The nervous system Flashcards
what is the CNS made up of
The brain (85-100 billion neurones) and spinal cord (69 million neurones)
what is the PNS made up of
Cranial nerves, spinal nerves, ganglia, enteric plexus and sensory receptors in the skin
what is the enteric plexus
layers of nervous tissue that control movements in the esophagus, stomach, and intestines
what are the functions of the nervous system
-It regulates and maintains homeostasis along with the endocrine system
-It connects the entire body together and communicates using electronic impulses, which are rapid and specific and cause almost immediate responses
-The master of control and communication system of the body
-Responsible for our thoughts, feelings, behaviours, emotions, memories and initiates voluntary movement.
It makes us who we are!
the three basic functions
1
-Sensory receptors monitor changes know as stimuli.
-Gathered information is known as sensory input
2
-The CNS processes and interprets the sensory input and decides what should be done at each moment – a process called integration
3
-It then causes a response or effect by activating muscles / glands (effectors) via motor output
subdivisions of the nervous system
- Central Nervous System (CNS) “Command centres”
-Brain
-Spinal Cord - Peripheral Nervous System (PNS) - “Communicators”
-Afferent (sensory)
-Efferent (motor)
>Somatic (voluntary)
>Autonomic (involuntary) – No conscious control e.g heart
*Sympathetic
*Parasympathetic
what is a neurone
-AKA nerve cell.
-Highly specialised to transmit messages (nerve impulses) from one part of the body to another.
-Is the primary functional unit of the nervous system.
-Neurons can differ structurally but share common features.
what are dendrites
-Branch like processes that receive electrical messages and transmit these towards the cell body.
-Each neuron can have up to 100 dendrites depending on the structural type.
-These contain lots of receptors that are designed to pick up signals from other neurons that come in the form of chemicals known as neurotransmitters
what is the cell body
-AKA the “soma”
-Is the metabolic centre of the neuron.
-Contains all the usual organelles.
what is the nucleus of a neurone
-The nucleus contains the instruction of the neuron and keeps it functioning.
-Together the soma & nucleus collect the information from all the dendrites and send it through the axon hillock.
what is a axon hillock
-Cone like region of the cell body
-Gives rise to the axon.
-Acts as an “administrator”, sums up the total signals received, both inhibitory and excitatory signals. If this sum exceeds the limiting threshold, the action potential (nerve impulse) is triggered.
what is the axon
-Processes that generate nerve impulses that are conducted away from the cell body.
-Each neuron only has one axon.
-Axons can be 1mm to 1m in length.
-Axons bundled together is what makes up our nerves
what are Schwann cells
-A type of glial cell that surrounds neurons in the PNS.
-Single cells that form the myelin sheaths that wrap around a single axon.
-They play essential roles in the development, maintenance, function, and regeneration of peripheral nerves.
what are myelin sheaths
White fatty and waxy material which cover axons
Myelin protects and insulates nerve fibres and increase the speed of nerve impulse transmission.
Works like insulation in wires of an electrical cord.
what are nodes of ranvier
Because the myelin sheath is formed by many individual Schwann cells, it has gaps or indentations known as nodes of ranvier at regular intervals.
what is saltatory conduction
-Signals jump between nodes of Ranvier
-Results in faster conduction
-More energy efficient then unmyelinated nerve fibres.
-This will be explained further when we discuss action potentials in depth
nerve conduction speed
*Unmyelinated neurons:
-Speed = 0.5-10 m/s
-Equates to 1-20mph
*Myelinated neurons
-Speed = up to 150 m/s
-Equates to 335mph
what is the axon terminal
-Axon branches off at its terminal end to form (hundreds to thousands) axon terminals
-These terminals contain hundreds of tiny vesicles or membranous sacs that contain chemicals called neurotransmitters.
-When signals reach the axon terminal it stimulates the release of these neurotransmitters into the extracellular space between this neuron and its target cell. This space is known as the synaptic cleft.
-Target cells can be other neurons, muscles or glands.
what is the synaptic cleft
-Each axon terminal is separated from its target cell (in this case, a neuron) by a tiny gap called the synaptic cleft.
-Although very close, neurons and their target cells never touch
what is a synapse
-This is where a nerve impulse is transmitted to the next cell and is known as a synapse.
-Neurotransmitters are released into the cleft which travel to and then trigger an action potential in the target cell.
conductivity of a neurone
ZONE 1:
Part where incoming signals are received from other neurons
ZONE 2:
Part where action potentials are initiated
ZONE 3:
Part that conducts action potentials in an undiminishing fashion, often over long distances.
Axons can be 1mm to >1m in length.
ZONE 4:
Part that releases a neurotransmitter that influences other cells.
what is a unipolar neurone
-So named due to having a single process emerging from the cell body.
-However, it has very proximal (central) and distal (peripheral) processes
-The end of the peripheral process are dendrites which receive the signal
-The axons conduct signals both to and from the cell body (but still only in 1 direction)
-Sensory neurons in the PNS are this kind
what is a bipolar neurone
-Have 2 processes separated by a cell body
-These are very rare. Only found in special sense organs (ear nose) where they act in sensory processing as receptor cells.
what is a multipolar neurone
-Have more than two processes, a single axon and multiple dendrites
-All motor and association neurons are this kind these are the most common type of neuron
-Named due to multiple number of processes extending from the cell body.
