Chapter 11 Nerves

Homeostasis

relative stability in the body --> balance / nervous system purpose is to regulate body structure and maintain homeostasis

Nervous System

made up of brain, spinal cord, nerves and various sensory structures / sensory input, integration, motor output

Sensory Input

moves signals from sense organs to brain

Integration

interpretation of signals in the form of an appropriate response / CNS

Motor Output

conduct signals to body effectors (muscles and glands)

Central Nervous System (CNS)

consists of brain and spinal cord / responsible for integrating and processing incoming signals from nerves

Peripheral Nervous System (PNS)

made up of all the nerves and sensory receptors that send information to and from the nervous system

2 Main Types of Cells

Glial Cells = responsible for nourishing, protecting, and maintaining neurons

Neurons (nerve cells) = basic structural and functional units of the nervous system

Purpose of Neurons

1. respond to chemical and physical stimuli

2. conduct electrical impulses

3. release chemicals that regulate various body functions

Each Neuron Consists Of

Cell Body = cell's life support center

Dendrites = receives messages from other cells

Axon = passes messages away from cell body to other neurons (membrane prevents oppositely charged ions to become attracted / stores potential energy)

Myelin Sheath = covers axon and some neurons to help speed up impulses

Terminal Branches = form junctions with other neurons

Synapse

gap between 2 neurons that do not physically connect

Types of Neurons

Sensory = gather information from senses and turn it into electrochemical impulses that get carried to spinal cord and brain / blood pressure, taste buds, photo and pain receptors

Motor Effectors = move information from brain and spinal cord to muscles and glands (effectors)

Interneuron = found in CNS and acts as a link between sensory and motor neurons

Direction of Nerve Flow

sensory (afferent) --> interneuron (in CNS)

--> motor (efferent)

Reflex Arc

connection of neurons that models the basic organization of the nervous system / moves directly through the brain and spinal cord without the conscious mind being involved

Reflex Flow

stimulus --> pain receptor --> sensory neuron --> interneuron --> spinal cord

--> motor neuron --> effector (muscle) --> response

Ions

inside of an inactive axon has a negative charge and the outside of the nerve cell has a positive charge / difference in charge is due to the concentrations of + and - charged particles / movement causes an electrical current

Resting Potential

voltage is -70mV / positively charged sodium (Na+) ions are constantly being transported out of the cell making the outside of the cell positively charged

Sodium-Potassium Pump

Na+ is constantly transported out of the cell by active transport / 3 NA+ out and 2 K+ (potassium) in / requires ATP energy

Action Potential

neuron becomes excited due to a stimulus / explosion of electrical activity created by the movement of ions / occurs in depolarization and repolarization

Depolarization

stimulus will cause Na+ ions to leak into cell creating a more positive cell

Threshold Potential

-55mV / voltage regulated channels open and all the sodium ions that are built up outside of the cell flood in / up until +45mV has been reached

Repolarization

the change to +45mV causes sodium channels to close and causes potassium (K+) channels to open and they rush out of the cell

Hyper-Polarization

ions are on wrong sides of membrane (K+ on outside and Na+ on inside) so the sodium-potassium pump works to re-regulate the concentration

"All Or None" Principle

there is no big or small action potential, they are all the same size / the neuron either does not reach threshold potential or a full action potential is fired

Nerve Impulse

electrical signal that travels from dendrites, past the cell body, and along the axon toward the axon terminal / some axons are encased in myelin sheath

Myelin Sheath

fatty and insulating layer around nerve axons

Shwann Cells

type of glial cell / actual cell on axon

Nodes of Ranvier

points along the axon where signals are transmitted / spaces in between each schwann cell / speed up signal transmission as action potentials jump from one node to the next

Saltatory Conduction

nerve impulse conduction in myelinated nerve fibres because they jump from node to node

White Matter & Grey Matter

CNS myelinated fibres are found in white matter / unmyelinated fibres are found in grey matter / most PNS neurons are myelinated