Biology Lesson 16: Nervous System

nervous system

organ system in animals made up of nerves that transmit chemical/electrical signals throughout the body. includes brain, spindal cord, and nerves. divided into central nervous system and peripheral nervous system

neurons

specialized cells designed to transmit chemical/electrical impulses through the body

glial cells

non-neuronal cells of the nervous system that support, regulate, and nourish neurons (most brain cells caused by mutations in these)

cell body

the part of a neuron that houses the nucles and most other organelles

dendrites

short, highly branched extensions of a neuron that receive signals from other neurons

axon

a long extension of a neuron that carries nerve impulses away from the cell body toward target cells

myelin sheath

a fatty insulating coat formed by special glial cells that insulate axon

3 major types of neurons

sensory neurons, motor neurons, interneurons (relay)

sensory neurons

a nerve cell that recieves information from the internal or external environment and transmits signals to the central nervous system

motor neurons

a nerve cell that transmits signals from the brain or spinal cord to muscles or glands

interneurons (relay)

a nerve cell within the central nervous system that forms synapses with sensory and/or motor neurons and integrates sensory input and motor output.

membrane potential

difference in electrical charge across a cell membrane due to the differential distribution of ions. - the charge of this membrane can change in response to neurotransmitter molecules released from other neurons and environmental stimuli

signals are possible because

each neuron has a charged cellular membrane (a voltage difference between the inside and the outside)

sodium potassium pump

a transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell *uses ATP to pump AGAINST concentration gradients. Maintains membrane potential in neurons

charge across a membrane

pump moves 3 positively charged ions (Na+) out of the cell and only 2 positively charge ions (K+) into the cell - net positive charge on the outside of the cell creating membrane potential

resting membrane potential

the membrane potential charasteristic of a nonconducting excitable cell, with the inside of the cell more negative than the outside

it is created and maintained by increasing the concentration of cations outside the cell relative to inside the cell

ion channel

a transmembrane protein channel that alllows a specific ion to diffuse across the membrane DOWN its concentration ro electrochemical gradient (they regulate the relative concentrations of different ions inside and outside the cell)

action potential

a rapid, temporary change in the electrical potential of a neuron’s membrane that is used to transmit signals down an axon

action opotential are facilitated by

changing the concentration positive ions inside and outside of the cell

depolarization

a change in a cells membrane potential such that the inside of the membrane becomes LESS negative relative to the outside

repolarization

the process of a cell restores its negative internal charge after an aciton potential event

hyperpolarization

a temporary change in a cells membrane potential such that the inside of the membrane becomes MORE negative than normal resting potential

action potential step 1

at resting state, most voltage-gated sodium and potassium channels are closed

action potential step 2

stimulus reaches membrane, causing sodium channels to open and sodium rushes into cell (depolarization)

action potential step 3

sodium concentration increases in a positive feedback cycle, facilitating action potential

action potential step 4

sodium channels close, potassium channels open, potassium rushed out the cell (hyper polarization)

action potential step 5

For a brief period, potassium rushing out of the cell causes hyperpolarization, which makes it very difficult for neurons to fire. cell resets to resting state

Action potential stimulus causes action potential to

travel down neuron

synapse

the space between neurons where neurotransmitters are transferred between neurons for communcation

neurotransmitters

chemicals that transmit a signal from one neuron to another across a synapse (dopamine, serotonin)

chemical synapse step 1

depolarization along axon causes voltage-gated Ca 2+ channels to open

chemical synapse step 2

Ca2+ ions initiate a signaling cascade that causes synaptic vesicles, containing neurotransmitter molecules, to fuse with the presynaptic membrane

chemical synapse step 3

fusion of a vesicle with the presynaptic membrane causes neurotransmitter to be released into the synaptic cleft

chemical synapse step 4

neurotransmitters bind to postsynaptic ion channel receptors which initiates depolarization in the postsynaptic neuron

chemical synapse step 5

Neurotransmitters are then removed from the synapse.

nervous system divided into

central nervous system and peripheral nervous system

central nervous system (CNS)

includes the brain and spinal cord

lies in the midline of the body

—in vertebrates, it develops from dorsal, hollow nerve cord, spinal cord carries messages to/from brain, also produces reflexes, allows body to act quickly to stimuli independently of brain

peripheral nervous system (PNS)

contains cranial nerves and spinal nerves connected to brain and spinal cord

lies outside the CNS

gathers information from stimuli and sends that information to CNS

includes somatic and autonomic nervous system

*transmits information to and from central nervous system

peripheral nervous system divided into two parts

somatic nervous system , autonomic nervous system

somatic nervous system

part of the peripheral nervous system that oversees voluntary control of muclse tissue

—transmits sensory and motor signals from sensory receptors to the CNS

—transmits signals from central nervous system to cause muscle contraction and movement

autonomic nervous system

part of peripheral nervous system that controls involutary actions

—heart rate, blood pressure, respiration, digestion, sexual arousal

—operates largely unnoticed 24/7 to maintain homeostasis

—can be further divided into the sympathetic and parasympathetic divisions

sympathetic division

a division of the autonomic nervous system; generally increases energy expenditure and prepares the body for action (fight or flight)

parasympathetic division

a division of the autonomic nervous system; generally enhances body activities that gain and conserve energy, such as digestion and reduced heart rate (“rest and digest”)

vertebrate brain divided into 3 main regions

forebrain, midbrain, hindbrain

forebrain

region of the brain responsible for high level cognition, voluntary action, language, emotion,etc.

cerebrum

an integrating center of the vertebrate forebrain. integrates information to for memory, learning, emotions, voluntary movement

midbrain

region of the brain that acts as relay center between forebrain and hindbrain, for sensory and motor information

hindbrain

region of the brain responsible for involuntary actions (heart rate, digestion, breathing) reflexes (sneezing, coughing, swallowing, and refines muscle responses)

-most ancestral part of brain

nervous system disorders

schizophrenia, depression, alzheimer’s, parkinsons, etc

-in USA disorders result in more hospitalizations than heart disease or cancer

-active area of research, understanding genes and environmental variables that contribute to these disorders