Nervous System Overview

• The chapter covers the structure and function of neurons and myelin sheaths, action potential transmission, synapses, and key neurotransmitters like norepinephrine, acetylcholine, and cholinesterase in the nervous system.

Nervous System Structures

• Key concepts include the central and peripheral nervous systems' structures and their roles in regulating voluntary (somatic) and involuntary (autonomic) functions.
• Focus is given to the components and functions of cerebral hemispheres, lobes, cerebellum, pons, medulla oblongata, hypothalamus, spinal cord, sympathetic and parasympathetic nervous systems, and the sensory-somatic nervous system.

Reflex Arcs

• Topics include the organization of neurons into nerves and the composition and function of reflex arcs using examples such as the patellar and pupillary reflexes.

Bodily Communication

• The nervous system communicates using a complex series of cells and chemicals in the body.
• The nervous system uses both electrical impulses, neurotransmitters, and hormones to transmit information.

Nervous System Divisions

• The central nervous system (CNS) consists of the brain and spinal cord.
• Coordinating mechanical and chemical actions is controlled by the CNS.
• The peripheral nervous system (PNS) relays information between the central nervous system and the other parts of the body.

PNS Subgroups

• The PNS can be further divided into subgroups, including the somatic and autonomic systems.
• The somatic system is the voluntary nervous system, controlling muscle movements, skeletal tissues, skin, and sensory inputs.
• The autonomic which is is akin to an automated system, controls internal organs and reflexes without active thought or voluntary action.

Neural Cells

• Nerve cells are categorized into two types: neurons and glial cells.
• Neurons are the fundamental functional units of the nervous system and conduct electric current to convey and process information.
• Glial cells are non-conductive cells that provide both structural support and metabolism assistance for other nerve cells.

Neurons

• Neurons contain dendrites, cell bodies, and axons.
• Dendrites receive stimuli or information, which can come as sensory input from the environment or signals from neighboring neurons.
• The cell body houses the Nucleus and redirects incoming signals toward the cell body for processing.
• The cell body contains cytoplasm and the nucleus.
• The axon directs signals from the cell body towards a target organ, muscle, or another neuron.
• Each neuron has only one axon, but that axon can divide and branch with many different terminus.
• Axons are thin and very delicate, with 100 human axons being able to fit into a single human hair.
• Axon terminals are called effectors.

The Myelin Sheath

• The Myelin Sheath is a coating of fatty white protein that covers and insulates the axon.
• Myelination is the process of covering cells with myelin.
• The myelination process are cause by a special glial cell called the Schwann cell.
• The insulation prevents loss of charged ions from the nerve cell.
• Nodes of Ranvier are the areas between Schwann cells.

Nodes of Ranvier

• As a nerve impulse travels, it leaps from one node then to the next.
• This leaping effect accelerates the transmission of information.
• Myelinated axons transmit impulses much faster than unmyelinated cells.
• Size plays a role in the speed of nerve transmission.

Neurilemma and Fiber Types

• All nerve fibers found within the peripheral nervous system have a thin outer membrane called the neurilemma.
• The neurilemma is formed by Schwann cells and aids in the regeneration of damaged axons.
• White matter is myelinated fibers in the brain, while gray matter lacks myelination.
• Nerve fibers in the PNS are myelinated and have neurilemma, while those in the CNS may lack myelin and neurilemma.
• The absence of neurilemma in parts of the CNS leads to many injuries in the brain and spine being permanent.

Neuron Classifications

• Sensory neurons relay information from sensory receptors about the environment to the CNS to allow processing.
• Sensory neurons tend to cluster around the spinal cord in groupings called ganglia.
• Sensory neurons are also called afferent neurons.
• Interneurons exist in the CNS to transmit information from one group of neurons to the next, interpreting information and communicating impulses to the motor neurons.
• Interneurons are sometimes called associated neurons.
• Motor neurons relay information to effectors like cells, organs, or muscles to respond to stimuli.
• Muscles, organs, and glands are all classified as effectors.
• Motor neurons are sometimes called efferent neurons.

CNS Constraints

• The central nervous system does not support nerve growth the way the PNS does because of a glial limiting membrane in the CNS, which reduces the growth of Schwann cells. Lack of schwann cells means no myelin and no neurilemma

Reflex Arc Characteristics

• The reflex arc is a specialized pathway in the body used to quickly respond to dangerous stimuli.
• It communicates the information about the danger directly to the effector.

Electrochemical Communication

• Nerves communicate by electrochemical messages created by the movement of ions through the nerve cell membrane.

Action and Resting Potentials

• Action potential is the term used to describe the reversal of the cell electronegativity from the resting potential to a positive electrical potential.
• Resting potential is when the cell membrane returns to its original -70mV electric potential difference.

Ion Imbalance Importance

• Cells in the body rely on potassium ions (K+) and sodium ions (Na+).
• A higher concentration of an ion of either kind on one side of the cell membrane than the other creates an electrical imbalance at the cell wall.
• This creates an electrical imbalance across the membrane to restore balance.

Location of Ions in Cell

• Inside the cell there is a concentration of potassium (K+) ions.
• Outside the cell there is a higher concentration of sodium ions (Na+).
• The imbalance leads to the sodium wanting to be in the cell, and the potassium wanting to leave the cell.

Selective Cell Walls

• Plasma membrane is only selectively permeable to ions at specific sites.
• Facilitated diffusion occurs through gated ion channels to allow the ions to move.

Equilibrium and Pumps

• Cells contain a sodium/potassium pump to maintain electric equilibrium, utilizing active transport to move potassium back into the cell and sodium back out.

Polarized Membranes

• Positive ions align on the exterior of the cell wall, while negative ions accumulate on the inner wall which creating a polarized membrane.
• The value of -70mV denotes the difference between internal and external ion concentrations and this number is generally higher depending on that value.

Action Potential: Process

• The neuron receives stimulus during which the cell membrane becomes more permeable to sodium ions.
• The permeability change faciliates the shift by opening the sodium gates and closing the potassium gates.
• Sodium ions flood the cell due to the concentration imbalance.
• A rapid flood of sodium causes the inside charge in the inside of the cell to become positive.

Action Potential Graphs

• Each action potential graph has key features such as:
  • Rest Potential
  • Depolarization
  • Repolarization
  • Hyperpolarization

Saltatory Conduction

• In myelinated axons, depolarization is isolated to the nodes of Ranvier, so the signal is forced to "jump" from node to node..
• Saltatory conduction sends signals at about 150m/s, while unmyelinated axons send signals at about 0.5 - 10m/s.

All-or-Nothing Response

• Every neuron has a threshold value, this dictates the stimulus required to warrant a depolarization event.
• Neurons only fire when the threshold stimuli is met at the same speed and intensity.
• There are factors that affect rate at which the impulses are being fired, and different specific neurons will react differently even if with the same stimuli.

Synaptic Transmission

• The action potential travels to the end of an axon then this information is relayed along the neural network through synaptic transition.
• Axons end in a terminal sometimes referred to as a synaptic knob, that connects to other components of the nervous system.
• The connection may be between neurons or a neuron and an effector with the signal being relayed with the help of neurotransmitters

Synapses Explained

• Synapses happen when the presynaptic neuron propagates an electric signal that stimulates the neurotransmitters to release stimulating to a new postsynaptic neuron.
• An electric signal at the end plate triggers a then at the synapse calcium allows neurotransmitters into into the synaptic cleft.
• The neurotransmitters are received by a specialized receptors, which depolarizes the postsynaptic membrane and propagates a new electrochemical signal.
• The neurotransmitters are received by a specialized receptor that when stimulated will depolarize the postsynaptic membrane and propagate a new electrochemical signal.

Neurotransmitters Role

• Neurotransmitters are a classification of chemicals that alter the membrane potentials of post synaptic neurons.
• There are two primary types of neurotransmitters: excitatory and inhibitory.
• Excitatory neurotransmitters triggers the opening sodium channels in a postsynaptic neuron, depolarizes the membrane, and initiates a new reversal of charge, and subsequently a new impulse.
• Inhibitory neurotransmitters open a potassium channel further reinforcing the negative potential in the cellular membrane, preventing an impulse from being sent.
• Enzymes are then released to target and destroy and neurotransmitter in order to absorb or destroy them within the cell.

Common chemicals

• Acetylcholine is common neurotransmitter that triggers excitory responses from generally found in the end plates of nerve cells.
• Cholinesterase is the enzyme which breaks down the receptor for the acetylcholinesterase

Summation

• An action potential is only triggered in one direction and the force which either inhibits or allows certain responses..

• Postynpatic neurons utilize spatial and temporal summation

  • Spatial summation is when two separate neurotransmitters both trigger, whereas otherwise they would be too weak

• Another type of summation is temporal:

  • Temporal Summation - when two neurotransmitters are release in close succession resulting in action

Brain Function

• The brain divides certain processing functions to unique physiological localities within it.
• Scientists can test brain function during open brain surgeries by asking questions and observing the response.

Cerebral Cortex

• Brains primary area of focus contains the:
  • Cereum: Two hemispheres acting indeendently center brain information.
  • Sensory cortex: Speech recognition and accompanied functions
  • Cerebal cortex: Surface of the cerebrum composed of matter and fissures

Brain Lobes

• The brain contains 4 lobes: Based on the unique section of brain. Areas stimulated by electric proves will have a unique section.
• There are more neurons to control finer movements like fingers compared to arms.
• Frontal Lobe
  • Movement of muscles -Personality, reasoning, and decision-making take place. -It also controls inhibition, aspects of memory, and is considered to be the area that active thought takes place in.

Brain: Additional Parts

• Temporal Lobe

  • Associated withvision and hearing. -Areas are linked withmemory and interpretation sensory information.

• Parietal Lobe -Associated with sensory including touch and temperature- - The parietal lobe links The parietal lobe is linked to the emotions and interpreting speech, specifically speech.

• .Occipital Lobe

  • Sensoty function

• -Cerrbelum

  • Largest part of of brain
    • controls like movements
    • balances

Brain Comms

• The brain's left and right hemispheres operate independently.
• The right side is associated with the tasks of visual patterns, and spatial awareness; the left is associated with the verbal skills.
• Learning abilities are related to the dominance of one hemisphere or the other, however their ability to communicate is key.
• Communication allows for a larger range of emotions

Corpsus Collusm

• Large bundler
• Fibers connect with the two hemispheres
• Neurons composs brain

Brain Parts

• Forebrain
  • structure called the
  • hypothalamus -bulb

Midbrain

• grey -eye/ear -Hind -Cerrbelm -Pons -Oblangota

Perhiperal Nervous System

• Sensory Somatic System
  • Gather Information
  • Sketal muscles
  • Voluntary way - act
    • 12 Cranical nerves -- some motor other sensort all paird - contro vision taste movemnt

Autonomic System

• Nerves- motor are separated by gulaglion
  • groups smoothe - internal orags group
• Catefies based on -stimpus - present - Sympathetic - designed to to make stress - aredrnaline ficitons - Para Symthathit - cope with stess - storage flow

Gangilon

• Sympthic use short Pre - Long Post

Parasmythic

            - neurotransmitter acetyl choline present for system however
                -  uses norephinephrine

Test your knowledge of neuron action potential and membrane potential. Understand the role of ion channels, sodium-potassium pump, and depolarization/repolarization phases. Learn about the electrical signals in neurons.