Intro to PNS

Question 1

what is the difference between afferent + efferent nerves

Answer 1

Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain, while efferent neurons are motor neurons that carry neural impulses away from the central nervous system and towards muscles to cause movement.

Question 2

Sensory (afferent) neurons have two sets of dendrites-like processes:
1) ___
2) ____
To avoid confusion, sensory “anatomical axons” in the limbs and body are usually referred to as sensory nerve fibres
There are no synapses on sensory cell bodies in dorsal root ganglia

Answer 2

Sensory (afferent) neurons have two sets of dendrites-like processes:
1) one in the periphery
2) one in the spinal cord
To avoid confusion, sensory “anatomical axons” in the limbs and body are usually referred to as sensory nerve fibres
There are no synapses on sensory cell bodies in dorsal root ganglia

Question 3

Most sensory fibres & motor axons have a sheath of fatty insulation called myelin wrapped around them
Myelin is produced by connective tissue cells called _____ ______

Answer 3

Most sensory fibres & motor axons have a sheath of fatty insulation called myelin wrapped around them
Myelin is produced by connective tissue cells called SCHWANN CELLS

Question 4

What is the function of the myelin sheath?

Answer 4

electrical insulation that increases the speed of conduction

→ The multiple layers of lipid membrane provide an electrically insulating sheath around the nerve fibre
Increases the resistance across the membrane=> increases the speed of conduction of the action potential along the nerve

The myelin sheath protects the axons and helps speed nerve transmissions. If the myelin sheath is damaged, these nerve signals will travel more slowly or be blocked completely

Question 5

what do we mean by dorsal root ganglia

Answer 5

Anatomically, a dorsal root ganglion (DRG) emerges from the dorsal root of the spinal nerves. They carry sensory messages from various receptors (i.e., pain and temperature) at the periphery towards the central nervous system for a response. The role of DRG in chronic pain has been well established.

Question 6

what are the nodes of ranvier and their function

Answer 6

Nodes of Ranvier are the small gaps between two myelin sheaths

The current flow in and out of the nerve fibre can only occur at the nodes of Ranvier
;Nodes are about 5-10 mm apart in large myelinated axons

Because the myelin sheath is largely composed of an insulating fatty substance, the nodes of Ranvier allow the generation of a fast electrical impulse along the axon. This rapid rate of conduction is called saltatory conduction.

The nodes of Ranvier allow for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon

Question 7

to speed up a signal in an axon is to insulate it with myelin, a fatty substance. In the peripheral nervous system, myelin is found in Schwann cell membranes. In the central nervous system, ________ are responsible for insulation.

Answer 7

to speed up a signal in an axon is to insulate it with myelin, a fatty substance. In the peripheral nervous system, myelin is found in Schwann cell membranes. In the central nervous system, OLIGODENDROCYTES are responsible for insulation.

Question 8

In the CNS the myelinated fibres are ‘_____ matter’
The non-myelinated cells are known as ‘_____ matter’

Answer 8

In the CNS the myelinated fibres are ‘white matter’
The non-myelinated cells are known as ‘grey matter’

Question 9

what is the outer layer of the myelin sheath called

Answer 9

the outermost layer of the myelin sheath that contains the nucleus and cytoplasm is the neurilemma (also called the neurolemma, sheath of Schwann, and Schwann’s sheath)

Question 10

a whole peripheral nerve consists of several fascicles bundled together with blood vessels + fatty tissue and are all surrounded by an ______ (aka the epineurial sheath)

Groups of functionally related nerve fibres are collected in nerve fascicles

each fasicle is surrounded by _______

Individual sensory or motor fibres are surrounded by a thin protective membrane called the ____________

Answer 10

a whole peripheral nerve consists of several fascicles bundled together with blood vessels + fatty tissue and are all surrounded by an EPINEURIUM (aka the epineurial sheath)

Groups of functionally related nerve fibres are collected in nerve fascicles

each fasicle is surrounded by PERINEURIUM

Individual sensory or motor fibres are surrounded by a thin protective membrane called the ENDONEURIUM

Question 11

EPINEURIUM is slightly longer than the nerve fibres, what is the function of this?

Answer 11

EPINEURIUM is slightly longer than the nerve fibres which allows for a slight degree of stretch (aka if nerve cells are snapped its some flex so they can stretch a little but if u crush nerve cell too much it wont function

Question 12

Define ganglion (ganglia)

Answer 12

a group of nerve cell bodies located in a peripheral nerve or root; it forms a visible lump e.g. dorsal root ganglia, trigeminal ganglion

ganglion is a collection of neuronal bodies found in the voluntary and autonomic branches of the peripheral nervous system (PNS). Ganglia can be thought of as synaptic relay stations between neurons. The information enters the ganglia, excites the neuron in the ganglia and then exits.

Question 13

when referring to sensory receptors, what do we mean by ‘free nerve endings’ and ‘encapsulated nerve ending’

Answer 13

free nerve endings= the sensory nerve branches profusely + ends up lying in the extracellular space between tissue cells (these respond to TISSUE DAMAGE and/or temperature changes)

encapsulated nerve ending= the nerve ending is surrounded by a specialised connective tissue aka ‘the capsule’

Question 14

what is a merkel disk receptor

Answer 14

Merkel disk receptors are mechanoreceptors used to detect the shape and pressure exerted by an object on the skin. They are important for discrimination of the detail in small objects

Question 15

define mechanoreceptor

Answer 15

receptors that respond to 1 or more kind of mechanical deformation of tissue e.g. pressure, strech, vibration

Question 16

what are Ruffini endings

Answer 16

Ruffini endings are mechanoreceptors that detect pressure and stretch of skin and are important for detecting the heaviness of objects and proprioception (joint position sense). They are found in deep tissue and joints.

Question 17

what are Meissner’s corpuscles

Answer 17

Meissner’s corpuscles are mechanoreceptors that are important for detecting the texture of surfaces

Question 18

what are Pacinian corpuscles

Answer 18

Pacinian corpuscles are mechanoreceptors that detect vibration

Question 19

what is a nociceptor?

Answer 19

Slowly adapting receptors that form a very fine nerve plexus in the dermis and many other tissues. They are found in all tissues= known as NOCICEPTORS

Question 20

THE WIDER THE NERVE FIBER THE _______ THE CONDUCTION VELOCITY

Answer 20

THE WIDER THE NERVE FIBER THE FASTER THE CONDUCTION VELOCITY

Larger diameter axons have a higher conduction velocity, which means they are able to send signals faster. This is because there is less resistance facing the ion flow. We have a lot of ions flooding into the axon, so the more space they have to travel, the more likely they will be able to keep going in the right direction. An axon is still part of the cell, so it’s full of cytoplasmic proteins, vesicles, etc. The larger the diameter of the axon, the less likely the incoming ions will run into something that could bounce them back.

Question 21

what is a proprioreceptor

Answer 21

a proprioreceptor is a sensory receptor that is located deep in the tissues (as in skeletal or heart muscle, tendons, the gastrointestinal wall, or the carotid sinus) and that functions in proprioception (as in response to changes of physical tension or chemical condition within the body)

Question 22

define what we mean by a receptive field

Answer 22

a receptive field = area of skin innervated by a single nerve fibre

Question 23

what is a dermatome

Answer 23

A dermatome is an area of skin supplied by a single spinal nerve

Question 24

if the zone of loss does not correspond to a dermatome, where is the damage?

Answer 24

The zone of loss of sensation does NOT correspond to a dermatome:
the damage is in a peripheral nerve

The zone of loss of sensation is a dermatome:
the injury is probably in the corresponding spinal nerve or dorsal root ganglion in the intervertebral foramen
(could be down to compression due to a fracture or a slipped disk)

Question 25

what do we mean by cholinergic? also define nicotinic, muscarinic.

Answer 25

cholinergic =refers to those receptors which respond to the transmitter acetylcholine and are mostly parasympathetic. There are two types of cholinergic receptors, classified according to whether they are stimulated by the drug nicotine or by the drug muscarine

The nicotinic receptor is a channel protein that, upon binding by acetylcholine, opens to allow diffusion of cations.
The muscarinic receptor, on the other hand, is a membrane protein; upon stimulation by neurotransmitter, it causes the opening of ion channels indirectly, through a second messenger

Question 26

peristalsis (smooth muscle contraction of food) is controlled by which plexus

Answer 26

myenteric plexus

Question 27

define proprioception

Answer 27

Imagine you are walking along and suddenly you trip and begin to fall. Luckily, your body senses that your limbs are in the wrong place and instead of falling to the ground, you just stumble a little. This sense of knowing where you are in space is known as proprioception,