The brain and spinal cord

Question 1

describe the structure of the grey matter of the spinal cord

Answer 1

middle of the cord that looks like an ‘H’
made of neurones and other cells

Question 2

describe the structure of the white matter of the spinal cord

Answer 2

outside of cord
made up of fibres that carry information up and down

Question 3

what is the dorsal horn

Answer 3

the back of the spinal cord where sensory information is localised (e.g. touch, proprioreception)

Question 4

what is the ventral horn

Answer 4

contains motor neurones which make direct contact onto muscles
stimulation of these neurones cause movement

Question 5

what is somatotopy

Answer 5

mapping areas of the brain in relation to their function and the area of the body that they control

Question 6

what are spinal white matter tracts?

Answer 6

tracts that carry information to and from the brain
there are 2 major ascending and 2 major descending systems

Question 7

two major ascending systems of spinal white matter

Answer 7

medial lemniscus/ dorsal column pathway
spinotalmic tract

Question 8

two major descending systems of spinal white matter

Answer 8

lateral descending system
medial descending system

Question 9

what is the lateral descending system?

Answer 9

fibres located in dorsolateral part of spinal cord and connect to motor neurones in lateral part of ventral horn
influences lateral musculature
corticospinal fibres strongly influence movement of every part of the body
rubrospinal tract can compensate almost completely for loss of descending corticospinal input but cannot compensate for use of individual fingers

Question 10

what is the medial descending system

Answer 10

fibres located in ventromedial part of white matter
connect to motor neurones in medial part of ventral horn and influence medial musculature
control of balance and posture
functions happen with little conscious control
-vestibulospinal tract retains balance when body is moved (external disturbance)
-reticulospinal tract retains posture nad balance during our own volitional movements (internal disturbance)

Question 11

what is the medial lemniscus/ dorsal column pathway?

Answer 11

carries sensory information from the joint and skin and skin about: vibration, two point discrimination and proprioreception

Question 12

spinothalmic tract

Answer 12

conveys crude touch, pain and temperature

Question 13

how does information pass in and out of the spinal cord

Answer 13

cell bodies of incoming sensory neurones lie outside the spinal cord in a series of ganglian
both sensory and motor axons run in the same nerves (spinal nerves)
there are 31 pairs of spinal nerves

Question 14

what is a dermatome

Answer 14

area of skin that is supplied by nerves from a single spinal root

Question 15

how do motor systems control muscles?

Answer 15

muscles controlled by a motor ‘pool’ pf neurones
each muscle fibre innervated by a single neurone but a single neurone may innervate many fibres in the same muscle
muscles capable of fine movements are innervated by more neurones

Question 16

what is a motor unit?

Answer 16

the motor neurone and all the muscle fibres it connects

Question 17

how does information floe in the spinal segment

Answer 17

dorsal horn receives sensory information and sends this to the brain
ventral horn sends messages directly to the muscles
intermediate zone integrates the information

Question 18

how does coding occur in the nervous system?

Answer 18

by action potentials

Question 19

how does coding occur in the sensory system?

Answer 19

stimulus intensity determines frequency of action potentials.
firing frequency codes for intensity of contrast between two levels
size of stimulus determines rate of firing

Question 20

how does coding occur in motor systems

Answer 20

rate code signals the amount of force to be exerted by a muscle
-increase in rate of APs fired causes increase in force generated
-at maximal contraction tetanus is reached and muscle cannot relax between APs