The Nervous System

homeostasis/equilibrium

balance, state of balance, keeping a constant internal environment

the main processes of the nervous system

1. sensory input

2. integration

3. motor output

sensory input

using senses/sensory receptors, the nervous system receives information about our internal/external environments

integration

interpreting what the received information means, and what needs to happen consequentially

motor output

in situations where it is necessary, effector organs are told to respond and fix the issue

effector organs and examples

the part of the body that carries out the response, example: legs run, pancreas produces insulin

the central nervous system

• composed of the brain and the spinal chord

• coordinates and processes the incoming and outgoing information

  • spinal chord acts as a highway between the body and the brain

how does the CNS protect the brain and spinal chord

the spinal chord: bone coverings (the vertebrae)

the brain: bone coverings (the skull)

• protective membranes called meninges

the three layers of meninges

• outer layer: dura mater

• middle layer: arachnoid

• inner layer: pia meter

cerebral spinal fluid

shock absorber between the pia meter (inner layer of meninge) and the arachnoid (middle layer of meninge) and at the central canal of the spinal chord

forum magnum

opening in skull for spinal chord

gray matter

unmyelinated neurons/axons which leads to increased processing power

• forms the surface of your brain

• present in the brain, and throughout the spinal chord

• memory trick: people who are smart and think a lot give off the vibe of seeming sad and grey

white matter

myelinated interneurons that connect spinal chord to brain

• really speed, made for fast message sending/receiving

• found in almost all long nerve fibers, and often connects grey matter

• memory trick: associated with fast fashion loving WHITE counter top owning millennials

the dorsal nerve

brings sensory information in, usually on top of the ventral nerve

the ventral nerve

carries motor information out to the effectors, usually beneath the dorsal nerve

the three regions of the brain and their function

• the forebrain: reason, intellect, memory, personality, language

• the mid brain: relay center for eyes and ears

• the hind brain: muscles, balance, autonomic control

cerebrum and cerebral cortex

outer layer of brain, cerebral cortex is very outer layer of brain

• grey matter: unmyelinated and processing power

• coordinating center for motor actions, speech, memory, and personality

two hemispheres of the cerebrum and their function

• right brain: visual and spatial awareness

• the left brain: verbal skills and speech

each hemisphere of the brain has 4 lobes: frontal, temporal, parietal, occipital

corpus callosum

communication bridge between the left and right brain

thalamus

imbedded deep in the mid brain, the thalamus is the relay center for sensory and motor signals

hypothalamus

inferior (beneath) the thalamus the hyp0thalamus plays an important role in maintaining homeostasis

• instructs the pituitary to produce hormones

• instructs the medulla Omblongota to send a nerve signal (autonomically)

olfactory bulbs

detect smell

the hindbrains cerebellum

controls limb movement, balance, and muscle tone

the hindbrains pons

relay station between cerebellum and medulla (like a bridge)

medulla oblongota

joins spinal chord to cerebellum, the site of autonomic nerve control

the somatic NS division of the periphery nervous system

• the somatic NS: consists of the nerves connected to sensory receptors and skeletal muscles

• permits voluntary action

• controls all of the nerves involved in body movement (with the exception of reflexes)

somatic NS is composed of

12 paired cranial nerves: controls senses, and facial, tongue, head and neck movement

31 paired spinal nerves: controls skeletal muscles

the autonomic NS division of the PNS

• controls involuntary homeostatic control

• involuntary function of all of the organs in our body

• consists of the sympathetic and parasympathetic systems

two types of ANS nerves

preganglionic: sends message from brain to ganglion (cell body within the PNS)

post ganglionic: delivers message from the ganglion to the effector organ

the parasympathetic system

THE OFF SWITCH: rest and digest

• restores balance

• long preganglionic nerves

• releases acetylcholine

the master “off” nerve of the PNS

the vagus nerve: has control over heart, liver, digestive tract. and bronchi

acetylcholine

important neurotransmitter that is released in the CNS and PNS

• excitatory: causes nerve sells to fire off

• stored at the ends of nerve cells, moves across the synapse and binds to receptors on the post-synaptic nerve, is reabsorbed

what breaks down acetylcholine for reabsorption

acetylcholinesterase

the sympathetic system of PNS

ON SWITCH: activates flight or fight

• prepares the body for stress

• short (really fast) preganglionic nerve

• preganglionic nerves release acetylcholine, post ganglionic nerves release adrenaline

glial cells

support cells: neurons are to basic to function by themselves, so glial cells hold them in place, provide them with nutrients, defend against infection, and clean up a neuron if it dies

sensory neurons

afferent, carry information towards the CNS, 90% are found in PNS

• first to receive information

• relay information about the bodies internal/external environments

• responsible for sensory input

interneurons

100% found in the CNS, link neurons in the spinal chord to neurons in the brain

• responsible for integration

motor neurons

efferent, carry impulses from CNS to effector organs

• responsible for motor output

cell body

functional portion of the cell, when found in PNS they are called ganglions

dendrites

appears like the arms of the cell body, are an extension of the cell body that is used to receive signals from other neurons or the environment

• able to connect to another cell body

axon

the long extension of the cell body that transmits impulses away to other neuron or towards the effector organs

the neurillema

membrane that surrounds the axon and promotes cell regeneration

myelin sheath

FAT/white insulation that surrounds axons

• created by shwann cells

• acts as insulator that prevents the loss of charged ions

• allows nerve impulses to be translated across axon MUCH faster

nodes or ranvier

the gaps between sections of myelin sheath (gaps in fat along axon)

reflexes

involuntary actions that initially surpass interpretation by the brain

• the action is still processed by the nervous system before the action, but the brain gives no thought to it → this is called the reflex arc

the process of a reflex

1. stimulus

2. receptors

3. sensory neuron

4. inter neuron

5. motor neuron

6. effector organ

   = a response (leg has kicked or whatever)

two states of a nerve

resting potential and action potential

resting potential

nerves are polarized: off and just resting, their internal charge is -70 mV

action potential

nerves are depolarized: turned on, internal charge is +40 mV

sodium potassium pumps and polarization

used ATP to pump 3 sodium ions in and two potassium ions out- unequal distribution which leads to a polarized membrane

two methods of maintaining polarization that don’t have to do with sodium/potassium pump

• the precensce of negatively charged plasma proteins that never move: example Cl-

• potassium channels that allow potassium to naturally leak out of the inside of the axon

the steps of action potential

1. depolarization

2. repolarization

3. refractory period

depolarization in action potential

stimulus bypasses threshold, which causes internal charge to jump from -70mV to +40mV

• sodium channels open, and more open

repolarization in action potential

Na+ (sodium) channels close and K+ (potassium) channels open causing potassium to diffuse out of the cell and which restores original polarization (-70mV)

refractory period

the recovery time that is necessary before a neuron can return to it’s original resting potential

saltatory conduction (in myelinated axons)

HOP SCOTCH → action potential jumps over myelin sheath from node of ranvier to node of ranvier

• this results in faster conduction of action potential as opposed to the conduction on an unmyelinated axon

threshold level

the minimum amount of stimulus required to get a response

• a charge that is greater than the minimum amount of stimulus will not fire off more neurons or get an increased response- nerves are all or nothing

how is message priority determined

1. the more frequencies of impulses

2. some neurons have increased threshold levels which are only set off with increased stimulus, therefor the more impulses reaching the brain the greater the response

the synapse

the space between that divides neurons

pre-synaptic neurons

release neurotransmitters into the synapse

post-synaptic neurons

receives neurotransmitters from the synapse

neurotransmitters

chemical messenger for neurons

Action potential is required to BLANK to bridge the synapse

be converted into chemical energy

how is action potential converted into chemical energy

1. the presynaptic membrane is depolarized (with the aid of calcium- Ca2+)

2. synaptic vesicles release neurotransmitters (ACETYLCHOLINE) from the axon bulbs/end plate

3. neurotransmitters diffuse and bind to receptors on post synaptic dendrites

4. post synaptic membrane opens either ion channel

   • Na+ flows in= excitatory

   • K+ flows out = inhibitory

5. - neurotransmitters are broken down by enzyme (cholinesterase) and ion gates close

   - neurotransmitters are absorbed by pre-synaptic neurons for rebuilding

common neurotransmitters

dopamine, serotonin, endorphins

excitatory in action potential

when Na+ flows in

• triggers receptors in post synaptic cleft that allow positive ions in → this leads to depolarization

inhibitory

when potassium goes out

• triggers potassium channels to open → this leads to hyperpolarization (cells are more negative then usual)

summation

the effect of the accumulation of neurotransmitters, can be inhibitory or excitatory

PET scan

tracks activity and usage- radioactive glucose is consumed in certain parts of the brain and when that part of the brain is used it will light up with different colors on the scan.

MRI

giant magnets that detect changed in H+ that emit radio signals