L7&8 Neuro/Nervous System

Body Systems

A group of organs which work together to perform common functions

Neuron

a specialised small body cells with long extensions for transmitting impulses which can generate and conduct action potentials

Nerves

A collection of neurons

Neuroglia

Connective tissue that binds together neurons and protects them

Receptor

a body structure that monitors changes in a controlled condition and sends input to a control centre

Control Centre

in the body for example in the brain this evaluates the input it receives from receptors and generates output commands when they are needed

Effector

a body structure that receives output from the control centre and produces a response or effect that changes the controlled condition

Synapse

a region where communication occurs between two neurons or between a neuron and a cell

Functions of the Nervous System

Rapid way of maintaining Homeostasis, creating rapid signals and change within the body in response to internal and external signals to co-ordinate responses of cells and tissues

Two main divisions of the Nervous System

Central (CNS) and Peripheral (PNS)

Central Nervous System

consisting of the brain and the spinal cord this system processes sensory information to better understand it and help us respond appropriately

Brain

Receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions

Spinal Cord

conducts signals to and from the brain, controls reflect activity

Peripheral Nervous System

this system has neurons that feeds information (sensory) and pushes instructions out (motor)

What makes up the PNS

consists of everything outside the CNS, nervous tissue etc.,

Two main divisions of the PNS

Motor and Sensory Neurons

Efferent

conducted or conducting outwards or away from something

Afferent

conducted or conducting inwards or towards something

Sensory/Afferent Neurons

detects stimuli, carries impulses from receptors in the body to the CNS for processing

Motor/Efferent Neurons

carries impulses from CNS to effectors elsewhere in the body for action and change in response to stimulus that has already been processed in the brain

Two divisions of Motor Neurons

Somatic and Autonomic Nervous System

Somatic Nervous System

Controls voluntary movement

Autonomic Nervous System

Controls involuntary responses, coordinating activities of alertness and rest in the form of sympathetic or parasympathetic divisions

Two divisions of Autonomic Nervous System

Sympathetic and Parasympathetic divisions

Sympathetic response

Fight or flight

Parasympathetic response

Rest and digest

Relay neurons

carry messages from one part of the CNS to another, involved in reflex reactions

What occurs within the nerve cell body

synthesis and transport

Dendrites

forming a large surface area shooting out of the cell body information arrives through these into the cell body to collect information from other neurons 

Type of information dendrites collect

sensory from receptors or information from another synapse with another neuron

Axon

a single nerve conducting in only one direction carrying a nerve impulse away from the CNS and towards the region of the body in which an effect is made

Axon Hillock

the area where the Axon is leaving the cell body

Axon terminals

branches at the end of the Axon which may synapse signals to other neurons or receptors 

Trigger zone

the initial area between the axon hillock and the initial segment where the nerve impulses begin

Myelin Sheath

a multi-layered lipid and protein insulating coverage that wraps around long and wide axons in intervals 

Functions of Myelin Sheath

speeds up and makes conduction more efficient by electrically insulating the axon

Myelin created by in PNS

Schwann cells

Myelin created by in CNS

Oligodendrocytes

Current

the flow or movement of charge (energy) between two points

Example of current in NS

from the cell body the trigger of nerve conduction from the axon hillock along the axon to the axon terminals

Voltage

the potential for movement

Voltage relationships

the bigger the difference between the two points the bigger potential for movement

Example of voltage in NS

the difference in charge between the inside and the outside of the axon

Resistance

either to movement or to the current moving along an axon which can disrupt a signal therefore affecting the voltage

Ions moved across membranes

Sodium and potassium from the axon hillock along the axon

Resting potential

the potential difference across a neurons membranes when no nerve impulses are being actively transmitted

Threshold potential

the minimum level of membrane depolarization a neuron must reach to fire an action potential

Action Potential

a sequence of rapidly occurring events that initiates a rapid rise and fall in voltage across a cell membrane

Depolarisation

the process where a cell's internal electrical charge becomes less negative, shifting closer to zero

Repolarisation

the process by which a cell returns to its negative resting membrane/potential

Resting potential Voltage

-70mv

Threshold potential

-55mv

Action potential Voltage

up to 40mv

Process explained (basic)

Prior to the signal the cell will be at resting/voltage potential (-70mv), incoming signals from dendrites diffuse to the axon hillock, if a threshold potential (-55mv) is reached a an action potential will be generated (up to 40mv) travelling down the axon towards the axon terminal

Refractory period

after repolarisation the membrane drops down towards resting potential but decreases too far passing it, during which the neuron cannot be restimulated until the membrane is reset back to resting potential

Ion channels

spanning the phospholipid bilayer of the plasma membrane, these protein cross-membrane pores can open to allow ions to pass through to the cell membrane therefore creating an intercellular ion balance

Passive Channels

located in some areas of the body these channels are always open

Mechanical Channels

gated channels that open in response to mechanical stimulus (touch, pressure, vibration or tissue stretching)

Ligand-gated ion channels

gated channels that open in response to binding specific molecules such as neurotransmitters allowing for cell to cell communication and a wave of current to pass from one neuron to the next

Examples of ligand-gated ion channels

from axon terminals to dendrite of next neuron/cell where the effect or change from stimulus must occur

Voltage-gated ion channels

gated channels that open in response to voltage stimulus/change in membrane potential allowing a wave of depolarisation to move along the membrane

Example of voltage-gated ion channel

the signal conducted from the axon hillock along the axon to the axon terminals through these

Nodes of Ranvier

signals jump between this unmyelinated areas of the axon as areas of it with the myelin sheath cannot be depolarised

Saltatory Conduction

action potential jumps which occurs across myelinated axons only

Impact of size of axons

larger neurons with bigger and wider axons have less resistance therefore more rapid conduction

Non-myelinated axons

slow as each neighbouring Na+ channel must be open

Na+

Sodium

Process explained (advanced)

Prior to the signal the cell will be at resting/voltage potential (-70mv), incoming signals from dendrites diffuse to the axon hillock, if a threshold potential (-55mv) is reached an action potential will be generated (up to 40mv) and voltage gated sodium channels will open resulting in movement of Na+ channels across the axon membrane causing a state of depolarisation, at this point potassium channels open and further movement of ions occurs causing repolarisation of the membrane dropping back down towards its resting potential instead decreasing past it to the refractory period continuing down the axon until the signal reaches the axon terminal

K+

Potassium

A Fibres

myelinated with large diameter allowing signals to pass at 300mph

B Fibres

light myelination with medium diameter allowing signals to pass at 30mph

C fibres

no myelination with smaller diameter allowing signals to pass at 2mph

Ca

Calcium

Vesicles

organelles in a neuron's axon terminal that store and transport neurotransmitters

Neurotransmitters

chemical messengers that transmit signals from one neuron to another across a synapse, or from a neuron to a muscle or gland cell

Examples of neurotransmitters

adenosine, acetylcholine, dopamine, noradrenaline, serotonin

How does an action potential travel across a synapse?

An action potential arrives at the pre-synaptic terminal and depolarises the membrane, voltage gated Ca channels open and enter the axon, Ca stimulates vesicles containing neurotransmitters to be released into synaptic cleft, neurotransmitter diffuses across the synaptic cleft using simple/passive diffusion, Neurotransmitter binds to receptor on post synaptic terminal, action potential can continue

Coding 

the frequency of action potentials that are generated by a stimulus dependant on the size of the stimulus

Coding Example

the larger the stimulus the greater the frequency of action potentials sent to the CNS and sustained depolarisation at the axon hillock therefore an increased intensity of perception of stimulus for example difference between warm and hot

Multiple Sclerosis MS

this is an autoimmune disease whereby immune cells are activated against antigens of the CNS, demyelinating axons meaning reduced action potential transmission and eventual loss of the neuron

A

Frontal lobe - memory

B

Temporal lobe - hearing

C

Parietal lobe - sensory (pain, heat, pressure)

D

Occipital lobe - sight and visual processing

E

Cerebellum - balance and posture

F

Spinal cord

Meninges (layers of brain)

Dura mater, Arachnoid mater, Subarachnoid space, Pia mater

Dura mater

outer layer lining skull

Arachnoid mater

contains blood vessels

Subarachnoid space

filled with cerebral spinal fluid

Pia mater

covers brain

Cerebral spinal fliud

provides nourishment, waste removal, protection and is the optimum environment for nerve signalling

Blood-brain barrier

tight junctions that seal together endothelial cells of capillaries and basement membrane that surrounds capillaries

Functions of blood-brain barrier

Glucose able to travel across via active transport, trauma, inflammation and toxins such as alcohol and opioids can break down (not all drugs can)

A

Cervical spine vertebrae

B

Thoracic spine vertabrae

C

Lumber spine vertebrae

D

Sacrum

E

Coccyx

Vertebrae of spine

born with 33 vertebrae, by adulthood have 24 due to sacrum and coccyx fusing as well as others