nervous system

central nervous system CNS

brain and spinal cord

peripheral nervous system PNS

outside of CNS, spinal nerves, peripheral nerves and cranial nerves

afferent (sensory) division

• nerve fibers that send impulses to the CNS from sensory receptors (somatic & visceral)

efferent (motor) division

• nerve fibers that send impulses from the CNS to the effector organs causing a motor response

somatic nervous system (SNS)

• conscious voluntary control of skeletal muscle

autonomic nervous system ANS

• control over automatic or involuntary responses (smooth & cardiac muscle)

sympathetic nervous system

fight or flight

Parasympathetic nervous system

craniosacral

stimuli

a change in the environment causing a response by the body

sensory input

information gathered by the body from the stimuli

integration

• the processing and interpreting of sensory input and deciding what should be done at each moment

motor output

activation of effectors (muscles or glands) by the nervous system

neuroglia

regulate environment around neurons

neurons

nerve cells

cell body (soma)

• metabolic center of cell, no centrioles (no mitosis), contains large round nucleus w/ prominent nucleolus

• Lack centrioles (no cell division)

nissl substance

• clusters of rough ER and free ribosomes, function in protein synthesis

processes (fibers)

vary in length microscopic

dendrites

carry impulses to the cell body

axon

 generate impulses and send them away from the cell body

axon hillock

• cone like region of the cell body that leads to the axon

synaptic (axon) terminal

• branching end of the axon furthest from the cell body, contain vesicles

Neurotransmitter

• chemicals released from the vesicles (send message)

synaptic cleft/synapse

• tiny gap that separates one neuron from another or a neuron from the cell it stimulates

myelin sheath

• fatty whitish material that covers and protects the axon and speeds up impulse transmission (Schwann cells – outside CNS)

multipolar

 2+ dendrites and single axon (all motor & association – common in CNS)

bipolar

• 1 axon and 1 dendrite, rare in adults, special sense organs (eye, nose), act as receptor cell 

unipolar

• have single process, short, but divides into proximal (central) & distal (peripheral) processes, only small branches are dendrites, rest of peripheral & central are axons and serve to both carry away and take in impulses (ie – sensory neurons in PNS ganglia)

interneurons (association neurons)

• connect motor and sensory neurons, cell bodies are in CNS

somatic motor muscle

effect skeletal muscle

visceral motor neurons

effect cardiac or smooth muscle glands

motor unit

a motor unit and the muscle fibers it stimulates

receptors

 found in dendrite endings, activated by specific changes nearby

Somatic sensory receptors

detect information about the outside world or our physical position in it

external cutaneous receptors

• touch, temperature, pressure, sight, smell, hearing

proprioceptors

• Monitor position and movement of skeletal muscles and joints

visceral or internal receptors

• Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) 

• Internal senses (taste, deep pressure, pain)

astrocytes

in CNS, star-shaped, function in exchanges between capillaries & neurons, protect from harmful substances in the blood, control chemical environment of brain (maintain blood-brain barrier)

microglia

• in CNS, spider-like phagocytes, get rid of dead brain cells & bacteria, rare

ependymal cells

• n CNS, line cavities of brain & spinal cord, cilia help circulate cerebrospinal fluid (CSF)

oligodendrocytes

• in CNS, wrap flat extensions around nerve fibers creating insulating myelin sheaths (see next slide for more) 

Schwann cells

• in PNS, form myelin sheaths around axons, outer surface of cells called the neurilemma

satellite cells

in PNS, protective cushioning cells

ion

• An atom or molecule in which the total number of electrons is not equal to the total number of protons 

• Has a net positive (+) or negative (-) charge

• Important to neurons because all plasma (cell) membranes produce electrical signals by ion movements

common body ions

• Na+ (sodium)

• K+ (potassium)

• Ca2+ (calcium)

• Cl- (chloride)

• OH- (hydroxide

membrane potential

• (transmembrane potential or membrane voltage) – difference in electrical charge between the inside and outside of a cell

concentration gradient

Na+ outside, K+ inside

channel proteins

• selectively allow ions to cross cell membrane (sodium channels, potassium channels)

passive or leak channels

• always allow ions thru

active or gated channels

• only open when stimulated

resting potential

•  membrane potential of a resting cell

  • Outside of cell (+) charge, inside of cell (-) charge

  • Cell in state of  polarization with fewer K+ inside than Na+ outside

graded potential

• temporary, localized change from resting potential caused by a stimulus where the charges are slightly more positive on the inside of the cell – if it reaches a specific threshold, an action potential occurs

action potential

• shortlasting event  where the electrical membrane potential of a cell rapidly changes to (+) charge and (-) charge outside cell

nerve impulses

• neurons have 2 major functional properties: irritability and conductivity

conductivity

ability to transmit an electrical impulse

irritability (generation and propaganda of an action potential)

• the ability to respond to a stimulus & convert it into a nerve impulse

refractory period

From the moment the voltage-gated sodium channels open at threshold until repolarization (Steps 2-3) is complete, the membrane cannot respond normally to further stimulation

myelinated axon

contains sections of myelin around axon

nodes of ranvier

• gaps between sections of myelinated axon

unmyelinated axon

axons w/o myelin

white matter

white areas of CNS containing myelinated axons

gray matter

darker areas of CNS consisting mostly of neuron cell bodies (little myelination)

continuos propagation

•  occurs along unmyelinated axons – travels along entire axon

saltatory propagation

 faster type of impulse conduction that occurs in myelinated fibers where the impulse jumps from node of ranvier to node of ranvier

synaptic activity

• Action potentials transmitted from presynaptic neuron to postsynaptic neuron (neuron to neuron communication) or  postsynaptic cell (neuron to other tissue/organ)

presynaptic

• neurotransmitters released

postsynaptic

• binds neurotransmitters, either excites or inhibits the neuron/cell

acetylcholine (Ach)

• usually promotes action potentials, but in cardiac neuromuscular junctions it inhibits (slows) heart rate

Norepinephrenine (NE)

• ncreases heart rate, fight or flight response

dopamine

• movement, emotional response, ability to experience pleasure and pain, high levels linked to schizophrenia, low levels linked to Parkinson’s

gamma aminobutyric acid GABA

• inhibitory, low levels linked to extreme anxiety

serotonin

• mood control, regulation of sleep, pain perception, body temperature, blood pressure and hormonal activity, low levels linked to depression

meninges

• 3 protective tissue coverings (membranes) that cover & protect the CNS from physical impacts and blood-borne pathogens/compounds

dura mater

• outermost layer; tough, double-layered membrane; surrounds entire brain

periostea layer/periosteum

• attached to inner surface of skull

meningeal layer

forms outermost covering of brain & continues as dura mater of spinal cord

dural fold

help hold brain in place

arachnoid mater

• middle meningeal layer separated from dura mater by subdural space

subarachnoid space

deep to arachnoid mater; filled with cerebrospinal fluid (CSF) (circulates)

arachnoid villi

• projections of arachnoid membrane; place where CSF is absorbed into venous blood

pia mater

innermost membrane, extremely vascularized to provide oxygen for very high rate of metabolism (3 lb. brain at rest = 61 lbs. skeletal muscle in O2 usage)

• Cerebrospinal fluid (a.k.a. CSF)

• – fluid containing less protein & more vitamin C; formed from blood by choroid plexuses (capillaries)

  • Protects and cushions brain and spinal cord from trauma (circulates)

  • Forms and drains at a constant rate

  • Presence of blood cells or change in composition 🡪 meningitis, brain tumor,  multiple sclerosis

blood brain barrier

• keeps neurons separate from bloodborne substances; least permeable capillaries in entire body - only glucose, water, & essential amino acids through, while metabolic wastes (urea, toxins, proteins, & most drugs) are prevented from entering brain tissue; forms after 2 years

left hemisphere

• dominant for speech and motor activity

right hemisphere

dominant for spatial (recognition of shape and form) and temporal (timing, music) activities

parietal lobe

• the somatic sensory area is located in the parietal lobe posterior to the central sulcus- impulses traveling from body’s sense receptors (pain, cold, touch), except special senses, are localized and interpreted here

occipital lobe

visual

temporal

auditory

frontal lobe

• The primary motor area (allows us to consciously move our skeletal muscles) is anterior to the central sulcus in the frontal lobe 

diencephalon / inter brain

• sits atop brain stem, linking it to the cerebrum, and is enclosed by cerebral hemispheres

thalamus

• encloses 3rd ventricle

  • a complex relay station for sensory impulses passing upward to the sensory                                                 cortex (except smell)

  • get crude recognition of whether sensation we’re about to experience is pleasant or unpleasant; actual interpret. is done in sensory cortex

  • regulates states of sleep and wakefulness

  • plays a major role in regulating arousal, levels of awareness and activity

  • damage to area can cause permanent coma

hypothalamus

• makes up floor of diencephalon

  • important autonomic nervous system center b/c it plays a role in regulation of body temp., water balance and metabolism

  • Hormone production

  • deals with sleep/wake cycle

limbic system

•  “emotional-  “visceral” brain made up of many different brain areas

  • deals with emotion, motivation, and emotions associated with memory

  • influences formation of memory by   integrating emotional states with stored memories of physical sensations

amygdala

 aggression, jealousy, and fear

Hippocampus

long term memories

pituitary glands

•  hangs from anterior floor of hypothalamus by a slender stalk

  • center for many drives (hunger, thirst, sex- pain and pleasure) and emotions (therefore an important part of limbic system)

mammillary bodies

• reflex centers involved in olfaction; bulge from floor of hypothalamus, may be important for memory

epithalamus

forms roof of third ventricle

pineal gland

melatonin, induce sleep

chord plexus

forms CSF, knots of capillaries within each ventricle

brain stem

• provides pathways for ascending and descending tracts, has many small gray matter areas, which are part of cranial nerves and control vital activities (breathing, blood pressure…)