Nervous System

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nervous system

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a complex network of nervous tissue that carries electrical messages throughout the body

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two basic types of nerve cells

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neurons and glial cells

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neurons

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structural and functional units of the nervous system and transmits electrical impulses

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glial cells

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provide support for neurons like nutrients and other materials

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three basic parts a neuron consists of

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cell body, dendrites and axon

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cell body

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contains the nucleus and other cell organelles

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dendrites

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extend from the cell body and receives nerve impulses from other neurons

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axon

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· a long extension of the cell body that transmits nerve impulses to other cells

· branches at the end, forming axon terminals

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axon terminals

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points where the neuron communicates with other cells

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myelin sheath

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· an outer layer that the axon of some neurons have

· acts like a layer of insulation

· allows nerve impulses to travel more quickly

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what is myelin?

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a lipid (fat) produced by a type of glial cell known as Schwann cell

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nodes of Ranvier

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space in between myelin on the axon

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what are neurons classified by?

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on the direction in which they carry nerve impulses

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sensory neurons

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carry nerve impulses from tissues and organs to the spinal cord and brain

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motor neurons

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carry nerve impulses from the brain and spinal cord to muscles and glands

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interneurons

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· link together neurons

· carry nerve impulses back and forth between sensory and motor neurons

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what do nerve impulses result from?

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a difference in electrical charge across the plasma membrane of a neuron

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what causes a difference in electrical charge?

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ions: electrically charged atoms or molecules

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when is a neuron in a resting state?

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when a neuron is not actively transmitting a nerve impulse

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what happens during a resting state?

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· sodium potassium pump uses energy in ATP to pump sodium ions out of the cell and potassium ions into the cell

· inside neuron becomes electrically charged

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why is a neuron during a resting state negatively charged?

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it has more positive ions outside the cell than inside the cell

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resting potential

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difference in electrical charge during resting state

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action potential

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a sudden reversal of the electrical charge across the membrane of a resting neuron

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when does a nerve impulse (or action potential) begin?

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· when the neuron receives a chemical signal from another cell

· signal causes gates in sodium ion channels to open, allowing positive sodium ions to flow back into the cell

· the inside of the cell becomes positively charged compared to the outside of the cell

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charge of a generated action potential

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positive

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what's special about the myelin sheath?

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·ions flow across the membrane only at the nodes between sections of myelin

· the action potential (or nerve impulse) jumps along the axon membrane from node to node rather than spreading smoothly across the entire membrane

· increases speed

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synapse

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a place where an axon terminal meets another cell

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what is an axon terminal and other cell separated by?

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narrow space called synaptic cleft

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what happens when action potential reaches the axon terminal?

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· it releases molecules of a chemical called a neurotransmitter

· neurotransmitter molecules travel across the synaptic cleft and bind to receptors on the membrane of the other cell

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two main divisions of the nervous system

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central nervous system and peripheral nervous system

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what does the CNS contain?

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the brain and spinal cord

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what happens to every nerve impulse?

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it goes to the brain or spinal cord

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what kind of reflex does not go to the brain or spinal cord?

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spinal reflex

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brain

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· the most complex organ and control center of the nervous system

· controls mental processes like reasoning, imagination, memory, and language and interprets info from the senses

· controls basic physical processes such as breathing and heartbeat

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three major parts of the brain

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cerebrum, cerebellum and brain stem

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cerebrum

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· largest part of the brain

· controls conscious functions such as reasoning, language, sight, touch and hearing, perception and learning

· divided into two hemispheres

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what connects the two hemispheres?

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corpus callosum

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cerebellum

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· just below the cerebrum

· coordinates body movements like balance and physical movements you're used ex. walking

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brain stem

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· lowest part of the brain

· connects the rest of the brain with the spinal cord

· passes nerve impulses between the brain and spinal cord

· controls unconscious functions such as heart rate and breathing

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brain stem consists of two parts

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upper (thalamus and hypothalamus)lower (midbrain, pons, medulla oblongata)

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spinal cord

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· thin, tubular bundle of nervous tissue that extends from the brainstem and continues down the center of the back to the pelvis

· it passes messages from the body to the brain and from the brain to the body

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nerve

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cable-like bundle of axons

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longest human nerve

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sciatic nerve- runs from the spinal cord in the lower back - down the left leg - all the way to the toes of the left foot

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peripheral nervous system

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· consists of all the nervous tissue that lies outside the central nervous system

· connected to the central nervous system by nerves

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two divisions of the peripheral nervous system

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somatic nervous system (sensory) and autonomic nervous system (motor division)

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somatic nervous system

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· part of the PNS

· controls mainly voluntary activities under conscious control

· made of nerves that are connected to skeletal muscles

· controls some unconscious movements called reflexes

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reflex

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· a very rapid motor response that is not directed by the brain

· nerve impulses travel to and from the spinal cord in a reflex arc

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autonomic nervous system

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· part of the PNS

· controls all other involuntary activities not under conscious control

· nerves of ANS are connected to glands and internal organs

· controls basic functions like heart rate, breathing, digestion and sweat production

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two subdivisions of autonomic nervous system

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sympathetic and parasympathetic

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sympathetic division

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· deals with emergency situations· prepares the body for "fight or flight"

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parasympathetic division

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· controls involuntary activities that aren't emergencies (routine activities)

· ex. like organs of digestive system

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what makes white neurons white?

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myelin sheaths

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what does the sensory division of the PNS include?

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eyes, ears, mouth, nose, and skin

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sensory receptors

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specialized nerve cell that responds to a particular type of stimulus such as light or chemicals

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mechanoreceptors

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respond to physical stimuli such as pressure or tension and are located in our skin

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thermoreceptors

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· located in the skin and hypothalamus · detect changes in temperature

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what are the neurons in the cerebral cortex responsible for?

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processing information from sensory organs

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pupil

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the opening of the eye that light enters

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retina

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· located at the back of the eye

· light sensing portion of the eye and where light focuses

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occipital lobe

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lobe that processes sight information

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what does the retina contain?

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photoreceptors: rods and cones

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rods

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help us see in dim light

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cones

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gives us the ability to sense colors

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optic nerve

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carries nerve impulses from photoreceptors to the brain

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cochlea

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· part of the ear that helps you hear

· contains mechanoreceptors called hair cells

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semicircular canal

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· part of the ear that helps you keep your balance

·fluid filled chamber in the inner ear that contains hair cells

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temporal lobe

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where hearing takes place

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chemoreceptors

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taste cells on the tongue

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olfactory receptors

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located in the nasal passage of the nose

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where do you not have pain receptors

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in your brain

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what does the thalamus do?

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relays information from the sense organs to certain regions of the cerebral cortex.

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what does the hypothalamus do?

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help with breathing and heart

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parietal lobe

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controls taste and sensory function

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frontal lobe

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controls smell, speech, motor function, processing of consequences of actions

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drug

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a chemical that alters body structures or biological functions

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psychoactive drugs

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drugs that alter the functioning of the central nervous system (brain and spinal cord)

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examples of psychoactive drugs

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caffeine, alcohol, nicotine and marijuana

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drug abuse

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the use of a drug without the advice of a medical professional and for reasons not originally intended

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drug addiction

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where the drug user is unable to stop using the drug

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where do ions come from?

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electrolytes

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what happens if an axon has a larger diameter?

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it can also travel faster

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postsynaptic cleft

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receives the nerve impulses

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presynaptic cleft

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transmits nerve impulse