Peripheral Nervous System Tissue

Question 1

Neuron definition

Answer 1

Cells that respond to stimuli by altering the ionic gradient across their plasma membranes. Functional units of both the CNS and PNS.

Question 2

Three main parts of neurons

Answer 2

Cell body (soma), dendrites and axon

Question 3

Cell body function

Answer 3

contains nucleus and most of the cell’s organelles and serves as as the synthetic or trophic centre for the entire neuron

Question 4

Cell body components

Answer 4

Numerous free polyribosomes and highly developed RER, indicating active production of cytoskeletal proteins for transport and secretion. Basophilic Nissl polysomes appear under a light microscope. Golgi apparatus, located in cell body, mitochondria found throughout the cell.

Question 5

Dendrite function

Answer 5

principle signal reception and processing sites on the neurons. conduct electrical impulses to cell body.

Question 6

Dendrite structure

Answer 6

Short branched projections leading to the cell body. Thinner dendritic processes as they bench, with cytoskeletal elements predominating in the distal regions.

Question 7

Dendritic spine function

Answer 7

Most synapses on dendrites in the CNS occur at the dendritic spines, which are dynamic membrane protrusions on the dendritic branches.

Question 8

What sort of structures are dendritic spines?

Answer 8

Plastic, as they change morphology depending on actin filaments (neural plasticity)

Question 9

What is neural plasticity involved in?

Answer 9

Underlies adaptation, learning and memory development

Question 10

What are axons?

Answer 10

Long slender projections that arise from the cell body and conduct electrical impulses away from the soma to other cells

Question 11

Axon structure

Answer 11

Very long process, that can be up to a metre in length. Plasma membrane of the axon is called the axolemma and its contents are the axoplasm.

Question 12

Where does the axon originate from?

Answer 12

The Axon hillock on the soma

Question 13

What is terminal aborisation?

Answer 13

Axons have small branches called collaterals, which each end with an axon terminal (terminal bouton). This contacts another neutron at a synapse to initiate an impulse in that cell.

Question 14

What do axons lack and how is this overcome?

Answer 14

Axons lack a protein synthesis machinery, so all the organelles and proteins required by the axon (neurotransmitters) must be transported from the cell body after synthesis.

Question 15

Anterograde transport and the microtubule involved

Answer 15

Movement away from the cell body, kinesin

Question 16

Retrograde transport and the microtubule involved

Answer 16

Movement along dynein towards the soma.

Question 17

What is transported via anterograde transport?

Answer 17

organelles and macromolecules synthesised by the cell body

Question 18

What is transported via retrograde transport?

Answer 18

Materials taken up by endocytosis, including viruses and toxins

Question 19

Two types of polarity exhibited by neurons

Answer 19

Structural and functional

Question 20

Explain structural polarity

Answer 20

One end of the neurone specialised to receive impulses (dendrites contain neurotransmitter receptors at synapses) the other end is specialised to send signals (axon terminals contain vesicles with acetylcholine)

Question 21

Explain functional polarity

Answer 21

Unidirectional impulse propagation

Question 22

How is neuronal form maintained?

Answer 22

By the cytoskeleton

Question 23

Cytoskeletal components

Answer 23

microtubules, neurofilaments and microfilaments

Question 24

Microfilaments function

Answer 24

Actin molecules allow changes in shape at dendritic spines, neural plasticity. Act as a scaffold for signal transduction systems

Question 25

Neurofilament functions

Answer 25

Maintain axonal structure

Question 26

What are Schwann cells + function?

Answer 26

A special form of glial supporting cell, provide axon insulation and maintain a constant ionic microenvironment.

Question 27

Structure of myelin sheath

Answer 27

In myelinated neurones in the PNS, Schwann Cells wrap around the axon to form multiple layers of Schwann cell membrane called the myelin sheath, which is mainly lipid. The Schwann cell membranes fuse together to form the mesaxon.

Question 28

What are the spaces between myelin sheath called?

Answer 28

Nodes of Ranvier

Question 29

Function of nodes of Ranvier

Answer 29

Increase the speed of transmittance, as saltatory conduction can take place

Question 30

Satellite cells structure

Answer 30

Form a thin glial layer around each large neuronal cell body in the ganglia of the PNS

Question 31

Satellite cell functions

Answer 31

Trophic or supportive effect on the neurones, insulating, nourishing and regulating their micro environments

Question 32

Difference in structure in unmyelinated axons

Answer 32

Still enveloped in Schwann cells, however they do not wrap many times to form a myelin sheath. Have a uniform distribution of voltage gated ion channels and no nodes of Ranvier so conduction is much slower

Question 33

How are nerve fibres organised in nerve?

Answer 33

- individual cell wrapped in endoneurium - group of cells with endoneurium wrapped in perineurium to form fasicles - fascicles are grouped together and covered by one final epineurium

Question 34

What are the coatings all examples of?

Answer 34

Connective tissue

Question 35

Structure of each connective tissue

Answer 35

endoneurium- reticular fibres, scattered fibroblasts and capillaries perineurium- flat fibrocytes, edges sealed together by tight junctions, form 2-6 layers epineurium- dense irregular fibrous coat

Question 36

Function of perineurium

Answer 36

Regulates diffusion, thus acts as the blood b nerve barrier

Question 37

Structure of dorsal root

Answer 37

- white matter surrounding brown matter - afferent root is the dorsal root, containing a dorsal root ganglia just before hand - sympathetic soma present in ganglia

Question 38

Sensory ganglia structure

Answer 38

contains large neuronal soma associated with sheetlike extensions of small glial satellite cells. cells supported by a distinct connective tissue capsule.

Question 39

Autonomic ganglia structure

Answer 39

intramural ganglia- found present in certain organs, associated with parasympathetic neurones paravertebral- found adjacent to vertebral column

Question 40

Enteric ganglia

Answer 40

2 types -myenteric and submucosal plexuses

Question 41

Sensory neurone terminal structure

Answer 41

axon terminals called terminal boutons are distal terminations of the telondendria of an axon

Question 42

somatic motor neurone terminal structure

Answer 42

Neuromuscular junction that releases ACh onto a motor end plate. End plate is studded with nAChRs

Question 43

sympathetic autonomic motor neurone terminal structure

Answer 43

axon contains many varicosities that release neurotransmitter

Question 44

6 different types of sensory nerve endings

Answer 44

Hairs, Meissner corpuscle, Ruffini endings, Merkel discs, Pacinian Corpuscle and free nerve endings

Question 45

Explain root hair plexus

Answer 45

A web of sensory fibres surrounding the base of hair follicles in the reticular dermis that detects the movement of hairs

Question 46

Merkel cell structure and function

Answer 46

Each associated with expanded nerve endings which function as tonic receptors for light touch and sensing an object's texture

Question 47

Meissner's corpuscle structure and function

Answer 47

elliptical structure consisting of a sensory axon among flattened Schwann cells arranged perpendicular to the epidermis in the dermal papillae. Initiate impulses when light touch disturb the shape, enabling the mechoreceptor to transduce an impulse

Question 48

Ruffini cell structure and function

Answer 48

collagenous fusiform capsules, anchored firmly to the surrounding connective tissue with sensory axons stimulated by stretch and torque

Question 49

Pacinian Corpuscle structure and function

Answer 49

large, oval shaped structures found deep in the reticular dermis and hypodermic with an outer capsule formed of thin concentric lamellae of flattened Schwann cells and collagen. Surround a highly branched, unmyelinated axon. Stretch mediated sodium channels sense coarse touch, rough textures, pressure and vibrations. Also located in walls of bladder, where detects if bladder is full

Question 50

Free nerving ending structures and functions

Answer 50

Found in the papillary dermis and extend into the lower epidermal layers which respond primarily to high and low temperatures, pain and itching