Biology 30: Nervous System

• Biology 30 covers the Nervous and Endocrine Systems, focusing on Unit A.
• Chapter 13 focuses on the Nervous System

Key Learning Ideas for the Nervous System

• General structure/function of neurons and myelin sheaths
• Formation/transmission of action potentials, including all-or-none & intensity responses
• Signal transmission across synapses, involving norepinephrine, acetylcholine, and cholinesterase
• Principal structures of the central and peripheral nervous systems (CNS and PNS)
• These structures regulate voluntary (somatic) and involuntary (autonomic) systems
• The somatic and autonomic systems include: cerebral hemispheres/lobes, cerebellum, pons, medulla oblongata, hypothalamus, spinal cord, sympathetic/parasympathetic nervous systems, and the sensory-somatic nervous system
• Organization of neurons into nerves
• Composition/function of reflex arcs, exemplified by patellar and pupillary reflexes

Upcoming Topics

• CNS and PNS relating to bodily organization of information, brain and spinal cord composition, and somatic and autonomic functions
• Examination of nerve cells using microscopes
• Nerve cell organization
• Nerve cell communication via information; reflex arcs, synapses, and chemical transmitters
• Quiz that will summate chapter 13

Nervous System Essentials

• Nightly review of textbook readings and notes is essential
• The course is intensive so use provided materials
• An outcome list and a timeline for course completion are available
• PowerPoints are released the day after completion

The Nervous System

• Communication network using cells and chemicals throughout the body
• Composed of electrical impulses, neurotransmitters, and hormones
• A large amount of memorization is required

Divisions of the Nervous System

• Two primary groups: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)
• The CNS consists of the brain and spinal cord
• The PNS consists of nerves carrying information between body organs and the CNS

Functions of CNS and PNS

• The CNS coordinates mechanical and chemical actions of the body
• The PNS relays information between the central nervous system and the other parts of the body, excluding the brain and spinal cord

PNS Subdivisions

• The PNS divides into the somatic and autonomic systems
• The somatic system is the voluntary nervous system that controls muscle movements, skeletal tissues, skin, and sensory inputs
• The autonomic system controls internal organs and reflexes, functions typically not consciously controlled

Neurons vs Glial Cells

• Nerve cells are categorized into two types: neurons and glial cells
• Neurons are the functional units of the nervous system that conduct electric current for conveying and processing information
• Glial cells do not conduct and support both structually and metabolically

Neuron Subcomponents

• Neurons have dendrites, cell bodies, and axons
• Dendrites receive stimuli or information, either from the environment or from neighboring neurons
• The cell body houses the nucleus and redirects incoming signals
• Axons carry signals away from the cell body to target organs/muscles or other neurons

Myelin Sheath

• The Myelin Sheath is a fatty white protein coating that insulates the axon
• Covering cells with myelin insulates and is called myelination
• Myelination is caused by glial cells known as Schwann cells
• The insulation prevents charged ions from escaping the nerve cell
• The Node of Ranvier is the area between two Schwann cells

Nodes of Ranvier

• Nerve impulses leap from one node to the next
• This leaping accelerates transmission of information
• Myelinated axons transmit impulses faster than unmyelinated ones
• Axon size contributes to the speed of nerve transmission

Neurilemma

• A thin outer membrane called the neurilemma is found in all nerve fibers within the PNS
• Formed by Schwann cells that facilitate the regeneration of damaged axons
• Myelinated fibers are called white matter
• The absence of myelin and neurilemma in fibers result in grey matter

PNS vs CNS

• The PNS is myelinated and has neurilemma
• The CNS contains both myelin and neurilemma
• Absence of neurilemma in the CNS leads to permanent brain and spine injuries, and is called gray matter

Neuron Classifications

• Three categories for Neurons: sensory, interneurons, and motor neurons
• Sensory neurons relay information from sensory receptors to the CNS for processing, clustering around the spinal cord in ganglia (ganglion one)
• Sensory Neurons are called Afferent neurons
• Interneurons exist in the CNS and transit information from one group of neurons to the next and interpret them
• Interneurons are called associated neurons
• Motor neurons relay information to effectors that tell a cell, organ, or muscle to respond
• Effectors are all Muscles, organs, and glands
• Motor Neurons are called efferent neurons

CNS Nerve Growth

• The central nervous system does not support nerve growth in the way that the PNS does
• There is a glial limiting membrane in the CNS that reduces the growth of Schwann cells
• This means no myelin and neurilemma in the CNS

Reflex Arcs

• Specialized pathways in the body for rapid response to dangerous stimuli
• Reflex arcs communicates with the effector directly with information about danger
• The Effector reacts before CNS processes the information
• Signal sequence: Skin - Spinal Ganglion - Dorsal root - Interneuron - muscle - ventral root

Testing Reflex Arcs

• Reflex arcs can test the health of the body
• A poorly transmitted impulse means there is an issue with the interneuron
• Also could mean issues with the CNS or with the effector

Action Potential

• Nerve cells communicate using an electrochemical process involving the movement of ions
• Resting membrane measures approximately -70mV
• Experimental evidence proves if you add an electrode to the nerve cell a rapid change happends
• Action and resting potential is lumped as action potential

Action vs Resting Potential

• Action potential is the reversal of the cell electronegativity from the resting potential to positive electrical potential
• Resting potential is when the cell membrane returns to origninal measures, -70mV

Resting Potential

• Neurons maintain a resting potential (typically -70mV) when not actively transmitting signals
• Achieved through the selective movement of ions across the cell membrane

Ion Imbalance

• Cells maintain a supply of potassium (K+) and sodium (Na+) ions in order to have function
• An electrical imbalance is created by placing a higher concentration of one ion on one side of the cell membrane as opposed to the other

Ion Concentration

• Inside the resting cell, there is a concentrated of potassiums
• Outside the resting cell, there are substantially much more sodiums

Facilitated Diffusion

• Facilitated diffusion happens when Ions move via gated ion channels
• The membrane is selectively permeable to the ions
• Ion channels are specific to each ion

Sodium-Potassium Pumps

• All cells continously pump potassium back in and sodium back out
• Uses an active transport that stabilizes a cell

Electrical Potential

• Negative ions exist already within a given cell
• When potassium leaves it generates a negative potential
• If Sodium enters, it attempts to balance it, but rate of diffusion is too slow

Polarized Membrane

• Positive ions align with the exterior of the cell
• Negative ions accumulate on the exterior wall
• The resulting polarized membrane difference is typically measured -70mV

The Steps of Action Potential

• Stimulus: The neuron recognizes stimulus and becomes more permeable to sodium
• Concentration: Sodium desperately wants to equalize and flood the cell
• Depolarization: No longer at resting potential and polarized membrane
• Gate Changes: The permeability is achieved by opening the sodium gates and the potassium gates close
• Charge Reversal: Sodium floods and charge inside is positive, and charge outside is now negative

Action Potential Visualized

• A graph of action potential should show a rest potentional with a depolarization, repolarization, and hyperpolarization

The resting state

• Electrical by which the bell is poralized and ready for stimulus
• Usually averages a measurment of is -70mV

Depolarization

• This happens when a stimulus is upward trending
• Stimulus triggers sodium channels to open
• The electric potential ramps to positive

Repolarization

• A downward trend
• Sodium gates are immediately closed when the cell is positively charged
• Natural diffusion happens once pottasium gates reopen

Hyperpolarization

• Potassium gates remain open for longer than initially planned
• The state becomes highly charged in outside, while it is highly negatively charged in charge
• This makes the resting potential negatively charged

Refractory Period

• Time between firing and resting
• A cell cannot fire a potential action for a second time until resting

Action Potential Movement

• Depolarization: shifting change of electronegativity in cellular membrane creates disturbance
• Effect : That disturbace can create depolarization at the adjacent part of the membrane
• Purpose: hyperpolarization makes disturbances to travel in specific direction

Saltatory Conduction

• In myelinated axons, depolarization is isolated to the nodes of ranvier forcing the signal to "jump" from node. The wave of depolarization moves much faster.

Conduction Speed

• Saltatory conduction travels at 150m/s
• Unmyelinated axons averages at 0.5 - 10m/s

Types of Response

• A neurons function to the point of meeting the value of stimuli
• A higher input does not grant unique response
• There are rates to solve apparent paradox
• brain quickly receives depolarizing impulses
• solution with variable threshold allows for the differentiation of two temperature

End of an Axon and the resulting actions

• At the end of action, the process moves down the next effector to transfer sequence
• Process will now under go synaptic processes

Axon Terminals

• Terminal knob will connect to other parts to make nervous system
• The terminals can be between neurons between effector

End Process for Synapse

• Diagram used in left part will have connections to 2 neurons

Triggers Signal for Receptors

• A Ca2+ will allow calcium to enter Synapse
• Signal will then trigger the vesicles which trigger neurotransmitters across and in synaptic cleft

Diffusion Speed and Process

• Neurons will need to cross space of an average diffusion for what's to be 20cm nm

Neurotransmission

• A chemical classification is needed to alter membrane of post synaptic neurons
• 2 Groups -1) excirotory and 2) inhibitory
• Category determined on locality of what's in the body

Neurotransmission

• Electrical pulses will end in a synapse
• Synapse will release neurotransmitter will be specific based membrane of ions
• Initial will have new impulse or prevent previous part from what's been removed
• enzymes release will effect neurotransmitters ending their effects with synapse will absorb and destroy

Spatial vs Temporal Summation

• Spatial will create neurons in postsynaptic and those will be in simultanoes fires to create impluse
• fires must in postsynaptic to take action Temporal Summations: creates synapes by needing neurons and will fire multiple fire from previous sections to be efficient

Considerations to Understand

• Know how a Inhibitants and excite can effect the way the nervous system flows
• Understand the way the body and function are connected by considerations