Nervous System Flashcards

• The main job of the NS is to acheive homeostasis/equilibrium (balance). The three processes that occur in the NS are:
• 1. Sensory Input: In which the NS monitors both internal AND external environments.
• 2. Integration: The body processes the sensory inputs it receives and often integrates it with stored information.
• 3. Motor Input: After integration, if it is nessecary, the body will signal effector organs to make an appropriate response (does not always involve muscles).

• The central nervous system is the brain and spinal cord, they coordinate incoming and outgoing information.
• The Peripheral nervous system, carries information between the organs, effectors and the CNS

• The somatic NS consists of nerves connected to sensory receptors and skeletal muscles it permits voluntary action (writing your name).
• Autonomic NS consists of the sympathetic and parasympathetic systems (on/off switch). This systems permits the involuntary functioning of blood vessels, glands, and internal organs such as the bladder stomach and heart.

• There are neurons which are the functioning unit of the NS and glial cells which assists neurons (hold in place, provide food, insulate, clean waste and defend against infection). The three main jobs of neurons are input, integration and output.
• The 3 types of neurons are:
• 1. Sensory/Afferent Neurons (take info IN): They relay information about the environment from sensory receptors to the CNS.
• 2. Interneurons: They link neurons to other neurons (they are found only in CNS).
• 3. Motor/Efferent neurons (OUT) carry impulses from the CNS to the effectors (muscles, organs, glands), they produce responses (do not always have to include movement).

• The cell body is the functional portion, when they are in groups outside of the CNS they are caleld ganglion. 
• Dendrites are short extensions that recieve signals from other neurons or the environment
• Axons are long extensions that transmit impulses away to other neurons or effectors. Larger diameter of axon = faster nerve impulses

• The parts of myelinated neurons are:
• The myelin sheath which is a white insulation around axons which acts as an insulator preventing the loss of charged ions from the axon, and allows conduction of faster nerve impulses.

Schwann cells which form the myelin sheath by swirling the axon

The areas between myelin sheaths are called nodes of Ranvier

The Neurilemma is the membrane surrounding the axon that promotes regeneration.

• Multiple sclerosis is a disorder in which myelin around the axon gets damaged, this causes nerve signal loss as the ions are not as well insulated. This affects the brain, muscles and other organs.
• The reflex arc is an involuntary response that initially bypasses interpretation by the brain. It starts with a stimulus (like a hot stove) which a receptor detects the receptor information is then relayed to a sensory neuron which sends it the info to an interneuron from there information is sent to a motor neuron (also to the brain through another neuron which is the secondary respons) which gets an effector organ to create a response.

• 1. Resting potential: Resting potential is the base state of a nerve, in this state the nerve is polarized with a charge of -70 (constant) mV.
• 2. Action potential: This is an excited (depolarized) nerve, in this state the charge of a nerve jumps all the way to +40mV (average in nerves), it lasts only milliseconds. The Action potential is only activated if a stimulus reaches a nerves threshold potential.

• The steps in action potential are 1. Depolarization: The nerve becomes more permeable to highly concentrated sodium than potassium. This rapid influx of Na+ causes -70 to jump to +40mV. 
• 2. Repolarization: Sodium channels close, potassium gates open, and potassium difuses out of the cell restoring the original polarization.
• 3. Then the refractory period occurs: The recovery time of a nerve is 1-10ms, the refractory period is required before a neuron can return to resting potential. This is the pumping time required to produce another action potential. During this period hyperpolarization occurs; since potassium gates close slowly, more potassiumions move out than normal leaving the nerve with an even more negative charge inside. Hyperpolarization in the previous area of a nerve stops impulses from traveling backwards.

• 1. Sodium potassium pums use ATP (active transport) to pump 3 sodium ions out and 2 potassium ions in. This unequal distribution of ions leads to a polarized membrane.
• 2. The presence of negatively charged plasma proteins and ions
• 3. Potassium leak channels that allow potassium to leave the inside of the axon.

In a nerve a minimum stimulus is required to produce a response (threshold potential) when this threshold is met there is an all response: nerves or muscles respond to a full extent, if the threshold is not met there will be no response at all. A stronger impulse than the minimum threshold will not produce an increased response.

• Message priority in neurons is determined by: 1. Higher speed of impulses (spinal gate theory), 2. Some neurons having higher threshold levels, only set off with an increased stimulus. Therefore the greater the number of impulses reaching the brain only then is the intensity of the response increased. 
• Saltatory conduction in myelinated axons allows faster conduction than unmyelinated action potential. This is due to the fact that myelin sheathing has bare patches of axon called nodes of Ranvier which insulate the axon causing action potentials to jump from node to node (saltatory conduction) instead of having to depolarize the whole axon.

• The synaptic cleft/synapse is the space in between two or more neurons it is about 20nm. Presynaptic neurons carry impulses to the synapse. Postsynaptic neurons carry impulses away from the synapse.
• Signals move across different neurons at the synapse, action potentials do not transfer across, instead neurotransmitters that are activated when the action potential reaches the presynaptic neuron will brave the gap by diffusion from the end plate of the presynaptic to receptors on the postsynaptic. 
• The mechanism of neurotransmission begins (1.) when the action potential reaches the end plate. (2.) Ca2+ gates open to cause an influx of + ions. (3.) build up of Ca2+ causes the release of acetylcholine. (4.) Acetylcholine is released in vesicles through exocytosis. (5.) Acetylcholine binds with Na+ channels opening them (postsynaptic receptor sites). (6.) Na+ causes depolarization in the postsynaptic. (7.) The action potential continues through the dendrite of the post synaptic neuron. (8.) Presynaptic endplate membrane releases cholinsterase (enzyme) which breaks down acetlycholine (into acetyl CoA and choline). (9.) Na+ gates close and the recovery phase begins in postsynaptic.

• There are excitatory neurotransmitters which trigger receptor proteins in post synaptic cleft to allow positive ions in (ex. sodium) this leads to depolarization and lowered threshold level.
• Then there are inhibitory which rigger potassium channels to open which leads to hyperpolarization, increasing threshold level. Examples of common neurotransmitters are:
• Dopamine, dopamine's job is to provide the sensation of pleasure and allow body movment
• Serotonin, it regulates body temperature, helps with perception and mood control
• Endorphins, these are our natural painkillers and help create emotions
• Norepineepherine, it works with epinephrine to create the fight or flight response
• Gaba, is inhibitory, it is a natural tranquilizer

Each neuron is dedicated to one neurotransmitter.

Summation is the effect produced by the accumulation of transmitter chemicals from two or more neurons. It can be inhibitory ofr excitatory. Ex: a and b alone cannot give enough response to stimulate D but when both send signals their combined threshold may stimulate neuron D.

Parkinsons disease is when inadequate dopamine (inhibitory) causes involuntary mucle contraction. Alzheimer's disease is when inadequate acetylcholine production causes the deterioration of memory and mental capacity.

Drugs affect synaptic transmission and they can either be downers (inhibitory) by physically blocking the release of neurotransmitters and/or blocking the receptors for neurtransmitters or they can be uppers (excitatory) by enhancing the release of neurotransmitters, mimicking neurotransmitters or stopping the enzymatic breakdowns of neurotransmitters.

• 1. There is the bone coverings (skull/vertebrae)
• 2. The brain is surrounded by protective membranes, the 3 meninges (Outer layer: dura mater, Middle layer: arachnoid, Inner layer: pia mater)
• 3. Cerebrospinal fluid: It is the transport medium & shock absorber that circulates inbetween the inner and middle meninges and the central canal of the spinal cord (brain and spine cerebrospinal fluid are the same).

• The spinal cord carries sensory nerve messages from receptors to the brain and relays messages from the brain to the effectors (mucles, organs and glands). The foramen magnum is the opening in the skull for the spinal cord which travels within the vertebral backbone.
• Gray matter is unmyelinated neurons/axons (interneurons), while white is myelinated motor and sensory neurons that connect the spinal cord to brain. Dorsal nerves bring sensory information in (located on back side of spine), ventral nerves carry motor information out to the effectors (muscles/glands) (front side).

• The Forebrain is responsible for reasoning, intellect, memory, language, personality.
• The forebrain contains the cerebrum which is the largest portion of the brain, the surface of it is the cerebral cotrex (gray matter), it coordinates the motor actions, speech, reasoning, memory, personality, there are two seperate hemispheres (left controls: verbal skills and right side of body, right: visual/spacial awareness and left side of body) the two hemispheres are linked by the corpus callosum (commmunication bridge).
• The thalamus interprets sensory information (relay station), The hypothalamus and pituitary unite the nervous and endocrine systems (autonomic functions), The olfactory bulbs detect smell

• THe 4 lobes are the Frontal, temporal, parietal and occipital.  The frontal lobe is repsonsible for voluntary muscles (walking and speech peroformed by the motor cortex), personality, memory, planning, thinking. The Temporal lobe interprets sensory information (sound and smell), The parietal creates touch, temperature, taste, pains, and interprets speech and creates emotions, and the Occipital is responsible for vision (right eye=left brain and vice versa).
• Broca's area coordinates speech muscles and translates through speech (creates languages, located in frontal lobe), Wernicke's area is responsible fore language comprehension and storage (recieves and interprets language, in left temporal lobe)

The mid brain the a relay center for eye and ear reflexes. The hind brain contains the cerebellum which controls limb movement, balance, muscle tone and muscle memory, the pons (bridge) which is the relay station between two regions of cerebellum and the medulla and the medulla oblangata which joins spinal cord to cerebellum, it is the site of autonomic nerve control (breathing movements, diameter of blood vessels...)

Brain mapping tells us each areas specific function and proves that other areas can substitue for damaged areas. PET's consume radioactive glucose in certain areas of the brain. MRI's are giant magnets that detect changes in H+ that emit radio signals.

THe two parts of the peripheral nervous system is the Autonomic system which are the nerves designed to maintain internal homeostasis (not under concious control) and the Somatic system which is designed to adjust to external stimuli by controlling skeletal muscle (under concious control) exception -  reflexes. Both types contain sensory and effector nerves.

• The sensory somatic system is composed of 12 paired cranial nerves which control vision, hearing, balance, taste, smell, face, tongue, neck and head movement and 31 paired spinal nerves which control skeletal muscles.
• There are two types of ANS nerves preganglionic (ns-> ganglion) and postganglionic (ganlion -> organ/gland/muscle), the ANS controls smooth muscle, internal ogans and glands.

• 1. Sympathetic (on), this is portion that prepares the body for stress (fight or flight), it has short preganlionic nerves which release acetylcholine and the postganlionic nerves release norepinepherine. It originates from the thoracic (ribs) and lumbar (bend of back) vertebrae.
• 2. Parasympathetic (off), it restores balance (rest and digest) has long preganglionic nerves which releases acetlycholine and so do the post ganglionic nerves. This section originates from the cranial, cervical (neck) or the caudal (tail bone) areas of the spine. 
• The nagus nerve is considered the master "off" nerve as it controls the heart (slows heartrate), bronchi(slows breathing), liver, pancreas and digestive tract (promotes digestion).

A stimulus is a source of energy converted from one form to another (ex. light waves to chemical electrical impulses). Sensory receptors are modified ends of sensory neurons that are activated by specific stimuli. (sensory receceptor -> sensation (in brain) -> perception). Sensory adaptation is what occurs when you have adjusted to a change in your environment (ex: wearing clothes or old lady perfume).

• Photoreceptors: Eyes (rods, cones)
• Chemoreceptors: Toungue (taste buds) & nose (olfactory cells), carotid arteries & brain (blood pH)
• Mechanoreceptors: Ear (inner ear hair cells - balance and sound), proprioreceptors & touch (skin)
• Thermoreceptors: Skin (hot & cold)

• 1. The Sclera, the outermost layer, is the protective layer, it is covered by a cornea (transparent tissue that refracts light towards the pupil). This layer has no blood vessels so it gets its O2 from dissolved tears and nutrients from the acqueous humour. Lack if O2 and nutrients is called glaucoma. 
• 2. The choroid layer is the middle layer that has pigments that prevent scattering by absorbing stray light. It has many blood vessels, the iris is a coloured muscle regulating the amount of light entering the eye, the opening for light to go in is called the pupil. The lens focuses images on the retina by action of dorsal and ventral ciliary muscles. The vitreous humour is cloudy, jellyliker material that maintains eye shape and lets light through.

• The retina, is the innermost layer composed of three layers of cells: The light sensitive rods and cones, bipolar cells which pass messages from rods and cones to cells of the optic nerve and optic nerve cells called ganglion cells.
• Rods are used in dim light and only see in black and white, while cones are used for identifying colours (RGB cones)
• The forvea centralis is an area of closely packed cones at the center of the retina; it is the most sensitive area of the eye. The blind spot is an area with no rods and cones, where the optic nerve comes in contact with the retina.

• Light entering the eye is bent/focused by the cornea towars the pupil, then the lens further bends (refracts) the light to a focal point (fovea centralis), this image is ineverted. Accomodation is the adjustments made to the lens and pupil to view near or far objects. 
• Eyes focus for close vision by thickening the lens shape by flexing ciliary msucles allowing tendons to relax. Eyes focus for distant vision by thinning the lens by ciliary muscles relaxing and tendons pulling.

Catracts are when the lens or cornea beoms clouded, the solution is too replace the cloudy lens with a plastic one or remove the lens and use glasses instead. Astigmatism is abnormal curvature of the cornea or surface of the lens the solution is unevenly ground lenses. Nearsightedness (myopia) is when the image is focused in front of the retina, glasses with concave lens will solve this. Farsightedness (hyperopia) is when the image is focused beyond the retina (eyeball too small). The solution is glasses with a convex lens. Colourblindness is an inherited condition where one lacks certain cones (r,g, or g) the solution is special glasses or contacts (more common in males).

• The ear is used for hearing and balance (equilibrium), both done by mechanoreceptors. The inner ear cells have tiny cillia (30-150), which respond to mechanical stimuli which causes the nerve cell to generate an impulse. The three sections are the inner, middle and outer.
• 1. Outer ear - The Pinna, the outer flap of the ear, acts like a sound funnel directing waves to the auditory canal- The Auditory Canal it is the channel that carries sound waves to the eardrum. specialized sound wabes produce earwax to trap invading particles.

• 2. Middle ear
• - Begins at the Eardrum (Tympanic membrane) ends at the Vestibule
• - Ossicles amplify/pass sound waves from the eardrum to the oval window, there are 3 small bones: the malleus (hammer), incus (anvil) and stapes (stirrup)
• - The Oval Window is a small membrane covered opening that amplifies sound
• - The Eustachian tube is an air filled tube that equalizes pressure between the internal and external ear. It also drains excessive fluid to nasal cavity.
• 3. The inner ear
• - The Vestibule is connected to the middle ear by the oval window, it houses two small sacs (the utricle and saccule) which are involved in head balance (static equilibrium)
• - The Semicircular Canals are 3 fluid filled canals that help the body balance (dynamic equilibrium)
• - The Cochlea is a coiled snail shell structure, lined with different hair cells that respond to different sound waves and frequencies and convert them to nerve impulses
• - Lastly, the Auditory nerve transmits signals to the CNS

Sound energy waves get converted to a chemical signal. Sound must travel through a medium to be heard (ex: solid, liquid, gas). The ossciles move a shorter distance than the eardrum = the amplification of sound. Intense noise causes musles around the ear to contract which restricts movement and pulls the stapes away from the oval window (less sound amplified &transmitted)

As the Oval window (flaplike bone) is pushed inward, the round window moves outward to keep pressure constant. The pushing triggers waves in fluid within the inner ear to the cochlea, which converts the waves to electrical impulses. The organ of corti is the primary sound receptor within the cochlea. It is composed of 1 inner row and 3 outer rows of hair cells. The basilar membrane anchors the receptor hair cells to the organ of corti. Fluid vibrations move the BM and the hair cells bend against the tectorial membrane, which stimulates the sensory nerves that send the auditory signal to the brain. The tectorial membrane does not move, hair cells on BM are pushed against its surface to cause a depolarization. Hairs near the middle ear (beginning of cochlea) are thin and rigid for high pitched sounds. Hairs that are further down are wide and elastic for low pitch sounds. Each pitch terminates in a specific part of the auditory cortex.

There is conductive hearing loss which can be caused by wax build up, middle ear infection or a punctured eardrum. There is also sensorineural hearing loss which is when the auditory nerve is severed or cochlear hair cells are damaged.

TO treat hearing loss issues you can either use a hearing aid which amplifies sound and transmits it to the eardrum. Or cochlear implants can be implanted, they convert sound (speech processor) to electrical impulses that are sent to your auditory nerve.

• All of your movements are controlled by balance and muscles, the fluid in your inner ear is responsible for your balance. The liquid in your ear moves when we move and thick liquid movement sends info. to the brain to tell it how we are moving. Body Balance is maintained by 3 fluid filled semicircular canals each canal has a pocket (ampulla) that contains hair (cilia) that moves with the gel like cupula, it is pulled by gravity or centrifugal force. Movement causes the fluid to bend the cilia initiating a nerve impulse.
• Head balance is maintained by 2 fluid filled sacs in the vestibule called the saccule and utricle. In each sac are hair like receptor suspended in a jelly like material that contain calcium carbonate granules (tiny stones) called otoliths. When the head bens gravity pulls the otoliths and the gelatinous material causing hairs to bend which stimulate sensory receptors to send messages to the brain.

• The 5 types of taste that are stimulated by dissolved chemicals in specific taste buds are sweet, salty, sour, bitter and umami. 
• Smell works through the detection of specific airborne chemical that stimulates an olfactory cell to produce an action potential which is percieved in the olfactory bulbs.
• Each mechanoreceptor is a modified dendrite of a sensory neuron.