Cellular biology of neurones

Question 1

What are the two main parts that the nervous system is divided into?

Answer 1

The Central nervous system (CNS)- made up of the brain and spinal cord
The peripheral nervous system (PNS)- made up of the nerves which run between the CNS and other tissues, together with nerve relay stations called ganglia.

Question 1

What are ganglia?

Answer 1

Nerve relay stations that are found throughout the body in the PNS that carry nerve signals to and from the CNS. Ganglion are a collection of neurone cell bodies in the PNS.

Question 2

What are nerves connected to the brain called?

Answer 2

Cranial nerves

Question 3

What are nerves connected to the spinal cord called?

Answer 3

Spinal nerves

Question 4

What is the ENS?

Answer 4

The enteric nervous system. This networks the digestive tract.

Question 5

What is the Afferent division of the PNS?

Answer 5

Brings sensory information from receptors in the peripheral tissues and organs to the CNS.

Question 6

What is the Efferent division of the PNS?

Answer 6

Carries motor commands from the CNS to muscles and glands (Effectors)

Question 7

What are the 2 components of the Efferent division?

Answer 7

The Somatic (voluntary) nervous system- conscious skeletal muscle contractions
The autonomic (Visceral) nervous system- includes and sympathetic and parasympathetic nervous divisions and provides contractions at a subconscious level (e.g. cardiac muscle and glandular secretions)

Question 8

What is the difference between the sympathetic nervous system and the parasympathetic nervous system?

Answer 8

The sympathetic nervous system accelerates heart rate while the parasympathetic nervous system slows the heart rate.

Question 9

What are neuroglia?

Answer 9

These are specialised cells that are specific to nervous tissue and support support neurones.
There role is to:
Separate and protect neurones, provide a supportive network and framework for neural tissue, act as phagocytes, and help regulate the composition of interstitial fluid.

Question 10

What are the 4 types of neuroglia?

Answer 10

Astrocytes (structural role and involved in fluid transport in the brain), oligodendrocytes (produce myelin in the CNS), ependyma (like epithelial cells and they line the cavities in the brain) and microglial cells (specialised immune cells in the CNS)

Question 11

What is the role of endoneurium, perineurium and epineurium in nerves?

Answer 11

Endoneurium- is a delicate layer of loose connective tissue that encloses each axon and the associated Schwann cells too
Perineurium- Connective tissue that binds groups of axons together into bundles called fascicles.
Epineurium- Tough fibrous sheath that encloses all the fascicles to form nerves

Question 12

What is a neurone?

Answer 12

A type of nerve cell that sends messages all over the body

Question 13

What is the equivalent to astrocytes, in the PNS?

Answer 13

Satellite cells. They look after the neurone.

Question 14

What is the role of macrophages in the PNS?

Answer 14

They monitor and support cell health by sensing damaged tissue and recognising viruses and other pathogens

Question 15

What produces myelin sheaths in the PNS?

Answer 15

Schwann cells

Question 16

Why do K+ and Na+ not just diffuse away from the axon surface?

Answer 16

Endoneurium keep these ions close and prevent them from diffusing away. This allows axons to maintain action potentials.

Question 17

How do epineurium and endoneurium layers protect axons?

Answer 17

Epineurium is full of collagen, strong and relatively rigid.
Endoneurium is softer, more elastic and spongy and contains more lipids. This creates a shock absorbing layer around axons which prevents them from being damaged when limbs bend or get knocked.

Question 18

What is a neurone made up of?

Answer 18

A cell body (soma)- contains the nucleus and most of the organelles that maintain the cell
Dendrites- Increase the surface area available for connecting with axons of other neurones.
Axon- Stretching from the cell which transmits signals from the neuron to other cells
Synapse- Special type of cell junction that allows direct cell communication between neurones

Question 19

How does a nucleus within the brain differ from a nucleus within a neurone?

Answer 19

A nucleus, in a neuron, contains the DNA for the cell. However, in the brain, it refers to a collection of neuron cell bodies and possibly synaptic regions.

Question 20

What are multipolar neurones?

Answer 20

They have three or more processes- one axon and the rest dendrites. (Major neurone type in the CNS and all neurones that control skeletal muscles are multipolar).
They can be interneurones (conduct impulses within the CNS), a chain of CNS neurones, a single neuron connecting sensory and motor neurones or motor neurons (conduct impulses from CNS to effector by efferent pathway)

Question 21

What are bipolar neurones?

Answer 21

They have two long processes- an axon and one dendrite. Found in the retina of the eye for example. They are all part of the afferent pathways so are sensory neurones.

Question 22

What are Unipolar neurones?

Answer 22

The cell body appears outside the long processes so the dendrite process and axon process appear fused. Found in the ganglia in the PNS. Most are sensory neurones that conduct impulses along afferent pathways to the CNS

Question 23

What type of neuron is virtually all sensory neurones?

Answer 23

Unipolar

Question 24

What is the difference between somatic sensory neurones and visceral sensory neurones?

Answer 24

Somatic monitor the outside environment and our position within it. Visceral monitor internal conditions and the status of other organ systems

Question 25

Explain what Exteroceptors, Proprioceptors and interoceptors are?

Answer 25

Exteroceptors- provide information of the external environment in the form of touch, temperature or pressure sensation (Sight, Smell and hearing) Proprioceptors- monitors the position and movement of skeletal muscles and joints. Monitors are position in the external environment Interoceptors- Monitor the digestive, respiratory, cardiovascular, urinary, an productive systems and provide sensations of taste, deep pressure and pain. Signals are relayed by visceral sensory neurons.

Question 26

What are motor neurones?

Answer 26

Neurones that carry information from the CNS to the Effectors.

Question 27

Where are the cell bodies found in Afferent Neurones and efferent neurones?

Answer 27

Afferent- Located outside of the spinal cord Efferent- located in the ventral horn of the spinal cord

Question 28

Describe what the dorsal and ventral roots are?

Answer 28

Dorsal- transmits sensory information from the PNS to the CNS (enters back of the spinal cord) Ventral- Carry impulses from the CNS to effectors (exit the front of the CNS)

Question 29

What is Motor Neurone disease?

Answer 29

A progressive disease in which symptoms include weakness of voluntary muscles caused by the death of motor neurones.

Question 30

What is Multiple Sclerosis?

Answer 30

The myelin of the CNS is the target of attack by the immune system in MS. Causes paralysis, loss of sensation and or loss of coordination.

Question 31

What is gliosis?

Answer 31

When neurones die, the dead cells are removed by macrophages by phagocytosis. The damaged area is then repaired by proliferation of astrocytic cells which filled the defects and form an astrocytic scar.

Question 32

What is the difference between nucleus and ganglion?

Answer 32

Nucleus is a collection of neurone cell bodies in the CNS. Ganglion is a collective of neurone cell bodies in the PNS.

Question 33

What is the difference between a nerve and a tract?

Answer 33

A nerve is a collection of axons (nerve fibres) in the CNS while a tract is a collection of axons in the PNS

Question 34

Why does a person addicted to cocaine, crave higher doses over time?

Answer 34

Cocaine blocks dopamine reabsorption receptors on the presynaptic membrane which means that dopamine remains in the synaptic cleft for longer causing a greater feeling of pleasure for a short period of time as postsynaptic receptors are triggered over and over again. However, repeated doses of cocaine cause the body to release less and less dopamine. This means that there is a lack of dopamine without taking cocaine so the person is always sad. They then require cocaine to get there dopamine levels to normal and even higher doses to experience this original level of pleasure.