1 - Introduction to neuro

Question 1

Outline the basic organisation of the nervous system.

Answer 1

CNS - brain and spinal cord

PNS - nerves and ganglia (clusters of neuronal cell bodies) outside the brain and spinal cord

Question 2

How is the PNS organised?

Answer 2

Somatic PNS - Controls motor and sensory function for the body wall, e.g. skin [sensory neuron], skeletal muscles [motor neuron])

Autonomic nervous system - (Also called visceral PNS, vegetative NS, involuntary NS). Regulates function of the viscera: internal organs, smooth (involuntary) muscle, pupils, sweating, blood vessels, bladder, intestine, glands etc, and controls heart contraction rate. Has sympathetic & parasympathetic arms.

Question 3

What are the 2 directions that information can flow in the nervous system?

Answer 3

Afferent or efferent.

Question 4

Axons enter and leave the CNS via which pairs of nerves?

Answer 4

Cranial and spinal

Question 5

What is an afferent axon?

Answer 5

Axons that propagate action potentials towards the brain & spinal cord from the PNS (e.g. sensory neurons, both somatic and ANS).

Question 6

What is an efferent axon?

Answer 6

Axons that propagate action potentials from the brain and spinal cord to the periphery (e.g. motor neurons, both somatic and ANS)

Question 7

What are Interneurons?

Answer 7

CNS neurons that synapse with other CNS neurons within the brain or spinal cord.

Question 8

Describe the basic anatomy of the Cerebral cortex. (Cerebrum) What does it do?

Answer 8

Two hemispheres.

In general, each receives sensory info from and controls movement of the opposite side of the body.

Question 9

What does the cerebellum do?

Answer 9

“little brain” - controls coordination of movement

Question 10

What is the brainstem?

Answer 10

is the most primitive part. Contains densely packed fibres.

Regulates vital functions (e.g. consciousness, breathing). Damage here is usually fatal.

Question 11

How is the CNS spine structured?

Answer 11

Spinal cord (CNS) contains ascending and descending tracts to and from the brain as well as reflex circuits.

Voluntary movement and sensation involves communication to and from the brain via the ascending and descending tracts.

Question 12

How does a reflex circuit work?

Answer 12

Somatic sensory neurons, which have their cell bodies outside the spinal cord, have their axons projecting into the spinal cord where they form synapses with interneurons, which in turn synapse with somatic motor neurons in the spinal cord.
These are needed for a fast reflex response.

Question 13

What route do sensory pathways use to enter the spine?

Answer 13

Dorsal roots

Question 14

What route to motor pathways use to leave the spine?

Answer 14

Ventral roots

Question 15

Where does the CNS end?

Answer 15

The margins of the spinal cord.

The dorsal and ventral roots that emerge from the spinal cord being part of the PNS

Question 16

What is in the grey matter and what is in the white matter?

Answer 16

Neuronal cell bodies are in the grey matter.

Ascending and descending axon tracts are in the white matter.

Question 17

How are spinal nerves (PNS) arranged?

Answer 17

Contain both afferent and efferent axons.
They are bundled into fascicles surrounded by perineurium.
The whole nerve is in a tough epineurium capsule.

Question 18

What are individual axons wrapped in?

Answer 18

Myelin & endoneurium.

Some are unmyelinated e.g. nociceptive (pain) neurones.

Question 19

What is the function of a neurone?

Answer 19

To transmit and receive action potentials, or stimulate target tissue, e.g. contraction of skeletal/smooth muscle, secretions from glands.

Question 20

What happens when an action potential reaches a synapse?

Answer 20

When action potentials reach a neuronal chemical synapse, neurotransmitters released by a presynaptic terminal bind to post-synaptic receptors of the neuron/muscle/gland it is synapsing with.

Question 21

What is the difference between regeneration of axons in the PNS and CNS?

Answer 21

Axons in peripheral nerves can regenerate after injury.

Axons in the CNS have limited regenerative capacity.

Question 22

How are axons in the PNS regenerated?

Answer 22

Injury leads to stimulation of phagocytes which remove debris. This debris would otherwise inhibit regrowth.
It can be compromised by aberrant axon sprouting and non-specific target reinnervation- This can lead to neuropathic pain.

Question 23

Why do axons in the CNS have limited regenerative capacity?

Answer 23

Glia have an inhibitory influence on regeneration.
Glial scars form in place of injured brain tissue.
Absence of guidance cues that stimulate axon growth.