Nerves

13 pairs that connect w/ brain + spinal cord

attaches to spine via dorsal + ventral roots

Dorsal Root

sensory neurons transmit incoming AP

Ventral Root

motor neurons carry AP away from spinal cord to rest of body

involves storing info + retrieving it later as needed

Short-Term Memory

occurs in limbic system

when receiving new sensory info, stimulus triggers quick bursts of action potentials to limbic system

remember things for a few seconds or minutes because the neurons that have just fired are easier to fire again in the short term

Long-Term Memory

if info is important it should be said out loud or written down so info may be transmitted to cerebral cortex for storage in long-term memory centers

neurons undergo permanent chemical or physical change

memory storage creates additional synapses b/w connecting neurons (makes it easier to activate circuits in the future)

Trauma

physical injury to either brain or spinal cord that can be dangerous because brain controls so many functions + spinal cord is pathway to all organs

Concussion

violent blow to head or neck

brief period of unconsciousness where electrical activity of neurons is disrupted

biggest danger is subdural hematoma or hemorrhage

bleeding increases pressure within skull + disrupts function

Spinal Cord Injury

impairs sensation + body function below injured area

injuries below neck cause paraplegia (legs + trunk)

injuries to neck cause quadraplegia (legs, arms, trunk)

Infections

brain + spinal cord are spared of most infections because of blood-brain barrier

Encephalitis

inflammation of brain

caused by herpes + HIV

symptoms include headache, fever, fatigue, hallucination, confusion, trouble speaking + remembering, + seizures

Meningitis

inflammation of meninges b/c of viral or bacterial infection

Rabies

infections viral brain disease in mammals

transmitted by direct contact

goes from sensory neurons to brain where it multiplies + kills cells

symptoms include swollen lymph glands, painful swallowing, vomiting, choking, fever + mental derrangement

Brain Tumours

abnormal growth in or on brain

rising pressure disrupts normal brain function

symptoms include headache, vomiting, visual impairment, confusion, muscle weakness + seizures

Neural + Synaptic Disorders

Epilepsy

characterized by transient, recurring bouts of abnormal brain cell activity

fatigue, stress or flashing lights may trigger seizures

appears during childhood or adolescence

Parkinsons

progressive degenerative disorder

affects primarily physical activity

caused by degeneration of dopamine-releasing neurons in area of midbrain that coordinates muscle movement

Alzheimers

common cause of dementia

general term for memory loss + other intellectual abilities

starts off slowly + progressively gets worse

caused by large deposits of beta amyloid proteins