Nervous system - neural structure and organisation

What is the nervous system?

An organisms control centre

What is the nervous system responsible for?

• Sensory input : monitoring the internal and external world vi millions of receptor cells

• Integration : processing and interpreting sensory no non sensory information, deciding what to do

• Motor output : activating effector organs (muscles, g,ands)

What is the order if these 3 responsibilities?

Sensory input → integration → motor output (refkex arc)

What are the 2 principal divisions if the nervous system?

CNS

• brain, including retina

• Spinal cord

PNS

• motor nerves (efferent or motor system, have an effect on world)

• Sensory nerves (afferent or sensory system, affected by the world)

What can the efferent (or motor) system be further subdivided into?

Somatic (voluntary)

Autonomic (involuntary)

Which muscles are under the voluntary ir somatic system?

• Skeletal,

• located inside skeletal muscles,

• attach bone to skin

Which muscles are under the involuntary or somatic system?

• cardiac, located in the heart

• Smooth, located in the walls of hollow organs

What an the autonomic pathway be further subdivided into?

• sympathetic , fight or flight

• Parasympathetic , rest and digest

What are the signs of sympathetic vs parasympathetic systems?

How many pairs of nerves connect the CNS to the rest of the body, and why in pairs?

• 43

• Pairs as all animals are bilateral symmetric (have a left and right side)

Of the 43, how many are cranial nerves exit the brain, and what type are they?

12 pairs of cranial nerves

• 3 sensory (efferent) only

• 5 mainly motor (afferent) but some efferent too

• 4 mixed

How many nerves remain, what type are they, and and where do they exit?

• 31 pairs remaining

• Exit various parts of the spinal cord

• All mixed

What is the nervous system primarily made if ?

Nervous tissue

What were the 2 competing theories for what is nervous tissue?

• reticular theory - network if interconnected structure

• Cell theory - composed of discrete cells with gaps in between

Which theory was right and how was it proven?

• Golgis silver staining technique, stains a limited number if cells at random in their entirety

• Showing many discrete cells with different shores and sizes, in CNS tissue

• CELL THEORY CORRECT

• Cajal used Golgi staining and saw lots of different types of cells, founding modern neuroscience

describe the morphology of the neurone

What is the function of the neuron?

Transmission and processing if information, via electrical impulse

What is the role of the dendirites?

• neuritis that receive incoming signals (neurones input regions)

How are dendrites adapted to their functions?

• large surface area

• Due to lots if branching (bifurcation)

• Spines in the dendrite

What is the role of the soma (cell bidy)?

• Sums incoming electrical signals from the dendrites ,, considered part of the input region

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What is the diameter of the soma?

5 to 40 um

What is included inside the soma?

• usual cell organelles

Also key organelles included in o rite in synthesis (which are not present in neuritis):

• rough endoplasmic reticulum (produces proteins)

• Nucleus , contai)img nucleolus , (processes rRNA, instructions on how to assemble new proteins)

How are soma cowards?

• most cell bodies like to hide in the CNS , protected by the bones of the skull and spinal column

What are clusters of cell bodies in the CNS called?

Nuclei

What are clusters of cell bodies lying along the nerves of the PNS called?

Ganglia

What is the role of the axon?

Neurone that genetertes and transmits electrical impulses (action potentials) away from the soma, conducting region if the neuron

How long are axons?

Vary in length from virtually non existent to over a meter long

Describe the features if the axon within the neuron

• Jojns soma at the axon hillock, a cone shaped area where signal is generated

• Ends in axon terminals (synapses) that contact other neurones

• Coated in between with myelin sheath (insulating layer if fat and protein )

What dies the axon contain?

• phospholipid bilayer → embedded with proteins that act as ion channels

• Cytoplasm (axoplasm) → containing essential element manufactured by nucleus e Golgi, vesicles, proteins etc)

  
  

What is a problem that can arise in the axon and how can it be solved?

• Axons are very long so it may take a long time to rely on passive diffusion to get elements where they need to be

• Instead they rely on axonal transport

What is involved in axonal transport?

• various cytoskeleton components(neurofilaments, microtubules, microfilaments) form a series of train tracks

• Motor proteins (kinesin, dynein) act as locomotives pulling essential elements down the tracks

In axonal transport, what is transport away from the nucleus called?

Anterograde

In axonal transport, what is transport back towards from nucleus called?

Retrograde

What us the speed of axonal transport?

40 cm a day

Describe axon terminals

Describe the morphology and physiology of neurons

Highly polar, meaning;

• their structure , morphology, is not symmetrical

• They transmit signals (physiology) in one direction

What is the difference between a neuron and a nerve (in the PNS)?

• Nerve is a collection of neurones

  
  

Dies a single nerve contain efferent ir afferent fibres?

can contain both

Describe the morphology if neurones and eventually nerves

Are all inputs mediated through the dendrites?

• no

• Most are from axon to dendrites (axodendritic)

• But some are form axon to soma (axosomatic)

• Or to the axon (axonaxoic)

What are axon collaterals?

• when the axon occasionally branches

• Usually around 90 degrees

• > 10 um in length

• They can regulate nerve activity, branch back onto other cells

Do all neurons have multiple dendrites, no have an axon?

No

What are the 5 morphological types if nerve cell?

What are the neural support cells called and how much if the nervous system do they make up?

• called glia ( means glue)

• Make up 50% of the nervous system

What are the functions if the glia?

• Helpjngnto hold neurons in place

• Supplying oxygen and nutrients to neuron

• Electrically insulating nueron

• Removing pathogens and dead neurones

• Aiding neurotransmission

What are the glia in the CNS?

• oligodendrocytes

• Microglia

• Ependymal cells

• Astrocytes

What are the glia in the PNS?

• Schwann cells

• Satellite cells

Describe Schwann cells

Are small axons myelinated?

• sometimes they are non myelinated

• rather than being wrapped in Shawn cell membrane , they lie in a groove on the surface of such a cell

• A single Schwann cell can partially enclosed 15 or more axons this way

D3cribe oligodendricytes

• Equivilent to Schwann cells (that exist in the PNS) , but in the CNS

• Unlike Schwann cells, a single oligo can myelinate multiple axons, wg 50-60

Describe astrocytes

Describe satellite cells

Describe microglia

Describe ependymal cells